Retrograde axonal transport of horseradish peroxidase from spinal cord to brain stem cell groups in the cat

Localization of forebrain neurons which project directly to the medulla and spinal cord of the rat by retrograde tracing with wheat germ agglutinin

Wheat germ agglutinin (WGA) in a slow-release polyacrylamide gel pellet was implanted in the medulla or spinal cord of the rat. Large numbers of retrogradely labeled cells were visualized by immunocytochemical procedures in specific nuclei of the forebrain mainly ipsilateral to the implant site following implants as far caudal as the sacral segments of the spinal cord. Total average number of labeled forebrain cells (three brains per category; 100 micron per 150 micron of brain tissue were examined microscopically): medulla, 2,115; cervical, 1,878; lumbar, 1,017; sacral, 385. After WGA-gel implants in the medulla or cervical cord the majority of retrogradely labeled neurons were seen in the lateral hypothalamic area, the zona incerta, and in subdivisions of the paraventricular nucleus. A continuum of labeled cells extended from the caudal part of the paraventricular nucleus into the posterior hypothalamus and into the central gray of the midbrain. Labeled cells were also seen in the medial basal hypothalamus and the rostral part of the bed nucleus of the stria terminalis. A few labeled cells were observed in the medial and lateral preoptic areas, the rostral part of the paraventricular nucleus, and in the arcuate nucleus. Following WGA-gel implants in the lumbar or sacral cord many retrogradely labeled cells were observed mainly in the paraventricular nucleus, the lateral hypothalamus, zona incerta, medial basal hypothalamus, and posterior hypothalamic area. The continuum of labeled cells described above was also seen following these implants. Our data indicate that the lateral hypothalamus and zona incerta, as well as specific parts of the paraventricular nucleus, are major loci of neurons which project directly to the medulla and spinal cord of the rat. The consistency with which labeled cells were localized across all brains examined within categories of implant sites and the large numbers of labeled cells counted within these areas appeared to verify the sensitivity of our retrograde tracing method. Therefore, we interpret the paucity or absence of labeled cells in particular brain regions to indicate that cells of these regions do not project to the medulla or spinal cord.

An investigation into the mechanism of cardiovascular responses elicited by electrical stimulation of locus coeruleus and subcoeruleus in the cat

Electrical stimulation of locus coeruleus (LC) and subcoeruleus (SC) elicited an increase in heart rate (HR) and blood pressure (BP). Adrenergic neurone blockade in the posterior hypothalamus with guanethidine and also bilateral adrenalectomy completely blocked the LC stimulation induced cardiovascular responses. The cardiovascular responses elicited by electrical stimulation of SC were, however, unaffected by the former and only partially inhibited by the latter. It is suggested that the LC stimulation-evoked rise in HR and BP is mediated by catecholamine release from the adrenal medulla due to an activation of the hypothalamic-adrenal axis. The cardiovascular responses elicited by stimulation of SC are mainly due to activation of the sympathetic preganglionic neurones and are further augmented by the adrenal catecholamine release.

The effects of lesions of medullary midline and lateral reticular areas on inhibition in the dorsal horn produced by periaqueductal grey stimulation in the cat

In barbiturate-anaesthetized cats, the excitation of lumbar dorsal horn neurones by impulses in unmyelinated primary afferent fibres was inhibited by electrical stimulation in the periaqueductal grey matter. This inhibition was slightly reduced by extensive electrocoagulation of the medullary midline and para-medial areas including the raphé, but significantly reduced by small bilateral lesions in the region of the caudal lateral reticular nuclei. When the lateral lesions were made subsequent to midline coagulation, the inhibition from periaqueductal grey stimulation was abolished. An important component of spinal inhibition from periaqueductal grey stimulation appears to relay in lateral reticular areas of the medulla.

Release of immunoassayable neurohypophyseal peptides from rat spinal cord, in vivo

The subarachnoid space of the spinal cord was perfused in vivo in urethane-anesthetized rats and perfusates were assayed for arginine-vasopressin (AVP) and oxytocin immunoreactivity. In control perfusates, oxytocin concentrations were 3 times those of AVP. Electrical stimulation of the paraventricular nucleus (PVN) of the hypothalamus, but not of other hypothalamic areas, yielded increased amounts of immunoassayable peptides in the spinal cord perfusates. Intravenous infusion of AVP did not elevate AVP concentrations in the cord perfusates. These data suggest that electrical stimulation of PVN neurons caused release of AVP and oxytocin from spinal cord terminals and support the concept that these peptides are neurotransmitters in the cord.

Edinger-Westphal nucleus: cholecystokinin immunocytochemistry and projections to spinal cord and trigeminal nucleus in the cat

Immunocytochemical methods were used to determine the distribution of cells with cholecystokinin-like immunoreactivity (CCK-LI) in the cat Edinger-Westphal complex (EW). Numerous cells with CCK-LI are found throughout the length of EW. The distribution and frequency of such cells are similar to the pattern of EW neurons that show substance P-like immunoreactivity (SP-LI). Companion retrograde transport experiments reveal that EW neurons which project to spinal cord or the region of the caudal trigeminal nucleus are found throughout the length of EW, and that some EW neurons which project to spinal cord also show CCK-LI.

Observations on the brainstem-spinal descending systems of normal and reeler mutant mice by the retrograde HRP method

Brainstem neurons which project to the lumbar spinal level were identified in both reeler mutant mice and normal controls (Balb/c mice) by the retrograde horseradish peroxidase (HRP) technique. In normal controls after HRP injection into the lumbar cord, retrogradely labelled neurons were observed in (1) the lateral vestibular nucleus, (2) the pontine and medullary reticular formations including the nucleus centralis caudalis pontis, nucleus gigantocellularis, nucleus paragigantocellularis, nucleus raphe magnus et pallidus, and nucleus centralis medullae oblongatae pars ventralis et dorsalis, and (3) the dorsal column nuclei, i.e., the nucleus gracilis and nucleus cuneatus medialis. In reeler mutant mice, labelled neurons were again seen in the nuclei referred to above, and their cellular type and distribution patterns within the corresponding nuclei were similar to those of the normal controls. These observations suggest that (1) the brainstem nuclei of reeler mutant mice which project to the lumbar spinal cord are cytoarchitecturally normal, (2) the reeler genetic locus (rl) does not affect the nonlaminated structures in the brainstem, at least those referred to above, and (3) the motor dysfunctions observed in the reeler, such as action tremor, dystonic posture, and reeling ataxic gait, are not attributable to the brainstem-spinal descending systems.

Brainstem projections to the phrenic nucleus: a HRP study in the cat

Brainstem neurones which project to the phrenic nucleus were identified using retrogradely transported horseradish peroxidase (HRP) as a marker. Following iontophoretic injection of HRP into the phrenic nucleus, labelled cells were encountered throughout large areas of the medulla and pons, but occurred with characteristic high densities in those regions known to contain phasic respiratory neurones: namely, the ventrolateral solitary tract nucleus (vl-NTS), known as the dorsal respiratory group (DRG), the ambiguus complex or ventral respiratory group (VRG) and the parabrachial pontine nuclei (BCM-KF). In 12 cats a total of 1540 cells was identified within these regions, the relative contralateral and ipsilateral contributions were respectively 72%:28% (vl-NTS), 65%:35% for the ambiguus complex, and 5%:95% (BCM-KF). In addition, labelled cells, predominantly ipsilateral, were observed in the pontine and medullary reticular formation and the vestibular nuclei. The labelled cells of the DRG had round, oval or triangular perikarya. Their mean soma diameter was 18.3 micrometers. The HRP-positive cells of the VRG had slightly larger somas (mean 21.2 micrometers) and they were fusiform and triangular. The neurones labelled in the BCM-KF nuclei were more heterogeneous with a mean soma size of 14.9 micrometers. The bilateral projections to the phrenic nucleus from the DRG and the VRG, and the predominantly ipsilateral projection from the BCM-KF are discussed in relation to current electrophysiological and autoradiographic findings.

