Primary afferent projections of the octavus nerve to the inferior reticular formation and adjacent nuclei in the elasmobranch, Rhinobatos sp.

Using a method to visualize HRP-containing cells in the geniculate ganglion (GG) in situ after decalcifying surrounding bone, we found that about 30% of the total (about 1000) GG cells contributed sensory fibers to the posterior auricular branch of the facial motor nerve. These cells are relatively large for GG cells in general. The remaining facial motor nerve branches, including those involved in vibrissal movement, contained few sensory afferent fibers originating from GG cells.     

The sensory component of the facial nerve of a reptile (Lacerta viridis).

The sensory fibers of the facial nerve in Lacerta viridis have been studied with a silver impregnation method to follow the course of axonal degeneration. Destruction of the geniculate ganglion demonstrated the degenerated sensory component of the facial nerve adjacent to the anterior vestibular root. Within the lateral vestibular area the facial sensory fibers consist of numerous rootlets separated by vestibular fibers and cells. These rootlets may join to form a main or paired sensory tract that passes through the vestibular nuclei to enter the tractus solitarius and divide into a small ascending prefacial component and a major descending prevagal division. A few fibers continue into the postvagal part of tractus solitarius and extend caudally to terminate in the nucleus commissura infima. Prefacial fibers terminate along the periventricular gray while prevagal fibers terminate within the tractus solitarius on the dendrites of cells of nucleus tractus solitarius and near the periphery of the dorsal motor nucleus of X. There was no noticeable degeneration in the descendens tractus trigemini. Terminal degeneration to descendens nucleus trigemini and motor nucleus of VII followed the tractus solitarius course. Most facial sensory fibers are probably related to taste and other visceral information.     

Electrophysiological findings in a case of congenital lower limb hypoplasia

Limb hypoplasia is a rare congenital disorder. Is usually encountered in patients with segmental spinal dysplasia (SSD), in progressive facial hemiatrophy (Parry-Romberg syndrome) and in other rare conditions. We performed an extensive electrophysiological study in a 18-year-old female with congenital left lower limb hypoplasia, but with no motor and sensory deficit. Electrophysiological investigation comprised motor and sensory nerve conduction velocities, needle EMG, quantitative sensory studies and SEP with standard techniques. The study showed markedly involved large diameter peripheral sensory nerve fibers and intact motor and small diameter peripheral sensory nerve fibers. Extensive electrophysiological investigation in cases of limb hypoplasia has not been previously performed. In this patient congentital hypoplasia of the muscles also involved the peripheral large diameter sensory nerve fibers.     

Peripheral nerve carbonic anhydrase activity and chronic acetazolamide treatment of rats

Examination of cranial nerves shows that the sensory infraorbital branch of the trigeminal nerve contains many carbonic anhydrase-reactive axons whereas axons of the motor facial nerve are non-reactive. This motor/sensory axon staining difference holds for both cranial and spinal nerves. Chronic treatment with acetazolamide produced no apparent changes in carbonic anhydrase histochemical activity or the structure of peripheral nerve fibers.     

Development and innervation of the paratympanic organ (Vitali organ) in chick embryos

The paratympanic organ (Vitali organ) is a small sensory organ in the middle ear of birds. It possesses a sensory epithelium with hair cells similar to those of the inner ear. Injections of fluorescent carbocyanine tracers into the paratympanic organ of 9- to 11-day-old chick embryos labeled ganglion cells in the facial ganglia. Paratympanic nerve fibers enter the brainstem with the facial nerve but proceed to vestibular brainstem nuclei. A dorsal branch terminates in ventral areas of the cerebellum, while a ventral component projects to the descending vestibular nucleus, with some fibers turning medially into lateral parts of the medial vestibular nucleus. No fibers were labeled in the motor or sensory facial nucleus or in auditory brainstem nuclei. This projection pattern suggests a function of the paratympanic organ in equilibrium rather than audition. Projections similar to those of the paratympanic nerve have been reported for the lagenar nerve. Immunocytochemical techniques using an antiserum to gamma-aminobutyric acid (GABA) demonstrate that hair cells in the paratympanic organ develop GABA immunoreactivity at 5 days of incubation (E5), 2-4 days earlier than GABA immunoreactivity can be detected in hair cells of the inner ear, i.e. in the saccule (E6.5-7.0), the utricle (E7), the cristae (E8-9) and the cochlea (E9-9.5). Afferent fibers that are transiently GABAergic are rare in the paratympanic organ (1-2 fibers), though present from E6 to E7.5. The early onset of GABA immunoreactivity in the paratympanic organ may indicate that this organ matures (and possibly functions) earlier in ontogenetic development than its counterparts located in the inner ear. The present findings are consistent with the hypothesis that the paratympanic organ is homologous with the spiracular sense organ of fishes. The paratympanic organ of birds may represent a sense organ that is derived phylogenetically and ontogenetically from the lateral-line system.     

