Mesencephalic projections to the facial nucleus in the cat. An autoradiographical tracing study

In 33 cats the projections of different parts of the mesencephalon to the facial nucleus were studied with the aid of the autoradiographical tracing method. The results indicate the existence of many different mesencephalo-facial pathways. The dorsomedial facial subnucleus, containing motoneurons innervating ear muscles, receives afferents from 4 different mesencephalic areas: a, the most rostral mesencephalic reticular formation; b, the nucleus of Darkschewitsch and/or the ventral part of the rostral PAG; c, the interstitial nucleus of Cajal and/or the mesencephalic tegmentum dorsomedial to the red nucleus. These areas project bilaterally by way of an ipsilateral medial tegmental pathway. The medial part of the deep tectum. This area projects bilaterally by way of the tecto-spinal tract. The lateral mesencephalic tegmentum close to the parabigeminal nucleus. This area projects mainly contralaterally by way of a separate contralateral lateral tegmental fiber bundle. The mesencephalic tegmentum just dorsolateral to the red nucleus and perhaps from the dorsolateral red nucleus itself. This area projects contralaterally by way of the rubrospinal tract. The intermediate facial subnucleus containing motoneurons innervating the muscle around the eye, receives afferents from two different mesencephalic areas: The dorsal part of the rostral as well as caudal red nucleus (but not from its caudal pole) and from the dorsally adjoining mesencephalic tegmentum including the area of the nucleus of Darkschewitsch and the interstitial nucleus of Cajal. These areas project contralaterally by way of the contralateral rubrospinal tract. The nucleus of the optic tract and/or the olivary pretectal nucleus. This area projects contralaterally by way of a contralateral medial tegmental pathway. The lateral and ventrolateral facial subnuclei containing motoneurons innervating the muscles around the mouth receive afferents from two different mesencephalic areas: The lateral part of the deep tectal layers. This area projects contralaterally by way of the tecto-spinal tract. The nucleus raphe dorsalis and perhaps the nucleus centralis superior. This area projects by way of the lateral tegmentum of caudal pons and medulla.     

Projections from the dorsal column nuclei and the spinal cord to the red nucleus in cat

The projections of the red nucleus (RN) from the dorsal column nuclei (DCN) and the spinal cord have been investigated in cats with the degeneration method. After electrolytic DCN lesions and unilateral cordotomies including the lateral and ventral funiculi, the degeneration was studied in Fink-Heimer stained sections. Contralateral to a DCN lesion terminal degeneration was found along the whole rostrocaudal extent of the red nucleus. In most portions the degeneration was scattered, but dense zones were present, too. Terminal fibers were present in both magnocellular and parvocellular parts. After a gracile lesion the degenerating fibers were restricted to the ventral part of the RN, while the terminal patterns did not differ significantly after cuneate and large DCN lesions. The spinal fibers were found ipsilateral to the cordotomy. Like the DCN fibers, the spinal fibers were present along the whole rostrocaudal extent of the RN and in both magno- and parvocellular zones. Their distribution in the transverse plane was similar, as well. However, the present material was not sufficient to show subtle differences between the DCN and spinal projections, nor to show a possible somatotopical organization of the spinal projection.     

Some anatomical observations on the projections from the hypothalamus to brainstem and spinal cord: an HRP and autoradiographic tracing study in the cat

