The seventh cranial nerve of the rat. Visualization of efferent and afferent pathways by cobalt precipitation

Events Occurring in the Axotomized Facial Nucleus

Transection of the rat facial nerve leads to a variety of alterations not only in motoneurons, but also in glial cells and inhibitory neurons in the ipsilateral facial nucleus. In injured motoneurons, the levels of energy metabolism-related molecules are elevated, while those of neurofunction-related molecules are decreased. In tandem with these motoneuron changes, microglia are activated and start to proliferate around injured motoneurons, and astrocytes become activated for a long period without mitosis. Inhibitory GABAergic neurons reduce the levels of neurofunction-related molecules. These facts indicate that injured motoneurons somehow closely interact with glial cells and inhibitory neurons. At the same time, these events allow us to predict the occurrence of tissue remodeling in the axotomized facial nucleus. This review summarizes the events occurring in the axotomized facial nucleus and the cellular and molecular mechanisms associated with each event.

Response of the GABAergic System to Axotomy of the Rat Facial Nerve

The responses of inhibitory neurons/synapses to motoneuron injury in the cranial nervous system remain to be elucidated. In this study, we analyzed GABA_A receptor (GABA_AR) and GABAergic neurons at the protein level in the transected rat facial nucleus. Immunoblotting revealed that the GABA_ARα1 protein levels in the axotomized facial nucleus decreased significantly 5-14 days post-insult, and these levels remained low for 5 weeks. Immunohistochemical analysis indicated that the GABA_ARα1-expressing cells were motoneurons. We next examined the specific components of GABAergic neurons, including glutamate decarboxylase (GAD), vesicular GABA transporter (VGAT) and GABA transporter-1 (GAT-1). Immunoblotting indicated that the protein levels of GAD, VGAT and GAT-1 decreased transiently in the transected facial nucleus from 5 to 14 days post-insult, but returned to the control levels at 5 weeks post-insult. Although GABA_ARα1 protein levels in the transected nucleus did not return to their control levels for 5 weeks post-insult, the administration of glial cell line-derived neurotrophic factor at the cut site significantly ameliorated the reductions. Through these findings, we verified that the injured facial motoneurons suppressed the levels of GABA_ARα1 protein over the 5 weeks post-insult, presumably due to the deprivation of neurotrophic factor. On the other hand, the levels of the GAD, VGAT and GAT-1 proteins in GABAergic neurons were transiently reduced in the axotomized facial nucleus at 5-14 days post-insult, but recovered at 4-5 weeks post-insult.

Epibranchial placode-derived neurons produce BDNF required for early sensory neuron development

In mice, BDNF provided by the developing taste epithelium is required for gustatory neuron survival following target innervation. However, we find that expression of BDNF, as detected by BDNF-driven β-galactosidase, begins in the cranial ganglia before its expression in the central (hindbrain) or peripheral (taste papillae) targets of these sensory neurons, and before gustatory ganglion cells innervate either target. To test early BDNF function, we examined the ganglia of bdnf null mice before target innervation, and found that while initial neuron survival is unaltered, early neuron development is disrupted. In addition, fate mapping analysis in mice demonstrates that murine cranial ganglia arise from two embryonic populations, i.e., epibranchial placodes and neural crest, as has been described for these ganglia in non-mammalian vertebrates. Only placodal neurons produce BDNF, however, which indicates that prior to innervation, early ganglionic BDNF produced by placode-derived cells promotes gustatory neuron development.

