CYCLIC-AMP MODULATES FAST AXONAL-TRANSPORT IN APLYSIA BAG CELL NEURONS BY INCREASING THE PROBABILITY OF SINGLE ORGANELLE MOVEMENT

Stimulation of Aplysia bag cell neurons triggers elevation of cAMP and prolonged secretion of ELH neuropeptide. Using video-enhanced microsc opy to track individual organelle movements in bag cell neurons, we fi nd that organelle translocation consists of periods of movement interr upted by stationary episodes, cAMP elevation leads to a 2- to 3-fold e nhancement of the average rate of organelle transport in both anterogr ade and retrograde directions. This effect does not result from altera tion of the instantaneous velocity of organelle transport along microt ubules, but rather from an increase in the proportion of time individu al organelles spend in motion. Biochemical measurements also provided evidence that cAMP elevation promotes ELH peptide translocation from t he somata into axons. Enhanced transport of ELH as a result of these e ffects may contribute to the replenishment of neuropeptide-containing vesicles at release sites during prolonged periods of secretion.