The hypothalamus is closely involved in a wide variety of behavioral, autonomic, visceral, and endocrine functions. To find out which descending pathways are involved in these functions, we investigated them by horseradish peroxidase (HRP) and autoradiographic tracing techniques. HRP injections at various levels of the spinal cord resulted in a nearly uniform distribution of HRP-labeled neurons in most areas of the hypothalamus except for the anterior part. After HRP injections in the raphe magnus (NRM) and adjoining tegmentum the distribution of labeled neurons was again uniform, but many were found in the anterior hypothalamus as well. Injections of 3H-leucine in the hypothalamus demonstrated that: The anterior hypothalamic area sent many fibers through the medial forebrain bundle (MFB) to terminate in the ventral tegmental area of Tsai (VTA), the rostral raphe nuclei, the nucleus Edinger-Westphal, the dorsal part of the substantia nigra, the periaqueductal gray (PAG), and the interpeduncular nuclei. Further caudally a lateral fiber stream (mainly derived from the lateral parts of the anterior hypothalamic area) distributed fibers to the parabrachial nuclei, nucleus subcoeruleus, locus coeruleus, the micturition-coordinating region, the caudal brainstem lateral tegmentum, and the solitary and dorsal vagal nucleus. Furthermore, a medial fiber stream (mainly derived from the medial parts of the anterior hypothalamic area) distributed fibers to the superior central and dorsal raphe nucleus and to the NRM, nucleus raphe pallidus (NRP), and adjoining tegmentum. The medial and posterior hypothalamic area including the paraventricular hypothalamic nucleus (PVN) sent fibers to approximately the same mesencephalic structures as the anterior hypothalamic area. Further caudally two different fiber bundles were observed. A medial stream distributed labeled fibers to the NRM, rostral NRP, the upper thoracic intermediolateral cell group, and spinal lamina X. A second and well-defined fiber stream, probably derived from the PVN, distributed many fibers to specific parts of the lateral tegmental field, to the solitary and dorsal vagal nuclei, and, in the spinal cord, to lamina I and X, to the thoracolumbar and sacral intermediolateral cell column, and to the nucleus of Onuf. The lateral hypothalamic area sent many labeled fibers to the lateral part of the brainstem and many terminated in the caudal brainstem lateral tegmentum, including the parabrachial nuclei, locus coeruleus, nucleus subcoeruleus, and the solitary and dorsal vagal nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)     

Projections from brainstem nuclei to the nucleus paragigantocellularis lateralis in the cat

Afferent projections from the pons and medulla to the nucleus paragigantocellularis lateralis (PGL) have been mapped in the cat using retrograde transport of horseradish peroxidase (HRP). In the caudal medulla, the major sources of afferents were the medial and lateral divisions of the solitary nuclei complex and the contralateral trigeminal nucleus caudalis. Labelled cells were also present in the dorsal column nuclei, nucleus intercalatus and praepositus hypoglossi but this may have been due to uptake of HRP into fibres of passage. In the dorsolateral medulla and pons, neurones in the vestibular complex and in the parabrachial nucleus were labelled bilaterally. Nucleus raphe magnus and raphe obscurus were both found to send projections to the PGL and labelled cells were also present throughout the pontine and medullary reticular nuclei as well as in PGL on the side opposite to the injection of HRP. These findings are discussed in relation to the role of the PGL in cardiovascular regulation and in the control of pain.     

The mormyrid brainstem. I. Distribution of brainstem neurones projecting to the spinal cord in Gnathonemus petersii. An HRP study

The sources of the descending spinal tracts were identified in the teleost fish Gnathonemus petersii by retrograde HRP transport. HRP injections were made at two spinal levels, either at level of the caudal end of the dorsal fin, anterior to the electric organ, or at the pectoral fin. In both cases all labeled cells were found in the rhombencephalon and the mesencephalic tegmentum. No labeled cells were observed either in the cerebellum and lateral line lobes or in the dorsal mesencephalon i.e. torus semicircularis and mesencephalic tectum or in the telencephalon. Following caudal spinal injections, the majority of the labeled cells were grouped in a median and a ventrolateral column of the rhombencephalic reticular formation. The latter is composed of three parts corresponding to the nucleus reticularis inferior, medius and superior. Both Mauthner cells, all the cells in the medullary relay nucleus controlling the electric organ discharge and a few cells in the posterior part of the magnocellular octaval nucleus were labeled. In the mesencephalon, four nuclei were identified by HRP labeling: the nucleus of the medial longitudinal fasciculus, the nucleus reticularis mesencephali and the anterior and posterior tegmental mesodiencephalic nuclei. The rostral injections revealed several additional spinal projections from the descending vestibular and tangential nuclei, from the medial part of the magnocellular nucleus and, finally, from the rostral periventricular gray of the mesencephalon. Also, after such injections, a greater number of cells were labeled in the reticular formation, especially in the median column and in the inferior reticular nucleus. The results suggest that the rostral spinal cord has a larger connection with the acoustico-vestibular area and the medullary reticular formation than the caudal spinal cord. In contrast, the mesencephalic nuclei, probably linked to the mesencephalic tectum and the pretectal area, appears to be a coordinating apparatus between the visual system and the trunk/tail musculature. Thus, it appears that teleost fish possess the same basic equipment of descending spinal pathways as higher vertebrates.     

