Effect of adenosine A1 receptor agonist induced‐hibernation on the arousal pathway in the Arctic Ground Squirrel

Abstract

Hibernation is a seasonal phenomenon and in the arctic ground squirrel (AGS), the effect of seasonal changes is very evident. In late fall AGS decrease their metabolic demand followed by the entry into hibernation in winter. Previously in the lab it has been shown that N6‐cyclohexyladenosine (CHA), an A1 adenosine receptor agonist, induces hibernation in AGS in a seasonally dependent manner. In winter AGS treated with CHA experience a decrease in metabolic demand and temperature as seen during natural hibernation. However, in summer CHA triggers a brief and transient metabolic suppression that does not lead to hibernation onset.As adenosine is known to promote sleep, we decided to investigate if the sleep‐arousal pathways were affecting the seasonal difference in response to CHA. The tuberomammillary nucleus (TMN) is a nucleus of the ascending arousal pathway characterized by fast firing rates to promote wakefulness. Previously we showed a decrease in neuronal activation in the TMN in AGS treated with CHA in both summer and winter seasons.Here we test the hypothesis that seasonal response to CHA is associated with difference in activation in another nucleus of the ascending arousal pathway, the locus coeruleus (LC).AGS implanted with body temperature (Tb) transmitter, were treated with CHA or vehicle (0.5mg/kg, IP). AGS were perfused with 4% paraformaldehyde and brains were dissected and cryoprotected in 5%, 10%, 15%, 20%, 30% sucrose. We performed free‐floating immunohistochemistry on 40μm brain slices in four experimental groups: winter CHA, winter control, summer CHA and summer control. We sectioned brains from eight AGS per group for a total of 32 animals and identified active nuclei with cFos immunoreactivity (mouse anti‐cFos 1:20,000, Santa Cruz) and active tyrosine hydroxylase neurons (rabbit anti‐TH). Blinded analysis of cFos immunoreactive neurons was done using bright field microscopy and Metamorph software. Statistical analysis was performed on R.CHA produced a hibernation‐like response measured by a decrease in Tb in winter AGS but not in the summer. We did not observe any significant difference in neuronal activation in the LC, thus CHA is associated with a decreased neuronal activity in the TMN, resulting in the TMN being the major wakefulness center affected by CHA but not by seasons.Support or Funding InformationResearch was supported by NIH R03 NS081637, NSF IOS‐1258179, RL5GM118990 and Alaska INBRE P20GM103395. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.