Cyclic adenosine monphosphate, metabolites, and phosphorylase in neural tissue: a comparison a methods of fixation.

Fixation of rat brain tissue by freeze-blowing, microwave irradiation, immersion of whole rats in liquid nitrogen, and decapitation into liquid nitrogen indicates that postmortem changes in metabolites and enzyme forms are minimal in freeze-blown brains. Cyclic adenosine monophosphate levels are lowest in microwave-irradiated brains, which has been interpreted by some investigators to indicate rapid fixation and minimal anoxia. However, the changes in phosphocreatine, adenosine triphosphate, lactate, and phosphorylase clearly demonstrate that fixation by freeze-blowing or immersion in liquid nitrogen more closely approximate the state in vivo.