Experimental chronic entrapment of the sciatic nerve in adult hamsters: an ultrastructural and morphometric study

Entrapment neuropathy is a group of clinical disorders involving compression of a peripheral nerve and interference with nerve function mostly through traction injury. We have investigated the chronic compression of peripheral nerves as an experimental procedure for detecting changes in ultrastructural nerve morphology. Adult hamsters (Mesocricetus auratus, N = 30) were anesthetized with a 25 percent pentobarbital solution and received a cuff around the right sciatic nerve. Left sciatic nerves were not operated (control group). Animals survived for varying times (up to 15 weeks), after which they were sacrificed and both sciatic nerves were immediately fixed with a paraformaldehyde solution. Experimental nerves were divided into segments based upon their distance from the site of compression (proximal, entrapment and distal). Semithin and ultrathin sections were obtained and examined by light and electron microscopy. Ultrastructural changes were qualitatively described and data from semithin sections were morphometrically analyzed both in control and in compressed nerves. We observed endoneurial edema along with both perineurial and endoneurial thickening and also the existence of whorled cell-sparse structures (Renaut bodies) in the subperineurial space of compressed sciatic nerves. Morphometric analyses of myelinated axons at the compression sites displayed a remarkable increase in the number of small axons (up to 60 percent) in comparison with the control axonal number. The distal segment of compressed nerves presented a distinct decrease in axon number (up to 40 percent) comparatively to the control group. The present experimental model of nerve entrapment in adult hamsters was shown to promote consistent histopathologic alterations analogous to those found in chronic compressive neuropathies

Extracellular matrix molecules play diverse roles in the growth and guidance of central nervous system axons

Axon growth and guidance represent complex biological processes in which probably intervene diverse sets of molecular cues that allow for the appropriate wiring of the central nervous system (CNS). The extracellular matrix (ECM) represents a major contributor of molecular signals either diffusible or membrane-bound that may regulate different stages of neural development. Some of the brain ECM molecules form tridimensional structures (tunnels and boundaries) that appear during time- and space-regulated events, possibly playing relevant roles in the control of axon elongation and pathfinding. This short review focuses mainly on the recognized roles played by proteoglycans, laminin, fibronectin and tenascin in axonal development during ontogenesis

Topographic organization in the anterior commissure of developing hamsters

The present study has examined the existence of a topographic organization in the anterior commissure (AC) of developing hamsters. Fluorescent carbocyanine crystals (DiI and/or DiA) were implanted into different rostrocaudal and dorsoventral sectors of the paleocortex of hamsters ranging in age from E15 to P10 (E16 = P1 = date of birth). The cerebral hemispheres of each brain were cut horizontally and sagittally, respectively, and the sections were observed under a fluorescence microscope coupled to a computerized reconstruction system. A distinct topographic organization of AC fibers was observed along the rostrocaudal axis starting at E15, and continued unchanged thereafter. These results support the hypothesis that the orderly pattern of AC fibers is achieved by active positioning during the first days after crossing the midplane rather than by a regressive sculpting from an initially disorganized pattern.

Pioneer axons in the anterior commissure of hamster embryos

The existence and the morphological characteristics of pioneer axons in the anterior commissure (AC) were investigated in hamster embryos using fluorescent carbocyanine crystals implanted into the paleocortex. On embryonic days 12-13(E12-E13), a group of tortuous fibers was seen close to the midline. After this group of fibers reached the midline on E13.5-E14, pioneer axons were seen in the AC, and from E14.5 to E15.5 both pioneers and followers approached the targets, the former ahead of the latter by about 500 µm. Arborization took place as soon followers approached the targets, the former ahead of the latter by about 500 µm. Aarborization took place as soon as the followers reached the targets (E15.5-E16). The pioneer cells were labeled retrogradely and were seen in the most superficial layears of the paleocortex, along the rostrocaudal extent of the hemisphere. The fact that pionners appear only during or after crossing suggests the existence of factors either in the midline region and/or in the opposite hemisphere, which selectively accelerate the growth of the pioneers or decelerate the growth of the followers