Effects of lesions in the substantia innominata on active avoidance task and cerebral glucose metabolism

Abnormalities in the central cholinergic system have been reported in Alzheimer disease. The present study was designed to evaluate the effects of the central cholinergic neurons in the substantia innominata on cognitive functions and cerebral metabolism in rats. Forty-nine Wistar rats were trained for an active avoidance task for 5 days. On Day 5, rats which had acquired the avoidance response were divided into two groups. The lesioned group (n = 7) received ibotenic acid in the substantia innominata bilaterally and the sham-operated group (n = 7) received the vehicle only. From Day 8 to 12, the rats were again trained for the avoidance task. On Day 12, the local cerebral metabolic rate for glucose was measured by the 14C-2-deoxyglucose method. The rats in the lesioned group revealed severe deficits in retention and re-acquisition of the active avoidance task. In addition, the glucose metabolism was decreased in the cerebral cortices, especially in the frontal cortex (p less than 0.05). The central cholinergic neurons of the substantia innominata may be closely related to cognitive functions and to glucose metabolism in the cortices.