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)     

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.     

Nuclei of origin of monoaminergic, peptidergic, and cholinergic afferents to the cat trigeminal motor nucleus: a double-labeling study with cholera-toxin as a retrograde tracer.

The aim of the present study was to determine the brainstem afferents and the location of neurons giving rise to monoaminergic, cholinergic, and peptidergic inputs to the cat trigeminal motor nucleus (TMN). This was done in colchicine treated animals by using a very sensitive double immunostaining technique with unconjugated cholera-toxin B subunit (CT) as a retrograde tracer. After CT injections in the TMN, retrogradely labeled neurons were most frequently seen bilaterally in the nuclei reticularis parvicellularis and dorsalis of the medulla oblongata, the alaminar spinal trigeminal nucleus (magnocellular division), and the adjacent pontine juxtatrigeminal region and in the ipsilateral mesencephalic trigeminal nucleus. We further observed that inputs to the TMN arise from the medial medullary reticular formation (the nuclei retricularis magnocellularis and gigantocellularis), the principal bilateral sensory trigeminal nucleus, and the dorsolateral pontine tegmentum. In addition, the present study demonstrated that the TMN received 1) serotonergic afferents, mainly from the nuclei raphe obscurus, pallidus, and dorsalis; 2) catecholaminergic afferent projections originating exclusively in the dorsolateral pontine tegmentum, including the K?lliker-Fuse, parabrachialis lateralis, and locus subcoeruleus nuclei; further, that 3) methionin-enkephalin-like inputs were located principally in the medial medullary reticular formation (nuclei reticularis magnocellularis and gigantocellularis and nucleus paragigantocellularis lateralis), in the caudal raphe nuclei (Rpa and Rob) and the dorsolateral pontine tegmentum; 4) substance P-like immunoreactive neurons projecting to the TMN were present in the caudal raphe and Edinger-Westphal nuclei; and 5) cholinergic afferents originated in the whole extent of the nuclei reticularis parvicellularis and dorsalis including 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 possible physiological involvement of TMN inputs in the generation of the trigeminal jaw-closer muscular atonia occurring during the periods of paradoxical sleep in the cat.     

Spinal projections from the nucleus locus coeruleus and nucleus subcoeruleus in the cat and monkey as demonstrated by the retrograde transport of horseradish peroxidase

The rostral pons of the cat and rhesus monkey were examined for the presence of labeled cells following injections of horseradish peroxidase (HRP) into the lumbar spinal cord. Labeled cells were found in the ipsilateral dorsolateral pontine tegmentum and in the contralateral ventrolateral pontine reticular formation. In both the cat and monkey, labeled cells were located in the nucleus locus coeruleus, nucleus subcoeruleus, in or near the Kölliker-Fuse nucleus, and in the ventral part of the lateral parabrachial nucleus. There is a striking similarity between the distribution of HRP-labeled cells in the dorsolateral pontine tegmentum of the cat and monkey and that of catecholamine-containing cells observed in this area in previous studies.     

Projections of the locus coeruleus and adjacent pontine tegmentum in the cat.

The projections of the locus coeruleus and adjacent pontine tegmentum have been studied using anatomical and physiological methods in the cat. Axonal trajectories were traced using either the Fink-Heimer I method following electrolytic lesions, or the autoradiographic method after injection of tritiated proline into the nucleus. Results with both methods were similar. Axons of locus noeruleus neurons ascended ipsilaterally through the mesencephalon lateral to the medial longitudinal fasiculus, ventrolateral to the central gray. In the caudal diencephalon, the ascending fibers entered the centrum medianum-parafascicular complex where they diverged into two fascicles: a dorsal fascicle which terminated in the intralaminar nuclei of the thalamus, and a ventral fascicle which gave off fibers to the ventrobasal complex and reticular nucleus of the thalamus while continuing centrolaterally into the lateral hypothalamus medial to the internal capsule. Fibers of the ventral fascicle ascended in the lateral hypothalamus and zona incerta and were traced through the preoptic region into the septum. Fibers could not be consistently traced to the cerebral cortex, and were not seen at all in the cerebellum. Throughout the ascending course of the path from the locus coeruleus, axons were given off to the pretectal area, the medial and lateral geniculate nuclei and the amygdala; fibers passed contralaterally through the posterior commissure, the midline thalamus, and the supraoptic commissure. Fibers descending from the locus coeruleus surrounded the intramedullary portion of the facial nerve and further caudally were observed ventrolateral to the hypoglossal and dorsal vagal nuclei. The axonal trajectories visualized with degeneration and autoradiographic methods followed closely those previously shown for reticular formation neurons, but were also similar to locus coeruleus projections revealed by histofluorescence methods. After injections of horseradish peroxidase into the centrum medianum-parafascicular complex, lateral hypothalamus or preoptic region, labeled neurons were located in the locus coeruleus, nucleus subcoeruleus, and lateral parabrachial nucleus. Reticular formation neurons were not labeled. Neurons in locus coeruleus and adjacent pontine tegmentum could be antidromically activated by stimulation in the rostral midbrain or caudal diencephalon. Our data indicate that both adrenergic and non-adrenergic neurons of the dorsolateral pontine tegmentum have similar projections.     

