Free-operant and auto-titration brain self-stimulation procedures in the rat: a comparison of drug effects.
Rats were implanted with bipolar stimulating electrodes aimed at the medial forebrain bundle of the lateral hypothalamus, and trained to press a lever in one of two different procedures in order to receive electrical stimulation through the electrodes. In a free-operant procedure, each response produced a 200 msec train of electric pulses at a suprathreshold current, the intensity of which remained constant throughout the session. In an auto-titration procedure, each response produced an electrical stimulus which was initially set at a suprathreshold intensity. Every 15th response reduced the stimulation current by 3 muA. The animal could reset the current to its initial intensity at any time by pressing a second lever in the test chamber. The average current at which the animal pressed the reset lever was defined as the reinforcement threshold. Dose-response functions were determined for d- and l-amphetamine, alpha-methyltyrosine, and haloperidol. The reinforcement threshold was decreased by both d- and l-amphetamine, increased by haloperidol, and not changed by alpha-methyltyrosine. These effects on reinforcement threshold were not consistently related to the drug-induced changes in response rate in either procedure. The auto-titration procedure may be useful for distinguishing between drugs which cause nonspecific changes in the rate of ongoing behavior and those which specifically modify the reinforcement efficacy of brain stimulation.
D000661:Amphetamine / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D003216:Conditioning, Operant / Q000187:drug effects*; D004558:Electric Stimulation; D006220:Haloperidol / Q000494:pharmacology; D008297:Male; D008781:Methyltyrosines / Q000494:pharmacology; D051381:Rats; D012653:Self Stimulation / Q000187:drug effects*
D008781:Methyltyrosines; D000661:Amphetamine; D006220:Haloperidol