Capsazepine affects thermal preferences of the American cockroach (Blattodea: Blattidae)

Abstract

ISSN (online): 1802-8829 http://www.eje.cz capsaicin induces preferences for lower temperatures in Rhodnius prolixus, while capsazepine treatment cause the opposite behav-iour. The aim of our study was to assess the effect of capsazepine (TRPV1 antagonist) on the thermal preference of the American cockroach, Periplaneta americana. American cockroach has TRP receptors. Wicher et al. (2005) screened the Periplaneta cDNA library for members of the TRPC family and found a homolog of the Drosophila TRPɣ channel. It is proposed that it is involved in forming the channel that conducts the Ca 2+ background current in DUM neurons. Recently, French et al. (2015) demonstrated that the TRPL channel has a major role in Periplaneta phototransduc-tion. Based on our preliminary results we hypothesized that capsaz-epine infl uences thermoregulatory processes in insects. To con-fi rm this hypothesis, we examined thermal preferences of cock-roaches treated with fi ve different capsazepine concentrations and released in a thermal gradient system. To establish whether cap-sazepine may act as a capsaicin antagonist in insects, we assessed the insect thermoregulatory response to capsaicin following pre-treatment with capsazepine. We assumed that capsazepine blocks the insects' hypothermic response to capsaicin, as in mammals (Dogan et al., 2004). MATERIALS AND METHODS Insects American cockroaches Periplaneta americana L. were reared in plastic containers at ~ 26°C under a natural photoperiod. They were fed with oat fl akes and apples and received drinking water at regular intervals. Only adult individuals were selected for the experiments. Experiments were performed separately on males Abstract. Capsazepine is a competitive antagonist of capsaicin, a TRPV1 agonist responsible for the spicy taste of pepper. TRPV1 agonists and antagonists are known to affect mammalian body temperature, but their action on thermoregulation in in-sects is poorly known. In this study we evaluated the effect of capsazepine on the thermal preference of the American cockroach, Periplaneta americana using a thermal gradient. Our results revealed that capsazepine in submicromolar concentrations induces a preference for higher ambient temperatures when compared to the control insects. To assess whether capsazepine may act also as an antagonist of capsaicin in insects, we determined this insects' thermal behaviour when capsazepine was applied before capsaicin. The hypothermic response to capsaicin was clearly blocked by pre-treatment with capsazepine only in female American cockroaches. Our results indicate the involvement of structures functionally similar to TRPV1 in insect thermosensation.