Effects of feeding and insulin on extracellular acetylcholine in the amygdala of freely moving rats

Extracellular levels of acetylcholine (ACh) were measured in the central nucleus of the amygdala using microdialysis in 20-min intervals before, during, and after 1 h feeding in food-deprived rats. The results were compared to the effects of peripheral injections of glucose or 'low' (200 mU) and 'high' (1 U) doses of insulin. Feeding caused a 40% increase in extracellular ACh in the amygdala during the hour-long meal. Acetylcholine returned to baseline 1 h after food was removed. Systemic injections of either glucose or insulin in ad Libitum fed rats also resulted in an increase in ACh levels (+50-60%), but with a different time course. Glucose elevated ACh to a plateau within 20 min for an hour's duration; whereas both doses of insulin caused a peak in ACh release in the first 20 min followed by gradual return to baseline. The 'low' and 'high' doses of insulin had similar effects on ACh release even though they had different hypoglycemic potency as measured in blood samples. These results suggest that ACh in the AMY is involved in feeding and the response to glucose utilization. (C) 1998 Elsevier Science B.V.