Changes in Body Temperature and Sleep-Wakefulness After Intrapreoptic Injection of Methoxamine in Rats

Several pieces of evidence suggest that the noradrenergic afferents in the medial preoptic area produce sleep and hypothermia by acting on α(1) adrenergic receptors. On the other hand, in a few studies monitoring body temperature with a rectal probe, preoptic injection of the α(1) adrenergic agonist methoxamine produced contradictory changes in body temperature and sleep-wakefulness. Such contradictions call for the re-examination of methoxamine induced body temperature changes using a better technique like telemetric recording. In the present study, we monitored body temperature and sleep-wakefulness simultaneously after the micro-injection of 0.5, 1, and 2 μmol methoxamine, into the medial preoptic area of adult male Wistar rats. Methoxamine injection produced hypothermia but no major change in sleep-wakefulness during the 3 hours after drug injection, except for a short period (15 min) of sleep after 120 min of injection. A short period of wakefulness, coinciding with the maximum fall in body temperature (30 min after injection) occurred when methoxamine was administered at higher doses. The results of this study indicate that 1 adrenergic receptors participate in preoptically mediated thermoregulatory measures that reduce body temperature. Hypothermia induced by methoxamine might have masked the hypnogenic action of this drug.