Involvement of the Hippocampus in Central Nervous System-Mediated Glucoregulation in Rats

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Abstract
To find out whether the hippocampus is involved in central nervous system-mediated glucoregulation, we injected saline, neostigmine, dopamine, norepinephrine, bombesin, .beta.-endorphin, somatostatin, and prostaglandin F2.alpha. into the dorsal hippocampus in anesthetized fed rats. After injection of dopamine, norepinephrine, bombesin, .beta.-endorphin, somatostatin, or prostaglandin F2.alpha., the level of hepatic venous plasma glucose did not differ from that in saline-treated control rats. However, neostigmine, an inhibitor of acetylcholine esterase, caused a dose-dependent increase in the hepatic venous plasma glucose concentration. This neostigmine-induced hyperglycemia was dose-dependently suppressed by coadministration of atropine, but not by hexamethonium. Injection of neostigmine (5 .times. 10-8 mol) resulted in an increase not only in glucose but also in glucagon, epinephrine, and norepinephrine in hepatic venous plasma. In bilateral adrenalectomized rats, neostigmine-induced hyperglycemia was suppressed, but the hepatic venous plasma glucose concentration still increased significantly. These results indicate that the hippocampus is involved in central nervous system-mediated glucoregulation through cholinergic muscarinic activation, partly via epinephrine secretion.