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Biomedical subjects

M L Weiss

Publications and source records attributed to M L Weiss.

At least 19 recordsLinked to original sources
PubMed1995

Direct retinal communication with the peri-amygdaloid area.

Retinal projections to the basal forebrain in male Syrian hamsters were examined at the ultrastructural level following bilateral intraocular injections of horseradish peroxidase conjugated to either cholera toxin (CT-HRP) or wheat germ agglutinin (WGA-HRP). Light level microscopic analysis confirmed retinal projections along basal telencephalon, and examination on the electron microscope of individual fibers from the peri-amygdaloid area revealed en passant synaptic profiles. Sections from animals treated with WGA-HRP showed evidence of transsynaptic communication in the form of labeled dendrites in the peri-amygdaloid area. Taken together, these data show that the retina communicates directly with the periamygdaloid area, where photic and chemosensory information may be integrated to modulate reproductive behavior.

Amygdala↗
PubMed1992

Intravenous injection of Evans Blue labels magnocellular neuroendocrine cells of the rat supraoptic nucleus in situ and after dissociation.

Previous work has demonstrated that intravenous injection of neuronal tracers, e.g. horseradish peroxidase or Fast Blue, can retrogradely label neurons in brain areas that project outside the blood-brain barrier, e.g. magnocellular neuroendocrine neurons of the hypothalamus. Here we have shown that 24 h after intravenous injection of the fluorescent retrograde tracer Evans Blue, the same population of magnocellular neuroendocrine neurons is labeled in the paraventricular, supraoptic and accessory magnocellular nuclei. Parvicellular neuroendocrine cells in the paraventricular nuclei are also labeled. Most Evans Blue-labeled magnocellular neuroendocrine cells in the supraoptic nucleus could be stained immunocytochemically for neurophysins, suggesting that these neurons continue to produce their peptide hormones after taking up the fluorescent dye. Ultrastructural observation of supraoptic cells retrogradely labeled with Evans Blue shows that 95% of the neurons appeared healthy. There was no ultrastructural evidence of degeneration, hyperstimulation, or interruption of the axoplasmic flow. Labeling the neuroendocrine cells with Evans Blue did not alter the size of magnocellular cells, the animal's fluid balance or ingestive behavior. Following enzymatic/mechanical dissociation of the supraoptic nucleus from animals that had been injected with Evans Blue 24 h previously, phase-bright neurons that often contained fluorescent material were observed, thus identifying these neurons as neuroendocrine. Recording from identified neuroendocrine cells showed that these neurons generated spontaneous or current-evoked overshooting action potentials with an afterhyperpolarization and had negative resting membrane potentials. Action potential broadening, a feature of magnocellular neurons, was observed during bursts of action potentials elicited by depolarizing current injection. Taken together, this work would suggest that Evans Blue is non-toxic at the doses used and that it provides a method to identify single neuroendocrine cells in primary cell cultures made from adult hypothalamus for voltage-clamp recordings.

Animals↗
PubMed1992

Supraoptic nucleus afferents from the accessory olfactory bulb: evidence from anterograde and retrograde tract tracing in the rat.

Our earlier electrophysiological work provided evidence of a direct input to the supraoptic nucleus (SON) from the olfactory bulbs; however, these experiments could not determine if the input originated in the main and/or accessory portions of the olfactory bulb. Here, a connection between the accessory olfactory bulb (AOB) and the SON of the rat was examined using a combination of anatomic techniques. We employed neurophysin immunocytochemistry to delineate the morphological boundaries of the SON and the proximal arborizations of supraoptic dendrites. Accessory olfactory bulb efferents to the SON were studied by injection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the AOB. The distribution of retrogradely labeled cells within the AOB was also determined after injection of either rhodamine-labeled latex microspheres (rhodamine beads) or Fluoro-Gold (FG) into the SON. Neurophysin immunocytochemistry revealed that SON dendrites extended beyond the generally accepted boundaries of the nucleus, coursing ventrolaterally along the surface of the periamygdaloid cortex. Anterograde tract tracing with WGA-HRP labeled AOB efferents including a dense plexus of terminals and fibers around the ipsilateral SON along the path of the ventrally projecting dendrites. Injections of retrograde tracers into the SON resulted in rhodamine bead or FG labeling of mitral cells throughout the ipsilateral AOB. Taken together, these anatomic studies suggest a direct projection from the accessory olfactory bulb to the SON of the rat and thus a vomeronasal organ to SON pathway.

