Convergence of small molecule and peptide transmitters on a common molecular cascade

This chapter summarizes the evidence that a conventional transmitter, serotonin, and the small cardioactive peptides—SCP_A and SCP_B—can modulate a specific K⁺ channel by means of cyclic adenosine monophosphate. Although the information is still fragmentary, there is the possibility that a third class of transmitter, yet unidentified, works by the same mechanism. In modulating this K⁺ channel, each of these transmitters also regulates transmitter release at a specific set of synapses involved in two short-term forms of memory, each lasting minutes to hours: the memory for short-term behavioral sensitization and for classical conditioning. The specific set of connections modulated during short-term sensitization also undergoes a prolonged modulation lasting days and weeks, which contributes to long-term memory for sensitization. The ion channel gated by transmitters consists of at least three functional components: (1) a receptor or recognition site, (2) a channel, and (3) a gate. The receptor recognizes the transmitter and instructs the gate to open or close the channel. The channel conducts ions only when it is gated open.