Are hypothalamo-cerebellar fibers collaterals from the hypothalamo-spinal projection?

Retrograde transport of fluorescent tracer molecules (Fast Blue and Nuclear Yellow) was used to restudy the feline hypothalamo-cerebellar and hypothalamo-spinal projections in order to decide whether hypothalamo-cerebellar and hypothalamo-spinal fibers are branches of the same axons. The finding of a significant hypothalamo-cerebellar projection from lateral, dorsal and posterior hypothalamic areas is confirmed. Scattered hypothalamo-cerebellar fibers were found to come from the supraoptic, dorsomedial, periventricular, infundibular and paraventricular nuclei, tuber cinereum and the anterior hypothalamic area. A topographical organization is proposed for the hypothalamo-cerebellar projection; the cerebellar anterior lobe receives fibers mainly from the rostral (anterior) hypothalamus while the posterior lobe receives fibers mainly from its caudal (posterior) part. The hypothalamo-spinal pathway originates principally within the dorsal, posterior and lateral hypothalamic areas, but receives small contributions also from the periventricular and paraventricular nuclei, tuber cinereum and the anterior hypothalamic area. Hypothalamic neurons retrogradely labeled from the spinal cord and from cerebellum were often located adjacent to each other, but only few double labeled neurons were found. This indicates that spinal and cerebellar projecting cells are mainly two different populations.

Behavioral evidence for a cholinoceptive pontine inhibitory area: descending control of spinal motor output and sensory input

Earlier studies have shown that microinjection of the cholinergic agonist carbamylcholine (carbachol) into the rostral pontine tegmentum of the cat elicits postural atonia. However, conflicting reports exist regarding other concomitant behavioral changes. The present study has demonstrated that a variety of functions supporting animals' responsiveness to external stimuli including postural somatomotor, sympathetic visceromotor and nociceptive somatosensory functions are differentially affected depending upon the injection sites. Sites associated with maximal effects on each of these functions are clustered in the dorsal pontine tegmentum, i.e. cholinoceptive pontine inhibitory area (CPIA). In a medial area of CPIA, which corresponds to an area caudal to the ventral tegmental nucleus of Gudden and ventromedial to the principal nucleus of locus coeruleus, postural somatomotor and sympathetic visceromotor functions were maximally suppressed. In a laterally adjacent area ventral to the principal nucleus of locus coeruleus, somatomotor function was predominantly suppressed. Nociceptive somatosensory function was primarily suppressed following microinjections into a more lateral area surrounding the lateral half of the brachium conjunctivum. Several lines of evidence suggest that each of these phenomena ultimately involves descending influences on the spinal motor output and/or sensory input. There was no correlation between maximal suppression of these spinal cord functions and signs of desynchronized sleep such as rapid eye movement. Carbachol microinjection into wide areas of CPIA also suppressed orienting behaviors. Taken together, these data suggest that CPIA is a system which primarily regulates animals' responsiveness to external stimuli, in part by influencing segmentally organized behaviors.

Electrophysiological characteristics of lumbosacral evoked potentials in patients with established spinal cord injury

Surface electrodes positioned over the S1 and T12 vertebrae and referenced to T6 were used to record spinal potentials evoked by unilateral stimulation of the posterior tibial nerve at the knee. Data were collected on 24 patients who received spinal cord injuries 2 months to 31 years previously. The recording sites were below the level of spinal injury. The lumbosacral evoked potentials (LSEPs) were compared with the results of measurements obtained from 19 neurologically healthy subjects. Additional data were collected on each patient to characterize segmental reflex responses and preservation of sensory and motor functions associated with the L5 through S2 segments of the spinal cord. Assuming that the LSEP reflects the activity of spinal cord interneurons, the results demonstrate a degree of spinal cord dysfunction caudal to the area of injury in a substantial number of the patients with spinal cord injury which we studied.

A diffuse alpha MSH-immunoreactive projection to the hippocampus and spinal cord from individual neurons in the lateral hypothalamic area and zona incerta

The course, distribution, and possible neurotransmitter specificity of a projection from the lateral hypothalamic area (LHA) and zona incerta to the hippocampal formation (dentate gyrus, Ammon's horn, subicular region, and entorhinal area) and spinal cord were examined anatomically in the adult rat. First, small injections of the fluorescent tracer fast blue were made into either the septal part of the dentate gyrus and Ammon's horn or the entorhinal area, and the distribution of retrogradely labeled cells was plotted. In each experiment many cells were labeled in the LHA and zona incerta, and little evidence for a topographically organized projection to different parts of the hippocampal formation was found. Second, a combined retrograde transport-immunofluorescence method was used to show that some 95% of the fast blue-labeled neurons in the LHA and zona incerta were also stained with an antiserum to the opiate peptide alpha-melanocyte-stimulating hormone (alpha MSH), but not an antiserum to adrenocorticotropin (ACTH)1-24. It was also found that small numbers of retrogradely labeled neurons were stained with antisera to somatostatin 14 and 28, dynorphin (1-17), and angiotensin II. Third, the distribution of alpha MSH-immunoreactive fibers was plotted, and they were found to form a diffusely organized plexus throughout all of the subfields of the hippocampal formation. These fibers were virtually eliminated after transections of the fimbria and the region between the entorhinal area and the caudal amygdala. Forth, the course of fibers from the LHA and zona incerta was examined with the anterogradely transported lectin Phaseolus Vulgaris Leucoagglutinin (PHAL). Such fibers reach the hippocampal formation by a dorsal route through the septal region and fimbria, and by a ventral route through the amygdala. And fifth, double retrograde transport and immunohistochemical methods were used to show that at least some alpha MSH-stained neurons in the LHA and zona incerta give rise to collaterals that innervate both the hippocampal formation and the spinal cord. Alpha MSH-stained fibers in the spinal cord also form a widely scattered plexus with no obvious circumscribed terminal fields. It is suggested that the diffusely organized projection from the LHA to the cerebral cortex and spinal cord may play a role in the general arousal associated with a variety of motivated behaviors.

Pontomedullary raphe neurons: intracellular responses to central and peripheral electrical stimulation

The responses of pontomedullary raphe neurons to electrical stimulation of the medullary reticular formation (MRF) and the mesencephalic ventral periaqueductal gray region (PAG) were studied using intracellular methods in chloralose-anesthetized cats. Single shock stimulation of PAG at the level of the trochelear nucleus evoked short latency, monosynaptic excitatory postsynaptic potentials (EPSPs) in antidromically identified raphe-spinal neurons. Similar large EPSPs were produced by medullary reticular stimulation of either side. The large majority of raphe-spinal neurons responded to sciatic nerve shock, and most responded to tooth pulp or forepaw shock as well; these responses were always bilateral. The responses of cells that could not be antidromically invaded from spinal cord were similar to those of raphe-spinal neurons, but tended to be more variable. Intracellular injection of horseradish peroxidase into electrophysiologically characterized cells revealed that most recordings were made from large and medium sized raphe neurons. These findings are discussed in the context of a potential role for pontomedullary raphe neurons in nociception.

