Spinal neurons reaching the lateral reticular nucleus as studied in the rat by retrograde transport of horseradish peroxidase

An anatomical technique based on the retrograde transport of horseradish peroxidase (HRP) was used to investigate the projections of spinal cord neurons to the lateral reticular nucleus (LRN). Labeled cells were found at all spinal levels and in particular large numbers in cervical and lumbar segments. Various spinal areas gave rise to cells of origin of this tract, which appears to be more prominent than any other tract previously studied with a similar approach. Labeling common to all spinal segments was observed in (1) ventromedial parts of both intermediate zone and ventral horn (laminae VII, VIII and X), mainly contralaterally; (2) the reticular extension of the neck of the dorsal horn, partly bilateral; and (3) superficial layers of the dorsal horn and nucleus of the dorsolateral funiculus (NDLF), mainly contralateral and projecting essentially to the lateral zone of the LRN. Additional labeling was observed at cervical and lumbar levels, each with specific qualities: (1) the cervical enlargement, which displayed labeling in the central part of the ipsilateral intermediate zone (lamina VII); (2) the rostral lumbar levels, which had projections from the contralateral median portion of the neck of the dorsal horn. These latter projections appear to be specific to pathways reaching the lateral reticular nucleus and the inferior olive. Control injections in neighboring structures demonstrated the similarity between the afferents to the lateral reticular nucleus and the inferior olive. Control injections in neighboring structures demonstrated the similarity between the afferents to the lateral reticular nucleus and the inferior olive (except lamina I and NDLF projections) and the differences between these afferents and those projecting to the dorsal reticular formation, i.e., the nucleus reticularis ventralis.     

The origin of brainstem-spinal pathways in the north american opossum (didelphis virginiana). Studies using the horseradish peroxidase method

Brainstem neurons which project to lumbar, thoracic and cervical spinal levels have been identified in the North American opossum by the horseradish peroxidase (HRP) technique. Neurons which relay to all of the levels studied are located within the medullary and pontine reticular formation as well as within the nucleus cuneatus, the nucleus of the tractus solitarius, the lateral reticular nucleus, the medullary and caudal pontine raphe nuclei, the lateral, medial and inferior vestibular nuclei, the nucleus “F,” the nucleus coeruleus, and the nucleus coeruleus, para α, the red nucleus, and the interstitial nucleus of Cajal. The lateral vestibulospinal and rubrospinal systems are topographically organized, although neurons projecting to different cord levels show considerable intermingling. Our material also provides evidence that raphe-spinal and reticulospinal connections are organized to some degree. Neurons which backfill after cervical and thoracic placements, but not after lumbar injections, are distributed within the caudal spinal trigeminal nucleus, the nucleus intercalatus, the dorsal vagal nucleus, the cuneiform area of Castaldi, the fields of Forel, and the nucleus of Darkschewitsch. Reactive neurons are present within the lateral, dorsal and posterior hypothalamic areas as well as within the periventricular and paraventricular nuclei after thoracic placements and within the superior colliculus after injections within the cervical cord. Additionally, neurons are reactive in the nucleus ambiguus, the interpolar division of the spinal trigeminal nucleus and the rostral division of the oculomotor nucleus (Oswaldo-Cruz and Rocha-Miranda, '68) after HRP placements into the third and fourth cervical segments.     

The anatomical organization of the cerebello-olivary projection in the cat.

