NMDA receptors induce somatodendritic secretion in hypothalamic neurones of lactating female rats (original) (raw)
Related papers
Journal of Neuroendocrinology, 2003
Despite several studies showing that the rat supraoptic (SON) and paraventricular (PVN) nuclei are innervated by noradrenergic afferents, the respective contribution of these inputs to the oxytocinergic and vasopressinergic neuronal populations remains to be clearly defined. In the present study, we used the unbiased disector method to estimate the numerical density of noradrenergic varicosities on identified oxytocinergic and vasopressinergic somata in the rat SON and PVN. The analysis was carried out on semithin (1 mm) plastic sections cut from vibratome slices (50 mm) of the SON and PVN which had been double-labelled for noradrenaline (NA) and oxytocin-or vasopressinrelated neurophysin. These preparations displayed many noradrenergic varicosities which electron microscopy showed to represent, in the main, synaptic boutons. Our quantitative analysis revealed that noradrenergic varicosities contacted oxytocinergic and vasopressinergic somata to a similar extent in male and female rats, under basal conditions of hormone secretion. The incidence of these axo-somatic contacts was similar in the SON and PVN. In contrast, in lactating rats, in which oxytocin secretion is enhanced, there was a significant increase in the density of noradrenergic varicosities apposed to oxytocinergic somata, in both nuclei. Our observations indicate that, in male and female rats under normal conditions, noradrenergic afferents innervate each type of neurosecretory somata, in both magnocellular nuclei, in a similar fashion. They reveal, moreover, that noradrenergic afferents participate in lactation-induced structural plasticity of synapses impinging on oxytocinergic somata.
Somatodendritic secretion in oxytocin neurons is upregulated during the female reproductive cycle
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2003
During the female reproductive cycle, hypothalamic oxytocin (OT) neurons undergo sharp changes in excitability. In lactating mammals, bursts of electrical activity of OT neurons result in the release of large amounts of OT in the bloodstream, which causes milk ejection. One hypothesis is that OT neurons regulate their own firing activity and that of nearby OT neurons by somatodendritic release of OT. In this study, we show that OT neuron activity strongly reduces inhibitory synaptic transmission to these neurons. This effect is blocked by antagonists of both adenosine and OT receptors and is mimicked by OT application. Inhibition of soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex formation by tetanus toxin completely blocked the stimulation-induced reduction in inhibitory input, as did the calcium chelator BAPTA. During lactation, the readily releasable pool of secretory vesicles in OT cell bodies was doubled, and calcium currents were upregulated. This...
Novel localization of NMDA receptors within neuroendocrine gonadotropin-releasing hormone terminals
Experimental biology and medicine (Maywood, N.J.), 2007
About 1000 hypothalamic neurons synthesize and release gonadotropin-releasing hormone (GnRH), the master molecule of reproduction in all mammals. At the level of the median eminence at the base of the brain, where GnRH and other hypothalamic releasing hormones are secreted into the capillary system leading to the anterior pituitary gland, there is non-synaptic regulation of neurohormone release by a number of central neurotransmitters. For example, glutamate, the major excitatory amino acid in the brain, directly regulates GnRH release from nerve terminals via NMDA receptors (NMDARs). Moreover, the effects of glutamate action on GnRH secretion are potentiated by estrogens, and this relates to the physiologic control of ovulation by the hypothalamus. We sought to determine the ultrastructural relationship between GnRH neuroterminals and NMDARs, and this regulation by estradiol. Using immunofluorescent confocal microscopy, postembedding immunogold electron microscopy, fractionation, a...
Brain Research, 1998
. Ž . Application of N-methyl-D-aspartate NMDA to the supraoptic nucleus of the hypothalamus SON generates clustered firing that may be important in hormone release. However, synaptically evoked EPSPs recorded from SON neurons exhibit varying contributions from NMDA receptors. We used the high resolution of single-channel recording to examine the receptor and ion channel properties of NMDA receptors expressed by SON neurons in 'punch' culture. Biocytin introduced into individual neurons during patch clamp Ž . Ž . recording revealed large 32.1 " 3.3 mm , oblong somas and bipolar extensions typical of magnocellular neuroendocrine cells MNCs .
Lactation induces increased IPSC bursting in oxytocinergic neurons
Physiological Reports
Hypothalamic magnocellular neurosecretory cells (MNCs) undergo dramatic structural reorganization during lactation in female rats that is thought to contribute to the pulsatile secretion of oxytocin critical for milk ejection. MNCs from male rats generate robust bursts of GABAergic synaptic currents, a subset of which are onset-synchronized between MNC pairs, but the functional role of the IPSC bursts is not known. To determine the physiological relevance of IPSC bursts, we compared MNCs from lactating and non-lactating female rats using whole-cell recordings in brain slices. We recorded a sixfold increase in the incidence of IPSC bursts in oxytocin (OT)-MNCs from lactating rats compared to non-lactating rats, whereas there was no change in IPSC bursts in vasopressin (VP)-MNCs. Synchronized bursts of IPSCs were observed in pairs of MNCs in slices from lactating rats. Our data indicate, therefore, that IPSC bursts are upregulated specifically in OT-MNCs during lactation, and may, therefore, contribute via rebound depolarization to the spike trains in OT neurons that lead to reflex milk ejection.
Molecular and Cellular …, 2005
Expression, functional properties, and clustering of A1-, A2-, and A3subunit containing GABA A receptors (GABA A Rs) were studied in dorsomedial SON neurons of the adult female rat supraoptic nucleus (SON) around parturition. We show that, although the decay time constant (t decay ) of GABAergic postsynaptic currents between and within individual recordings was very diverse, ranging from fast (i.e., A1-like) to significantly slower (i.e., non-A1-like), there was an overall shift towards slower decaying synaptic currents during the onset of lactation. This shift is not due to changes in mRNA expression levels, because real-time quantitative PCR assays indicated that the relative contribution of A1, A2, and A3 remained the same before and after parturition. Also, changes in phosphorylation levels are not likely to affect the t decay of postsynaptic currents. In A-latrotoxin (A-LTX)induced bursts of synaptic currents from individual synapses, the t decay of consecutive synaptic events within bursts was very similar, but between bursts there were large differences in t decay . This suggested that different synapses within individual SON neurons contain distinct GABA A R subtypes. Using multilabeling confocal microscopy, we examined the distribution of postsynaptic A1-, A2-, and A3-GABA A Rs, based on colocalization with gephyrin. We show that the three GABA A R subtypes occurred either in segregated clusters of one subtype as well as in mixed clusters of two or possibly even three receptor subtypes. After parturition, the density and proportion of clusters containing A2-(or A3-) but not A1-GABA A Rs, was significantly increased. Thus, the functional synaptic diversity at the postsynaptic level in dorsomedial SON neurons is correlated with a differential clustering of distinct GABA A R subtypes at individual synapses.