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 insects 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.
Highlights
The main pungent alkaloid responsible for the spicy taste of pepper is capsaicin
We previously demonstrated that capsaicin and capsazepine affect the behavioural thermoregulation of the mealworm, Tenebrio molitor
During the first 24 h the thermal preferences of American cockroaches were affected by the substances tested, both of females (ANOVA: F6.126 = 51.629, P < 0.001) and males (ANOVA: F6.126 = 9.813, P < 0.001)
Summary
The main pungent alkaloid responsible for the spicy taste of pepper is capsaicin. It acts on the mammalian vanilloid receptor TRPV1 and induces a burning sensation (Caterina et al, 1997). The transient potential vanilloid receptor subtype 1 (TRPV1) is a member of a large group of the TRP family of receptors. Mammalian TRPV1 is a heat, ligand and proton-activated nonselective cation channel. This receptor is a nociceptor involved in body temperature regulation (Caterina, 2007). Some exogenous substances are known to affect organisms’ thermoregulation via TRPV1. Capsaicin and other TRPV1 agonists induce a hypothermic response in mammals, while antagonists are known to induce a short hyperthermic effect (Gavva et al, 2007)
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