J Comp Physiol B DOI 10.1007/s00360-010-0490-x 123 ORIGINAL PAPER Cyclic nucleotide-gated channels are involved in phototransduction of dermal photoreceptors in Lymnaea stagnalis Sabrina Pankey · Hiroshi Sunada · Tetsuro Horikoshi · Manabu Sakakibara Received: 11 February 2010 / Revised: 21 April 2010 / Accepted: 6 June 2010  Springer-Verlag 2010 Abstract Dermal photoreceptors in the pond snail Lymnaea stagnalis mediate the whole-body withdrawal response, including pneumostome closure, elicited by a shadow passing over the pneumostome area. The pneumos- tome closure response is part of the defense reaction in Lymnaea. The shadow or ‘light-oV’ stimulus elicits activity in a higher order interneuron, RPeD11, which has a major role in mediating defensive withdrawal behavior elicited by noxious or threatening stimuli. Here, we tested our hypoth- esis that cyclic nucleotide-gated (CNG) channels are involved in the dermal photoreceptor-mediated transduc- tion of the shadow stimulus. The response to the shadow stimulus recorded in RPeD11 was abolished by 500 M cis-diltiazem, which blocks cGMP-activated conductance of CNG channels. On the other hand, the shadow response elicited in RPeD11 was not blocked by 2-amino ethyldiphe- nyl borate (2-APB), a transient receptor potential (TRP) channel blocker. Consistent with the electrophysiologic data, cis-diltiazem blocked the shadow-evoked withdrawal response, whereas 2-APB did not block the withdrawal response evoked by the shadow stimulus in intact freely behaving Lymnaea. Together, these Wndings support the hypothesis that the second messenger in dermal photore- ceptors involves CNG and not TRP channels. Keywords Dermal photoreceptor · Cyclic nucleotide- gated (CNG) channel · Transient receptor potential (TRP) channel · Withdrawal behavior · Right pedal dorsal 11 neuron Introduction The perception of light in many animals, even those lacking eyes, is mediated by a diVuse system of photoreceptive neu- rons, sometimes referred to as ‘the dermal light sense’ (Millot 1968; Steven 1963). Such nonvisual photoreception may represent an ancient mechanism predating the evolu- tion of eyes (Fernald 2006). Indeed, nonvisual photorecep- tors have been implicated in several biologic processes, ranging from predator avoidance to circadian rhythm and migration to bioluminescence regulation (Arikawa et al. 1991; Horne and Renninger 1988; Yamashita and Tateda 1986; Yoshida 1979; Young et al. 1979). The phototrans- duction mechanisms of ocular photoreceptors in vertebrate and invertebrates are well characterized. Ocular photore- ceptor cells are subdivided into two types based on their electrophysiologic, morphologic, and molecular character- istics. One type is the vertebrate ciliary photoreceptor cell, characterized by a hyperpolarizing photoresponse involving cyclic nucleotide-gated (CNG) channels. The other type is the invertebrate rhabdomeric photoreceptor cell, characterized Communicated by G. Heldmaier. S. Pankey and H. Sunada contributed equally to this work. S. Pankey Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106-6110, USA H. Sunada · T. Horikoshi · M. Sakakibara Graduate School of Bioscience, Tokai University, Numazu, Shizuoka 410-0321, Japan T. Horikoshi · M. Sakakibara (&) Laboratory of Neurobiological Engineering, Department of Biological Science and Technology, School of High-Technology for Human Welfare, Tokai University, Numazu, Shizuoka 410-0321, Japan e-mail: manabu@tokai.ac.jp; msakaki@chime.ocn.ne.jp