J. therm. Biol. Vol. 12, No. 1. pp. 27-37. 1987 03064565/87 $3.00+0.00 Printed in Great Britain. All rights reserved Copyrighl (C/ 1987 Pergamon Journals Ltd

A TWO-PEAK CIRCADIAN SYSTEM IN BODY TEMPERATURE AND ACTIVITY IN THE DOMESTIC CAT,

FELLS CA TUS L.

WALTER RANDALL I, J. THOMAS CUNNINGHAM 1, STEFFANIE RANDALL ), JOHN LIITP3CHWAGER 2 and RALPH F. JOHNSON ~

~Department of Psychology and 2Department of Industrial and Management Engineering, University of Iowa, Iowa City, IA 52242, U.S.A.

(Received 21 January 1986; accepted 26 September 1986)

Abstract--l. The body temperature and activity of cats exhibit two-peak patterns during the 24 hr period. 2. The two peaks are retained when the temperature and activity are permitted to frcerun. 3. A third prominent peak appears in the aetograms in cats in the main colony, induced by the presence

of humans.

Key Word Index--Body temperature; activity patterns; time series; Fourier transform; circadian; cats, Felts catus.

INTRODUCTION Aschoff (1962) reviewed the literature on 24-h activity rhythms and found two peaks for most species. The two-peak pattern was found in insects, crustaceans, fishes, reptiles, birds, and 45 different species of mammals. In a mouse, Tribukait (1956) found that one of the two peaks freeran in an LD cycle of 20 h (the total light plus dark time was 20 h), while the other peak stayed entrained. In even shorter LD cycles, both peaks freeran. In a subsequent review, Aschoff (1966) added other species to his long list and demonstrated that the two peaks in activity of greenfinches were present in constant light.

Since AschotVs reviews, additional studies report- ing two peaks continue to appear: rodents with the basic two-peak pattern include the African four- striped grass mouse (Baumgardner et al., 1980), the Mongolian gerbil (Pietrewicz et al., 1982), the golden hamster (Pickard et al., 1984), and the muskrat (Macarthur, 1980). The two-peak pattern in body temperature, food intake, and activity appears well established for trout and salmon (e.g. reviews by Bachman et al., 1979; Brett, 1983). Douglas (1982) demonstrated that the "crepuscular" pattern of ret- inal changes that occur at dawn and dusk in rainbow trout as adaptations to the environmental lighting continues in constant darkness. The gaz ing pattern of free-ranging shorthorn cows exhibits two large peaks, one in the morning and one in the afternoon (Low et al., 1981). Wolf-coyote hybrids (Roper et al., 1977), black bears (Garshelis and Pelton, 1980), "and some foxes, genets, ringtails, and coatis (Kavanau and Ramos, 1975) exhibit two activity peaks that are crepuscular in most cases. Thach (1969) reviews the literature on primates, noting that howler monkeys, red-tailed monkeys, gibbons, chimpanzees, and gor- illas exhibit a two-peak pattern in activity as indi- cated by field studies. In a laboratory setting, Thach (1969) found two peaks in the social behaviour of baboons maintained in constant light. In a hospital

setting, body temperature, measured at the axilla with clinical thermometers once every three hours, exhibi- ted a two-peak pattern in two of six manic-depressive patients (Nikitopouiou and Crammer, 1976). In a whitefooted mouse, the basic two peak pattern was formed from two independently freerunning "split" components of the circadian system when en- trainment was obtained to an LD cycle (Pittendrigh and Daan, 1976). A two-peak pattern as a basic design in the circadian system is of compelling inter- est because of the evidence that there are at least two circadian oscillators (e.g. splitting, internal de- synchronization) and because two oscillators are involved in what may be an important hypothesis for photoperiodic induction (the "internal coincidence hypothesis", e.g. review by Pittendrigh, 1981).

The domestic cat has circadian rhythms (Johnson et al., 1983; Johnson and Randall, 1985; Randall et al., 1985) and a photoperiodically-induced change in behaviour (Randall, 1981; Johnson and Randall, 1983). Although the typical circadian phenomena (entrainment to LD cycles, transients and rcentrain- ment to phase shifts in the LD cycle, freeruns, spontaneous changes in the period of freeruns, mask- ing and entrainment by "social" cues) were found in these studies using the typical methods (actograms and "thermograms" and displays of averages), little indication of a basic two-peak pattern was apparent on visual inspection of these data. Two of ten cats exhibited two prominent bands of activity during freeruns (Randall et al., 1985), and two small peaks were present in a least-squares plot of average body temperature for four cats in LD 10:14 (Johnson et al., 1985). Aschoff (1962) comments on a potential difficulty with averaging: minor differences among individuals may obscure a basic activity pattern. Thus in the present study, longitudinal data on body temperature and activity in individual cats were collected and analyzed with time series and cor- relational methods. A two-peak pattern of activity

27

28 WALTER RANDALL et a[.

and body temperature was present in LD cycles and freeran in constant light and constant darkness.

METHOD

Subjects and apparatus

Ten adult male cats were studied in two settings, seven in a main animal colony in which other cats were housed and three in isolation, in sound- attenuating Industrial Acoustic Corporation (IAC) chambers (Model 5). In both settings, the ambient temperature was maintained at 22 _+ 2°C, and food (Purina dry cat chow) and water were available continuously.

In the main colony, the cats were housed in Acme stainless steel cat cages (0.45 x 0.61 x 0.80m), and the lighting, provided by G. E. Chroma 50 fluorescent lamps (which emit a spectrum similar to sunlight), was controlled by an automatic clock. All the data in the main colony were collected during an LD* 10:14 cycle (10 h of "daylight" followed by 14 h of "star- light"), with onset of lights at 0700 h CST. No daylight entered the room. In the L phase of the cycle, the illuminance inside the cages ranged from 4 to 400 lx (measured with a Tektronix J l6 digital pho- tometer). Incandescent lamps were placed above the false, perforated ceiling so that the fronts of the cages were diffusely illuminated with 0.03 Ix (to simulate starlight). Each day at 0700 hr, the colony room was entered for approximately two hours of care and cleaning. To obtain activity data, an infrared photo- beam was placed through the front of each cage, and the total time that a cat was in the photobeam for every 10-min period was recorded with an S-100 based microcomputer. These 10-minute sets of data were plotted in actogram format in the usual way, by arranging 24-h periods of the activity in a vertical sequence of successive days. To obtain these plots, a software program generated a mark for each time the photobeam was interrupted and generated additional marks that were proportional to the time that the cat stayed in the photobeam. The statistical analyses of the activity data were conducted on hourly totals obtained from the 10-min periods, The activity data were collected for intervals of 15-30 days for the individual cats.

