THE ROLE OF ALPHA-2 RECEPTORS IN THE MEDIAL PREOPTIC AREA IN THE REGULATION OF SLEEP-WAKEFULNESS AND BODY-TEMPERATURE

The study was conducted on 48 free-moving male rats to find out the ro le of the medial preoptic alpha(2) receptors in the regulation of slee p and body temperature. Recording electrodes for assessment of sleep-w akefulness, and injector cannulae for injection of drugs in the medial preoptic area were chronically fixed on the skulls of the animals. Th e noradrenergic fibres projecting to the medial preoptic area were des troyed in 24 rats by administration of 6-hydroxydopamine at the ventra l noradrenergic bundle. Though arousal was produced in normal rats by the injection of the alpha(2) adrenergic agonist, clonidine, at the me dial preoptic area, it induced sedation in rats with noradrenergic fib re lesion. Clonidine did not alter the rectal temperature in normal ra ts but it induced hypothermia in lesioned rats. Injection of alpha(2) antagonist, yohimbine, at the medial preoptic area induced sleep in ra ts with intact noradrenergic fibres. However, the sleep inducing effec t of this drug was very much attenuated in the lesioned animals. There was no significant change in body temperature, in both these groups o f animals, after yohimbine administration. The study indicates the rol e of presynaptic alpha(2) adrenergic receptors in arousal response and indirectly supports the contention that the alpha(1) postsynaptic rec eptors at, the medial preoptic area are involved in hypnogenesis. It a lso suggests that the thermal changes induced by adrenergic system are mediated through alpha(1) postsynaptic receptors. But the thermal cha nges do not contribute towards the induced alterations in sleep-wakefu lness. It is proposed that there should be separate sets of noradrener gic terminals for regulation of sleep and body temperature. (C) 1998 I BRO. Published by Elsevier Science Ltd.