Differential modulatory actions of serotonin in aplysia sensory neurons: Implications for development and learning

We have addressed whether mechanisms of adult plasticity reflect conserved forms of developmental processes by comparing the effects of serotonin (5HT) in juvenile and adult Aplysia sensory neurons. We show that the effects of 5HT can be dissociated into two functional classes which (i) contribute differentially to short- and long-term synaptic plasticity in adults and (ii) emerge differentially during development. We propose a model in which one class of mechanism mediates structural changes early in development and is retained in the adult to subserve long-term memory, while the second class develops late and contributes only to short-term memory in the adult.