The ovarian innervation in the dog: a preliminary study for the base for electro-acupuncture.

The origin of the canine ovarian sensory and sympathetic nerves was studied by applying horseradish peroxidase (HRP) or wheat germ agglutinin conjugated to HRP (WGA-HRP) to the ovarian stroma and into the ovarian bursa. HRP/WGA-HRP positive neurons were found bilaterally in the dorsal root ganglia of T10 to L4 segment with the majority located in T13 to L2. In sympathetic paravertebral ganglia, labeled neurons were distributed bilaterally in ganglia from T11 to L4 with the majorities located in segments T13 to L2. Both distributions show ipsilateral predominance. Labeled prevertebral neurons were mainly located in the aorticorenal ganglion, ovarian ganglia and caudal mesenteric ganglion. No labeled neurons were found in the dorsal motor nucleus of vagus, nodose ganglia or sacral segment from S1 to S3. This study provides the possible morphological basis of electro-acupuncture concerning the somato-visceral reflex of the ovary.     

Localization of sympathetic and sensory neurons innervating the rat kidney

Following injection of horseradish peroxidase (HRP) into the hilar region of the left kidney of the rat, 66% of labeled sympathetic neurons were located in the ipsilateral paravertebral ganglia, with most cells in T13 and L1, and 14% were located in equivalent segments of the contralateral chain. A similar distribution of sympathetic neurons projected to the right kidney, with most cells in T12 and T13 paravertebral ganglia. Only 20% of the total sympathetic supply to either kidney arose from the prevertebral ganglia. The renal sensory innervation was also bilateral in origin, with about 80% of the neurons arising from ipsilateral dorsal root ganglia. Injection of HRP into the caudal and rostral poles of the left kidney labeled paravertebral neurons which were concentrated in ganglia L1 and T13, respectively, but did not label any sensory neurons. We conclude that most of the renal sympathetic innervation is paravertebral in origin, and that a substantial bilateral component exists for both sympathetic and sensory supplies. Neurons arising from the contralateral side have their cell bodies in segments that provide the main ipsilateral innervation to the same kidney. The majority of sensory axons appear to be restricted to subcortical areas.     

Origins of the renal innervation in the primate, Macaca fascicularis

The origins of the renal efferent and afferent nerves in 5 cynomolgus monkeys (Macaca fascicularis) were studied by using the retrograde transport of horseradish peroxidase (HRP) and horseradish peroxidase-wheat germ agglutinin (HRP-WGA). The cut ends of the right renal nerves were soaked for 30-45 min in solutions consisting of 15% HRP and 1% HRP-WGA. Three or four days later the animals were killed and the tissues examined for the presence of retrogradely labeled neurons, HRP-filled cells were observed, with rare exceptions, only in ganglia ipsilateral to the side of tracer application. Renal efferent neurons (4648-14565 cells per animal) were found in relatively equal numbers in prevertebral and paravertebral (sympathetic chain) ganglia. Labeled prevertebral cells were distributed among the renal (52%), aorticorenal (32%) and superior mesenteric (16%) ganglia, whereas labeled paravertebral neurons were mainly located in chain ganglia T11-L3, with 94% of these located in L1-3. Labeled renal sensory neurons (31-543 per animal) constituted less than 5% of all labeled cells and were found in ipsilateral dorsal root ganglia T10-L3, with (80%) in T12 and L1. The labeled sensory neurons ranged from 18-64 microns in diameter (X = 32.4 microns). With the exception of a single cell in one animal, no labeled neurons were observed in the nodose ganglia. Many parallels were observed between the organization of the renal plexuses of macaques and humans, suggesting the utility of the non-human primate as an experimental model for functional studies of renal innervation in humans.     

Organization of sensory and motor nuclei of the trigeminal nerve in lampreys

Anterograde and retrograde HRP transport were used to elucidate the primary central projections of the trigeminal nerve in a lamprey, Lampetra japonica, by application to the ophthalmic, apical, basilar, suborbital, and mandibular branches of the trigeminal nerve. (1) Most of the trigeminal and a few facial ganglion cells were labeled. The ganglion cells of each nerve were distributed in separate areas within their respective ganglia. (2) Some ipsilateral medullary and spinal dorsal cells were labeled after HRP application to the ophthalmic and apical nerves, but there was no contralateral labeling. (3) Most of the neurons of the trigeminal motor nucleus were labeled, and when the apical or the basilar nerve was labeled, in each case a cluster of small motor neurons was found ventrolateral to the classic motor nucleus. (4) Miscellaneous neurons were found scattered along the course of the descending trigeminal tract and nucleus in all cases except after application to the mandibular branch. The shape, size, and distribution patterns of these neurons were varied, and several characteristics indicated that they were sensory in nature. (5) In the rostral part of the medulla, sensory fibers of each nerve showed restricted localization within the descending trigeminal tract and nucleus. When compared to the distribution of the same fibers in the hagfish Eptatretus burgeri, another member of the cyclostomes, the distribution pattern in the lampreys studied was closer to the type seen in gnathostomes.     

