Role of TRPV4 channels in thermoregulation in endotherms

Abstract

The thermo-TRPV4 channels are expressed in various tissues, including peripheral sensors in birds and peripheral and central sites in mammals. In rats, we have demonstrated that peripheral TRPV4 (possibly skin) appear active in a range of ambient temperature (Ta) higher than 22 ° C and lower than 32 ° C, being involved in activation of heat loss responses, both autonomic (tail vasodilation and inhibition of thermogenesis) and behavioral (selection of lower Tas). In these animals, in addition to the location on skin, TRPV4 are also expressed in the medial preoptic area (MPO), an important region involved in regulation of body temperature (Tc). There is evidence of increased expression of TRPV4 in MPO induced by systemic inflammation with endotoxin (LPS). From pilot experiments, showing an increase of Tc after TRPV4 antagonist intra-MPO injection, our hypothesis is that such channels act in the MPO as modulators of the activity of both autonomic and behavioral thermoeffectors during systemic inflammation. Testing this hypothesis is the first objective of the present study and, therefore, the following protocols will be performed: 1.1) - effect of the microinjection of HC-067047, selective antagonist of TRPV4 channels, in MPO on Tc, oxygen consumption (index of thermogenesis) and heat loss index (HLI) in control and LPS-treated rats in Ta below the activation range of peripheral TRPV4 (~ 21oC); 1.2) - effect of the microinjection of HC-067047 in the MPO on Tc, oxygen consumption and the HLI in control and LPS-treated rats in Ta within the activation range of peripheral TRPV4 (~ 28oC); and 1.3) - effect of the microinjection of HC-067047 in the MPO on Tc and preferred Ta of control and LPS-treated rats. Regarding birds, the picture is much less clear than in mammals. Despite the recognized presence of the TRPV4 in epithelial sensors in birds, the thermosensorial role of TRPV4 in these animals is still a matter for investigation. In this sense, using chickens as a model of precocious birds, the second aim of this study is to investigate whether the peripheral TRPV4 act as thermosensors and modulate autonomic and behavioral effectors in these animals. To this end, we will use 5 days old (Ta comfort ~ 32oC) and 3 weeks old (Ta comfort ~ 28oC) chicks to perform the following protocols: 2.1) - effect of chemical stimulation of peripheral TRPV4 with the agonist RN1747 on Tc, oxygen consumption and pulmonary ventilation (index of evaporative heat loss in birds) in 5-day old chicks in thermal comfort (Ta= 32 ° C); 2.2) - the effect of peripheral injection of antagonist HC067047 on Tc, oxygen consumption and ventilation in chicks in different Tas (26, 28, 30 and 32 ° C); 2.3) - the effect of antagonist and agonist injections on huddling behavior in 5-day old chicks; 2.4) - the effect of peripheral injection of antagonist HC067047 on Tc, oxygen consumption and ventilation of 3 weeks old chicks in different Tas (24, 26, 28 and 30 ° C); 2.5) - effect of inhibition of peripheral TRPV4 on the preferred Ta in thermal gradient after exposure to heat stimulus in 3 weeks old chicks; 2.6) - effect of chemical stimulation of peripheral TRPV4 on the preferred Ta in thermal gradient of 3 weeks old chicks. (AU)