The facial "motor" nerve of the rat: control of vibrissal movement and examination of motor and sensory components

Rhythmical whisking of the mystacial vibrissae at about 7 Hz during exploration is one of the most conspicuous behavioral patterns in the rat. To identify the final common pathway for vibrissal movement, individual motor branches of the facial nerve, including the posterior auricular, temporal, zygomatic, buccal, marginal mandibular, cervical, stylohyoid, and posterior digastric branches, were cut, either singly or in various combinations. We found that vibrissal movement could be abolished only by transection involving the buccal branch and the upper division of the marginal mandibular branch. To trace back the central origins of the buccal and marginal mandibular, as well as the other branches of the facial nerve, all distal to the stylomastoid foramen, horseradish peroxidase (HRP) was applied to the cut proximal ends of these individual branches. The retrograde HRP labelling in the facial motor nucleus revealed topographical representation of these branches in which the buccal and marginal mandibular branches were represented laterally. The stylohyoid and posterior digastric branches originated from cells in the suprafacial nucleus. Consistent with earlier observations with intramuscular HRP injections, the motoneuronal population devoted to vibrissal movement did not seem to be substantially larger than that for other facial movements. An additional examination was made of the labelled afferent component of the facial motor nerve. We confirmed and extended previous findings that none of the above facial motor nerve branches, except the posterior auricular branch, contained a significant number of afferent fibers originating from the geniculate ganglion, the sensory ganglion of the seventh nerve. In addition, no labelling was seen in the mesencephalic trigeminal nucleus or trigeminal ganglion. These findings, in combination, suggest that, with the exception of the posterior auricular branch, all the facial motor nerve branches, including those involved in vibrissal movement, are almost entirely efferent.     

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.     

Differential atrophy of sensory and motor fibers following section of cat peripheral nerves

Differential effects of peripheral nerve section on myelinated sensory and motor fiber populations were investigated in 5 hindlimb nerves of cats. Upon electrical stimulation of each nerve, monophasic compound action potentials were recorded from the L6, L7 and S1 dorsal and ventral roots, and the impedance of each root was measured. The decline in the electrical charge computed from potentials 43 to 252 days after nerve section gave a measure of the effect of axotomy on the diameters of sensory and of motor fibers in each nerve. No significant difference in the rate of atrophy of sensory and motor fibers was observed after about 45 days following nerve section. After about 145 and 245 days, however, dorsal root charge contributions had decreased significantly more than ventral root values. Exponential decay curves were fitted separately to charge data for sensory and for motor fibers. The calculated value for the endpoint of the decay was about 35% of the control value for motor fibers, and not significantly different from zero to sensory fibers. These results suggest that in response to axotomy, myelinated motor fiber diameters decline at first but later stabilize, while myelinated sensory fibers continue to decline and may atrophy completely if regeneration is prevented. Possible roles of electrical activity and of 'trophic' interactions with the periphery in the maintenance of cell properties are discussed.     

Chronic Schwann cell denervation and the presence of a sensory nerve reduce motor axonal regeneration