The cerebello-olivary pathway in the cat has been examined using orthograde and retrograde neuroanatomical tracing techniques. The orthograde transport of 3H-leucine from injection sites in the deep cerebellar nuclei labeled dentate and interpositus projections to the rostral two-thirds of the contralateral inferior olivary complex. These projections are topographically organized, with the dentate nucleus projecting to the principal olivary nucleus and the posterior and anterior interpositus nuclei projecting to the medial and dorsal accessory olives respectively. Fibers from the ventral half of the dentate nucleus terminate in the lateral bend and ventral lamina of the principal olive, whereas the medial and lateral parts of the dorsal half of the nucleus project to the medial and lateral regions of the dorsal lamina respectively. It is apparent that the more caudal parts of the interpositus nuclei project to areas of the medial and dorsal accessory olives near the caudal end of the principal olivary nucleus, whereas neurons in the more rostral parts of the interpositus nuclei project to the more rostral areas of the accessory olivary nuclei. A connection between the fastigial ncleus and the inferior olive could not be demonstrated. The retrograde transport of horseradish peroxidase (HRP) from injections sites in the inferior olive labeled cells throughout the contralateral dentate and interpositus nuclei. The labeled cells were especially numerous in the ventral parts of the dentate and posterior interpositus nlclei. These HRP-positive neurons were consistently small (10--15 mu) ovoid or spindle-shaped cells, with relatively large nuclei and light-staining Nissl substance. This evidence strongly suggests that the cerebello-olivary pathway originates from a population of small neurons in the dentate and interpositus nuclei and projects to specific, topographically defined areas in the contralateral inferior olive.     

Ascending and descending projections from nucleus reticularis magnocellularis and nucleus reticularis gigantocellularis: an autoradiographic and horseradish peroxidase study in the rat

The projections of the rostal medulla were studied using retrograde and orthograde transport techniques in the rat. The present horseradish peroxidase (HRP) studies indicate that the ventral portion of nucleus reticularis (NGC) and nucleus reticularis magnocellularis (NMC) project to both rostral and caudal levels of the spinal cord, while dorsal NGC projects only to the rostral cord. A differential density distribution of labeled cells was observed, with the greatest density of NGC-spinal neurons located rostral to the level of the inferior olive; and the greatest density of NMC-spinal neurons located caudally.This differential density distribution, when coupled with microiontophoretic application of [³H]amino acids allowed relatively independent labeling of the adjacent NGC- and NMC-spinal systems. On the basis of the HRP and autoradiographic studies 3 separate regions were delineated: dorsal NGC, ventral NGC and NMC. Descending projections from NGC were observed to the lateral vestibular nucleus, facial nucleus, hypoglossal nucleus and cuneatus. At cervical levels NGC fibers projected through the ventral and ventrolateral columns. Terminal fields were observed in laminae VII, VIII and to a lesser extent in IX. Labeled NGC fibers became difficult to follow by thoracic levels, which is consistent with the present HRP results. A continuum of descending NGC projections was observed with dorsally located NGC neurons projecting bilaterally through the ventral columns, and ventrally located NGC cells projecting through the ipsilateral ventrolateral columns. Ascending projections from NGC to the motor nucleus of V, trochlear nucleus, oculomotor nucleus, Edinger-Westphal nucleus, the ventral aspect of the periaqueductal gray, the deep and intermediate layers of the superior colliculus, nucleus parafasicularis and centromedianus, the Fields of Forel and the dorsal and lateral hypothalamic nuclei were observed. Descending projections from NMC to the dorsal nucleus of the vagus, hypoglossal nucleus, nucleus commissuralis and intercalatus were observed. At cervical levels, fibers project through the ipsilateral lateral columns, particularly its dorsal aspect. Terminal fields are located ipsilaterally in lamonae IV, V and VI, and bilaterally in VII, VIII and X. NMC projections continue through cadual levels of the spinal cord including a projection to the ipsilateral intermediolateral columns. Ascending NMC projections are limited to the ventral pontine reticular formation.The differing projections and cytoarchitecture of the rostral medulla of the rat observed in the present study are compared to that of the cat and opossum, with implications for the subdivision of this region discussed. The possible involvement of NMC and NGC projections in the modulation of pain is reviewed.     