The origins of innervation of the esophagus of the dog

This study defined the origins of extrinsic efferent and afferent innervation of the normal canine esophagus. When all the layers of the wall of the 3 esophageal regions (cervical, thoracic and abdominal) were injected with horseradish peroxidase (HRP), labeled nerve cells were found in the nucleus ambiguus (NA) and parasympathetic nucleus of X (PX) of the brainstem. Most labeled cells in the NA were located in the compact column (retrofacial nucleus) while labeled cells in the PX were located in separate rostral and caudal areas. There was no somatotopic organization in either the NA or PX. Labeled sympathetic postganglionic neurons were found in the cranial cervical, middle cervical, cervicothoracic, thoracic sympathetic trunk and celiacomesenteric ganglia. The HRP injection of the esophageal wall labeled sensory cell bodies in the glossopharyngeal, proximal and distal vagal, and C2-T6 spinal ganglia. There was no discernible pattern of distribution of labeled cells in the autonomic or sensory ganglia. When the HRP injections were confined to the mucosa-submucosa layers of the thoracic esophagus, a small number of labeled cells were identified in the NA; however, no labeled cells were found in the NA when injections were confined to the mucosa-submucosa of either the cervical or abdominal esophageal regions. With these confined injections, the labeled nerve cells appeared in the rostral part of the PX. Thus, it appeared that the internal tunics of the esophagus (i.e., the mucosa and submucosa) were innervated by neurons in the rostral PX while the muscular tunic was innervated by neurons in the caudal PX and the rostral NA. After mucosa-submucosa injections, labeled sympathetic neurons appeared in the same ganglia that were identified after whole wall injections and these had a similar random distribution. These injections also labeled neurons in the glossopharyngeal, proximal vagal, and distal vagal ganglia, but unlike the whole wall injections there was no labeling in the spinal ganglia. This suggested that the labeled cells of the spinal ganglia seen after whole wall injections conveyed impulses from the tunica muscularis and serosa.     

The distribution of the cat''s carotid sinus nerve afferent and efferent cell bodies using the horseradish peroxidase technique

The location of both afferent and efferent carotid sinus nerve (CSN) cell bodies in the cat has been determined using the horseradish peroxidase (HRP) technique. Following a limited exposure of the central cut end of the CSN to HRP, labeled sensory ganglion cells were found in both the petrosal and superior ganglia of the IXth cranial nerve. An average of 387 in the former and 16 cells in the latter ganglion were labeled.

Retrogradely labeled neurons were found only within the ipsilateral medulla. These cells were both round and spindle shaped and had an average somal diameter of 19 μm. The number of these CSN efferent cell bodies ranged from 1 to a maximum of 20 in a given animal. They were found in both the nucleus parvocellularis and the retrofacial nucleus. In 8 cases axonal labeling was observed. Axons generally projected dorsomedially from the ventrolateral medulla.     

Motor and sensory centers for the innervation of mandibular and sublingual salivary glands: A horseradish peroxidase study in the dog

Horseradish peroxidase was injected at multiple sites in the mandibular and sublingual salivary glands in order to label the preganglionic salivatory neurons in the brain stem. The same injections resulted in retrograde labeling of the sympathetic and sensory neurons that project to these glands.Labeled fusiform and multipolar salivatory neurons were found ipsilaterally in the lateral reticular formation of the medulla where they extended over the rostral four-fifths of the facial nucleus and the caudal one-third of the dorsal nucleus of the trapezoid body. The vast majority of the small and medium-sized, labeled neurons appeared in the nucleus reticularis parvocellularis. Labeled neurons also appeared occasionally at the ventral and lateral aspects of the facial nucleus.Enzyme injections into these glands labeled sympathetic neurons that were concentrated in the caudal one-third of the ipsilateral cranial cervical ganglion. Labeled sensory neurons were distributed randomly in the ipsilateral proximal vagal and geniculate ganglia. Large numbers of sensory neurons were concentrated ventromedially within the mandibular zone of the trigeminal ganglion.     