Distribution of neurons in the lateral pontine tegmentum projecting to thoracic, lumbar and sacral spinal segments in the cat

The course of descending fibers projecting to the spinal cord and the arrangement of their parent cells located in various nuclei of the dorso-lateral pontine tegmentum were studied using the horseradish peroxidase (HRP) retrograde axonal transport technique. Retrogradely labeled neurons were found in the locus coeruleus (LC), subcoeruleus (SC), K?lliker-Fuse nucleus (KF) and in the lateral parabrachial nucleus (LPB) after HRP injections into various spinal segments. Neurons innervating the thoracic spinal cord were found to be arranged in the ventral portion of the LC and in the entire SC; their axons descended ipsilaterally. Neurons with descending axons to lumbar segments were seen mainly in the ventral portion of the LC and in the medial portion of SC. Most of their axons were also seen to descend ipsilaterally. Neurons projecting to sacral segments occurred in the entire LC and in the medial portion of the SC. Large part of descending fibers crossed the midline at the level of (or near) the termination site. Neurons of all portions of the KF and LPB projected to the thoracic spinal cord only ipsilaterally, while many descending fibers innervating the sacral segments crossed the midline.     

Spinal projections from the lower brain stem in the cat as demonstrated by the horseradish peroxidase technique. II. projections from the dorsolateral pontine tegmentum and raphe nuclei

The descending projections to the spinal cord arising from the dorsolateral pontine tegmentum and brain stem raphe nuclei have been investigated by means of the horseradish peroxidase (HRP) technique. Particular attention was taken to clarify the cells of origin and the funicular trajectory of these spinal projections.After injections of HRP into the spinal cord, a significant number of HRP labeled neurons were observed in the following dorsolateral pontine tegmental structures: (1) an area ventral to the nucleous cuneiformis; (2) principal locus coeruleus; (3) locus coeruleus α; (4) locus subcoeruleus; (5) Kölliker-Fuse nucleus; and (6) nucleus parabrachialis lateralis. As a rule, the projections are ipsilateral and the descending fibers course in the ventral part of the lateral funiculus.As concerns the raphe-spinal projections, we have demonstrated that the nucleus raphe dorsalis also sends axons to the cervical segment of the spinal cord. Furthermore, in accord with previous reports, HRP labeled cells were also identified in the nucleus raphe magnus, pallidus and obscurus, but not in the nucleus raphe centralis superior and pontis.On the whole the present study further clarified the organization of spinal projections from the dorsolateral pons and raphe nuclei and provided some additional anatomical data for the physiology of the tegmentospinal and raphe-spinal projections.     

Parabrachial nucleus projections to midline and intralaminar thalamic nuclei of the rat

