Central adrenoceptors modify hypothalamic thermoregulatory patterns of autonomic activity in conscious rabbits.

In conscious rabbits with indwelling intracisternal (i.c.) catheters i.c. injection of noradrenaline (range 20 - 2000 ng) elicited dose-related cutaneous vasoconstriction of the ear skin vessels and reduction in renal sympathetic vasoconstrictor activity (integrated mass discharge). In addition there was shivering and a rise in the animals "core" temperature, so that the injections of noradrenaline mimicked the normal thermoregulatory pattern of cooling. In 5 other rabbits with implanted hypothalamic thermodes we studied the responses of the ear temperature, renal sympathetic nerve activity and respiration rate to hypothalamic heating and cooling. The animals were studied: (i) under control conditions; (ii) after i.c. administration of noradrenaline: (iii) 24 h after 6-hydroxydopamine (6-OHDA) when there is marked depletion of CNS noradrenergic transmitter stores. After the drugs the temperature-response curves were displaced from control in approximately parallel fashion with little change in gain. Noradrenaline elicited shifts that were directionally opposite to those produced by 6-OHDA, suggesting that the changes in thermoregulatory properties were specific effects of the transmitter. Previous studies also suggest that the site of modulation of the thermoregulatory response is at bulbospinal levels, at least as far as the renal sympathetic response was concerned.