The ultrastructural identification of vagal terminals in the solitary nucleus of the cat after anterograde labelling with horseradish peroxidase

Xenobiotic pulmonary exposure and systemic cardiovascular response via neurological links

The cardiovascular response to xenobiotic particle exposure has been increasingly studied over the last two decades, producing an extraordinary scope and depth of research findings. With the flourishing of nanotechnology, the term "xenobiotic particles" has expanded to encompass not only air pollution particulate matter (PM) but also anthropogenic particles, such as engineered nanomaterials (ENMs). Historically, the majority of research in these fields has focused on pulmonary exposure and the adverse physiological effects associated with a host inflammatory response or direct particle-tissue interactions. Because these hypotheses can neither account entirely for the deleterious cardiovascular effects of xenobiotic particle exposure nor their time course, the case for substantial neurological involvement is apparent. Indeed, considerable evidence suggests that not only is neural involvement a significant contributor but also a reality that needs to be investigated more thoroughly when assessing xenobiotic particle toxicities. Therefore, the scope of this review is several-fold. First, we provide a brief overview of the major anatomical components of the central and peripheral nervous systems, giving consideration to the potential biologic targets affected by inhaled particles. Second, the autonomic arcs and mechanisms that may be involved are reviewed. Third, the cardiovascular outcomes following neurological responses are discussed. Lastly, unique problems, future risks, and hurdles associated with xenobiotic particle exposure are discussed. A better understanding of these neural issues may facilitate research that in conjunction with existing research, will ultimately prevent the untoward cardiovascular outcomes associated with PM exposures and/or identify safe ENMs for the advancement of human health.

Ultrastructure of glutamate and GABA immunoreactive axon terminals of the rat nucleus tractus solitarius, with a note on infralimbic cortex afferents

The principal fast neurotransmitters in the CNS are glutamate and GABA. Our aim was to provide a baseline account on the ultrastructure of the axon terminals immunoreactive to glutamate or GABA present in the nucleus tractus solitarius (NTS) of the rat. In addition, we wanted to complete our study of cortico-solitary afferents at the electron microscopic level, by analyzing the inputs from the infralimbic cortex. Using post-embedding immunogold, we found that nearly 61% of the axon terminals were glutamatergic, and 36% were GABAergic in the rat visceral NTS. In general, axons making asymmetric synaptic contacts were enriched in glutamate, compared to axons involved in symmetric synapses. In contrast, the vast majority of the GABAergic axon terminals made symmetric synaptic contacts. We could discern five types of glutamatergic and two types of GABAergic axon terminals that differed in their fine structure. Afferents from the infralimbic cortex were small, with clear synaptic vesicles and no dense core vesicles; they made asymmetric contacts with fine dendrites, and were glutamatergic. We conclude that most axon terminals in the NTS use glutamate or GABA as fast transmitters, in addition to being a heterogeneous population of morphological types.

Glutamate immunoreactivity of insular cortex afferents to the nucleus tractus solitarius in the rat: a quantitative electron microscopic study

Corticosolitary axons and their terminals were labeled by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, after injections into the rat insular cortex. The ultrastructure of these cortical afferents was analysed in the medial and commissural subnuclei of the nucleus tractus solitarius. Cortical terminals had a mean area of 0.36 microns 2, and were among the smallest terminals in the nucleus. They made single, asymmetric synaptic contacts with thin dendritic stems or with spines. The average diameter of the dendrites postsynaptic to cortical axons was 0.59 microns, and significantly smaller (P < 0.01, Kolmogorov-Smirnov test) than the mean (0.87 microns) of the population of dendrites in the same region of the nucleus tractus solitarius. Cortical boutons contained closely packed round and clear synaptic vesicles of diameter ca. 28 nm, a few mitochondria, and no dense core vesicles. Postembedding immunogold analysis showed that the anterogradely labeled cortical axon terminals were immunoreactive to glutamate, but not to GABA. Cortical afferents had on average four times the glutamate immunoreactivity (assessed by gold particle density) than local dendrites or terminals making symmetric synaptic contacts. Similarly, most of the unlabeled axon terminals participating in asymmetric synaptic contacts were highly enriched in glutamate immunoreactivity, suggesting that glutamate may be a most prevalent transmitter in the nucleus tractus solitarius. Terminals immunoreactive to GABA always made symmetric synapses, mostly with dendritic shafts and perikarya. We concluded that insular cortex axons made single, asymmetric synaptic contacts with thin, probably distal dendrites in the nucleus tractus solitarius. Cortical terminals are immunoreactive to glutamate, and morphologically different from primary afferents and from terminals immunoreactive to GABA.

