Plasticity of acid phosphatase (FRAP) afferent terminal fields and of dorsal horn cell growth in the...

THE JOURNAL OF COMPARATIVE NEUROLOGY 240~414-422 (1985)

Plasticity of Acid Phosphatase (FRAP) Afferent Terminal Fields and of Dorsal Horn Cell Growth in the

Neonatal Rat

MARIA FITZGERALD AND GERTA VRBOVA Department of Anatomy, University College London, London WClE 6BT, United

Kingdom

ABSTRACT Peripheral nerve section results in depletion of fluoride-resistant acid

phosphatase (FRAP) from the nerve terminals in the dorsal horn of the spinal cord (Schoenen et al., '68) and this has been used in the past to map the termination field of individual nerves (Rustioni et al., '71; Devor and Claman, '80). In the present study we show that a similar central depletion occurs following sciatic nerve section or crush in neonatal rats. Unlike adults, however, the area of depletion is rapidly filled by sprouting of FRAP- containing afferent terminals from nearby intact peripheral nerves. The sprouting is extensive but never completely fills the depleted area. After nerve crush there is some recovery of FRAP from the sciatic nerve terminals themselves as well as from nearby nerve terminals. The source of recovered FRAP is demonstrated by resectioning or recrushing the nerves. The sprouting occurred when the sciatic was injured on day 1 but failed to take place when the injury was applied on or after day 10.

Sciatic nerve section on day 1 also produces marked growth retardation of the ipsilateral dorsal horn gray matter that becomes more apparent as the rat matures. Nerve crush produces a less marked shrinkage that is slower in onset. If the nerve is crushed repeatedly, however, so that regeneration is prevented, the shrinkage is analogous to that following nerve section. No shrinkage occurs if the nerve is cut or crushed on day 10.

The results show that separation of the spinal cord from its peripheral input at a critical stage in development results in disruption of the somatotopic organization of the C fibre afferent input to the dorsal horn and in slowing of growth of the dorsal horn gray matter.

Key words: development, spinal cord, sprouting, transneuronal atrophy

The dependence of the final adult organization of the CNS on normal afferent input during postnatal development has been well demonstrated in sensory systems. For example, monocular enucleation produces considerable changes in circuitry in the lateral geniculate nucleus and the visual cortex (Kalil, '80; Wiesel, '82). Destruction of individual vibrissae in neonatal rodents prevents the development of the characteristic barrel-shaped structures formed by neurons in the medulla, thalamus, or somatosensory cortex (van der Loos and Woolsey, '73; Killackey and Shinder, '82).

The cellular mechanisms underlying these changes are not fully understood but one factor involved is the reaction of nearby intact afferent inputs to the removal of their

0 1985 ALAN R. LISS, INC.

neighbours. In sensory systems where the pattern of afferent terminations in the adult is highly ordered in its representation of the periphery to the CNS, destruction of a discrete part of the afferent input during development dis- torts this, leading to enlargement of nearby intact afferent terminal fields into the denervated region of the CNS. This is a result of either failure to eliminate excess connections as in the visual system (Rakic, '81) or to sprouting of intact terminals as in the trigeminal system (Rhoades et al., '83).

Accepted May 22, 1985.

NEONATAL PLASTICITY IN THE DORSAL HORN

In the companion paper we have shown that central afferent sprouting of nearby intact dorsal root afferents occurs in the spinal cord if a peripheral nerve is cut or crushed within a critical postnatal period (Fitzgerald, '85). The primary afferent input to the dorsal horn of the spinal cord normally terminates in a highly ordered, nonoverlapping somatotopic pattern (Swett and Woolf, '85) but this is dis- rupted by neonatal nerve injury.

The aim of this study was to investigate this neonatal plasticity in the dorsal horn further and concentrate on three aspects of it. Firstly, results of HRP studies suggested that the sprouting fibres were from unmyelinated C fibre afYerents but this required further investigation (Fitzger- ald, '85). Fifty percent of afferent C fibres contain an enzyme, fluoride-resistant acid phosphatase (FRAP), which can be used as a histochemical marker of C fibre terminals in the dorsal horn (Dodd et al., '84). We have used this marker to test whether C fibre af€erents give rise to the sprouting following neonatal peripheral nerve damage. Sec- ondly, we have made a preliminary investigation into the postsynaptic consequences of neonatal peripheral nerve damage by studying the effect of nerve injury on the growth of the dorsal horn in segments that would normally receive input from these afferents. Lastly, we have begun to investigate some of the factors responsible for this plasticity of the dorsal horn. Using both cut and crush nerve injuries at different times after birth and charting the time course of the resulting changes we have assessed the importance of connections with the periphery on the development of both pre- and postsynaptic organization in the dorsal horn.

