Physiology and Behavior, Vol. 12, pp. 49"/-498. Brain Research Publications Inc., 1974. Printed in the U.S.A.

BRIEF COMMUNICATION

Cholecystokinin does not Produce Bait Shyness in Rats 1

JONATHAN HOLT, JOSEPH ANTIN, JAMES GIBBS, 2 ROBERT C. YOUNG, AND GERARD P. SMITH

Edward W. Bourne Behavioral Research Laboratory New York Hospital-Cornell Medical Center, Westchester Division

White Plains, New York 10605

(Received 31 October 1973)

HOLT, J., J. ANTIN, J. GIBBS, R. C. YOUNG AND G. P. SMITH. Cholecystokinin does not produce bait shyness in rats. PHYSIOL. BEHAV. 12(3) 497-498, 1974. - Four groups of rats were injected intraperitoneaUy with an extract contain- ing cholecystokinin (CCK, 40 Ivy dog units/kg), the synthetic C-terminal octapeptide of CCK (40 units/kg), apomorphine HC1 (6 mg/kg), or 0.15 M NaC1, each immediately following repeated exposures to a 0.1% saccharin solution. Neither CCK nor octapeptide produced a taste aversion, while apomorphine produced a marked and sustained aversion. These results indicate that the previously reported inhibition of feeding caused by exogenous CCK is not due to illness; they support the hypothesis that CCK is a satiety signal in the rat.

Bait shyness Cholecystokinin Satiety Taste aversion

CHOLECYSTOKININ (CCK), a hormone released by food in the small intestine [4], suppresses feeding when admin- istered exogenously to rats [2,3]. This observation suggests that CCK may act as a satiety signal during normal feeding in the rat.

In order to establish CCK as a physiological satiety sig- nal, one requirement is that CCK not inhibit feeding by inducing nausea or other subclinical sickness. We reported [3] that rats injected regularly with CCK appeared healthy and eager to eat, maintained "control food intake over several months, and did not exhibit a taste aversion after a single exposure to a novel taste paired with an injection of CCK; we interpreted this observation as evidence that the animals were not made ill by CCK. However, Garcia et al [1] showed that repeated pairings of taste and test sub- stance are a more sensitive measure of whether that sub- stance causes "bait shyness" [5] than a single pairing.

We report here that repeated exposure to the novel taste of saccharin, paired at each exposure with the injection of a large dose of impure CCK or the synthetic C-terminal octa- peptide of CCK, does not induce an aversion to the taste of saccharin.

METHOD

The animals were 24 male Sprague-Dawley albino rats

(Hormone Assay, Chicago, Illinois), weighing 4 0 0 - 5 0 0 g. They were maintained and tested in individual cages on an artificial 12-h light schedule. Food (Purina Rat Chow) was available ad lib. The experimental procedure was modeled after the design reported by Garcia et al [ 1 ]. Tap water (25 -+ 2 °C) was presented in graduated tubes for only 10 min each day during the afternoon. The rats were thus trained to consume all of their daily water in this 10 min period. Immediately following this period each rat was injected intraperitoneally with one ml of 0.15 M saline. The rats were maintained on this regime for one week, and testing began after their water consumption stabilized.

Six rats were randomly assigned to each of four groups. On the eighth day, a 0.1% sodium saccharin solution (25 -+ 2°C) was presented instead of tap water. Immediately fol- lowing a 10 min exposure to this novel taste, groups of rats were injected intraperitoneally with either (1) 0.15 M saline, (2) 6 mg/kg body weight of apomorphine HC1 dis- solved in 0.15 M saline, (3) partially purified porcine CCK (10%w/w, GIH Research Unit, Karolinska Instituter, Stockholm, Sweden), 40 Ivy dog units/kg body weight dis- solved in 0.15 M saline, or (4) the synthetic C-terminal octapeptide of CCK (SQ 19,844, the gift of Miguel Ondetti, Squibb Laboratories, Princeton, New Jersey), 40 Ivy dog units/kg body weight dissolved in 0.15 M saline.

t This research was supported by a fellowship from Foundations' Fund for Research in Psychiatry (to James Gibbs) and by USPHS Career Development Award KO4-NS 38601 and USPHS Grant NS 08402 (to Gerard P. Smith).

2 Requests for reprints should be sent to James Gibbs, Edward W. Bourne Behavioral Research Laboratory, New York Hospital Cornell Medical Center, Westchester Division, 21 Bloomingdale Road, White Plains, New York 10605.

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FIG. 1. Consumption (mean number of ml -+ SEM) of 0.1% sodium saccharin solution during a 10-min interval following 24 hr of water deprivation. Immediately after each exposure to saccharin, rats were injected intraperitoneally with either CCK (40 Ivy dog units/kg), the synthetic C-terminal octapeptide of CCK (40 units/kg), apomorphine HC1 (6 mg/kg), or 0.15 M NaCI. Asterisks mark points of significant

difference from saline control: *p<0.05, **p<0.01, t-test, two-tailed.

Each group was treated every third day in the manner described. On the two intervening days, all rats were pre- sented with tap water for 10 min and were injected with one ml of 0.15 M saline. Consumpt ion o f water or saccharin was measured after each presentat ion. Statist ical compari- sons be tween groups of rats receiving saline or test injec- t ions were made with a t-test ( two-tai led).

RESULTS AND DISCUSSION

Nei ther impure CCK nor the synthet ic C-terminal octa- pept ide o f CCK produced a taste aversion to saccharin (Fig. 1). On only one test (Day 4) o f seven daily tests was the CCK-injected group significantly d i f ferent f rom the saline-injected cont ro l group (84.3% of saline, p<0 ,05 ) , but this di f ference was no t sustained.

The dose o f CCK and oc tapept ide used (40 Ivy dog uni ts /kg) was large: It is eight t imes the threshold dose for the suppression of feeding, and is sufficient to cause a 50% decrease in food intake [3] . The test condi t ions in this a t t empt to produce a taste aversion with CCK were sen- sitive: Using a dose of apomorph ine small enough that a statistically significant decrease in saccharin consumpt ion was not obtained after one exposure , we de tec ted a taste aversion on test Day 3 (39.0% of saline, p < 0 . 0 1 ) w h i c h became progressively more marked with repeated exposures (Fig. 1 ).

The results of this s tudy indicate that the previously repor ted inhibi t ion of feeding caused by CCK is not due to illness and therefore suppor t the hypothesis that CCK is a sat iety signal in the rat.

REFERENCES

1. Garcia, J., F. R. Ervin and R. A. Koelting. Learning with pro- longed delay of reinforcement. Psychon. Sci. 5: 121-122, 1966.

2. Gibbs, J., R. C. Young and G. P. Smith. Effect of gut hor- mones on feeding behavior in the rat. Fedn Proc. 31: 397, 1972.

3. Gibbs, J., R. C. Young and G. P. Smith. Cholecystokinin de- creases food intake in rats. J. comp. physiol. Psychol. 84: 488-495, 1973.

4. Meyer, J. and M. I. Grossman. Release of secretin and chotecys- tokinin. In: Gastrointestinal Hormones, edited by L. Demling. Stuttgart: Georg Thieme Verlag, 1972, pp. 43-55.

5. Rz6ska, J. Bait shyness, a study in rat behaviour. Br. J. Anita. Behav. 1: 128-135, 1953.