The use of microwave radiation in the determination of acetylcholine in the rat brain

Cholinesterase (ChE) activity and acetylcholine (ACh) concentration in rat brains were determined following microwave irradiation. Twenty-second irradiation abolished all brain ChE activity in 230-g rats. Termination of brain ChE activity corresponded to temperatures of 60-75°C. The rate of temperature rise was found to be inversely proportional to weight of tissue irradiated. Decapitation prior to irradiation caused a significant decrease in brain ACh levels when compared to live irradiated controls. This decrease was assumed to be caused by increased susceptibility of ACh to hydrolysis by ChE due to decapitation and to presacrifice stress. It was postulated that the high brain ACh values (21-24 nmoles/g) obtained resulted from rapid inactivation of brain enzymes and to reduction of presacrifice and sacrifice stress. ACh concentrations in discrete brain areas were determined after irradiation and large differences between areas were shown to exist. It was concluded that sacrificing rats by microwave irradiation, coupled with pyrolysis-gas chromatographic analysis of ACh, permitted a more accurate and convenient determination of in vivo levels of ACh in brain areas.