Projections from the nucleus tractus solitarii to the spinal cord

Projections from the nucleus tractus solitarii (NTS) to the spinal cord were demonstrated in the male Sprague-Dawley rat. In retrograde transport studies, a horseradish peroxidase conjugate or a fluorescent dye, Fluoro Gold, were injected into midcervical or upper thoracic spinal segments. Most solitariospinal neurons were multipolar or bipolar and located between the obex and spinomedullary junction. Solitariospinal neurons were concentrated in proximity to the ventral border of the solitary tract and extended dorsally into the intermediate division and ventrolaterally into the intermediate reticular zone (IRt) of the lateral tegmental field. This subgroup predominantly projects to midcervical spinal segments. A subset of small neurons was retrogradely labeled from cervical or thoracic spinal segments in the medial commissural nucleus and contiguous with a periventricular group surrounding the central canal. In anterograde transport studies, iontophoretic deposits of Phaseolus vulgaris leucoagglutinin were centered stereotaxically on sites in NTS identified by retrograde transport data. The lectin was incorporated by neurons of the solitary complex and transported bilaterally by axons that emerged from the nucleus and entered the reticular formation. The solitario-reticular (transtegmental) pathway irradiated diagonally across the IRt and extended caudally into the cervical lateral funiculus and spinal gray. A small periventricular-spinal pathway also descended longitudinally to the neuraxis. Solitariospinal neurons project to superficial lamina of the dorsal horn, laminae VII and X and ventral horn. The projections are predominantly contralateral to phrenic and intercostal motor nuclei and ipsilateral to the intermediolateral cell column. The solitariospinal projection represents the shortest route in the central nervous system, other than the local intraspinal reflex, through which first order visceral afferents signal cardiorespiratory and alimentary motor nuclei. © 1993 Wiley-Liss, Inc.     

Afferent projections to the orbicularis oculi motoneuronal cell group. An autoradiographical tracing study in the cat

The motoneurons innervating the orbicularis oculi muscle from a subgroup within the facial nucleus, called the intermediate facial subnucleus. This makes it possible to study afferents to these motoneurons by means of autoradiographical tracing techniques. Many different injections were made in the brainstem and diencephalon and the afferent projections to the intermediate facial subnucleus were studied. The results indicated that these afferents were derived from the following brainstem areas: the dorsal red nucleus and the mesencephalic tegmentum dorsal to it; the olivary pretectal nucleus and/or the nucleus of the optic tract; the dorsolateral pontine tegmentum (parabrachial nuclei and nucleus of K?lliker-Fuse) and principal trigeminal nucleus; the ventrolateral pontine tegmentum at the level of the motor trigeminal nucleus; the caudal medullary medial tegmentum; the lateral tegmentum at the level of the rostral pole of the hypoglossal nucleus and the ventral part of the trigeminal nucleus and the nucleus raphe pallidus and caudal raphe magnus including the adjoining medullary tegmentum. These latter projections probably belong to a general motoneuronal control system. The mesencephalic projections are mainly contralateral, the caudal pontine and upper medullary lateral tegmental projections are mainly ipsilateral and the caudal medullary projections are bilateral. It is suggested that the different afferent pathways subserve different functions of the orbicularis oculi motoneurons. Interneurons in the dorsolateral pontine and lateral medullary tegmentum may serve as relay for cortical and limbic influences on the orbicularis oculi musculature, while interneurons in the ventrolateral pontine and caudal medullary tegmentum may take part in the neuronal organization of the blink reflex.     

Projections of the medial cerebellar nucleus to oculomotor-related midbrain areas in the rat: an anterograde and retrograde HRP study.

