Sympathetic and hyperthermic reactions by orexin A: Role of cerebral catecholaminergic neurons

This experiment tested the effect of a lesion of cerebral catecholaminergic neurons on the sympathetic and thermogenic effects induced by an intracerebroventicular (icv) injection of orexin A. The firing rates of the sympathetic nerves to the interscapular brown adipose tissue (IBAT), along with IBAT, colonic temperatures and heart rate were monitored in urethane-anesthetized male Sprague–Dawley rats before an injection of orexin A (1.5 nmol) into the lateral cerebral ventricle and over a period of 150 min after the injection. Three days before the experiment, the rats were pre-treated with an icv injection of 6-hydroxydopamine (6-OHDA) or 6-OHDA plus desipramine or saline. The results show that orexin A increases the sympathetic firing rate, IBAT, colonic temperatures and heart rate in the rats pre-treated with saline. This increase is blocked by the pre-treatment with 6-OHDA alone or 6-OHDA plus desipramine. These findings indicate that cerebral catecholaminergic neurons (particularly the dopaminergic pathway) play a fundamental role in the complex reactions related to activation of the orexinergic system.