Synaptic connections between spinal motoneurons and dorsal root ganglion cells in the cat

Light- and electron-microscopical horseradish peroxidase (HRP) studies have been employed in conjunction with a degeneration study in order to clarify the origin and axonal passage of afferent synaptic terminals in cat dorsal root ganglia. After injection of HRP into ganglia (C3) without involvement of the ventral roots and spinal nerves, a few ipsilateral spinal ventral horn neurons (C3) were retrogradely labeled with HRP. The labeled neurons were localized in the dorsomedial and the ventromedial nuclei. Following ventral rhizotomy of C3, the afferent terminals in the ganglia (C3) anterogradely degenerated and contained accumulated and disintegrated neurofilaments, depleted, aggregated and enlarged synaptic vesicles. Subsequent to an HRP and wheat germ agglutinin (WGA)-HRP-mixture injection into the dorsal neck or suboccipital muscles, many spinal motoneurons (C3) were labeled retrogradely with an HRP mixture. On the other hand, the afferent synaptic terminals in ganglia contained the membrane-bound and electron-dense bodies which were anterogradely labeled with an HRP mixture in addition to the normal synaptic elements. The present findings strongly suggest that some spinal motoneurons send their axon collaterals to the dorsal root ganglia, in which the terminals of the axon collaterals directly synapse with the dorsal root ganglion cells.     

An HRP study of the central projections of primary trigeminal neurons which innervate tooth pulps in the cat

Trigeminal ganglia and brain stem of adult cats were studied following HRP injections into tooth pulps or after exposure of the cut end of the inferior alveolar nerve to HRP. Ipsilateral ganglion cells within a wide range of sizes were labeled in both experimental situations, whereas no labeled cells were observed in the contralateral ganglion in any animal. Labeled central branches of tooth pulp and inferior alveolar neurons were observed in all subdivisions of the ipsilateral trigeminal sensory complex. Terminal labeling in the tooth pulp experiments was confined to the dorsomedial parts of the main sensory nucleus and subnuclei oralis and interpolaris. Caudal to the obex terminal labeling was restricted to the medial halves of laminae I, IIa and V of the medullary dorsal horn. In the inferior alveolar nerve experiments dense terminal labeling was observed in the dorsal parts of the main sensory nucleus and subnuclei oralis and interpolaris. Caudal to the obex terminal labeling was located throughout laminae I to V in contrast to the tooth pulp experiments. Neither of the two experimental situations offers any evidence for a bilateral or contralateral brain stem projection of primary trigeminal neurons.     

Proprioceptive reflex connections of head musculature and the mesencephalic trigeminal nucleus in the carp

The location of the sensory cells concerned with the proprioception of respiratory and extraocular musculature in the carp was studied by retrograde transport of horseradish peroxidase. Sensory cell labeling after intramuscular HRP injection was exclusively found in the trigeminal-facial-anterior lateral line ganglion complex. The muscles innervated by the trigeminal system are represented in the more rostral ganglion areas, the muscles innervated by the facial system in the more caudal ganglion parts. Nearly all labeled cells were situated on the ipsilateral side. Sensory cells labeled after extraocular muscle injection were also found all over the V-VII ganglion, however, to a considerable degree also on the contralateral side. All muscle injections failed to give mesencephalic trigeminal cell labeling. The results of intranerve HRP injections in peripheral trigeminal nerve branches strongly suggests a perioral mechanoreceptive function for the mes.V neurons. A bisynaptic proprioceptive reflex model is described for respiratory musculature consisting of a sensory cranial ganglion component connected to the descending trigeminal nucleus, which on its turn links the proprioceptive ganglion cells to the trigeminal and facial motorneurons. Monosynaptic proprioceptive reflex circuits are discussed on neurophysiological grounds.     

