Hormones, feeding and temperature in sheep following cerebroventricular injections of neurotransmitters and carbachol

Abstract

1. The neural mechanisms involved in the control of prolactin and growth hormone secretion, body temperature and feeding in castrated male sheep were investigated by the lateral cerebroventricular injection of several putative neurotransmitters and carbachol. 2. Feeding was inhibited by 10 and 20 microgram carbachol and by 400 microgram histamine. 100 microgram Noradrenaline stimulated, but 200 microgram inhibited, feeding; however, both results were non-significant compared with controls. 3. 20 microgram Carbachol elicited a highly significant rise in plasma growth hormone, suggesting a cholinergic component in the neural control of growth hormone in sheep. Noradrenaline, dopamine and 5-hydroxytryptamine, but not melatonin, significantly depressed plasma prolactin concentration indicating a similar neural control for the hormone's release in sheep as in other species. 4. Deep body temperature appeared unaffected by any ofthe injected drugs. 5. The possible interrelationships between feeding behaviour and the circulating levels of growth hormone in ruminants is discussed. 6. A method for the radioimmunoassay of ovine growth hormone is described and validated.