Biosynthesis of acetylcholine in different brain regions in vivo following alternative methods of sacrifice by microwave irradiation.

Endogenous acetylcholine and biotransformation of tritium-labelled choline (3H-CH) were studied in mouse brain regions following different methods of sacrifice, viz. dislocation of the spine (7 min until enzymes inactivated), whole body microwave irradiation (7 s) and irradiation of the head (0.25 s). The brain temperature was measured in different locations 10 to 60 s after irradiation. The slope of the temperature time curves indicated a brain temperature of about 85-90 degrees C at the termination of exposure to both types of irradiation. Acetylcholinesterase (AChE) and choline acetyltransferase (CAT) were practically completely inactivated when measured one to two min after sacrifice. For turnover studies, mice were killed 1, 5, 10 or 20 min after i.v. injection of 15 nmol of 3H-Ch. The brains were dissected into 6 regions, extracted and analysed. No significant difference (except in cortex) in the amount of endogenous ACh was found when whole body irradiation was used in comparison to dislocation of the spine. However, the amount of 3H-acetylcholine (3H-ACh) was much higher in the striatum, hippocampus and cortex, in particular. With the shorter inactivation time (head irradiation) endogenous ACh was markedly increased in the striatum, cortex, medulla, oblongata and midbrain. However, there was no further increase in the radioactive ACh. The difference regarding the post-mortem sensitivity of endogenous and radioactive ACh does not seem to have been due to methodological artifacts but rather suggests that they are handled differently by the brain tissue. Plots of the specific radioactivity (SA) of Ch and ACh vs. time indicated fairly distinct precursor-product relationship in the different regions, when the animals were sacrificed by irradiation of the head.