Primary sensory ganglion cells projecting to the principal trigeminal nucleus in the mallard, Anas platyrhynchos

The trigeminal and glossopharyngeal ganglia of the adult mallard were studied following HRP injections into the principal trigeminal nucleus (PrV). The PrV consists of the principal trigeminal nucleus proper (prV) and the principal glossopharyngeal nucleus (prIX). After an injection into the prV, the labeled cells were found in the ipsilateral trigeminal ganglion. After an injection into the prIX, labeled cells were found in the ipsilateral distal glossopharyngeal ganglion, but not in the proximal ganglion of the IX and X cranial nerve (pGIX + X). In Nissl preparations, two types of ganglion cells in the trigeminal ganglion, pGIX + X, and distal ganglion of N IX could be distinguished: larger light cells and smaller dark cells. We could not determine whether the HRP-labeled cells belonged to both types or to one of them; but because all the labeled cells were over 20 microns, we concluded that the smallest cells (10-19 microns) in the trigeminal ganglion and distal ganglion of N IX did not project to the PrV. The labeling of the cells in the distal ganglion of N IX (average 34.5 microns) was uniformly moderate. In the trigeminal ganglion there were two types of labeled cells: heavily labeled cells (average 29.1 microns) and moderately labeled cells (average 35.1 l microns). These two types of labeling (moderate and heavy) may reflect two types of primary sensory neurons: cells with ascending, nonbifurcating axons, and cells with bifurcating axons. We speculate that the former are proprioceptive neurons and the latter tactile neurons. Labeled bifurcating axons in the sensory trigeminal complex gave off collaterals to all parts of the descending trigeminal nucleus except to the caudalmost laminated spinal part.     

Segmental distribution and central projectionsof renal afferent fibers in the cat studied by transganglionic transport of horseradish peroxidase

The segmental and central distributions of renal nerve afferents in adult cats and kittens were studied by using retrograde and transganglionic transport of horseradish peroxidase (HRP). Transport of HRP from the central cut ends of the left renal nerves labeled afferent axons in the ipsilateral minor splanchnic nerves and sensory perikarya in the dorsal root ganglia from T12 to L4. The majority of labeled cells (85%) were located between L1 and L3. A few neurons in the contralateral dorsal root ganglia were also labeled. Labeled cells were not confined to any particular region within a dorsal root ganglion. Some examples of bifurcation of the peripheral and central processes within the ganglion were noted. A small number of preganglionic neurons, concentrated in the intermediolateral nucleus, were also identified in some experiments. In addition, many sympathetic postganglionic neurons were labeled in the renal nerve ganglia, the superior mesenteric ganglion, and the ipsilateral paravertebral ganglia from T12 to L3 Transganglionic transport of HRP labeled renal afferent projections to the spinal cord of kittens from T1 1 to L6, with the greatest concentrations between Ll and L3. These afferents extended rostrocaudally in Lissauer's tract and sent collaterals into lamina I. In the transverse plane, a major lateral projection and a minor medial projection were observed along the outer and inner margins of the dorsal horn, respectively. From the lateral projection many fibers extended medially in laminae V and VI forming dorsal and ventral bundles around Clarke's nucleus. The dorsal bundle was joined by collaterals from the medial afferent projection and crossed to the contralateral side. The ventral bundle extended into lamina VII along the lateroventral border of Clarke's nucleus. Some afferents in the lateral projection could be followed ventrally into the dorsolateral portion of lamina VII in the vicinity of the intermediolateral nucleus. In the contralateral spinal cord, labeled afferent fibers were mainly seen in laminae V and VI These results provide the first anatomical evidence for sites of central termination of renal afferent axons. Renal inputs to regions (laminae I, V, and VI) containing spinoreticular and spinothajamic tract neurons may be important in the mediation of supraspinal cardiovascular reflexes as well as in the transmission of activity from nociceptors in the kidney. In addition, the identification of a bilateral renal afferent projection in close proximity to the thoracolumbar autonomic nuclei is consistent with the demonstration in physiological experiments of a spinal pathway for the renorenal sympathetic reflexes.     

Isthmic afferent neurons identified by the retrograde HRP method in a teleost, Navodon modestus

Isthmic afferent neurons were investigated by the retrograde horseradish peroxidase (HRP) method in a teleost, Navodon modestus. Following HRP injections into the nucleus isthmi, large pyriform neurons are labeled in the ipsilateral optic tectum. Very large and multipolar neurons are also labeled in the ipsilateral nucleus pretectalis. No labeled neurons were found in other areas.     

Medullary proprioceptive neurons from extraocular muscles in the pigeon identified with horseradish peroxidase

Three to five microliters of 50% HRP in saline was injected along a central axis into one of the 6 extraocular muscles in each of 18 adult pigeons. The brain was fixed and serially sectioned 16-20 h postinjection and the HRP reacted with tetramethylbenzidine (TMB). HRP-labeled proprioceptive neurons were located in the ipsilateral nucleus descendens nervi trigemini (TTD) for all muscle injections. The labeled neurons were further subdivided into two groups based on size and shape. In each experiment the number of labeled proprioceptive cells relative to the number of labeled motoneurons ranged between 4.9 and 15.5%. There were no labeled cells in the trigeminal mesencephalic nucleus or contralateral TTD. The study suggests that at least partial afferent (proprioceptive) innervation of the extraocular muscles in the pigeon derived from neurons in the ipsilateral TTD.     

