Effects of tonic immobility and corticosterone on mitochondria metabolism in pectoralis major muscle of broiler chickens

Tonic immobility (TI), which can be divided into short (STI) or long (LTI) duration, is a trait related to fear and stress response. In a previous study, we found that in broilers that LTI phenotype and chronic corticosterone (CORT) administration caused retarded growth and lower muscle weight compared with their control counterparts. The aim of this study is to determine whether the mitochondrial DNA (mtDNA) copy number and mitochondrial oxidative phosphorylation (OXPHOS), the vital factors involved in regulating energy homeostasis, have been changed by LTI or CORT treatment. The results showed that STI broilers had higher mtDNA copy number and cytochrome c oxidase (COX) enzyme activity compared with LTI broilers. Analysis of mtDNA-encoded OXPHOS genes revealed that the mRNA expression of the COX subunit 1, 2, NADH dehydrogenase (ND) subunits 1, 3 and 6, were also increased in STI broilers compared with LTI broilers. Regarding the transcriptional regulation of mtDNA-encoded OXPHOS genes, no difference was found in the methylation of the mitochondria control region between the TI phenotypes or the CORT treatments. The PGC-1 protein level was higher in STI broilers, but the av uncoupling proteins, did not show significant difference at the protein level between TI phenotypes. These results suggest that the mitochondrial function in pectoralis major muscle of STI broilers is better than that of LTI counterparts. However, chronic CORT administration did not affect the mitochondrial metabolism, indicating the mitochondrial insensitivity to CORT treatment in pectoralis major muscle.