Exposure to electromagnetic field (EMF) induces physiological changes in organism that are observed at different levels—from biochemical processes to behavior. In this study, we evaluated the effect of EMF exposure (50 Hz, 7 mT) on cockroach’s response to noxious heat, measured as the latency to escape from high ambient temperature. We also measured the levels of lipid peroxidation and glutathione content as markers of oxidative balance in cockroaches exposed to EMF. Our results showed that exposure to EMF for 24, 72 h and 7 days significantly increases the latency to escape from noxious heat. Malondialdehyde (MDA) levels increased significantly after 24-h EMF exposure and remained elevated up to 7 days of exposure. Glutathione levels significantly declined in cockroaches exposed to EMF for 7 days. These results demonstrate that EMF exposure is a considerable stress factor that affects oxidative state and heat perception in American cockroach.

The aim of the presented study was to assess the applicability of capsaicin as a synergist for organophosphate insecticide against the Colorado potato beetle (Leptinotarsa decemlineata Say). We recorded the death rate, behavioral thermoregulation and metabolic rate of the examined insects after intoxication with capsaicin and organophosphate pesticide. The results obtained showed that the tested substances changed the thermal preferences of the potato beetle, causing the beetles to prefer a decrease in temperature in the thermal gradient system. We also observed an increase in the metabolic rate of the beetles intoxicated with capsaicin and organophosphate insecticide. The addition of capsaicin in a concentration of 10 -7 M (dissolved in alcohol) to insecticide resulted in an increase in the death rate of the insects by 24% in 35°C and 73% in 15°C, in comparison to organophosphate alone. Our results show that capsaicin in low concentrations may be an efficient synergist for organophosphate insecticides against the Colorado potato beetle.

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.

ISSN (online): 1802-8829http://www.eje.cz capsaicin induces preferences for lower temperatures in Rhodnius prolixus, while capsazepine treatment cause the opposite behaviour.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 phototransduction.Based on our preliminary results we hypothesized that capsazepine infl uences thermoregulatory processes in insects. To confi rm this hypothesis, we examined thermal preferences of cockroaches treated with fi ve different capsazepine concentrations and released in a thermal gradient system. To establish whether capsazepine may act as a capsaicin antagonist in insects, we assessed the insect thermoregulatory response to capsaicin following pretreatment with capsazepine. We assumed that capsazepine blocks the insects' hypothermic response to capsaicin, as in mammals (Dogan et al., 2004). MATERIALS AND METHODS InsectsAmerican 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 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.

Some natural alkaloids, e.g. capsaicin and camphor, are known to induce a desensitization state, causing insensitivity to pain or noxious temperatures in mammals by acting on TRP receptors. Our research, for the first time, demonstrated that a phenomenon of pharmacological blockade of heat sensitivity may operate in American cockroach, Periplaneta americana (L.). We studied the escape reaction time from 50°C for American cockroaches exposed to multiple doses of different drugs affecting thermo-TRP. Capsaicin, capsazepine, and camphor induced significant changes in time spent at noxious ambient temperatures. Moreover, we showed that behavioral thermoregulation in normal temperature ranges (10–40°C) is altered in treated cockroaches, which displayed a preference for warmer regions compared to non-treated insects. We also measured the levels of malondialdehyde (MDA) and catalase activity to exclude the secondary effects of the drugs on these processes. Our results demonstrated that increase in time spent at 50°C (five versus one trial at a heat plate) induced oxidative stress, but only in control and vehicle-treated groups. In capsaicin, capsazepine, menthol, camphor and AITC-treated cockroaches the number of exposures to heat had no effect on the levels of MDA. Additionally, none of the tested compounds affected catalase activity. Our results demonstrate suppression of the heat sensitivity by repeated capsazepine, camphor and capsaicin administration in the American cockroach.