2-PHOTON SCANNING PHOTOCHEMICAL MICROSCOPY - MAPPING LIGAND-GATED ION-CHANNEL DISTRIBUTIONS

The locations and densities of ionotropic membrane receptors, which ar e responsible for receiving synaptic transmission throughout the nervo us system, are of prime importance in understanding the function of ne ural circuits. It is shown that the highly localized liberation of ''c aged'' neurotransmitters by two-photon absorption-mediated photoactiva tion can be used in conjunction with recording the induced whole-cell current to determine the distribution of ligand-gated ion channels. Th e technique is potentially sensitive enough to detect individual chann els with diffraction-limited spatial resolution. Images of the distrib ution of nicotinic acetylcholine receptors on cultured BC3H1 cells wer e obtained using a photoactivatable precursor of the nicotinic agonist carbamoylcholine.