Embryonic origin of gustatory cranial sensory neurons

Cranial nerves VII, IX and X provide both gustatory (taste) and non-gustatory (touch, pain, temperature) innervation to the oral cavity of vertebrates. Gustatory neurons innervate taste buds and project centrally to the rostral nucleus of the solitary tract (NTS), whereas neurons providing general epithelial innervation to the oropharynx project to non-gustatory hindbrain regions, i.e., spinal trigeminal nucleus. In addition to this dichotomy in function, cranial ganglia VII, IX and X have dual embryonic origins, comprising sensory neurons derived from both cranial neural crest and epibranchial placodes. We used a fate mapping approach to test the hypothesis that epibranchial placodes give rise to gustatory neurons, whereas the neural crest generates non-gustatory cells. Placodal ectoderm or neural crest was grafted from Green Fluorescent Protein (GFP) expressing salamander embryos into unlabeled hosts, allowing us to discern the postembryonic central and peripheral projections of each embryonic neuronal population. Neurites that innervate taste buds are exclusively placodal in origin, and their central processes project to the NTS, consistent with a gustatory fate. In contrast, neural crest-derived neurons do not innervate taste buds; instead, neurites of these sensory neurons terminate as free nerve endings within the oral epithelium. Further, the majority of centrally directed fibers of neural crest neurons terminate outside the NTS, in regions that receive general epithelial afferents. Our data provide empirical evidence that embryonic origin dictates mature neuron function within cranial sensory ganglia: specifically, gustatory neurons derive from epibranchial placodes, whereas neural crest-derived neurons provide general epithelial innervation to the oral cavity.

Direct projections from the cardiovascular nucleus tractus solitarii to pontine preganglionic parasympathetic neurons: a link to cerebrovascular regulation

Peripheral or central interruption of the baroreflex or the parasympathetic innervation of cerebral vessels leads to similar changes in regulation of cerebral blood flow. Therefore, we sought to test the hypothesis that the cardiovascular nucleus tractus solitarii, the site of termination of arterial baroreceptor nerves, projects to pontine preganglionic neurons whose stimulation elicits cerebral vasodilatation. The current study utilized both light and electron microscopic techniques to analyze anterograde tracing from the cardiovascular nucleus tractus solitarii to preganglionic parasympathetic neurons in the pons. We further used retrograde tracing from that same pontine region to the cardiovascular nucleus tractus solitarii and evaluated the confluence of tracing from the cardiovascular nucleus tractus solitarii to pontine preganglionic neurons labeled retrogradely from the pterygopalatine ganglia. The cardiovascular nucleus tractus solitarii projected to pontine preganglionic parasympathetic neurons, but more rostral and caudal regions of nucleus tractus solitarii did not. In contrast, all three regions of nucleus tractus solitarii projected to the nucleus ambiguus and dorsal motor nucleus of the vagus. Although not projecting to pontine preganglionic parasympathetic neurons, regions lateral, rostral, and caudal to cardiovascular nucleus tractus solitarii sent projections through the pons medial to the preganglionics. The study establishes the presence of a direct monosynaptic pathway from neurons in the cardiovascular nucleus tractus solitarii to pontine preganglionic parasympathetic neurons that project to the pterygopalatine ganglia, the source of nitroxidergic vasodilatory innervation of cerebral blood vessels. It provides evidence that activation of those preganglionic neurons can cause cerebral vasodilatation and increased cerebral blood flow. Finally, it demonstrates differential innervation of medullary and pontine preganglionic parasympathetic neurons by different regions of the nucleus tractus solitarii.

Main trajectories of nerves that traverse and surround the tympanic cavity in the rat

To guide surgery of nerves that traverse and surround the tympanic cavity in the rat, anatomical illustrations are required that are topographically correct. In this study, maps of this area are presented, extending from the superior cervical ganglion to the otic ganglion. They were derived from observations that were made during dissections using a ventral approach. Major blood vessels, bones, transected muscles of the tongue and neck and supra and infrahyoid muscles serve as landmarks in the illustrations. The course of the mandibular, facial, glossopharyngeal, vagus, accessory and hypoglossal nerves with their branches, and components of the sympathetic system, are shown and discussed with reference to data available in the literature. Discrepancies in this literature can be clarified and new data are presented on the trajectories of several nerves. The course of the tympanic nerve was established. This nerve originates from the glossopharyngeal nerve, enters the tympanic cavity, crosses the promontory, passes the tensor tympani muscle dorsally, and continues its route intracranially to the otic ganglion as the lesser petrosal nerve after intersecting with the greater petrosal nerve. Auricular branches of the glossopharyngeal and of the vagus nerve were noted. We also observed a pterygopalatine branch of the internal carotid nerve, that penetrates the tympanic cavity and courses across the promontory.

