The Capillary Pattern in Human Masseter Muscle During Ageing

Abstract

The effect of ageing on the capillary network in skeletal muscles has produced conflicting results in both, human and animals studies. Some of the inconsistencies are due to non-comparable and biased methods that were applied on thin transversal sections, especially in muscles with complicated morphological structures, such as in human masseter muscle. We present a new immunohistochemical method for staining capillaries and muscle fibres in 100 µm thick sections as well as novel approach to 3D visualization of capillaries and muscle fibres. Applying confocal microscopy and virtual 3D stereological grids, or tracing capillaries in virtual reality, length of capillaries within a muscle volume or length of capillaries adjacent to muscle fibre per fibre length, fibre surface or fibre volume were evaluated in masseter muscle of young and old subjects by an unbiased approach. Our findings show that anatomic capillarity is well maintained in masseter muscle in old subjects; however, vascular remodelling occurs with age, which could be a response to changed muscle function and age-related muscle fibre type transformations.

Horizontal deformation of skeletal muscle thick sections visualised by confocal microscopy

“…In skeletal muscle research, 3D analysis is especially important for studying changes in microvasculature, since the capillary network is a complex interwoven 3D structure which cannot be reliably estimated by stereological methods in 2D 4–6 . One of the well‐established methods for visualising tissue structure and cellular or subcellular particles in 3D is fluorescence confocal and multiphoton microscopy of thick tissue sections 4,7,8 . However, thick tissue sections are prone to artefacts, especially section deformations that may significantly influence some stereological and morphometric results like muscle fibre diameter and capillary length, but not dimensionless parameters like object number and Euler‐Poincaré characteristics 1 …”