Comparative topography of projections from the mesodiencephalic junction to the inferior olive, vestibular nuclei, and upper cervical cord in the cat

Distributions of neurons located in the central rostral mesencephalon and caudal diencephalon that project to the upper cervical spinal cord, vestibular nuclei, or inferior olive were studied in the cat by using retrograde axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Afferent sources to all of these targets were observed in the interstitial nucleus of Cajal (INC), the region surrounding the fasciculus retroflexus (PF), and the nucleus of the fields of Forel (NFF). Three-dimensional reconstruction revealed differences in densities of cells projecting from these common areas. Spinal projecting cells were present in slightly greater numbers in the caudal two-thirds of the INC, whereas those projecting to the vestibular complex were more numerous in the rostral two-thirds of this nucleus. A relatively smaller number of olivary projecting cells were dispersed throughout the INC. Olivary afferent sources outnumber those with spinally directed or vestibularly directed axons in the PF region. In the fields of Forel, cells projecting to the vestibular nuclei or inferior olive were concentrated medially, whereas cells projecting to the spinal cord appeared both medially and laterally. Each type of afferent source was also seen in the nucleus of the posterior commissure and the posterior ventral lateral hypothalamic area. Unique sources of afferents to the inferior olive were observed in the parvicellular red nucleus (ipsilateral to the injections) and the anterior and posterior pretectal nuclei. A large number of labeled neurons was seen in the nucleus of Darkschewitsch after injections of tracer into the inferior olive, but this projection did not appear to be unique, as small numbers of labeled cells were also seen after injections into the cervical spinal cord. The Edinger-Westphal nucleus and the adjacent somatic oculomotor nucleus contained cells which projected separately to the spinal cord or the vestibular complex, and the superior colliculus contained cells which projected separately to the contralateral spinal cord or the contralateral inferior olive. In this study, it was also noted that neurons in the medial terminal nucleus of the accessory optic tract projected to the ipsilateral inferior olive or to the contralateral vestibular complex. These differences in locations and densities of cells projecting to the cervical spinal cord, vestibular complex, and inferior olive may underlie functional specializations in these areas in relation to vertical eye and head movement control and to neural systems controlling postural adjustments accompanying limb movements.     

Contralateral projections of trigeminal mandibular primary afferents in the guinea pig as seen by transganglionic transport of horseradish peroxidase

Transganglionic transport of horseradish peroxidase (HRP) was used to investigate contralateral projections of trigeminal mandibular fibers in the guinea pig. After application of HRP to the buccal, lingual, auriculotemporal, mylohyoid, mental and inferior alveolar nerves, crossing fibers and contralateral endings were found in the caudal region of the nucleus of the solitary tract (most of these belonging to the buccal and lingual nerves), the dorsomedial region of the subnucleus caudalis of the trigeminal sensory nuclear complex (TSNC), and the dorsal horns of the first 5 cervical spinal cord segments (C1-C5). The greatest numbers of crossing fibers in the medullary and cervical dorsal horn segments belonged to the mental and mylohyoid nerves, though these nerves did not project contralaterally to C4-C5. Contralateral buccal and lingual endings were scattered sparsely from the subnucleus caudalis to C5, and only very few contralateral auriculotemporal terminals were observed. Though laminae I-V of the dorsomedial region of the medullary and cervical dorsal horns all exhibited contralateral endings of the mental and mylohyoid nerves, most such endings were found in laminae IIi-III, followed by lamina IV, which suggests their involvement in the reception of mechanical stimuli and in the sensory motor reflexes of the orofacial region. The contralateral buccal and lingual terminals were distributed somatotopically in the first 5 cervical cord segments, with the lingual endings rostral to the buccal terminals within each segment. In C4 and C5 lingual endings appeared exclusively in laminae I and IIo, suggesting that like the ipsilateral lingual projections at this level, which also terminate in these laminae, they may be involved in pain and temperature sensation.     