For the cats in isolation, the IAC chambers were modified for long-term studies by adding a large food hopper, a continuously flowing fountain of water, and a large tray of chemically- treated absorbent especially designed for cats (Deodor grade San-I- Cell). The exhaust of the IAC air-exchange system was directed to the outside so that the 100% fresh air exchanges maintained a clean and odorless atmos- phere inside the chambers. Activity data were ob- tained from an infrared photobeam placed across the food hopper and were plotted as described above, and data on body temperature were obtained concur- rently from radiocapsules placed in the greater omen- turn. Before implanting the radiocapsules (Barrows Co., Woodside, Calif.), they were calibrated over a range of 35-41"C in a water bath using a digital ther- mometer. A linear relationship between transmitted frequency and temperature was found in this range. Loop antennae of 14-conductor ribbon cable were installed in the IAC chambers and led to AM radios.

The signals from the radios were led to Schmidt triggers for waveform shaping, and the shaped wave- forms, as digitized signals, were monitored with the microcomputer. For each cat ten l-s samples of the signal were collected for every 10-min period. A software filter excluded any l-s sample that deviated more than 50 Hz (approximately 0.8~'C) from the previous 10-min average value. The nonexctuded samples that remained were averaged to represent the radio frequency for the 10-rain interval. Thus 144 radio frequency averages were collected for each cat for each day with approximately 10% of the averages lost because of high frequency static. For the 90% of the 10-min averages that were available, hourly aver- ages were calculated and plotted as thermograms and used in the statistical analyses. Estimates of the hourly averages existed for approximately 99% of the hours for each cat, except for one week when an equipment failure went unnoticed. The averaged radio frequencies were converted to C, using the parameters of the least-squares fitted straight line from the calibration procedure.

The temperature data were plotted in actogram format ("thermograms") by plotting the hourly values of body temperature that were 0.2~C above the mean body temperature for each cat. These were "peak" thermograms. "Trough" thermograms were obtained by plotting, in actogram format, all the values that were 0.2°C below the mean.

In each IAC chamber the main source of lighting was provided by a 60-W General Electric incan- descent lamp that provided a range of illuminance from 3 to 538 lx within the chambers. In the initial LD cycle (LD I0: 14) the D phase was total dark. In the other LD cycles (LD* 12:12 and LD* 15:9), a small source of light provided by a 12-V lamp (General Electric nr. 1820 bulb) was on continuously, illuminating the D phase of the cycles with simulated starlight (as denoted by D*, 0.00 to 0.05 lx within the chambers). Five different lighting conditions were imposed successively in the IAC chambers; in order of occurrence (and the number of days that they were in effect) they were LD 10:t4 (for 27 days), DD (for 42 days), LD* 12:12 (for 27 days), D 'D* (for 27 days), and LD* 15:9 (for 44 days).

Data analysis Estimates of the period. Periodograms were ob-

tained with the fast Fourier transform algorithm of Singleton (1967), using the FFTRC software of the University of Iowa Weeg Computing Centre (IMSL Library Reference Manual, 1982). FFTRC accepts a data vector of length N (e.g. the successive 480 l-h estimates of body temperature for one cat for 20 days) and computes (N/2)a, and (N/2)b,, where a~ and b~ are the Fourier coefficients with i = I, 2 . . . . . N/2. The output of the FFTRC program is then converted to a~ + b, 2 and plotted as ordinate values with frequency on the abscissa. This plot is one form of the "periodogram," and the a,: + b~ values are referred to as "intensities"; ai and bi also are the least-squares derived regression coefficients of the Fourier series,

y, = a0 + ~ (a~ cos 2rtit/k + b, sin 2rtit/k ), r - I

Circadian rhythms in the cat 29

where y is the fitted value at time t, a0 is the grand mean of all the observations, k is the number of observed values within the fundamental period, and j is the index of the last harmonic ( j = [k/2], where [] denotes the integer part of the argument). This equation is used in the regression analysis (see below).

The periodograms obtained with the F F T algor- ithm provide estimates of the intensities from a period of the total interval of the data vector to the Nyquist period (a period of 2 h in our case). To increase the resolution of the periodogram analysis, estimates of the intensities were obtained for the tenth harmonics of data vectors with N from 200 to 300 (200, 201, 202 . . . . . . 300). Thus the intensities of the tenth harmonics were determined for 101 data vectors. These harmonics have periods of 20.0, 20.1, 20.2 . . . . . 30.0 hours. The tenth harmonic with the largest intensity indicated the period of the data. Estimates of the period also were obtained by visual inspection of the actograms and thermograms (by drawing what appeared to be the best straight line through the onsets or offsets of activity or through the peaks or troughs of body temperature) and by the slope of the regression line on phase angle for succes- sive 24-h periods (Bliss, 1970, pp. 257 f). The different methods agreed within 0.1 h and were used because of the importance of providing the correct period for the periodic regression analyses.

Periodic regression analysis. When replicates of a known period can be formed (the table of Buys Ballot, 1847), the column means provide a good representation of the rhythm because the random components in the data tend to cancel out; if the incorrect period is provided, the rhythm may cancel out. The estimates of the period obtained from the methods described above were used to form Buys Ballot tables, i.e. replicates (R) of the indicated period (P) were formed into R by P matrices, using the equation of Enright (1965, p. 431) when the indicated period was not 24.0. These reformatted matrices were obtained for each cat for both activity and body temperature data and then individually subjected to the periodic regression analysis. The periodic regression of y, on the Fourier series can be decomposed into an analysis of variance with k/2 components independently distributed as a multiple of Chi-square with 2d.f. and with sum of squares equal to a multiple of the intensities, (k/2)(a~ + b~). A Fortran program (Sharma, 1968) provided all the calculations and plots as described by Bliss (1970, Chap. 17, pp. 219-287) which includes analysis of variance tables, the least-squares derived coefficients, confidence limits for the coefficients, linear regression analysis of the slope of the phase angles of successive replicates (the "Test for Trends . . . . " Bliss, 1970, p. 257), and the least-squares derived family of Fourier curves. Homogeneity of variance is tested with both Bartlett 's and Cochran's statistics, and transformations are available in the program if the variances are heterogeneous. The activity data, x, were transformed to ln(x + 1), a transformation which abolished the heterogeneity of variance that may have existed because of the zero scores. The Fortran program first tests for linear trend; when linear trend is present, it is partitioned out and the Fourier series fitted to the detrended values.

