'Neurosecretion' by aminergic synaptic terminals in vivo--a study of secretory granule exocytosis in the corpus cardiacum of the flying locust.

Most nerve terminals forming typical synaptic junctions contain both synaptic vesicles and larger 'secretory granules' with electron-dense contents. Visualization of granule exocytosis from within terminals in the corpus cardiacum is facilitated by injection of tannic acid which immobilizes granule cores as they are discharged. The process of discharge is stimulated by flight-induced activation of the neurones and there is a correlated response by the innervated cells. In contrast to synapses with their vesicle clusters, granule discharge is not targeted upon the postsynaptic cells. These findings have general implications for mechanisms of discharge of neuropeptides and other transmitters from synaptic terminals.