The small cardioactive peptides: a class of modulatory neuropeptides in Aplysia

Abstract

Two members of a new class of neuropeptides, termed the small cardioactive peptides (SCPs), were recently purified from Aplysia and sequenced. The sequence of the precursor for the two SCPs was obtained by molecular genetic analyses. SCPs are synthesized in, and released from, individual identified neurons, some of which also contain classical transmitters such as acetylcholine or in some cases other neuropeptides. SCPs are present in neuronal cell bodies, fibres and varicosities throughout the nervous system and peripheral tissues, and appear to be released locally near their sites of action. The peptides have widespread modulatory actions on spontaneously active tissues such as heart or gut and on synaptic transmission at central and peripheral synapses. Most of these modulatory actions are also produced by serotonin and are mediated by increased intracellular cAMP levels.