The mesencephalic projections of the medial cerebellar nucleus (MCN) were studied in the rat by using the method of anterograde transport of wheat germ agglutinin/horseradish peroxidase to establish connections of the nucleus with oculomotor-related nuclei as a basis for its proposed role in eye movement. The principal targets of projections were the supraoculomotor ventral periaqueductal gray (PAG) and lateral PAG, and paraoculomotor cell groups (nucleus of Darkschewitsch and medial accessory nucleus of Bechterew). Lesser projections were observed to the intermediate layer of the superior colliculus, nucleus of the posterior commissure, and prerubral field. Following transcannular HRP gel implants into the oculomotor complex that included adjacent paraoculomotor nuclei, the largest number of retrogradely labeled cells was found in the caudal MCN. The findings suggest that the caudal MCN in the rat, like the primate fastigial nucleus, is involved in the control of eye movement.     

Projections from the spinal trigeminal nucleus to the entire length of the spinal cord in the rat

In order to confirm the multiple neurotransmitter biosynthetic ability, the possibility to separation of the activities of tyrosine hydroxylase (TH), choline acetyltransferase and glutamic acid decarboxylase was tested by subcloning of a clonal rat pheochromocytoma PC12 cell line. All of 9 subclones obtained showed significant activities of above 3 enzymes, indicating that the PC12 cell has multi-functional properties of neurotransmitter syntheses. One of the subclones, designated PC12h, was demonstrated to have nerve growth factor- (NGF) responsive TH activity. The ED50 value of NGF to increase the TH activity was 1.7 ng/ml (6.5 X 10-11 M). A simultaneous addition of saturating amounts of NGF (50 ng/ml) and dexamethasone (10-6 M) resulted in the increase of TH activity that is equal to the sum of those achieved when either effector was added separately, indicating that the NGF- mediated increase of TH activity in PC12h cells was independent upon the effect of dexamethasone. And also, the TH activity increased by NGF was somewhat potentiated in PC12h cells cultured in a hormone- supplemented serum-free medium.     

Projections from the commissural subnucleus of the nucleus of the solitary tract: an anterograde tracing study in the cat.

The commissural subnucleus (COM) of the nucleus of the solitary tract (NTS) is known to receive primary afferents from the lungs and other viscera innervated by the vagus nerve, and thus to participate in central autonomic and respiratory control. The aim of the present study was to identify the areas of terminal arborizations of COM neurons in order to examine brainstem sites which may be involved in reflex responses mediated by these neurons. The projections were studied in cats, using biocytin as an anterograde tracer. Labeled fibers and terminal boutons were visualized by horseradish-peroxidase histochemistry, 2-3 days after microinjection of the tracers into the COM 1-2 mm caudal to the obex. Labeled axons were examined in the brainstem from the rostral pons to the caudal medulla and were found bilaterally, with an ipsilateral predominance, mainly in the following regions: (1) The dorsolateral rostral pons. Terminal boutons were observed in the lateral and medial parabrachial nuclei, K?lliker-Fuse nucleus, and around the mesencephalic trigeminal tract. This area corresponds to the pontine respiratory group also known as the "pneumotaxic center." (2) The pontine area dorsolateral to the superior olivary nucleus. This region contains the A5 noradrenergic cell group; (3) Near the ventral surface, below the facial nucleus. This area overlaps with the 'retrotrapezoid nucleus.' (4) Respiration-related areas of the medulla, including the dorsal and ventral respiratory groups, and the B?tzinger complex. (5) The dorsal motor nucleus of the vagus. These results suggest that the COM is involved in reflex arcs, which have both respiratory functions and autonomic functions. The pathway to the dorsolateral pons, which has been identified in our recent electrophysiological study is likely to play a role in mediating respiratory responses from pulmonary rapidly adapting receptors. Other pathways may represent additional projections from second-order neurons receiving input from this group of lung receptors, or projections from as yet unidentified neurons that relay information from different afferents terminating in the COM.     

