An electrophysiological dissection of the hypothalamic regions which regulate the pre‐ovulatory secretion of luteinizing hormone in the rat

Publisher Website
Google Scholar
Abstract
1. Extracellular action potentials were recorded from 299 single units in the preoptic and anterior hypothalamic areas of fifty-two female rats anaesthetized with urethane. The units were categorized by their response to single biphasic pulses (ca. 1 mA; 1 msec duration) applied to the ventromedial/arcuate region of the hypothalamus.2. Experiments with five lactating rats demonstrated that the effective zone of stimulation was confined within the ventromedial/arcuate region. This observation was supported by further evidence obtained during unit recording sessions.3. Antidromic action potentials were recorded from 122 (41%) of the neurones monitored in preoptic and anterior hypothalamic areas. These Type A cells were characterized by their very slow discharge rate (median for spontaneously active units 1.2 spikes/sec) when contrasted with adjacent cells (median 3.9 spikes/sec). Orthodromic action potentials were not observed in thirty-six Type A cells. The antidromically identified neurones had an average conduction rate of 0.32 m/sec. The absolute refractory period of the soma, computed by separation of the IS and SD components of the antidromic action potentials recorded from forty-four neurones, ranged from < 3.0 to > 100 msec. With ten units it was not possible to obtain a soma dendritic (SD) wave by antidromic activation even though the initial segment (IS) wave was seen clearly and the orthodromic potentials consisted of both IS and SD waves.4. Type B cells (32% of population) were excited and/or inhibited by the ventromedial/arcuate stimulation but were not antidromically activated. This post-stimulatory change in discharge rate lasted for up to 400 msec.5. Type C cells (27% of population) showed no change in spontaneous activity after stimulation of the ventromedial arcuate area. These neurones had discharge rates similar to Type B cells.6. The previously reported prooestrous increase in firing rate, recorded from neurones in the ventral part of the preoptic/anterior hypothalamic area was restricted to cell Types B and C.