Modulation of the Critical Small Ventrolateral Pacemaker Neurons in Drosophila.

Abstract

Almost every organism on earth carries with it a timepiece that bestows a critical sense of time. In many organisms, including humans, that timepiece is a network of neurons that each expresses an ancient molecular circadian clock. Like setting a clock, modulation of clock neurons adjusts the timing of an organism’s daily rhythms. However, it is not well understood how neuronal modulation of clock neuron activity translates into adjustments of molecular clocks and synchronization of daily rhythms to environment cycles. To investigate this question, I looked to the fruit fly’s small ventral lateral clock neurons (s-LNv), which are not only located in a rich medulla of environmental and interneuronal inputs, but are critical components of the fly’s timepiece. To survey these small clock neurons, I employed, validated and expanded a burgeoning method of genetically encoded circuit interrogation to determine s-LNv receptivity and connectivity. Acetylcholine and GABA are neuromodulators from the visual system and sleep/arousal circuits, respectively. I found that cholinergic agonists and GABA inversely modulate Ca2+ and cAMP levels in the s-LNv. Cholinergic modulation likely comes from the fly’s eyelets, as I further showed that activation of the larval and adult eyelets lead to increases in Ca2+ and cAMP from the s-LNv. The results of my studies identify concrete neuronal connections between the s-LNv and the visual system. My work also suggests that the mechanism by which environmental and interneuronal modulation adjusts the clock is through modulation of critical signaling molecules like cAMP. Overall, this work contributes to a growing body of evidence that shows cAMP to be a conserved signaling molecule involved in clock resetting in mammals and insects. Furthermore, the results of this study support continued investigation into the simple fruit fly to understand the more complex circuitry that underlies the rhythms of our life.