Motor axonal regeneration is compromised by chronic distal nerve stump denervation, induced by delayed repair or prolonged regeneration distance, suggesting that the pathway for regeneration is progressively impaired with time and/or distance. In the present experiments, we tested the impacts of (i) chronic distal sensory nerve stump denervation on axonal regeneration and (ii) sensory or motor innervation of a nerve graft on the ability of motoneurons to regenerate their axons from the opposite end of the graft. Using the motor and sensory branches of rat femoral nerve and application of neuroanatomical tracers, we evaluated the numbers of regenerated femoral motoneurons and nerve fibers when motoneurons regenerated (i) into freshly cut and 2-month chronically denervated distal sensory nerve stump, (ii) alone into a 4-cm-long distally ligated sensory autograft (MGL) and, (iii) concurrently as sensory (MGS) or motor (MGM) nerves regenerated into the same autograft from the opposite end. We found that all (315 +/- 24: mean +/- SE) the femoral motoneurons regenerated into a freshly cut distal sensory nerve stump as compared to 254 +/- 20 after 2 months of chronic denervation. Under the MGL condition, 151 +/- 5 motoneurons regenerated, which was not significantly different from the MGM group (134 +/- 13) but was significantly reduced to 99 +/- 2 in the MGS group (P < 0.05). The number of regenerated nerve fibers was 1522 +/- 81 in the MGL group, 888 +/- 18 in the MGM group, and 516 +/- 44 in the MGS group, although the high number of nerve fibers in the MGL group was due partly to the elaboration of multiple sprouts. Nerve fiber number and myelination were reduced in the MGS group and increased in the MGM group. These results demonstrate that both chronic denervation and the presence of sensory nerve axons reduced desired motor axonal regeneration into sensory pathways. A common mechanism may involve reduced responsiveness of sensory Schwann cells within the nerve graft or chronically denervated distal nerve stump to regenerating motor axons. The findings confirm that motor regeneration is optimized by avoiding even short-term denervation. They also imply that repairing pure motor nerves (without their cutaneous sensory components) to distal nerve stumps should be considered clinically when motor recovery is the main desired outcome.     

Reflex connections of the facial and vagal gustatory systems in the brainstem of the bullhead catfish, Ictalurus nebulosus

The primary gustatory sensory nuclei in catfish are grossly divisible into a vagal lobe and a facial lobe. In this study, the reflex connections of each gustatory lobe were determined with horseradish peroxidase (HRP) tracing methods. In addition, in order to determine the loci and morphology of the other brainstem cranial nerve nuclei, HRP was applied to the trigeminal, facial, glossopharyngeal, or vagus nerve. The sensory fibers of the facial nerve terminate in the facial lobe. The facial lobe projects bilaterally to the posterior thalamic nucleus, superior secondary gustatory nucleus, and medial reticular formation of the rostral medulla. The facial lobe has reciprocal connections with the n. lobobulbaris, medial reticular formation of the rostral medulla, descending trigeminal nucleus, medial and lateral funicular nuclei, and the vagal lobe, ipsilaterally; and with the facial lobe contralaterally. In addition, the facial lobe receives inputs from the raphe nuclei, from a pretectal nucleus, and from perilemniscal neurons located immediately adjacent to the ascending gustatory lemniscal tract at the level of the trigeminal motor nucleus. The gustatory fibers of the vagus nerve terminate in the vagal lobe, while the general visceral sensory fibers terminate in a distinct general visceral nucleus. The vagal lobe projects ipsilaterally to the superior secondary gustatory nucleus, lateral reticular formation, and n. ambiguus; and bilaterally to the commissural nucleus of Cajal. The vagal lobe has reciprocal connections with the ipsilateral lobobulbar nucleus and facial lobe. In addition, the vagal lobe receives input from neurons of the medullary reticular formation and perilemniscal neurons of the pontine tegmentum. In summary, the facial gustatory system has connections consonant with its role as an exteroceptive system which works in correlation with trigeminal and spinal afferent systems. In contrast, the vagal gustatory system has connections (e.g., with the n. ambiguus) more appropriate to a system involved in control of swallowing. These differences in central connectivity mirror the reports on behavioral dissociation of the facial and vagal gustatory systems.     

Manually-stimulated recovery of motor function after facial nerve injury requires intact sensory input

We have recently shown in rat that daily manual stimulation (MS) of vibrissal muscles promotes recovery of whisking and reduces polyinnervation of muscle fibers following repair of the facial nerve (facial-facial anastomosis, FFA). Here, we examined whether these positive effects were: (1) correlated with alterations of the afferent connections of regenerated facial motoneurons, and (2) whether they were achieved by enhanced sensory input through the intact trigeminal nerve. First, we quantified the extent of total synaptic input to motoneurons in the facial nucleus using synaptophysin immunocytochemistry following FFA with and without subsequent MS. We found that, without MS, this input was reduced compared to intact animals. The number of synaptophysin-positive terminals returned to normal values following MS. Thus, MS appears to counteract the deafferentation of regenerated facial motoneurons. Second, we performed FFA and, in addition, eliminated the trigeminal sensory input to facial motoneurons by extirpation of the ipsilateral infraorbital nerve (IONex). In this paradigm, without MS, vibrissal motor performance and pattern of end-plate reinnervation were as aberrant as after FFA without MS. MS did not influence the reinnervation pattern after IONex and functional recovery was even worse than after IONex without MS. Thus, when the sensory system is intact, MS restores normal vibrissal function and reduces the degree of polyinnervation. When afferent inputs are abolished, these effects are eliminated or even reversed. We conclude that rehabilitation strategies must be carefully designed to take into account the extent of motor and/or sensory damage.     