N-methyl-D-aspartate and vasopressin activate distinct voltage-dependent inward currents in facial motoneurones

Facial motoneurones of the rat respond to arginine vasopressin by generating a voltage-dependent inward current which is sodium-dependent and is resistant to tetrodotoxin. In the present study, we have investigated the action of N-methyl-D-aspartate (NMDA) on these same neurones. We have obtained single-electrode voltage-clamp recordings from brainstem slices of newborn rats. In a majority of vasopressin-sensitive facial motoneurones, NMDA induced an inward current. This action was direct, was concentration-related and could be suppressed by the specific competitive antagonist D-2-amino-5-phosphopentanoic acid (D-AP5). The NMDA-evoked current increased in amplitude as the neuronal membrane was depolarized. It could be blocked by the noncompetitive antagonist MK-801. It was potentiated following removal of extracellular magnesium, and was attenuated or suppressed when the external magnesium concentration was increased from 1 to 10 mM. By contrast, none of these treatments affected the vasopressin-induced current. These results show that facial motoneurones in the rat possess functional NMDA receptors and indicate that NMDA and vasopressin affect the bioelectrical properties of these neurones by turning on distinct voltage-dependent inward currents.

CNS projections to the pterygopalatine parasympathetic preganglionic neurons in the rat: a retrograde transneuronal viral cell body labeling study

The retrograde transneuronal viral cell body labeling method was used to study the CNS nuclei that innervate the parasympathetic preganglionic neurons which project to the pterygopalatine ganglion. Small injections of a suspension of pseudorabies virus (PRV) were made in the pterygopalatine ganglion of rats and after 4 days their brains wer e processed for immunohistochemical detection of PRV. Some of the tissues were stained with a dual immunofluoresence method that permitted the visualization of PRV and neurotransmitter enzyme or serotonin immunoreactivity in the same cell. Retrograde cell body labeling was detected in the ipsilateral ventrolateral medulla oblongata in the region that has been termed the superior salivatory nucleus. This area was the same region that was retrogradely labeled after Fluoro-Gold dye injections in the pterygopalatine ganglion. Retrograde transneuronally infected cell bodies that provide putative afferent inputs to the pytergopalatine parasympathetic preganglionic neurons were mapped throughout the brain. In the medulla oblongata, transneuronally labeled neurons were seen in the nucleus tractus solitarii, dorsomedial part of the spinal trigeminal nucleus and gigantocellular reticular nucleus. In most experiments, some A1 catecholamine cells and serotonin neurons of the raphe magnus, raphe pallidus, raphe obscurus, and parapyramidal nuclei were labeled. In the pons, labeled cells were found in the parabrachial nucleus. A5 catecholamine cell group, and non-catecholamine part of the subcoeruleus region. In the midbrain, cell body labeling was located in the central gray matter and retrorubral field. In the diencephalon, labeling was found mainly in the hypothalamus. The areas included the lateral hypothalamic area, lateral preoptic area, dorsomedial and paraventricular hypothalamic nuclei, and ventral zona incerta. Contralateral second order cell body labeling was seen in the tuberomammillary nucleus of the hypothalamus. Some of these cells were histidine decarboxylase-immunoreactive. In the forebrain, the bed nucleus of the stria terminalis, substantia innominata, and an area of the cerebral cortex called the amygdalopiriform transition zone were labeled.

Contribution of centrifugal innervation to choline acetyltransferase activity in the cat cochlear nucleus

Using a quantitative microchemical mapping approach combined with surgical cuts of fiber tracts, the contributions of centrifugal pathways to choline acetyltransferase activity were mapped three-dimensionally in the cat cochlear nucleus. Large reductions of choline acetyltransferase activity, averaging 70%, were measured in almost all parts of the lesion-side nucleus following transection of virtually all its centrifugal connections. More superficial cuts, penetrating just through the olivocochlear bundle, also led to significant reductions of enzyme activity, especially most rostrally in the anteroventral cochlear nucleus and superficial granular region, where the reductions were similar to those following the complete cuts. Lesions encroaching upon the superior olivary complex gave bilateral effects. Transverse cuts between rostral and caudal parts of the cochlear nucleus gave some small effects. The results suggest that, as in rats, most choline acetyltransferase activity in the cat cochlear nucleus is associated with its centrifugal innervation. However, unlike the situation in rats, the enzyme activity in cats is related more to olivocochlear branches than to ventral fibers in the trapezoid body region. Also, the choline acetyltransferase activity related to olivocochlear collateral innervation is much less uniformly distributed within the cochlear nucleus in cats than in rats.

