Chronic marijuana smoke exposure in the rhesus monkey. II: Effects on progressive ratio and conditioned position responding.

Sixty-two male rhesus monkeys were trained to respond in an operant test battery that included tasks thought to allow measurement of aspects of motivation and color and position discrimination. Subjects were assigned to eight treatment groups (n = 7-8) based upon behavioral performance. There were two behavioral groups: ACTIVE = behavior assessed throughout the 365 days of active exposure and beyond, and RESIDUAL = behavior assessed beginning 2 months after the last exposure. Each behavioral group had four dose groups: HI = smoke from one marijuana (MJ) cigarette/day 7 days/week; LO = MJ smoke only on weekends; EX = smoke from one extracted MJ (placebo) cigarette/day 7 days/week; SH = sham exposure 7 days/week. For the motivation task, both HI and LO ACTIVE groups earned significantly fewer reinforcers than did both ACTIVE control groups during the last several months of exposure. These effects disappeared within 2 to 3 months of cessation of treatment, and no similar effect was present when RESIDUAL groups were tested. Performance of the color and position discrimination task was adversely affected in one of eight HI ACTIVE subjects throughout most of the chronic exposure, and there was a trend toward residual deficits in performance of this task in the HI RESIDUAL group compared to both SH and EX RESIDUAL controls. These data could be interpreted to mean that during periods of chronic use, MJ produces an amotivational-like syndrome in rhesus monkeys and that this syndrome disappears only several weeks to months after the last exposure.