Synaptic organization of the interstitial subdivision of the nucleus tractus solitarii and of its laryngeal afferents in the rat

The nucleus tractus solitarii, the first central relay for gustatory and a variety of visceral afferents, is also an integrative center for numerous functions. Its interstitial subdivision is involved in swallowing and respiratory reflexes. The ultrastructural characteristics of this subdivision and of its laryngeal afferents were investigated in adult rat by a serial-section study and by application of wheat germ agglutinin-horseradish peroxidase conjugate to the peripheral afferent fibers. The interstitial subnucleus contained scattered small neuronal cell bodies with such ultrastructural features as a large nucleus with deep indentations and an organelle-poor cytoplasm. On the basis of their size and vesicular content, the axon terminals were classified into three categories. Group I and group II terminals were small or large, respectively, and contained mainly small, round, and clear synaptic vesicles. Group III terminals were also small but contained small, pleomorphic, and clear vesicles. Axodendritic synapses were the most numerous. They were either asymmetrical, comprised of group I and II terminals, or symmetrical, comprised of group III terminals. More than 50% were part of complex synaptic arrangements in the form of rosettes or glomeruli. Axosomatic contacts involved both group I and group III terminals and were always symmetrical. A high frequency of axoaxonic synapses was found. They were symmetrical, comprised of group III terminals on group I or II terminals. Different types of symmetrical synaptic contacts made by dendrites were also found. This study indicates also that the ipsilateral interstitial subdivision constitutes the preferential site of termination for superior laryngeal afferents. The labeled axon terminals belonged exclusively to groups I and II and were involved in both axodendritic and axoaxonic synapses. Some of the axodendritic synapses were part of rosettes or glomeruli. All these synaptic arrangements may be considered a morphological substrate for important processing of afferent information in the nucleus tractus solitarii. They may account for some of the integrative functions of the interstitial subnucleus such as physiological processes triggered from the superior laryngeal nerve.

Synaptic connections of central carotid sinus afferents in the nucleus of the tractus solitarius of the rat. I. An electron microscopic study

A transganglionic transport technique was used to study the synaptic connections of the central carotid sinus afferents in the nucleus of the tractus solitarius of the rat by electron microscopy. The caudal part of the nucleus was profusely innervated. Labelled fibres extended to the contralateral nucleus, and to the ipsilateral dorsal motor nucleus of the vagus nerve, nucleus ambiguus, spinal nucleus of the trigeminal nerve and the area postrema. The labelled terminals were densely packed with clear, predominantly spherical vesicles about 50 nm in diameter and a few often swollen mitochondria. The terminals synapsed on dendrites of various calibres, spindle- or pear-shaped somal profiles with short axes lesser than 8 microns, and axon terminals. In axo-axonal synapses, most labelled terminals appeared to be presynaptic. Frequently, profiles of labelled terminals were in direct apposition with one another. The latter may represent the morphological substrate of the interaction between baro- and chemoreceptor inputs in the nucleus of the tractus solitarius and warrants further study. The present results indicate that in addition to direct inputs, the carotid sinus afferents are able to influence second-order neurons in the nucleus of the tractus solitarius indirectly through presynaptic modulation.

Ultrastructural organization of the interstitial subnucleus of the nucleus of the tractus solitarius in the cat: identification of vagal afferents

This electron microscopic study, based on serial section analysis, describes the synaptic organization of the interstitial subnucleus of the nucleus of the solitary tract and identifies the terminals of the vagal primary afferents utilizing degeneration and HRP transport. The interstitial subnucleus contains sparsely scattered cell bodies, numerous dendrites and axon terminals, and bundles of unmyelinated and myelinated axons. The cell bodies which are small in diameter have an organelle poor cytoplasm and a large invaginated nucleus. Axon terminals can be classified into two main types according to their vesicular shape. The first type contains clear, round vesicles and can be further subdivided into two subgroups on the basis of their morphology and the size of their vesicles. In the first subgroup the terminals are small, contain a few mitochondria and their vesicles are densely packed with an homogeneous size. In the second subgroup the terminals which vary from small to large, contain many mitochondria and contain round vesicles which are heterogeneous in size. The second main terminal type consists of axon terminals containing pleomorphic vesicles which are associated with asymmetrical or symmetrical synaptic contacts on dendrites. Axo-axonic contacts are present in the interstitial subnucleus. In general, the presynaptic axon terminals contain pleomorphic vesicles and the postsynaptic elements contain round vesicles of varying size. In some dendrites, identified by the presence of ribosomes, groups of round and/or pleomorphic vesicles are found associated with synaptic contacts. These dendrites are presynaptic to conventional dendrites and postsynaptic to axon terminals. After removal of the nodose ganglion, degenerative alterations are seen only at the caudal and middle levels of the interstitial subnucleus. Degeneration occurs in a few myelinated axons and in axon terminals which usually contain a mixture of small and larger round, clear vesicles. After HRP injection into the vagus nerve, the HRP reaction product is visible in axon terminals filled with clear, round vesicles which are heterogeneous in size. The labelled axon terminals establish single or multiple synaptic contacts. This study demonstrates that terminals of vagal primary afferents consist principally of terminals of the second subgroup. The morphology of these terminals are compared to primary afferents in the brainstem and spinal cord.