Evidence for cholecystokinin-like immunoreactive neurons in the rat medulla oblongata which project to the spinal cord

The distribution of cholecystokinin-like immunoreactive (CCK-LI) neurons has been mapped in the rat medulla after local and intracerebroventricular colchicine injections. CCK-positive neurons were found in the nucleus raphe magnus, nucleus raphe pallidus, nucleus raphe obscurus, nucleus paragigantocellularis pars alpha, and a population of ventral medullary neurons. Combined retrograde tracing with the fluorescent dye True Blue and indirect immunofluorescence for visualizing CCK neurons suggested that there was a CCK-LI system originating in the medulla and projecting to the spinal cord. Additional double labelling experiments established that some of these CCK-LI containing neurons also contain 5-HT.

Comparison of the effects of ventral medullary lesions on systemic and microinjection morphine analgesia

The effects of electrolytic lesions of the nucleus raphe magnus (NRM), nucleus reticularis paragigantocellularis (PGC) and nucleus raphe alatus (NRA) on analgesia elicited in the rat from systemic morphine and morphine microinjection into the periaqueductal gray (PAG) were evaluated using the tail flick test. No consistent change in baseline pain sensitivity was observed following lesions of the NRM, PGC or NRA. To determine the effect of ventral medullary lesions on systemic morphine analgesia, pain sensitivity was assessed prior to and 40 min after 6 mg/kg morphine administration (i.p.) at 2 days preceding lesioning and 5, 12 and 19 days post-lesion. NRM and PGC lesions produced only slight reductions in analgesia at 5 days after surgery. It was observed that large NRM, large PGC, and NRA lesions significantly attenuated analgesia evaluated at 12 days post-lesion. Smaller lesions confined within the NRM or PGC were reliably less effective than the larger lesions in reducing analgesia. In a subsequent study, 5 micrograms morphine in 0.5 microliter saline was microinjected into the ventral PAG at the level of the dorsal raphe. Identical testing procedures were used and the analgesia was assessed at 2 days before lesioning and 5 and 12 days post-lesion. In contrast to the previous study, large NRM lesions abolished analgesia as early as 5 days following lesioning. Small NRM lesions were less effective and PGC lesions were generally ineffective in attenuating analgesia induced by morphine microinjection. We conclude that the NRA may act as a functional unit in the mediation of systemic morphine analgesia. In contrast, analgesia elicited from intracerebral (PAG) morphine microinjection is mediated via the NRM.

Descending serotonergic, peptidergic and cholinergic pathways from the raphe nuclei: a multiple transmitter complex

The localization of serotonergic, various peptidergic and possibly cholinergic neurons in the medullary raphe nuclei that project to the lumbosacral spinal cord have been studied using a retrograde transport method combined with immunocytochemical and histochemical techniques. Spinally projecting neurons stained for serotonin-like, substance P-like, enkephalin-like and thyrotropin-releasing hormone-like immunoreactivity and for the histochemical marker acetylcholinesterase were all observed in each of the raphe nuclei of the medulla, as well as in the adjacent ventrolateral reticular formation. The similar distributions of the descending serotonergic and peptidergic neurons in the raphe nuclei as well as quantitative data on their relative numbers suggest that a large fraction of raphe-spinal neurons contain serotonin co-existing with one or more peptides in the same cell.

Afferent and efferent connections of the medial, inferior and lateral vestibular nuclei in the cat and monkey

Attempts were made to determine the afferent and efferent connections of the medial (MVN), inferior (IVN) and lateral (LVN) vestibular nuclei (VN) in the cat and monkey using retrograde and anterograde axoplasmic transport technics. Injections of HRP and [3H]amino acids were made selectively into MVN, IVN and LVN and into: (1) MVN and IVN, (2) LVN and IVN and (3) all 4 VN. Contralateral afferents to MVN arise from (1) the nuclei prepositus (NPP) and intercalatus (NIC), (2) all parts of MVN and cell group 'y' and (3) parts of the superior vestibular nucleus (SVN), IVN and the fastigial nucleus (FN). Ipsilateral projections to MVN arise from: (1) a central band of the flocculus and the nodulus and uvula, (2) the interstitial nucleus of Cajal (INC), and (3) visceral nuclei of the oculomotor nuclear complex (OMC). Efferent projections of MVN are to: (1) the ipsilateral supraspinal nucleus (SSN), and (2) the contralateral central cervical nucleus (CCN), MVN, SVN, cell group 'y', the rostroventral region of LVN, the trochlear nucleus (TN) and the INC. Projections to the abducens nuclei (AN) and the OMC are bilateral. Some ascending fibers in the cat cross within the OMC. In the monkey fibers from MVN end in a central band of the ipsilateral flocculus. Afferents to IVN arise ipsilaterally from SVN, the nodulus, the uvula and the anterior lobe vermis. Contralateral afferents arise from: (1) parts of CCN, MVN, SVN, IVN and cell group 'y' and (2) the central third of the FN. IVN receives bilateral projections from the perihypoglossal nuclei (PH) and the visceral nuclei of the OMC. Efferents from IVN project: (1) ipsilaterally to nucleus beta of the inferior olive, (2) contralaterally to parts of MVN, SVN and cell group 'y' and (3) bilaterally to the paramedian reticular nuclei. No commissural fibers interconnect cell groups 'f' and 'x'. Ascending fibers from IVN terminate contralaterally in the TN and the OMC. In the monkey fibers from IVN terminate in the ipsilateral nodulus, uvula and anterior lobe vermis; no fibers project to FN in either the cat or the monkey. Afferents to the LVN arise primarily from the ipsilateral anterior lobe vermis and bilaterally from rostral parts of the FN. No commissural fibers interconnect the LVN. Projections of the LVN are primarily to spinal cord via the vestibulospinal tract (VST); collaterals of the VST terminate in the lateral reticular nucleus (LRN). Ascending uncrossed projections from LVN in the cat terminate in the medial rectus subdivision of the OMC.(ABSTRACT TRUNCATED AT 400 WORDS)

Reticulospinal and vestibulospinal pathways in the snake Python regius

In the present HRP study extensive reticulospinal projections and more modestly developed vestibulospinal pathways have been demonstrated in the snake Python regius. The funicular trajectories of the main reticulospinal pathways have been shown: via the lateral funiculus pass spinal projections of the nucleus reticularis superior pars lateralis, the nucleus reticularis inferior and nucleus raphes inferior; via the ventral funiculus fibers arising in the nucleus reticularis superior and nucleus reticularis medius. Spinal projections of the locus coeruleus and subcoeruleus area reach their targets via both the lateral and ventral funiculi. Two vestibulospinal pathways have been demonstrated: an ipsilateral tractus vestibulospinalis lateralis arising in the ventrolateral vestibular nucleus, and a contralateral tractus vestibulospinalis medialis from the descending and ventromedial vestibular nuclei. After HRP gel implants into the vestibular nuclear complex direct vestibulocollic projections to motoneurons in the rostral spinal cord were observed. Spinal projections from the ventral part of the nucleus reticularis inferior and the descending and ventromedial vestibular nuclei are mainly aimed at the thin "neck area" (approximately the first 50 spinal segments). This area is extensively used in such acts as orientation and prey-catching, requiring a rather delicate brain stem control.

