Descending projections of the posterior nucleus of the hypothalamus: Phaseolus vulgaris leucoagglutinin analysis in the rat

No previous report in any species has systematically examined the descending projections of the posterior nucleus of the hypothalamus (PH). The present report describes the descending projections of the PH in the rat by using the anterograde anatomical tracer, Phaseolus vulgaris leucoagglutinin. PH fibers mainly descend to the brainstem through two routes: dorsally, within the central tegmental tract; and ventromedially, within the mammillo-tegmental tract and its caudal extension, ventral reticulo-tegmental tracts. PH fibers were found to distribute densely to several nuclei of the brainstem. They are (from rostral to caudal) 1) lateral/ventrolateral regions of the diencephalo-mesopontine periaqueductal gray (PAG); 2) the peripeduncular nucleus; 3) discrete nuclei of pontomesencephalic central gray (dorsal raphe nucleus, laterodorsal tegmental nucleus, and Barrington's nucleus); 4) the longitudinal extent of the central core of the mesencephalic through medullary reticular formation (RF); 5) the ventromedial medulla (nucleus gigantocellularis pars alpha, nucleus raphe magnus, and nucleus raphe pallidus); 6) the ventrolateral medulla (nucleus reticularis parvocellularis and the rostral ventrolateral medullary region); and 7) the inferior olivary nucleus. PH fibers originating from the caudal PH distribute much more heavily than those from the rostral PH to the lower brainstem. The PH has been linked to the control of several important functions, including respiration, cardiovascular activity, locomotion, antinociception, and arousal/wakefulness. It is likely that descending PH projections, particularly those to the PAG, the pontomesencephalic RF, Barrington's nucleus, and parts of the ventromedial and ventrolateral medulla, serve a role in a PH modulation of complex behaviors involving an integration of respiratory, visceromotor, and somatomotor activity. © 1996 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.     

Brainstem reticular nuclei that project to the cerebellum in rats: a retrograde tracer study.

The nuclear origins of projections from the brainstem reticular formation to the cerebellum were examined using four retrograde tracer substances: horseradish peroxidase, wheat germ agglutinin-horseradish peroxidase conjugate, Fluoro-Gold, and rhodamine beads. Tracer injections were made into each of the three major longitudinal zones of the cerebellar cortex (vermis, paravermal hemisphere, and lateral hemisphere) as well as into the various deep cerebellar nuclei. Counts of retrogradely labeled cells were done on a large sample of select cases. The data generated by these cell counts indicate that the strongest reticulocerebellar projections arise from the three specialized pre-cerebellar reticular nuclei: the lateral reticular nucleus, the medullary paramedian reticular nucleus, and the reticulotegmental nucleus. The presumed noradrenergic locus coeruleus (A6 cell group) was also densely packed with retrogradely labeled neurons. However, strong reticulocerebellar projections also arose from other presumed catecholamine cell groups such as those in the ventrolateral medulla (the A1/C1 complex) and the caudal pons (A5). Substantial cerebellar projections originated from most of the various presumed serotonergic brainstem raphe cell groups (particularly raphe obscurus in the medulla), as well as from the presumed cholinergic Ch5 cell group (the pedunculopontine pars compactus nucleus). Labeled cells were also seen in several nonaminergic isodendritic reticular nuclei thought to be involved in visuomotor activity (e.g. paragigantocellularis dorsalis, raphe interpositus, and the pontine dorsomedial tegmental area), as well as in the lateral reticular zone of the medulla and lower pons (reticularis dorsalis and parvocellularis). Tracer injections into the deep nuclei produced relatively greater numbers of labeled neurons in large-celled medial reticular nuclei associated with skeletomotor activity, such as gigantocellularis, magnocellularis, and pontis caudalis. Reticular nuclei conspicuous in their lack of projections to the cerebellum included reticularis ventralis in the medulla, pontis oralis, and both subdivisions of the midbrain reticular formation (cuneiformis and subcuneiformis). As a whole, the various isodendritic reticular nuclei project most strongly to midline cerebellar structures (vermal cortex or fastigial nuclei), less strongly to the paravermal cortex or interposed nuclei, and least strongly to the lateral cortex or dentate nucleus. Within individual reticular nuclei, the morphology of labeled neurons is identical to that reported previously by this laboratory subsequent to spinal or cortical HRP injections, thus strengthening this laboratory's hypothesis that the various brainstem reticular nuclei can be distinguished on the basis of neuronal morphology.     

