Cerebral regional concentrations of acetylcholine (ACh) were measured in two acute (with or without portacaval shunt) and one subacute (average 3 days) models of ammonia-induced coma in rats. The animals were sacrificed by total-body or head-focused microwave irradiation which, respectively, decreases or essentially eliminates post mortem degradation of ACh. In the two acute models of coma, normal levels of ACh were found in cortex, midbrain, and brainstem. A small decrease in striatal ACh was noted in rats without portacaval shunt given ammonia, but not in the other acutely intoxicated group. By contrast, in the subacute model (portacaval shunted rat given ammoniated resin by gavage) ACh fell by 14, 20, 33 and 39%, respectively, in the cortex, corpus striatum, midbrain, and brainstem. It is suggested that this decrease in brain ACh is a concomitant finding and not the cause of the coma.
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