BACLOFEN INFUSED IN RAT HIPPOCAMPAL-FORMATION IMPAIRS SPATIAL-LEARNING

Recent studies show that baclofen, a selective GABA(B) agonist, impair s different kinds of learning. In the present study we investigated th e effect of microinfused baclofen into the hippocampus of male Wistar rats, on the performance in the Morris water maze. Rats of 8-10 weeks of age were implanted with cannulae aimed bilaterally at the hippocamp al formation. Baclofen (1 mu l of 0.2 mM, 2.0 mM, and 20.0 mM) or ster ilized saline was microinfused 1 h before each daily session (3 trials /session, 1 session/day) for 4 days. On the fifth day, the animals did not receive drug or saline injections and the retention of the locati on of the escape platform was tested in a 30 s free swim trial. Result s from the free swim trial indicate that the doses of baclofen used du ring training affected the ability of the rats to swim to the target q uadrant. Although no significant difference compared with the saline g roup was observed, the experimental rats showed a more generalized swi m trajectory in the area of the target and both adjacent quadrants. Mo reover, 1 mu l of 20.0 mM baclofen also impaired the acquisition. We s uggest that baclofen has an impairing action on spatial learning, alth ough more studies should be conducted to reach a more precise conclusi on. (C) 1998 Wiley-Liss, Inc.