Physiological and behavioral evidence of a capsaicin sensitive TRPV-like channel in the medicinal leech

Abstract

Abstract Transient receptor potential vanilloid (TRPV) channels are found throughout animal kingdom where they play an important role in sensory transduction. In this study we combined physiological studies with in vivo behavioral experiments to examine the presence of a putative TRPV-like receptor in the medicinal leech, building upon earlier studies in this lophotrochozoan invertebrate. The leech polymodal nociceptive neuron was activated by both peripheral and central application of the TRPV1 activator capsaicin in a concentration-dependent manner, with 100 μM being the lowest effective concentration. Responses to capsaicin were inhibited by the selective TRPV1 antagonist SB366791. The polymodal nociceptive neuron also responded to noxious thermal stimuli (>40°C) and this response was also blocked by SB366791. Capsaicin sensitivity was selective to the polymodal nociceptor with no direct response being elicited in the mechanical nociceptive neuron or in the non-nociceptive touch- or pressure sensitive neurons. Capsaicin also elicited nocifensive behavioral responses (withdrawals and locomotion) in a concentration-dependent manner and these behavioral responses were significantly attenuated with SB366791. These results suggest the presence of a capsaicin-sensitive TRPV-like channel in the medicinal leech CNS and are relevant to both the evolution of nociceptive signaling.