M2 muscarinic receptors in pontine reticular formation of C57BL/6J mouse contribute to rapid eye movement sleep generation

Abstract

Microinjecting the acetylcholinesterase inhibitor neostigmine into the pontine reticular formation of C57BL/6J (B6) mouse causes a rapid eye movement (REM) sleep-like state. This finding is consistent with similar studies in cat and both sets of data indicate that the REM sleep-like state is caused by increasing levels of endogenous acetylcholine (ACh). Muscarinic cholinergic receptors have been localized to the pontine reticular formation of B6 mouse but no previous studies have examined which of the five muscarinic receptor subtypes participate in cholinergic REM sleep enhancement. This study examined the hypothesis that M2 receptors in pontine reticular formation of B6 mouse contribute to the REM sleep-like state caused by pontine reticular formation administration of neostigmine. B6 mice ( n=13) were implanted with electrodes for recording states of sleep and wakefulness and with microinjection cannulae aimed for the pontine reticular formation. States of sleep and wakefulness were recorded for 4 h following pontine reticular formation injection of saline (control) or neostigmine. Experiments designed to gain insight into the muscarinic receptor subtypes mediating REM sleep enhancement involved pontine reticular formation administration of neostigmine after pertussis toxin, neostigmine after methoctramine, and neostigmine after pirenzepine. Pertussis toxin was used to block effects mediated by M2 and M4 receptors. Methoctramine was used to block M2 and M4 receptors, and pirenzepine was used to block M1 and M4 receptors. Pertussis toxin and methoctramine significantly decreased the neostigmine-induced REM sleep-like state. In contrast, pretreatment with pirenzepine did not significantly decrease the REM sleep-like state caused by neostigmine. These results support the interpretation that M2 receptors in the pontine reticular formation of B6 mouse contribute to the generation of REM sleep.