Alterations of "sleeping time" in the rat induced by drugs which modulate central monoaminergic systems

The effects of adrenoceptor agonists and antagonists have been determined on "sleeping time" in the rat--that is, with the animal immobile and adopting a sleeping posture. Alterations in their gross behaviour patterns were assessed also. The specific alpha 2-adrenoceptor agonists (yohimbine, WY 26393, RX 781094 and RS 21361) decreased sleeping time, as did the beta-adrenoceptor agonist clenbuterol. The specific alpha 2-adrenoceptor agonist clonidine gave a large increase in sleeping time at doses in excess of 25 micrograms kg-1. The same effect was seen with the beta-antagonist propranolol and the specific beta 2-antagonist ICI 118551.