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G I Hatton

Publications and source records attributed to G I Hatton.

At least 19 recordsLinked to original sources
PubMed1995

NMDA and non-NMDA receptors on rat supraoptic nucleus neurons activated monosynaptically by olfactory afferents.

The recently discovered efferent projections from the main and accessory olfactory bulbs to the supraoptic nucleus (SON) were further investigated. Intracellular electrophysiological methods were used to determine (a) if these projections are monosynaptic, (b) which excitatory amino acid (EAA) receptor subtypes mediate responses to activation of these pathways and (c) whether the same receptor subtypes mediate responses of phasically firing (vasopressin) and continuously firing (putative oxytocin) neurons. Recordings were made from SON neurons in large explants and 500 microns thick horizontal slices, containing 2-6 mm of the piriform cortex and lateral olfactory tract (LOT). This allowed recording of synaptic responses to selective stimulation of the LOT. EPSPs in SON neurons faithfully followed stimulus frequencies of 50-100 Hz, indicating that these inputs were monosynaptic. Stimulus-evoked EPSPs were blocked by the non-specific EAA antagonist, kynurenate. Perifusion of the slice with Mg(2+)-free medium revealed the presence of NMDA receptors in addition to the non-NMDA receptors on both phasically and continuously firing cells, indeed, on all cells tested. Partial blockade of these EPSPs in Mg(2+)-free medium could be achieved with either the NMDA antagonist, AP5, or the non-NMDA antagonist, CNQX or NBQX. Full blockade of the stimulus-evoked EPSPs was effected by adding both types of antagonists to the medium, although spontaneous EPSPs were still observed in several cells. These results are consistent with prior studies showing both receptor subtypes in the SON. This is the first demonstration that afferent stimulation activates both subtypes in the same SON neuron regardless of its peptide content.

2-Amino-5-phosphonovalerate↗
PubMed1995

Taurine immunoreactivity in the rat supraoptic nucleus: prominent localization in glial cells.

Taurine is an inhibitory amino acid that hyperpolarizes magnocellular neurosecretory neurons. To determine which cell types in the rat supraoptic nucleus contain taurine, we used a monoclonal antibody raised against a taurine conjugate. Preembedding immunocytochemistry was carried out at the light and electron microscopic levels using diaminobenzidine and gold-substituted silver-intensified peroxidase as markers. We report the presence of taurine in all cellular compartments of the supraoptic nucleus, except axons, with variable labeling intensities among the different compartments. Few cell bodies of magnocellular neurons were immunoreactive, but many distal dendrites and some proximal ones showed weak-to-moderate levels of immunoreactivity. Strong immunoreactivity was found over glial cell bodies and their processes, in particular in the ventral glial lamina of the supraoptic nucleus. Large astrocytic processes labeled with the taurine antibody included the endfeet participating in the glial limitans around capillaries and at the ventral surface of the hypothalamus. Other types of immunoreactive astrocytic profiles were found scattered within the neuropil where these processes participated in different interactions with the neuronal elements of the supraoptic nucleus. Immunoreactive glial expansions, sometimes even the main process of the glial cell, engulfed axonal boutons. Other labeled glial processes were found between two magnocellular perikarya or closely apposed to the membrane of axonal boutons contacting the neuronal cell bodies. The frequent finding of closely apposed glial and dendritic elements bearing different levels of taurine-like immunoreactivity suggests that exchange of taurine between those two compartments may occur. We propose that taurine could be released from supraoptic glia by a small decrease in osmolarity or by receptor-mediated mechanisms during conditions of low hormonal (vasopressin and/or oxytocin) needs. Such released taurine could then act on presynaptic or postsynaptic sites, or both, to exert its neuromodulatory actions.

3,3'-Diaminobenzidine↗
PubMed1994

Incidence of neuronal coupling in supraoptic nuclei of virgin and lactating rats: estimation by neurobiotin and lucifer yellow.

