Evidence for a role of GABA and Mas-allatotropin in photic entrainment of the circadian clock of the cockroach Leucophaea maderae.

Accumulating evidence suggests that the accessory medulla is the location of the circadian pacemaker in the fruit fly Drosophila melanogaster and the cockroach Leucophaea maderae. gamma-Aminobutyric acid (GABA) and Mas-allatotropin are two putative neurotransmitters, in the accessory medulla in the cockroach Leucophaea maderae. Neurons immunoreactive to the neuropeptide Mas-allatotropin are local neurons with arborizations in the noduli of the accessory medulla, while GABA-immunoreactive neurons connect the noduli of the accessory medulla to the medulla and to the lamina via processes in the distal tract. Injections of GABA and Mas-allatotropin into the vicinity of the accessory medulla resulted in stable phase-dependent resetting of the circadian locomotor activity of the cockroach. The resulting phase response curves closely matched light-dependent phase response curves, suggesting that both substances play a role in circuits relaying photic information from circadian photoreceptors to the central pacemaker.