Neuronal control of suppression, initiation and completion of egg deposition in Drosophila melanogaster

Egg-laying in Drosophila is the product of post-mating physiological and behavioural changes that culminate in a stereotyped sequence of actions. While egg-laying behaviour has been mostly used as a system to understand the neuronal basis of decision making in the context of site selection, it harbours a great potential as a paradigm to uncover how, once a site is selected, the appropriate motor circuits are organized and activated to deposit an egg. To study this programme, we first describe the different stages of the egg-laying programme and the specific actions associated with each stage. Using a combination of neuronal activation and silencing experiments we characterize the role of three distinct neuronal populations in the abdominal ganglion with different contributions to the egg deposition motor elements. Specifically, we identify a subset of glutamatergic neurons and a subset of cholinergic neurons that promote the initiation and completion of egg expulsion respectively, while a subset of GABAergic neurons suppresses egg-laying. This study provides insight into the organization of neuronal circuits underlying complex motor behaviour.