Studies on AMP deaminase and 5′-nucleotidase in rat brain under different experimental conditions

Adenosine monophosphate (AMP) deaminase and 5′‐nucleotidase, the two enzymes involved in the disposal of AMP, have been detected in different regions of normal rat brain and in animals subjected to heightened neuronal activity (leptazol‐induced convulsions) and to depression of the central nervous system (CNS) by the administration of barbiturates. They have also been estimated in the CNS of animals subjected to anoxia or treated with lithium and ammonium salts. The AMP deaminase activity was found to be highest in cerebellum and lowest in cerebral cortex, while the 5′‐nucleotidase activity was found to be highest in brain stem and lowest in cerebellum. The AMP deaminase activity was elevated in all the regions of brain during the preconvulsive and convulsive periods. The activity returned to normal during recovery. The activity of 5′‐nucleotidase was found to be depressed in the preconvulsive and post‐convulsive periods. The enzyme was also found to be depressed in all three regions after the administration of barbiturates. Administration of lithium or ammonium salts or induction of anoxic states resulted in an increase in the activity of AMP deaminase in all the three regions of brain. These results are discussed in relation to the probable production of cyclic AMP and cyclic guanosine monophosphate (GMP) which may have depressive and excitatory roles, respectively, in brain. It appears that increased AMP deaminase activity is associated with increased neuronal activity while depression of 5′‐nucleotidase activity is associated with conditions of decreased CNS excitability.