Adrenalectomy-induced memory deficits: role of plasma glucose levels

Circulating glucose levels regulate memory storage under several conditions. This study examined the contribution of blood glucose levels to the transient memory impairment seen in adrenalectomized rats. Inhibitory (passive) avoidance retention performance, blood glucose levels, and glycemic responses to footshock were tested 1, 2, and 8 days after adrenalectomy. Adrenalectomized animals demonstrated a transient inhibitory avoidance deficit 1 and 2 days after surgery which recovered by 8 days. The adrenalectomy-induced memory deficit was accompanied by decreased resting blood glucose levels. In animals tested 2 days after adrenalectomy, this decrease in baseline blood glucose levels was exacerbated by further reductions, rather than the normal increases, in circulating glucose levels after training. The magnitude of blood glucose increases after glucose injection was decreased in adrenalectomized animals tested 2 days after surgery. Posttraining glucose injections restored the retention performance of animals trained 2 days after adrenalectomy to that of sham-operated animals. These findings suggest that abnormalities in blood glucose regulation may contribute, in part, to the transient memory impairment seen after adrenalectomy. Additionally, the results further implicate blood glucose in the regulation of CNS information processing systems.