Contribution of degeneration of motor and sensory fibers to pain behavior and the changes in neurotrophic factors in rat dorsal root ganglion

To elucidate the role of the degeneration of motor and sensory fibers in neuropathic pain, we examined the pain-related behaviors and the changes of brain-derived neurotrophic factor (BDNF) in the L4/5 dorsal root ganglion (DRG) and the spinal cord after L5 ventral rhizotomy. L5 ventral rhizotomy, producing a selective lesion of motor fibers, produced thermal hyperalgesia and increased BDNF expression in tyrosine kinase A-containing small- and medium-sized neurons in the L5 DRG and their central terminations within the spinal cord, but not in the L4 DRG. Furthermore, L5 ventral rhizotomy up-regulated nerve growth factor (NGF) protein in small to medium diameter neurons in the L5 DRG and also in ED-1-positive cells in the L5 spinal nerve, suggesting that NGF synthesized in the degenerative fibers is transported to the L5 DRG and increases BDNF synthesis. On the other hand, L5 ganglionectomy, producing a selective lesion of sensory fibers, produced heat hypersensitivity and an increase in BDNF and NGF in the L4 DRG. These data indicate that degeneration of L5 sensory fibers distal to the DRG, but not motor fibers, might influence the neighboring L4 nerve fibers and induce neurotrophin changes in the L4 DRG. We suggest that these changes of neurotrophins in the intact primary afferents of neighboring nerves may be one of many complex mechanisms, which can explain the abnormal pain behaviors after nerve injury. The ventral rhizotomy and ganglionectomy models may be useful to investigate the pathophysiological mechanisms of neuropathic pain after Wallerian degeneration in motor or sensory or mixed nerve.     

Rubrobulbar projections in the rabbit. A light and electron microscopic study

The crossed rubrobulbar fibers coursing in association with the classical rubrospinal tract in the rabbit were investigated by means of the Nauta and the Fink-Heimer methods. The synaptic organization within the terminal areas of the rubrobulbar fibers were also studied electron microscopically. The crossed rubrobulbar fibers are distributed to the ventral portion of the reticular area intercalated between the motor and the main sensory nuclei of the trigeminal nerve, to the ventrolateral part of the lateral parvocellular reticular formation, the dorsal region of the facial nucleus, the subtrigeminal portion of the lateral reticular nucleus, and the rostrolateral part of the main portion of the lateral reticular nucleus. Small to medium-sized, electron-dense, degenerated synaptic knobs were observed in the dorsal region of the facial nucleus and in the rostrodorsolateral part of the lateral reticular nucleus. All of the synaptic vesicles contained in the degenerated synaptic bags were spherical. Almost all of the degenerated synaptic terminals were in contact with dendritic profiles. Sporadic electron-dense synaptic knobs contacting the soma of nerve cells were encountered only in the dorsal aspect of the facial nucleus.     

Trigeminal-palatal synkinesis

A patient developed synkinetic movements of facial musculature and "crocodile tears" following the removal of a large acoustic neurinoma. A reflex palatal movement resulted from tactile stimulation of the lower part of the face as well. Analysis of the palatal movement suggested action of the tensor veli palatini muscle, acting in isolation. We believe the palatal contraction represents a synkinetic phenomenon involving both sensory and motor nerve fibers within the motor root of the trigeminal nerve.     