415

METHODS Wistar rat pups of both sexes were used for this study. At

various postnatal ages from day 1 (the day after birth) to day 25, the pups were anaesthetized with ether and with the use of sterile procedures the sciatic nerves on one side were exposed above the knee. The nerve was either sectioned and ligated or crushed with a pair of watchmaker's forceps for 3 seconds. The wound in the leg was then care- fully sutured and the pups were allowed to recover from the anaesthetic. They were then returned to their mother and recovered uneventfully. In some cases the whole proce- dure of cutting or crushing the same sciatic nerve was repeated at a later date.

At various times after the nerve injury the animals were perfused and processed for fluoride-resistant acid phosphatase (FRAP) histochemistry. This involved perfusing the rats transcardially first with normal saline at 5°C and then with 1% CaClz in 10% formalin at 5°C. The lumbar cord was dissected out on ice and the segments were marked with vertical pins. It was postfixed in formalin with 10% sucrose for 24 hours and then stored in 10% sucrose all at 5°C until ready for processing. Frozen 50-pm transverse sections were cut, saving one section in two for neonates under 14 days old and one in three for older rats. The staining method was based on the Gomori method and has been described in detail elsewhere (Ainsworth et al., '81).

Maps of the dorsal horn were constructed from the serial transverse sections by using camera lucida drawings. The method is illustrated in Figure 1. The extent of FRAP depletion was measured from each section by drawing a horizontal line through the centre of the line of FRAP stain in lamina 11. The midline, medial edge of the dorsal horn, medial border of FRAP stain, and lateral edge of the dorsal horn were marked along the line. The measurements from

Fig. 1. A diagram illustrating the method used to calculate the area of FRAP depletion. On the left is a camera lucida drawing of L4 dorsal horn marking the layer of FRAP stain in lamina 11. Measurements are made of the width of the dorsal horn (a c), the distance of the midline from the medial edge of the dorsal horn (c - d), and the length of the "gap" in the FRAP stain (b - c). These measurements are then plotted consecutively (right-hand side) to give a map of the lamina I1 gray matter from L2 to L5 as a horizontal sheet viewed as if from above.

each section were drawn in sequence down a page and the points joined together to form an outline around the dorsal horn gray matter and the FRAP stain. The result is a horizontal sheet of dorsal horn through lamina TI from the rostral border of L2 to the caudal border of L5 viewed as if from above. The area of the FRAP depletion in the sheet was measured with a computerized drawing pad and area- measurement programme and was expressed as a percentage of the total area of gray matter in the sheet. Naturally, this method of reconstruction provides only a simplified view of the dorsal horn. In particular, the ventral bend of lamina I1 on the lateral edge of the dorsal horn is not taken into account. However, since the sciatic nerve distribution and hence the FRAP depletion in the cord is entirely medial and never involves this lateral edge, this is a reasonable approximation. The method allows a simple but consistent measure of the extent of FRAP depletion that can be expressed as a proportion of the normal total FRAP distribution and can be compared between animals of different ages.

The same measurements of the width of the dorsal horn were used to assess growth retardation. The width of the dorsal horn in six sections, three caudal and three rostral to the L 4 L 5 junction, was measured in each rat. The mean value of the treated side was expressed as a percentage of the mean value for the untreated, opposite side.

RESULTS FRAP staining in control rats

In adult rat cord, a clear band of FRAP staining is consis- tently observed in lamina II of the dorsal horn and has been well described (Gerebtzoff and Maeda, '68; Coimbra et al., '70; Knyihar-Csillik and Csillik, '81). The staining is of the same intensity throughout lamina 11, sometimes inter- rupted by large myelinated fibres entering the gray matter.