The procedure for selecting one of the family of Fourier curves (or rejecting all of them) is described in detail by Bliss (1970), and the method has been applied intensively in our study of biological rhythms in the cat (e.g. Johnson and Randall, 1985; Randall 1981; Randall and Parsons, 1974; Randall and Liittschwager, 1967). in brief, a least-squares fit of the first set of fitting functions (i = I) is effected. The least-squares derived coefficients, aj and b~, reduce the sum of squares about the fitted curve, and this reduction is tested with an F-test. The residual scatter about the fitted curve is then tested with an F-test, and if significantly greater than the random error, the second set of fitting functions (i = 2) is fitted and the least-squares derived coefficients a2 and b 2 evaluated with an F-test. Then the new and smaller residual scatter about the fitted curve is retested. This step- wise addition of successive terms (i = 1,2 . . . . . [k/2]) is continued until the residual scatter about the fitted curve is no longer significantly larger than the ob- served error. Then F-tests are made for each pair of independent, orthogonal Fourier coefficients (a, and b,) of the Fourier series. A good model is one in which all the scatter is accounted for parsimoniously, i.e. with only a few terms, with each term accounting for statistically significant portions of the sum of squares.

RESULTS

The cats in isolation The initial analyses of the LD cycles on body

temperature with the periodograms for the three cats in the IAC chambers indicated that the intensities were concentrated at frequencies of one and two cycles/day (e.g. Fig. 1). For periods between 20 and 30 h, the "tenth harmonic" analyses indicated that the intensity of the 24,0 h harmonic was greatest. When the data were arranged in Buys Ballot matrices with the period set at 24 h (i.e. with one days-by- hours matrix for each cat for each LD cycle) and then subjected separately to the periodic regression anal- yses, the least-squares fitted curves exhibited two peaks (Fig. 2). Examples of the analyses of variance that were used to select the curves in Fig. 2 are provided in Table 1. In Table 1, the F-rat ios for testing the significance of the harmonics (rows 2 and 4) were formed conservatively by using the appropri- ate interaction terms (rows 3 and 5). The random error (row 7) was used as the denominator in forming the other F-ratios. In the analysis of the temperature data for LD 10:14 (Table 1, first column), the scatter about the average two-term Fourier curve (row 6) is significantly larger than the random error (row 7). However, both the first and second harmonics ac- counted for significant portions of the sum of squares (rows 2 and 4) and together accounted for over 90% of the sum of squares due to trend. The third and higher harmonies did not significantly reduce the remaining trend nor account for a statistically significant portion of the sum of squares. Thus the two-term Fourier equation is an appropriate model. In the other three cases in Table 1, all of the trend is accounted for by the first two harmonics (i.e. the scatter about the fitted curve, row 6, has been reduced

30

58

0 . 0 5 "

0 . 0 0 3

LO 10 :14

WALTER RANDALL e t al.

DO

0 . 0 7 0 0 5

.1 ; " . . . . . . , 0.00 il,,L[ /j_ ; I , . 0.00 5 7 9 1fl d 3 5 7 9 t i

L D " 12 :12

i / 1 3 5 7 9

8 0

0 . 0 5 0 .05 0 .05

E

0.00 3 5 7 9 11

0.00 I 3 5 7 9 11

0 . 0 0

I I i , L , i . . . . . . . . . .

1 3 5 7

8 3

0 . 0 5 0 . 0 5 0 . 0 8

o.oo 1.1, I , , ,t • : 'I ' ' t ' 0 . 0 0 , ,' " ' ' , 0 . 0 0 3 5 r 9 1t I 3 5 7 9 11

1..[~,..t a 3 5 7 9

C y c t e s / d o y

Fig. 1. Examples of the periodograms (the discrete Fourier transforms) for the three cats (58, 80, and 93) individually isolated in sound-attenuated chambers. The sum of the squared Fourier coefficients (a ~ + b ~) are the ordinate values. For each cat and each condition, a separate data vector of hourly measures was subjected to the Fourier transform. The 24- and 12-hour harmonics provide the prominent intensities.

to the level of the random error, row 7, by the two term model).

By these criteria illustrated in Table 1 (i.e. statisti- cally significant sum of squares assigned to the har- monics and 90% or more of the trend thus accounted for), 28 two-peak patterns and one one-peak pattern were found. One set of temperature data was lost because of equipment failure (there were 30 sets of data: activity and temperature for three cats in 5 lighting conditions). The estimated periods in DD

and D ' D * ranged from 23.8 h (e.g. cat 80 in DD) to 24.4h (e.g. cat 83 in D ' D * ) . No difference in the period were detected for activity and temperature. The two-peak pattern was present in D D and in D ' D * (e.g. Fig. 3).

The thermograms and actograms

The thermograms (Fig. 4) are suggestive of a two-peak pattern in some cases (for cat 58 and 83 where the peaks are plotted, and the plots of the

38.7

38.6

38.5 q o

38.4

E~ 38.3

38.2

Circadian rhythms in the cat

2.5

I 4 8 12 16

T ime of (lay ( h )

qr 9- 2.0

,J '1.5

÷

0.5

l I l I I I 20 4 e t2 16 20

T i rne(h o f the d o y )

Fig. 2. The two-peak pattern of body temperature and activity. The three cats were isolated separately in sound-attenuated chambers and subjected to the same LD 10:14 cycle, with onset o f lights at 0800 h. The Buys Ballot tables with periods of 24 h were subjected to the periodic regression method, and Table

1 indicates how these Fourier curves were selected.

31

troughs for cat 83). For the other cases, single peaks and troughs are indicated. The relatively shallow secondary trough indicated by the least-squares fitted curves is the major factor contributing to the appear-

ance o f s ingle peaks a n d t r o u g h s in the t h e r m o g r a m s : in the t h e r m o g r a m s o f the t r o u g h s all values 0 .2°C be low the m e a n a re p l o t t ed a n d thus in ca t 58 a n d 80 on ly a s ingle t r o u g h is i nd i ca t ed because the s econd-

Table 1. Summary of the periodic regression analyses for cat 58 in LD 10:14 and DD

Temperature in Activity in Temperature in Activity in LD 10:14 LD 10:14 DD DD

Row Term df ms F df ms F df ms F df ms F

1 Among days 16 0.3 15" 25 5.8 0.8 9 0.2 10" 29 4.2 0.5 2 First harmonic

(a~ and bm) 2 2.2 22* 2 15.7 7.5* 2 5.6 70* 2 48 28* 3 First harmonic

interactions 32 0.I 5* 51) 2.1 0.3 18 0.8 4* 58 1.7 0.2 4 Second harmonic

(a 2 and b2) 2 2.2 55* 2 24.3 5.7* 2 1.7 28* 2 45 20* 5 Second harmonic

interactions 32 0.04 2* 50 4.2 0.6 18 0.06 3 58 2.2 0.03 6 Remaining trend 19 0.05 2.5* 19 7.1 0.9 18 0.03 1.5 18 9.3 1.2 7 Random error 304 0.02 475 7.5 162 0.02 522 7.6

*P < 0.01.

