In vitro Neurophysiology of Identified Rat Hypothalamic ‘Neuroendocrine’ Neurons

Abstract

Stable synaptic and antidromic electrophysiological recordings were obtained for 10–15 h from identified neurohypophyseal and tuberoinfundibular neurons using an acute explant of rat hypothalamus maintained in vitro through perfusion of the carotid artery with oxygenated artificial media. Synaptic potentials from preoptic and median eminence stimulation were blocked during perfusion with 12 m M Mg⁺⁺-containing solutions. Antidromic and spontaneous action potentials recorded in neurohypophyseal neurons were followed by a transient after-hyperpolarization of 3–10 mV, due primarily to a brief increase in potassium conductance. Evidence favoring the existence of a synaptic recurrent inhibitory pathway was present in records obtained from tuberoinfundibular neurons, but not from neurohypophyseal cells.

Activity dependence and functional role of the apamin‐sensitive K+ current in rat supraoptic neurones in vitro.

“…(Blatz & AMagleby, 1987). (Bourque & Renaud, 1990Dyball et al 1991 (Poulain & Wakerley, 1982). It has been proposed that the gradual onset of a slow Ca2+-activated K+ conductance could contribute to the reduction in firing rate seen at the start of a phasic burst, as well as to the eventual termination of the burst itself (Andrew & Dudek, 1984b;Bourque et al 1985).…”

“…Spontaneous phasic bursts recorded in vivo and in vitro feature a brief (-1 s) initial period of rapid firing which quickly diminishes to a lower rate that is maintained for the remainder of the burst. In the neurohypophysial axon terminals this initial period of high frequency firing may precipitate action potential broadening (Bourque, 1990) and spike-evoked Ca2+ influx (Jackson, Konnerth & Augustine, 1991), thereby facilitating peptide release (Bicknell, 1988). However, previous experiments have shown that sustained repetitive stimulation at high frequencies causes fatigue of hormone release from the neurohypophysis (Ingram, Bicknell, Brown & Leng, 1982).…”

“…They were therefore considered to be MNCs since such properties are regarded as being specific to supraoptic neurones projecting to the neurohypophysis in vivo Dyball, Tasker, Wuarin & Dudek, 1991) and in vitro (Bourque & Renaud, 1990), but not to neighbouring non-neurosecretory cells. The neurones analysed showed resting input resistances greater than 120 MQl, membrane potentials of less than -50 mV and action potential amplitudes measured from baseline of greater than 70 mV.…”

“…Modulation of IAHP amplitude, therefore, has been proposed as a mechanism for the regulation of DAP amplitude and phasic firing (Bourque, 1986;Bourque & Renaud, 1990). However, the onset of phasic bursts arises from the summation of the DAPs that follow individual spikes (Andrew & Dudek, 1983, 1984aBourque, 1986).…”

Electrophysiology of guinea‐pig supraoptic neurones: role of a hyperpolarization‐activated cation current in phasic firing.

“…The supraoptic nucleus (SON) in mammals chiefly contains magnocellular neurosecretory cells (MNCs) which secrete arginine vasopressin (AVP) or oxytocin (OT) into the bloodstream via axon terminals in the neurohypophysis (Silverman & Zimmerman, 1983). Studies in the rat utilizing in vivo (Dutton & Dyball, 1979;Moos & Richard, 1983;Cirino & Renaud, 1985;Belin & Moos, 1985; Blackburn, Leng & Russell, 1987), or in vitro (Armstrong & Sladek, 1982;Mason, 1983;Bourque & Renaud, 1983Andrew & Dudek, 1983 techniques, have characterized the AVP-secreting neurones as firing in repeated bursts of action potentials (phasic firing), whereas OT-secreting neurones fire in a slow, irregular pattern. OT cells also fire in continuous high-frequency bursts during milk ejection.…”