Direct pathway from cardiovascular neurons in the ventrolateral medulla to the region of the intermediolateral nucleus of the upper thoracic cord: an anatomical and electrophysiological investigation in the cat

Horseradish peroxidase (HRP) and single unit recording experiments were done in cats to identify neurons in the ventrolateral medulla (VLM) projecting directly to the intermediolateral nucleus (IML) of the thoracic cord and relaying cardiovascular afferent information from the buffer nerves and hypothalamus. In the first series, HRP was allowed to diffuse from a micropipette into the region of the IML at the level of T2. After a survival period of 30-138 h, transverse and horizontal sections of the brainstem were processed according to the tetramethyl benzidine method. Labeled neurons were found in the VLM 1-5 mm rostral to the obex, bilaterally, but with an ipsilateral predominance. The majority were observed in sections 2-4 mm rostral to the obex, clustered in an area lateral to the inferior olivary nucleus around the intramedullary rootlets of the hypoglossal nerve. Additional labeled neurons were found scattered along the ventral surface of the medulla; most of these neurons were oval in shape, 15-30 micron in diameter, and had dendritic processes which lay parallel to the ventral surface. In the second series, the region of the VLM shown to contain labeled neurons was systematically explored for single units antidromically activated by electrical stimulation of the IML in chloralosed, paralyzed and artificially ventilated animals. These antidromically identified units were then tested for their responses to electrical stimulation of the carotid sinus (CSN) and aortic depressor (ADN) nerves, and the paraventricular nucleus (PVH). Ninety-four single units in the VLM were antidromically activated with latencies corresponding to a mean conduction velocity of 19.1 +/- 1.5 m/s. Of these units 52% (49/94) were orthodromically excited by stimulation of buffer nerves; 12 by stimulation of the CSN only (mean latency, 16.0 +/- 3.6 ms), 5 by stimulation of the ADN only (mean latency, 9.5 +/- 2.0 ms), 7 by both buffer nerves, and the remaining 25 units responded to at least one of the buffer nerves and to PVH. Stimulation of PVH excited orthodromically 42 of the 94 units (45%), of which 17 responded only to stimulation of PVH (mean latency, 17.9 +/- 3.5 ms). These experiments provide anatomical and electrophysiological evidence for the existence of a direct cardiovascular pathway from the VLM to the region of the IML and suggest that neurons in the VLM are involved in the integration of cardiovascular afferent inputs from buffer nerves and the hypothalamus to provide an excitatory input to vasoconstrictor neurons in the IML.

Long descending projections of the hypothalamus in the pigeon, Columba livia

An autoradiographic analysis was performed on the descending projections of nucleus periventricularis magnocellularis (PVM) of the hypothalamus in the pigeon. A PVM-medullospinal pathway was observed coursing posteriorly through the lateral hypothalamus, ventrolateral midbrain tegmentum, and into the spinal lemniscus (ls) in the ventrolateral pons and medulla. In the pons, some fibers course dorsomedially from ls and terminate at the lateral border of the locus coeruleus. At medullary levels, fibers from ls sweep dorsomedially in the plexus of Horsley and project to certain regions of the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (NX). Specifically, PVM fibers project heavily into NTS subnuclei medialis superficialis, medialis ventralis, and lateralis (sulcalis) dorsalis as well as into the ventral parvocellular subnucleus of NX. Fibers in ls were traced caudally into the lateral funiculus as far as upper cervical levels of the spinal cord. Although autoradiographs of lower cervical or thoracic spinal cord sections were not available, PVM fibers do descend to thoracic spinal cord levels, as evidenced by the retrograde transport of horseradish peroxidase. In addition to the medullospinal pathway, the autoradiographs demonstrated PVM projections to septum, diencephalon, and midbrain. Labeled PVM fibers are found in the lateral septal nucleus, nucleus of the anterior pallial commisure, dorsomedial thalamic nucleus, dorsolateral anterior thalamic nucleus (pars ventralis), median eminence, medial and lateral hypothalamus, medial mammillary area, and nucleus intercollicularis and central gray of the midbrain. The projection of fibers to medullospinal regions and median eminence suggests that PVM is homologous to the mammalian paraventricular nucleus. These projections to specific subnuclei of NTS and NX denote hypothalamic control over certain autonomic functions.

Studies of the principal sensory and spinal trigeminal nuclei of the rat: projections to the superior colliculus, inferior olive, and cerebellum

We have analyzed the connections between the sensory trigeminal nuclei and two major sensorimotor areas (i.e., the superior colliculus and crura I and II of the cerebellar cortex) in which tactile input from peri-oral and other facial regions is a prominent feature. Following injections of horseradish peroxidase into the superior colliculus, retrogradely labeled cells occupy the ventral one-third of the contralateral principal sensory and spinal trigeminal nucleus; trigeminocollicular neurons are especially numerous within the subnucleus interpolaris (Svi). Injections of either 3H-proline or horseradish peroxidase (HRP) into the Svi reveal that trigeminocollicular axons reach the rostral two-thirds to three-quarters of the contralateral superior colliculus, where they distribute in a nonuniform, patchy manner within layers IV-VI. In addition to demonstrating the trigeminocollicular projection, anterograde and retrograde transport studies of the Svi also reveal a trigeminoolivary projection which terminates primarily within the contralateral rostral dorsal accessory (DAO) and adjacent principal (PO) olives; some of the Svi neurons innervate both the superior colliculus and the DAO-PO via axon collaterals. Data from a final set of retrograde tracing experiments show that the trigeminorecipient zone of the DAO-PO contains neurons which project to crura I and/or II of the cerebellar cortex. Of the various submodalities conveyed by the trigeminal system, it is likely that the trigeminal connections we have demonstrated are carrying tactile information. This is indicated by the fact that responses to tactile stimulation of the face have been reported for cells in (1) the deeper collicular layers, (2) the trigeminorecipient zone of the DAO-PO, and (3) cerebellar targets of this zone, crura I and II. All data are discussed in the context of the anatomical and physiological literature.

Lateral reticular regions and the descending control of dorsal horn neurones of the cat: selective inhibition by electrical stimulation

In barbiturate-anaesthetized cats, brainstem sites were electrically stimulated while studying the synaptic responses of lumbar dorsal horn neurones. The excitation of these neurones by impulses in unmyelinated primary afferents was selectively inhibited by stimulation of the ventrolateral medulla in the region of the caudal lateral reticular nucleus. The significance of this inhibition was heightened by the finding that stimulus currents producing inhibition from this area were less effective in the raphé region and not effective at intervening or dorsal sites. Bilateral lesions of the inhibition-producing ventrolateral sites reduced tonic descending inhibition of the responses of dorsal horn neurones to impulses in C fibres. The lateral reticular regions of the medulla may thus exert a considerable control over the transmission of nociceptive information in the cat spinal cord.

Relation between cell size and response characteristics of medullary reticulospinal neurons to labyrinth and neck inputs

The activity of presumably inhibitory reticulospinal neurons with cell bodies located in the medial aspects of the medullary reticular formation and axons projecting to lumbosacral cord has been recorded in decerebrate cats and their response characteristics to sinusoidal stimulation of labyrinth receptors (134 neurons) and neck receptors (110 neurons) have been related to cell size inferred from the conduction velocity of the corresponding axons. No significant correlation was found between resting discharge and conduction velocity of the axons. Among the recorded reticulospinal neurons, 64/134 (i.e. 47.8%) units responded to roll tilt, while 66/110 (i.e. 60.0%) units responded to neck rotation (0.026 Hz, +/- 10 degrees). A positive correlation was found between gain (imp./s/deg) of the labyrinth and neck responses and conduction velocity of the axons. Thus, due to absence of correlation between resting discharge and conduction velocity of the axons, larger neurons exhibited a greater percentage modulation (sensitivity) to the labyrinth and the neck input than smaller neurons. These findings are attributed to an overall increase in density or efficacy of the synaptic contacts made by the vestibular and neck afferent pathways on reticulospinal neurons of increasing size. Units receiving neck-macular vestibular convergence showed on the average an higher gain of the neck (GN) response with respect to the labyrinth (GL) response (GN/GL: 1.95 +/- 1.49, S.D.; n = 43); however, due to a parallel increase in gain of the reticulospinal neurons to both neck and labyrinth inputs, the relative effectiveness of the two inputs did not vary in different units as a function of cell size. The reticulospinal neurons were mainly excited by the direction of animal orientation and/or neck displacement. In particular, most of these positional sensitive units were excited by side-up animal tilt (37/58, i.e. 63.8%) and by side-down neck rotation (47/60, i.e. 78.3%). These predominant response patterns were particularly found between large size neurons, whereas small size neurons tended to show also other response patterns. The evidence indicates that in addition to intrinsic neuronal properties related to cell size, the quantitative and qualitative organization of synaptic inputs represents the critical factor controlling the responsiveness of reticulospinal neurons to vestibular and neck stimulation.