The projections from the parabrachial nucleus to the midline and intralaminar thalamic nuclei were examined in the rat. Stereotaxic injections of the retrograde tracer cholera toxin-beta (CTb) were made in each of the intralaminar nuclei of the dorsal thalamus (the lateral parafascicular, medial parafascicular, oval paracentral, central lateral, paracentral, and central medial nuclei), as well as the midline thalamic nuclei (the paraventricular, intermediodorsal, mediodorsal, paratenial, rhomboid, reuniens, parvicellular part of the ventral posterior, and caudal ventral medial nuclei). The retrograde cell body labeling pattern within the parabrachial subnuclei was then analyzed. The paracentral thalamic nucleus received an input only from the internal lateral parabrachial subnucleus. However, this subnucleus also projected to all the other intralaminar thalamic nuclei, except for the central lateral thalamic nucleus, which received no parabrachial afferent inputs. The external lateral parabrachial subnucleus projected to the lateral parafascicular, reuniens, central medial, parvicellular part of the ventral posterior, and caudal ventromedial thalamic nuclei. Following CTb injections in the paraventricular thalamic nucleus, retrogradely labeled cells were found in the central lateral, dorsal lateral, and external lateral parabrachial subnuclei. The medial and ventral lateral parabrachial subnuclei projected to the oval paracentral, parafascicular, and rhomboid thalamic nuclei. Finally, the waist area of the parabrachial nucleus was densely labeled after CTb injections in the parvicellular part of the ventral posterior thalamic nucleus. Nociceptive, visceral, and gustatory signals may reach specific cortical and other forebrain sites via this parabrachial-thalamic pathway.     

Brainstem innervation of prefrontal and anterior cingulate cortex in the rhesus monkey revealed by retrograde transport of HRP

The cells of origin of projections from the brainstem to the dorsolateral and orbital prefrontal granular cortex and to the anterior cingulate cortex of the rhesus monkey were analyzed by means of retrograde axonal transport of the enzyme horseradish peroxidase (HRP). Following injections in various portions of the dorsolateral prefrontal and in the cingulate cortex, HRP-positive neurons were found in three main locations: (1) the ventral midbrain including the anterior ventral tegmental area, the medial one-third of the substantia nigra pars compacta, and the retrorubral nucleus; (2) the central superior nucleus and the dorsal raphe nucleus, primarily in its caudal subdivision; and (3) the locus coeruleus and adjacent medial parabrachial nucleus. Labeled neurons in the raphe nuclei and locus coeruleus were distributed bilaterally. A basically similar pattern of labeled somata was found in the brainstem with HRP injections in the orbital prefrontal cortex. Scattered HRP-positive cells were found throughout the ipsilateral ventral tegmental area and in ventromedial portions of the retrorubral nucleus, and a large number of HRP-positive cells were distributed bilaterally in the dorsal raphe and central superior nuclei as well as the dorsolateral pontine tegmentum. However, in contrast to the results obtained with injections on the dorsolateral and medial aspects of the hemisphere, labeled neurons were not found in any portion of the substantia nigra. The neurons labeled retrogradely after injection of HRP in these various regions of the frontal lobe in rhesus monkey correspond both in location and morphology to the monoamine-containing neurons of the brainstem and are thus very likely the source of dopamine, norepinephrine, and serotonin found in the frontal cortex of the same species.     

Afferent projections to the dorsal and ventral respiratory nuclei in the medulla oblongata of the cat studied by the horseradish peroxidase technique

The central afferent projections to cells in the region of the dorsal and ventral groups of respiratory neurones of the medulla were studied in the cat using the retrograde axonal transport of horseradish peroxidase (HRP).HRP was injected electrophoretically either in the ventrolateral nucleus of the solitary tract (the dorsal group), or into the nucleus ambiguus and retroambigualis (the ventral group). Microelectrode recordings of the activity of the respiratory neurones in these locations were obtained prior to the iontophoretic injections of the enzyme.Projections from the parabrachial region of the pons (nucleus locus coeruleus and subcoeruleus, lateral and medial parabrachial nuclei, Kölliker-Fuse nucleus), nucleus reticularis pontis oralis, retrofacial nucleus, nucleus paragigantocellularis lateralis and ventrolateral nucleus of the solitary tract to the nucleus ambiguus and retroambigualis were identified.The ventrolateral nucleus of the solitary tract was found to receive an input from the retrofacial and lateral paragigantocellular nuclei, and to have strong reciprocal connections with the nucleus paragigantocellularis dorsalis of the medulla upon which pontine Kölliker-Fuse nucleus projects, and some of the primary respiratory and cardiovascular afferences are thought to converge.     

