Glutamate Is a Wake-Active Neurotransmitter in Drosophila melanogaster

In mammals, there is evidence that glutamate has a role as a wake-active neurotransmitter. So using video-based analysis of Drosophila behavior, we undertook a study to examine if glutamate, which has been previously shown to have an excitatory role in neuromuscular junctions in Drosophila, may have a conserved wake-active role in the adult brain.

Using 6- to 9-day-old female flies, we examined the effect of perturbations of the glutamatergic signaling on total wakefulness and wake bout architecture. We increased and decreased neuronal activity of glutamatergic neurons in the brains of adult flies using Upstream Activating Sequence (UAS) NaChBac and UAS EKO, respectively. We blocked neurotransmission from glutamatergic neurons in adult flies using the UAS-driven temperature-sensitive dynamin mutation shibirets. We examined the behavior of flies with loss of function mutations of individual subunits of brain-specific ionotropic glutamate receptors.

Increasing the activity of glutamatergic neurons in the adult brain led to a significant increase in wakefulness compared to the control groups both in the daytime and nighttime and decreasing the activity of these same neurons reduced wakefulness in the nighttime. Blocking neurotransmitter release in glutamatergic neurons significantly reduced wake in the nighttime. The ionotropic receptor mutants had significantly less wake in the nighttime than their respective genetic background controls.

The results show the following: glutamate is indeed a wake-active neurotransmitter in Drosophila; there is a major time of day effect associated with loss of glutamatergic neurotransmission; and it is a major wake-active neurotransmitter in the nighttime.