The distribution of substance P-containing neurons in the cat Edinger-Westphal nucleus: relationship to efferent projection systems

The light microscopic localization of substance P-like immunoreactivity (SPLI) was examined in the cat Edinger--Westphal complex using the peroxidase--antiperoxidase method. A high density of cell bodies and processes staining for SPLI were found in the caudal part of the Edinger--Westphal complex (EWc) capping the somatic divisions of the oculomotor nucleus. This distribution continued rostrally into the anteromedian nucleus (AM). Cells labeled with SPLI were also found arranged in a thin layer dorsally capping the oculomotor nucleus, and scattered cells were found in the periaqueductal gray region at the same level. This distribution of SPLI-positive cells was then compared with the distribution of cells in EWc and AM that are retrogradely labeled by horseradish peroxidase or Nuclear Yellow injections into spinal cord, cerebellum, or ciliary ganglion. Injections of horseradish peroxidase into both cervical and lumbar cord labeled a large number of cells throughout the length of EWc and the more rostral AM. A similar pattern of labeling was seen following injections of Nuclear Yellow into the deep cerebellar nuclei. In contrast, cells innervating the ciliary ganglion were found predominantly outside of the Edinger--Westphal complex in AM, the rostral periaqueductal region, and the tegmentum ventral to the oculomotor complex. The distribution of cells projecting to spinal cord or cerebellum and the pattern of SPLI staining was found to closely overlap, evidence that substance P may be contained in cells that give rise to the central projections of the Edinger--Westphal complex.

Diamidino yellow dihydrochloride (DY . 2HCl); a new fluorescent retrograde neuronal tracer, which migrates only very slowly out of the cell

Earlier studies showed that Nuclear Yellow (NY), True Blue (TB) and Fast Blue (FB) are transported retrogradely through axons to their parent cell bodies. NY produces a yellow fluorescent labeling of the neuronal nucleus at 360 nm excitation wavelength, while TB and FB produce a blue fluorescence of the cytoplasm at this same wavelength. Therefore, NY may be combined with TB or FB in double-labeling experiments demonstrating the existence of axon collaterals. However, retrograde neuronal labeling with TB or FB requires a relatively long survival time, while NY requires a short survival time since NY migrates rapidly out of the retrogradely labeled neurons. This complicates double-labeling experiments since TB and FB must be injected first and NY later, a short time before the animal is sacrificed. We report a new yellow fluorescent tracer which labels mainly the nucleus and migrates much more slowly out of the retrogradely labeled neurons than NY. This new tracer can be used instead of NY in combination with TB or FB in double-labeling experiments and unlike NY can be injected at the same time as TB or FB. The new tracer is a diamidino compound (no. 28826) which is commercially available. It will be referred to as Diamidino Yellow Dihydrochloride (DY . 2HCl). According to the present study DY . 2HCl is transported over long distances in rat and cat, and produces a yellow fluorescence of the neuronal nucleus at 360 nm excitation wavelength, resembling that obtained with NY. When combined with TB or FB, DY . 2HCl is as effective as NY in double labeling of neurons by way of divergent axon collaterals.

Projections from brain stem nuclei to the spinal trigeminal nucleus in the cat

Afferent projections to the trigeminal nucleus oralis and caudalis from the brain stem have been investigated by the use of retrograde transport of horseradish peroxidase in the cat. Both n. oralis and n. caudalis receive a projection from nucleus raphe magnus but not from other raphe nuclei in the medulla or pons. N. oralis and n. caudalis receive a bilateral projection from n. paragigantocellularis lateralis. N. oralis receives a projection from n. reticularis gigantocellularis and n. reticularis parvocellularis but not from n. reticularis magnocellularis. N. caudalis receives only sparse projections from n. reticularis gigantocellularis, n. reticularis parvocellularis and n. reticularis magnocellularis but receives an input from a layer of cells over the pyramids in the rostral medulla, here named n. paramagnocellularis ventralis. The study also revealed the presence of ascending and descending interconnections between n. oralis and n. caudalis, as well as contralateral trigeminal interconnections. Projections from the medial vestibular nuclei, n. praepositus hypoglossi and the facial nucleus to the spinal trigeminal nucleus were also noted. Since the spinal trigeminal nucleus has only sensory functions, the results indicate the source of projections, mainly from raphe and reticular nuclei, which are involved in sensory control in the trigeminal system.

Edinger-Westphal neurons that project to spinal cord contain substance P

Combined retrograde transport and immunocytochemical methods were used to determine whether Edinger-Westphal neurons projecting to spinal cord also demonstrate substance P-like immunoreactivity (SPLI). Large injections of horseradish peroxidase (HRP) into cervical and lumbar enlargements retrogradely labeled cells throughout the length of the Edinger-Westphal complex (EW). Nearly all HRP-labeled EW neurons also stained for SPLI, evidence that EW is the origin of a direct substance P pathway linking rostral mesencephalon with spinal cord.

Efferent connections of the subfascicular area of the mesodiencephalic junction and its possible involvement in stimulation-produced analgesia

Stimulation-produced analgesia (SPA) can be induced in animals and humans from an ill-defined area of the mesodiencephalic junction lying beneath the parafascicular complex of the medial thalamus. Neurons projecting to the spinal cord, the subnucleus caudalis of the trigeminal complex, the nuclei raphé magnus and dorsalis, the inferior olivary complex and the amygdala could be observed in this area, using the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. On the basis of the locations of the neurons projecting to these different areas, 3 subnuclei were delineated: the rostral interstitial nucleus of the MLF lying laterally along the medial tip of the medial lemniscus, containing a few neurons projecting to the raphé nuclei and the inferior olivary complex; the subparafascicular nucleus (spf) lying medially in the rostralmost part of the area and containing neurons projecting to the amygdala and basal ganglia; the subfascicular area of the mesodiencephalic junction lying medially and caudal to the spf and containing neurons projecting to the raphé nuclei, the inferior olive, the caudalis subnucleus of the trigeminal complex and the spinal cord. The possibility that the subfascicular area of the mesodiencephalic junction is the effective site for SPA is discussed.

Morphology and location of tectal projection neurons in frogs: a study with HRP and cobalt-filling

Tectal projection neurons were labeled by retrograde transport of horseradish peroxidase (HRP) or cobaltic-lysine. The tracer substances were delivered iontophoretically or by pressure injection or diffusion into various regions of the brain or spinal cord. Histochemical procedures allowed identification of labeled cells projecting to the injected regions. Many neurons were filled with cobaltic-lysine, resulting in a Golgi-like staining. After cobalt injections in the diencephalon most of the labeled cells, identified as small piriform neurons, were located in layer 8 of the tectum. Two types of small piriform neurons were distinguished. Type 1 neurons have flat dendritic arborizations confined to lamina D, while the dendrites of type 2 cells may span all of the superficial tectal strata. In smaller numbers large piriform, pyramidal, and ganglionic cells of the periventricular tectal layers were labeled after diencephalic injections. Rhombencephalic cobalt and HRP injections labeled cells whose axons form the tectobulbospinal tract. The neurons most frequently labeled were large ganglionic cells. Ipsilaterally, the majority of their somata were located in layer 7, and their dendrites arborized mainly in lamina F. Contralaterally, labeled ganglionic cell somata occupied the top of layer 6, and most of their dendritic end-branches entered lamina B. The possible functional significance of this anatomical arrangement is discussed. After tectal cobalt injections the topography of the tectoisthmic projection and the terminals of tectal efferent fibers in the diencephalon and brainstem were observed. It is concluded that the organization of frog tectofugal pathways is very similar to that of mammals.

