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A D Loewy

Publications and source records attributed to A D Loewy.

At least 91 records · Page 5Linked to original sources
PubMed1981

Organization of some brain stem afferents to the paraventricular nucleus of the hypothalamus in the rat.

Brain stem afferents to subnuclei of the paraventricular nucleus of the hypothalamus were studied by the anterograde autoradiographic technique in the rat. The parabrachial nuclei and locus coeruleus project to the posterior, periventricular, parvocellular and dorsal divisions. The ventral medulla projects to the posterior, medial, lateral, parvocellular and dorsal divisions. The A1 catecholamine cell group projects to the posterior, medial, lateral, parvocellular and dorsal divisions, and the nucleus of the solitary tract to the parvocellular and dorsal divisions. The A1 region and the ventral medulla also project to the supraoptic nucleus.

Afferent Pathways↗
PubMed1981

A morphological study of cat dorsal spinocerebellar tract neurons after intracellular injection of horseradish peroxidase.

This work represents an attempt to elucidate structural features of electrophysiologically characterized, individual cat dorsal spinocerebellar tract (DSCT) neurons by using intracellular application of horseradish peroxidase (HRP). Intracellular recordings and HRP injections were made in DSCT neurons of the Clarke's column in cat lumbar (L3) spinal cord. The units were identified by antidromic invasion following electrical stimulation of the ipsilateral dorsolateral funiculus at C1. In addition, sensory inputs to the DSCT neurons were determined by natural (adequate) stimuli applied to the hind limb with intact innervation. The morphological analysis is based on data obtained from 19 well-stained electrophysiologically identified neurons located in Clarke's column. Thirteen of these units received excitatory sensory inputs from muscle receptors, two were activated by cutaneous afferents only, and four had a convergent (muscle + cutaneous) input. The DSCT--muscle cells were equivalent to the large Clarke cells (class C of Leowy, '70). Their dendrites were oriented primarily in the rostro--caudal direction (up to 2500 micron) and appeared generally smooth except for some branchlets. In four of these cells, the axon was traced into the lateral funiculus. In light microscopic analysis there was no evidence that axon collaterals arose from these axons during the initial trajectory through the spinal grey matter. The four DSCT--convergent neurons were similar in shape to the DSCT--muscle units although they appeared to have somewhat smaller cell bodies. Of the two DSCT--cutaneous neurons one was found to be of the B type, with the dendritic tree having fewer branches and oriented mainly in the medio--lateral direction. The other cell, however, turned out to be similar in appearance to the C type Clarke neurons.

Afferent Pathways↗
PubMed1981

Descending pathways to sympathetic and parasympathetic preganglionic neurons.

In this review a summary of some of the neural pathways that appear to be involved in central cardiovascular control is given. The efferent connections of the nucleus tractus solitarius are described. Particular emphasis is placed on those projections that go to nuclei that have direct connections with the intermediolateral cell column (viz. paraventricular hypothalamic nucleus, Kõlliker-Fuse nucleus, A5 catecholamine cell group, the chemosensitive region of the ventral medulla, and possibly the region of the A1 catecholamine cell group). In addition, some fo these nuclei also have direct or indirect connections with the paraventricular and/or supraoptic hypothalamic nuclei. This suggests that some of the pathways that project to the cardiovascular preganglionic neurons may also influence the release of vasopressin.

Amygdala↗
PubMed1981

The role of descending monoaminergic systems in central control of blood pressure.

The descending projections to the intermediolateral cell column arise from several sources. The serotonergic inputs come from the raphe pallidus, raphe obscurus, raphe magnus nuclei, and ventral medulla. The A5 cell group provides a norepinephrine input to the intermediolateral cell column and the A1 cell group appears to be the main source of the epinephrine input. The functional role of monoamines on sympathetic preganglionic neurons is unclear. Iontophoresis studies indicate that serotonin excites and norepinephrine inhibits sympathetic preganglionic neurons. Pharmacological studies indicate that an alpha-2 receptor is located on or near these neurons. In contrast, electrical stimulation of the monoamine cell bodies produces opposite results. Stimulation of the raphe nuclei causes an inhibition of the sympathetic outflow whereas stimulation of some of the noradrenergic cell groups causes pressor responses. The role of monoamines in various cardiovascular reflexes and in experimental hypertension is discussed.