Brainstem projections to the rat cuneate nucleus

Neurons in the pontomedullary tegmentum have been proposed as a final common pathway subserving descending inhibition in the dorsal column nuclei. To investigate the anatomical substrate for these descending effects, brainstem projections to the cuneate nucleus of rats were studied with injections of lectin-conjugated horseradish peroxidase. In rats with iontophoretic tracer injections in this nucleus, many labeled neurons were detected near the injection site, especially ventral and caudal to it. Intrinsic reciprocal projections were observed after injections in caudal, middle, or rostral levels of the cuneate nucleus. Neurons were labeled in the red nucleus, in agreement with previous anatomical studies, and also in the trigeminal, vestibular, and cochlear nuclei. An ipsilateral dorsomedial group of neurons was labeled in the upper cervical segments and scattered neurons were also labeled bilaterally near the central canal. Sparse retrograde labeling in the tegmentum was focused in the lateral paragigantocellular nucleus and caudal raphe. Consistent with the retrograde experiments, anterograde labeling after pressure injections of lectin-conjugated horseradish peroxidase in the pontomedullary tegmentum was very sparse within the dorsal column nuclei; labeling was dense, however, in the region immediately ventral to these nuclei. These results confirm previous work indicating that the activity of cuneate neurons is modulated by brainstem sensory nuclei. However, it appears that direct projections to the cuneate nucleus from pontine and rostral medullary regions are sparser than previously suggested. The last link of a polysynaptic descending inhibitory pathway may include GABAergic neurons immediately adjacent to the dorsal column nuclei and/or intrinsic to these nuclei.     

Descending projections of the locus coeruleus and subcoeruleus/medial parabrachial nuclei in monkey: Axonal transport studies and dopamine-β-hydroxylase immunocytochemistry

Spinal projections originating in the dorsolateral pons in the ventral locus coeruleus and in the subcoeruleus and medial parabrachial nuclei were identified in monkeys (Macaco fascicularis) using the retrograde horseradish peroxidase tracing technique. Anterograde autoradiographic tracing studies were then carried out to determine the brain stem and spinal cord terminations of the neurons. Finally, results obtained with the axonal transport tracing methods were compared with the pattern of staining for noradrenergic cells and terminals revealed immunocytochemically with an antibody to dopamine-β-hydroxylase (DβH), the synthesizing enzyme for norepinephrine. The major findings of these studies are that two presumed noradrenergic cell groups of the dorsolateral pons, one corresponding to the nucleus locus coeruleus, the second to the subcoeruleus/medial parabrachial nuclei, give rise to descending project-ions. They differ significantly in their patterns of termination in the lower brain stem and spinal cord. Among the major terminations of the locus coeruleus pathway are projections to parasympathetic neurons of the dorsal motor nucleus of the vagus, the region of the nucleus ambiguus, and the sacral spinal cord. The terminations of the descending subcoeruleus/medial parabrachial pathway, in contrast, include project-ions to sympathetic preganglionic neurons of the intermediolateral cell column of the thoracic cord and heavier projections to somatic cranial nerve nuclei. Both pathways have additional widespread and bilateral terminations in various nuclei of the reticular formation, in the spinal dorsal horn (including the marginal zone), in the region around the central canal and in the ventral spinal gray matter. Since the origins and terminations of both these pathways correspond closely to the locations and patterns of terminations of noradrenaline-containing neurons, demonstrated here with DβH immunocytochemistry, norepinephrine (or epinephrine) is suggested to be the transmitter in both these descending systems.     

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.     

An autoradiographic study of the projections of the central nucleus of the monkey amygdala

The efferent connections of the central nucleus of the monkey amygdala have been studied using the autoradiographic method for tracing axonal projections. Small injections of 3H-amino-acids which are largely confined to the central nucleus lead to the labeling of several brainstem nuclei as far caudally as the spinomedullary junction. Specifically, in the forebrain, the central nucleus projects heavily to the bed nucleus of the stria terminalis, the basal nucleus of Meynert, the nucleus of the horizontal limb of the diagonal band, and more lightly to the substantia innominata and the preoptic area. In the hypothalamus, label is found over the dorsomedial nucleus, the perifornical region, the lateral hypothalamus, the supramammillary area, and most heavily in the paramammillary nucleus. In the thalamus, all components of the nucleus centralis medialis and the nucleus reuniens receive fibers from the central nucleus and there is a light projection to the medial pulvinar nucleus. In the mesencephalon, there is heavy labeling dorsal to the substantia nigra ad over the peripeduncular nucleus and lighter labeling within the substantia nigra pars compacta and the ventral tegmental area; the midbrain central gray is also labeled. More caudally, fibers from the central nucleus travel in the lateral tegmental reticular fields and contribute collaterals to the raphe nuclei, the cuneiform nucleus, and the central gray substance. Perhaps one of the heaviest terminal zones is the parabrachial region of the pons, both the lateral and the medial nuclei of which receive a prominent central nucleus projection. Only the ventral aspect of the adjacent locus coeruleus appears to receive a substantial input, but there is labeling also over the area of the nucleus subcoeruleus. Finally, there is heavy labeling around the dorsal motor nucleus of the vagus and over the parvocellular component of the nucleus of the solitary tract. A number of intra-amygdaloid connections between the basal and lateral nuclei of the amygdala and the central nucleus are also described. The present findings, taken together with recently reported widespread projections from the temporal association cortex to the amygdala, point out a potentially trisynaptic route between neocortical association regions and a variety of brainstem nuclei, many of which are related to autonomic function.     