The sources of supraspinal afferents to the spinal cord in a variety of limbed reptiles. I. Reticulospinal systems

Horseradish peroxidase was injected into various levels of the spinal cord of turtles (Pseudemys and Chrysemys), lizards (Tupinambis, Iquana, Gekko, Sauromelus, and Gerrhonotus), and a crocodilian (Caiman). The results suggest that brainstem reticulospinal projections in limbed reptiles rival mammalian reticulospinal systems in complexity. The reptilian myelencephalic reticular formation can be divided into four distinct reticulospinal nuclei. Reticularis inferior pars dorsalis (RID) contains multipolar neurons which project bilaterally to the spinal cord. Reticularis inferior pars ventralis (RIV), which is only found in lizards and crocodilians, contains fusiform neurons with horizontally running dendrites and it projects ipsilaterally to the spinal cord. Reticularis ventrolateralis (RVL), which is found only in field lizards, contains triangular neurons whose dendrites parallel the ventrolateral edge of the brainstem and it projects ipsilaterally to the spinal cord. The myelencephalic raphe (RaI) varies considerably. RaI of turtles contains large reticulospinal neurons which form a continuous population with more laterally situated RID cells. RaI of lizards contains a few small reticulospinal neurons. RaI of the crocodilian Caiman contains giant reticulospinal neurons with laterally directed dendrites. The caudal metencephalic reticular formation of reptiles can be divided into two distinct reticulospinal nuclei. Reticularis medius (RM) contains large neurons with long, ventrally directed dendrites; it projects ipsilaterally to the spinal cord. Reticularis medius pars lateralis (RML) contains small neurons with laterally directed dendrites; it projects contralaterally to the spinal cord. The rostral mesencephalic and caudal mesencephalic reticular formation of reptiles can be divided into three distinct reticulospinal nuclei. Reticularis superior pars medialis (RSM) consists mostly of small, spindle-shaped neurons which project bilaterally to the spinal cord. In the lizard Tupinambis, however, large multipolar, ipsilaterally projecting neurons are occasionally seen in RSM. Reticularis superior pars lateralis (RSL) contains large, ipsilaterally projecting neurons with long, ventrolaterally directed dendrites. SRL in lizards can be divided into a dorsomedial portion, which projects ipsilaterally to the spinal cord, and a ventrolateral portion which projects contralaterally. The locus ceruleus-subceruleus field (LC-SC) contains small spindle-shaped neurons which project bilaterally to the spinal cord. Labelled reticulospinal neurons were also observed in the rostral metencephalic raphe (RaS) of the turtle brainstem. These cells are small, spindle-shaped neurons which resemble the small cells of the adjacent RSM field.

Noradrenergic projections to the spinal cord of the rat

Noradrenergic terminals were identified in the spinal cord of rats by immunocytochemical staining for dopamine-beta-hydroxylase. Although immunoreactive fibers and terminals were observed throughout the spinal grey matter, heavier accumulations of terminal labeling were observed in the marginal layer of the dorsal horn, in the ventral horn among motoneurons, and in the autonomic lateral cell columns of the thoracic and sacral spinal cord. Two specific retrograde transport techniques were employed to identify the origins of these noradrenergic terminations in the spinal cord. Cells of origin were observed in the locus coeruleus, the subcoeruleus, the medial and lateral parabrachial, and the Kölliker-Fuse nuclei, as well as adjacent to the superior olivary nucleus. These regions correspond to the A5-A7 cell groups of the pons. No spinally projecting noradrenergic cells were ever observed in the medulla. It was concluded that pontine noradrenergic cell groups are the sole source of noradrenergic terminals in the spinal cord.

An electrophysiological analysis of caudally-projecting neurones from the hypothalamic paraventricular nucleus in the rat

Using anaesthetized rats, experiments were performed to test whether neurones located in the hypothalamic paraventricular nuclei and sending axons caudally, could be identified electrophysiologically. Neurones projecting caudally were localized by antidromic invasion following electrical stimulation within the region of the dorsal motor nucleus of the vagus, the nucleus of the tractus solitarius and the hypoglossal nucleus. Stimulation of more ventral regions in the medulla oblongata was not effective. Caudally-projecting neurones were dispersed throughout the paraventricular nuclei and were often found close to magnocellular neurones antidromically invaded by stimulation of the pituitary stalk. About one-third of the caudally-projecting neurones were synaptically activated by pituitary stalk stimulation, but only at currents sufficient to antidromically invade the magnocellular neurones. This suggests a synaptic interaction between magnocellular and some caudally-projecting paraventricular neurones. The possible physiological significance of these findings is discussed.

Hyperalgesia and the reduction of monoamines resulting from lesions of the dorsolateral funiculus

Unilateral lesions of the dorsolateral funiculus (DLF) in the rat resulted in unilateral hyperalgesia as revealed by a hindpaw withdrawal test to heat. Larger lesions involving the dorsal column and ventrolateral quadrant did not cause hyperalgesia. The levels of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), noradrenaline (NA) and dopamine (DA) were measured in the lumbar dorsal quadrant using high performance liquid chromatography (HPLC). In hyperalgesic animals DLF lesions caused an ipsilateral reduction of all the amines and a contralateral reduction of 5-HT and NA. This suggests that serotonergic and noradrenergic axons in the DLF give a contralateral innervation. A correlation was sought between the reduction of amine level and the degree of hyperalgesia shown by individual rats on lesioned and unlesioned sides of the cord. No consistent correlation was found with any of the amines.

Projections of upper structure to the spinal cardioacceleratory center in cats: an HRP study using a new microinjection method

We studied, with the horseradish peroxidase (HRP) method, the supraspinal structure projections to the cardioacceleratory center in the intermediolateral nucleus (ILN) of T3-4 segments of the cat spinal cord. A fiber-filled double-barrel coaxial electrode was devised. The inner barrel electrode, filled with 3 M NaCl solution, was used for stimulating intraspinal structures to determine the cardioacceleratory center. The outer barrel electrode with an Agar stop, filled with a 20% HRP solution, was used for injecting HRP by pulses of positive electric current. In every experiment, HRP was injected into 3 points within the cardioacceleratory center at intervals of 1 mm. Out of 36 experiments, 10 showed that the HRP injection sites were centered in and almost confined to the ILN, and the population of the HRP-labeled cells was not less than 50. Some 1146 HRP-labeled cells were thus identified. They were distributed in the medulla oblongata (72.1%), pons (10.2%), midbrain (8.5%) and hypothalamus (9.2%). They were concentrated in the medullary reticular formation (37.8%), median raphe (26.9%) and pontine reticular formation (10.2%). Contrary to expectation, the HRP-labeled cells were few in the nucleus tractus solitarii (3.7%), paraventricular hypothalamic area (3.3%) and nucleus locus coeruleus (none).