Dye coupling among neurons has been shown to reflect electrotonic coupling. Recent work in retina has revealed that the incidence of coupling is greater when estimated by neurobiotin (NB) transfer than by Lucifer yellow (LY). Several previous studies have shown that the incidence of LY coupling among supraoptic nucleus (SON) neurons of lactating rats is 2- to 4-fold higher than is observed in virgin females. We compared the incidence of coupling among SON neurons following simultaneous injections of LY and NB into the same cells in slices from virgin or lactating rats. As seen in previous studies, there were 4-fold more LY-coupled neurons per injection in lactating as compared to virgin rats. Under both conditions, the numbers of NB-coupled neurons per injection were 4-fold greater than was observed for LY; possible mechanisms are discussed. Individual NB-filled neurons were coupled to as many as 10 other cells distributed over a large area of the SON. These results confirm previous findings of more coupling in lactating than virgin SONs, and suggest that both the incidence and spatial extent of interneuronal coupling are greater and thus probably more important functionally than has been heretofore appreciated.

Animals↗
PubMed1994

Histamine mediates fast synaptic inhibition of rat supraoptic oxytocin neurons via chloride conductance activation.

Axons from the histaminergic neurons of the tuberomammillary nucleus project to both the anterior and tuberal portions of the supraoptic nucleus. Histamine is known to activate vasopressin neurons via a histamine receptor subtype 1 and to increase release of vasopressin, but effects on oxytocin neurons have been previously unexplored. Here we investigated the effects of tuberomammillary nucleus electrical stimulation as well as of histamine antagonists on supraoptic nucleus oxytocin and vasopressin neurons in slices of rat hypothalamus. Electrical stimulation evoked short constant latency (approximately 5 ms), fast (4-6 ms onset to peak) inhibitory postsynaptic potentials in oxytocin neurons and, as shown previously, fast excitatory postsynaptic potentials in vasopressin neurons. These synaptic responses followed paired-pulse stimulus frequencies up to 100 Hz and were, thus, probably reflecting monosynaptic connections. Inhibitory postsynaptic potentials were selectively blocked by histamine receptor subtype 2 antagonists (either cimetidine or famotidine) and by picrotoxin but not by histamine receptor subtype 1 antagonists or bicuculline. Similar synaptic responses to tuberomammillary nucleus stimulation were found in 16 of 16 neurons immunocytochemically identified as oxytocinergic and in seven putative oxytocin neurons. Perifusion of the slice with low chloride medium (4.8 mM) reversed stimulus-evoked inhibitory postsynaptic potentials. We conclude that histaminergic neurons monosynaptically contact both oxytocin and vasopressin cells of the supraoptic nucleus and inhibit the former via activation of chloride channels which can be blocked by the histamine receptor subtype 2 antagonists, famotidine and cimetidine.

Animals↗
PubMed1994

Maternal behaviors: evidence that they feed back to alter brain morphology and function.

We review evidence suggesting that the brain of maternally behaving rats is altered as a result of the behavior of the animal towards her pups. Morphological changes seen in the supraoptic nucleus, which contains oxytocinergic neurons important for lactation, are observed not only in parturient, lactating animals but also in virgin animals induced by the presence of rat pups to behave maternally. The supraoptic nuclei of lactating and maternally behaving virgin animals have a higher incidence of dendritic bundling relative to non-maternal virgin animals. Also, stimulation of the lateral olfactory tract in in vitro brain slices elevates electrotonic coupling among supraoptic neurons only in maternally behaving animals and not in male or non-maternal virgins. In general the evidence presented supports the idea that maternal behavior in lactating and non-lactating animals, can have profound effects on the morphology and physiological functioning of oxytocinergic neurons in the hypothalamus.

Animals↗
PubMed1992

Arginine vasopressin mobilises intracellular calcium via V1-receptor activation in astrocytes (pituicytes) cultured from adult rat neural lobes.

