Microinjection of cyclic nucleotides provides evidence for a diffusional mechanism of intraneuronal control.

Cyclic 3',5'-AMP and cyclic 3',5'-GMP injected into large neurons of the snail Helix lucorum altered neuron activity. The effect of cAMP is usually depolarizing and that of cGMP hyperpolarizing. The results are specific for 3',5'-cyclic nucleotides. The experiments support the hypothesis that reaction-diffusion processes involving cyclic nucleotides form the basis of an intraneuronal system of information processing.