Axonal transport and distribution of endogenous calcitonin gene-related peptide in rat peripheral nerve

Calcitonin gene-related peptide (CGRP) has been found in both sensory and motor neurons. It has been suggested that CGRP is transported from neuron cell bodies to their terminals, where it may act as an anterograde trophic factor. However, it is not known how fast CGRP is transported or whether CGRP found in the innervated target organ indeed originated in neural tissues. We have quantified endogenous CGRP in the rat peripheral nerve by a newly developed enzyme immunoassay. The CGRP immunoreactive material obtained from neural tissues coincided with synthetic rat CGRP in fractional distributions separated by gel filtration. After ligation of the sciatic nerve, tissue CGRP accumulated in the segment central to the ligature. The rate of anterograde transport of CGRP was about 1 mm/hr in both sensory and motor fibers. In the sciatic nerve, only a small fraction of CGRP measured was found to originate from the motor nerve fibers. This may be due in part to the disproportionately large number of sensory fibers in the sciatic nerve and in part to the possible presence of CGRP in sympathetic nerve fibers. The CGRP content in the dorsal root fibers was significantly lower than that in the peripheral processes of the sensory neurons. The CGRP content in the hind leg muscle was much higher than that expected from the amount of CGRP per nerve fiber in the sciatic nerve. Most CGRP in muscle disappeared following denervation. It is concluded that CGRP highly concentrated in nerve terminals is supplied by axonal transport from the neuron cell bodies.     

Localization, origin and fine structure of calcitonin gene-related peptide-containing fibers in the vestibular end-organs of the rat

The localization, origin and fine structure of nerve terminals immunoreactive for calcitonin gene-related peptide (CGRP) were examined in the vestibular end-organs of rats using immunocytochemistry. Many CGRP-like immunoreactive (CGRP-IR) fibers were observed in the vestibular sensory epithelial layer. By electronmicroscopy, CGRP-IR terminals were found to make synaptic contacts with the chalyces of the vestibular nerves terminating on type I cells. The origin of these vestibular CGRP-IR fibers was examined by a combination of a retrograde fiber tracing technique (using Fast blue) and immunocytochemistry. Injections of the tracer into the vestibular cistern, resulted in fast blue-labeled neurons bilaterally in the area dorsolateral to the genu of the facial nerve; these labeled neurons also contained CGRP. These findings indicate that CGRP-IR fibers originate bilaterally from the area dorsolateral to the genu of the facial nerve and that CGRP plays a modulatory role in the transmission of vestibular information from type I cells.     

Facial nerve dysfunction in hereditary motor and sensory neuropathy type I and III.

Facial nerve function was studied in 19 patients with hereditary motor and sensory neuropathy type I (HMSN I) and 2 patients with hereditary motor and sensory neuropathy type III (HMSN III, Déjérine-Sottas), and compared to that in 24 patients with Guillain-Barré syndrome (GBS). The facial nerve was stimulated electrically at the stylomastoid fossa, and magnetically in its proximal intracanalicular segment. Additionally, the face-associated motor cortex was stimulated magnetically. The facial nerve motor neurography was abnormal in 17 of 19 HMSN I patients and in both HMSN III patients, revealing moderate to marked conduction slowing in both the extracranial and intracranial nerve segments, along with variable reductions of compound muscle action potential (CMAP) amplitudes. The facial nerve conduction slowing paralleled that of limb nerves, but was not associated with clinical dysfunction of facial muscles, because none of the HMSN I patients had facial palsy. Conduction slowing was most severe in the HMSN III patients, but only slight facial weakness was present. In GBS, conduction slowing was less marked, but facial weakness exceeded that in HMSN patients in all cases. We conclude that involvement of the facial nerve is common in HMSN I and HMSN III. It affects the intra- and extracranial part of the facial nerve and is mostly subclinical.     

The peripheral distribution and central projections of the sensory rami of the facial nerve in goldfish, Carassius auratus

Taste buds in goldfish and other cyprinids are found not only within the oropharyngeal cavity but also scattered over the external body surface. The external taste buds are innervated by branches of the facial nerve that terminate centrally in an enlargement of the medulla termed the facial lobe. The peripheral distribution and areas of innervation of the rami of the facial sensory nerve were determined by using a modification of the Sihler technique and by examination of a Bodian-stained head series. The central projections of individual rami of the facial sensory nerve were traced by means of the horseradish peroxidase (HRP) technique. Fibers of the facial sensory nerve distribute over the head and trunk via nine rami. The supraorbital ramus distributes fibers to taste buds above the eye. The palatine, maxillary, and mandibular rami innervate taste buds of the rostral palate, upper lip, and lower lip, respectively. The three rami of the hyomandibular trunk innervate taste buds on the operculum, branchiostegal rays, and in the lower cheek region. A facial recurrent ramus was also found that distributes fibers to taste buds on the trunk and pectoral fin via two rami, the lateral recurrent ramus and pectoral recurrent ramus. The facial sensory rami map somatotopically on the facial lobe. Overall, the projections follow an anteroposterior orientation with the long axis of the body tilted slightly ventrally. The lips and rostral palate make up a disproportionately large portion of the map, taking up nearly the entire ventral extent of the lobe. The trunk and pectoral fin regions map broadly across the dorsal portion of the lobe. Further, projections to the nucleus of the descending trigeminal tract were observed with labeling of the supraorbital, maxillary, and mandibular rami, and the rami of the hyomandibular trunk. Projections to the facial motor nucleus were also observed with labeling of maxillary and mandibular rami, perhaps indicating a monosynaptic reflex are. These projections have not been reported in previous studies on the teleostean facial taste system.     

