Evidence for local hormonal communication between neurones in Aplysia.

IT has been suggested that in certain systems, communication between neurones is mediated, not by conventional synaptic transmission, but by a mechanism in which substances are dispersed over relatively long distances to act on target neurones1–3. The marine mollusc Aplysia may be useful for cellular studies of this novel mode of communication. Activation of spike activity in a group of neurones, the bag cells, produces several types of response in nearby identified cells4–7. These responses have slow onsets and prolonged durations compared to those at conventional synapses. We describe here the response of one of the target neurones, cell R15, which involves a distinctive change in the cell's activity lasting for as long as three hours. When the release of neurosecretory product from the bag cells is simulated by brief local application of bag-cell extract to the target cell, an apparently identical response is produced. These results, combined with previous anatomical data, support the hypothesis that the bag-cell induced responses are mediated by a local hormonal interaction, one that is intermediate between blood-borne hormonal and synaptic interactions.