Biomedical subjects

G I Hatton

Publications and source records attributed to G I Hatton.

At least 73 records · Page 4Linked to original sources

PubMed1988

Direct evidence for electrical coupling among rat supraoptic nucleus neurons.

Transfer of the fluorescent dye, Lucifer yellow (LY), from an intracellularly injected neuron to one or more other neurons is accepted as indirect evidence of electrotonic interactions among such dye coupled cells. Direct evidence requires that at least two coupled cells be recorded from simultaneously and such evidence in the CNS has been gained only for hippocampal pyramidal neurons. Since interpretations of the functional significance of dye coupling among magnocellular neuroendocrine cells depend upon its relation to electrical coupling, we sought to obtain direct evidence for electrotonic interactions in such neurons. Over 150 pairs of supraoptic nucleus (SON) neurons in hypothalamic slices were recorded from intracellularly using one LY and one potassium acetate electrode in each instance. Of these, 9 pairs were studied in sufficient detail to determine that they were electrically coupled. Most of the remaining pairs were determined not to be coupled. In each coupled pair of cells, membrane voltage changes due to spontaneously occurring or current evoked action potentials, as well as current evoked hyperpolarizations, in one cell were reflected in similar, though attenuated changes in the other cell. All of these changes occurred simultaneously in the two neurons. Spontaneously arising postsynaptic potentials in the two cells were temporally uncorrelated. In each case that electrical coupling was observed, dye coupling resulted from LY injection. Coupling ratios ranged from 0.05 to 0.2. Capacitative coupling between the recording electrodes as an artifact was ruled out since cells in the same tissue penetration as the coupled cell showed no responses to membrane voltage changes in the primary cell; no responses were seen with the second electrode placed extracellularly or in the medium; and similar coupling potentials were also seen when one cell was recorded without a second electrode present. We conclude that electrical coupling exists among magnocellular neurons of the SON and that the incidence of dye coupling is a reasonable estimate of the incidence of electrical coupling. These electrotonic interactions probably play important roles in the coordination of firing among magnocellular neurosecretory neurons.

Action Potentials↗

PubMed1988

Ultrastructural changes in the rat neurohypophysis following castration and testosterone replacement.

Ultrastructural changes in male rat neurohypophyses were studied 8 or 30 days after castration, with or without testosterone (T) replacement via capsule implants. Morphometric analyses determined the: (a) amount of neural contact at the basal lamina (BL) of the neurovascular contact zone, (b) average length of individual terminal contacts with the BL, (c) number of neurosecretory terminals per 100 micrograms of BL, and (d) mean number of enclosed axonal processes per pituicyte. Eight days after castration there was decreased neural/BL contact and increased pituicyte enclosure of neurosecretory processes, conditions associated with decreased hormone release. In contrast, T replacement resulted in increased individual nerve terminal length, a measure associated with increased hormone demand. This observation may indicate a stimulatory effect of continuous high-normal circulating levels of testosterone from the capsule implants. There were no differences from control in 30-day castrate rats, but the 30-day rats with T replacement showed morphological indications of increased hormone release. These consisted of increased neural contact with the BL apparently through a significant increase in the number of neurosecretory terminals per unit length of BL. These findings support studies showing a complex feedback interaction between circulating levels of testosterone and vasopressin release.

Animals↗

PubMed1988

Synaptic inputs and electrical coupling among magnocellular neuroendocrine cells.

This paper first briefly reviews the evidence for synaptic and nonsynaptic plasticity among the neurons and glia of the magnocellular hypothalamo-neurohypophysial system. Emphasis is placed upon the importance of the roles played by astrocytes in the remodeling of the magnocellular nuclei under various conditions of increased hormone demand. Evidence is then reviewed from more recent studies showing that there is electrical coupling among magnocellular neurons, and that this coupling shows plasticity similar to that shown for other characteristics of the system (e.g., chemical synapses, dendritic bundling etc.). Further, evidence is presented that extent of electrical coupling can be modified not only by manipulating the physiological state of the animal (such as lactation), but also by electrical stimulation of newly described olfactory afferent inputs to the cells of the supraoptic nucleus. The possible functional significance of these findings is discussed in relation to the behavior of nursing rats.

Animals↗

PubMed1988

Alterations in supraoptic nucleus ultrastructure of maternally behaving virgin rats.