Sympathoadrenal preganglionic neurons: their distribution and relationship to chemically-coded fibers in the kitten intermediolateral cell column

The location of those sympathetic preganglionic neurons in the spinal cord that project to the adrenal medulla--the sympathoadrenal preganglionic (SAP) neurons--was studied by the method of retrograde axonal transport of the fluorescent dye Fast Blue. The distribution of chemically-coded fibers and their relationship to the SAP neurons was also investigated using the indirect immunofluorescence technique. In kittens, 5 microliters of a 1% solution of Fast Blue was injected into the medulla of the left adrenal gland. After a survival period of 5 days, the spinal cords from C8 to L5 were sectioned and processed for the localization of enkephalin-, neurophysin-, oxytocin-, serotonin-, substance P- and somatostatin-like immunoreactivity. Retrogradely labeled neurons were found in the ipsilateral intermediolateral cell column (IML) (89.8% of all retrogradely labeled neurons) from T1 to L4, and in the contralateral IML (10.2%) from T1 to L4. The enkephalin, serotonin and substance P immunoreactive fibers appeared to surround both the retrogradely labeled and unlabeled IML neurons. The somatostatin immunoreactive fibers were observed only in proximity to the retrogradely labeled neurons. Only a sparse population of neurophysin and oxytocin immunoreactive fibers were observed in IML, and were not seen to be in apposition to the retrogradely labeled neurons.

Hypothalamic pathways involved in metabolic regulatory functions, as identified by track-tracing methods

The present review of the fiber connections of the hypothalamus has been concerned basically with recent data obtained by the aid of the autoradiographic and HRP tracer techniques. Evidence presented has shown that, besides confirming many of the older data, recent studies have resulted in the introduction of several conceptual modifications into the classic picture of hypothalamic hodological relationships. Among these conceptual modifications, the following can be mentioned: (1) the medially placed nuclei of the hypothalamus have a great number of long efferent and afferent connections with many extrahypothalamic structures; (2) many hypothalamic nuclei send direct projections to cell territories in the brainstem and spinal cord that contain preganglionic autonomic motor neurons; (3) several neural districts that lie caudal to the mesencephalon send direct projections to the hypothalamus; (4) in addition to the olfactory channel, other sensory pathways (including interoceptive and gustatory conduction lines) have a relatively direct access to hypothalamic mechanisms; (5) the hypothalamus sends fibers to several brainstem territories that give rise to widespread monoaminergic projections; and (6) there are anatomical pathways that establish reciprocal connections between the hypothalamus and the basal ganglia. Some of the possible physiological correlates of these anatomical findings in the context of metabolic regulatory functions have been briefly indicated.

Cytoarchitecture, neuronal morphology, and some efferent connections of the interstitial nucleus of Cajal (INC) in the cat

This study describes the cytoarchitecture and neuronal morphology of the interstitial nucleus of Cajal (INC) in the cat. In addition, the efferent projections of this nucleus to the spinal cord and inferior olive were studied by retrograde labelling with horseradish peroxidase (HRP). The INC was shown to extend rostrocaudally for slightly more than 2 mm. Caudally, the nucleus consists of a small number of loosely aggregated neurons lying lateral to the ventral periaqueductal gray matter at a rostrocaudal level corresponding to the rostral one-fifth of the somatic cell columns of the oculomotor nucleus. Rostrally, the INC increases in size and reaches its maximum development in its rostral half, where it lies ventrolateral to the nucleus of Darkschewitsch (ND). Rostrally the INC is bounded by the dorsoventrally aligned fibres of the fasciculus retroflexus. Two groups of neurons could be distinguished within the INC in both normal and HRP-injected material. One group consists of a relatively small number of large, oval, pyramidal, fusiform, or multipolar neurons with mean dimensions of 40 X 26 micrometers. The second group consists of numerous small to medium-sized neurons with mean dimensions of 20 X 14 micrometers. Large neurons and some cells of the second group contain substantial amounts of Nissl substance throughout their perikarya. Some medium-sized to small neurons exhibit indentations in their nuclei, and glial cells are often apposed to their cell membranes. Golgi-Kopsch preparations taken from kitten showed that INC neurons possess sparsely branched, radiating dendritic trees with few spinous processes. The majority of INC neurons retrogradely labelled with HRP exhibited similar dendritic patterns. Injections of HRP into lesions at cervical, thoracic, or lumbar levels of the spinal cord resulted in retrograde labelling of neurons of all sizes and shapes throughout the entire length of the INC. However, the greatest number of HRP-labelled cells in INC were observed subsequent to injections of the enzyme into cervical levels of the cord. Following injections of HRP into the inferior olive only small to medium-sized neurons were labelled in the nucleus, the majority of which are located in rostral levels of the INC. A substantial olivary projection was observed to originate in the nucleus of Darkschewitsch (ND) and the nucleus parafascicularis (NPF). The sizes of the projections from these two nuclei to the inferior olive appeared to be much larger than that from the INC. Smaller numbers of neurons were also observed in the rostral parvocellular red nucleus (RN) and mesencephalic reticular formation (MRF).

The influence of the paraventriculo-spinal pathway, and oxytocin and vasopressin on sympathetic preganglionic neurones

In anaesthetized rats the effect of two procedures was studied on antidromically identified sympathetic preganglionic neurones (SPN) in the second thoracic (T) segment of the spinal cord: the application of iontophoresed oxytocin and vasopressin, and bipolar electrical stimulation of the paraventricular nucleus of the hypothalamus (PVN). In the majority of cases (16/23) oxytocin inhibited SPN firing, 1/23 being excited. Vasopressin inhibited 8/14 neurones and excited 4/14. PVN stimulation inhibited SPN apparently by an action on the membrane of SPN. The possibility that oxytocin and vasopressin act as transmitters in the paraventriculo-spinal pathway, and their possible involvement in the mediation of PVN evoked inhibition of SPN activity has been discussed.

Spinal projections from the periaqueductal grey and dorsal raphe in the rat, cat and monkey

There is considerable evidence that the periaqueductal grey and the dorsal raphe contribute to an endogenous analgesia system and to the regulation of a wide variety of other responses, many of which involve spinal sites of action. To map the areas of the periaqueductal grey and dorsal raphe which contain neurons that project to the spinal cord, wheat germ agglutinin conjugated to horseradish peroxidase was injected into hemisected spinal cords in rat, cat, and monkey. After cervical or lumbar injections labelled neurons were found in the periaqueductal grey and dorsal raphe in all species examined. In the rat, labelling of the dorsal raphe is sparse but numerous labelled neurons are present in the mid and rostral periaqueductal grey. In the cat, the number of retrogradely-labelled neurons in both the dorsal raphe and the periaqueductal gray are considerable. In the monkey, like the rat, the labelling in the dorsal raphe was light but numerous labelled neurons were present in the periaqueductal grey and the adjacent nucleus cuneiformis. Injections into the lumbar spinal cord produced the same pattern of labelling as seen after cervical level injections with approximately 40% fewer labelled cells in all areas. Thus, while each species had a similar pattern of spinal projections from the periaqueductal grey and dorsal raphe, quantitative differences were evident among the species examined. These results suggest that the number of periaqueductal grey and dorsal raphe neurons projecting to the spinal cord in the rat, cat and monkey are considerably more numerous than previously reported and that the effects described during the stimulation of these regions could be, at least partly, due to the involvement of these direct pathways.