6o 60

i 2o 2o

6 0 o 0

o o

-20 G - 2 0

l I 4 8 t2 16 20 4 8

C i r c o d i o n t ime ( h ) C i r¢odton t ime (h)

I I I 12 16 2O

Fig. 3. The two-peak pattern persists in constant lighting conditions. After the freerunning periods were estimated, Buys Ballot tables at the estimated period were formed and then subjected to the periodic regression analyses. Four of the least-squares fitted Fourier curves are illustrated here, and Table l indicates how they were selected. The freerunning period is divided equally into 24 ("circadian t ime") on the abscissa. In both sets o f curves, the activity peaks earlier than the temperature. Circadian time "zero"

is taken as midnight.

32 WALTER RANDALL e t a/.

0

10

20

30

40

50

60

70

80

90

"100

110

120

,130

~ 4 0

58 80

T i m e ( h ) T i m e (h)

4 8 ,12 ,16 20 24 4 8 12 16

l l l o ' -

"10:14

D O

12:12

O~D ~

,ib

" l 15:9

0 0

10

2O

30

40

50

60

7O

8 0

90

d10,

120 '

20 24 0 4

85

T i m e ( ~ )

8 12 16 20 24

:'~4

)

:12

D t

:9

0 4 / i m ' e ( h l 6 20 24 0 4 eT ime(h~e zo z4 o 4 8 T i l e ( h ~ e 20 24

o ~ " ~ . ~ ~ r ~ m ~ ' - - " , 0 . - - ' . ' . _L ' . . - - o

• ~..,,,,1...-n.-'t: i ~ l , o ~ . ~ t :1" " lo:1, 10-I. t " " - l i t " 1 I°:1" ~°1 m 1 1 I . ~ ' " I lO:I~ 2 o ~ - - r -~. ~ ' 2 I-- i" " / - , . :~ . : / 1 . - . . I r.~" /

zoo-. -.= r- 2°T ",u-' .fliP: r--

~ o ~ ; '1.--"- l 3o~ Z . : . , - - ' ~ : - - / ~o ~.;i~ "":" . - / . . . . . , o l I a a m • oai[. :.:::'.~-Ioo ° o ~ . : : j~ . - - Ioo ~ ~ : ~ . Ioo : . ~ - : ' ~" /

~o L~ . : ~ - - , i / ~o.L ..,,-----': ;~.".~.,:,,,__._ / ~o.~'.'~-. . ~ , - - - / I . . . . , . . . . . / t::':,..~_ -ii:_.~":.; /

e o r . . , , , - . ' : - ~ l w ~o~_ . i':._"~_,"r.. 1 - ~ ° f . - : - - I - _ _ ~ ' ~ P - - " - " ' - 70 i n . . . . . = ~ ~ . 70 . . "

~o .,,, . ~ L ..J ~ L f :~" " "" ,;" ": r F

' . " o'o" ~ ° ° I " • I o ' o ' ~ ° ° ~ b - o - l~O~-.-,t,~- . :':k" ,o,-_ .....,~, 1~o.~ . . ,-- -__..._,

~ o t ~ " ~ - ~ - " " " . . . . . . - . ~ ". " ' l - " ~ ' 1 I~:~ ~ ' . - - - , . , . .~ ' t

~ : o ~ -... ~ o - , : . ~ . ..-i,-r., t " - o i l l l ,mll m . m,~ I /

Fig. 4. The thermograms of the three cats in isolation with troughs plotted above and peaks plotted beirut. All values that differcd from the individual means by more than 0.2' C are plotted. Entrainment, frecruns,

and transients are evident in these body temperature peaks and troughs.

ary minima are too high to be "clipped" by the 0.2'C criterion. Similarly, the thermograms of the peaks are formed by plotting all values 0.2'C above the mean and thus present views that are too "'deep" for visualizing the two scparate peaks in every lighting condition. Prominent transients occur on occasion (e.g. cat 58 at the switch to LD* 12:12), and en- trainment to the LD cycles is evident as well as freeruns that originate from the entrained peaks and troughs. Equipment failure occurred for part of D ' D * .

The actograms, which were obtained concomi- tantly with the thermograms are characterized by an unusual brevity o f the period of rest, which forms a narrow channel which is difficult to fol low through the record (Fig. 5). However, the narrow channel that begins just before the onset of lights at 0800 h in LD 10:14 may be traced through most of the records, indicating entrainment, freeruns and transients in all three actograms. Immediately bet'ore the onset of lights, a brief period of inactivity appears for most of the LD cycles, a period of inactivity which in most

Circadian rhythms in the cat 33

ro CO

0 CO

C0 LO

A J=

F-

. - - . - . . - - . ~'.- - . . . - . - . . - . - . ; - . _ . : _ . . - . . . . . - .

.:---:----:-:: :,;--':---. • -~-

" " Z ' . " ' - " - - . . - - - - - - . - ~ " - - ' , , , . ' . - ' . - - . - - ' -

. . _.-,..-": ~ - ; - ~ - . - .,,..- . . . . : - . - - . .-.- , . . . . - - . " - . ; . . . . . , , . . - . .

. . . . . . . . . . - - - . . . - " , . . , : . - . . . . ,,. - . - ~ , , , , . . , . • - ; . " . - . - Z . - . - - - ~ . . . . . . - . . . . . " , , - , , , , ~ - " : . . - - , . "

-

" " "

. . . - . . . - - - . . . , . . ' . . - - . . . - ,.,. _.. ,-

; ' - . . ~ ,~ " . ' . " " ~ ' " " " - " . " . , , . : " - " " - " " . ' - - " ~ ' . . - -Z - . " - " Z . ' . - " . . " - - - ~ " . - .-L" ." " .'" . ::.. -: - .," -- " . .- :" ~ :. .-" .... "~ ' - " " _ ' , , ~ ."

- ~ 1 - . ' , - ," " , ; ' , . ; - - " , ." ; - , '," , ." , . " , ' ' , - , ' : , - , -

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

_ -- . ::. -

- . ~-." -.-.~..%.-_ .-..- "-.- =... - -'...o - ..

_E T~"-:''-'-" " --" -''-:-" : " ~- _.-. -.- ,--- :-..-..- --.

I " " " " "I" " " * " " "

. - . . . . , . . . . - . . ; " , , , . . . - - . " " ,,, .,. - _ . . . . . . . - . - . . , - ; . . ; - - - • ab e. - " ~ ' ~ " ~ • "- e" - . ;~ - ' " ~ "~ - - e . e " - .~" - . " "

• ~ - - . - - . " , , . . . . - . . . . . - . - ; . . . . ; . . . ~ , ; , . - . . - . . . - - . - - . . • . - . ' . . ~ . . . - - - , . , . - - . . . . . . - .

o " - : , ' = ' : " , < " ; . - " , ' - - " , " , . ' ~ - 1" , - , " " F - - - . ' - - T - " , - - " : " , " - " , " " : o o o o o o o o o ~ o o o o o o o

o .