FRAP is not observed in neonatal cord until 12-24 hours after birth (Mattio et al., '81; Fitzgerald and Gibson, '84). After this time it becomes visible as a weak, diffuse band

416 M. FITZGERALD AND G. VRBOVA

of staining in lamina 11. This weak stain is of equal intensity throughout the dorsoventral, mediolateral, and rostro- caudal extent of the cord. Over the following week of postnatal life, the FRAP staining becomes more intense and by day 5 it is sufficiently strong to form a clear bound- ary. The band of FRAP in neonatal cord appears at first to be wider in the dorsoventral direction than in the adult. This is not actually the case. The upper dorsal horn in neonates is large relative to the ventral horn and is exag- gerated due to the scarcity of surrounding white matter (Rexed, ’52), making the FRAP staining appear relatively larger than in the adult.

Section of the sciatic nerve in adult rats The sciatic nerve was sectioned in four adult rats and the

effect on FRAP staining in the lumbar dorsal horn examined. The characteristic U-shaped depletion described by Devor and Claman (‘80) was observed, extending from rostral L2 to caudal L5. The edges of the FRAP stain were clearly defined and measuring the area of depletion (see Methods) showed that it occupied 49.6 k 1.0% (n = 4) of the L2-5 lamina I1 gray matter. This exactly corresponds to the reported area occupied by sciatic nerve terminals in the dorsal horn as measured by HRP labelling (Swett and Woolf, ’83); Fitzgerald and Swett, ’83). The area of FRAP depletion following sciatic nerve section in adults has been shown to remain unaltered for at least 6 months (Devor and Claman, ’80).

Section of the sciatic nerve in day 1 neonates The sciatic nerve was sectioned on day 1 in 18 rat pups

and the FRAP staining in the cord studied on day 5 (n = 41, day 12 (n = 41, days 20-30 (n = 4), day 60 (n = 41, and adulthood (n = 2). The results are summarized in Figure 4. FRAP is depleted from the dorsal horn following day 1 sciatic nerve section leaving a U-shaped gap in the stain similar to the gap following adult nerve section. This area of depletion decreases, however, with time after the section (Fig. 4). On day 5 (the earliest age of reliable FRAP staining) the mean gap is already only 29.5 * 1.2% (n = 4) of the lamina II gray matter (Figs. 2A, 3A). On day 12 it has fallen to 27.5 k 1.1% (n = 4) and by day 30 to 22.7 f 1.5% (n = 4) (Figs. 2B, 3B). After this time (day 60 and adult) the area remains the same, never completely filling in, but smaller than control values. The shrinkage of the area of depletion is due to a “filling in” of the sciatic terminal region with a thinner, less densely stained line of FRAP. While clearly defined and easy to detect, this “new” FRAP staining is rarely as intense as the original. The new FRAP comes from the lateral caudal, and rostra1 edges of the sciatic field where it abutts the fields of adjacent nerves.

Resectioning the sciatic nerve To investigate the origin of the returning FRAP, five rats

whose sciatic nerve had been sectioned on day 1 were oper- ated on once more on day 20-25. The sciatic nerve was resectioned 1 mm proximal to the first section. Five days later the area of FRAP depletion was measured in the dorsal horn. The mean value was 23.1 * 1.1% of the lamina II, which is the same as the value in rats of this age whose sciatic nerves were sectioned only once, on day 1. The resection therefore has no effect on the “filling-in” of FRAP into the sciatic terminal field, suggesting that the source is from FRAP-containing terminals other than those of the sciatic nerve itself (Figs. 2C, 3C).

L4

_ _ _ - i L5 I I ______._ 2 L L. _ _ _ _ _ J d

250

Fig. 2. Horizontal maps of the lumbar spinal cord reconstructed from serial transverse sections. The vertical lines represent the midline. The outline is that of the lamina I1 gray matter and the extent of FRAP depletion within that area is marked as a shaded area. A. Map of FRAP depletion of a 12-day-old rat pup following sciatic nerve section on day 1. The dotted line shows the theoretical total sciatic nerve terminal field. B. A 30-day-old rat following sciatic nerve section on day 1. C. A 30-day-old rat following sciatic nerve section on day 1 and resection on day 25.

