Biomedical subjects

Q Z Yang

Publications and source records attributed to Q Z Yang.

At least 19 recordsLinked to original sources

PubMed2001

Ionotropic histamine receptors and H2 receptors modulate supraoptic oxytocin neuronal excitability and dye coupling.

Histaminergic neurons of the tuberomammillary nucleus (TM) project monosynaptically to the supraoptic nucleus (SON). This projection remains intact in our hypothalamic slices and permits investigation of both brief synaptic responses and the effects of repetitively activating this pathway. SON oxytocin (OX) neurons respond to single TM stimuli with fast IPSPs, whose kinetics resemble those of GABA(A) or glycine receptors. IPSPs were blocked by the Cl(-) channel blocker picrotoxin, but not by bicuculline or strychnine, and by histamine H(2), but not by H(1) or H(3) receptor antagonists, suggesting the presence of an ionotropic histamine receptor and the possible nonspecificity of currently used H(2) antagonists. G-protein mediation of the IPSPs was ruled out using guanosine 5'-O-(2-thiodiphosphate) (GDP-betaS), pertussis toxin, and Rp-adenosine 3',5'-cyclic monophosphothioate triethylamine (Rp-cAMPs), none of which blocked evoked IPSPs. We also investigated the effects of synaptically released histamine on dye coupling and neuronal excitability. One hundred seventy-three OX neurons were Lucifer yellow-injected in horizontal slices. Repetitive TM stimulation (10 Hz, 5-10 min) reduced coupling, an effect blocked by H(2), but not by H(1) or H(3), receptor antagonists. Because H(2) receptors are linked to activation of adenylyl cyclase, TM-stimulated reduction in coupling was blocked by GDP-betaS, pertussis toxin, and Rp-cAMPs and was mimicked by 8-bromo-cAMP, 3-isobutyl-1-methylxanthine, and Sp-cAMP. Membrane potentials of OX and vasopressin neurons were hyperpolarized, accompanied by decreased conductances, in response to bath application of 8-bromo-cAMP but not the membrane-impermeable cAMP. These results suggest that synaptically released histamine, in addition to evoking fast IPSPs in OX cells, mediates a prolonged decrease in excitability and uncoupling of the neurons.

Animals↗

PubMed1999

Nitric oxide via cGMP-dependent mechanisms increases dye coupling and excitability of rat supraoptic nucleus neurons.

Unlike many neuron populations, supraoptic nucleus (SON) neurons are rich in both nitric oxide synthase (NOS) and the NO receptor-soluble guanylyl cyclase (GC), the activation of which leads to cGMP accumulation. Elevations in cGMP result in increased coupling among SON neurons. We investigated the effect of NO on dye coupling in SONs from male, proestrus virgin female, and lactating rats. In 167 slices 263 SON neurons were recorded; 210 of these neurons were injected intracellularly (one neuron per SON) with Lucifer yellow (LY). The typically minimal coupling seen in virgin females was increased nearly fourfold by the NO precursor, L-arginine, or the NO donor, sodium nitroprusside (SNP). L-Arginine-induced coupling was abolished by a NOS inhibitor. In slices from male and lactating rats who have a higher basal incidence of coupling, SNP increased coupling by approximately twofold over control (p < 0.03). SNP effects were prevented by the NO scavenger hemoglobin (20 microM) and by the selective blocker of NO-activated GC, ODQ (10 microM). These results suggest that NO released from cells within the SON can expand the coupled network of neurons and that this action occurs via cGMP-dependent processes. Because increased coupling is associated with elevated SON neuronal excitability, we also studied the effects of 8-bromo-cGMP on excitability. In both phasically and continuously firing neurons 8-bromo-cGMP (1-2 mM), but not cGMP, produced membrane depolarizations accompanied by membrane conductance increases. Conductance increases remained when depolarizations were eliminated by current-clamping the membrane potential. Thus, NO-induced cGMP increases SON neuronal coupling and excitability.

