The hypothalamo‐hypophyseal rat explant in vitro: endocrinological studies of the pars intermedia dopaminergic neural input.

Abstract

to the perfusion medium not only completely and reversibly blocked the stimulusinduced inhibition of MSH release but by itself, significantly increased the basal secretion rate.6. Applied to the isolated n.i.l., 1-sulpiride did not alter release but did prevent the inhibitory response caused by exogenously applied dopamine (01 ,uM).7. The y-aminobutyric acid receptor antagonist, bicuculline (001-10 AM), had no effect on any of the parameters studied.8. In explants, cutting the infundibular stalk linking the mediobasal hypothalamus with the n.i.l., mimicked the effects of 1-sulpiride by interrupting impulse flow to the gland.9. Thus, electrical stimulation of hypothalamic neurones in these explants appar-* Current address:

Intracellular Recordings from Neurons of the Arcuate Nucleus in Superfused Explants of Rat Hypothalamus

“…In agreement with previous anatomical and electrophysiological studies in vivo (17,18,30], our results sug gest that a number of ARN neurons project to the neu rointermediate lobe ( fig. 6A), where they may release neurotransmitters (e.g.…”

“…A first class, the tuberoinfundibular (TI) neurons, project toward the median eminence where their axon terminals form neurohaemal contacts with the pri mary plexus of the hypophysial portal system to secrete hypophysiotrophic substances [16]. A second group of cells, the tuberohypophysial (TH) neurons, are known to project their axons into the neurointermediate lobe of the pituitary, where neurotransmitters are released to regu late the secretion of pro-opiomelanocortin-derived pep tides from secretory cells of the pars intermedia [17,18].…”

Orexin A activates leptin-responsive neurons in the arcuate nucleus

“…Stimulation of neurons in the ARC releases NPY [24,32] and inhibits the release of α-MSH in the hypothalamus [3]. Therefore, we suspect that rapid activation of ARC neurons by orexin would similarly increase NPY and decrease α-MSH release in brain areas where axons of ARC neurons terminate and thereby stimulate food intake.…”

Nicotinic acetylcholine receptors in porcine hypophyseal intermediate lobe cells.

“…Likewise, excitatory effects are expected when activating postsynaptically situated central nicotinic receptors. Responses would then be expected to be more rapid than the indirect process of disinhibition which is generally believed to be the essential mechanism by which hypothalamic afferents stimulate pituitary function in the IL (Douglas & Taraskevich, 1982;Davis 1986).…”

“…Indeed IL cells are inserted in the dopaminergic neuropile issued from the tubero-infundibular pathway, and they display the highest density of functional dopamine D2 receptors in the brain (see Fig. 15 in Sales, Martres, Bouthenet & Schwartz, 1989, and references in Davis, 1986). However, until recently little attention was paid to cholinergic mechanisms in this structure, except for a preliminary report describing muscarinic and nicotinic stimulation of z-MSH release from dispersed frog IL cells (Louiset, Lamacz, Basille, Van De Put, Tonon, Vaudry & Cazin, 1989).…”