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 microliter/h; 0.2, 1 and 5 micrograms/microliter) 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.