Columnar cholinergic neurotransmission onto T5 cells of Drosophila
A large variety of acetylcholine receptors (AChRs), nicotinic and muscarinic, are expressed in the brain of Drosophila melanogaster. Nonetheless, how AChRs affect brain function remains poorly understood. T5 cells are the primary motion-sensing neurons in the OFF-motion pathway and receive visual input from four different columnar cholinergic neurons, Tm1, Tm2, Tm4 and Tm9. We reasoned that different postsynaptic AChRs might also contribute to T5 function. We demonstrate that the nicotinic nAChRalpha1, nAChRalpha4, nAChRalpha5 and nAChRalpha7 subunits localize on T5 dendrites. By targeting synaptic markers specifically to each cholinergic input neuron, we uncover a prevalence of the nAChRalpha5 in Tm1, Tm2 and Tm4 synapses and of nAChRalpha7 in Tm9 synapses on T5 dendrites. Knock-down of nAChRalpha4, nAChRalpha5, nAChRalpha7, and mAChR-B individually alters the optomotor response and reduces T5 directional selectivity. Our findings expose the complex molecular mechanisms underlying motion detection in T5 cells and offer a system to study AChRs in visual information processing.