Seasonal decrease in thermogenesis and increase in vasoconstriction explain seasonal response to (6)N-cyclohexyladenosine-induced hibernation in the Arctic Ground Squirrel (Urocitellus parryii).

• Published in: Journal of Neurochemistry
• Main Authors: Frare, C., Jenkins, M.E., McClure, K. M., Drew, K.L.
• Format: Text
• Language: English
• Published: 2019
• Subjects: Article; Arctic; Arctic ground squirrel; Urocitellus parryii
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6819227/; http://www.ncbi.nlm.nih.gov/pubmed/31273780; https://doi.org/10.1111/jnc.14814

Hibernation is a seasonal phenomenon characterized by a drop in metabolic rate and body temperature. Adenosine A(1) receptor agonists promote hibernation in different mammalian species, and the understanding of the mechanism inducing hibernation will inform clinical strategies to manipulate metabolic demand that are fundamental to conditions such as obesity, metabolic syndrome and therapeutic hypothermia. Adenosine A(1) receptor agonist-induced hibernation in arctic ground squirrels is regulated by an endogenous circannual (seasonal) rhythm. This study aims to identify the neuronal mechanism underlying the seasonal difference in response to the adenosine A(1) receptor agonist. Arctic ground squirrels were implanted with body temperature transmitters and housed at constant ambient temperature (2°C) and light cycle (4L:20D). We administered CHA ((6)N-cyclohexyladenosine), an adenosine A(1) receptor agonist in euthermic-summer phenotype and euthermic-winter phenotype and used cFos and phenotypic immunoreactivity to identify cell groups affected by season and treatment. We observed lower core and subcutaneous temperature in winter animals and CHA produced a hibernation-like response in winter, but not summer. cFos-ir was greater in the median preoptic nucleus and the raphe pallidus in summer after CHA. CHA administration also resulted in enhanced cFos-ir in the nucleus tractus solitarius and decreased cFos-ir in the tuberomammaliary nucleus in both seasons. In winter, cFos-ir was greater in the supraoptic nucleus and lower in the raphe pallidus than in summer. The seasonal decrease in the thermogenic response to CHA and the seasonal increase in vasoconstriction, assessed by subcutaneous temperature, reflect the endogenous seasonal modulation of the thermoregulatory systems necessary for CHA-induced hibernation.