Brainstem projections to the major respiratory neuron populations in the medulla of the cat

Efferent and afferent connections of the dorsal and ventral respiratory groups in the medulla of the cat were mapped by axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase. Injections of wheat germ agglutinin-horseradish peroxidase into the dorsal respiratory group and the three principal subdivisions of the ventral respiratory group (caudal, rostral, and B?tzinger Complex) revealed extensive interconnections between these regions and with a limited number of other brainstem neuron populations. Major neuron populations with efferent projections to the regions of the dorsal and ventral respiratory groups include the parabrachial nuclear complex (medial parabrachial, lateral parabrachial, and K?lliker-Fuse nuclei), subregions of the lateral paragigantocellular reticular nucleus, subregions of the lateral and magnocellular tegmental fields, inferior central and postpyramidal nuclei of the raphe, and sensory trigeminal nuclei. A previously unidentified neuron population with extensive efferent projections to the dorsal and ventral respiratory groups was found near the ventral surface of the rostral medulla; we refer to this group as the retrotrapezoid nucleus. The results suggest that the dorsal and ventral respiratory groups form an extensively interconnected neuronal system receiving convergent inputs from the same brainstem nuclear groups, consistent with the hypothesis that the dorsal and ventral groups are primarily sites for integration of sensory and premotor respiratory drive inputs. Neuron populations in the rostral ventrolateral medulla with projections to both the dorsal and ventral respiratory groups, particularly the retrotrapezoid nucleus and neighboring subregions of the lateral paragigantocellular reticular nucleus, are candidate sites for participation in respiratory rhythmogenesis or other critical functions of the brainstem respiratory control system such as intracranial chemoreception.     

Organization of the projections of a circumventricular organ: the area postrema in the rat

The projections of the rat area postrema were analysed using anterograde and retrograde axonal transport techniques. Discrete injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the area postrema produced anterograde labeling in specific medullary and pontine nuclei. In the medulla, anterograde labeling was present in the internal solitary zone and dorsal division of the medial solitary nucleus, both of which also contained a small number of retrogradely labeled perikarya. Prominent projections to the dorsal motor nucleus of the vagus were seen only if the WGA-HRP injections in the area postrema invaded dorsal solitary nuclei. In the pons, anterograde labeling was present in the parabrachial nuclei, the dorsolateral tegmental nucleus, and the pericentral division of the dorsal tegmental nucleus. By far the major pontine projection was to the dorsolateral region of the middle one-third of the rostrocaudal extent of the parabrachial nuclei. Retrograde fluorescent tracing studies indicated that most area postrema neurons take part in this parabrachial projection. The area postrema projection to the parabrachial nuclei was bilaterally distributed, whereas that from the dorsal solitary nuclei was primarily ipsilateral. The external solitary zone, immediately subadjacent to the area postrema, neither received area postrema projections nor participated in the projections to the parabrachial nuclei. Fluorescent retrograde double labeling studies confirmed the bilateral nature of the area postrema projection to the parabrachial nuclei. In addition, because no doubly labeled neurons were observed it appears that individual area postrema neurons project to either side but not both sides of the dorsal pons. Thus, numerous neuronal pathways exist for the transfer of blood-borne information (that cannot cross the blood-brain barrier) from the area postrema to other brain regions.     