I ; ID-

0

0

:..- ~ ' . , ~ . . : - . - . j -:....... -..-..- -...--.. ?.-,..,-:-.-'-. -.-,,.....-.. -.-... --...,,..-~,~. . - ; - - ' ; , " - ' - . . . - . L'. ; . - " ~.,~,~'..- ~ . - . . - . . ' . ' . . "

, . - , . . . . _ . . ~ - ~ ~ - . . . . . . . - . ~ - . - ~ - • -• ° • - ,.'.- . ~. • - ° - --I • - o ~ . • .~ - • o -,i- . - -l. ,,l-.-. . .

, ~ - - . . . - ; . - . . . - ~ . . - : ' . - - . - . , i , . - . . . - " . " . . . " ' % - ; - " . . i ' " "

L . "~ " " : " - - - - - . . - . ; ' ~ . a . - " - ' , - . " . " . , , . , . , . ' " . i f ' ' . . .

- - . ,,~ . . . . ~ - . , . - . " . . ' ~ ' , - . . ' o = . . . - . . . - . .= - . - . . % ; ~ ; . . - . ~ . , . ~ - - . . - , . . . . . . " . - . . . . . . . " , - . . . ~ - . ,,. . . . . . . . -

~ _ _ o , , . . " . - ,.-. ".".,. - . _ . -

. . . - . . . - . _ . . - - : . - - . . -_ . . . : . . . - - . ! . ; - ; . -

- T" : ' : ,~ " "~ . - ~ ' - - - ' ~ " ' -"--'-.-'-~.-" - ' ' ' ' - - - ' , - ' - " " - ' " ' . " - . ' : - - o o o o o o o o o o o ~,

.?. E

,m o

. = -

E ~

, . - , E

>,~

6 ~

~._=

;,-,

0

. = "~

_~= 0 "~

6 ~ i , .

r = o 0

t ' - -

v'-;

34 WALTER RANDALL el al.

cases extends into the L phase of the LD cycle; this is the major trough in the least-squares represen- tations. The phase of the trough appears to vary with LD cycle; thus in LD 10:14, the inactive periods occur earlier relative to the onset of lights than in the other two LD cycles. Effects of the offset of lights also are evident (e.g. cat 80, where a narrow band of activity appears when the lights are switched off, a narrow band which freeruns in the subsequent DD and is associated with the main peak in the thermo- gram). In LD 10: 14, the slight attentuation of activity in the D phase of the cycle at about 2000 h represents the minor trough of the least-squares representation. Both these troughs are apparent in the thermogram for cat 83. The transients and freeruns in the thermo- grams and actograms are concomitant with the one exception of cat 83 in D ' D * , where an instantaneous

phase shift of the temperature rhythm occurs in the first day of D 'D* .

Cats in the main colon),

In the main colony (in LD 10:14) where daily caretaking and other daily human activities occurred (e.g. removing and returning cats from other ongoing experiments), several bands of activity clearly were evident in the actograms (Fig. 6). The outcome of the periodicregression analysis, when applied individu- ally to each of the seven cats, indicated three peaks throughout the 24-h period. Neither interactions in phase nor amplitude were detected by the analysis of variance, and a similarity in the pattern of changes among the cats across the day was evident. Therefore, the column means for each cat were obtained and resubmitted for the periodic regression analysis.

4 8 7 5

T i m e ( h )

0 4 8 1 2 1 6 7 '0 7 '4

0 ~i I I , ' i I t I ! , I ,~ ,I i l l I ,I

" :' 'r , "d,"l"1, ; , ' , ', , y ' *',,',, , ' I i I l i l l l I ~ I ~ l ~ • i I II IN, i l l I ! i i

'1 I 11 ~ N~ II + I l i I II

2 0 t / ' , i ' '1 " ' " " [ " ' t ,'

i11~ :1~ , , lIE I1 ~1 , ' : i~ 1, [ I ; I 1 11 , r ' i , ,1 ' 11 ,~ ~ "1

T i m e ( h )

0 4 8 12 '16 2 0 2 4

] ~ I , ; 0 ' " " , " ', • : ~'~,, " , " ~ '~ ' . . , ~ t " , - ,.'~ l'!,',r, "1 , . . a l , ' ~ f P , . , . . , , , . ' { . , . t , . . ,, ,

/ ' ,, ' ? ' , ' , , ' ''~.. 'L ' ' " 'I ~ '~,Ll '?q, I , "~ ' . , ,, I ~'' J . . . . . . ~ . . . . . . . . I ~ . . . . . . . . . . . . . .

5 6

9 3

T i m e ( h

o 4 8 0 I I

~ " ' " ~ " ' L : ' ; I !" ;'

,~, ~ ~: ,,~,,

e • , ,i , , , . ,

. ?, It I

'12 `16 2 0

~, ,, *, ,~ . ,

.i

' #ii i *1 I'i, i '1' *" |

3 9

2 4 I

,r

' I i "

T i m e ( h )

0 4 8 "12 '16 2 0 2 4

0 I 1 J • I I '2" I , . I* ' ,dl, , ' ? ; ; " ' " " ' , ' " ' ,

. , , , , ; ,

'° L I ' " " , " ' .... ' ' ' : " ," ' ! I ' : ',IL, "~ . , " '

77

Time ( h )

0 4 B 1 2 1 6 20 24

0 I I I I ' " "+ " ' . , I.:",. . . . . ,, , , • , e I1' II .m ' |

L , I . i " i , " 111 • n : " # ' ; . • ' " ' , I , i I U I~ I , T " , l ~ ' , . i l l P H , i rl ~, , ,

I~ ,. ' ,,,~'r'. ,~, . ' ,',, ,, , . . , / , ., -1, . . . . ',,'r ~ . . . . . . . ~{ ' j r , ' , . , , . , , .~ , ,~ , , ; , : , , , , , : : : . , , ' ,

1 0

2 0

T i m e ( h

0 4 8 1 2 1 6 2 0 2 4

I t r i I ,

,J ., , * . , r i1 , , . . . . I 'd ' , . ,. ,, L , " . ' '|,,:h , . , ] I ~ ' , " % " . " " II " ' . . . . . I . ~ #" 1;I . . . . ~ t • . . , . - , . . r . . , , , , , , , ,. ,