Raphe projections to the locus coeruleus in the rat

Afferent projections to the locus coeruleus from the various raphe nuclei, particularly of the midbrain (nuclei raphe dorsalis and medianus) and pons (nuclei raphe pontis and magnus), have been studied in the rat by retrograde transport methods using horseradish peroxidase (HRP). The locus coeruleus, in both its dorsomedial and ventrolateral divisions, and in its various anterior-posterior components, were injected with 0.05 μl of horseradish peroxidase following which various structures of the brainstem, particularly the raphe nuclei, were examined for HRP reactive cells. It was found that injections in most components of the locus coeruleus were associated with HRP positive cells in varying degrees of density in the nuclei raphe dorsalis, medianus, pontis, and magnus, with considerably sparser labelling in the anterior aspects of the medullary raphe nuclei pallidus and obscurus. Labelled cells were also seen in the nuclei of the solitary tract, contralateral locus coeruleus, lateral reticular areas of the pons and midbrain, nuclei pontis oralis and caudalis, vestibular nuclei, mesencephalic nucleus of the trigeminal nerve, fastigial nuclei of cerebellum and medial parabrachial nuclei. These data, showing widespread innervation of the locus coeruleus from all raphe nuclei, as well as many other brainstem areas, in the rat support the general view of heavy innervation of the locus coeruleus from both extra-raphe and raphe nulcei. These latter raphe projections, probably serotonergic in nature, provide anatomical support for the various experiments indicating considerable regulation of locus coeruleus activities, such as phasic events of REM sleep, among others, by most of the raphe nuclei. Thus, various activities of the locus coeruleus could be modulated or regulated by widespread projections from most raphe nuclei as well as several other regions of the brainstem.     

A PHA-L analysis of ascending projections of the dorsal raphe nucleus in the rat.

Ascending projections from the dorsal raphe nucleus (DR) were examined in the rat by using the anterograde anatomical tracer, Phaseolus vulgaris leucoagglutinin (PHA-L). The majority of labeled fibers from the DR ascended through the forebrain within the medial forebrain bundle. DR fibers were found to terminate heavily in several subcortical as well as cortical sites. The following subcortical nuclei receive dense projections from the DR: ventral regions of the midbrain central gray including the 'supraoculomotor central gray' region, the ventral tegmental area, the substantia nigra-pars compacta, midline and intralaminar nuclei of the thalamus including the posterior paraventricular, the parafascicular, reuniens, rhomboid, intermediodorsal/mediodorsal, and central medial thalamic nuclei, the central, lateral and basolateral nuclei of the amygdala, posteromedial regions of the striatum, the bed nucleus of the stria terminalis, the lateral septal nucleus, the lateral preoptic area, the substantia innominata, the magnocellular preoptic nucleus, the endopiriform nucleus, and the ventral pallidum. The following subcortical nuclei receive moderately dense projections from the DR: the median raphe nucleus, the midbrain reticular formation, the cuneiform/pedunculopontine tegmental area, the retrorubral nucleus, the supramammillary nucleus, the lateral hypothalamus, the paracentral and central lateral intralaminar nuclei of the thalamus, the globus pallidus, the medial preoptic area, the vertical and horizontal limbs of the diagonal band nuclei, the claustrum, the nucleus accumbens, and the olfactory tubercle. The piriform, insular and frontal cortices receive dense projections from the DR; the occipital, entorhinal, perirhinal, frontal orbital, anterior cingulate, and infralimbic cortices, as well as the hippocampal formation, receive moderately dense projections from the DR. Some notable differences were observed in projections from the caudal DR and the rostral DR. For example, the hippocampal formation receives moderately dense projections from the caudal DR and essentially none from the rostral DR. On the other hand, virtually all neocortical regions receive significantly denser projections from the rostral than from the caudal DR. The present results demonstrate that dorsal raphe fibers project significantly throughout widespread regions of the midbrain and forebrain.     

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.     

Serotonergic neurons in the brainstem of the wallaby, Macropus eugenii.