Afferent Pathways↗
PubMed1991

Retinohypothalamic tract in the female albino rat: a study using horseradish peroxidase conjugated to cholera toxin.

There are several anatomically and functionally distinct retinofugal pathways, one of which is the retinohypothalamic tract (RHT). In this study, horseradish peroxidase conjugated to cholera toxin (CT-HRP), a sensitive neural tracer, was employed to describe the RHT in the female albino rat. Following uniocular injection of CT-HRP, both medial and lateral components of the RHT were evident. The medial component swept caudally into and through the suprachiasmatic nucleus (SCN) and dorsally to the subparaventricular zone. Terminal label was seen in the medial preoptic region, peri-SCN area, retrochiasmatic area, periventricular nucleus, anterior and central parts of the anterior hypothalamic area, and the subparaventricular zone. In contrast to the more focused and symmetrical medial component, the lateral component was diffuse with light terminal label in the lateral preoptic region, olfactory tubercle, lateral hypothalamus, supraoptic nucleus, and medial and posteroventral medial amygdaloid nuclei. The striking exception to this diffuse pattern of the lateral component was an extremely dense columnar terminal field over the dorsal border of the supraoptic nucleus. Whereas the intensity of label in terminal fields of the medial component was often similar on the sides ipsilateral and contralateral to the injection, the lateral component was consistently asymmetrical with greater labeling on the side contralateral to the injection. In addition, a light projection arrived at several thalamic nuclei by returning toward the thalamus from the tectal or pretectal areas via stria medullaris, and thus was not a part of the RHT. Implications for circadian as well as noncircadian photobiologic effects are discussed.

Animals↗
PubMed1991

Retinofugal projections to the hypothalamus, anterior thalamus and basal forebrain in hamsters.

In Part a of the study, the retinal inputs to the hypothalamus, anterior thalamus and basal forebrain of Syrian hamsters were studied using intraocular injections of horseradish peroxidase conjugated to cholera toxin (CT-HRP). In the hypothalamus, the heaviest retinal input was to the suprachiasmatic nucleus (SCN), however, many labeled fibers coursed through the SCN to reach more caudal, periventricular and lateral sites including the anterior and lateral hypothalamus, the paraventricular nucleus (PVN), the subparaventricular zone, the ventromedial nucleus and the pars compacta of the dorsomedial nucleus. Some of these fibers continued dorsally into the zona incerta (ZI). Other fibers emerged from the lateral optic chiasm and traveled either rostro-medially to end in the preoptic area (POA) or further laterally to reach the supraoptic nucleus. A subset of fibers extended laterally from the chiasm to form a well-defined tract which provided input to the pyriform cortex. The extrageniculate retinal input to the thalamus was to the anterior thalamic area (AT) via the stria terminalis. In Part b, injections of rhodamine-labeled latex microspheres were made in three brain areas that contained labeled fibers after intraocular injections of CT-HRP. Injections in the AT, PVN/ZI area and POA consistently produced a small number of labeled retinal ganglion cells, whereas control injections did not. Taken together, these results indicate that many regions of the brain involved in the control of reproductive and regulatory functions receive photic informations via direct retinal inputs. These retinal inputs may play a role in the photoperiodic modulation of physiology and behavior.

Animals↗
PubMed1991

[Reoperations in primary hyperparathyroidism].