Experimental study of spinal nerve repair after plexus brachialis injury in newborn rats: a horseradish peroxidase study.

As an animal model of nerve injury at delivery, traction injury was made to the plexus brachialis nerves of newborn rats. By traction, spinal root avulsion or plexus brachialis injury was produced. Horseradish peroxidase (HRP) was injected into the denervated biceps or triceps brachii muscle at various intervals after the experimental nerve injury. Four weeks after the injury, HRP-labeled neurons were identified in the ventral horn of the injected side. In the experimental animals the labeled neurons were found in the ipsilateral ventral horn of the C₄ through T₁ levels regardless of whether the injection was into the denervated biceps or triceps brachii muscle. In the control animals the distribution of the labeled neurons differed depending on the site of injection; labeled neurons were found in the ipsilateral ventral horn of C₄ through C₈ after the injection of HRP into the biceps and in that of C₅ through C₈ after injection into the triceps. Within the same level of the cord, the labeled neurons in the experimental animal showed more widespread distribution in the vental horn than those in the control animal. Regeneration of the injured nerves by axonal sprouts from the proximal stumps with subsequent confusion of growth was supported by the present study. In a small number of experimental animals, the labeled neurons were identified not only in the ipsilateral but also in the contralateral ventral horns, suggesting the persistence of an immature mode of innervation of the forelimb muscle by bilateral ventral horn neurons. We also correlated the results of the study and the peculiar clinical findings that follow recovery of the nerve injury during delivery.     

Origin of sympathetic and sensory innervation of the elbow joint in the rat: A retrograde axonal tracing study with wheat germ agglutinin conjugated horseradish peroxidase

After injection of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) into the elbow joint of adult rats, labeled neurons were found in the stellate and the T2-T4 ganglia of the ipsilateral sympathetic trunk, and also in dorsal root ganglia at the C4–T4 levels. Most labeled sympathetic cells, 90% or more, were located in the stellate ganglion. The sensory innervation to the joint originated mainly from the dorsal root ganglia at the levels of C7–T1.     

Sexual dimorphism in sympathetic preganglionic neurons of the rat hypogastric nerve

Horseradish peroxidase (HRP) applied to one hypogastric nerve labelled sensory neurons in T11-L3 dorsal root ganglia (DRG) bilaterally and preganglionic neurons (PGN) in the spinal cord segments T13-L3. An average of 130 small DRG neurons were labelled per animal (male or female). These were concentrated in the L1 + L2 DRGs (92%). About 75% were located ipsilateral to the site of HRP application. Central projections from DRG neurons were noted throughout Lissauer's tract and in the marginal zones (medial and lateral) near the borders of Lissauer's tract. A short projection was also seen extending to the dorsolateral funiculus. More than 90% of the preganglionic neurons were located in segments L1 + L2. Most of these were found in the dorsal commissural nucleus (75%) and most of the remainder were located bilaterally in the intermediolateral columns. Somewhat more intermediolateral neurons were labelled on the ipsilateral side than on the contralateral side. There were a few intercalating neurons and a very few funicular cells. An average of 415 PGNs were labelled in the male animals and 110 in the females, demonstrating a strong sexual dimorphism. No dimorphism was found in the sensory components.     

Sympathetic and afferent somata projecting in hindlimb nerves and the anatomical organization of the lumbar sympathetic nervous system of the rat