Direct vagal input to neurons in the area postrema which project to the parabrachial nucleus: an electron microscopic-HRP study in the cat

This study in cat examines the synaptic relationship of vagal afferents to parabrachial projecting neurons in the area postrema (AP) using anterograde and retrograde transport of horseradish peroxidase (HRP). Wheat germ agglutinin-HRP injected into the parabrachial nucleus (PBN) produced retrograde neuronal labeling in the AP and in the nucleus of the tractus solitarius bilaterally, but with an ipsilateral predominance. Labeled neurons were confined mainly to the caudal 2/3's of the AP. Following injection of WGA-HRP into the PBN and HRP into the nodose ganglion in the same animal, examination of sections of the AP with the electron microscope revealed anterogradely labeled axon terminals in apposition to retrogradely labeled somata and dendrites. In some instances, labeled terminals were observed to form synaptic contacts with retrogradely labeled neurons. We conclude that in the cat a vagal input to neurons in the AP is monosynaptically relayed to the PBN.

Rapidly adapting pulmonary receptor afferents: II. Fine structure and synaptic organization of central terminal processes in the nucleus of the tractus solitarius

The nucleus of the tractus solitarius (nTS) is a site for termination of primary afferents originating from a variety of different visceral sensory endings (Kalia and Mesulam: J. Comp. Neurol. 193:523-553, '80). The light and electron microscopic evaluation of bouton terminals of slowly adapting lung stretch (SAR) afferent fibers originating from the tracheobronchial tree has been described previously (Kalia and Richter: J. Comp. Neurol. 241:503-520, 521-535, '85). The companion article (Kalia and Richter: J. Comp. Neurol. 273:000-000, '88) describes details of the light microscopic organization of a second group of pulmonary afferents, the rapidly adapting receptors (RARs), that are known to signal transient volume changes in airways (Sellick and Widdicombe: J. Physiol. (Lond.) 203: 359-381, '69; Q.J. Exp. Physiol. 55:153-163, '70). Terminals from RAR afferents are concentrated within two specific subnuclear groups of the nTS (dnTS and nI) and are distributed over 4 mm of the medulla oblongata rostrocaudally. Within the nTS, axon collaterals of RAR afferents remain myelinated up to a diameter of 0.4-1.0 microns. Preterminal processes are always unmyelinated and range in diameter from 0.15 to 0.3 microns. Bouton terminals (1.0-2.0 microns) are of both the en passant and end terminal varieties. The synaptic profiles formed by 143 bouton terminals of RAR afferents, were examined in uninterrupted sequential sections and are described in this paper. All the bouton terminals examined under the electron microscope were found to contain clear, round synaptic vesicles. Boutons made synaptic contact with different profiles in each of the two subnuclei (dnTS and nI) examined. Contacts were usually asymmetrical (type I) containing clear, round synaptic vesicles 35-50 nm in diameter. In the dorsal subnucleus of the nTS (dnTS), the synaptic arrangement of RAR boutons did not appear to be complex. The RAR bouton terminal was usually located in juxtaposition to unlabeled axon terminals of similar morphological characteristics. Typically, the RAR bouton terminal made synaptic contact with a medium-sized spiny dendrite. No axosomatic contacts involving RAR afferents were observed in this subnucleus. In the intermediate subnucleus of the nTS (nI), the most common synaptic arrangement of RAR bouton terminals was in the form of a "glomerulus," which was formed by five to seven different types of neuronal profiles surrounding the labeled RAR bouton terminal.(ABSTRACT TRUNCATED AT 400 WORDS)

Gastric distention increases [14C]2-deoxyglucose uptake in the rat nucleus tractus solitarius

Stomach balloons were inflated with 20 ml of warm water in anesthetized rats who had a left cervical vagotomy. This increased [14C]2-deoxyglucose (2-DG) uptake in the commissural and medial portions of the right nucleus solitarius. This effect was not present in controls which received 2 ml of water in their stomach balloons.

