Functional characterization of enteric neurons that innervate the hindgut in Drosophila melanogaster

Abstract

Defecation is an essential physiological process for maintaining homeostasis and is controlled by a complex neural circuitry that includes the enteric nervous system. Although enteric neurons involved in defecation have been identified in both vertebrates and invertebrates, the neurons responsible for the final motor output of defecation in adult Drosophila remain unclear. In this study, I generated transgenic lines targeting specific enteric neurons using the split-GAL4 system and evaluated roles of the enteric neurons in defecation. Among the 30 split- GAL4 combinations, the EN2-263 line exhibited a robust phenotype in regulating excreta size. Morphological analyses revealed that EN2-263 consists of four cell bodies located in the abdominal ganglion (AbG) of the ventral nerve cord (VNC) and extends neural projections toward the rectum. Furthermore, synaptotagmin-based synaptic polarity analysis found that their axon termini innervate the sphincter, suggesting that EN2-263 functions as a motor neuron. Analysis of synaptic partners using the retro-Tango and trans-Tango systems showed no pre- or postsynaptic signals in the rectum; however, presynaptic inputs from ascending AbG neurons were detected within the VNC. Postsynaptic signals were also observed in the VNC using the trans-Tango system. These observations suggest that EN2-263 integrates VNC circuit signals to regulate excreta size, although their functional roles remain unknown. In this study, I identified the EN2-263 line that target candidate motor neurons determining excreta size in adult Drosophila. This study provides better insights into the basic architecture of the neural circuits underlying defecation control in Drosophila.