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 adrenalectomy (i.e. 12-13 weeks) on memory for spatial and cued learning in a water maze. In sham amygdala-lesioned rats, adrenalectomy induced impairments in acquisition and retention performance for the spatial, but not the cued water-maze task. The adrenalectomized rats sustained selective degeneration and death of granule cells in the dentate gyrus dorsal blade. Continuous supplementation of the animals' drinking water with an extremely low dose of corticosterone (20 microg/ml) did not block the retention deficit, but blocked the acquisition deficit and the dentate gyrus neurodegenerative changes. The finding that the memory impairments 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 time of learning. In adrenalectomized rats which received corticosterone as well as those which did not, lesions of the basolateral amygdala blocked the impairing effects of adrenalectomy on spatial learning and memory. However, the basolateral amygdala lesions did not affect the neurodegenerative changes in the dentate gyrus. In conclusion, the present findings provide further evidence that the basolateral amygdala is involved in regulating stress hormone effects on learning and memory.