Patch-clamp analysis of spontaneous synaptic currents in supraoptic neuroendocrine cells of the rat hypothalamus

Abstract

Spontaneous synaptic currents were recorded in supraoptic magnocellular neurosecretory cells using whole-cell patch-clamp techniques in the rat hypothalamic slice preparation. Numerous spontaneous excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) were observed in the 27 cells recorded. The rate of occurrence of the spontaneous currents and the relative proportion of EPSCs versus IPSCs varied significantly from cell to cell. Miniature EPSCs and IPSCs were clearly distinguished from background noise in TTX (n = 3 cells at 0.5 micrograms/ml). The frequency of EPSCs and IPSCs decreased by approximately 70% and the largest events were blocked in TTX, but the peaks of the amplitude histograms were shifted by only a few picoamperes. Bicuculline (n = 10 cells at 10 microM and 2 cells at 20 microM) blocked completely all the IPSCs without any detectable effect on the frequency or amplitude of the EPSCs. No slow spontaneous outward currents, indicative of a K+ current from activation of GABAB receptors, were observed. The alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate-type glutamate receptor antagonist 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (CNQX; n = 7 cells at 10 microM) consistently blocked all EPSCs without any apparent effect on the frequency or amplitude of the IPSCs. No synaptic events could be detected when CNQX was applied in combination with bicuculline (n = 4). The decay phase of averaged spontaneous IPSCs and EPSCs recorded at resting membrane potential could be well fitted by single exponential functions in most cells. The time constants ranged from 0.92 to 3.0 msec for EPSCs (five cells) and from 5.3 to 6.6 msec for IPSCs (four cells). A second, slower time constant of 4-15 msec was found in the largest averaged EPSCs (> or = 40 pA). The amplitude of this slow component was -2 to -4 pA. These results suggest that, in the in vitro slice preparation, glutamate mediates all the spontaneous EPSCs in magnocellular neurosecretory cells by acting primarily on AMPA/kainate-type receptors at resting membrane potential and that activation of GABAA receptors mediates most if not all IPSCs.

Progesterone-metabolite prevents protein kinase C-dependent modulation of gamma -aminobutyric acid type A receptors in oxytocin neurons

“…Synchronous firing of magnocellular neurons in the supraoptic nucleus (SON) and the paraventricular nucleus triggers oxytocin release. The spiking frequency of these neurons is under control of a GABAergic input (1)(2)(3). The postsynaptic ␥-aminobutyric acid type A (GABA A ) receptors that mediate this input are susceptible to allosteric interaction with the neurosteroid allopregnanolone 3␣-OH-DHP during some stages of the female reproductive cycle, in particularly during pregnancy (4,5).…”

Pre‐ and postsynaptic modulation of the electrical activity of rat supraoptic neurones

“…The release of the two hormones is closely related to the electrical activity of the magnocellular neurones, which is known to be modulated by various neurotransmitters and neuromodulators (for recent reviews, see Hatton, 1990; Armstrong, 1995; Leng et al 1999). The site of modulation is thought to be mainly at the soma or dendrites, aiid fast synaptic inputs via ionotropic GABA and glutamate receptors play major roles in this modulation (Wuarin & Dudek, 1993).It has been reported that GABA and glutamate are present in approximately 50% and 30%, respectively, of the total presynaptic neurones in the region of the supraoptic nucleus (Meeker et al 1993) and that spontaneous excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) in supraoptic neurones directly reflect the spontaneous release of glutamate and GABA from the terminals of presynaptic neurones at the supraoptic nucleus (Wuarin & Dudek, 1993; Kabashima et al 1997). Many different types of receptors are present at presynaptic sites in the supraoptic nucleus, but whether or not the ligands that activate these receptors influence the release of the two major neurotransmitters remains to be elucidated.…”

“…The release of the two hormones is closely related to the electrical activity of the magnocellular neurones, which is known to be modulated by various neurotransmitters and neuromodulators (for recent reviews, see Hatton, 1990; Armstrong, 1995; Leng et al 1999). The site of modulation is thought to be mainly at the soma or dendrites, aiid fast synaptic inputs via ionotropic GABA and glutamate receptors play major roles in this modulation (Wuarin & Dudek, 1993).…”

“…It has been reported that GABA and glutamate are present in approximately 50% and 30%, respectively, of the total presynaptic neurones in the region of the supraoptic nucleus (Meeker et al 1993) and that spontaneous excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) in supraoptic neurones directly reflect the spontaneous release of glutamate and GABA from the terminals of presynaptic neurones at the supraoptic nucleus (Wuarin & Dudek, 1993;Kabashima et al 1997). Many different types of receptors are present at presynaptic sites in the supraoptic nucleus, but whether or not the ligands that activate these receptors influence the release of the two major neurotransmitters remains to be elucidated.…”

Symposium Proceedings

“…1983) and in vitro (Randle & Renaud, 1987). Furthermore, all spontaneous inhibitory postsynaptic potentials in supraoptic neurones in vitro are GABA mediated (Randle et al 1986;Wuarin & Dudek, 1993). The important role of GABA in control of VP and OT neuronal activity suggested by anatomical and electrophysiological evidence has been further supported by functional studies.…”