-1 . . . . . ,t. ,:l.,,~ ,,,~l,,~=.,~r,.=,~ . . . . . . . . . . . . I . . . . " ' , " , . ' ' . ' ' : ' I , 1 . " . " , , ; , ' '! ' ' I . ' , I ., ; .,I I . . . . ~ ,, .... " ,:J'~',. i , ' . . , *,l~ ,, ,~, I ~ I , , . . . . , , ~ ' " . . ',, ' , , , ' I U : , f l l L ' " , , , , , ' , , . " , , ' ,

"' ' " " r " F ~ i " ~ ' i ' : J ! ,," ~= ;':* '~"t ~ ' , ' "

79

T i m e ( h )

0 4 B `12 16 2 0 2 4

O " I L ~ J L ;

-~,' % I . . " . , , , ' I 1 ' , ' , ~ . , , " . % ' " , ' " ; P . I , " ' , i t i ~l i , q . i I , r

t o ~ " , ~ " ',.."' I, , • , , , ' , & ",, ,, ,,",, ' ', . ; * " ..'1 ' ,', ; ' ! ' , ~ ' , ' '~

j ' " , , , , " , ,~ ~ " h , , ,,, , " ,' , ' , , , . , , ! r , ,I' i'

Fig. 6. Actograms of seven cats from the main colony in LD 10: 14, with onset of lights and care and cleaning at 0700 h. H u m a n s were present only during the L phase of the LD cycle and especially near

light offset, at 1700 h.

Circadian rhythms in the cat 35

:5.0 -

o 2.5 ¢3

f~.

4-

2.0

~.5

I I I I I 4 8 12 16 20

Time ( h o f the doy)

Fig. 7. The Fourier curve fitted to the seven sets of column means from Fig. 7. All the trend of the averaged column means is accounted for by this Fourier curve with three

harmonics.

When this matrix (7 cats by 24 h) was analyzed with the periodic regression technique, three peaks were found (Fig. 7), with the middle peak corresponding to the daily care and cleaning. The first and third peaks are somewhat similar to the two peaks that were obtained in the IAC chambers. A comparison of the actograms in the main colony and the I A C chambers indicates four similarities: (1) the existence of an inactive period before the onset of light (onset of light occurred at 0700 h in the main colony); (2) a decrease in activity that occurred after the onset of darkness; (3) the absence of a clear nocturnal or diurnal pattern as a species characteristic, although a slight tendency for "nocturnalism" is present in both settings; (4) the presence of a band of activity clus- tered about the transition from light to dark, a band of activity enhanced in the main colony and probably attributable to a response of the cats to human activity.

DISCUSSION

The data indicate that domestic cats, like over 50 other species of mammals, have an activity pattern with two peaks. The activity pattern of the cat has been described as diurnal (Szymanski, 1919), noc- turnal (Macdonald and Apps, 1978), crepuscular (Kavartau, 1971), and polycyclic (Lucas et aL, 1974). Aschoff (1962) properly rejects these labels because the same individual animal may exhibit the different patterns on different occasions. Eriksson (1978) re- views the literature on seasonal inversion in fishes and presents the definitive study indicating that trout undergo Systematic seasonal changes in how they entrain to LD cycles (i.e. these fishes are diurnal, crepuscular and nocturnal depending on the time of year). Nocturnal and diurnal patterns that have been found in the same species of rodents are discussed by Aschoff (1962), Baumgardner et al. (1980), and Pietrewicz et al. (1982) but no definitive studies exist which specify the sources of these variations in activity. Season and method are mentioned as the possible sources for the different patterns of activity.

However, neither season nor method are essential in generating these differences in the cat. One cat may display a diurnal pattern, another a nocturnal pat- tern, another a "polycyclic'" pattern with the cats in the same conditions (i.e. in adjacent cages). These different patterns in LD cycles were found to be idiosyncratic patterns that persist with changes in the LD cycle, changes in the light intensity, and changes in the size and shape of the enclosure for the cat (Randall et al., 1985). Therefore, history or genetic differences are involved in generating the different patterns of the domestic cat rather than season or method. As in the present study, the actogram data for the cat often are impossible to classify with any of the traditional labels. Two peaks may be the one factor that is common to the idiosyncratic patterns of entrainment in this species.

Although prominent two-peak patterns are not always visible in raw data representations of activity and body temperature of the cat, two peaks is the consistent finding with time series methods. Dorrscheidt and Beck (1975) developed a means of statistically evaluating the periodogram and applied the techniques to actogram data. They found that the conservative statistical procedures detected signifi- cant peaks in the data that were not detectable by visual inspection. Visual inspection of actograms may be the weakest of all methods for rhythm detection, with only robust rhythms readily apparent. The 19th century advance by Buys Ballot is a definite im- provement because the periods of interest are aver- aged and the visualization of a rhythmic component is enhanced. The Buys Ballot table provides column means that improve the signal to noise ratio, and it is the trend in these column means that is evaluated with the periodic regression technique. However, the circadian rhythms in the cat often are robust, just as in other species, and no statistical treatments are necessary. For example, the two-peak patterns in melatonin concentration in CSF and the two-peak pattern in drinking (Reppert el al., 1982, their Fig. 8) and the two-peak patterns in REM and slow wave sleep (Bowersox et al., 1984) are obviously present in the raw data so that time series analyses are unneces- sary. In the cat, freerunning circadian rhythms in activity and body temperature that are prominent and robust are detectable on actograms without time series methods (e.g. Johnson et al., 1983; Johnson and Randall 1985; Randall et al., 1985). However, the deceptions and limitations of visual perception are well known, and the proper use of the proper analytic methods serve their typical function of revealing and establishing what is not available to mere visual inspection,

In some fish species, a function of the two-peak pattern in body temperature, food intake and behav- iour has been established. In sockeye salmon, a "bioenergetic hypothesis" has been proposed (that metabolic efficiency is obtained with the crepuscular changes) and tested. In this species, body temperature may undergo a daily fluctuation as great as 17°C, a crepuscular fluctuation that is behaviourally induced by vertical migrations in deep lakes. When the growth rate of two groups was compared, one group main- tained at constant temperature and another subjected to "crepuscular" fluctuations in temperature (and

36 WALTER RANDALL et al.

with the suitable control groups), the growth was optimized in the "crepuscular" temperature environ- ment (Biette and Geen, 1980). Foerster (1954) had previously demonstrated the adaptive value of growth within the range of these experimental findings.

The ubiquity of the two-peak pattern suggests some general and important function, like, for ex- ample, a "bioenergetic" advantage, which, how- ever slight, may be adaptive. Tides and twilight may have provided important temporal niches: most inter- tidal zones are subjected to semidiurnal tides, and dawn and dusk are moderate times of the day with regard to some variables (e.g. temperature, illumi- nance, humidity). If crepuscular fishes, birds or rodents provided a major dietary component in the evolutionary history of the cat, two peaks in the general physiology and behaviour might arise and be maintained as a temporal adaptation to the availability of prey.