An extremely close association exists between the membranes of the neurosecretory endings and the resident astrocytes (pituicytes) of the neurohypophysis. Indeed, synaptoid contacts involving neurosecretory vesicle-containing axons contacting pituicytes have been observed, suggesting pituicytes as targets of the products released from neurosecretory axons. We have investigated the effects of various neural lobe peptides on pituicytes in primary culture from adult neurohypophyses. Using Fura-2 loaded cells and dynamic ratio imaging, we have determined that arginine vasopressin (AVP) or V1- but not V2-receptor agonists, mobilise pituicyte intracellular Ca2+ ([Ca2+]i) in the absence of extracellular Ca2+. AVP was consistently effective at concentrations of 10 nM or higher in elevating [Ca2+]i by 200-1000 nM. These responses could be blocked by V1-antagonists and were shown to be associated with accumulation of phosphoinositides. Oxytocin was also found to mobilise [Ca2+]i but was effective only at higher concentrations than for AVP. Oxytocin-evoked [Ca2+]i elevations were also blocked by V1-antagonists. Raising [K+]0 was ineffective in changing [Ca2+]i suggesting that these cells lack voltage-gated Ca2+ channels. We conclude that pituicytes possess V1-receptors, activation of which mobilises [Ca2+]i, possibly functioning to initiate a Ca(2+)-activated K+ conductance which could contribute to further depolarisation of secretory terminals and facilitate exocytosis.

Animals↗
PubMed1992

Effects of ovariectomy and estrogen replacement on dye coupling among rat supraoptic nucleus neurons.

Among magnocellular neurosecretory neurons (MNCs), the frequency of dye coupling, and thus also of electrotonic coupling, is reduced in male rats following castration. Testosterone replacement prevented this reduction suggesting a modulatory role for gonadal steroids. To determine whether gonadal steroids in females influenced coupling incidence, Lucifer yellow CH injections were made in MNCs in slices taken from ovariectomized rats, either untreated or implanted with capsules containing estradiol-17 beta or estradiol-17 alpha, or from sham operated rats. In groups without biologically active estradiol, incidence of dye coupling was increased by 138-169% over those with normal plasma levels, as measured by radioimmunoassay. We conclude that estradiol and testosterone have opposite effects on coupling frequency among MNCs and that the facilitatory effects of testosterone in males are unlikely to be via its aromatization to estrogen.

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↗
PubMed1992

Rapid morphological changes in supraoptic nucleus and posterior pituitary induced by a single hypertonic saline injection.

Neurosecretory neurons of the supraoptic nucleus (SON) which manufacture, transport, and secrete neuropeptide hormones are activated by administration of hypertonic NaCl. Male rats were given single intraperitoneal injections of isotonic (0.15 M) or hypertonic (1.5 M) NaCl solution and sacrificed 5 h after injection. Electron micrographs were compared to determine morphological differences in the SON and in the neural lobe in the two conditions. In the SON, significant decreases were found in the extent of glial contact with the magnocellular neuroendocrine cell (MNC) membrane; the amount of nerve terminal contact and amount of apposition of MNC membrane with other MNC cell bodies or dendrites increased. The number of multiple synapses (one terminal contacting two or more cells) per 100 microns of somatic membrane in the 1.5 M NaCl condition was double that found in the 0.15 M NaCl condition. Size of nucleoli, overall cell body size, and amount of Golgi apparatus were significantly larger in the animals injected with 1.5 M NaCl. The neural lobes of animals receiving 1.5 M NaCl injections showed increased neural contact with the basal lamina and decreased cytoplasmic enclosure of axon terminals. The large and rapid changes induced by this stimulus suggest that it is an extremely effective activator of morphological plasticity in the hypothalamo-neurohypophysial system.

Animals↗
PubMed1992

Reevaluation of the plasticity in the rat supraoptic nucleus after chronic dehydration using immunogold for oxytocin and vasopressin at the ultrastructural level.

