Muscarinic and adenosine receptor mechanisms contributing to rapid eye movement sleep in C57BL/6J mouse.

Abstract

The recent derivation of the mouse genome has made the mouse the most important animal model in biomedical research. Little is known about the neuropharmacology of arousal state control in mouse. The three studies that comprise this thesis sought to elucidate the pontine muscarinic and adenosine receptor mechanisms contributing to the rapid eye movement (REM) phase of sleep in C57BL/6J (B6) mouse. The first study used drug delivery by microinjection to test the hypothesis that M2 muscarinic receptors in the pontine reticular formation (PRF) of B6 mouse contribute to the REM sleep-like state caused by PRF administration of the acetylcholinesterase inhibitor neostigmine. The neostigmine-induced REM sleep-like state was inhibited by pertussis toxin and the M2/M4 muscarinic antagonist methoctramine but not by the M1/M4 muscarinic antagonist pirenzepine. The second study used microdialysis to test the hypothesis that muscarinic autoreceptors in the PRF modulate ACh release. ACh release was increased by the muscarinic antagonists scopolamine, AF-DX 116, and pirenzepine and decreased by the muscarinic agonist bethanechol. The third study used microdialysis and EEG analysis to test the hypothesis that activation of adenosine A_2A receptors in the PRF increases ACh release and enhances REM sleep. The A_2A receptor agonist CGS 21680 (3 muM) increased ACh release in the PRF. Co-administration of the A_2A receptor antagonist ZM 241385 prevented the CGS 21680-evoked increase in ACh release. Additionally, PRF dialysis with CGS 21680 (3 muM) increased NREM and REM sleep. Regression analysis revealed that CGS 21680-evoked ACh release in the PRF accounted for 83% of the variance in REM sleep. Together, these studies show for the first time in B6 mouse that (1) M2 receptors in the PRF contribute to the generation of REM sleep, (2) muscarinic autoreceptors modulate ACh release in the PRF, and (3) A_2A receptors in the PRF contribute to the regulation of REM sleep, in part, by modulating ACh release. The results demonstrate the feasibility of using cholinergic neurotransmission as a phenotype in the B6 mouse and encourage additional phenotyping of mouse strains in which genetic factors have been demonstrated to modulate arousal.