Crushing the sciatic nerve on day 1 The sciatic nerve was crushed on postnatal day 1 in 18

rats and the FRAP depletion examined on postnatal day 5 (n = 4), day 12 (n = 41, days 20-30 (n = 41, day 60 (n = 41, and adulthood (n = 2). On postnatal day 5 , the area of depletion was comparable to that following nerve section and occupied 31.4 * 1.5% of the gray matter area. Again the area continues to fill in with time but does so more rapidly and completely than after nerve section. On day 12 the area is 24.7% +_ 0.9% (Fig. 5A,D), but by days 20-30 (Fig. 5B) it is only 16.8 k 1.6% and by day 60 the gap is no longer detectable (Fig. 4).

Recrushing the sciatic nerve To test the origin of the FRAP recovery following day 1

nerve crush, four rat pups whose sciatic nerves had been crushed on day 1 were reoperated upon. Their sciatic nerves were recrushed on day 10 and again on day 18. The FRAP

NEONATAL PLASTICITY IN THE DORSAL HORN 417

Fig. 3. A. 50-pm transverse section of a 5-day-old rat cord at L4 stained for FRAP. The sciatic nerve was sectioned on day 1 and the medial depletion of FRAP can be seen. Scale bar = 100 pm. B. A 50-pm transverse section of a 30day-old rat cord at L4 stained for FRAP. The sciatic nerve was sectioned

on day 1. Scale bar = 100 pm. C. A 50-pm transverse section of a 30-day-old rat cord at L4 where the sciatic nerve was sectioned on day 1 and again on day 25. Scale = 100 pm.


Fig. 4. Diagrammatic representation of the results of FRAP depletion in lamina I1 of the L2-L5 dorsal horn following sciatic nerve injury. The results are expressed as a percentage of the total gray matter terminal area in lamina 11. On the left (single black bar) is the control value, i.e., the percentage area occupied by FRAP terminals of the sciatic nerve in the adult as revealed by the depletion following adult sciatic nerve section. In the centre, black bars represent the percentage areas following sciatic nerve section on day 1 of life measured on days 5,12,20-30,60, and in adulthood. White bars are the same measures taken after nerve crush. On the far right the black bar marked (0) represents the area following section on day 1 and resection on day 25 and perfusion on day 30. The white bar marked (0) represents the area following crush on day 1 and recrush on days 10 and 18 and perfusion on day 25. The results are mean values k S.E. For pool sizes see text.

stain in the cord was examined on day 25 (Fig. 5C,E). The depleted area was 25.1 k 1.3% of the lamina I1 gray matter, a value somewhat larger compared to the area at day 25 after a single nerve crush, but still considerably smaller than the known field of sciatic nerve terminals (Fig. 4). This implies that after crushing a nerve on day 1 there is sprouting from nearby intact FRAP-containing terminals, but in addition there is some recovery of FRAP within the sciatic terminals themselves.

Critical period for FRAP terminal sprouting In four rats the sciatic nerve was sectioned on days 10-18

of life, rather than on day 1. In these cases the FRAP depletion was 48 k 2.0% of the total lamina I1 area, i.e., it occupied the full terminal field of sciatic nerve afferents. There was no sign of sprouting from nearby terminals to fill in the gap. The same was found if the nerve was crushed twice: once on day 10 and again on day 18 (n = 4) (Fig. 6 A,B).

Postsynaptic effects of neonatal sciatic nerve injury in the dorsal horn

In addition to producing sprouting of nearby afferents, injury to the sciatic nerve on day 1 resulted in considerable slowing of growth of the dorsal horn on the treated side so that it appeared shrunken in comparison with the untreated side. This retardation of growth was in both the mediolateral and dorsoventral dimensions and was maximal in the caudal L4 and rostra1 L5 segments.

Figure 7 shows the maximal effect on the growth of the dorsal horn in the mediolateral dimension with time after sciatic nerve section on day 1. Eighteen rat pups were studied on days 5 (n = 4),12 (n = 4),20-30 (n = 4), 60 (n = 4), and adulthood (n = 2). The effect is small in the first week but gradually increases such that by day 12 the treated side is 18.0 k

Sciatic nerve section or crush on day 1.

B C -

250

Fig. 5. A-C. Horizontal reconstruction of lumbar spinal cords showing the depletion of FRAP (shaded area) following: (A) crush of the sciatic nerve on day 1, perfusion on day 12; (B) crush on day 1, death on day 26; (C) crush on day 1, day 10, and day 18 and perfusion on day 25.

