alpha-Melanocyte-stimulating hormone (alpha-MSH) release from perifused rat hypothalamic slices.
A perifusion system was developed to investigate the control of alpha-melanocyte-stimulating hormone (alpha-MSH) release from rat brain. Hypothalamic slices were perifused with Krebs-Ringer bicarbonate (KRB) medium supplemented with glucose, bacitracin and bovine serum albumin. Fractions were set apart every 3 min and alpha-MSH levels were measured by means of a specific and sensitive radioimmunoassay method. Hypothalamic tissue in normal KRB medium released alpha-MSH at a constant rate corresponding to 0.1% of the total hypothalamic content per 3 min. The basal release was not altered by Ca2+ omission in the medium or addition of the sodium channel blocker tetrodotoxin (TTX). Depolarizing agents such as potassium (50 mM) and veratridine (50 microM), which is known to increase Na+ conductance, significantly stimulated alpha-MSH release in a Ca2+-dependent manner. When Na+-channels were blocked by TTX (0.5 microM) the stimulatory effect of veratridine was completely abolished whereas the K+-evoked release was unaffected. These findings suggest that: voltage-dependent sodium channels are present on alpha-MSH hypothalamic neurons; depolarization by K+ induces a marked stimulation of alpha-MSH release; K+- and veratridine-evoke releases are calcium-dependent. Altogether, these data provide evidence for a neurotransmitter or neuromodulator role for alpha-MSH in rat hypothalamus.
D000818:Animals; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D066298:In Vitro Techniques; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D008854:Microscopy, Electron; D011188:Potassium / Q000494:pharmacology; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013779:Tetrodotoxin / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology
D013779:Tetrodotoxin; D014701:Veratridine; D009074:Melanocyte-Stimulating Hormones; D011188:Potassium