Animals↗

PubMed1997

Electrophysiology of excitatory and inhibitory afferents to rat histaminergic tuberomammillary nucleus neurons from hypothalamic and forebrain sites.

Anatomical evidence exists for projections to the tuberomammillary nucleus (TM) from the nucleus of the diagonal band of Broca (DBB) and the lateral preoptic area (LPO). The physiological effects of activating these inputs were studied by recording postsynaptic responses intracellularly from TM cells during both electrical stimulation and local nanodrop application of glutamate in horizontally cut brain slices. Electrical stimulation of the DBB, LPO and anterior lateral hypothalamic area (LH) usually evoked fast IPSPs (approximately 75% of responses) which were blocked by bicuculline or picrotoxin, suggesting GABA(A) mediation. The remaining excitatory responses evoked by stimulation of the LPO and LH were blocked by non-NMDA receptor antagonists (CNQX or NBQX) and the NMDA receptor antagonist, AP-5. Glutamate applied to the above areas induced postsynaptic responses in TM cells similar to those seen with electrical stimulation. Spontaneous firing in TM cells was suppressed by glutamate applied in the DBB. Glutamate applied in the LPO or LH evoked both inhibitory and excitatory responses. Changes in PSPs and firing rates were interpreted to result from glutamate activation of the neurons in the DBB, LPO and LH areas with inhibitory or excitatory connections to recorded TM neurons. These results support previous anatomical findings and suggest that inhibitory and excitatory synaptic control of TM activity is exerted by the DBB, LPO and LH areas.

Afferent Pathways↗

PubMed1996

Effect of pretreatment counseling on discontinuation rates in Chinese women given depo-medroxyprogesterone acetate for contraception.

The study examined the effect of pretreatment counseling upon discontinuation of 150 mg depo-medroxyprogesterone acetate (Depo-Provera (DMPA)), given for contraception. A total of 421 Chinese women participated, 204 receiving detailed structured pretreatment and ongoing counseling on the hormonal effects and probable side effects of DMPA and 217 receiving only routine counseling. The primary study endpoint was termination rate; secondary endpoints were frequency of medical events and reasons for termination. Study termination rates were significantly lower in the intensive structured counseling group than in the routine counseling group. At one year, the total cumulative termination rates were 11% (23/204) and 42% (92/217), respectively (p < 0.0001). The most common reasons for terminating DMPA were menstrual changes. No pregnancy, serious or unexpected medical events were reported, nor were statistically or clinically significant changes in vital signs observed. We conclude that pretreatment counseling on expected side effects increases the acceptability of DMPA.

Adolescent↗

PubMed1996

Synaptically released histamine increases dye coupling among vasopressinergic neurons of the supraoptic nucleus: mediation by H1 receptors and cyclic nucleotides.

Activating direct olfactory (glutamatergic) inputs to supraoptic nucleus (SON) neurons increases interneuronal coupling in slices from lactating but from not virgin or male rats. Studied here were influences on coupling of another monosynaptic input to SON, the histaminergic tuberomammillary nucleus (TM) projection, activation of which selectively excites phasically firing (putative vasopressin) cells. Effects of TM stimulation and its possible downstream consequences on Lucifer yellow (LY) dye coupling among putative vasopressin cells were determined in male rat SONs. In unstimulated slices, 12 LY injections (1 cell/SON) yielded eight single and four pairs of coupled neurons. In slices in which TM was stimulated for 10 min at 10 Hz, 13 injections yielded 4 single and 28 coupled cells, with groups of 2 to 4 cells coupled to the injected neuron, a threefold increase in the number of coupled cells per injection (p < 0.02). Bathing slices in medium containing 10 microM pyrilamine (H1 antagonist) blocked this stimulation-induced coupling increase, suggesting mediation by activation of guanylate cyclase-cGMP to which H1 receptors often are linked . Bathing slices in medium containing 0.5-1 mM 8-bromo-cGMP yielded results similar to those of TM stimulation, a 2.5-fold increase over control in the number of coupled cells per injection. Effects of TM stimulation on coupling also were blocked by bathing slices in a guanylate cyclase inhibitor (10 microM LY83583). In contrast to cGMP, 1 mM 8-bromo-cAMP significantly reduced coupling. We conclude that synaptically released histamine increases coupling via cGMP-dependent mechanisms.

