THE POSSIBLE INVOLVEMENT OF ASPARTATE RECEPTORS IN CENTRAL THERMOREGULATION IN THE SHEEP

¹ Agricultural Research Council Institute of Animal Physiology, Babraham, Cambridge CB2 4AT

Experiments have been done to investigate the possible existence of aspartate receptors on the hypothalamic pathways which control thermoregulation in the sheep. The effect of intracerebroventricular (I.C.V.) injections of the excitatory amino acid receptor blocker DL-,-aminopimelic acid (DAPA) on thermoregulatory effector mechanisms and rectal temperature (T_re) has been examined in sheep at different ambient temperatures. At low ambient temperatures, DAPA causes a decrease in heat production and conservation and a fall in T_re. At higher ambient temperatures there is some evidence for a decrease in heat loss and a rise in T_re. DAPA attenuated the stimulatory effect on heat-production/conservation mechanisms produced by I.C.V. injections of L-aspartate but was without effect on the thermoregulatory responses to I.C.V. injections of carbachol and 5-hydroxytryptamine or I. V. injections of a pyrogen. I.C.V. injections of the L-aspartate analogue, N-methyl-DL-aspartate produced similar effects to L-aspartate. The results provide support for the suggestion that aspartate receptors may be present on the hypothalamic pathway between cold-sensors and heat-production/conservation effectors. Evidence for the existence of such receptors on the pathway between warm-sensors and heat-loss effectors remains scant.