The organisation and cytoarchitecture of the serotonergic neurons in a diprotodont marsupial were examined by using serial sections of the brainstem processed for serotonin immunohistochemistry and routine histology. The topographic distribution of serotonergic neurons in the brainstem of the adult wallaby (Macropus eugenii) was similar to that of eutherian mammals. Serotonergic neurons were divided into rostral and caudal groups, separated by an oblique boundary through the pontomedullary junction. Approximately 52% of the serotonergic neurons in the wallaby brainstem were located in the rostral midline nuclei (caudal linear nucleus, dorsal, median, and pontine raphe nuclei and the interpeduncular nucleus), whereas 21% were found in the caudal midline region (nuclei raphe magnus, obscurus, and pallidus). The remaining serotonergic neurons (27%) were located in more lateral regions such as the pedunculopontine tegmental nuclei, the supralemniscal nuclei (B9 group), and the ventrolateral medulla. The largest serotonergic group, the dorsal raphe, contained one-third of the brainstem serotonergic neurons and showed five subdivisions, similar to that described in other species. In contrast, the median raphe did not show clear subdivisions. The internal complexity of the raphe nuclei and the degree of lateralisation of serotonergic neurons suggest that the wallaby serotonergic system is similar in organisation to that described for the cat and rabbit. This study supports the suggestion that the serotonergic system is evolutionally well conserved and provides baseline data for a quantitative study of serotonergic innervation of the developing cortex in the wallaby.     

Anatomic relationships of the human nucleus paragigantocellularis lateralis: a DiI labeling study

The nucleus paragigantocellularis lateralis (PGL) is located in the rostral ventrolateral medulla (RVLM), a brainstem region that regulates homeostatic functions, such as blood pressure and cardiovascular reflexes, respiration. central chemosensitivity and pain. In the present study, we examined anatomic relationships of the human nucleus paragigantocellularis lateralis using a bidirectional lipophilic fluorescent tracer, 1,1'-dioctadecyl-3,3.3',3'-tetramethylindocarbocyanine perchlorate (DiI), in nine postmortem human fetal midgestational brainstems. The areas which were labeled by diffusion of DiI from the nucleus paragigantocellularis lateralis included the arcuate nucleus (ARC) of the medulla, caudal raphe (nucleus raphe obscurus and pallidus), hilum and amiculum of the inferior olive, bilateral "reticular formation" (including the nucleus paragigantocellularis lateralis, nucleus gigantocellular-is and the intermediate reticular zone (IRZ)). vestibular and cochlear nuclei, cells and fibers at the floor of the fourth ventricle with morphologic features of tanycytes, parabrachial nuclei (PBN), medial lemniscus, lateral lemniscus, inferior cerebellar peduncle and cerebellar white matter, central tegmental tract, and the capsule of the red nucleus. This pattern of DiI labeling bears many similarities with the pattern of connections of the nucleus paragigantocellularis lateralis previously demonstrated by tract-tracing methods in experimental animals, and is consistent with the role of the nucleus paragigantocellularis lateralis in central regulation of homeostatic functions. In contrast to the animal studies, however, we did not demonstrate connections of the nucleus paragigantocellularis lateralis with the nucleus of the tractus solitarius (nTS) (only connections with the rostral subdivision were examined), locus coeruleus, or the periaqueductal gray (PAG) in the human midgestational brainstem. In our previous studies, six medullary areas showed reduced serotonin receptor binding in a subset of victims of sudden infant death syndrome (SIDS). The present study demonstrated DiI labeling in all of these six areas, suggesting that they are interconnected.     

Monoaminergic, peptidergic, and cholinergic afferents to the cat facial nucleus as evidenced by a double immunostaining method with unconjugated cholera toxin as a retrograde tracer

Using a sensitive double immunostaining technique with unconjugated cholera-toxin B subunit as a retrograde tracer, the authors determined the nuclei of origin of monoaminergic, peptidergic, and cholinergic afferent projections to the cat facial nucleus (FN). The FN as a whole receives substantial afferent projections, with relative subnuclear differences, from the following areas: 1) the perioculomotor areas, the contralateral paralemniscal region, and the mesencephalic reticular formation dorsal to the red nucleus; 2) the ipsilateral parabrachial region and the nucleus reticularis pontis, pars ventralis; and 3) the nuclei reticularis parvicellularis, magnocellularis, ventralis, and dorsalis of the medulla. In addition, the present study demonstrated that the lateral portion of the FN receives specific projections from the contralateral medial and olivary pretectal nuclei and the ipsilateral reticular formation of the pons. It was also found that the FN receives: 1) serotoninergic inputs mainly from the nuclei raphe obscurus, pallidus, magnus, and the caudal ventrolateral bulbar reticular formation; 2) catecholaminergic afferent projections from the A7 noradrenaline cell group located in the K?lliker-Fuse, parabrachialis lateralis, and locus subcoeruleus nuclei; 3) methionin-enkephalin-like inputs originating in the pretectal complex, the nucleus paragigantocellularis lateralis and the caudal raphe nuclei; 4) substance P-like afferent projections mainly from the Edinger-Westphal complex and the caudal raphe nuclei; and 5) cholinergic afferents from an area located ventral to the nucleus of the solitary tract at the level of the obex. In the light of these anatomical data, the present report discusses the physiological significance of FN inputs relevant to tonic and phasic events occurring at the level of the facial musculature during the period of paradoxical sleep in the cat.     