The distribution of corticotropin releasing factor-like immunoreactive neurons in rat brain

Using the indirect immunofluorescent technique, corticotropin releasing factor (CRF)-like immunoreactive nerve fibers and cell bodies were observed to be widely distributed in rat brain. A detailed stereotaxic atlas of CRF-like immunoreactive neurons was prepared. Large numbers of CRF-containing perikarya were observed in the nucleus paraventricularis, with scattered cells in the following nuclei: accumbens, interstitialis stria terminalis, preopticus medialis, supraopticus, periventricularis hypothalami, amygdaloideus centralis, dorsomedialis, substantia grisea centralis, parabrachialis dorsalis and ventralis, tegmenti dorsalis lateralis, vestibularis medialis, tractus solitarius and reticularis lateralis. The most intense staining of CRF-containing fibers was observed in the external lamina of the median eminence. Moderate numbers of CRF-like fibers were observed in the following nuclei: lateralis and medialis septi, tractus diagonalis, interstitialis stria terminalis, preopticus medialis, supraopticus, periventricularis thalami and hypothalami, paraventricularis, anterior ventralis and medialis thalami, rhomboideus, amygdaloideus centralis, habenulae lateralis, dorsomedialis, ventromedialis, substantia grisea centralis, cuneiformis, parabrachialis dorsalis and ventralis, tegmenti dorsalis lateralis, cerebellum, vestibularis medialis, reticularis lateralis, substantia gelatinosa trigemini and lamina I and II of the dorsal horn of the spinal cord. The present findings suggest that a CRF-like peptide may be involved in a neurotransmitter or neuromodulator role, as well as a hypophysiotropic role.

Spinal cord development in anuran larvae: II. Ascending and descending pathways

The ontogeny of ascending and descending spinal pathways was examined in bullfrog (Rana catesbeiana) tadpoles using the transported histochemical marker, horseradish peroxidase (HRP). The adult pattern of brainstem projections to lumbar spinal cord is evident as early as larval stage I (Taylor and Kollros, Anat. Rec., 94:7-24, 1946), although the number and size of projecting cells increases as the animal matures. These projections arise from presumptive hypothalamic neurons at the diencephalic-mesencephalic border as well as from neurons of the vestibular nucleus, oculomotor nucleus, and reticular formation. In contrast to the stability of the pattern of descending projections, the sources of fibers ascending to the brainstem change during larval life. In early larval stages, brainstem projections from lumbar spinal cord arise primarily from Rohon-Beard cells and neurons of the superficial dorsal horn. In later stages, neurons in the intermediate and ventral areas of the spinal gray can also be retrogradely labeled by HRP application to the brainstem at the level of the VIIIth nerve. Evidence of the existence of dorsal column and lateral cervical nuclei in adult frog and tadpoles older than stage VIII is presented. The ascending projections of embryonically born primary neurons were also investigated. Rohon-Beard cells, which are sensory neurons with their cell bodies in the spinal cord, were found to send ascending processes as least as far rostral as the level of the VIIIth nerve entry zone. Anterolateral and dorsal marginal cells, probable homologs, respectively, of mammalian spinal border cells and cells of Waldeyer (1888), were also found to project rostrally at least to the rhombencephalon. These marginal cells persisted through metamorphosis into adulthood.

Organization of tectospinal neurons in the cat and rat superior colliculus

Neurons in the superior colliculus which send axons to the spinal cord were identified by the retrograde axonal transport method. Injections of the retrograde axonal tracer, horseradish peroxidase, made into different levels of the cervical spinal cord indicate that the spinally projecting neurons in the superior colliculus are topographically organized. Tectospinal neurons projecting to the rostral segments of the cervical spinal cord are found over a larger extent of the contralateral superior colliculus than those terminating in the cervical enlargement. The tectospinal projection to the cervical enlargement in both rats and cats arises almost exclusively from the caudolateral quadrant of the contralateral superior colliculus, whereas the tectal projection to the rostral (upper) cervical spinal cord originates, in cats, from almost the entire extent of the colliculus and, in rats, from its greater part. No evidence for tectospinal projections to the thoracic or lumbar levels of the spinal cord was found. In the context of the hypothesis that, in these species, head and body movements which orient the animal toward stimuli in its environment may be mediated by the superior colliculus, these data are consistent with the view that direct tectospinal connections may play a role in such movements.

Raphespinal projections in the North American opossum: evidence for connectional heterogeneity

Retrograde transport studies revealed that the nuclei pallidus, obscurus, and magnus raphae as well as the adjacent reticular formation innervate the spinal cord in the opposum. HRP-lesion experiments showed that a relatively large number of neurons within the nucleus obscurus raphae and closely adjacent areas of the nucleus reticularis gigantocellularis project through the ventrolateral white matter and that many cells within the nucleus magnus raphae, the nucleus reticularis gigantocellularis pars ventralis, and the nucleus reticularis pontis pars ventralis contribute axons to the dorsal half of the lateral funiculi. Neurons within the rostral pole of the nucleus magnus raphae and the adjacent nucleus reticularis pontis pars ventralis may project exclusively through the latter route. Each of the above-mentioned raphe and reticular nuclei contain nonindolaminergic as well as indolaminergic neurons (Crutcher and Humbertson, '78). When True-Blue was injected into the spinal cord and the brain processed for monoamine histofluorescence evidence for True-Blue was found in neurons of both types. Injections of 3H-leucine centered within the nuclei pallidus and obscurus raphae and/or the closely adjacent nucleus reticularis gigantocellularis labeled axons within autonomic nuclei and laminae IV-X. Labeled axons were particularly numerous within the intermediolateral cell column and within laminae IX and X. Injections of the caudoventral part of the nucleus magnus raphae or the adjacent nucleus reticularis gigantocellularis pars ventrialis labeled axons in the same areas as well as within laminae I-III. When the injection was placed within the rostral part of the nucleus magnus raphae or the adjacent nucleus reticularis pontis pars ventralis axons were labeled within laminae I-III and external zones of laminae IV-VII, but not within lamina IX. The immunohistofluorescence method revealed evidence for indolaminergic axons in each of the spinal areas labeled by injections of 3H-leucine into the raphe and adjacent reticular formation. They were particularly abundant within the intermediolateral cell column and within laminae IX and X. These data indicate that raphe spinal systems are chemically and connectionally heterogeneous.

Medullary axonal projections of respiratory neurons of pontile pneumotaxic center

In decerebrate, cerebellectomized, vagotomized, paralyzed and ventilated cats, activities were recorded from the phrenic nerve and single respiratory neurons in the area of the nucleus parabrachialis medialis and Kölliker-Fuse nucleus. Stimuli were delivered in the medulla and cervical spinal cord to elicit antidromic action potentials for these neurons and, hence, establish their axonal projections. Antidromic activation was obtained for 18 of 193 neurons following medullary stimulations. Following spinal stimulations, only two respiratory neurons exhibited some responses characteristic of antidromic activation. In the same pontile areas, a number of neurons with no respiratory-modulated or spontaneous activities were antidromically activated by medullary or spinal stimulations. Results are considered in the context of neuroanatomical studies which have established possible interconnections within the brainstem respiratory control system, and hypotheses for functions of the pontile pneumotaxic center in ventilatory control.

The distribution of serotonin, met-enkephalin and beta-lipotropin-like immunoreactivity in neuronal perikarya of the cat brainstem

The distribution of methionine-enkephalin, serotonin and beta-lipotropin-containing neurones has been mapped immunohistochemically in the brainstem of the cat after local colchicine injections. Serotonin-containing neurons were found in th raphe in nucleus raph magnus (NRM), nucleus raphe pallidus (NRP) and nucleus raphe obscurus (NRO) and in a band extending cross the ventral reticular formation into nucleus paragigantocellularis lateralis (PGL) and nucleus lateralis reticularis (LRM). Enkephalin-positive cell bodies were also found in these raphe nuclei and in most divisions of the caudal reticular formation. Double labelling studies established that enkephalin and serotonin co-exist within some neurons in NRM and NRP. beta-Lipotropin-positive cell bodies were found principally within NRP and within the ventrolateral reticular formation in PGL and LRM.