ABSTRACT
Light and electron microscopy and quantitative morphometry were used to determine the effects of exercise and mesterolone on the soleus muscles of mice. Both exercise and mesterolone caused a significant hypertrophy of extrafusal muscle fibres. The hypertrophy of Type I fibres was greater than that of Type II fibres. There was no hyperplasia. Mitochondria were more numerous and larger than in the muscles of sedentary animals. Capillarity increased and small centrally nucleated muscle fibres appeared, usually in small clusters and most often in the muscles of animals exposed to mesterolone. A small proportion of satellite cells exhibited signs of activation but there were more in the muscles of mesterolone-treated animals than after exercise. Muscles from animals that had been both exercised and treated with mesterolone exhibited the largest changes: muscle mass and muscle fibre hypertrophy was greater than in all other groups of animals, capillarity was higher and >30% of all recognized satellite cells exhibited signs of activation. Groups of small centrally nucleated muscle fibres were commonly seen in these muscles. They appeared to be the result of splits in the form of sprouts from existing muscle fibres. With both exercise and mesterolone, alone or in combination, there was an increase in the proportion of Type I muscle fibres and a decrease in the proportion of Type II.
Subject(s)
Anabolic Agents/pharmacology , Mesterolone/pharmacology , Muscle, Skeletal/drug effects , Muscle, Skeletal/ultrastructure , Physical Exertion , Anabolic Agents/administration & dosage , Animals , Humans , Hypertrophy , Male , Mesterolone/administration & dosage , Mice , Microscopy/methods , Microscopy, Electron, TransmissionABSTRACT
The nervous system is highly plastic. Its development and maturation is characterised by neuronal proliferation, specialisation and loss and the sorting of synaptic connectivity. Transmission (chemical and electrical), receptor and ion channel transcription and distribution all contribute to the emerging selectivity of action. Numerous factors especially genetic and autoimmune and extrinsic factors synthetic and natural toxic chemicals disrupt this process of development and maturation or interfere with the function and structure of the mature system. In this review, the response of the peripheral nervous system to such influences is discussed.