Pontomedullary distribution of 5-HT2A receptor-like protein in the rat

Serotonin (5-HT) exerts excitatory effects in many brainstem regions involved in autonomic, somatic, motor, and sensory functions, and in control of vigilance. To determine the potential role of 5-HT2A receptors in these effects, we immunohistochemically mapped the distribution of 5-HT2A receptor-like protein in the rat pontomedullary brainstem. Areas containing the densest labeling included the trigeminal, facial, hypoglossal, dorsal vagal motor nuclei, medullary linear nucleus, and the inferior olive. In the nucleus ambiguus, labeled cells were located in the areas containing pharyngeal and laryngeal motoneurons. Intensely labeled cells were loosely scattered in the reticular formation adjacent to the raphe magnus and obscurus nuclei, in the gigantocellular region, in the caudal pedunculopontine and laterodorsal tegmental nuclei, dorsomedial pontine reticular formation, and nucleus subcoeruleus. In the nucleus prepositus hypoglossi, all vestibular, abducens, cuneate, and lateral reticular nuclei, labeled neurons commingled with unlabeled ones. Few labeled neurons were located in the rostral and caudal ventrolateral medulla and parvicellular reticular formation. In the nucleus of the solitary tract, two patches of diffuse labeling not associated with cellular profiles were present: one in the medial, and the other in the interstitial subnucleus. Similar diffuse labeling was present in the lateral parabrachial region and the lateral rim of the caudal spinal trigeminal sensory nucleus. No labeled cells were found in the locus coeruleus, dorsal raphe, superior olive, or area postrema. The distinct pontomedullary distribution of 5-HT2A receptors, combined with the known arousal-dependent activity of serotonergic neurons, show that these receptors may mediate post- and presynaptic effects in the motor, selected somatic and visceral sensory, oculo-vestibulo-precerebellar, and sleep-related regions.     

The distribution and morphological characteristics of serotonergic cells in the brain of monotremes

The distribution and cellular morphology of serotonergic neurons in the brain of two species of monotremes are described. Three clusters of serotonergic neurons were found: a hypothalamic cluster, a cluster in the rostral brainstem and a cluster in the caudal brainstem. Those in the hypothalamus consisted of two groups, the periventricular hypothalamic organ and the infundibular recess, that were intimately associated with the ependymal wall of the third ventricle. Within the rostral brainstem cluster, three distinct divisions were found: the dorsal raphe nucleus (with four subdivisions), the median raphe nucleus and the cells of the supralemniscal region. The dorsal raphe was within and adjacent to the periaqueductal gray matter, the median raphe was associated with the midline ventral to the dorsal raphe, and the cells of the supralemniscal region were in the tegmentum lateral to the median raphe and ventral to the dorsal raphe. The caudal cluster consisted of three divisions: the raphe obscurus nucleus, the raphe pallidus nucleus and the raphe magnus nucleus. The raphe obscurus nucleus was associated with the dorsal midline at the caudal-most part of the medulla oblongata. The raphe pallidus nucleus was found at the ventral midline of the medulla around the inferior olive. Raphe magnus was associated with the midline of the medulla and was found rostral to both the raphe obscurus and raphe pallidus. The results of our study are compared in an evolutionary context with those reported for other mammals and reptiles.     