Respiratory neurons in the medulla of the rabbit: distribution, discharge patterns and spinal projections

To determine distribution, discharge patterns and the spinal projections of medullary respiratory neurons (RNs), a systematic mapping of 806 RNs was made in the medulla of anesthetized rabbits. In disagreement with previous reports that there are no discrete medullary respiratory neuronal groups in rabbits, two neuronal groups were identified: (1) dorsal respiratory group (DRG), associated with the nucleus tractus solitarius; and (2) ventral respiratory group (VRG), associated with the nucleus ambiguus compact formation. The density of RNs in the DRG was much lower than that in the VRG. In the VRG, 3 subdivisions of RN populations were found: predominantly expiratory neurons in the caudal and the rostral parts, and mainly inspiratory neurons in the intermediate region. Nine distinct types of RNs were classified on the basis of firing patterns. Nearly all types were found in both the DRG and each VRG subdivision. Antidromic mapping of 64 VRG neurons revealed that 67% projected to the spinal cord. Expiratory bulbospinal neurons in the rostral subdivision of the VRG projected only to the cervical cord (mainly ipsilaterally). Most neurons of the intermediate and caudal subdivisions of the VRG (74%) appeared to project either contralaterally or ipsilaterally below T. The axonal conduction velocity was 40-50 m/s by two-point determinations. We conclude that respiratory neuronal groups in the medulla of the rabbit are generally similar to those of the cat. Nearly equal proportions of bulbospinal RNs projected to the ipsilateral vs contralateral spinal cord.     

Gracile,cuneate, and spinal trigeminal projections to inferior olive in rat and monkey

In the cat, somatosensory nuclei send substantial projections to the inferior olive, where they terminate in a somatotopic fashion. Although the organization of the cat inferior olive has been used to interpret data from other species, published data suggest this organization may not occur universally. The present study investigated whether the inferior olive in albino rats and cynomolgus monkeys receives the same brainstem somatosensory inputs, whether these inputs are organized somatotopically and, if so, how the organization compares with that in the cat. Projections from the gracile, cuneate and spinal trigeminal nuclei were labeled with wheat germ agglutinin conjugated to horseradish peroxidase or with biotinylated dextran. The results were compared with data from cats (Berkley and Hand [1978] J. Comp. Neurol. 180:253-264). In the rat and monkey, the gracile, cuneate and spinal trigeminal nuclei all project to the contralateral inferior olive, where each nucleus has a distinct preferred terminal field. As in the cat, projections to the medial accessory olive and caudal dorsal accessory olive did not terminate in a precisely organized fashion. Projections to the rostral dorsal accessory olive, however, formed a clear somatotopic map. These somatotopic maps differed from those in the cat in that input from the trigeminal nucleus was confined rostrally, so that the caudal end only received input from the gracile and cuneate nuclei. These data indicate that similar organizational principles characterize the somatosensory projections to the inferior olives of the three species. Nevertheless, distinct species differences occur with regard to the details of this organization. © 1996 Wiley-Liss, Inc.     

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.     

Efferent projections from temperature sensitive recording loci within the marginal zone of the nucleus caudalis of the spinal trigeminal complex in the cat

The efferent projections from nucleus caudalis of the spinal trigeminal complex in cats were studied with retrograde and anterograde axonal transport techniques combined with localization of recording sites in the thalamus and marginal zone of nucleus caudalis to innocuous skin cooling. Results showed brainstem projections from nucleus caudalis to rostral levels of the spinal trigeminal complex, to the ventral division of the principal trigeminal nucleus, the parabrachial nucleus, cranial motor nuclei 7 and 12, solitary complex, contralateral dorsal inferior olivary nucleus, portions of the lateral reticular formation, upper cervical spinal dorsal horn and, lateral cervical nucleus. Projections to the thalamus included: a dorsomedial region of VPM (bilaterally) and to the main part of VPM and PO contralaterally. Neuronal activity was recorded in the dorsomedial region of VPM to cooling the ipsilateral tongue. HRP injections in this thalamic region retrogradely labeled marginal neurons in nucleus caudalis. These results show that marginal neurons of nucleus caudalis provide a trigeminal equivalent of spinothalamic projections to the ventroposterior nucleus in cats.     

