Acetylcholine release in the pontine reticular formation of C57BL/6J mouse is modulated by non-M1 muscarinic receptors

Pontine acetylcholine (ACh) contributes to the regulation of electroencephalographic and behavioral arousal in all mammals so far investigated. The mouse is recognized as a powerful model for pharmacogenomics but the synaptic mechanisms regulating ACh release in mouse pontine reticular formation have not been characterized. Drug delivery by microdialysis was used in isoflurane-anesthetized C57BL/6J (B6) mice (n=33) to test the hypothesis that muscarinic autoreceptors modulate ACh release in the pontine reticular nucleus, oral part (PnO). Dialysis delivery of tetrodotoxin to the PnO significantly decreased ACh by 58% below control levels, confirming that measured ACh reflected neurotransmitter release. The muscarinic antagonist scopolamine increased ACh release in the PnO by 21% (3 nM), 48% (10 nM), 56% (30 nM), and 104% (100 nM). The muscarinic agonist bethanechol dialyzed into the PnO significantly decreased ACh release by 60% compared with control. Dialysis delivery of relatively subtype selective muscarinic antagonists to the PnO revealed the following order of potency for increasing ACh release: scopolamine (3 nM)>AF-DX 116 (100 nM)=pirenzepine (100 nM). These data support the conclusion that ACh release in PnO of B6 mouse is modulated by non-M1 muscarinic receptors.