DEVELOPMENTAL EMERGENCE OF DIFFERENT FORMS OF NEUROMODULATION IN APLYSIA SENSORY NEURONS

The capacity for neuromodulation and biophysical plasticity is a defin ing feature of most mature neuronal cell types. In several cases, modu lation at the level of the individual neuron has been causally linked to changes in the functional output of a neuronal circuit and subseque nt adaptive changes in the organism's behavioral responses. Understand ing how such capacity for neuromodulation develops therefore may provi de insights into the mechanisms both of neuronal development and learn ing and memory, We have examined the development of multiple forms of neuromodulation triggered by a common neurotransmitter, serotonin, in the pleural sensory neurons of Aplysia californica. We have found that multiple signaling cascades within a single neuron develop sequential ly with some being expressed only very late in development. in additio n, our data suggest a model in which, within a single neuromodulatory pathway, the elements of the signaling cascade are developmentally exp ressed in a ''retrograde'' manner with the ionic channel that is modul ated appearing early in development, functional elements in the second messenger cascade appearing later, and finally, coupling of the secon d messenger cascade to the serotonin receptor appearing quite late. Th ese studies provide the characterization of the development of neuromo dulation at the level of an identified cell type and offer insights in to the potential roles of neuromodulatory processes in development and adult plasticity.