1.0% smaller than the contralateral, untreated side, and by day 60 it is 22.0 & 0.7% smaller. When the rats reach adulthood the treated side is 40.0 k 2% smaller (see Figs. 2B,C).

Growth is also impeded following sciatic nerve crush on day 1 (n = 18) but the extent and time course are different from that following nerve section (Fig. 7). The difference in the two sides of the cord is very small, less than lo%, until day 60, when a clear, persistent difference between the two sides of 20 1.6% is observed. The effect is never as great as that following nerve section.

Recrushing the sciatic nerve. Crushed nerves are able to regenerate and make contact with the periphery again, so here we tested the effect of preventing that. In four animals the nerve was crushed once on day 1, then again on day 10, and again on day 18, and the rat was perfused on day 25 (Fig. 7). The growth retardation of the dorsal horn under these circumstances was 19.7 & 1.1%, the same


Fig. 5. D. Transverse 50-pm section of spinal cord at L4 segment stained for FRAP from the rat in A. Scale = 100 pm. E. Transverse section (50 pm) from the rat in C. Scale = 100 pm.

as rats of the same age whose sciatic nerves had been sectioned on day 1 (Fig. 5E).

Critical period. Crushing a sciatic nerve on day 10 and again on day 18 and perfusing on day 25 (n = 4) had no effect on the growth of the dorsal horn (Fig. 6B).

DISCUSSION Neonatal peripheral nerve injury has been shown, by

HRP labelling, to induce central sprouting in the dorsal horn of the terminals of nearby intact nerves (Fitzgerald, '85). Here we have shown that this sprouting occurs in C fibre sensory afferent terminals in lamina I1 or substantia

gelatinosa. The results used FRAP-containing afferent terminals as a marker for C fibres. FRAP is an extralysomal enzyme manufactured in 50% of the small "B"-type dorsal root ganglion cells and transported along the peripheral and central processes of sensory C fibres (Knyihar-Csillik and Csillik, '81; Dodd et al., '84). It is apparently restricted to cutaneous and visceral C afferents and not found in muscle C fibres (McMahon et al., '85). Its function is not known but it aroused considerable interest when it was reported that the peripheral nerve section or crush resulted in a depletion of FRAP from the dorsal root ganglia and central terminals in the dorsal horn in the absence of de-

420

generation (Schoenen et al., '68; Knyihar and Csillik, '76). Blockade of peripheral axon transport by local capsaicin or vinblastine also results in central FRAP depletion (Ain- sworth et al., '81; Fitzgerald et al., '84). This depletion, leaving a clear gap in the dorsal horn FRAP stain, has been used to map the termination field of peripheral nerves in the dorsal horn and medulla (Rustioni et al., '71; Devor and Claman, '80) and here we have confirmed that in the adult

M. FITZGERALD AND G. VRBOVA

day1 section 0 resection 0 ,I C N S h o recrush

100

A f - - - - 'I

Fig. 7. Diagrammatic representation of the lack of growth of the caudal L4 dorsal horn following neonatal peripheral nerve injury. The results are expressed as the width of lamina I1 of the dorsal horn on the treated side a5 a percentage of the untreated side. A value of 100% shows no difference between the two sides. Black bars represent the widths after sciatic nerve section on day 1 of life, and the white bars widths after day 1 nerve crush, measured on days 5, 12, 20-30, 60, and adulthood. The black bar marked (0) represents the width after sciatic nerve section on day 1 and resection on day 25 and perfusion on day 30. The white bar marked (0) represents the width after sciatic nerve crush on day 1, recrush on days 10 and 18, and perfusion on day 25. The results are means f S.E. from several animals (for pool sizes see text).

250urn

this method gives results for the sciatic nerve terminal field that exactly match those from HRP labelling (Swett and Woolf, '85). Recovery of FRAP occurs about a year after nerve section in adult rats and is not due to sprouting of nearby afferent terminals since recutting the nerve results in prompt depletion again (Devor and Claman, '80). Recov- ery is more rapid, in about 68-80 days, following adult nerve crush due to regeneration of the damaged nerve (Knyihar-Csillik and Csillik, '81).