Animals↗
PubMed1980

Efferent connections of the parabrachial nucleus in the rat.

The efferent connections of the parabrachial nucleus have been analyzed in the rat using the anterograde autoradiographic method. Fibers originating from the lateral parabrachial nucleus (PBl) ascend in the periventricular system, the dorsal tegmental bundle and the central tegmental tract. The PBl projects to the dorsal raphe nucleus, the superior central raphe nucleus, and the Edinger-Westphal nucleus. It also innervates the intralaminar (centromedian, centrolateral, paracentral, parafascicular), the midline (paraventricular, reuniens), and the ventromedial basal (VMb) thalamic nuclei as well as much of the hypothalamus, including the dorsomedial, the ventromedial, the arcuate and the paraventricular nuclei, the lateral hypothalamic and the lateral preoptic areas. The PBl sends fibers via the ansa peduncularis into the amygdala, innervating the anterior, the central, the medial, the basomedial, and the posterior basolateral nuclei. In addition, it projects to the lateral part of the bed nucleus of the stria terminalis. Descending PBl fibers travel mainly through the ventrolateral medulla, passing through the region of the A1 and A5 catecholamine cell groups, the ventrolateral reticular formation and the region that contains parasympathetic preganglionic neurons. A small component travels in Probst's bundle to the ventral part of the nucleus of the solitary tract. Only a few PBl axons continue caudally into the lateral funiculus of the spinal cord, but these could not be followed beyond the first few cervical segments. The projections of the medial parabrachial nucleus (PBm) are similar to those of PBl, but two major differences have been noted. One difference is that the PBm provides a direct input to 4 regions of cerebral cortex: (1) the granular insular cortex; (2) the deep layers of the frontal cortex; (3) the septo-olfactory area; and (4) the infralimbic cortex. The other difference is that unlike the PBl, the PBm appears to provide almost no input to the medial hypothalamic nuclei (dorsomedial, ventromedial, arcuate nuclei) nor to the medial amygdaloid nucleus. The PBm projects heavily to the nucleus ambiguus and there was no evidence for an input to the nucleus of the solitary tract. The projections of the Kölliker-Fuse nucleus (KF) are distinct from those of either PBm or PBl. The KF projects via the central tegmental tract to the lateral hypothalamic area, the lateral preoptic area, and the central nucleus of the amygdala. The contralateral projection to the zona incerta, the lateral hypothalamic area, and the lateral preoptic areas is more prominent than the ipsilateral projections. Descending KF fibers travel mainly through the ventrolateral medullary reticular formation passing through regions which give rise to parasympathetic preganglionic fibers of the VIIth, IXth and Xth cranial nerves and the A1 and A5 catecholamine cell groups. In one experiment, fibers could be followed to the intermediolateral cell column of the upper thoracic spinal cord.

Animals↗
PubMed1980

The neuroanatomical basis of central cardiovascular control.

A brief review is given of some of the recent neuroanatomical studies of the central autonomic pathways. Two major points are discussed. 1) There are several descending inputs to the intermediolateral cell column that have recently been demonstrated; these include the A5 catecholamine cell group, certain of the raphe nuclei, the nucleus of the solitary tract, the Kölliker Fuse nucleus, and the paraventricular nucleus of the hypothalamus. 2) Certain nuclei of the brain that function as autonomic centers are extensively interconnected: the nucleus of the solitary tract, the parabrachial nucleus, the paraventricular nucleus of the hypothalamus, the central nucleus of the amygdala, and the bed nucleus of the stria terminalis. This network may play an important role in cardiovascular regulation and related neuroendocrine functions.

Amygdala↗
PubMed1978

Nuclei of the solitary tract: efferent projections to the lower brain stem and spinal cord of the cat.

