Complete inhibition of adrenocortical responses following sciatic nerve stimulation in rats with hypothalamic islands

Previous studies from this laboratory have demonstrated that in rats with hypothalamic islands the adrenocortical response to photic and acoustic stimulation was partially inhibited indicating that they were at least to a certain degree neurally mediated, though ether stress produced normal adrenocortical responses. With the purpose of determining to what extent afferent somatosensory connections to the hypothalamus participate in the activation of adrenocortical responses following sciatic nerve stimulation, the effects of this stimulus applied through chronically implanted electrodes were studied on the plasma corticosterone levels in pentobarbital anaesthetized intact animals and in rats with hypothalamic islands. Ether stress or sciatic nerve stimulation for 2 min in intact rats produced a rise of plasma corticosterone to 32.1 plus or minus 1.2 and 32.1 plus or minus 1.8 mug/100 ml, respectively. However, in animals with hypothalamic islands the corresponding values were 29.2 plus or minus 1.8 and 12.4 plus or minus 0.8 mug/100 ml, respectively. The latter value was not significantly different from the basal corticosterone levels (13.0 plus or minus 1.2 mug/100 ml) found in rats 15 min after pentobarbital anaesthesia, the time when the sciatic stimulus was applied. The present data indicate that the adrenocortical discharge following sciatic nerve stimulation is completely inhibited by hypothalamic deafferentation and therefore depends entirely on the activation of the afferent neural pathways to the hypothalamus.