Adenosine 3':5'-cyclic monophosphate in nerve-terminal fractions from neocortical tissues: its augmentation by a post-stimulation process [proceedings].

An increase in the cyclic AMP of nerve terminals has been proposed as intermediary in neurotransmitter release and synthesis (Wooten et al., 1973; Roth et al., 1975). However, de Belleroche et al. (1 974) were unable to increase the cyclic AMP content of synaptosome preparations after their isolation from rat neocortex, using as stimulating agents electrical pulses, noradrenaline or elevated K+ concentrations, under circumstances in which these agents increased the cyclic AMP content of rat neocortical tissue. These agents also increase the cyclic AMP of guinea-pig neocortical tissues (Kakiuchi et al., 1969), and previous work from these laboratories has enabled subcellular fractionation to be carried out with preincubated guinea-pig neocortex as starting material (Kuroda & Mcllwain, 1973). When such fractionation was performed with tissues which had been electrically stimulated, the cyclic AMP content was markedly increased, both in the total tissue and in the nerve-terminal fraction derived from it (Table I). Immediately after lOmin stimulation, the nucleotide content of the synaptosome fraction had altered less than that of the tissue as a whole, but in the 6min after stimulation ceased, the cyclic AMP of the synaptosome preparation increased, whereas that of the total tissue decreased. Known sites of cyclic AMP formation in cerebral systems are probably localized in nerve-cell bodies, as concluded from immunofluorescence (Siggins et al., 1973) and