EFFECTS OF LESIONS OF THE SUBSTANTIA INNOMINATA/VENTRAL PALLIDUM, GLOBUS PALLIDUS AND MEDIAL SEPTUM ON RAT'S PERFORMANCE IN OBJECT-RECOGNITION AND RADIAL-MAZE TASKS: PHYSOSTIGMINE AND AMPHETAMINE TREATMENTS

Abstract

The present study examined the effects of electrolytic lesions of the Medial Septum/Vertical Diagonal Band of Broca (MS/VDBB), the Globus Pallidus (GP) and the Substantia- Innominata/Ventral Pallidum (SI/VP) on the performance of rats in object-recognition memory and radial-maze learning tests. In the latter test, subgroups of sham-operated, MS/VDBB, SI/VP and GP rats were treated with saline, amphetamine or physostigmine. (1) In the object recognition task, the level of discrimination wa s significantly lower in GP compared to SI/VP and in both GP and SI/VP compared to Control and MS/VDBB groups, however, only GP did not discriminate between new and familiar objects; (2) in the radial-maze task, GP and SI/VP lesions produced weak and tran sient impairment whereas MS/VDBB lesions produced a large deficit; (3) in the radial-maze task, performance of normal rats was improved with physostigmine and impaired with amphetamine. The effect of amphetamine was significant on non-memory measures only ; (4) neither amphetamine nor physostigmine improved memory performances of lesioned rats. These results suggest that the septo–hippocampal projections are involved in spatial memory but not in object recognition whereas the integrity of Substantia Inno minata/Ventral Pallidum does not seem critical for either task. The cholinergic nature of the deficit produced by the medial septal lesion remains in question because of improvements seen in sham-operated rats but not in lesioned rats.