Selective stimulation of motor fibres in the sciatic nerve of a rat

The aim of this study was to test the possibility of selective activation of slow and fast fibres within the rat tibialis anterior muscle, via selective stimulation of corresponding motor fibres within the sciatic nerve. For this purpose the implantable cuffs containing two and three platinum ring-electrodes were constructed and surgically fitted on the left and right sciatic nerve in five Wistar rats. In the left nerve, conventional, rectangular stimuli were delivered bipolarly via double-ring cuffs. In the right nerve quasitrapezoidal stimuli were delivered tripolarly via treblering cuffs. After 60 s of simultaneous and continuous stimulation of both nerves the left and right anterior tibialis muscle were isolated and immediately frozen in liquid nitrogen. Each muscle was completely cut in step serial sections. Glycogen depletion was demonstrated by Periodic acid-Schiff (PAS) reaction. In one randomly selected rat an immunohistochemical profile of muscle fibres (type I, IIA, IIB, and IIX) was determined with antibodies against myosin heavy chain isoforms. In other rats typing of glycogen depleted fibres was performed according to muscle fibre diameters. Preliminary results show that glycogen depleted fibres in the selected rat were type IIB fibres in both types of stimulation, except for a few type I fibres, stimulated by quasitrapezoidal impulses. In other rats glycogen depleted fibres were always the fibres of the largest diameter, most probably also type IIB fibres in both types of stimulation. Glycogen depletion of type I fibres was never observed in muscles stimulated by rectangular stimuli.