Análise histológica e imuno-histoquímica de músculos de contração rápida e lenta em camundongos com déficit colinérgico

Abstract

The Skeletal Muscle is a widely innervated and vascularized tissue and has a great importance on voluntary muscle contraction. Has great plasticity and can change its phenotype during neuromuscular diseases, physical stimulation and during aging process. The contraction of the muscle fibers can occur in a fast or in a slow way and this characteristic is dependent on the expression of four Myosin Heavy Chain (MyCH) isoforms, which can be classified in type I (slow) and three types of the II isoform (IIA, IIX and IIB- fast). Nerve stimulation is fundamentally important for muscles to contract and in mammals, it happens when the neurotransmissor, acetylcholine is released in the synaptic cleft and binds to nicotinic receptors at the post synaptic membrane. The correct storage of acetylcholine in synaptic vesicles is essential for cholinergic neurotransmission. This storage is promoted by a protein that is localized in the synaptic vesicle membrane called, Vesicular Acetylcholine Transporter (VAChT). In order to understand the effects of a cholinergic dysfunction, Prado et al., (2006) developed by homologue recombination a strain of mice that present reduced levels of the VAChT protein (VAChT KDHET and KDHOM). These animals have respectively 40% and 70% reduction in this protein levels and motor performance studies showed a significant deficit in muscle strength. Therefore our aim is to evaluate qualitatively and quantitatively by histological techniques, the general morphology, the total number and distribution of muscle fibers and the CSA and perimeter of slow and fast muscle fibers from different muscles in these animals, as well as evaluate by immunofluorescence possible alterations in the expression pattern of the MyHC isoforms. Our results show that the Soleus, a slow twitch muscle present a reduction in the distribution of fibers per area in KDHOM and an increase in the CSA and perimeter in KDHET and KDHOM, compared to control. Differently, the Extensor Digitorum Longus muscle (EDL), a fast twitch muscle in KDHOM mice presented an increase in the total number of fibers and a reduction in the CSA and perimeter of this muscle, suggesting an atrophy of these fibers. The qualitative evaluation of the MyHC isoforms just showed a possible increase in the expression of the type I. Thereby, our results show that cholinergic activity plays a role in the establishment of muscle fibers phenotype and disturbances in this system, exemplified by this mice model is capable to interfere with the correct function of these muscles.