Orally delivered pentobarbital was established as a reinforcer for five 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-hr blackouts. In the initial phase, water was delivered after each lip-contact response both within the 3-hr sessions and between sessions. During the 2nd hr of the daily 3-hr session, each lever press produced one 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 to 45 mg/kg/3-hr 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-hr 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 decreased to low levels. 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-hr session) and the number of liquid deliveries first increased and then decreased.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - 1981|
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