Adult, nulliparous female rats were induced to behave maternally via constant cohousing with rat pups. After exhibiting maternal behaviors for 3 days, the animals were transcardially perfused, the supraoptic nuclei (SON) excised and examined quantitatively by transmission electron microscopy. Relative to virgin controls, the animals behaving maternally were found to have significant increases in: a) mean number of dendrites in large (9-12) dendritic bundles, b) mean area per single dendritic profile, c) area of the dendritic zone occupied by dendritic profiles and d) size of the dendritic zone. No significant changes were observed in the cell body zone or in the number of double synapses in the dendritic region. The observed changes are likely to be at least in part associated with the oxytocin-containing cells of the SON. These observations suggest a role for the SON in promoting maternal behaviors and constitute a novel demonstration of a neural modification in the mammalian central nervous system that appears conjointly with a complex set of behaviors.

Animal Husbandry↗

PubMed1988

Pituicytes, glia and control of terminal secretion.

Once thought to be hormone-synthesizing cells, the pituicytes are now known to be the resident astroglia of the neurohypophysis (also referred to here as the posterior pituitary). Early investigators interpreted light microscopic observations as demonstrating pituicyte secretion, since pituicytes appeared to contain neuro-secretory material when hormone demand was low and not when it was increased. Ultrastructural studies have shown that pituicytes actually engulf or completely surround neurosecretory axons and axonal endings under basal conditions, and release these neural processes when conditions require increased hormone output. Thus, the pituicytes appeared to the early workers to contain and release hormone when they actually contained and released axons and terminals in which the hormone was, in fact, contained. Dynamic interactions of pituicytes with various of the other elements in the gland have also been demonstrated. When hormone demand is low, the pituicytes not only engulf the neurosecretory processes but also interpose their own processes between the secretory endings and the basal lamina. Since any hormone that is secreted must pass through the basal lamina and into the perivascular spaces in order to enter the fenestrated capillaries, pituicyte interpositions form physical, and perhaps chemical, barriers to hormone entering the circulation. Increasing hormone demand results in retraction of pituicyte processes from the basal lamina, permitting increased neural contact. Studies of isolated neurohypophysis and of cultured adult rat pituicytes have shown that these glia undergo appropriate morphological changes in response to osmotic stimuli or to receptor-mediated activation of adenylate cyclase. Both these events are thought to be effectors of the alterations seen in vivo. Some possible mechanisms by which pituicytes may participate in the control of secretory events are discussed.

Animals↗

PubMed1987

Morphological adaptability at neurosecretory axonal endings on the neurovascular contact zone of the rat neurohypophysis.

To compare the effects of a variety of acute and chronic stimuli that bring about or terminate hormone release the ultrastructure of nerve terminal contact at the basal lamina of the neurohypophysial neurovascular contact zone was examined quantitatively in young adult rats of the following treatment groups: untreated virgin females, untreated male rats, prepartum (day 21 of gestation), postpartum (on the day of parturition), lactating (14 days of suckling), mothers 10 days after their pups were weaned, 48 h water-deprived males, males given 2% saline solution (dehydrated) for 10 days, males given 2% saline as described then given tap water to rehydrate for 2 or 5 weeks. Morphometric analysis of electron micrographs revealed that all stimuli leading to increased hormone release were accompanied by both increased occupation of the basal lamina by nerve terminals as well as decreased enclosure of neurosecretory processes by pituicyte cytoplasm. Neural occupation of the basal lamina remained significantly elevated 10 days post-weaning and at 2 weeks (but not 5 weeks) of rehydration following 10 days of dehydration. Pituicyte enclosure of neurosecretory axons had returned to control values in the postweaning and 5 week (but not 2 week) rehydrated animals. The mean length of individual nerve terminal contact with the basal lamina was found to increase under some, but not all, conditions associated with increased hormone release (i.e. parturition, acute and chronic dehydration, but not during lactation) and to decrease below control values in prepartum females and after 5 weeks of rehydration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Dye coupling among immunocytochemically identified neurons in the supraoptic nucleus: increased incidence in lactating rats.

The hypothesis that electrotonic spread among oxytocinergic neurons contributes to synchronized bursting in the lactating rat leads to the prediction that coupling among oxytocinergic neurons would be stronger and more abundant in lactating than in non-lactating animals. We tested this prediction using, as an index of electrical coupling, transfer among neurons of the fluorescent dye Lucifer Yellow CH, which crosses gap junctions. Intracellular injections (total of 159) of the dye were made in supraoptic nucleus neurons in hypothalamic slices from virgin female and lactating rats. In virgins, 86 injections resulted in 76 single, 8 coupled pairs and 2 triplets of dye-filled neurons. In contrast, 73 injections in lactators yielded 51 single, 16 coupled pairs and 6 triplets, (greater than 100% increase) a difference significant at P less than 0.001. Immunocytochemical identification of the dye-filled cells revealed that there was an increase over virgins in coupling among both oxytocinergic and vasopressinergic neurons. These results are consistent with the hypothesis that electrical coupling is involved in synchronizing oxytocin cell bursting in lactators. They are also consistent with published data indicating that vasopressin neurons are metabolically activated (show increased glucose uptake) during suckling and may show correlated activity.