Most of the studies on the circadian system of the cat involve daily interruptions for care and cleaning (e.g. Hawking et aL, 1971; Reppert et aL, 1981, 1982, 1983; Lucas, 1978; Lucus and Harper, 1976; Sterman et al., 1965; Ursin, 1970) or periodic disturbance to obtain blood for chemical analyses (e.g. Krieger et al., 1968; Johnston and Mathew, 1979). Enright (1965) has demonstrated in simulation studies that "disturbances" during the day (between 0800 and 1700h) generate false rhythms when the data are analyzed with his root mean square technique. These disturbances were superimposed on noise and varied randomly within the daily period, occurring once every two to four days, Even though the "dis- turbances" did not occur at 24 intervals or at multi- ples of 24-h intervals, a 24-h rhythmic component was indicated by the time series analysis. The simu- lation was done to evaluate the effect of daily care and feeding that was incompletely randomized in this fashion.

Thus any rhythm detected by this method in a setting where care and cleaning occurs at random times during the day may be attributed to the activity generated by the care and cleaning. The cat is easily disturbed by the presence of humans and by human noises (Randall et al., 1985), and, in the present study, care and cleaning produced a prominent peak in the actogram and in the least-squares represent- ation (Fig. 7), a peak that did not appear in the IAC chambers where the cats were isolated from humans and human noises (Fig. 2). The mere existence of this prominent peak that reoccurs predictably every 24 h is irrelevant to any questions about entrainment or about the existence of circadian rhythms. As Aschoff and his colleagues (1962, 1981, 1982) have indicated in their concern with masking phenomena, a study of the circadian variable in freeruns is essential if cir- cadian rhythms and entrainment are to be demon- strated. Freeruns that originate from the entrained activity bands assist in the elimination of masking as the alternate explanation to entrainment. Thus very little of the "circadian" literature on the cat provides evidence for an innate oscillator. Some studies which use the periodogram of Enright (1965) ignore short periods (e.g. less than 20 h) and thus systematically ignore the basic two-peak pattern, which is often

discernible in the data. Enright (1965, p. 438) was careful to point out this "'complication" and to provide an example of an analysis of tidal heights where the 12.4 lunar-tidal rhythm generated a peak at 24.8 on the periodogram.

Our data indicate that the cat is like other mam- mals in providing a challenge for the existing nomen- clature, in possessing a circadian system, and in having a two-peak pattern as an integral part of the circadian system. The available data suggest that a two-peak circadian system may be ubiquitous, a taxonomic character of high order, and a general feature in the architecture of physiological and be- havioural function.

SUMMARY

Circadian rhythms in activity and body tempera- ture were examined in the domestic cat using photo- cells and radiotelemetry. The amount of time that a cat was in an infrared photobeam was the measure of activity. Radiocapsules whose transmission fre- quency was a function of temperature were implanted in the peritoneal cavity and antennae in the cages led to AM radios. The output of the radios and the infrared phototransistors were monitored by a laboratory computer. The cats were studied in two settings, in a large animal colony where they were not isolated from other cats or from humans, and in isolation, in especially constructed sound-attenuating rooms. The data were displayed in actogram format and analyzed with time series methods. These methods indicated that cats in isolation have two peaks in their circadian activity and temperature rhythms (Table I, Figs 1 and 2). The two peaks freeran in the constant lighting conditions (Fig. 3). The thermograms (Fig. 4) and actograms (Fig. 5) indicated entrainment to the LD cycles, freeruns in the constant lighting conditions, and transients when the lighting cycles were changed. In the colony set- ting, a third prominent peak in activity was associ- ated with the daily disturbances of humans in the room (Figs 6 and 7). Thus the cat in isolation exhibits a two-peak pattern that is easily modified by human activity. Other studies of the circadian system of the cat are briefly reviewed, and the ubiquity of the two-peak pattern is emphasized.

Acknowledgements--This research was supported in part by Grants MH-[5402-07 and MH-15773 from the National Institute of Mental Health and by a grant from the Epilepsy Foundation of America. The authors wish to express their appreciation to Professor G. Edgar Folk Jr for his advice and guidance on the radiotelemetry.

REFERENCES

Aschoff J. (1962) Spontane lokomotorische Aktivitat. Handbuch der Zoologic, 8. Band, 30. Lieferung, I 11 Tell, 1~ 84.

AschoffJ. ([966) Circadian activity pattern with two peaks. Ecology 47, 657 662.

Aschoff J. ( 1981 ) Circadian rhythms: Interference with and dependence on work-rest schedules. ,4dr'. Sh'ep Res. 7, II 34.

Aschoff J., Daan S. and Honma K. (1982) Zeitgebers. entrainment, and masking: Some unsettled questions. In Vertebrate Circadian Systems (Edited by Aschoff J. et ul. ), pp. (3 24. Springer. Berlin.

Circadian rhythms in the cat 37

Bachman R., Reynolds W. and Casterlin W. (1979) Diel locomotor activity patterns in wild brown trout (Salmo trullat L.) in an electronic shuttlebox. Hydrobiologia 66, 45-47.

Baumgardner D., Ward S. and Dewsbury A. (1980) Diurnal patterning of eight activities in 14 species of muroid rodents. Anon. Learn. Behav. g, 322-330.

Biette R. and Geen G. (1980) Growth of underyearling sockeye salmon (Oncorhynchus nerka) under constant and cyclic temperatures in relation to live zooplankton ration size. Can. J. Fish. Aquat. Sci. 37, 202-210.

Bliss C. (1970) Statistics in Biology, Vol. 2. McGraw-Hill, New York.

Bowersox S., Baker T. and Dement W. (1984) Sleep- wakefulness patterns in the aged cat EEG. Electro- encephalogr. Clin. Neurophysiol. 58, 240-252.

Brett J. (1983) Life energetics of sockeye salmon, Onco- rhynchus nerka. In Behavioral Energetics: The Cost t~f Survival in Vertebrates (Edited by Aspey W. et al.), pp. 29-63. Ohio State University Press, Columbus.

Buys Ballot C. (1847) Les Changements Periodiques de Temperature. Kemink & Fils, Utrecht.

Dorrscheidt G. and Beck L. (1975) Advanced methods for evaluating characteristic parameters (tau, alpha, rho) of circadian rhythms. J. Math. Biol. 2, 107-121.

Douglas R. (1982) An endogenous crepuscular rhythm of rainbow trout (Salmo gairdneri) photomechanical move- ments. J. exp. Biol. 96, 377-388.

