DIFFERENCES IN ACETYLCHOLINE BUT NOT CHOLINE IN BRAIN-TISSUE FIXED BYFREEZE FIXATION OR MICROWAVE-HEATING

Among the many rapidly metabolized compounds in the brain, acetylcholi ne is one of the most challenging to sample effectively due to its rap id synthesis, degradation and sequestration. To ascertain problems tha t invalidate sampling procedures two methods of tissue fixation, micro wave heat inactivation and freeze fixation, were used for obtaining mi ce and rat brain samples, respectively. The data show that acetylcholi ne levels obtained by microwave fixation were much higher than those o btained by freeze fixation. Choline levels were not affected by the fi xation methods used. Microwave fixation results in more accurate asses sment of acetylcholine levels than the freeze fixation method, even th ough the tissue fixation time was less than 1 s in both methods, becau se tissue integrity is maintained in the microwave fixation, but not d uring freeze fixation.