It has been shown that during physiological stimuli, such as dehydration, supraoptic nucleus (SON) neurons undergo profound morphological changes. However, little is known about how much each type of cell, oxytocin (OT) or vasopressin (VP), contributes to this plasticity during dehydration. Using postembedding immunogold cytochemistry for both OT and VP hormones at the electron microscopic level, we address this question. Rats were chronically dehydrated (given 2% saline to drink for 10 days) and their SON neurons were studied morphologically. The results were compared to control animals with free access to water. Both VP and OT somata showed an enlargement in size in dehydrated animals. Percentage of somasomatic/dendritic membrane contact increased significantly in both VP and OT neurons, with no significant changes in percentage of coverage of the cells by astrocytic membrane. Only the VP cells had a lesser amount of axosomatic membrane contact after dehydration, possibly due to an increase in cell size rather than a decrease in synaptic contact. Multiple synapses (MSs) (i.e., terminals that form more than one synapse with adjacent somata and or dendrites) occurred only between positively labeled cells and between negatively labeled cells, but not between positively and negatively labeled cells. The number of MSs per 100 microns OT somatic membrane or per 100 OT cells was significantly higher in dehydrated rats but was unchanged with regard to VP neurons. These findings indicate that both VP and OT neurons undergo morphological changes during chronic dehydration and, thus, that plasticity is not limited to OT cells as some earlier reports have suggested.

Animals↗
PubMed1991

Adrenalin activation of beta 2-adrenoceptors stimulates morphological changes in astrocytes (pituicytes) cultured from adult rat neurohypophyses.

Neurohypophysial astrocytes, the pituicytes, are known to undergo morphological changes in vivo in response to stimuli that increase the demand for hormone secretion. Similar changes have been induced by beta-adrenergic stimulation both in the isolated, but otherwise intact, neural lobe and in pituicytes cultured from adult rats. Since the predominant beta-receptor subtype in the neural lobe is beta 2, we investigated the possibility that beta 2-receptor activation is mainly responsible for the observed pituicyte responses. In one experiment, cultured pituicytes were induced by noradrenalin to change from flattened amorphous to stellate morphology. Addition of the beta 2-antagonist IPS 339, but not the beta 1-antagonist practolol, significantly reduced (by 30-60%) the number of cells transformed by noradrenalin. In a second experiment, adrenalin, by definition a more potent beta 2-agonist, transformed significantly more pituicytes into stellate shapes than did noradrenalin at the same concentrations (100% vs. 60% increase, respectively). These results support the idea that beta 2-adrenergic receptors are involved in neurohypophysial plasticity. Also, since the neural lobe is outside of the bloodbrain barrier, these findings suggest that adrenal catecholamines participate in altering pituicyte morphology.

Adrenergic beta-Agonists↗
PubMed1990

Activation of excitatory amino acid inputs to supraoptic neurons. I. Induced increases in dye-coupling in lactating, but not virgin or male rats.

Mitral cells of the main and accessory olfactory bulbs have been shown to project monosynaptically to the supraoptic nucleus (SON) via the lateral olfactory tract (LOT) which uses excitatory amino acid transmitters. Data collected during characterization of these projections suggested that synaptic activation of SON neurons via LOT stimulation in slices influenced the incidence of dye-coupling. The present study pursued this suggestion using horizontally cut slices from male, virgin female and lactating rats. Neurons were confirmed to be excited by electrical stimulation of the tract, injected with Lucifer yellow, and synaptically activated for 10 min at 10 Hz (n = 92). Another 94 neurons were similarly confirmed and injected, but received no further stimulation. In an additional 8 slices, injected neurons were antidromically activated for 10 min at 10 Hz. Analyses done on 194 injected neurons from the 3 groups showed that synaptic activation resulted in a significant (P less than 0.01) increase in the incidence of coupling only in tissue from lactating rats. This increase was entirely due to larger numbers of cells being coupled dendrodendritically to the injected cells in the stimulated slices. Antidromic activation did not influence coupling. Increased coupling occurred among both oxytocin and vasopressin cell types. This is the first report of increased coupling resulting from synaptic activation in mammalian CNS. Changes seen only in lactating rats may be related to their altered SON ultrastructural morphology (i.e. dendritic bundling). Strong olfactory and vomeronasal input associated with some maternal behaviors may increase neuronal coupling and enhance hormone release in response to other incoming stimuli (e.g. suckling, dehydration).

