BASOLATERAL AMYGDALA LESIONS BLOCK THE DISRUPTIVE EFFECTS OF LONG-TERM ADRENALECTOMY ON SPATIAL MEMORY

The present study examined, in rats with N-methyl-D-aspartate-induced lesions of the basolateral amygdala, the effects of long-term adrenale ctomy (i.e. 12-13 weeks) on memory for spatial and cued learning in a water maze. In sham amygdala-lesioned rats, adrenalectomy induced impa irments in acquisition and retention performance for the spatial, but not the cued water-maze task. The adrenalectomized rats sustained sele ctive degeneration and death of granule cells in the dentate gyrus dor sal blade. Continuous supplementation of the animals' drinking water w ith an extremely low dose of corticosterone (20 mu g/ml) did not block the retention deficit, but blocked the acquisition deficit and the de ntate gyrus neurodegenerative changes. The finding that the memory imp airments and dentate gyrus neurodegeneration are dissociable supports the view that the adrenalectomy-induced memory effects are due to the loss of activational effects of circulating adrenal hormones at the ti me of learning. In adrenalectomized rats which received corticosterone as well as those which did not, lesions of the basolateral amygdala b locked the impairing effects of adrenalectomy on spatial learning and memory. However, the basolateral amygdala lesions did not affect the n eurodegenerative changes in the dentate gyrus. In conclusion, the pres ent findings provide further evidence that the basolateral amygdala is involved in regulating stress hormone effects on learning and memory. (C) 1998 IBRO. Published by Elsevier Science Ltd.