We report on 14 patients suffering from persistent (n = 13) and truly recurrent (n = 1) primary hyperparathyroidism. Reoperations were successful in 13 cases. Cervical reexploration was only required for 5 patients who had previous operations by unexperienced surgeons in other clinics. In 5 out of 7 patients operated by us, the causes of the persistent primary hyperparathyroidism were 4 adenomas and one hyperplastic gland in the mediastinum found by median sternotomy. The remaining cases were a rare ectopic location of the inferior glands and an inadequate resection in four-gland-hyperplasia. Preoperative localization procedures were carried out for most patients. 201-Tl/99m-Tc-subtraction scintigraphy has proved for localization in both the cervical region and the mediastinum to be a highly sensitive method. Reoperative parathyroid surgery can be reduced with thorough initial cervical exploration by experienced surgeons in specialized clinics.

Adenoma↗
PubMed1990

Collateral input to the paraventricular and supraoptic nuclei in rat. II. Afferents from the ventral lateral medulla and nucleus tractus solitarius.

In the rat, medullary afferents to the hypothalamic magnocellular nuclei mediate the baroreceptor reflexes of vasopressinergic neurons and the cholecystokinin- or gastric distention-induced excitation of oxytocinergic neurons. One strategy that reflexes such as these may use to coordinate the activity of magnocellular neuroendocrine neurons is collateral branching of input. Previous work has shown that the distributions of medullary neurons projecting to the paraventricular and the supraoptic nuclei overlap and that their axons branch. Thus, we hypothesized that single neurons in the ventral lateral medulla and/or the nucleus tractus solitarius would project to both the paraventricular and supraoptic nuclei via collateral branches of their axons. Medullary afferent neurons were retrogradely labeled after injection into the paraventricular and the supraoptic nucleus on one side of the brain with two different fluorescent tracers: Fluoro-Gold or rhodamine-labeled latex microspheres. The topographic distribution of labeled cells in the medulla containing either a single fluorescent tracer or both tracers were plotted. Of these labeled neurons, a small percentage (7%) contained both dyes, suggesting that they send collateral branches to both of the magnocellular neuroendocrine nuclei injected. Single labeled cells were both ipsi- and contralateral to the injected side (53% ipsilateral), but most double-labeled cells were ipsilateral (84%). In rats, areas that project to both the paraventricular and the supraoptic nuclei may act upon both nuclei together. Thus, afferent inputs, in conjunction with the known inter- and intracellular changes that take place within the magnocellular nuclei, may be involved with the coordinated responses throughout magnocellular neuroendocrine system during medullary reflexes, i.e., the baroreceptor-mediated reflexes or the gastric distention reflexes.

Afferent Pathways↗
PubMed1990

Collateral input to the paraventricular and supraoptic nuclei in rat. I. Afferents from the subfornical organ and the anteroventral third ventricle region.

Injections of two fluorescent retrograde tracers were used to investigate the existence of collateral branching of input to the hypothalamic magnocellular neuroendocrine neurons. Injection of one tracer (either Fluoro-Gold or rhodamine-labeled microspheres) into the supraoptic nucleus and the other tracer into the ipsilateral paraventricular nucleus produced labeled neurons within the subfornical organ and the anteroventral third ventricle area. Some labeled cells were found to contain both fluorescent tracers (double-labeled cells), suggesting that they project to both the paraventricular and supraoptic nuclei via branching axons. Most double-labeled cells were found within the subfornical organ. Fewer of these cells were located within the nucleus medianus preopticus, and still fewer were distributed in the organum vasculosum lamina terminalis, the bed nucleus of the stria terminalis, and the medial and the lateral preoptic areas. These data present the first direct evidence that single cells may provide input to more than one magnocellular neuroendocrine nucleus. Hypothetically, hormonal release would require coordinated firing of many magnocellular cells. Thus, the branched input to these neurons may assist in the organization and the timely activation of this system in response to physiological stimuli.

Animals↗
PubMed1989

Supraoptic nucleus afferents from the main olfactory bulb--I. Anatomical evidence from anterograde and retrograde tracers in rat.