Action Potentials↗
PubMed1990

Activation of excitatory amino acid inputs to supraoptic neurons. II. Increased dye-coupling in maternally behaving virgin rats.

Electrical stimulation of the lateral olfactory tract (LOT) has been shown to excite, monosynaptically, supraoptic nucleus (SON) neurons in slices of hypothalamus taken from male, virgin female or lactating rats. Only in the last of these, however, did 10 min of 10 Hz stimulation produce an increase in the incidence of Lucifer yellow dye-coupling, an indicator of electrotonic interactions. This coupling is virtually exclusively dendrodendritic. Since virgin females that have been induced to show full maternal behavior have altered dendritic morphology reminiscent of lactating animals (but different from males and untreated virgins) we investigated the effects of LOT stimulation in slices from maternally behaving virgins. Similar to the data for lactating rats, electrical stimulation of this tract, the terminals of which release excitatory amino acid transmitter, increased the incidence of dye-coupling by 112% (P less than 0.01). Also similar to lactating rats, the coupling was dendrodendritic and the increase was due entirely to increasing the number of neurons coupled to the injected neuron. No increase in coupling was seen in stimulated slices from pup-exposed control rats. We conclude that the maternal behaviors engaged in by both real mothers and induced virgins 'primes' the supraoptic neurons to increase coupling in response to olfactory system stimulation. This priming may occur via olfactory and vomeronasal stimulation during such behaviors as sniffing and anogenital licking of the pups. That coupling increased in tissue from maternally behaving virgins comparably to that from nursing mothers further suggests that SON neurons may play a role in maternal behavior independent of its well-documented role in the milk ejection reflex.

Action Potentials↗
PubMed1990

Emerging concepts of structure-function dynamics in adult brain: the hypothalamo-neurohypophysial system.

As the first known of the mammalian brain's neuropeptide systems, the magnocellular hypothalamo-neurohypophysial system has become a model. A great deal is known about the stimulus conditions that activate or inactivate the elements of this system, as well as about many of the actions of its peptidergic outputs upon peripheral tissues. The well-characterized actions of two of its products, oxytocin and vasopressin, on mammary, uterine, kidney and vascular tissues have facilitated the integration of newly discovered, often initially puzzling, information into the existing body of knowledge of this important regulatory system. At the same time, new conceptions of the ways in which neuropeptidergic neurons, or groups of neurons, participate in information flow have emerged from studies of the hypothalamo-neurohypophysial system. Early views of the SON and PVN nuclei, the neurons of which make up approximately one-half of this system, did not even associate these interesting, darkly staining anterior hypothalamic cells with hormone secretion from the posterior pituitary. Secretion from this part of the pituitary, it was thought, was neurally evoked from the pituicytes that made the oxytocic and antidiuretic "principles" and then released them upon command. When these views were dispelled by the demonstration that the hormones released from the posterior pituitary were synthesized in the interesting cells of the hypothalamus, the era of mammalian central neural peptidergic systems was born. Progress in developing an ever more complete structural and functional picture of this system has been closely tied to advancements in technology, specifically in the areas of radioimmunoassay, immunocytochemistry, anatomical tracing methods at the light and electron microscopic levels, and sophisticated preparations for electrophysiological investigation. Through the judicious use of these techniques, much has been learned that has led to revision of the earlier held views of this system. In a larger context, much has been learned that is likely to be of general application in understanding the fundamental processes and principles by which the mammalian nervous system works.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
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↗