Innervation of the nucleus of the solitary tract and the dorsal vagal nucleus by thyrotropin-releasing hormone-containing raphe neurons

The nucleus of the solitary tract and the dorsal vagal nucleus are richly innervated by thyrotropin-releasing hormone (TRH)-containing fibers arising from the caudal raphe nuclei. After transection of vertically oriented fibers by a horizontal knife-cut in the medulla oblongata, TRH-staining disappeared from the vagal nuclei while it increased in transected nerve fibers ventral to the knife-cut. TRH-containing cells are mainly located in the nucleus raphe pallidus and raphe obscurus. TRH-containing fibers run dorsally within the raphe and enter the dorsal vagal complex at its rostral tip. Then they turn caudally and send branches laterally. Immediately caudal to the level of the obex, several TRH-containing fibers cross over the central canal. Cells in regions other than the raphe (hypothalamus or other rostral areas, ventrolateral medulla, cranial nerves) must contribute little to the TRH innervation of the nucleus of the solitary tract and dorsal vagal nucleus, since various knife-cuts transecting all above possible connections did not alter the TRH innervation pattern or TRH concentrations of these vagal nuclei.     

Brainstem projections to midline and intralaminar thalamic nuclei of the rat

The projections from the brainstem to the midline and intralaminar thalamic nuclei were examined in the rat. Stereotaxic injections of the retrograde tracer cholera toxin beta -subunit (CTb) were made in each of the intralaminar nuclei of the dorsal thalamus: the lateral parafascicular, medial parafascicular, central lateral, paracentral, oval paracentral, and central medial nuclei; in the midline thalamic nuclei-the paraventricular, intermediodorsal, mediodorsal, paratenial, rhomboid, reuniens, and submedius nuclei; and, in the anteroventral, parvicellular part of the ventral posterior, and caudal ventral medial nuclei. The retrograde cell body labeling pattern within the brainstem nuclei was then analyzed. Nearly every thalamic site received a projection from the deep mesencephalic reticular, pedunculopontine tegmental, dorsal raphe, median raphe, laterodorsal tegmental, and locus coeruleus nuclei. Most intralaminar thalamic sites were also innervated by unique combinations of medullary and pontine reticular formation nuclei such as the subnucleus reticularis dorsalis, gigantocellular, dorsal paragigantocellular, lateral, parvicellular, caudal pontine, ventral pontine, and oral pontine reticular nuclei; the dorsomedial tegmental, subpeduncular tegmental, and ventral tegmental areas; and, the central tegmental field. In addition, most intralaminar injections resulted in retrograde cell body labeling in the substantia nigra, nucleus Darkschewitsch, interstitial nucleus of Cajal, and cuneiform nucleus. Details concerning the pathways from the spinal trigeminal, nucleus tractus solitarius, raphe magnus, raphe pallidus, and the rostral and caudal linear raphe nuclei to subsets of midline and intralaminar thalamic sites are discussed in the text. The discussion focuses on brainstem-thalamic pathways that are likely involved in arousal, somatosensory, and visceral functions.     

Efferent projections of rat rostroventrolateral medulla C1 catecholamine neurons: Implications for the central control of cardiovascular regulation

A replication-defective lentivirus vector that expresses enhanced green fluorescent protein (EGFP) under the control of a synthetic dopamine-beta-hydroxylase (DbetaH) promoter was used to define efferent projections of C1 catecholamine neurons in rat rostral ventrolateral medulla (RVLM). EGFP expression was restricted to C1 neurons and filled their somatodendritic compartments and efferent axons 7-28 days after vector injection. This included the descending projections to thoracic spinal cord and a network in brainstem, midbrain, and diencephalon. In caudal brainstem, restricted terminal fields were present in the dorsal motor vagal complex, A1, raphe pallidus and obscurus, and marginal layer of ventrolateral medulla. Innervation of raphe nuclei was most dense at the level of RVLM, but rostral levels of pallidus were devoid of innervation. A sparse commissural projection to contralateral RVLM was observed, and pericellular arbors were present in the dorsal reticular formation among the projection pathway of catecholamine axons. Rostral brainstem contained a dense innervation of locus coeruleus and the nucleus subcoeruleus. A restricted innervation of the ventrolateral column of the periaqueductal gray distinguished the midbrain. Forebrain labeling was restricted to the diencephalon, where distinctive terminal fields were observed in the paraventricular thalamic nucleus; the lateral hypothalamic area; and the paraventricular, dorsomedial, supraoptic, and median preoptic nuclei of hypothalamus. Projection fibers also coursed through the tuberal hypothalamus into the median eminence. Collectively, these data demonstrate that RVLM C1 neurons modulate the activity of other central cell groups known to participate in the regulation of cardiovascular and autonomic function.     