The results reported here show that peripheral nerve injury in neonatal rats also results in FRAP depletion from central terminals but that if the injury is performed in the

Fig. G . A. Horizontal reconstruction of the lumbar spinal cord of a day 25 rat showing the FRAP depletion following sciatoc nerve crush on day 10

and day 18. B. A 50-pm transverse section through L4 of the same rat, stained for FRAP. Scale = 100 pm.


early neonatal period the depleted area is rapidly "filled in" again. Resection of the nerve did not alter the area of depletion, confirming the fact that this FRAP recovery was entirely due to afferents other than those of the cut nerve. Studies on sprouting using HRP labelling make it very likely that these FRAP afferents were from the adjacent saphenous nerve and other thigh and back nerves that terminate adjacent to the sciatic nerve terminals in the dorsal horn (Devor and Claman, '80; Swett and Woolf, '85). Crush injury on day 1 also induced adjacent afferent sprouting but here there was also some recovery of FRAP from the crushed sciatic nerve itself. This component was lost following recrushing a t day 10 and day 18 and therefore was likely to be a result of the regenerating nerve making contact with the periphery (Sunderland, '78). The sprouting of nearby FRAP afferents following nerve crush was not as extensive as that following nerve cut, confirming the results using HRP labelling (Fitzgerald, '85) and perhaps reflecting the less extensive cell death in the dorsal root ganglia which would follow the crush injury (Waite and Cragg, '82; Riding et al., '83).

One clear difference between the results reported here, using FRAP depletion, and those reported in the previous paper on sprouting (Fitzgerald, '85) using HRP labelling is that sprouting revealed by HRP labelling following neonatal cut or crush injury was fully established 5 days after injury whereas sprouting revealed by "filling in" of FRAP staining, although present at 5 days, is not fully established for several weeks. This discrepancy in timing is not surpris- ing when one considers that HRP is an exogenous marker, which when applied to a peripheral nerve is limited only by transport rate and will presumably label all central terminals, both new and old, equally. FRAP, on the other hand, is an endogenous marker, an enzyme whose presence in nerve terminals is determined by the metabolic state of the cell body (Dodd et al., '84). It seems likely that new sprouts may only acquire FRAP slowly and therefore not immediately contain the same amount as mature terminals. The fact that the area of FRAP depletion is never completely filled in suggests that some new sprouts may never acquire FRAP since the HRP labelling experiments (Fitzgerald, '85) suggest that sprouts from all the adjacent nerves should fill the area. Alternatively the subgroup of fierents containing FRAP could be more restricted in their ability to sprout.

Peripheral nerve injury at a critical neonatal stage not only has effects on nearby afferent terminals but also has an effect on the development of the dorsal horn neuropil, resulting in a considerable retardation of normal growth of the gray matter in the terminal region. Similar lack of growth was shown after dorsal rhizotomy in utero in sheep (Barron, '45). No change in dorsal horn dimension is seen after dorsal rhizotomy in adults (Brown et al., '79) and therefore it is not simply a result of loss of large myelinated fierents or of denervation atrophy in dorsal horn cells. More detailed study is needed to find the underlying cause for this lack of growth. It could be due to dorsal horn cell death (Kelly and Cowan, '72) or to soma shrinkage (Fukuda and Hsaio, '&I), dendritic shrinkage (Murphy et al., '751, or even dendritic distortion, whereby dendrites are attracted toward healthy d e r e n t s (Belford and Killackey, '80). Whatever the mechanism, the shrinkage provides a useful indicator of postsynaptic changes in the dorsal horn. It occurs when afferent input is withdrawn at a critical stage of development. Sensory stimulation is required for the

maturation of several neuronal circuits. Although the neurons originate and form connections according to a developmental timetable, many fail to fully mature in the absence of sensory stimulation (Jacobson, '78). Transneu- ronal atrophy as a result of neonatal removal of afferent inputs has been reported in the visual system (Guillery, '731, the auditory system (Trune, '82) and in Clark's column in the kitten spinal cord (Loewy, '72).

The failure of dorsal horn cells to mature fully after neonatal sciatic nerve section may itself be a trigger for sprouting of nearby afferents into the sciatic nerve terminal region. The timing of the two events, however, make this unlikely. Sprouting can already be observed on day 5 whereas postsynaptic changes cannot be observed until days 9-10. More important, sprouting is triggered by crushing a nerve but when. it regenerates so that contact is remade with the periphery there is no reversal of the sprouting. The new terminals become a fixed part of the organization of the afferent input to the dorsal horn, distorting the normal somatotopic map. Dorsal horn growth, however, is min- imally affected by crushing a nerve on day 1 and allowing it to regenerate. Repeated nerve crushes which prevent regeneration produce considerable growth retardation, comparable to that following nerve section. Continued isolation from the periphery is therefore necessary for postsynaptic effects whereas short-term isolation is sufficient to trigger sprouting as long as it begins in the early postnatal period.