The organization of neurons in the nucleus of the lateral lemniscus projecting to the superior and inferior colliculi in the rat

The topographic organization of neurons in the dorsal nucleus of the lateral lemniscus (DNLL) which project to the superior and inferior colliculi was studied using the retrograde horseradish peroxidase (HRP) and the fluorescent double labeling methods. Neurons projecting to the superior colliculus (SC) are situated in the rostral portion of the DNLL, whereas those to the inferior colliculus (IC) are found in the caudal area of this nucleus. These two portions are completely separated from each other and no neurons projecting to both the SC and the IC are observed. In the dorsolateral part of the rostral portion of the DNLL, neurons projecting to the ipsilateral SC are found, whereas neurons projecting to the contralateral SC are located in the central to medial part of the nucleus, but no neurons sending collateral axons to both sides of the SC were observed. Neurons located in the central part of the caudal area of the DNLL project to the ipsilateral IC and neurons in the lateral and medial parts project contralaterally to the IC. Some of the neurons in the caudal part of the DNLL have divergent axonal branching projecting to both sides of the IC. In the ventral nucleus of the lateral lemniscus, labeled neurons were observed only when the HRP was injected into the ipsilateral IC.     

The nucleus of the solitary tract in the monkey: projections to the thalamus and brain stem nuclei

The projections of the nucleus of the solitary tract (NST) were studied by autoradiographic anterograde fiber-tracing and horseradish peroxidase (HRP) retrograde cell-labeling. Tritiated proline and leucine were deposited in electrophysiologically identified regions of NST. Injections of NST at levels caudal to where the vagus enters the nucleus, from which responses were evoked by stimulation of cranial nerves IX and X, revealed topographically organized bilateral projections to, most prominently, the ventrolateral medullary reticular formation which contains neurons of the ambiguus complex, and to the lateral and medial parabrachial nuclei, including a small portion of the medially adjacent central gray substance. Labeled fibers in the ventrolateral reticular formation were present from the nucleus retroambigualis rostralward to the retrofacial nucleus, with the densest concentration located over the nucleus ambiguus proper. The parabrachial projection was confirmed using HRP and shown to originate from cells in the medial subdivision of NST. Due to the problem of fibers en passant, it was not possible to interpret conclusively the cell-labeling seen around the solitary tract after HRP injections made in the region of the nucleus ambiguus. Labeled fibers were also traced from caudal NST to the dorsal motor nucleus of the vagus, but their origin could not be determined with certainty. Other labeled axons, traced to circumscribed parts of the inferior olivary complex and via the contralateral medial lemniscus to VPL of the thalamus, were shown in HRP experiments to originate from the dorsal column nuclei rather than NST. No labeled fibers were traced into the spinal cord, nor were any cells labeled in NST after large HRP deposits in upper cervical segments. Isotope deposits at levels of NST rostral to the entrance of the vagus, from which responses were evoked by rapid stimulation of the tongue, revealed an ipsilateral projection which ascends as a component of the central tegmental tract to the parvicellular part of the ventral posteromedial thalamic nucleus (VPMpc). After small HRP deposits in VPMpc, labeled cells in NST were restricted to the rostral part of the lateral subdivision. No labeled axons were traced from rostral NST to the ambiguus complex or parabrachial area. Injections of 3H-amino acids at intermediate levels of NST resulted in fiber-labeling in VPMpc, the parabrachial area, and the ambiguus complex.     

Neurotransmitter-specific uptake and retrograde transport of [3H]glycine from the inferior colliculus by ipsilateral projections of the superior olivary complex and nuclei of the lateral lemniscus.