Pre- and post-ganglionic nerve fibres of the pterygopalatine ganglion and their allocation to the eyeball of rats

The origin, course and distribution of pre- and postganglionic neurons of the pterygopalatine ganglion (PPG) in the rat were studied using acetylcholinesterase staining, wheat germ agglutinin coupled to horseradish peroxidase (WGA-HRP) histochemistry and autoradiography. These methods were used in a selected and planned fashion to reveal details concerning the innervation of the lacrimal gland and portions of the eye. The PPG in rats consists of a rostral triangular portion and additional perikarya surrounding the distal part of the major petrosal nerve. Fibres from the superior cervical ganglion (SCG) reach the PPG via the inferior petrosal sinus. Application of WGA-HRP was made after transections: (1) rostral to the PPG; and (2) caudal to the PPG. The first of these applications labelled mainly fibres in the PPG; the second application labelled preganglionic parasympathetic brainstem neurons dorsolateral to the facial nucleus (i.e. the lacrimal nucleus), rostral cells in the SCG and trigeminal sensory fibres. WGA-HRP injections of the lacrimal gland, the conjunctiva and the anterior chamber of the eye all labelled cells in different parts of the PPG. This means that the PPG contains sensory and sympathetic nerve fibres and that the PPG has a topographical organisation along the rostrocaudal axis. Isotope injections of the PPG anterogradely labelled fibres passing through the ciliary ganglion that innervated the conjunctiva, the limbus and parts of the choroid.

Horseradish peroxidase and cobalt chloride as neuromarkers in the hypoglossal nucleus

The hypoglossal nucleus in 129 REJ normal mouse strains was investigated using two neuroanatomical markers, namely the cobalt chloride (CoCl2) and the horseradish peroxidase (HRP) techniques. CoCl2 was introduced through the cut end of the hypoglossal nerve. In one set of experiments HRP was injected into the hypoglossal nerve, while in the other it was injected into the tongue musculature. Results show that with these techniques the hypoglossal neurons are conspicuously stained and can be easily located among series of brainstem sections. The mean number +/- SD of neurons in the hypoglossal nucleus was 1,417 +/- 37, 846 +/- 28 and 1,272 +/- 42 using CoCl2 and HRP injected into the tongue musculature or the hypoglossal nerve, respectively. The estimated length of the nucleus was 0.92 mm with the CoCl2 technique.

Quantitative inter-strain comparison of the distribution of choline acetyltransferase activity in the rat cochlear nucleus

The distribution of choline acetyltransferase activity in the cochlear nucleus of Sprague-Dawley albino rats was quantitatively compared to those in two strains of pigmented rats, Long Evans hooded and Brown Norway, using microdissection and radiometric assay techniques. Although activities tended to be, on the whole, higher in the albino rats, the differences were fairly minor. The relative distributions of choline acetyltransferase activity were generally similar among the 3 rat strains, not only among regions, but also within regions. Stain for acetylcholinesterase activity in the cochlear nucleus also had a similar appearance among the 3 rat strains. These chemical results are consistent with previous anatomical and physiological studies suggesting that auditory differences between albino and pigmented animals may not be as great in the cochlear nucleus as in the superior olivary complex.

A subpopulation of preganglionic parasympathetic neurons in the rat contain adenosine deaminase

