Appearance of postural asymmetry of hind limbs in rats following unilateral colchicine block of axonal transport in corticolumbar projections

Abstract

To test this hypothesis the possibility of formation of functional asymmetry of the segmental apparatus, due to the appearance of PA factor in the cerebrospinal fluid (CSF) was studied after blocking of axonal transport in corticolumbar projections in the absence of organic damage to brain and spinal cord tissue. Axonal transport was blocked by colchicine. To identify disturbances of axonal flow the histochemical retrograde transport of horseradish peroxidase (HRP) method was used. EXPERIMENTAL METHOD Noninbred male rats weighing 180-220 g were used. Under ether anesthesia a microinjection of colchicine (from Merck, West Germany) in a dose of 1 ~g, in 1 D1 of physiological saline, was given into the motor cortex on the left side at a depth of 1 mm into the underlying white matter. The animals were then divided into groups and spinalized at level TI at different times after injection of colchicine. All the animals were tested for the presence of PA of the hind limbs visually and e!ectromyographically. EMGs of two groups of corresponding thigh muscles (biceps and quadriceps) of both hind limbs were analyzed. Steel bipolar needle electrodes (diameter 0.5 mm, interelectrode distance 3 mm) were used. The results were processed directly in the course of the experiment on a nonlinear MN-10M simulation apparatus by calculation of the coefficient of asyrmnetry, the ratio of the difference between bioelectrical activity of the homonymous muscles, integrated by frequency and amplitude, and their total. The results were subjected to statistical analysis by Student's test at a P < 0.05 level of significance. Blocking of axonal transport in corticolumbar projections was identified by microinjection of 0.1-0.2 pl of 30-40% solution of RRP (Sigma-VI) into the gray matter of the spinal cord. The animals were killed 48 h after injection by perfusion of the brain with physiological saline, followed by perfusion with a fixing solution consisting of 0.4% paraformaldehyde and 25% glutaraldehyde in 0.i M phosphate buffer, pH 7.4. The brain was removed and kept for 24 h at 4~ in the same fixing solution, after which it was transferred into 30% sucrose solution in 0.i M phosphate buffer, in which it remained for 24-48 h at 4~ Serial sections 40 ~ thick were then cut on a freezing microtome. The sections were stained by the histochemical method in [6]. Biological testing was used to reveal PA-inducing factors (PAF) in the CSF of the donor animals with blocked axonal transport in corticolumbar projections. For this purpose donors' CSF in a volume of 50 ~i was injected into the cerebromedullary cisterna of intact recipient rats. The recipients were spinalized 10-15 min later and tested for the presence or absence of PA.