Brainstem projections of sensory and motor components of the vagus nerve in the rat

The sensory and motor connections of the cervical vagus nerves and of its inferior ganglion (nodose ganglion) have been traced in the medulla and upper cervical spinal cord of 16 male Wistar rats by using horseradish peroxidase (HRP) neurohistochemistry. The use of tetramethyl benzidine (TMB) as the substrate for HRP permitted the visualization of transganglionic and retrograde transport in sensory nerve terminals and perikarya, respectively. The vagus nerve in the rat enters the medulla in numerous fascicles with points of entry covering the entire lateral aspect of the medulla extending from level +4 to - 6 mm rostrocaudal to the obex. Fascicles of vagal sensory fibers enter the dorsolateral aspect of the medulla and travel to the tractus solitarius (TS) which was labeled for over 8.8 mm in the medulla. The caudal extent of the TS receiving vagal projections was found in lamina V of the cervical spinal cord (C1 to C2). Sensory terminal fields could be visualized bilaterally in the nucleus of the tractus solitarius (nTS), area postrema (ap) and dorsal motor nucleus of the vagus nerve (dmnX). The ipsilateral projection to the nTS and the dmnX was heavier than that found on the contralateral side. The area postrema was intensely labeled on both sides. Motor fibers from HRP-labeled perikarya in the dmnX travel ventromedially in a distinct fascicle and subsequently subdivide into a number of small fiber bundles that traverse the medullary reticular formation in the form of a fine network of HRP-labeled fibers. As these fibers from the dmnX approach the ventrolateral aspect of the medulla they are joined by axons from the nucleus ambiguus (nA), nucleus retroambigualis (nRA) and the retro facial nucleus (nRF). These latter fibers form hairpin loops in the middle of the reticular formation to accompany the axons from the dmnX exiting from the medulla in a ventrolateral location. HRP-labeled perikarya, in contrast to transganglionically transported HRP in sensory terminals in the nTS, were visualized on one side only, thus indicating that motor control via the vagus nerve is exerted only by motor neurons located ipsilaterally. Sensory information on the other hand, diverges to many nuclear subgroups located on both sides of the medulla.     

Short-term observations of the regenerative potential of injured proximal sensory nerves crossed with distal motor nerves

Motor nerves and sensory nerves conduct signals in different directions and function in different ways.In the surgical treatment of peripheral nerve injuries,the best prognosis is obtained by keeping the motor and sensory nerves separated and repairing the nerves using the suture method.However,the clinical consequences of connections between sensory and motor nerves currently remain unknown.In this study,we analyzed the anatomical structure of the rat femoral nerve,and observed the motor and sensory branches of the femoral nerve in the quadriceps femoris.After ligation of the nerves,the proximal end of the sensory nerve was connected with the distal end of the motor nerve,followed by observation of the changes in the newly-formed regenerated nerve fibers.Acetylcholinesterase staining was used to distinguish between the myelinated and unmyelinated motor and sensory nerves.Denervated muscle and newly formed nerves were compared in terms of morphology,electrophysiology and histochemistry.At 8 weeks after connection,no motor nerve fibers were observed on either side of the nerve conduit and the number of nerve fibers increased at the proximal end.The proportion of newly-formed motor and sensory fibers was different on both sides of the conduit.The area occupied by autonomic nerves in the proximal regenerative nerve was limited,but no distinct myelin sheath was visible in the distal nerve.These results confirm that sensory and motor nerves cannot be effectively connected.Moreover,the change of target organ at the distal end affects the type of nerves at the proximal end.