Modulation of the aversive qualities of shock through a central inhibitory cholinergic system in the rat

Evidence has been supplied which suggests that a central inhibitory cholingeric (i.e., muscarinic) system may be involved in modulating the aversive qualities of electric shock in the rat. Central cholinergic stimulation via the administration of pilocarpine or arecoline the threshold for grid shock, while central acting anticholinergics (i.e., scopolamine and atropine) produced decrements in the threshold. Peripheral acting anticholinergics (e.g., methyl scopolamine, methyl atropine) were less potent than central acting drugs given in equivalent doses, while peripheral cholinergic stimulants (i.e., neostigmine, carbachol) were inactive. In addition, only the central acting stimulant pilocarpine, and not carbachol, was able to block the decrements noted in response to scopolamine hydrobromide administration. Finally, only arecoline, and not nicotine, was able to elevate the aversive threshold indicating that muscarinic receptor sites are probably involved in mediating the effects of central cholinergic stimulants.