Animals↗

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↗

PubMed1994

Development of early bovine embryos in different culture systems.

The objective of this study was to examine the effects of different culture systems on the development of early bovine embryos in vitro. A total of 1089 oocytes were aspirated from 2 to 5 mm follicles of ovaries collected at a local abattoir; a high proportion of the oocytes matured in vitro were fertilised by spermatozoa capacitated with caffeine and heparin. Seven to eight hours after insemination, the oocytes were transferred into three in vitro systems: A, TCM 199 + 10 per cent fetal calf serum culture medium, B, coculture with a monolayer of granulosa cells and C, coculture with bovine oviductal epithelial cells. The results showed that the proportion of the early bovine embryos which overcame the block at eight to 16 cells and developed to the morula and blastocyst stages in system C was significantly higher than in systems A or B.

Animals↗

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↗

PubMed1993

Biphasic action of sarin on monosynaptic reflex in the neonatal rat spinal cord in vitro.

The action of sarin, an organophosphorus (OP) compound, was examined in vitro for its effects on the spinal monosynaptic reflex (MSR) in neonatal rats. The effects of sarin were biphasic, i.e. facilitation at lower concentrations (2-20 nM) followed by depression of the MSR at concentrations above 30 nM. Facilitation of MSR was maximal (150% of control) at 20 nM sarin. The depression of MSR was maximal (70% of control) at 200 nM sarin, with half maximal inhibition occurring at 90 nM sarin. Atropine (200-500 nM) effectively reversed the depression caused by sarin, while pretreatment with low concentrations of atropine (10 nM) completely blocked the depression otherwise observed with sarin. Benactyzine was also effective in preventing sarin-induced depression, while pirenzepine was less effective. The nicotinic blocking agents tubocurarine and mecamylamine were, however, ineffective in preventing or reversing sarin-induced depression. The facilitation of MSR seen with lower concentrations (2-20 nM) correlated well with the blockade of late phase inhibition (between 30 and 50 ms conditioning-test interval) elicited in spinal cord by stimulating the adjacent dorsal root at various condition-test intervals, which has been shown elsewhere to be sensitive to bicuculline (Deshpande and Warnick 1988). Thus it is speculated that sarin at lower concentrations blocks GABA transmission, producing facilitation, and at higher concentrations activates the muscarinic receptors producing depression of MSR. The beneficial action of pretreatment with antimuscarinic agents may be attributed to the protection of the muscarinic receptors.

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↗

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↗

PubMed1989

Supraoptic nucleus afferents from the main olfactory bulb--II. Intracellularly recorded responses to lateral olfactory tract stimulation in rat brain slices.

To establish the functional nature of the anatomically demonstrated main olfactory bulb inputs to the supraoptic nucleus, electrophysiological responses of intracellularly recorded supraoptic neurons to lateral olfactory tract stimulation were recorded in horizontal slices of basal forebrain and hypothalamus. A total of 71 synaptically influenced neurons were studied in slices from adult rats of both sexes. Of these, 60 cells (84%) were monosynaptically activated by olfactory tract stimulation; seven cells (10%) were activated via polysynaptic pathways; and four cells (6%) were characterized by long latency inhibitory responses. Lucifer Yellow was injected into 64 cells and subsequent immunocytochemical identification of 44 of these neurons showed that both oxytocin and vasopressin cells, in approximately equal numbers, were excited by olfactory stimulation. Polysynaptically mediated excitation, however, was only associated with oxytocin cells (six of the six identified cells). These results corroborate anatomical tract tracing data showing main olfactory bulb efferents to both supraotic neurons and to neurons of the perinuclear zone. Also supported are earlier speculations of olfactory participation in release of oxytocin and vasopressin during various physiological states.

Action Potentials↗

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↗

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

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↗

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↗