Immunohistochemical staining and retrograde fluorescent tracing techniques were used to demonstrate the presence of adenosine deaminase in preganglionic parasympathetic neurons. Both brainstem and sacral spinal cord parasympathetic nuclei were found to contain a subpopulation of neurons immunoreactive for adenosine deaminase. Immunostaining of preganglionic neurons in brainstem was restricted to a group of cells which were shown by retrograde tracing with Fast Blue to project exclusively to the sphenopalatine ganglion. This group was defined as the lacrimo-nasopalatine parasympathetic nucleus. Neurons in all other cranial preganglionic centers were devoid of adenosine deaminase immunoreactivity. In spinal cord adenosine deaminase-immunoreactive neurons were found in the intermediolateral gray matter in the region of the sacral parasympathetic nucleus. Injections of Fast Blue into the pelvic ganglion labeled large numbers of neurons in this nucleus, only some of which contained adenosine deaminase. The majority of neurons immunoreactive for adenosine deaminase were also shown to be immunoreactive for choline acetyltransferase in both brainstem and sacral parasympathetic nuclei. The present results show that a subclass of preganglionic parasympathetic neurons are among the few structures in the central nervous system that express what appear to be high levels of adenosine deaminase. This observation together with evidence suggesting that purines serve as neurotransmitters in some sacral parasympathetic neurons supports the notion that adenosine deaminase may constitute a marker for adenine nucleoside and/or nucleotide neurotransmission.

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.

Morphology of motoneurons in a mixed motor pool of the cat facial nucleus that innervate orbicularis oculis and quadratus labii superioris, stained intracellularly with horseradish peroxidase

Retrograde tracing with horseradish peroxidase showed that motoneurons to two distinct muscles, the orbicularis oculis and quadratus labii superioris, are intermixed within the dorsolateral subnucleus of the cat facial nucleus. Intracellular electrodes were used to identify and fill the motoneurons of the dorsolateral subnucleus with horseradish peroxidase. Soma diameters averaged 55 micron. The average number of primary dendrites was 11.6. The area covered by the dendritic trees varied in shape according to the position of the soma within the subnucleus. Axon hillocks were seen arising in many orientations, bearing no apparent relation to subsequent axonal path, cell position within the nucleus or somatic geometry. Motoneurons to the two muscles appeared to be indistinguishable on the basis of morphology, even though they appear to be functionally independent. Their functional differences are not reflected in any measure of somadendritic shape studied here. Of further interest is the variability in shape associated with the neurons's position within the subnucleus. We conclude that many details of dendritic shape do not reflect specific physiological function.

Examination of geniculate ganglion cells contributing sensory fibers to the rat facial 'motor' nerve

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.

Aspartate aminotransferase activity in fiber tracts of the rat brain

Activity of aspartate aminotransferase, an enzyme which catalyzes the interconversion of the excitatory transmitter candidates, glutamate and aspartate, has been measured in fiber tracts of rat, with an emphasis on sensory and motor systems of the brain. Most tracts had significantly higher activities than the cholinergic facial nerve root, consistent with the possibility that a component of aspartate aminotransferase activity might serve as a marker for neurons using glutamate and/or aspartate as neurotransmitter. Highest activity was in the auditory nerve root. On the other hand, a close correlation was found between aspartate aminotransferase and malate dehydrogenase activities in the fiber tracts, raising the question whether aspartate aminotransferase activity may be more closely related to energy metabolism than to transmitter metabolism.

Choline acetyltransferase and acetylcholinesterase in centrifugal labyrinthine bundles of rats

Activities of choline acetyltransferase and acetylcholinesterase were measured for the acetylcholinesterase-positive fiber bundles containing axons projecting from the brainstem to the labyrinth of the rat. These activities were compared to those of a well-established cholinergic tract: the facial motor root. The choline acetyltransferase activities were roughly similar between the tracts, consistent with a conclusion that the centrifugal labyrinthine fibers are all cholinergic. The acetylcholinesterase activities were much higher in the centrifugal labyrinthine bundle than in the facial motor root, probably relating to the smaller diameters of the labyrinthine fibers. Transection of the centrifugal labyrinthine bundle led to virtually total loss of its choline acetyltransferase activity lateral to the cut, consistent with a centrifugal direction of all the fibers, but loss of only half its acetylcholinesterase activity, even after 34 days. These results agree with those for well-established cholinergic pathways, including the facial motor root in the present study, and with previous suggestions that a component of the acetylcholinesterase in cholinergic tracts might be synthesized by cells other than the neurons in the tract.