The corticofugal projections from the sensorimotor cortex to the spinal cord. A neuroanatomical and autoradiographical study in the cat with some methodological comments

An autoradiographical analysis of the corticospinal projections from the sensorimotor cortex of the cat using several 3H-labelled protein precursors showed a distribution of radioactivity on the contralateral side of the spinal cord in fairly good agreement with the findings using silver impregnation techniques. The findings on the ipsilateral side were sparse and the radioactivity was located to the transitional area of lamina VII and VIII almost as intensely as over the contralateral lamina VII. This pattern was more in line with that of the monkey and indicates a more common corticospinal terminal pattern in higher vertebrates. The corticospinal tracts were difficult to demonstrate even in horizontal sections apart from the crossed lateral tract. This was interpreted as a sign of insufficiency of the labelling considering the number of strongly labelled cortical cells. The lumbosacrally projecting neurons were rather difficult to demonstrate and most of them were situated in the more superficial areas around the cruciform sulcus. The investigation was mainly based on labelling the cortex with 3H-fucose which provided the most intense, differential and reproducable labellings. This was considered due to a lesser tendency to encounter selective neuronal uptake phenomenas. The transported amounts of radioactivity were relatively poor and unsuitable for studies of the finer somatotopics or EM-autoradiography of the synaptology.     

Relays from the spinal cord and solitary nucleus through the parabrachial nucleus to the forebrain in the cat.

Projections from the spinal cord and solitary nucleus to the lateral parabrachial nucleus (PBN1) in the cat were directly compared using double anterograde tracing methods. The two inputs were found to overlap within a well-circumscribed zone in the rostral 2/3 of PBN1. This zone was flanked ventrally by a zone receiving only solitary nucleus input and dorsally by a zone receiving only spinal input. Other authors have shown that neurons within these three recipient zones (overlap area, solitary nucleus and spinal cord) project to different forebrain targets (hypothalamus, amygdala and thalamus, respectively). This orderly input-output organization is likely to provide part of the framework for PBN's complex involvement in the coordination of respiratory and cardiovascular activities and their association with pain, visceral sensation and emotion.     

Efferent connections of the red nucleus in the brainstem and spinal cord of the Rhesus monkey

Three types of neuron with differences in Nissl pattern were found in the red nucleus of the rhesus monkey. Neurons with coarse Nissl bodies occurred only in the caudal third of the red nucleus except for a small number which extended rostrally a short distance along the dorsolateral margin. Neurons with fine Nissl bodies occupied the rostral two-thirds of the nucleus. Neurons with slight cytoplasmic basophilia (achromatic) were smaller than the other types and distributed throughout the red nucleus. Perikaryal areas of the coarse and fine neurons, measured with a computer, had widely overlapping distributions. Electrolytic lesions were made unilaterally in the red nucleus of nine monkeys. Ascending axonal degeneration was studied in sections stained by the Fink-Heimer method. Two separate descending tracts were followed. The rubrobulbo-spinal tract took origin from coarse neurons, crossed completely in the ventral tegmental decussation, and terminated as follows: in parts of the superior sensory trigeminal, motor facial and lateral reticular nuclei; in the gracile and cuneate nuclei; in the nucleus medullae oblongata, subnucleus dorsalis; in Rexed's laminae V, VI, VII at all levels of the spinal cord. In contrast, the rubroreticulo-olivary tract took origin from fine neurons, remained uncrossed, and terminated in some reticular nuclei (pedunculopontine, pontis oralis and caudalis, gigantocellularis) and in parts of the inferior olivary complex. Degeneration was profuse in the dorsal lamina of the main olive, abundant in the ventral lamina, particularly in its lateral side, sparse and inconstant in the medial accessory olive, and invariably absent in the dorsal accessory olive. Thus, nuclei which receive descending projections from the red nucleus may be grouped into those with connections to lower motor neurons, cerebellum, or thalamus.     

An HRP and autoradiographic study of the projection from the cerebellar cortex to the nucleus interpositus anterior and nucleus interpositus posterior of the cat.

