Sleep and Core Temperature Measures Following Microinjection of Muscimol into the Medial Preoptic Area in Rats

Anumber of compounds, including triazolam (1,2), pentobarbital (3), ethanol (4), and adenosine (5) have been shown to induce sleep when injected into the medial preoptic area of rats. The mechanism by which this occurs remains to be clearly elucidated, though the high affinity for triazolam for the benzodiazepine recognition site on the GABA-A-benzodiazepine receptor complex, and the interaction of pentobarbital and ethanol with its function, suggest that sleep may be initiated by increased GABAergic activity. In this view, the GABA recognition site and the benzodiazepine recognition site respond to binding of agonists by a complex interaction, the result of which is enhanced flux at the chloride ionophore (6,7). One difficulty with this approach has been two sets of studies, one of which indicated that microinjection of the GABAA agonist muscimol into the anterior hypothalamus of cats increases wakefulness instead of sleep (8), while another reported that when given peripherally to rats, muscimol and the benzodiazepine gypnotic midazolam have differing effects on EEG power spectra during NREM sleep (9), and may have opposite effects on the amount of REM sleep (10). In order to explore the possible role of enhanced GABAergic activity in the MPA on sleep, we are now reporting on a study in which we have administered muscimol into the MPA in rats. A finding that muscimol, Sleep and Core Temperature Measures Following Microinjection of Muscimol into the Medial Preoptic Area in Rats