A comparison of the distribution of central cholinergic neurons as demonstrated by acetylcholinesterase pharmacohistochemistry and choline acetyltransferase immunohistochemistry

The topographical distribution of cholinergic cell bodies has been studied in the rat brain and spinal cord by choline acetyltransferase (ChAT)-immunohistochemistry and acetylcholinesterase (AChE)-pharmacohistochemistry using diisopropylfluorophosphate (DFP). The ChAT-containing cells and the cells that stained intensely for AChE 4-8 hr after DFP were mapped in detail on an atlas of the forebrain (telencephalon, diencephalon) hindbrain (mesencephalon, rhombencephalon) and cervical cord (C2, C6). Striking similarities were observed between ChAT-positive cells and neuronal soma that stained intensely for AChE both in terms of cytoarchitectural characteristics, and with respect to the distribution of the labelled cells in many areas of the central nervous system (CNS). In the forebrain these areas include the caudatoputamen, nucleus accumbens, medial septum, nucleus of the diagonal band, magnocellular preoptic nucleus and nucleus basalis magnocellularis. In contrast, a marked discrepancy was observed in the hypothalamus and ventral thalamus where there were many neurons that stained intensely for AChE, but where there was an absence of ChAT-positive cells. No cholinergic perikarya were detected in the cerebral cortex, hippocampus, amygdala and dorsal diencephalon by either histochemical procedure. In the hindbrain, all the motoneurons constituting the well-established cranial nerve nuclei (III-VII, IX-XII) contained ChAT and exhibited intense staining for AChE. Further, a close correspondence was observed in the distribution of labeled neurons obtained by the two histochemical procedures in the midbrain and pontine tegmentum, including the laterodorsal tegmental nucleus, some areas in the caudal pontine and bulbar reticular formation, and the central gray of the closed medulla oblongata. On the other hand, AChE-intense cells were found in the nucleus raphe magnus, ventral part of gigantocellular reticular nucleus, and flocculus of the cerebellum, where ChAT-positive cells were rarely observed. According to both techniques, no positive cells were seen in the cerebellar nuclei, the pontine nuclei, or the nucleus reticularis tegmenti pontis. Large ventral horn motoneurons and, occasionally, cells in the intermediomedial zone of the cervical cord displayed ChAT-immunoreactivity and intense AChE staining. On the other hand, AChE-intense cells were detected in the dorsal portion of the lateral funiculus, but immunoreactive cells were not found in any portion of the spinal cord white matter.(ABSTRACT TRUNCATED AT 400 WORDS)

Central origin of canine vidian nerve studied by the HRP method

Central origin of the vidian nerve in the dog was investigated using the retrograde tracing technique of horseradish peroxidase (HRP). After HRP was applied to the vidian nerve, labelled neurons were found in the medulla oblongata and the geniculate ganglion but could not be found in the trigeminal ganglion. Labelled neurons in the medulla oblongata were found not only in the dorsal part but also in the ventral part to the facial motor nucleus and were maximum in number at the level of the rostral third of the facial motor nucleus. These labelled neurons were generally medium-sized multipolar neurons with well-developed dendrites.

Distribution of sensory ganglion cells innervating facial muscles in the cat. An anatomical study with the horseradish peroxidase technique

The question of a possible sensory component in branches of the facial nerve innervating facial mimetic muscles in the cat was examined by the technique of retrograde axonal transport of horseradish peroxidase (HRP). HRP was applied to the proximal cut end of facial nerve branches innervating different facial muscle groups. Following survival periods of 71-75 h the animals were fixed by perfusion. Certain craniospinal sensory ganglia and the brain stem were processed histochemically for demonstration of HRP. HRP-labelled cell bodies, structurally resembling sensory neurons, were consistently observed ipsilaterally in the geniculate and proximal vagal ganglia and under certain conditions in the trigeminal ganglion. Measurements of HRP-labelled neurons in the geniculate and proximal vagal ganglia showed a wide size range but a unimodal size distribution with peaks in the small size range. These findings support the view that facial nerve branches innervating the mimetic muscles contain different types of sensory fibers.