Enright J. (1965) The search for rhythmicity in biological time-series. J. Theor. Biol. 8, 426-468.

Eriksson L. (1978) Nocturnalism versus diurnalism-- Dualism within fish individuals. In Rhythmic Activity of

Fishes (Edited by Thorpe J.), pp. 69-89. Academic Press, New York.

Foerster R. (1954) On the relation of adult sockeye salmon (Oncorhynchus nerka) returns to known smolt seaward migrations. J. Fish. Res. Board. Can. 11, 339-350.

Garshelis D. and Pelton M. (1980) Activity of black bears in the Great Smoky Mountains National Park. J. Mam- mal. 61, 8-19.

Hawking F., Lobban M., Gammage K. and Worms J. (1971) Circadian rhythms (activity, temperature, urine and microfilariae) in dogs, cat, hen, duck, Thammomys and Gerbillus. J. lnterdiscipl. Cycle Res. 2, 455-473.

International Mathematics and Statistics Library Reference Manual (1982) IMSL, Inc., Houston.

Johnson R., Randall S. and Randall W. (1983) Freerunning and entrained circadian rhythms in activity, eating and drinking in the cat. J. Interdiscipl. Cycle Res. 14, 315-327.

Johnson R. and Randall W. (1983) Mediation of the photo- periodic effect on grooming reflexes by glucocorticoid hormones and serotonin. Behav. Neurosci. 97, 195-209.

Johnson R. and Randall W. (1985) Freerunning and en- trained circadian rhythms in body temperature in the domestic cat. J. lnterdiscipl. Cycle Res. 16, 49-61.

Johnston S. and Mathew E. (1979) Feline plasma corticol (hydrocortisone) measured by radioimmunoassay. Am. J. Vet. Res. 40, 190-192.

Kavanau J. (1971) Locomotor activity phasing of some medium-sized mammals. J. Mammal. 52, 386-403.

Kavanau J. and Ramos J. (1975) Influences of light on activity and phasing of carnivores. Am. Natur. 109, 391-418.

Krieger D., Silverberg A., Rizzo F. and Krieger H. (1968) Abolition of circadian periodicity of plasma 17-OHCS levels in the cat. Am. J. Physiol. 215, 959-967.

Low W., Tweedie R.. Edwards C., Hodder R., Malafant K. and Cunningham R. (1981 ) The influence of environment on daily maintenance behaviour of free-ranging short- horn cows in central Australia. Appl. Anita. Ethol. 7, 11-26.

Lucas E. (1978) A study of the daily sleep and waking patterns of the laboratory cat. Sleep Res. 7, 142.

Lucas E. and Harper R. (1976) Periodicities in the rate of on demand electrical stimulation of the mesencephalic reticular formation to obtain wakefulness. Exp. Neurol. 51,444-456.

Lucas E. and Sterman M. (1974) The polycyclic sleep-wake cycle in the cat: Effects produced by scnsorimotor rhythm conditioning. Exp. Neurol. 42, 347-368.

Macarthur R. (1980) Daily and seasonal activity patterns of the muskrat Ondatra zibethicus as revealed by radio- telemetry. Holarctic. Ecol. 3, 1-9.

MacDonald E. and Apps R. (1978) The social behaviour of a group of semi-dependent farm cats, Fells catus: A progress report. Carnivore Genetics Newsl. 3, 256-268.

Nikitopoulou G. and Crammer J. (1976) Change in diurnal temperature rhythm in manic-depressive illness. Br. Med. J. 1, 1311-1314.

Pickard G., Kahn R. and Silver R. (1984) Splitting of the circadian rhythm of body temperature in the golden hamster. Physiol. Behav. 32, 763-766.

Pietrewicz A., Hoff M. and Higgins S. (1982) Activity rhythms in the mongolian gerbil under natural light conditions. Physiol. Behav. 29, 377-380.

Pittendrigh C. (1981) Circadian systems: General perspec- tive. In Handbook of Behavioral Neurobiology: Vol. 4, Biological Rhythms (Edited by Aschoff A.), pp. 57-80. Plenum Press, New York.

Pittendrigh C. and Daan S. (1976) A functional analysis of circadian pacemakers in nocturnal rodents. J. Comp. Physiol. 106, 333-355.

Randall W. (1981) A complex seasonal rhythm controlled by photoperiod. J. Comp. Physiol. 142, 227-235.

Randall W., Johnson R., Randall S. and Cunningham T. (1985) Circadian rhythms in food intake and activity in the domestic cat. Behav. Neurosci. 99, 1162-1175.

Randall W. and Liittschwager J. (1967) The relationship between cyclic changes in thyroid function and behavior of cats with brain stem lesions. J. Psychiatr. Res. 5, 39-58.

Randall W. and Parsons V. (1974) A review of annual endocrine rhythms in cats with brain stem lesions. In Chronobiology (Edited by Scheving L. et al.), pp. 251-255. Igaku Skoin, Tokyo.

Reppert S. and Artman H. (1981) Vasopressin exhibits a rhythmic daily pattern in cerebrospinal fluid but not in blood. Science 213, 1256-1257.

Reppert S., Coleman R., Heath H. and Keutmann H. (1982) Properties of vasopressin and melatonin in cat eere- brospinal fluid. Am. J. Physiol. 243, E489-E498.

Reppert S., Schwartz W., Artman H. and Fisher D. (1983) Comparison of the temporal profiles of vasopressin and oxytocin in the cerebrospinal fluid of the cat, monkey and rat. Brain Res. 261, 341-345.

Roper T. and Ryon J. (1977) Mutual synchronization of diurnal activity rhythms in groups of red wolf/coyote hybrids. J. Zool., Lond. 182, 177"-185.

• Sharma K. (1968) A generalized program for treatment of periodic data. Unpublished master's thesis. The Univer- sity of Iowa, Iowa City.

Siegel S. (1956) Nonparametric Statistics for the Behavioral Sciences. McGraw-Hill, New York.

Singleton R. (1967) On computing the fast Fourier trans- form. Commun. Assoc. Comput. Mach. 10, 647-654.

Sterman M., Knauss T., Lehmann D. and Clemente C. (1972) Circadian sleep and waking patterns in the labora- tory cat. Electroencephalogr. Clin. Neurophysiol. 19, 509-517.

Szymanski J. (1919) Aktivitat und Ruhe bei Tieren und Menschen. Z. Allg. Physiol. 18, 105-162.

Thach J. (1969) A bigeminus pattern in social behavior. In Circadian Rhythms in Nonhuman Primates (Edited by Rohles F.), pp. 52-63. S. Karger, New York.

Ursin R. (1970) Sleep stage relations within the sleep cycles of the cat. Brain Res. 20, 91-97.