Neurotransmitter-specific uptake and retrograde axonal transport of [3H]glycine were used to identify glycinergic projections to the inferior colliculus in chinchillas and guinea pigs. Six h after injection of [3H]glycine in the inferior colliculus, autoradiographically labeled cells were found ipsilaterally in the ventral nucleus of the lateral lemniscus, the lateral superior olive and the dorsomedial periolivary nucleus. These 3 regions accounted for 95% of the labeled projection neurons, with the remainder scattered elsewhere in the ipsilateral superior olivary complex. No labeled cells were found contralaterally even after survival times as long as 24 h. Retrograde transport of HRP from the inferior colliculus in these same cases confirmed the presence of additional projections that did not accumulate [3H]glycine. These included ipsilateral projections from the medial superior olive and cochlear nucleus and contralateral projections from the inferior colliculus, dorsal nucleus of the lateral lemniscus, lateral superior olive, periolivary nuclei and cochlear nucleus. The results implicate uncrossed projections from the ventral nucleus of the lateral lemniscus, lateral superior olive, and dorsomedial periolivary nucleus as the principal sources of inhibitory glycinergic inputs to the inferior colliculus.     

Projections from the nucleus tractus solitarii to the rostral ventrolateral medulla

Projections from the nucleus tractus solitarii (NTS) to autonomic control regions of the ventrolateral medulla, particularly the nucleus reticularis rostroventrolateralis (RVL), which serves as a tonic vasomotor center, were analyzed in rat by anterograde, retrograde, and combined axonal transport techniques. Autonomic portions of the NTS, including its commissural, dorsal, intermediate, interstitial, ventral, and ventrolateral subnuclei directly project to RVL as well as to other regions of the ventrolateral medulla. The projections are organized topographically. Rostrally, a small cluster of neurons in the intermediate third of NTS, the subnucleus centralis, and neurons in proximity to the solitary tract selectively innervate neurons in the retrofacial nucleus and nucleus ambiguus. Neurons generally located in more caudal and lateral sites in the NTS innervate the caudal ventrolateral medulla (CVL). The RVL, CVL, and nucleus retroambiguus are interconnected. A combined retrograde and anterograde transport technique was developed so as to prove that projections from the NTS to the ventrolateral medulla specifically innervate the region of RVL containing neurons projecting to the thoracic spinal cord or the region of the nucleus containing vagal preganglionic neurons. When the retrograde tracer, fast blue, was injected into the thoracic spinal cord, and wheat germ agglutinin-conjugate horseradish peroxidase (HRP) was injected into the NTS, anterogradely labeled terminals from the NTS surrounded the retrogradely labeled neurons in the RVL and in the nucleus retroambiguus in the caudal medulla. Among the bulbospinal neurons in the RVL innervated by the NTS were adrenaline-synthesizing neurons of the C1 group. When fast blue was applied to the cervical vagus, and HRP was injected into the NTS, anterogradely labeled terminals from the NTS surrounded retrogradely labeled neurons in the rostral dorsal motor nucleus of the vagus, the region of the nucleus ambiguus, the retrofacial nucleus, and the dorsal portion of the RVL, a region previously shown to contain cardiac vagal preganglionic neurons. This combined anterograde and retrograde transport technique provides a useful method for tracing disynaptic connections in the brain. These data suggest that the RVL is part of a complex of visceral output regions in the ventrolateral medulla, all of which receive afferent projections from autonomic portions of the NTS. Bulbospinal neurons in the RVL, in particular the C1 adrenaline neurons, may provide a portion of the anatomic substrate of the baroreceptor and other visceral reflexes.     

HRP study of the organization of auditory afferents ascending to central nucleus of inferior colliculus in cat

