Laser-induced native fluorescence (LINF) imaging of serotonin depletion in depolarized neurons.

Since certain neurotransmitters exhibit native fluorescence we can monitor this property to disclose intracellular changes that result from neurotransmitter release. Isolated Retzius neurons of the leech are known to release serotonin (5-HT) during depolarization. Using intensified CCD technology coupled with UV laser (305 nm) excitation we observed depolarization and calcium-dependent reductions in native fluorescence in the axon, as well as in the cortex of the cell body. When taken together with data obtained from single-cell capillary electrophoresis, we demonstrate that this laser-induced native fluorescence can be reliably used to study spatial and temporal changes in intracellular transmitter content that accompany calcium-dependent secretion.