Optical probing of acetylcholine receptors on neurons in the medial habenula with a novel caged nicotine drug analogue

Key points: A new caged nicotinic acetylcholine receptor (nAChR) agonist was developed, ABT594, which is photolysed by one- and two-photon excitation. The caged compound is photolysed with a quantum yield of 0.20. One-photon uncaging of ABT594 elicited large currents and Ca²⁺ transients at the soma and dendrites of medial habenula (MHb) neurons of mouse brain slices. Unexpectedly, uncaging of ABT594 also revealed highly Ca²⁺-permeable nAChRs on axons of MHb neurons. Abstract: Photochemical release of neurotransmitters has been instrumental in the study of their underlying receptors, with acetylcholine being the exception due to its inaccessibility to photochemical protection. We caged a nicotinic acetylcholine receptor (nAChR) agonist, ABT594, via its secondary amine functionality. Effective photolysis could be carried out using either one- or two-photon excitation. Brief flashes (0.5–3.0 ms) of 410 nm light evoked large currents and Ca²⁺ transients on cell bodies and dendrites of medial habenula (MHb) neurons. Unexpectedly, photorelease of ABT594 also revealed nAChR-mediated Ca²⁺ signals along the axons of MHb neurons.