Animals↗

PubMed1987

Incidence of dye coupling among magnocellular paraventricular nucleus neurons in male rats is testosterone dependent.

Recently published work in the rat has shown that: the incidence of electrical coupling, as measured by dye coupling, is decreased from control levels by 8 days of drinking hypertonic saline; an index of circulating testosterone, seminal vesicle weight, is also decreased by 8 days of saline drinking; and both plasma and urinary vasopressin levels are reduced in castrated males, but can be returned to normal with testosterone replacement. These findings have led to the hypothesis that dye coupling, particularly that involving vasopressinergic cells, may be affected by gonadal steroids. We have investigated the effects of castration and testosterone replacement on the incidence of dye coupling among the neurons of the predominantly vasopressinergic magnocellular lateral paraventricular nucleus in slices of male rat hypothalamus. Incidence of dye coupling in this nucleus of castrated rats was found to be decreased by 67% from sham castrated control levels. Testosterone-filled Silastic capsules (but not empty capsules) implanted subcutaneously at the time of castration abolished the effect of castration on dye coupling. We conclude that testosterone has a powerful influence upon coupling among PVN vasopressinergic neurons and may participate in the control of vasopressin release in intact animals.

Animals↗

PubMed1987

Dye coupling among supraoptic nucleus neurons without dendritic damage: differential incidence in nursing mother and virgin rats.

To assess the possibility that dye coupling among neurons in hypothalamic slices might require dendrotomy, as has been suggested for neocortical neurons, dye coupling was studied in horizontally cut slices containing the supraoptic nucleus (SON). Since the dendrites of SON neurons project toward the pial surface, dendritic damage due to slicing can be avoided in the horizontal plane. Intracellular injections of Lucifer Yellow into individual SON neurons in slices from male, virgin female and lactating, mother rats yielded the following results. When dendrotomy occurred there was a significantly lower incidence of dye coupling than was observed when dendrites were intact. Higher order coupling (3 or more cells dye coupled after a single injection) was only seen among neurons without dendrotomy. Independently of dendritic damage, incidence of dye coupling in nursing mothers was reliably greater than for virgins, confirming previous results from coronal slices. The results of this study indicate that dendrotomy is not an inducer of dye coupling in SON neurons. Taken together with other recent findings, these data suggest that a reinterpretation of the effects of dendrotomy on cortical cell dye coupling may be in order.

Animals↗

PubMed1986

Immunoreactivity to vasopressin- but not oxytocin-associated neurophysin antiserum in phasic neurons of rat hypothalamic paraventricular nucleus.

Bursts of action potentials were recorded intracellularly from 11 phasically firing magnocellular neurons in the paraventricular nucleus in slices of rat hypothalamus. The bursts of overshooting, often broadening action potentials (63-87 mV peak-to-peak) were superimposed on depolarizing plateau potentials. Phasic activity was recorded before and/or after the neurons were injected with the fluorescent dye Lucifer Yellow CH. Injected neurons were first examined in whole slices, and subsequently, in sectioned material, characterized immunocytochemically using antisera to vasopressin- and oxytocin-associated neurophysins (VP-NP and OT-NP respectively). The 11 injections produced 8 single dye filled neurons and 3 pairs of dye-coupled neurons, 14 dye-filled cells in all. Six of the single cells and all the dye coupled pairs were immunoreactive with VP-NP antiserum and not reactive with OT-NP antiserum. Most of these neurons were in areas of the nucleus in which VP-NP reactive cells predominated, but two were surrounded by OT-NP reactive cells. Two single, dye-filled, phasically active, magnocellular neurons failed to show immunoreactivity to either antiserum.

Animals↗

PubMed1986

Vacant postsynaptic densities on supraoptic dendrites of adult rats diminish in number with chronic stimuli.