Catecholaminergic innervation of the spinal cord in the North American opossum, Didelphis virginiana

Axons presumed to contain catecholamines were visualized in the spinal cord of the spinal cord of the North American opossum using antibodies to tyrosine hydroxylase (TH) by an indirect antibody peroxidase-antiperoxidase (PAP) technique. Axons showing TH-like immunoreactivity (TH-IR) coursed primarily in the dorsal part of the lateral funiculus, although they were also present more ventrally. An occasional TH-IR axon was seen in the dorsal funiculus. Within the gray matter, TH-IR axons were distributed most densely within the intermediolateral cell column (ILC). Such axons were more numerous in the presumptive sacral parasympathetic nucleus than within the adjacent gray matter, but their density was less than that within the ILC. Many TH-IR axons were also found within laminae I-V and X, but the density of innervation in the ventral horn was relatively low. The brainstem origin of TH-IR axons in the spinal cord was studied using a combination of the retrograde transport of fluorescent dyes and immunofluorescence as well as the retrograde transport of horseradish peroxidase and PAP immunohistochemistry. The injections of retrograde markers were made at either cervical, thoracic or lumbar spinal levels. With both techniques, spinally projecting TH-IR neurons were located within the nucleus periventricularis hypothalami, the nucleus paraventricularis hypothalami dorsalis, the area hypothalamica posterior, the ventral part of the nucleus coeruleus, the nucleus coeruleus pars alpha, the lateral part of the nucleus reticularis pontis, and several nuclei of the ventrolateral medulla. Few or no cells within the parabrachial area, the region of the K?lliker-Fuse nucleus or the area adjacent to the superior olivary complex (the location of the A5 group of rats) provided TH-IR projections to the spinal cord. Our results suggest that catecholaminergic projections to the spinal cord of the marsupial opossum are similar in termination and origin to those described for rats and other placental mammals, but differences do exist.     

Efferent connections of the habenular nuclei in the rat.

The efferent connections of the medial (MHb) and lateral (LHb) habenular nuclei in the rat were demonstrated autoradiographically following small injections of tritiated amino acids localized within various parts of the habenular complex. Comparison of individual cases led to the following conclusions. MHb efferents form the core portion of the fasciculus retroflexus and pass to the interpeduncular nucleus (IP) in which they terminate in a topographic pattern that refects 90 degrees rotations such that dorsal MHb projects to lateral IP, medial MHb to ventral, and lateral MHb to dorsal IP. Most MHb fibers cross in the interpeduncular necleus in the "figure 8" pattern described by Cajal, and terminate throughout the width of IP with only moderate preference for the ipsilateral side. However, the most dorsal part of MHb projects almost exclusively to the most lateral IP zone in a cluster pattern that is particularly dense on the ipsilateral side. The MHb appears to have no other significant projections, but very sparse MHb fibers may pass to the supracommissural septum and to the median raphe nucleus. Except for some fibers passing ventrally into the mediodorsal nucleus, all of the LHb efferents enter the fasciculus retroflexus and compose the mantle portion of the bundle. No LHb projections follow the stria medullaris. In the ventral tegmental area LHb efferents become organized into groups that disperse in several directions: (a) Rostrally directed fibers follow the medial forebrain bundle to the lateral, posterior and dorsomedial hypothalamic nuclei, ventromedial thalamic nucleus, lateral preoptic area, substantia innominata and ventrolateral septum. (b) Fibers turning laterally distribute to the substantia nigra, pars compacta (SNC); a small number continue through SNC to adjacent tegmentum. (c) The largest contingent of LHb efferents passes dorsocaudally into paramedian midbrain regions including median and dorsal raphe nuclei, and to adjacent tegmental reticular formation. Sparse addition LHb projections pass to the pretectal area, superior colliculus, nucleus reticularis tegmenti pontis, parabrachial nuclei and locus coeruleus. No LHb projections appear to involve the interpeduncular nucleus. All of these connections are in varying degree bilateral, with decussations in the supramammillary region, ventral tegmental area and median raphe nucleus. On the basis of differential afferent and efferent connections, the LHb can be divided into a medial (M-LHb) and a lateral (L-LHb) portion. The M-LHb, receiving most of its afferents from limbic regions and only few from globus pallidus, projects mainly to the raphe nuclei, while L-LHb, afferented mainly by globus pallidus and in lesser degree by the limbic forebrain, projects predominantly to a large region of reticular formation alongside the median raphe nucleus. Both M-LHb and L-LHb, however, project to SNC. The reported data are discussed in correlation with recent histochemical findings.     

