We explored the involvement of oxytocin receptor (Oxtr)/transient-receptor-potential-vanilloid-1 (TRPV1) genes and oxytocin (Oxt) on the adaptation of skeletal muscle to cold stress challenge in mice. Oxtr expression in hypothalamic paraventricular (PVN), supraoptic nuclei (SON), and hippocampus (HIPP) were evaluated by immunohistochemistry in parallel with the measurement of circulating Oxt. The Oxtr and TRPV1 gene expressions in soleus (SOL) and tibialis anterior (TA) muscles were investigated by RT-PCR. Histological studies of the cardiac muscle after cold stress were also performed. Male mice (n = 15) were divided into controls maintained at room temperature (RT = 24°C), exposed to cold stress (CS) at T = 4°C for 6 h , and 5 days. Immunohistochemical studies showed that Oxtr protein expression increased by two-fold (P = 0.01) in PVN and by 1.5-fold (P = 0.0001) in HIPP after 6 h- and 5 days of CS but decreased by 2-fold (P = 0.026) in SON in 5 days. Both Oxtr and TRPV1 gene expression increased after 6 h and 5 days of CS in SOL and TA muscles. Oxtr vs TRPV1 gene expression in SOL and TA muscles evaluated by regression analysis was linearly correlated following CS at 6 h and 5 days but not at control temperature of 24 ± 1°C, supporting the hypothesis of coupling between these genes. The circulating levels of Oxt are unaffected after 6 h of CS but decreased by 0.2-fold (P = 0.0141) after 5 days-CS. This is the first report that Oxtr and TRPV1 expressions are upregulated in response to cold acclimation in skeletal muscle. The up-regulation of Oxtr in PVN and HIPP balances the decrease of circulating Oxt.
Keywords: TRPV1; brain; cold stress; oxytocin; skeletal muscles.