Distinct and common dynamics of central brain spontaneous neuronal activity across cell types during Drosophila pupal...

The frequency or degree of spiking activity and its relative timing, in pre- and post- synaptic neurons is a major determinant of the nature of synaptic plasticity. Such activity driven plasticity based on stimuli forms the basis of learning and formation of memory. However, in the absence of any sensory stimuli particularly during development, neurons are active and often in a synchronous manner. Such spontaneous activity driven plasticity is thought to underlie formation and development of circuits. Drosophila has become the species of choice for many neural developmental studies due to ease of handling and genetics. However, little is known in terms of spontaneous activity in the central brain of the Drosophila pupa and how such activity is distinct in different cell types during development. In the current work, using two-photon Ca²⁺ imaging, we obtain spontaneous activity of Drosophila pupae at different stages of development of 3 different cell types, namely, dopaminergic, cholinergic and GABAergic neurons. We show that all cell types follow a similar pattern over development with periodic synchronous activity separated by durations of silence. We find that the central brain spontaneous activity is different from what has been previously observed in the optic lobe, which is true across the cell types. However, the three cell types have different periodicities, spontaneous event timing precision and strength of spontaneous activity. Together our results can form the basis of understanding cell type specific circuit development and future investigations of alterations in spontaneous activity in different cell types with neurodevelopmental disorders.