Reduction of hibernation bout duration by intraventricular infusion of met-enkephalin

The potential of brain met-enkephalin (met-enk) systems to modulate central nervous system (CNS) activity during periods of general depression (modeled by the mammalian hibernation state) was studied in the ground squirrel ( Citellus lateralis). Following entrance into hibernation, continuous met-enk infusion into the lateral ventricle (1 μl/h; 0.2, 1 and 5 μg/μl) produced a dose-dependent reduction in bout duration ranging from 1.2 to 3.9 days (13.8–44.6% of baseline bout duration). We suggest that the activity of met-enk-releasing neurons may serve to increase the excitability of the depressed CNS, thus accelerating the termination of the hibernation bout.