Factors affecting the ultrastructural pattern of anterograde labeling in axon terminals with HRP

Comparisons of anterograde labeling of axon terminals originating from short and long projection neurons were made in the hypoglossal nucleus. Injections of dilute and concentrated horseradish peroxidase (HRP) or wheat germ-agglutinin-horseradish peroxidase (WGA-HRP) were made via a glass micropipette into the nucleus reticularis parvocellularis (RPc = short projection neurons) and the Spinal V trigeminal complex (Sp. V = long projection neurons). Axon terminals in the hypoglossal nucleus, a common projection site of the two efferent systems, were evaluated ultrastructurally using diaminobenzidine (DAB) as the chromogen for the cobalt-glucose oxidase (CO-GOD) method of HRP labeling. Labeled axon terminals from these two sources demonstrated different distribution patterns of the reaction product. For the short pathway, high concentrations of the tracers resulted in diffuse, agranular labeling in the majority of axon terminals. Dilute concentrations of the tracers were associated with membrane-bound, granular type of labeling. All anterograde labeling of terminals of long projection neurons (Sp. V) was membrane-bound and granular irrespective of the tracer concentration. The length of the pathway and the concentration of the enzyme tracers are factors that affect the pattern of anterograde label in axon terminals of hypoglossal afferents.

Morphology of physiologically identified slowly adapting lung stretch receptor afferents stained with intra-axonal horseradish peroxidase in the nucleus of the tractus solitarius of the cat. II. An ultrastructural analysis

The nucleus of the tractus solitarius is a site for termination of primary afferents originating from a variety of visceral receptors. The localization of bouton terminals of slowly adapting lung stretch (SAR) afferent fibers originating from the tracheobronchial tree have been described in the companion paper (Kalia and Richter, '85). The most conspicuous finding regarding the location of SAR terminals is that they are concentrated within specific subnuclear groups of the nucleus of the tractus solitarius (nTS) and are distributed widely in the rostrocaudal plane of the medulla oblongata. These light microscopic features have provided us with valuable information with regard to the organization of visceral afferents in the central nervous system. The synaptic profiles formed by the 476 bouton terminals of these HRP-labeled afferents have been described in this paper in serial thin sections. All of the bouton terminals examined under the electron microscope were found to contain round synaptic vesicles. Synaptic boutons (1.0-3.0 microns in diameter) were usually of the en passant variety and made contact with different structures depending upon the subnucleus which was examined. In the ventral (v) and the ventrolateral (vl) subnuclei of the nTS, asymmetrical (type I) synaptic contacts containing round, clear synaptic vesicles of 35-50 microns in diameter were found and these contacts were made with (1) the soma of cell bodies located in that subnucleus; (2) spiny dendrites in that nucleus; (3) vesicle-containing axon terminals that were presynaptic to the HRP-labeled bouton terminal; and (4) vesicle-containing dendrites in which the HRP profile was presynaptically located. The terminal axon remained myelinated till the last 1 micron before the bouton terminal was formed. There was no distinct, unmyelinated portion of the terminal axon. The synaptic bouton received axon-axonal synapses from unlabeled bouton terminals containing round, clear vesicles. This is the first report of the localization of these afferent fibers as well as of the regional variations in the ultrastructure of boutons of physiologically identified terminals. It appears likely that the lung stretch afferent fibers, by having axon-axonal as well as axon-somatic contact in the ventral, ventrolateral, and intermediate subnuclei of the nTS, can interact in a variety of different ways in this region. The significance of these features in relation to the precise influence of respiratory afferents on central respiratory mechanisms needs to be evaluated further.

The ultrastructural identification of reticulo-hypoglossal axon terminals anterogradely labeled with horseradish peroxidase

Injections of horseradish peroxidase (HRP) or wheat-germ agglutinin-horseradish peroxidase (WGA-HRP) into the nucleus reticularis parvocellularis (RPc) produced anterograde labeling of axon terminals within the hypoglossal nucleus. Based on morphological parameters of vesicle population, membrane specializations, and postsynaptic articulations, two types of axon terminals derived from neurons in RPc end on hypoglossal neurons. More than half of the terminals contained spherical vesicles (S-type), established asymmetrical membrane specializations and contacted proximal and medium-sized dendrites. The remaining labeled terminals had flattened vesicles (F-type), symmetrical membrane densities and apposed medium and small dendrites. The morphological differences expressed in the two types of terminals may reflect physiological and/or pharmacological differences in the action of RPc neurons on motoneurons in the hypoglossal nucleus.