The efferent projections from the solitary complex to the lower brain stem and spinal cord were studied in the cat with the autoradiographic anterograde axonal transport and retrograde horseradish peroxidase (HRP) techniques. A revised cytoarchitectonic description of the caudal two-thirds of the complex is presented in which the complex was subdivided into six nuclei: lateral, ventrolateral, intermediate, medial, parvocellular, and commissural solitary tract nuclei. Following injections of 3H amino acids into electrophysiologically defined regions of the complex in which cardiac or respiratory units were recorded, labeled fibers could be traced to a number of sites in the caudal brain stem including the medial and lateral parabrachial nuclei, Kölliker-Fuse nucleus and the area ventral to this nucleus, lateral periaqueductal gray matter, ambiguus complex, which consists of the retrofacial, ambiguus and retroambiguus nuclei, ventrolateral reticular nucleus (in an area equivalent to the A1 cell group of Dahlström and Fuxe, '64), medial accessory olive, paramedian reticular formation, and lateral cuneate nucleus. Descending solitario-spinal projections have been traced bilaterally, but predominantly to the contralateral side, to the region of the phrenic motor neurons in the C4-C6 ventral horn, to the thoracic ventral horn, and intermediolateral cell column. Confirmatory evidence of some of these projections was obtained from a series of HRP experiments. Mainly small neurons of the parvocellular, medial and commissural solitary tract nuclei project to the region of the parabrachial and Kölliker-Fuse nuclei. The lateral solitary nucleus projects almost exclusively to the ipsilateral medial accessory olive. It was not possible to interpret conclusively the labeling seen in the medium and large neurons of the ventrolateral solitary nucleus after HRP injections made in the region of the ambiguus-retroambiguus complex due to the problem of fibers of passage. Following injections of HRP into the cervical, thoracic, lumbar, or sacral spinal cord, retrograde cell labeling was seen in the solitary complex. Cells in the intermediate and commissural nuclei were labeled after all four types of experiments. In the ventrolateral nucleus, medium sized neurons were predominantly labeled after the cervical spinal cord experiments, while large sized neurons were labeled mainly after the thoracic spinal cord injections. The potential physiological significance of these connections is discussed in terms of central control of cardiovascular and respiratory functions.

Animals↗
PubMed1978

Edinger-Westphal nucleus: projections to the brain stem and spinal cord in the cat.

The efferent connections of the Edinger-Westphal (EW) nucleus of the cat have been examined using the autoradiographic anterograde axonal transport technique. Following injections of [3H]amino acids into the EW nucleus, fibers could be traced from this region to a number of sites in the caudal brain stem and spinal cord heretofore not known to receive an afferent input from this nucleus. Two descending pathways have been identified. One pathway travels in the medialmost aspect to the medial longitudinal bundle and terminates in the dorsal accessory olive. The other pathway leaves the nucleus laterally, coursing through the medial tegmentum, and then shifts to a ventrolateral position in the rostral rhombencephalon. Some fibers of this lateral pathway curve dorsally and terminate in the medial parabrachial nucleus. The remainder of this fiber system lies ventral to the spinal trigeminal complex, with some axons terminating in the subtrigeminal nucleus, while other fibers continue ventral to the caudal part of the spinal trigeminal nucleus and appear to terminate in the marginal layer and ventromedial part of this nucleus. Another component of this system terminates between the gracile and medial cuneate nuclei. The main pathways from the EW nucleus to the spinal cord include (1) some fibers which course through the dorsal column nuclei into the ventromedial part of the dorsal columns, and (2) other fibers which continue caudally immediately along the ventrolateral aspect of the spinal trigeminal nucleus and then proceed to the spinal cord in the region between the dorsal horn and the lateral cervical nucleus. These EW fibers appear to terminate mainly in Rexed's lamina I (marginal layer); other fibers, from both tracts appear to terminate in lamina V. There was no evidence for any ascending projections from the EW nucleus. Confirmatory data were obtained from a series of horseradish peroxidase (HRP) experiments, in which EW neurons were retrogradely labeled following injections into the dorsal column nuclei, spinal trigeminal nucleus, inferior olivary nucleus, or spinal cord. These results clearly indicate that the traditional view of the EW nucleus as merely a parasympathetic preganglionic nucleus should be seriously questioned.

Animals↗