Coexistence of several putative neurotransmitters in single identified neurons of Aplysia

By sensitive enzymatic micromethods several putative neurotransmitters were measured in four identifiable neurons of Aplysia californica (R-2, R-14, L-11, and C-1). Serotonin was found in all of these neurons, and octopamine in all but C-1. Acetylcholine has been previously reported to be present in R-2 and L-11. The catecholamines, norepinephrine and dopamine, were not detected in the four cells examined. The possible biological consequence of the presence of several putative transmitters in single identifiable neurons is discussed.