Nicotine does not improve discrimination of brain stimulation reward by rats.
Rats were trained to shuttle between two selected ("ON") arms of a Y maze, to obtain electrical stimulation of the medial forebrain bundle. Each shuttle response was rewarded with a brief pulse train. Repetitive entries into the same "ON" arm were not rewarded, nor were entries made into the third ("OFF") arm. Every 67s, stimulation was made available from a different pair of arms. Test sessions lasted for 80 min, beginning immediately after SC injection. Undrugged subjects responded faster, and with a greater proportion of rewarded responses, the higher the stimulation current. In non-tolerant rats, nicotine (0-0.4 mg/kg) depressed responding and induced ataxia shortly after injection; from 40 min, nicotine increased low rates of responding but decreased high rates. All these effects were dose-dependent. Mecamylamine (2.0 mg/kg) prevented the initial depressant action. With repeated daily injections of nicotine (0.4 mg/kg), a marked stimulant action emerged which replaced the initial depressant action, and this was dose-dependent. However, responding was increased by nicotine even when brain stimulation was not available ("time-out"). In contrast, an additional "rate-free" index based on discrimination showed that nicotine did not augment the rewarding properties of the brain stimulation.
D000818:Animals; D001921:Brain / Q000502:physiology*; D004192:Discrimination, Psychological / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D006801:Humans; D008297:Male; D008464:Mecamylamine / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology*; D051381:Rats; D012653:Self Stimulation / Q000187:drug effects*; D013375:Substance Withdrawal Syndrome / Q000523:psychology; D013997:Time Factors
D008464:Mecamylamine; D009538:Nicotine