Central distribution of afferent and efferent components of the chorda tympani in the cat as revealed by the horseradish peroxidase method

Central distribution of afferent and efferent components of the chorda tympani (CT) in the cat was examined by using the anterograde and retrograde tracing techniques of horseradish peroxidase (HRP). HRP was applied to the CT in the tympanic cavity. HRP-labeled CT fibers were traced to the brain stem along the ventral surface of the vestibular nerve. The afferent CT fibers were divided into ascending and descending components. The rostrally directed ascending fibers ended within and around the dorsomedial portions of the principal sensory trigeminal nucleus. The descending fibers entered the solitary tract to run caudally as far as the levels slightly rostral to the obex, giving terminals to the solitary nucleus. A cluster of HRP-labeled neurons were seen ipsilaterally in the lateral reticular formation medial to the spinal trigeminal nucleus; it was observed from the caudalmost levels of the exiting root of the facial nerve to the caudal levels of the facial nucleus. HRP-labeled axons arising from the HRP-labeled neurons firstly ran dorsomedially and then medially under the genu of the facial nerve to form a small genu at the region medial to the genu of the facial nerve. Subsequently the labeled axons ran laterally and ventrolaterally to join other CT fibers at the dorsomedial aspect of the spinal trigeminal tract.

New data on the precise location of the lacrimo-muconasal nucleus of the rat

Three methods (axonal degeneration, retrograde labelling with HRP and Golgi's silver impregnation) were used in the identification of a group of cells located in the ventrolateral part of the reticular formation of the pons, which are postulated to form the lacrimo-muconasal nucleus of the rat.

Central representation and somatotopic organization of the jaw muscles within the facial and trigeminal nuclei of the pigeon (Columba livia)

The location of facial and trigeminal brainstem motoneurons innervating the jaw muscles of the pigeon has been determined, using the technique of retrograde transport of horseradish peroxidase. Trigeminal motoneurons innervating the jaw closing muscles are located within the classically defined main trigeminal motor nucleus, and their organization exhibits approximately a mediolateral somatotopy. Trigeminal neurons innervating the opener muscle of the upper jaw are also located in the main trigeminal motor nucleus, but comprise a dorsomedial subnucleus which is continuous caudally with the dorsal facial nucleus whose neurons innervate the opener muscle of the lower jaw. The Vth and VIIth motor nuclei are thus linked in the rostrocaudal plane. The representations of other head muscles are arranged in a dorsoventral manner within the V-VII motor complex, with the lower eyelid muscle represented most dorsally and the hyoid and superficial neck muscles most ventrally. Jaw closing muscles were well represented in both the Gasserian ganglion and trigeminal mesencephalic nucleus. No such representation was found for either of the jaw opening muscles. The HRP data indicate that the V-VII motor complex in birds is far more extensive than has previously been suggested.

Central origins of cranial nerve parasympathetic neurons in the rat

The location of central neurons that contribute preganglionic parasympathetic axons to cranial nerves VII, IX, and X in rats has been identified using horseradish peroxidase (HRP) tracing methods. Collectively, these neurons form an uninterrupted dorsal column that extends over the entire length of the medulla. The cephalic end of this column turns ventrally with neurons scattered in the parvicellular reticular formation between the rostral pole of the nucleus of the solitary tract (NST) and the facial motor nucleus. Applying HRP crystals to the cut cervical vagus labels neurons in the classically defined dorsal motor nucleus. Rostrally, this distribution continues along the medial edge of NST, ending just caudal to neurons exiting in the lingual-tonsilar branch of IX. At the rostral pole of the NST and ventral to it, neurons occur that serve the lingual-tonsilar and tympanic branches of IX, as well as the chorda tympani and greater superficial petrosal (GSP) branches of VII. Central neurons of the chorda tympani and tympanic nerves spread ventrally from NST into a sparse but largely coextensive distribution in the reticular formation lateral to the ascending radiations of the facial motor nucleus. Immediately ventral to this distribution, a dense accumulation of GSP efferent neurons appears rostrolateral to the facial motor nucleus. Although they vary considerably in number and packing density, the neurons of the dorsal efferent column and those extending from it into the reticular formation have similar morphological characteristics. The somata are medium-sized, fusiform, or multipolar, but with usually no more than five or six major processes.

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.

Origin and course of an afferent component of the facial nerve within the central nervous system

The mesencephalic nucleus of trigeminal gives rise to an afferent component of the facial nerve. This nucleus contains large unipolar afferent cell bodies which give rise to an axon which courses caudally through the brainstem and exists via the facial nerve to terminate distal to the stylomastoid foramen.