The morphological features of a putative connection between the main olfactory bulb and the supraoptic nucleus of the rat was studied using a combination of anatomical techniques. Immunocytochemistry of neurophysin-containing processes were employed to delineate morphological features of supraoptic dendrites. Main olfactory bulb efferents to the supraoptic nucleus were studied by injection of the anterogradely transported substances, wheatgerm agglutinin conjugated horseradish peroxidase or Phaseolus vulgaris leucoagglutinin, into the main olfactory bulb. To confirm the results of these studies, the distribution of retrogradely labeled cells within the main olfactory bulb was determined after injection of rhodamine-labeled latex microspheres or Fluoro-Gold into the supraoptic nucleus. Neurophysin immunocytochemistry revealed the supraoptic nucleus dendritic plexus which coursed anteroposteriorly beneath supraoptic somata. Additionally, a portion of this plexus also projected ventrolaterally into periamygdaloid areas, a feature of supraoptic architecture which is not generally appreciated. The anterograde tracers labeled main olfactory bulb efferents including a dense plexus of terminals and fibers ventrolateral to the ipsilateral supraoptic nucleus. The pattern of anterogradely labeled fibers and terminals appeared to overlap with the distribution of ventrolaterally projecting neurophysin-containing processes. Since the latter consists of dendritic processes of supraoptic origin, this suggests that the main olfactory bulb projects to the supraoptic nucleus. Injections of rhodamine-labeled latex microspheres or Fluoro-Gold resulted in retrogradely labeled mitral cells throughout the ipsilateral main olfactory bulb. Taken together, these anatomical studies demonstrate a direct projection from the main olfactory bulb to the supraoptic nucleus of the rat. A comparison electrophysiological study confirmed these results.

Animals↗
PubMed1989

Magnocellular tuberomammillary nucleus input to the supraoptic nucleus in the rat: anatomical and in vitro electrophysiological investigations.

Anatomical and electrophysiological methods were used to investigate the existence and role of inputs from the magnocellular tuberomammillary nucleus to the supraoptic nucleus. After injecting either Fluoro-Gold or rhodamine-labeled latex microspheres into the supraoptic nucleus, consistent patterns of retrogradely labeled neurons within the tuberomammillary nucleus were observed. The results indicate that both subdivisions of the supraoptic nucleus, the tuberal and the anterior, receive input from the tuberomammillary nucleus. Injections into the tuberal supraoptic nucleus tended to label more cells in the contralateral tuberomammillary nucleus, while injections into the anterior supraoptic nucleus may label more cells on the ipsilateral side. The in vitro intracellular electrophysiological results support the anatomical findings and extend them in several ways. Some tuberomammillary neurons were found to project to the supraoptic nuclei on both sides of the brain. Intracellular Lucifer Yellow injections into tuberomammillary cells after electrophysiological recording revealed labeled axons that were traceable into the supraoptic nucleus, where apparent varicosities (possible en passant terminals) were seen. Magnocellular tuberomammillary nucleus neurons had characteristic passive and active membrane properties and morphology, similar to histaminergic neurons in this area studied by other workers. Finally, in two of the 21 cases, Lucifer Yellow injection into one neuron revealed dye-coupled pairs of tuberomammillary neurons. Previous work by others has shown that histamine excited cells in the tuberal subdivision of the supraoptic nucleus, stimulating vasopressin release, and that the tuberomammillary nucleus provides histaminergic input to the anterior portion of the supraoptic. The present findings show that the tuberomammillary nucleus supplies input to both subdivisions of the supraoptic nucleus and that this input is provided bilaterally. Taken together with previous work, these data suggest that the tuberomammillary nucleus provides histaminergic input to the supraoptic nucleus and may be involved specifically with vasopressin release.

Action Potentials↗
PubMed1987

A retinal projection to the paraventricular nuclei of the hypothalamus in the Syrian hamster (Mesocricetus auratus).

The retino-hypothalamic tract of the Syrian hamster (Mesocricetus auratus) was examined using intraocular injections of horseradish peroxidase conjugated to cholera toxin. In addition to the retinal input to the suprachiasmatic nuclei (SCN), a retinal projection to the caudal paraventricular nuclei was identified. This projection may mediate some effects of light upon pineal gland physiology independently of the SCN and the circadian-rhythm generating system.

Afferent Pathways↗