Abstract
Capsaicin is known to activate heat receptor TRPV1 and induce changes in thermoregulatory processes of mammals. However, the mechanism by which capsaicin induces thermoregulatory responses in invertebrates is unknown. Insect thermoreceptors belong to the TRP receptors family, and are known to be activated not only by temperature, but also by other stimuli. In the following study, we evaluated the effects of different ligands that have been shown to activate (allyl isothiocyanate) or inhibit (camphor) heat receptors, as well as, activate (camphor) or inhibit (menthol and thymol) cold receptors in insects. Moreover, we decided to determine the effect of agonist (capsaicin) and antagonist (capsazepine) of mammalian heat receptor on the American cockroach’s thermoregulatory processes. We observed that capsaicin induced the decrease of the head temperature of immobilized cockroaches. Moreover, the examined ligands induced preference for colder environments, when insects were allowed to choose the ambient temperature. Camphor exposure resulted in a preference for warm environments, but the changes in body temperature were not observed. The results suggest that capsaicin acts on the heat receptor in cockroaches and that TRP receptors are involved in cockroaches’ thermosensation.
Highlights
Capsaicin is known to induce changes in thermoregulatory processes of animals
We studied the effect of various ligands that have been shown to activate or inhibit warm receptors, as well as activate or inhibit cold receptors in insects
Ambient temperature preferred by American cockroaches was influenced by thermo-TRP ligands: camphor, allyl isothiocyanate (AITC), menthol and thymol (d.f. = 3, F = 140.438, p < 0.001), but the effect was not significantly different when analyzed for various concentrations of the ligands (d.f. = 4, F = 1.457, p = 0.213)
Summary
Capsaicin is known to induce changes in thermoregulatory processes of animals. In mammals, this alkaloid has been shown to induce hypothermia that occurs both at physiological (skin vasodilation, suppression of thermogenesis and salivation) and behavioral (cold-seeking behavior) response levels [1,2,3,4]. Some reports have shown the effect of capsaicin on thermoregulatory processes in invertebrates such as an induced preference for lower temperatures in Periplaneta americana [5]. Exposure to this alkaloid has been reported to change the responsiveness to noxious heat in the American cockroach [7] and in land snail Megalobulimus abbreviatus [8]. The mechanism by which capsaicin induces thermoregulatory responses in invertebrates has not been elucidated yet
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