Despite extensive sprouting, the nearby afferents are not able to stimulate or support the dorsal horn cell growth as effectively as the original afferents. Furthermore, other inputs to the dorsal horn, such as those descending from the brainstem, are also insufficient.

Several questions are raised by these results. It would be interesting to know more details of the contacts made by the sprouting afferents and the morphological changes that occur in dorsal horn cells. The role of peripheral and central trophic factors andor activity patterns should be investi- gated. More importantly, neurophysiological investigations are necessary to establish to what extent these changes cause real functional alterations in the somatosensory pathways in the dorsal horn.

ACKNOWLEDGMENTS We are indebted to P. Ainsworth for her skilled histology

and to P.D. Wall and C.J. Woolf for helpful discussions. The work was supported by the M.R.C.

LITERATURE CITED Ainsworth, A,, P. Hall, P.D. Wall, G. Allt, M. Lynn Mackenzie, S. Gibson,

and J.M. Polak (1981) Effects of capsaicin applied locally to adult peripheral nerve. II. Anatomy and enzyme and peptide chemistry of peripheral nerve and spinal cord. Pain II:379-388.

Barron, D.H. (1945) The role of sensory fibres in the differentiation of the spinal cord in sheep. J. Exp. Zool.IOOr431-444.

Belford, G.R., and H.P. Killackey (1980) The sensitive period in the development of the trigeminal system of the neonatal rat. J. Comp. Neurol. I93r335-359.

Brown, P.B., G.R. Busch, and J. Whittington (1979) Anatomical changes in cat dorsal horn cells after transection of a single dorsal root. Exp. Neurol. 64r453468.

Coimbra, A., M.B. Magalhaes, and B.P. Sodre Borges (1970) Ultrastructural localization of acid phosphatase in synaptic terminals of the rat substantia gelatinosa Rolandi. Brain Res. 22142-146.

Devor, M., and D. Claman (1980) Mapping and plasticity of acid phosphatase afferents in the rat dorsal horn. Brain Res. 19Ot17-28.

Dodd, J., G.E. Jahr, and T.M. Jessell (1984) Neurotransmitters and neuronal


markers at sensory synapses in the dorsal horn. In L. Kruger and J.C. Liebeskind (Eds.): Advances in Pain Research and Therapy, Vol. 6, Neural Mechanisms of Pain. New York: Raven Press, pp. 105-122.

Fitzgerald, M. (1985) The sprouting of saphenous nerve terminals in the spinal cord following early postnatal sciatic nerve section in the rat. J. Comp. Neurol. 240:407-413.

Fitzgerald, M., and S.J. Gibson (1984) The postnatal physiological and neurochemical development of peripheral sensory C fibres. Neurosci- ence 13t933-944.

Fitzgerald, M., and J. Swett (1983) The termination pattern of sciatic nerve d e r e n t s in the substantia gelatinosa of neonatal rats. Neurosci. Lett. 43t149-154.

Fitzgerald, M., C.J. Woolf, S.J. Gibson, and P.S. Mallaburn (1984) Altera- tions in the structure, function and chemistry of C fibres following local application of vinblastine to the sciatic nerve of the rat. J. Neurosci. 4:430441.

Fukuda, Y., and C.F. Hsaio (1984) Bilateral changes in soma size of genicu- lar relay cells and corticogeniculate cells after neonatal monocular enucleation in rats. Brain Res. 301:13-23.

Gerebtzoff, M.A., and T. Maeda (1968) Characteres et localisation histochi- mique d‘un isoenzyme fluororesistant de la phosphatase acide dane le moelle epiniere du rat. C.R. Soc. Biol. (Paris) 1622032-2035.

Guillery, R.W. (1973) Quantitative studies of transneuronal atrophy in the dorsal lateral geniculate nucleus of cats and kittens. J. Comp. Neurol. 149:423438.

Hopkins, W.G., and M.C. Brown (1984) Development of Nerve Cells and Their Connections. Cambridge: Cambridge University Press.