The ascending auditory projections to central nucleus of inferior colliculus its ventrolateral and dorsomedial subdivisions (IC_VI, and IC_DM) have been studied in cat using both pressure and electrophoretic injections of horseradish peroxidase (HRP). The results indicate that the predominant ascending projections to inferior colliculus orginate in (1) contralateral cochlear nucleus, (2) contralateral and ipsilateral lateral superior olive, (3) ipsilateral medial superior olive, (4) ipsilateral ventral nucleus of the lateral lemniscus, (5) ipsilateral and contralateral dorsal nucleus of the lateral lemniscus, and (6) contralateral inferior colliculus. In addition, ipsilateral cochlear nucleus, ipsilateral and contralateral intermediate nucleus of the lateral lemniscus, ipsilateral, and to a lesser extent contralateral, periolivary nuclei project to inferior colliculus. Of these nuclei, the lateral superior olive projects exclusively to IC_VL and ipsilateral cochlear nucleus and contralateral inferior colliculus project mostly, if not exclusively, to IC_DM. Many of these projections demonstrate a cochleotopic organization and frequently a nucleotopic organization as well. A cochleotopic organization of the projections is apparent for cochlear nucleus and superior olivary complex. A nucleotopic organization suggests that the heaviest terminations of contralateral inferior colliculus are medial and dorsal in inferior colliculus, of medial superior olive are dorsal and lateral, of superior olivary complex are rostral, of cochlear nucleus are caudal, and of ventral nucleus of the lateral leminiscus are caudal.     

Zonal organization of olivocerebellar projections to the uvula in rabbits

Olivocerebellar projections to the uvula were studied by means of retrograde axonal transport of horseradish peroxidase (HRP) in pigmented rabbits. The distribution pattern of labeled cells in the inferior olive was compared among cases following large- and microinjections of HRP into the uvula. Findings indicate topographically organized projections to longitudinally oriented zones. There are at least 6 zones in the rabbit's uvula. The caudal part of the nucleus beta projects contralaterally to a most medially located zone (caudal beta zone). The rostral part of the nucleus beta projects to a little more laterally located zone (rostral beta zone) at a distance of about 1 mm from the midline of the uvula. The caudolateral part of the MAO projects to a zone (caudolateral MAO zone) located laterally to the rostral beta zone. The dorsomedial cell column projects to a zone (dorsomedial cell column zone) located in the intermediate part of the uvula at about 2 mm from the midline. The rostrolateral part of the MAO projects to the most lateral zone (rostrolateral MAO zone) of the uvula. Finally, the ventral lamella of the PO projects to a zone (ventral lamella of PO zone) located between the rostrolateral MAO zone and the dorsomedial cell column zone.     

Olivary projections from the mesodiencephalic structures in the cat studied by means of axonal transport of horseradish peroxidase and tritiated amino acids

By means of horseradish peroxidase (HRP) and autoradiographic methods, olivary projections from mesodiencephalic structures were studied in the cat. Following HRP injections in various parts of the inferior olive, many cells were labeled ipsilaterally in the nucleus of Darkschewitsch, the nucleus accessorius medialis of Bechterew, the nucleus of the fields of Forel, and the subnucleus dorsomedialis and ventrolateralis of the parvocellular red nucleus. Some labeled cells also occurred ipsilaterally in the suprarubral reticular formation and a few labeled cells in the interstitial nucleus of Cajal. After injection of tritiated amino acids in different parts of the mesodiencephalic region mentioned above, labeled fibers were found in different parts of the inferior olive, presenting a high degree of the topographic correlation within the mesodiencephalo-olivary projection, which was exclusively ipsilateral. That is, the nucleus of Darkschewitsch was found to project to the rostral half of the medial accessory olive and the dorsomedial cell column. There was mediolateral topographic relation in this projection. The nucleus accessorius medialis of Bechterew was found to project to the ventral lamella and the lateral part of the dorsal lamella as well as to a small rostromedial part of the caudal half of the medial accessory olive. The subnucleus dorsomedialis and ventrolateralis of the parvocellular red nucleus projected to the rostral and caudal halves, respectively, of the medial part of the dorsal lamella. The subnucleus ventrolateralis of the parvocellular red nucleus also sent fibers to the lateral part of the ventrolateral outgrowth. The nucleus of the fields of Forel, suprarubral reticular formation, and interstitial nucleus of Cajal appeared to project to the caudal half of the medial accessory olive, the medial part of the ventrolateral outgrowth, the rostral part of the dorsal cap, and the caudal part of the dorsal accessory olive.     

