Morphine abstinence syndrome: Cholinergic mechanisms in the ventral periaqueductal gray of the dog

Central cholinergic systems appear to be involved in the opiate abstinence syndrome. To evaluate central cholinergic processes in the opiate abstinence syndrome we microinjected either carbachol, morphine, methylatropine or naloxone into the periaqueductal gray (PAG) and adjacent regions of 6 nondependent and 1 morphine-dependent dogs. Our purpose was to compare carbachol-elicited responses with those elicited by morphine withdrawal and naloxone in the morphine-dependent dog, to map the distribution of carbachol-elicited responses in the PAG region and to test whether atropine could reduce any of the withdrawal-like signs through its action in the PAG and surrounding sites.