Effects of tonic immobility (TI) and corticosterone (CORT) on energy status and protein metabolism in pectoralis major muscle of broiler chickens

Tonic immobility (TI), which can be divided into short (STI) or long (LTI) duration, is a character related to fear. Our previous study has demonstrated LTI phenotype and chronic corticosterone (CURT) administration retarded growth of breast muscle in broiler chickens. In order to investigate the mechanism behind the negative effects of LTI and CURT on growth, the level of mRNA transcription of several key genes linked to energy and protein metabolism was measured in muscle. LTI broilers showed lower levels of ATP, energy charge (EC) (p < 0.01), and lower muscle glycogen content (p < 0.05) but higher level of ADP (p = 0.08) than STI birds. CURT treatment elevated EC level (p < 0.05) and reduced liver glycogen content (p < 0.05). Real-time PCR results showed that STI chickens had higher mRNA expression of PPAR alpha (p = 0.06) and AMPK alpha (p = 0.09) than LTI. CURT significantly down-regulated a-enolase mRNA expression in breast muscle compared to control (p < 0.05). Neither TI nor CORT altered gene expression in Akt/mTOR/p70s6k cascade pathway in muscle (p > 0.05). However, western blot results showed that LTI chickens exhibited higher protein content of total Akt (p = 0.05) and phosphowlated Akt (p = 0.06) than STI. CURT treatment decreased the total protein content of Akt (p = 0.09) and p70s6k (p = 0.08). These results suggest that the retardation of muscle growth by LTI and chronic CURT administration parallels a strong alternation in energy status but slight changes of Akt/mTOR/p70s6k cascade, indicating that a decrease in muscle growth induced by LTI and CURT might not be mediated through mTOR-dependent signaling pathways. (C) 2014 Elsevier Inc All rights reserved.