Trained 23 male Wistar albino rats to press a bar for electrical stimulation of the brain on a 30-sec variable-interval schedule. Ss were tested weekly with 1 or more of the following drugs: physostigmine (50-400 MUg/kg), neostigmine (25-200 MUg/kg), atropine (2-16 mg/kg), methylatropine (2-16 mg/kg), scopolamine (400-1,600 MUg/kg), pilocarpine (500-4,000 MUg/kg), nicotine (100-800 MUg/kg), mecamylamine (1 mg/kg), and methamphetamine (500 MUg/kg). Results support the suggestion that the cholinergic system is composed of 2 reciprocally related components: (a) a muscarinic "no-go" portion, whose activation has an inhibitory effect on self-stimulation; and (b) a nicotinic "go" portion, whose excitatory effect on self-stimulation is (most probably) mediated by norepinephrine. (33 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)