Genetically encoded optical sensors of neuronal activity and cellular function

Fluorescent proteins (FPs) have been engineered to produce an optical repor t in response to cellular signals. FP fluorescence can be made directly sen sitive to the chemical environment, via specific mutations of or around the chromophore. Alternatively, FPs can be made indirectly sensitive to cellul ar signals by their fusion to 'detector' proteins that respond to specific cellular signals with structural rearrangements that act on the FP to alter fluorescence. These optical sensors of membrane voltage, neurotransmitter release, and intracellular messengers, including powerful new sensors of Ca 2+, cyclic nucleotides and nitric oxide, are likely to provide new insights into the workings of cellular signals and of information processing in neu ral circuits.