Effect of Capsaicin and Other Thermo-TRP Agonists on Thermoregulatory Processes in the American Cockroach

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

How to Improve the Antioxidant Defense in Asphyxiated Newborns—Lessons from Animal Models

Oxygen free radicals have been implicated in brain damage after neonatal asphyxia. In the early phase of asphyxia/reoxygenation, changes in antioxidant enzyme activity play a pivotal role in switching on and off the cascade of events that can kill the neurons. Hypoxia/ischemia (H/I) forces the brain to activate endogenous mechanisms (e.g., antioxidant enzymes) to compensate for the lost or broken neural circuits. It is important to evaluate therapies to enhance the self-protective capacity of the brain. In animal models, decreased body temperature during neonatal asphyxia has been shown to increase cerebral antioxidant capacity. However, in preterm or severely asphyxiated newborns this therapy, rather than beneficial seems to be harmful. Thus, seeking new therapeutic approaches to prevent anoxia-induced complications is crucial. Pharmacotherapy with deferoxamine (DFO) is commonly recognized as a beneficial regimen for H/I insult. DFO, via iron chelation, reduces oxidative stress. It also assures an optimal antioxidant protection minimizing depletion of the antioxidant enzymes as well as low molecular antioxidants. In the present review, some aspects of recently acquired insight into the therapeutic effects of hypothermia and DFO in promoting neuronal survival after H/I are discussed

Behavioral thermoregulation in cockroaches after repeated compound administration.

<p>Ambient temperature preferred (°C; mean±SEM) by American cockroaches exposed to vehicle, capsaicin 0.0001mM (C 0.1) and 0.1mM (C100), capsazepine 0.0001mM (CPZ), menthol 2mM (M), thymol 1mM (T), camphor 15mM (CMF) and allyl isothiocyanate 3mM (AITC). Cockroaches were exposed to the test compounds for five days–each dose was repeated every 24 hours and then the insect was placed in the thermal gradient for 24 hours (n = 12 for each substance). * indicates values statistically significant from vehicle group (Mann-Whitney U test with Holm adjustment, * p<0.05; **p<0.01; *** p<0.001).</p

Five-trial heat box test.

<p>Latency to escape from noxious heat—50°C (s; mean ± SEM) after administration of water (Con), vehicle (V), capsaicin 0.0001mM (C 0.1) and 0.1mM (C100), menthol 2mM (M), thymol 1mM (T), camphor 15mM (CMF), allyl isothiocyanate 3mM (AITC) and capsazepine 0.0001mM (CPZ) in American cockroaches. Insects were exposed to the test compound and placed at 50°C once a day for five days–each dose administration and exposure to heat was repeated every 24 hours—five trial heat box test. Letters indicate results statistically significant vs. control (A) or solvent (B) group in each tested day (Mann-Whitney U test with Holm adjustment).</p

Experimental design.

<p>The scheme of the experimental design.</p

Results of Wilcoxon-signed rank test for five-trial heat box test.

<p>Results of Wilcoxon-signed rank test for five-trial heat box test.</p

Heat box.

<p>Heat box used to measure the latency to escape from noxious temperature (50°C) in cockroaches.</p