Afferent fiber connections from the raphe nuclei to the cerebellar paramedian lobule. A histochemical study in the rabbit utilizing horseradish peroxidase as a retrograde marker

The distribution of labelled cells within the raphe nuclei has been studied after iontophoretic injections of horseradish peroxidase into various folia of the cerebellar paramedian lobule. Retrogradely marked neurons of all sizes and shapes were found in more caudally located raphe nuclei: obscurus, pallidus, magnus and pontis, as well as single neurons in nucleus centralis superior and dorsal raphe nucleus. The nuclei raphe pontis and obscurus send the greatest number of fibers to the paramedian lobule. Most of the projection takes origin from raphe neurons located in midline and ipsilaterally. Folia c and d are the recipients of most afferents from the raphe nuclei (pallidus, obscurus, pontis, magnus). On the other hand, folia f and e appear to receive contribution from nuclei raphe pontis and pallidus, while folia a and b from nuclei obscurus and magnus. Additionally single neurons in nucleus raphe dorsalis contribute to the projection onto the folia f and e, and from nucleus centralis superior to the folia c, d and occasionally to the sublobule a. The studies are discussed in relation to other investigations of afferent-efferent connections and already known functional role of the raphe nuclei.     

Projections from the red nucleus and surrounding areas to the brainstem and spinal cord in the cat. An HRP and autoradiographical tracing study

HRP injections at the C2, T1 and S1 spinal levels and in the medullary lateral tegmental field revealed that the contralaterally projecting rubro-bulbospinal neurons are located not only in the caudal but also to a certain extent in the rostral red nucleus (RN). These RN projections are somatotopically organized. Neurons projecting to the sacral cord are located in the ventrolateral RN, those projecting to the upper part of the spinal cord lie in the dorsomedial RN and those projecting to the medullary lateral tegmentum were found in the dorsal portions of the RN. These last neurons are smaller than many of the other RN neurons. The HRP results also revealed that the RN does not project to the caudal raphe nuclei. The autoradiographical results confirmed the HRP findings. They further indicated that the contralateral RN projections to the caudal brainstem precerebellar nuclei (nucleus corporis pontobulbaris, lateral reticular nucleus, lateral cuneate nucleus) and the dorsal column nuclei are also somatotopically organized. This was also true for the RN projections to the dorsomedial and intermediate facial subnuclei and the caudal pontine and medullary lateral tegmental field. These areas receive afferents from mainly the dorsal portions of the RN. Regarding the RN projections to the spinal cord, the autoradiographical tracing results revealed somatotopically organized contralateral RN projections to laminae V, VI and VII. Moreover, a small but distinct RN projection to a dorsolaterally located group of motoneurons at the C8-T1 level was demonstrated. Ipsilaterally a minor projection to the cervical and upper thoracic lateral intermediate zone was observed. Finally, strong ipsilateral projections from the rostral mesencephalon to the inferior olive were seen. These projections were derived from various rostral mesencephalic areas, including the nucleus of Darkschewitsch, the nucleus accessorius medialis of Bechterew, the interstitial nucleus of Cajal and the area of the rostral interstitial nucleus of the medial longitudinal fasciculus. In the cat it was difficult to define which of the mesencephalic areas projecting to the inferior olive represented the parvocellular RN. A new subdivision of the RN is proposed based on its projections and not on the size of its cells. In this concept the first group is formed by the RN neurons projecting contralaterally to the caudal brainstem and spinal cord. The second group consists of RN neurons projecting to the inferior olive.(ABSTRACT TRUNCATED AT 400 WORDS)     

大鼠中脑导水管周围灰质和中缝核簇内P物质受体定位分布的免疫细胞化学研究

本研究用免疫细胞化学染色技术对大鼠中脑导水管周围灰质（ＰＡＧ）和中缝核簇内Ｐ物质受体的精确定位分布进行了系统地观察。Ｐ物质受体阳性的神经元胞体和纤维主要密集地分布于ＰＡＧ吻段的背侧部、中段的外侧部和尾段的腹侧部。在线形核、中缝背核、中缝正中核、中缝桥核、中缝大核和中缝隐核可见中等密度至高密度的阳性神经元胞体和纤维；在中央下核和中缝苍白核内仅见少量阳性纤维。     