Sino-aortic denervation in the monkey

The aortic arch and carotid sinuses were denervated in eleven monkeys. The monkeys were subjected to four sequential surgeries which involved: (1) implantation of an aortic and left atrial catheter; (2) stripping of the adventitia from the aortic arch; (3) stripping the left carotid sinus and associated vessels; and (4) stripping the right carotid sinus and associated vessels. Blood pressure and pulse rate were recorded 6 days after each surgical procedure. Records were taken over a 6 h period while the monkeys were in their home cages. Baroreceptor denervation was confirmed by: (1) absence of heart rate response to blood pressure changes and (2) an increase in the variability of blood pressure. Veratridine given into the left atrium caused a Bezold-Jarisch reflex both before and after denervation verifying the integrity of the afferent and efferent vagus. Denervation of the baroreceptors resulted in a significant increase in blood pressure when measured from monkeys who were restrained in chairs in the laboratory; however, blood pressure was not significantly elevated in the baroreceptor denervated monkeys while they were tethered in their home cages. It is concluded that denervation of the sino-aortic baroreceptor does not result in a significant increase in systemic blood pressure.

A combined electron microscopic HRP and immunocytochemical study of the limbic projections to rat hypothalamic nuclei containing vasopressin and oxytocin neurons

Light microscopic studies in our laboratory have indicated that the lateral septum, amygdala, and ventral subiculum project in a perinuclear fashion to the paraventricular (PVN), supraoptic (SON), and suprachiasmatic (SCN) nuclei (Oldfield et al., '82; Silverman and Oldfield, '84). In the present paper a combined anterograde HRP and immunocytochemical procedure has been used to determine the connectivity between these limbic efferents and peptide-containing processes emanating from the above mentioned hypothalamic nuclei. Synaptic associations were found to exist between efferents from (1) the septum and both vasopressin (VP)- and oxytocin (OX)-positive dendrites derived from cells in the PVN and SON, (2) the septum and VP dendrites dorsal to the SCN, (3) the ventral subiculum and both VP and OX dendrites arising from the PVN and SON, and (iv) the amygdala and VP dendrites from the PVN. These observations help clarify an apparent discrepancy between electrophysiological data, in which limbic efferents have been shown to influence the activity of VP and OX neurons in the PVN and SON, and anatomical evidence which indicates only a perinuclear innervation from these sites not encroaching on the hypothalamic nuclei themselves. In each case the synaptic connections are made on dendrites external to the nucleus: those lateral and ventrolateral to the PVN, dorsal to the SON, and dorsal or dorsolateral to the SCN.

Vagal and gastric connections to the central nervous system determined by the transport of horseradish peroxidase

Horseradish peroxidase (HRP, Sigma Type VI) crystals were encased in a parafilm envelope and applied to the transected central ends of the left and right cervical vagus nerves and the anterior and posterior esophageal vagus nerves of adult male hooded rats. Injections of 30% HRP were made into the muscle wall of the fundus and antrum regions of the stomach. After 48 hr survival time, animals were perfused intracardially with a phosphate buffer plus sucrose wash followed by glutaraldehyde and paraformaldehyde fixative. The brain stem, spinal cord and corresponding dorsal root ganglia, superior cervical sympathetic ganglion, and the nodose ganglion were removed and cut into 50 micron sections. All tissue was processed with tetramethylbenzidine (TMB) for the blue reaction according to Mesulum and counterstained with neutral red. Sequential sections were examined under a microscope. Labeled neurons and nerve terminals were identified using bright and dark field condensers and polarized light. In tissue from animals that had HRP applied to the cervical vagus nerves, retrogradely labeled neurons were identified ipsilaterally in the medulla located in the dorsal motor nucleus of the vagus (DMN) and the nucleus ambiguus (NA). Labeled cells extended from the DMN into the spinal cord in ventral-medial and laminae X regions C1 and C2 of cervical segments. Many neurons were labeled in the nodose ganglion. Anterogradely labeled terminals were observed throughout and adjacent to the solitary nucleus (NTS) dorsal to the DMN and intermixed among labeled neurons located in the DMN. In tissue from animals that had HRP applied to the esophageal vagus nerves, similar labeling was observed. However, fewer neurons were identified in the NA, the nodose ganglion, and only in laminae X of the cervical spinal cord segments C1 and C2. Also, very little terminal labeling was observed in and adjacent to the NTS. Labeled neurons in tissue from animals that had HRP injected into the stomach wall were observed bilaterally in the DMN, nodose ganglion, and only in laminae X at the C1 and C2 levels of the spinal cord. Labeled neurons also were observed in the dorsal root ganglia of the thoracic cord. These data indicate that cervical cord and NA neurons are important in the supradiaphragmatic motor innervation by the vagus. Also, many afferents to the NTS originate above the diaphragm. In addition, some afferents from the stomach enter the central nervous system via the thoracic spinal cord.

