Cyclic adenosine monophosphate in the nervous system of Aplysia californica. I. Increased synthesis in response to synaptic stimulation.

In the isolated abdominal ganglion of Aplysia, previously incubated in adenine-(3)H, the amount of (3)H-labeled adenosine-3',5' monophosphate (cAMP) doubled after electrical stimulation of nerves at a physiological rate (1/sec). No change was detected after 4 min of stimulation. An increase in cAMP was first seen after 15 min; lengthening the period of stimulation to 1 hr did not increase the extent of the effect. ATP contained 50% of the total radioactivity taken up from adenine-(3)H, cAMP about 0.1%. During stimulation both the total amount and the specific radioactivity of adenosine triphosphate (ATP) did not change. Thus, the increased amount of radioactivity found in cAMP after stimulation represented an increase in its rate of synthesis. During stimulation formation of cAMP-(3)H was not altered in nerves or in the cell body of an identified neuron (R2). In addition, no changes were detected in the total amounts of cAMP in the ganglion and in the cell body of R2. It seems likely that the increase was initiated by synaptic activity rather than by action potentials. It was blocked by elevating the concentration of Mg, which also blocks synaptic activity without impairing conduction of impulses. Moreover, impulse activity induced by ouabain and glutamate did not result in increased formation of cAMP.