Inhibition of NMDA-type glutamate receptors induces arousal from torpor in hibernating arctic ground squirrels (Urocitellus parryii).
Hibernation is an adaptation to overcome periods of resource limitation often associated with extreme climatic conditions. The hibernation season consists of prolonged bouts of torpor that are interrupted by brief interbout arousals. Physiological mechanisms regulating spontaneous arousals are poorly understood, but may be related to a need for gluconeogenesis or elimination of metabolic wastes. Glutamate is derived from glutamine through the glutamate-glutamine cycle and from glucose via the pyruvate carboxylase pathway when nitrogen balance favors formation of glutamine. This study tests the hypothesis that activation of NMDA-type glutamate receptors (NMDAR) maintains torpor in arctic ground squirrel (arctic ground squirrel (AGS); Urocitellus parryii). Administration of NMDAR antagonists MK-801 (5 mg/kg, i.p.) that crosses the blood-brain barrier and AP5 (5 mg/kg, i.p.) that does not cross the blood-brain barrier induced arousal in AGS. Central administration of MK-801 (0.2, 2, 20 or 200 μg; icv) to hibernating AGS failed to induce arousal. Results suggest that activation of NMDAR at a peripheral or circumventricular site is necessary to maintain prolonged torpor and that a decrease in glutamate at these sites may contribute to spontaneous arousal in AGS.
Institute of Arctic Biology, Department of Chemistry and Biochemistry, Alaska Basic Neuroscience Program, University of Alaska Fairbanks, AK, USA.
Tulasi R
TR
Jinka
Brian T
BT
Rasley
Kelly L
KL
Drew
D000704:Analysis of Variance; D000818:Animals; D001110:Arctic Regions; D001143:Arousal / Q000187:drug effects / Q000502:physiology*; D001831:Body Temperature / Q000187:drug effects; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004333:Drug Administration Routes; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006605:Hibernation / Q000187:drug effects / Q000502:physiology*; D007276:Injections, Intraventricular; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D012589:Sciuridae / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D014326:Tropanes / Q000494:pharmacology; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D012702:Serotonin Antagonists; D014326:Tropanes; D016291:Dizocilpine Maleate; C056639:2-amino-5-phosphopentanoic acid; D014633:Valine; C042253:bemesetron