Hypothalamic cholinergic systems in mercuric chloride-induced hyperglycemia.

The roles of hypothalamic neuron mechanisms in regulation of blood glucose were studied in rats. Microinjection of HgCl2 and neostigmine into the third ventricle under anesthesia caused marked hyperglycemia. To characterize the effective neurons in the hypothalamus, tissue contents of neurotransmitters and extracellular levels of metabolites in the ventromedial part of the hypothalamus were measured by microwave irradiation and in vivo brain microdialysis. HgCl2 increased both the content and the extracellular levels of choline. Neostigmine increased the acetylcholine content. In both instances, norepinephrine (NE) and dopamine (DA) content were decreased. Extracellular levels of DA metabolites were increased. On the other hand, serotonin content and extracellular serotonin metabolite level remained constant. In medulloadrenalectomized and atropine-coadministered rats, no marked hyperglycemia was induced by HgCl2 or neostigmine. These results show that the muscarinic cholinergic system participates in the HgCl2-induced central hyperglycemic effect through the function of the adrenal medulla. NE neurons may also be related to hypothalamic glycoregulation, and DA neurons might modulate the regulatory mechanisms.