Adult skeletal muscle fibres are classified as type 1, 2A, 2X, and 2B. These classifications are based on the expression of the dominant myosin heavy chain isoform. Muscle fibre-specific gene ...expression and proportions of muscle fibre types change during development and in response to exercise, chronic electrical stimulation, or inactivity. To identify genes whose gain or loss-of-function alters type 1, 2A, 2X, or 2B muscle fibre proportions in mice, we conducted a systematic review of transgenic mouse studies. The systematic review was conducted in accordance with the 2009 PRISMA guidelines and the PICO framework. We identified 25 “muscle fibre genes” (Akirin1, Bdkrb2, Bdnf, Camk4, Ccnd3, Cpt1a, Epas1, Esrrg, Foxj3, Foxo1, Il15, Mapk12, Mstn, Myod1, Ncor1, Nfatc1, Nol3, Ppargc1a, Ppargc1b, Sirt1, Sirt3, Thra, Thrb, Trib3, and Vgll2) whose gain or loss-of-function significantly changes type 1, 2A, 2X or 2B muscle fibre proportions in mice. The fact that 15 of the 25 muscle fibre genes are transcriptional regulators suggests that muscle fibre-specific gene expression is primarily regulated transcriptionally. A reanalysis of existing datasets revealed that the expression of Ppargc1a and Vgll2 increases and Mstn decreases after exercise, respectively. This suggests that these genes help to regulate the muscle fibre adaptation to exercise. Finally, there are many known DNA sequence variants of muscle fibre genes. It seems likely that such DNA sequence variants contribute to the large variation of muscle fibre type proportions in the human population.
Housing conditions influence anatomy, physiology, and behaviour of animals. The aim of this study is to investigate whether the generation of fever, a defence response of the body, is also affected ...by housing conditions. Golden hamsters (Mesocricetus auratus) were housed in small cages, large cages, or large and enriched cages. After 9 weeks of exposure to their respective environments, the fever response to the administration of lipopolysaccharide (50 micrograms/kg from Salmonella typhosa) was tested. One hundred and twenty experiments in 30 hamsters demonstrated that housing in small cages diminished the fever responses (increase in core temperature and fever index) significantly by approximately 20%, and is likely to be due to a higher stress level. The findings demonstrate that the results of physiological experiments are not only influenced by the experimental design, but also by pre-experimental housing conditions.
In species with a carotid rete, the arterial blood destined for the brain can be cooled on its passage through the rete. The temperature difference between the blood before the rete and the brain is ...termed selective brain cooling (SBC). The onset and degree of cooling depend on internal body temperature. The aim of this study was to determine the brain sites where the temperature signals driving SBC are generated. Thirty-six experiments were performed in three conscious goats, which were prepared with an arteriovenous shunt, carotid loops, and hypothalamic thermodes to manipulate the temperatures of the trunk (Ttr), the hypothalamus (Thyp), the extrahypothalamic brain (Texh), or the whole brain (Tbr). In all experiments, Ttr was clamped at 39.5 degrees C. The increase of SBC was 2.1 degrees C per 1 degree C increase of Tbr (gain = 2.1). The rise of Thyp at constant Texh yielded a gain of 1.6, whereas the gain of Texh at constant Thyp was 0.7. It is concluded that onset and degree of SBC are predominantly determined by temperature signals generated in the hypothalamus itself.
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