Effect of caffeine on the neuromuscular system in rats: an immunohistochemical study

Caffeine (Caf) is a central nervous system stimulant, it is used to reduce physical fatigue and restore mental alertness. Caffeine (1,3,7-trimethylxantine) is one of the most consumed drugs in the world. It is a natural alkaloid present in coffee, tea and mate plants. There is a strong belief that Caf is an ergogenic aid to sports performance [1,2,]. Although much evidence suggests that Caf may improve endurance exercise performance, questions still remain with regard to its effects on neuromuscular function. At the cellular level, it stimulates the central nervous system (CNS), enhances neuromuscular transmission and improves skeletal muscle contractility [3]. Caf enters the bloodstream through the stomach and small intestine and can have its effects as soon as 15 minutes after it is consumed. Once in the body, it takes about 6 hours before to be eliminated. Since in scientific literature there are only few morphological studies about neuromuscular system, we performed an immunohistochemical study on neuropeptides expression in rat skeletal muscle after Caf oral administration: thirty male rats were divided into 3 groups, the first one with 16mg/kg Caf, the second one with 24mg/kg Caf, the last one was control group. The immunohistochemical study was performed with antibodies against Protein Gene Product 9.5 (PGP 9.5), Serotonin (5-HT), Vasointestinal Peptide (VIP) and Substance P (SP), on rat skeletal muscle. We observed an accentuated immunoreactivity for peptides in samples with higher concentration administration (24mg/kg Caf), compared with normo-fed rats (control group), in which was observed a small positivity for tested substances. Our results suggest that caffeine is able to increase muscular performance with a dose-dependent effect.