Neurotransmitter-specific uptake and retrograde transport of [H]glycine from the inferior colliculus by ipsilateral projections of the superior olivary complex and nuclei of the lateral lemniscus

Neurotransmitter-specific uptake and retrograde axonal transport of [³H]glycine were used to identify glycinergic projections to the inferior colliculus in chinchillas and guinea pigs. Six h after injections of [³H]glycine in the inferior colliculus, autoradiographically labeled cells were found ipsilaterally in the ventral nucleus of the lateral lemniscus, the lateral superior olive and the dorsomedial periolivary nucleus. These 3 regions accounted for 95% of the labeled projection neurons, with the remainder scattered elsewhere in the ipsilateral superior olivary complex. No labeled cells were found contralaterally even after survival times as long as 24 h. Retrograde transport of HRP from the inferior colliculus in these same cases confirmed the presence of additional projections that did not accumulate [³H]glycine. These include ipsilateral projections from the medial superior olive and cochlear nucleus and contralateral projections from the inferior colliculus, dorsal nucleus of the lateral lemniscus, lateral superior olive, periolivary nuclei and cochlear nucleus. The results implicate uncrossed projections from the ventral nucleus of the lateral lemniscus, lateral superior olive, and dorsomedial periolivary nucleus as the principal sources of inhibitory glycinergic inputs to the inferior colliculus.     

Primary afferent projections from the upper respiratory tract in the muskrat.

The central projections of the ethmoidal, glossopharyngeal, and superior laryngeal nerves were determined in the muskrat by use of the transganglionic transport of a mixture of horseradish peroxidase (HRP) and wheat germ agglutinin (WGA)-HRP. The ethmoidal nerve projected to discrete areas in all subdivisions of the ipsilateral trigeminal sensory complex. Reaction product was focused in ventromedial portions of the principal nucleus, subnucleus oralis, and subnucleus interpolaris. The subnucleus oralis also contained sparse reaction product in its dorsomedial part. Projections were dense to ventrolateral parts of laminae I and II of the rostral medullary dorsal horn, with sparser projections to lamina V. Label in laminae I and V extended into the cervical dorsal horn. A few labeled fibers were followed to the contralateral dorsal horn. The interstitial neuropil of the ventral paratrigeminal nucleus was densely labeled. Extratrigeminal primary afferent projections in ethmoidal nerve cases involved the K?lliker-Fuse nucleus and ventrolateral part of the parabrachial nucleus, the reticular formation surrounding the rostral ambiguous complex, and the dorsal reticular formation of the closed medulla. Retrograde labeling in the brain was observed in only the mesencephalic trigeminal nucleus in these cases. The cervical trunk of the glossopharyngeal and superior laryngeal nerves also projected to the trigeminal sensory complex, but almost exclusively to its caudal parts. These nerves terminated in the dorsal and ventral paratrigeminal nuclei as well as lamina I of the medullary and cervical dorsal horns. Lamina V received sparse projections. The glossopharyngeal and superior laryngeal nerves projected to the ipsilateral solitary complex at all levels extending from the caudal facial nucleus to the cervical spinal cord. At the level of the obex, these nerves projected densely to ipsilateral areas ventral and ventromedial to the solitary tract. Additional ipsilateral projections were observed along the dorsolateral border of the solitary complex. Near the obex and caudally, the commissural area was labeled bilaterally. Labeled fibers from the solitary tract projected into the caudal reticular formation bilaterally, especially when the cervical trunk of the glossopharyngeal nerve received tracer. Labeled fibers descending further in the solitary tract gradually shifted toward the base of the cervical dorsal horn. The labeled fibers left the solitary tract and entered the spinal trigeminal tract at these levels. Retrogradely labeled cells were observed in the ambiguous complex, especially rostrally, and in the rostral dorsal vagal nucleus after application of HRP and WGA-HRP to either the glossopharyngeal or superior laryngeal nerves. In glossopharyngeal nerve cases, retrogradely labeled neurons also were seen in the inferior salivatory nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)