Cyclic AMP and Cyclic GMP May Mediate Opposite Neuronal Responses in the Rat Cerebral Cortex

Electrophysiologically identified pyramidal tract neurons in the rat cerebral cortex were tested with norepinephrine, acetylcholine, adenosine 3',5'-monophosphate (cyclic AMP), and guanosine 3',5'-monophosphate (cyclic GMP) applied by microiontophoresis. The neurons were usually inhibited by norepinephrine and cyclic AMP, but excited by acetylcholine and cyclic GMP. These opposing responses of pyramidal tract neurons to cyclic AMP and cyclic GMP suggests that these two nucleotides could function as reciprocal intracellular second messengers for norepinephrine and acetylcholine, respectively.