In earlier ultrastructural studies of the supraoptic nucleus in adult rats we noted "free" and incompletely covered postsynaptic densities (collectively referred to here as vacant postsynaptic densities) on dendritic shafts. Free postsynaptic densities have been reported in other parts of the central nervous system of normal rodents. We investigated the possibility that physiological activation of the supraoptic cells, which produces changes in many aspects of their morphology, would alter the incidence of the free or incompletely covered postsynaptic densities on dendrites in the supraoptic basal dendritic zone. The cells of the supraoptic nucleus are activated to increase cell firing and secretion of oxytocin and/or vasopressin in response to dehydration, gestation, and lactation. We have examined: untreated virgin females; untreated males; 24 h water-deprived males; prepartum (21st day of gestation) females; postpartum females (on the day of parturition); lactating females (14 days of suckling); mothers 10 days after weaning their pups; females given 2% saline to drink (dehydrated) for 10 days; and females or males given 2% saline to drink for 10 days, then given tap water for 2 or 5 weeks to allow rehydration. Only long-term activation of the supraoptic nucleus by lactation or by drinking saline for 10 days brought about significant decreases in the percentage of dendrites with vacant postsynaptic densities. These densities did not reappear in saline treated rats which had been rehydrated for 2 weeks, but did return in both the 5-week rehydration and the 10-day postweaning groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Central release of oxytocin, vasopressin and neurophysin by magnocellular neurone depolarization: evidence in slices of guinea pig and rat hypothalamus.

Using slices of rat hypothalamus maintained in vitro, we have examined release of oxytocin and vasopressin under conditions of increased neuronal activity. We report here that when the supraoptic or paraventricular nucleus is depolarized with high K+ solutions, hormone is released into areas close to the nucleus. Similar experiments with guinea pig hypothalamus suggest that neurophysin may also be co-released with oxytocin and vasopressin. Use of acetylcholine to selectively stimulate vasopressin neurones appears to evoke a rise in local release of vasopressin but not oxytocin. These results suggest that under conditions of increased neuronal activity, hormones normally secreted from the neurohypophysis are secreted locally into the hypothalamus.

Acetylcholine↗

PubMed1986

Plasticity in the hypothalamic magnocellular neurosecretory system.

Over the past decade or so, plasticity has emerged as an important, quantifiable property of the mammalian hypothalamic magnocellular neurosecretory system. This plasticity has turned out to be genuinely related to normal function in the sense that it is a set of responses to physiological stimulation rather than only the sequelae of insult or injury, and it is generally completely reversible. This latter property, of course, distinguishes it further from the plasticity observed after injury. Four features of this magnocellular system that have been shown to display predictable and reversible intercellular plasticity are reviewed: the relationships between neurons and their associated astrocytic glia at various levels (dendritic somatic and terminal) of the magnocellular elements; the extent of terminal and glial contact with the basement lamina in the neurohypophysis; the type and possible efficacy of synaptic input, and the extent of electrotonic coupling among the magnocellular neurons.

Animals↗

PubMed1985

Neuronal/glial plasticity in the supraoptic dendritic zone in response to acute and chronic dehydration.

The magnocellular neurosecretory cells of the supraoptic nucleus increase production and secretion of oxytocin and/or vasopressin in response to dehydration, gestation and lactation. Dynamic neuronal/glial interactions have also been shown to occur in response to these stimuli, resulting in a reversible increase in soma-somatic direct membrane apposition at these times. Chronic (lactation, 10 days of saline drinking) but not acute stimuli (4-24 h water deprivation) are further accompanied by the reversible formation of axo-somatic double synapses (one presynaptic terminal contacting two postsynaptic elements), which are virtually absent in control animals. The dendrites of these cells course ventrolaterally toward the ventral glial lamina, and have also been shown to be involved in this plasticity: dendro-dendritic direct membrane apposition and axo-somatic double synapses significantly vary with gestation and parturition. The present study investigated the dendritic zone response to both chronic and acute dehydration and rehydration. Increased dendro-dendritic membrane contacts resulted from both stimuli. Rehydration following acute dehydration resulted in a dose-dependent return to control levels, while rehydrated chronic dehydrates did not show such a return until 35 days of rehydration. The percentage of dendrites contacted by double synapses did not vary with treatment, and there were no sex differences. The recalcitrance on the part of the dendrites to return to normal following chronic dehydration may reflect a readiness to respond to renewed hormone demand.

Acute Disease↗

PubMed1985

Lactation-associated redistribution of the glial fibrillary acidic protein within the supraoptic nucleus. An immunocytochemical study.