The origin of serotoninergic afferents to the cat's cerebellar nuclei

In the cat, serotoninergic (5HT) axons and terminals form a dense plexus that is present throughout the granule cell and Purkinje cell layers of the cerebellar cortex and all of the cerebellar nuclei. The intent of the present study was to identify the source of 5HT fibers in the cerebellar nuclei. The medial, interposed, and lateral cerebellar nuclei were selectively injected with either rhodamine or fluorescein-labeled latex microspheres that were retrogradely transported to brainstem neurons. Transverse sections of the brainstem were processed with a primary antibody to 5HT and secondary antibody tagged with either rhodamine or fluorescein. The location of neurons containing both serotonin-like immunoreactivity and retrogradely transported microspheres was plotted. All three of the cerebellar nuclei receive 5HT afferents from the nucleus locus coeruleus, the dorsal raphe nucleus, and the dorsal tegmental nucleus. In addition, the medial nucleus receives projections from the superior central nucleus, the nucleus raphe obscurus, the nucleus raphe magnus, and the periolivary reticular formation. The interposed nuclei receive additional projections from the nucleus raphe magnus, whereas the lateral nucleus receives additional projections from the superior central nucleus. In conclusion, the 5HT projections to the cerebellar nuclei do not appear to be collaterals of those projecting to the cortex (Kerr and Bishop, J Comp Neurol 304:502–515, 1991). These findings suggest that, although the cortex and nuclei are anatomically and physiologically related, they do not process all information in parallel. © Wiley-Liss, Inc.     

Lower brainstem afferents to the cat posterior hypothalamus: a double-labeling study

Using a double-immunostaining technique with cholera toxin (CT) as a retrograde tracer, the authors examined the cells of origin and the histochemical nature of lower brainstem afferents to the cat posterior hypothalamus. The posterior hypothalamus, in particular the lateral hypothalamic area, receives substantial afferent projections from: substantia nigra, peripeduncular nucleus, ventral tegmental area, periaqueductal grey, mesencephalic reticular formation, peribrachial region including the locus coeruleus complex, rostral raphe nuclei and the rostral part of the nucleus magnus. In addition, a moderate number of retrogradely labeled neurons was found in: Edinger-Westphal nucleus, nucleus reticularis pontis oralis, nucleus reticularis magnocellularis, caudal lateral bulbar reticular formation around the nucleus ambiguus and lateral reticular nucleus and the nucleus of the solitary tract. The posterior hypothalamus receives: 1) dopaminergic inputs from A8, A9 and A10 cell groups; 2) noradrenergic inputs from A6 and A7 pontine, as well as A1 and A2 bulbar cell groups; 3) adrenergic inputs from C1 cell group in the caudal medulla; 4) serotoninergic inputs from the rostral raphe nuclei (B6, B7 and B8 cell groups); 5) cholinergic inputs from the peribrachial region of the dorsal pontine tegmentum as well as from the nucleus reticularis magnocellularis of the medulla; 6) peptidergic inputs such as methionine-enkephalin, substance P, corticotropin-releasing factor and galanin that originate mainly in the mesencephalic periaqueductal grey, the dorsal raphe nucleus and the peribrachial region of the dorsal pontine tegmentum.     

Neuropathology of immunohistochemically identified brainstem neurons in Parkinson's disease

Regional loss of immunohistochemically identified neurons in serial sections through the brainstem of 4 patients with idiopathic Parkinson's disease was compared with equivalent sections from 4 age-matched control subjects. In the Parkinson brains, the catecholamine cell groups of the midbrain, pons, and medulla showed variable neuropathological changes. All dopaminergic nuclei were variably affected, but were most severely affected in the caudal, central substantia nigra. The pontine noradrenergic locus ceruleus showed variable degrees of degeneration. There was also a substantial loss of substance P-containing neurons in the pedunculopontine tegmental nucleus. However, the most severely affected cell group in the pons was the serotonin-synthesizing neurons in the median raphe. In the medulla, substantial neuronal loss was found in several diverse cell groups including the adrenaline-synthesizing and neuropeptide Y-containing neurons in the rostral ventrolateral medulla, the serotonin-synthesizing neurons in the raphe obscurus nucleus, the substance P-containing neurons in the lateral reticular formation, as well as the substance P-containing neurons in the dorsal motor vagal nucleus. Lewy bodies were present in immunohistochemically identified neurons in many of these regions, indicating that they were affected directly by the disease process. These widespread but region- and transmitter-specific changes help account for the diversity of motor, cognitive, and autonomic manifestations of Parkinson's disease.