Columnar cholinergic neurotransmission onto T5 cells of Drosophila

Abstract

Several nicotinic and muscarinic acetylcholine receptors (AChRs) are expressed in the brain of Drosophila melanogaster. However, the contribution of different AChRs to visual information processing remains poorly understood. T5 cells are the primary motion-sensing neurons in the OFF pathway and receive input from four different columnar cholinergic neurons, Tm1, Tm2, Tm4 and Tm9. We reasoned that different AChRs in T5 postsynaptic sites might contribute to direction selectivity, a central feature of motion detection. We show that the nicotinic nAChR1, nAChR4, nAChR5 and nAChR7 subunits localize on T5 dendrites. By targeting synaptic markers specifically to each cholinergic input neuron, we find a prevalence of the nAChR5 in Tm1-, Tm2- and Tm4-to-T5 synapses and of nAChR7 in Tm9-to-T5 synapses. Knock-down of nAChR4, nAChR5, nAChR7, or mAChR-B individually in T5 cells alters the optomotor response and reduces T5 directional selectivity. Our findings indicate a differential contribution of postsynaptic receptors to input visual processing and, thus, to the computation of motion direction in T5 cells.