The anatomy of the sympathetic pathways from the spinal cord to the lumbar sympathetic trunk and the inferior mesenteric ganglion was studied systematically in the rat. Details of the arrangements of white and gray rami communicantes, sympathetic trunk ganglia, the intermesenteric nerve, and the lumbar splanchnic nerves are summarized. A modified nomenclature for the segmental ganglia of the paravertebral sympathetic chain is proposed. Cell bodies of sensory and sympathetic axons projecting to the skin and skeletal muscle of the rat hindlimb were labeled retrogradely with horseradish peroxidase (HRP) in order to study numbers, segmental distribution, and location of the somata of these neurons quantitatively. HRP was applied to the nerves supplying skeletal muscle (gastrocnemius-soleus, GS), hairy skin (sural, SU; saphenous, SA) and to a mixed nerve (tibial, TI). All sensory somata and 96.4% of the sympathetic cell bodies were located ipsilaterally. Sensory somata were commonly restricted to two adjacent dorsal root ganglia (usually L3-4 for SA; L4-5 for GS, TI; L5-6 for SU). Although the sympathetic somata were more widely distributed rostrocaudally (four to six segments), their maximum was always located one or two segments more cranially than the sensory outflow, i.e., corresponding to the rami communicantes grisei. From the data, it is estimated that 420 sympathetic and 530 afferent neurons project into GS, 590 and 3,610 into SU, 920 and 3,750 into SA, and 1,070 and 5,760 into TI. These absolute neuron numbers are compared with electron microscopic fiber counts from the literature.     

Spinal origins of preganglionic B and C neurons that innervate paravertebral sympathetic ganglia nine and ten of the bullfrog

These experiments were designed to characterize the distribution, morphology, and number of spinal preganglionic neurons that selectively innervate the B- and C-type sympathetic neurons in paravertebral ganglia 9 and 10 of the bullfrog. For this purpose, horseradish peroxidase (HRP) was applied to the anterior end of the sectioned sympathetic chain between ganglia 8 and 9. Subsequent retrograde axonal transport of the HRP labeled ipsilateral spinal neurons whose cell bodies form a column having rostral and caudal boundaries that are, respectively, just caudal to the level of spinal nerve 4 and midway between the entry zones of spinal nerves 7 and 8. In all segments, the labeled preganglionic somata were found in the lateral half of the spinal gray and slightly dorsal to the central canal; a position analogous to that of the intermediolateral cell column in mammals. Most labeled preganglionic neurons were multipolar in shape, and the cell bodies lying between spinal nerves 4 and 5 were, on average, larger than those found between spinal nerves 7 and 8. In transverse sections that were cut near spinal nerve 5, the axons of preganglionic neurons could be seen to exit the cord through ventral roots. Counts of labeled preganglionic neurons indicate that an average +/- S.D. of 338 +/- 89 cells innervate ganglia 9 and 10. Selective labeling of preganglionic B neurons, by cutting spinal nerves 7 and 8 central to their rami communicantes at the time of HRP application, revealed an average +/- S.D. of 137 +/- 31 cells that lie exclusively between spinal nerves 4 and 6. By contrast, selective labeling of preganglionic C neurons, by cutting the sympathetic chain rostral to ganglion 7 at the time of HRP application, revealed an average +/- S.D. of 187 +/- 77 cells in an adjacent portion of the preganglionic column that is bounded by spinal nerve 6 and by a point midway between spinal nerves 7 and 8. These results thus demonstrate a clear segmental segregation between the preganglionic B and C neurons that innervate ganglia 9 and 10.     

Golgi-like immunoperoxidase staining of dopamine neurons in the reticular formation of the rat brainstem using antibody to tyrosine-hydroxylase

Cell bodies of sympathetic and sensory axons projecting via the superficial peroneal (SP) nerve supplying hairy skin of the distal hindlimb have been labeled retrogradely with horseradish peroxidase (HRP) on both sides of three cats in which the left SP nerve had been cut and ligated about 5 months previously. Three SP nerves from unoperated cats have also been studied. The location, size, and numbers of labeled somata have been determined from serial sections of lumbosacral dorsal root and sympathetic chain ganglia after standard histochemical processing. The numbers of myelinated fibers in each nerve have also been counted. The segmental distributions of both sympathetic and sensory cell bodies were identical bilaterally in each operated animal, but the number of labeled neurons was reduced on the lesioned side. There were only about 31% of sympathetic and about 51% of sensory somata relative to the numbers on the contralateral side. The average total number of neurons labeled from SP nerves in unoperated animals was about 8% higher than on the control side of operated animals. The average number of myelinated fibers in the neuromatized nerves was not reduced with respect to that in the contralateral nerve and both of these were not significantly different from the number in unoperated animals. The dimensions of samples of labeled sympathetic and sensory somata were reduced on the side with the neuroma, both in comparison with the contralateral side and with unlabeled neurons at the same levels. The mean cross-sectional area of profiles of sympathetic ganglion cells was 76% of the control; of sensory ganglion cells, 65% of the control. Assuming that HRP labeling was not impaired, we conclude that large numbers of neurons with unmyelinated axons had degenerated in the neuromatized cutaneous nerves.