Jacobson, M. (1978) Developmental Neurobiology. New York: Plenum Press. Kalil, R. (1980) A quantitative study of the effects of monocular enucleation

and deprivation on cell growth in the dorsal lateral geniculate nucleus of the cat. J. Comp. Neurol. 189:483-524.

Kelly, J.P., and W.M. Cowan (1972) Studies on the development of the chick optic tectum: 111. Effects of early eye removal. Brain Res. 42263-288.

Killackey, H.P., and A. Shinder (1981) Central correlates of peripheral pattern alterations in the trigeminal system of the rat: 11. The effect of nerve section. Dev. Brain Res. I:121-126.

Knyihar, E., and B. Csillik (1976) Effect of peripheral axotomy on the fine structure and histochemistry of the Roland0 substance. Exp. Brain Res. 26:73-87.

Knyihar-Csillik. E., and B. Csillik (1981) FRAP Histochemistry of the primary nociceptive neuron. Prog. Histochem. Cytochem. 14.1-137.

Loewy, A.D. (1972) The effects of dorsal root lesions on Clarke neurons in cats of different ages. J. Comp. Neurol. 145t141-164.

Mattio, T.G., T.H. Rosenquist, and M.L. Kirby (1981) Appearance of acid phosphatase in neonatal rat substantial gelatinosa. Exp. Brain Res. 41t411-413.

McMahon, S.B., E. Sykova, P.D. Wall, C.J. Woolf, and S.J. Gibson (1985) Neurogenic extravasation and substance P levels are low in muscle as compared to skin in the rat hindlimb. Neurosci. Lett. 52235-239.

Murphy, R.K., E. Menenhall, J. Palka, and J.S. Edwards (1975) Deafferen- tation slows the growth of specific dendrites of identified giant interneu- rones. J. Comp. Neurol., 159t407-418.

Rakic, P. (1981) Development of visual centres in the primate brain depends on binocular competition before birth. Science 214.928-931.

Rexed, B. (1952) The cytoarchitectonic organization of the spinal cord in the cat. J. Comp. Neurol. 96:415466.

Rhoades, R.W., J.M. Fiore, M.F. Math, and M.F. Jacquin (1983) Reorganiza- tion of trigeminal primary afferents following neonatal infraorbital nerve section in the hamster. Dev. Brain Res. 7:337-342.

Riding, M., H. Aldskogius, and C. Hildebrand (1983) Effects of sciatic nerve crush on the L7 spinal roots and dorsal root ganglia in kittens. Exp. Neurol. 79t176-187.

Rustioni, A,, Sanyal, S., and H.G.J.M. Kuypers (1971) A histochemical study of the distribution of the trigeminal divisions in substantia gelatinosa of the rat. Brain Res. 32:45-52.

Schoenen, J., C. Budo, and G. Poncelet (1968) Effect de la section du scia- tique sur l’activite de l’isoenzyme fluoresistant de la phosphatase acide dans la moelle epiniere du rat. C.R. soc. Biol. (Paris) 1622035-2937.

Sunderland, S. (1978) Nerves and Nerve Injury, 2nd edition. London: Churchill Livingstone.

Swett, J.E., and C.J. Woolf (1985) The somatotopic organization of primary afferent terminals in the superficial laminae of the dorsal horn of the rat spinal cord. J. Comp. Neurol. 23lt66-77.

Trune, D.R. (1982) Influence of neonatal cochlear removal on the development of mouse cochlear nucleus: I. Number, size, and density of its neurons. J. Comp. Neurol. 209:425-434.

van der Loos, H., and T.A. Woolsey (1973) Somatosensory cortex: Structural alterations following early injury to sense organs. Science 179:395-398.

Waite, P.M.E., and B.G. Cragg (1982) The peripheral and central changes resulting from cutting or crushing the afferent nerve supply to the whiskers. Proc. R. Soc. Lond. [Biol.] 214:191-211.

Wiesel, T.N. (1982) Postnatal development of the visual cortex and the influence of the environment. Nature 299:583-591.

Plasticity of acid phosphatase (FRAP) afferent terminal fields and of dorsal horn cell growth in the...

Documents

Transcript of Plasticity of acid phosphatase (FRAP) afferent terminal fields and of dorsal horn cell growth in the...