PACα - an optogenetic tool for in vivo manipulation of cellular cAMP levels, neurotransmitter release, and behavior in Caenorhabditis elegans

P>Photoactivated adenylyl cyclase alpha (PAC alpha) was originally isolated from the flagellate Euglena gracilis. Following stimulation by blue light it causes a rapid increase in cAMP levels. In the present study, we expressed PAC alpha in cholinergic neurons of Caenorhabditis elegans. Photoactivation led to a rise in swimming frequency, speed of locomotion, and a decrease in the number of backward locomotion episodes. The extent of the light-induced behavioral effects was dependent on the amount of PAC alpha that was expressed. Furthermore, electrophysiological recordings from body wall muscle cells revealed an increase in miniature post-synaptic currents during light stimulation. We conclude that the observed effects were caused by cAMP synthesis because of photoactivation of pre-synaptic PAC alpha which subsequently triggered acetylcholine release at the neuromuscular junction. Our results demonstrate that PAC alpha can be used as an optogenetic tool in C. elegans for straightforward in vivo manipulation of intracellular cAMP levels by light, with good temporal control and high cell specificity. Thus, using PAC alpha allows manipulation of neurotransmitter release and behavior by directly affecting intracellular signaling.