Electron-microscopic evidence indicates that during conditions of high hormone demand such as lactation there is a dramatic reduction in the number of fine glial processes which are normally interposed between magnocellular neuroendocrine cell somata in the supraoptic nucleus (SON). The purpose of this study was to corroborate these data at the light-microscopic level and to gain some insight into what underlying events might accompany these apparent morphological changes. The distribution of the glial fibrillary acidic protein (GFAP), an intermediate filament component of the astrocytic cytoskeleton, was visualized in lactating or estrous rats using peroxidase-antiperoxidae immunocytochemistry. Computerized image analysis was employed to determine and compare the staining distributions of this protein for the two groups of rats. Statistical analysis revealed a redistribution of GFAP immunostaining in the SONs of lactating animals as compared to controls. No differences in staining were found in a control area dorsolateral to SON. The pattern of change was to a less dense, more homogeneous distribution of GFAP in lactating rats, a change which could be interpreted as reflective of a reduction in the number of densely staining glial processes.

Animals↗

PubMed1985

Dye-coupled magnocellular peptidergic neurons of the rat paraventricular nucleus show homotypic immunoreactivity.

Magnocellular neurons in rat hypothalamic slices are known to exhibit dye coupling: the transfer of the fluorescent dye, Lucifer Yellow, from an intracellularly-injected neuron to one or more nearby neurons. The question of the hormonal identity of coupled cells and the possibility of dye coupling as an artefact led us to determine the immunoreactivity of dye-coupled magnocellular neurons in the paraventricular nucleus of the rat hypothalamus using antisera to oxytocin- and vasopressin-associated neurophysins. In 23 pairs, one triplet, and one quadruplet, immunoreactivity to one or the other antiserum was always exclusive, and dye coupling was always homotypic, that is, coupled neurons in each instance were reactive to the same antiserum. The quadruplet, triplet and 17 pairs were immunoreactive to vasopressin-associated neurophysin, and oxytoxin-associated neurophysin immunoreactivity was observed in the remaining pairs. Immunoreactivity to each antiserum was found for somasomatic and non somasomatic modes of coupling and for coupled neurons in the three magnocellular areas of the nucleus. A relationship between mode of coupling and hormone content was not detected. The data support the hypothesis that coupling is a real, functionally significant mechanism for coordinating neuronal activity in this nucleus, particularly under conditions of high hormone demand. They do not support the idea that coupling is artefact. The possibility of a relationship between hormone content and mode of coupling, and the projection pathway(s) of the coupled neurons of each type require further study.

Animals↗

PubMed1985

Extranuclear axon collaterals of paraventricular neurons in the rat hypothalamus: intracellular staining, immunocytochemistry and electrophysiology.

Recent studies have suggested that some paraventricular nucleus (PVN) neurons projected to more than one target and, thereby, perhaps coordinate some aspects of seemingly diverse functions. We have systematically investigated the existence, location, hormonal contents and functional integrity of some axon collaterals arising from PVN neurons. This was done using intracellular injections of the fluorescent dye, Lucifer Yellow, extracellular ejections of horseradish peroxidase (HRP), immunocytochemistry with antisera directed against vasopressin (VP) and oxytocin (OX) and electrophysiological analysis of synaptic activation of perifornical neurons in response to electrical stimulation of the PVN in hypothalamic slices. Each of the three morphological techniques revealed clear axon collaterals, arising in the lateral hypothalamus and generally ventrolateral to the PVN. Most branching axons appeared to have a small number of branch points, and many collaterals appeared to terminate near their parent axon. Electrical stimulation of the PVN was found to activate synaptically perifornical neurons located in the areas where the other methods revealed collaterals. Stimulation outside of the nucleus was ineffective unless current intensities were increased 10-30-fold over those applied to the PVN. We conclude that many PVN neurons, at least some of these containing OX and other VP, give rise to axons that branch in the perifornical and more ventral lateral hypothalamus, and that some of their collaterals probably terminate on neurons close to the PVN.

Animals↗

PubMed1984

Synapse formation and disappearance in adult rat supraoptic nucleus during different hydration states.

Activation of the adult rat supraoptic nucleus by a chronic stimulus (10 days of drinking 2% NaCl instead of tap water) brought about the appearance of newly formed specialized synapses onto the magnocellular neurosecretory cells. The increase in these synapses was reversed when the animals were allowed to rehydrate by drinking tap water. The apparent retraction and reinsertion of the thin glial processes from between the neurosecretory cell somata, which results in significant changes in soma-somatic direct membrane appositions, is most likely involved in the formation and elimination of these synapses.

Animals↗