Nonretinal projections to the medial terminal accessory optic nucleus in rabbit and rat: a retrograde and anterograde transport study

The distribution and density of the nonretinal projections to the rabbit medial terminal accessory optic nucleus (MTN) have been studied after injections of horseradish peroxidase (HRP) into the MTN in seven rabbits, and confirmation for the presence of certain of these projections has been made in the rabbit or rat by utilizing anterograde transport of tritiated leucine or leucine/proline after appropriate injections into cerebral cortical areas and brainstem nuclei. In seven cases studied by the retrograde axonal transport method, HRP-labeled neurons have been identified: (A) In four visual or preoculomotor nuclei in which available autoradiographic brain series have confirmed the presence of projections to the MTN: (1) The nucleus of the optic tract/dorsal terminal accessory optic nucleus, (2) the interstitial nucleus of the superior fasciculus (posterior fibers), (3) the periaqueductal gray (including its supraoculomotor portion), and (4) the medial division of the deep mesencephalic nucleus. (B) Within the ventral lateral geniculate nucleus, from which a projection to the MTN has been confirmed autoradiographically in the rat by other workers. (C) In brainstem nuclei and cerebral cortical areas in which available autoradiographic brain series fail to confirm the presence of afferents to the MTN: (1) The nucleus reticularis pontis, pars oralis and pars caudalis, (2) the intermediate interstitial nucleus of the medial longitudinal fasciculus, (3) the nucleus raphe pontis, and (4) five cerebral cortical areas (the area retrosplenialis granularis dorsalis, the striate area, the parietal area 3, the subicular cortex, and the regio praecentralis granularis). Finally, we report retrograde labeling which, on the basis of published connectional data, we believe to result from the spread to and uptake from axons en passant. The false-positive labeling in this category is likely to result from spread of HRP into ventral tegmental nuclei or tracts adjacent to the MTN. Thus, as a result, in the medulla and pons, labeled neurons are found in the medial, lateral, and superior vestibular nuclei, the medullary reticular formation including the nucleus reticularis gigantocellularis, the lateral reticular nucleus, the nucleus raphe magnus, the spinal nucleus of V, the nucleus gracilis/nucleus cuneatus, the dorsal and ventral divisions of the parabrachial nucleus, the central pontine gray, the nucleus K of Meessen and Olszewski, and the dorsal nucleus of the lateral lemniscus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Telencephalic projections from midbrain and isthmal cell groups in the pigeon. I. Locus coeruleus and subcoeruleus

Horseradish peroxidase (HRP) and amino acid autoradiography were used in pigeon to determine the trajectories and projection patterns of neurons within the locus coeruleus and subcoeruleus nuclei upon the cerebral hemispheres. The specific cell groups investigated include the locus coeruleus (LoC), nucleus subcoeruleus dorsalis, and nucleus subcoeruleus ventralis. Efferents from each of these nuclei ascend to the telencephalon via the medial and lateral forebrain bundles, ansa lenticularis, and the quintofrontal and occipitomesencephalic tracts. A separate dorsally situated bundle derived from LoC neurons reaches many dorsal thalamic nuclei. The telencephalic projections of the LoC and subcoeruleus nuclei are bilateral and symmetrical, although projections to the contralateral hemisphere are sparse. Crossing fibers project to contralateral targets primarily via the dorsal supraoptic decussation and along the dorsal and ventral margins of the anterior commissure. Within the telencephalon, the following neural structures receive input from neurons in the LoC and subcoeruleus cell groups: the paleostriatal complex including the paleostriatum augmentatum and lobus parolfactorius, septal nuclei, nucleus accumbens, olfactory tubercle, hippocampus and parahippocampal area, nucleus taeniae, dorsal archistriatum, lateral neostriatum, hyperstriatum dorsale, hyperstriatum ventrale, and preoptic area. Large portions of the cerebral hemispheres including the hyperstriatum accessorium, much of the neostriatum and hyperstriatum ventrale, and all but the dorsal portion of the archistriatum receive little or no input from either the locus coeruleus or subcoeruleus cell groups. This is apparently different from the condition in mammals in which virtually all cortical fields receive input from neurons within the LoC. Moreover, the pattern of projections of the subcoeruleus nuclei upon telencephalic fields described here as well as recent histochemical data suggest that these cell groups are comparable to the lateral tegmental (A8) cell group of mammals rather than to the mammalian subcoeruleus nuclei.