Pentobarbital drinking by rhesus monkeys: establishment and maintenance of pentobarbital-reinforced behavior
Meisch, R.A.; Kliner, D.J.; Henningfield, J.E.
Journal of Pharmacology and Experimental Therapeutics 217(1): 114-120
1981
ISSN/ISBN: 0022-3565 PMID: 7205645 Document Number: 178394
Orally delivered pentobarbital was established as a reinforcer for 5 rhesus monkeys. The monkeys were food deprived throughout the study. Liquid deliveries (0.5 ml) were contingent upon lip-contact responses on a drinking spout and food pellet deliveries were contingent upon lever-press responses. Three hour daily sessions were preceded and followed by 1 h blackouts. In the initial phase, water was delivered after each lip-contact response both within the 3 h sessions and between sessions. During the 2nd h of the daily 3 h session, each lever press produced 1 food pellet until a limit (65-100 pellets) was reached. This procedure resulted in elevated levels of water drinking that varied among monkeys from 334 to 983 ml/session. Subsequently, during sessions an increasing series of pentobarbital concentrations (from 0.0078-1 mg/ml) were provided via the drinking spout while between sessions water was available. Pentobarbital intake ranged from 12-45 mg/kg per 3 h session and intoxication was noted when intakes exceeded 20 mg/kg. In the next phase, the monkeys had limited access to food after each session, unlimited access to water between sessions and either pentobarbital or water during the 3 h sessions. Both the concentration of pentobarbital and the number of lip-contact responses required per drug delivery were gradually increased until the pentobarbital concentration was 4.0 mg/ml and the response requirement was 16 (monkeys M-H and M-P1), 32 (monkey M-BL), 45 (monkey M-P) or 64 (monkey M-W). During the phase when 4.0 mg/ml of pentobarbital was replaced by water, liquid deliveries increased to previous values when 4.0 mg/ml of pentobarbital was reintroduced. When the pentobarbital concentration was decreased (4.0 mg/ml, 2.0, 1.0,..), pentobarbital intake decreased (milligrams per kilogram per 3 h session) and the number of liquid deliveries first increased and then decreased.