LESIONS OF THE NUCLEUS BASALIS MAGNOCELLULARIS IN IMMATURE RATS - SHORT-TERM AND LONG-TERM BIOCHEMICAL AND BEHAVIORAL-CHANGES

Short- and long-term effects of unilateral lesions of the nucleus basa lis magnocellularis (NBM) on cortical choline acetyltransferase (ChAT) activity and passive avoidance conditioned responses were examined in immature rats. The lesions were made by stereotaxic injection of quis qualic acid on postnatal days 14 (P14), 17 (P17), and 21 (P21). A mark ed loss of ChAT activity was found 7 days after surgery in all age gro ups of lesioned rats. Unoperated P14 rats were unable to perform the p assive avoidance conditioned responses. Acquisition began on P17. Lesi ons made on P17 and P21 strongly impaired the acquisition and retentio n of the task, evaluated 7 days postoperation. No biochemical but a pa rtial behavioral recovery was observed 3 months after surgery in rats lesioned on P14. On the contrary, despite a persistent decrease in cor tical ChAT activity, rats lesioned on P21 were able to acquire and ret ain the passive avoidance conditioned response. These results indicate that destruction of NBM cholinergic neurons shortly after birth is no t compensated for by the developmental plasticity of the residual neur ons but results in permanent cholinergic hypofunction. They also demon strate that cholinergic NBM neurons play an important role in the acqu isition and retention of a passive avoidance task; nevertheless, a beh avioral recovery may take place 3 months after the lesion, even in the presence of a persistent cholinergic hypofunction.