The recently developed anatomical techniques of retrograde transport of the enzyme horseradish peroxidase (HRP), anterograde transport of tritiated amino acid, and intracellular injections of HRP were used to study the organization of the corticonuclear projection to the nucleus interpositus anterior (NIA) and the nucleus interpositus posterior (NIP) of the cat. Injections of HRP into the NIA and the NIP revealed that the major areas of the cortex which provided afferents to these two nuclei were the intermediate cortex of the anterior lobe (IAL) and the paramedian lobule (PML). There were, however, significant differences in the distribution of Purkinje (Pk) cells which projected to each nucleus. The NIA received afferents from all areas of the IAL while the NIP projection area was restricted to a band located at the medi-almost aspect of the lobe. All areas of the PML, in particular the intermediate folia, projected to the NIP, while the Pk cells which sent axons to the NIA were restricted to the rostral and caudal folia of this lobule. The projection from each area was somatotopically organized. The axons of intracellularly stained Pk cells were followed to their termination in the NIA and NIP confirming the results obtained with the two extracellular techniques. An attempt was made to examine the organization of the corticonuclear projection at the single cell level in the PML. Pk cells located in the same sagittal plane appeared to terminate in the same area of the same nucleus while Pk cells located not more than 500 micrometers medial or lateral to each other terminated in different nuclei. Basically, the organization of the corticonuclear projection from the IAL is longitudinally organized while the PML has a much more complex arrangement in which the Pk cells projecting to the NIA and NIP are interspersed.     

Cortical projections to the nucleus of the tractus solitarius: An HRP study in the cat

Recent evidence suggests that autonomic reflexes involving sensations such as olfaction and gustation may be cortically mediated via centripetal pathways to brainstem autonomic centers. A study was therefore undertaken to elucidate one of these pathways in greater detail. Lectin conjugated horseradish peroxidase was injected into the nucleus tractus solitarius. Following standard light microscopic histochemical procedures to reveal horseradish peroxidase activity, the distribution of retrogradely labeled neurons in the cortex was recorded. Retrogradely labeled somata were seen bilaterally in layer five of the orbital gyrus, anterior insular cortex and infralimbic cortex. In other cats, the same tracer was injected into the orbital gyrus or anterior insular cortex. Bilateral anterograde labeling was seen in various subnuclei throughout the rostrocaudal extent of the nucleus tractus solitarius, but was heaviest in rostral regions of the nucleus. Labeling was also seen bilaterally in the spinal trigeminal nucleus. The projection to the nucleus tractus solitarius could allow for cortical modulation of gustatory and visceral information which is conveyed to the brainstem via the facial, glossopharyngeal and vagus nerves.     

The location of cerebellar-projecting neurons within the lumbosacral spinal cord in the cat. An anatomical study with HRP and retrograde chromatolysis

The locations of lumbosacral spinocerebellar neurons were examined by two anatomical methods in kittens. In one group of animals chromatolytic changes were provoked by cerebellar lesions. In another group horseradish peroxidase (HRP) was injected into the cerebellum. Projection laterality was investigated by making unilateral spinal lesions prior to the cerebellar HRP injections. Diaminobenzidine (DAB) or tetramethylbenzidine (TMB) was used as substrate for HRP. The morphological characteristics of HRP-labeled neurons in the TMB-processed material were examined. Neurons marked by the two methods were located within the same regions. A greater number of cells were marked with the HRP method, however, than with the retrograde chromatolysis method. Spinocerebellar neurons were found in laminae IV–IX with large differences with regard to specific locations depending on segmental level. Numerous marked neurons were found in the following areas: laminae IV–VI in L3–L7, the column of Clarke in L3–L4, the medial part of lamina VII in L6–L7, the lateral part of lamina VII in L3–L4, the dorsolateral nucleus of lamina IX in L3–L6, the ventrolateral nucleus of lamina IX in L4–L5, and the ventromedial nucleus of lamina IX in S3 (and Ca1). Dorsally located neurons were in general more likely to project ipsilaterally than ventrally located neurons. Marked structural differences were frequently observed between spinocerebellar neurons in different locations. These results provide additional information on the anatomical complexity of the spinocerebellar pathways from the lumbosacral region in the cat. Together with results from some other recent anatomical studies on spinocerebellar tracts, they also form a basis for further anatomical and physiological investigations which could contribute to a better understanding of the organization of the spinocerebellar tracts.     