Central projections of gustatory nerves in the rat

The central distributions of gustatory and non-gustatory branches of cranial nerves V, VII, IX, and X were examined after application of horseradish peroxidase to the cut nerve. The nerves conveying gustatory information, chorda tympani (CT), greater superficial petrosal (GSP), lingual-tonsilar branch of IX (LT-IX), superior laryngeal branch of X (SL), distributed primarily to the lateral division of the nucleus of the solitary tract (NST) from its rostral pole to the obex. The CT and GSP distributions were coextensive and terminated most densely in the rostral pole of NST. The LT-IX distribution concentrated between this major CT/GSP distribution and the area postrema with a caudal extension into the interstitial nucleus of NST. This nerve also had a substantial projection, not found in other gustatory nerves, into the dorsolateral aspect of the medial NST. The SL distribution overlapped LT-IX in the caudal medulla. The lingual and inferior alveolar nerves, two oral trigeminal branches, projected to regions of NST innervated by the gustatory nerves. The cervical vagus nerve distributed primarily to the medial NST in the caudal half of the nucleus and exhibited only minimal overlap with gustatory nerve distributions. The nucleus of the solitary tract appears to have two major functional divisions--an anterior-lateral oral-gustatory half, and a posterior-medial visceral afferent half.

The primary afferent projection of the greater petrosal nerve to the solitary complex in the rat, revealed by transganglionic transport of horseradish peroxidase

The primary afferent projection of the greater petrosal nerve (GPN) to the solitary complex was studied following application of horseradish peroxidase (HRP) to the GPN just distal to the geniculate ganglion. Labeled fibers were traced to the most rostral part of the solitary tract. Numerous collaterals entered the solitary complex from its dorsal and lateral aspects, and formed a dense plexus. They terminated in the dorsal half of the medial solitary nucleus at the level of the rostral half of the solitary complex, and in the ventrolateral and commissural nuclei at the level of the caudal half. The densest termination was observed in the medial solitary nucleus. Labeled terminals were found to contain round, clear synaptic vesicles and to make asymmetrical synaptic contacts with dendritic profiles.

The sensory innervation of the ovary: a horseradish peroxidase study in the rat

Injections of horseradish peroxidase (HRP) into the right or left ovary of the rat produced labeling of perikarya in both nodose ganglia and ipsilateral dorsal root ganglia (DRGs) from T10 to L2. The greatest concentration of labeled cells was in T13 and L1, DRGs. It is suggested that visceral afferent fibers from the ovary may mediate visceral reflexes that modulate ovarian function.

Intraganglionic distribution of the primary afferent neurons in the frog glossopharyngeal nerve and its transganglionic projection to the rhombencephalon studied by HPR method

Anterograde transport of horseradish peroxidase (HRP) along the bullfrog IXth nerve was studied 6-16 days after application of HRP to the cut end of either the IXth nerve trunk or its distal 2 branches. The jugular and IXth nerve ganglia attached to the rhombencephalon were removed after fixation and serial sections of 50 microns in thickness were stained by the Graham and Karnovsky method. Of all the primary afferent neurons in the IXth nerve, 62% of the cell bodies were distributed within the IXth nerve ganglion, the remaining 38%, within the jugular ganglion. Similar distribution was found with the cells belonging to each of the IXth nerve branches. A part of the transganglionic IXth nerve fibers entering the medulla oblongata ascended to the cerebellar peduncle while the majority descended along the fasciculus solitarius. Some of the descending fibers in the fasciculus extended to the dorsal field of the spinal cord at the third spinal nerve, while some others run to join the descending tract of trigeminal nerve.