The effect of lesions in the mesencephalic reticular formation upon conditioned avoidance responses in rat. II. Lesions of the area cuneiformis.
Hooded rats of the Long-Evans strain were not able to acquire a conditioned avoidance response (CAR) in a jump test when they were injured by bilateral symmetric lesions in the area cuneiformis (CU) of the mesencephalic reticular formation. The acquisition of a simple CAR in a Y-maze was not impaired irrespective of the size of the lesion. However, lesioned rats ran significantly slowlier to the maze exit in simple and discrimination tasks and displayed more erroneous runs in dark-light discrimination sessions. These deficits were not observed when rats with small lesions in the anterior CU (CU-1 group) had preoperatively learnt the dark-light discrimination, but they were observed when preoperatively trained rats were injured by caudally extended lesions (CU-2 group). After preoperative training CU-1 rats had a great retention deficit in the jump test compared with no deficit in a sham-operated group. They were unable to relearn the task, whereas rats with dorsally extended lesions including the nucleus commissurae posterioris (NCP-CU group) had less deficit and relearnt the CAR in the jump test. Animals of this group performed an enhanced number of intertrial responses and showed increased arrest reactions with goal-directed attention evoked by the conditioned stimulus. The results indicate - together with the observed behavioural syndrome of disturbed locomotion, reduced orienting responses and exploratory behaviour - that the CU is an important structure for the integration of goal-directed behaviour.
D000818:Animals; D001362:Avoidance Learning / Q000502:physiology*; D003213:Conditioning, Psychological / Q000502:physiology*; D008297:Male; D008636:Mesencephalon / Q000502:physiology*; D009043:Motor Activity / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012154:Reticular Formation / Q000502:physiology*