Lesions of median raphe nucleus disrupt active avoidance behaviour.

Active avoidance of eighteen adult male hooded rats was investigated in an Y-maze and a jump test before and after small symmetric lesions of the median raphe nucleus (n. centralis superior, CES). Formation of conditioned avoidance responses (CAR) was impossible without preoperative experience. Retention of preoperatively learnt CAR was almost zero after lesions. Relearning was strongly delayed but possible in the jump test, however, not in the Y-maze. CES rats did not reach criterion in brightness discrimination. On the other hand, their spontaneous behaviour in the open field remained unchanged.