Projections from the spinal trigeminal nucleus to the cochlear nucleus in the rat

The integration of information across sensory modalities enables sound to be processed in the context of position, movement, and object identity. Inputs to the granule cell domain (GCD) of the cochlear nucleus have been shown to arise from somatosensory brain stem structures, but the nature of the projection from the spinal trigeminal nucleus is unknown. In the present study, we labeled spinal trigeminal neurons projecting to the cochlear nucleus using the retrograde tracer, Fast Blue, and mapped their distribution. In a second set of experiments, we injected the anterograde tracer biotinylated dextran amine into the spinal trigeminal nucleus and studied the resulting anterograde projections with light and electron microscopy. Spinal trigeminal neurons were distributed primarily in pars caudalis and interpolaris and provided inputs to the cochlear nucleus. Their axons gave rise to small (1-3 microm in diameter) en passant swellings and terminal boutons in the GCD and deep layers of the dorsal cochlear nucleus. Less frequently, larger (3-15 microm in diameter) lobulated endings known as mossy fibers were distributed within the GCD. Ventrally placed injections had an additional projection into the anteroventral cochlear nucleus, whereas dorsally placed injections had an additional projection into the posteroventral cochlear nucleus. All endings were filled with round synaptic vesicles and formed asymmetric specializations with postsynaptic targets, implying that they are excitatory in nature. The postsynaptic targets of these terminals included dendrites of granule cells. These projections provide a structural substrate for somatosensory information to influence auditory processing at the earliest level of the central auditory pathways.     

Projections between the hypothalamus and the dorsal vagal complex in the cat: An HRP and autoradiographic study

The hypothalamus is known to be intimately involved in the control of autonomic function. This study provides detailed information about pathways between the hypothalamus and the dorsal vagal complex in cat. Injection of horseradish peroxidase into the dorsomedial medulla produced retrograde neuronal labeling in the paraventricular nucleus of the hypothalamus. Injection of 3H-leucine into the paraventricular nucleus produced dense anterograde labeling in the dorsal motor nucleus of the vagus, and lighter labeling in the nucleus of the tractus solitarius, particularly in its medial subnucleus. The subnucleus gelatinous was virtually free of label, except in its medial and lateral portions. Anterograde labeling was distributed bilaterally, with an ipsilateral predominance. Injection of horseradish peroxidase into the area of the paraventricular nucleus produced retrograde neuronal labeling bilaterally in the nucleus of the tractus solitarius and the reticular formation ventrolateral to the dorsal vagal complex. anterograde terminal labeling overlapped the distribution of retrogradely labeled neurons. These findings are compared to those in rat, and discussed in relation to their functional implications.     

Projections to the spinal cord from medullary somatosensory relay nuclei.

Descending projections to the spinal card from the dorsal column nuclei were studied in the cat, rat and monkey with the retrograde horseradish peroxidase (HRP) technique, and in the cat with the autoradiographic anterograde axonal transport technique. Retrogradely labeled neurons were seen in the dorsal column nuclei after HRP injections at all levels of the spinal cord and additionally in the magnocellular division of the spinal caudalis nucleus of the trigeminal nerve after injections into cervical spinal segments in all three species. HRP-positive neurons were predominantly located along the middle of the rostro-caudal axis of the dorsal column nuclei and amongst the fusiform, triangular and polygonal cells that surround, especially ventrally, the cell nest zone containing thalamic relay neurons. The labeled neurons are densely concentrated in those portions of the dorsal column nuclei where most corticofugal and non-primary afferent projections terminate and where the terminal distribution of primary afferent fibers is overlapping and diffuse. Previous studies have shown that most neurons in this middle and ventral region do not project to the thalamus or cerebellum. The majority of the cells in the dorsal column nuclei with descending axons or axon collaterals project by way of the ipsilateral dorsal columns, but some fibers project into the dorsolateral funiculus; the descending trigeminal fibers course in the dorsolateral funiculus. The terminal fields for these fibers in the cervical spinal cord include the lateral cervical nucleus, laminae IV and V, and possibly lamina I. These results indicate that the dorsal column nuclei may contribute to a feedback mechanism regulating the flow of sensory information ascending along other somatosensory spinal pathways.