16 male Wistar mature rats were treated daily with cannabis extract (20 mg/kg tetrahydrocannabinol) for 3 mo. After a 1- to 4-mo drug-free period, residual effects on a variety of behaviors were studied and compared with behaviors of 16 matched controls who received a vehicle. No residual effects were found in learning of an 8-arm radial maze task, nor on a differential reinforcement of low-rate responding (DRL-20) task, nor in open field activity. Two-way shuttle box avoidance learning was facilitated by previous cannabis treatment, since cannabis-treated Ss exhibited shorter mean latencies to avoid footshock than controls. Findings indicate greater vulnerability of immature organisms (previous studies) than mature organisms (the present study) to long-term effects of chronic cannabis administration.

http://www.erowid.org/plants/cannabi...abstract.shtml