Axonal regeneration in an articular branch following rat sciatic nerve lesions

Correlation between motor function and axonal morphology in neonatally sciatic nerve-injured rats

The present study was conducted to investigate the correlation between motor function and axonal morphology in neonatally sciatic nerve-injured rats. The left sciatic nerve of newborn rats was transected or crushed, and functionality of the sciatic nerve was assessed by the static sciatic index after 8 weeks. After functional assessment, the common peroneal nerves in the control, nerve-transected, and nerve-crushed rats were removed and prepared for morphometric examinations. The cross-sectional area of the nerve, total number of myelinated axons, and size of each myelinated axon were analyzed for each group. The control rats showed normal motor function, whereas the nerve-transected rats showed severe motor dysfunction. The cross-sectional area of the nerve and total number of myelinated axons were reduced after nerve transection. Moreover, the percentage per size class of myelinated axons was almost uniform in the control rats, while the distribution was shifted to the left in the nerve-transected rats. Furthermore, no large myelinated axons were observed in the nerve-transected rats. The nerve-crushed rats showed various gait functions with various distribution patterns of axonal size, and the rats were divided into two groups with and without uninjured residual large axons. The results showed that the importance of regenerated medium-sized axons in cases without large axons and of residual large axons in cases with large axons in motor function. It was revealed that motor function was related closely to axonal size in neonatally nerve-injured rats.

Chapter 3: Histology of the peripheral nerve and changes occurring during nerve regeneration

Peripheral nerves are complex organs that can be found throughout the body reaching almost all tissues and organs to provide motor and/or sensory innervation. A parenchyma (the noble component made by the nerve fibers, i.e., axons and Schwann cells) and a stroma (the scaffold made of various connective elements) can be recognized. Although morphological analysis is the most common approach for studying peripheral nerve regeneration, researchers are not always aware of several histological peculiarities of these organs. Therefore, the aim of this review is to describe, at a structural and ultrastructural level, the main features of the parenchyma and the stroma of the normal undamaged nerve as well as the most important morphological changes that occur after nerve damage and during posttraumatic nerve regeneration. The paper is aimed at providing the reader with the basic framework information on nerve morphology. This would enable the correct interpretation of morphological data obtained by many experimental studies on peripheral nerve repair and regeneration such as those outlined in several other papers included in this special issue of the International Review of Neurobiology.

Functional evaluation of regenerated and misrouted low threshold mechanoreceptors and polymodal nociceptors in the skin of rat hindfeet after crush lesions to the sciatic nerve

Tracer studies on motor axons after nerve crush injuries have indicated that misrouting may occur even when the endoneurium is intact. Misrouting of regenerated polymodal nociceptive C-fibres and low threshold mechanoreceptive axons have been studied functionally in 50 rats three months after unilateral crush lesions to the sciatic nerve. Two weeks before evaluation the tibial fascicle (or the peroneal fascicle) above the lesion was cut and tied off. In this way only functional regeneration of misrouted axons was tested. Misrouted low threshold mechanoreceptive axons and polymodal nociceptor C-fibres were found after regeneration in both glabrous and hairy skin. We conclude that functional misdirection of both myelinated and unmyelinated sensory axons innervating either glabrous or hairy skin can occur after a crush lesion to a peripheral nerve in rats.

Inferior functional sensory regeneration after suture of sciatic neurotomy in newborns compared with mature rats

It is generally believed that nerve injuries in children regenerate better than those which occur in adults. However, there are no functional experimental studies that support this belief. This study evaluates the functional regeneration of polymodal C-fibres after nerve regeneration in newborn and mature rats 3 months after unilateral sciatic nerve neurotomy and suture. The distribution of polymodal C-fibres was tested by measuring the Evans blue-stained area in the skin after antidromic nerve stimulation. In the newborn group of regenerated animals showed that functional C-fibres were present in a significantly (P < 0.05) smaller area than found in the adult group. We conclude that the functional regeneration of C-fibres is superior in mature rats compared with newborns, 3 months after regeneration.

Effect of cavernous nerve freezing on protein and gene expression of nitric oxide synthase in the rat penis and pelvic ganglia

PURPOSE

Cryoablation of the prostate has been reported to induce impotence as a result of cavernous nerve injury. This study is designed to investigate the early and late effects of cavernosal nerve cryoablation on erectile function and nitric oxide synthase (NOS) containing nerves in the rat penis and pelvic ganglia.

MATERIALS AND METHODS

Forty male rats were divided into two groups (n = 20 each). The first group underwent unilateral cavernous nerve freezing (experimental group). Before their euthanization at 1 and 3 months (10 rats each), erectile function was assessed by electrostimulation of the cavernous nerves. The second group served as a control and was euthanized at the same time points. Nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining was used to identify NOS in the penile nerve fibers of the mid-shaft segment and neurons of the pelvic ganglia. Western blot, RT-PCR and immunostaining techniques were used to identify protein and gene expression of eNOS, iNOS, and nNOS.

RESULTS

One month after unilateral cavernosal nerve freezing, there was a significant decrease in NOS-containing nerve fibers in the dorsal and intracavernosal nerves and ipsilateral pelvic ganglia as compared with the intact side. At three months, the number of NOS containing nerve fibers in the above-mentioned nerves and ganglia showed a significant increase on the frozen side but not the intact side. Electrostimulation of the frozen nerve after three months revealed a significantly higher maximal intracavernosal pressure and a shorter latency period than the one-month group. At three months, immunoblot showed up-regulation of eNOS and nNOS protein expression in the penile tissue. RT-PCR showed up-regulation of nNOS gene expression in the pelvic ganglia of the frozen side. Immunostaining confirmed the results of western blot and showed significant increase of the nNOS positive staining in the frozen side of the penile tissue after three months. There was no difference in iNOS after three months between both sides. Our repeated eNOS immunostaining was not successful.

CONCLUSIONS

The results show that intracavernous pressure response to neurostimulation markedly decreased at one month and then partially recovered three months after cavernosal nerve freezing. A similar pattern of changes of the NOS-containing nerve fibers in dorsal nerves, intracavernosal nerves, and pelvic ganglia were observed. This alteration in erectile function and NOS-containing nerves was associated with differential gene and protein expression of the three subtypes of NOS.

Functional evaluation of regenerated and misrouted axons to glabrous and hairy skin of the rat hind foot after sciatic neurotomy and suture

The function of misrouted regenerated polymodal nociceptor C-fibers and low-threshold mechanoreceptive axons in the lateral plantar nerve (LPN) and in the foot branch of the superficial peroneal nerve (fSPN) was evaluated 3 months after unilateral sciatic neurotomy and suture. Two weeks before evaluation the tibial fascicle (or the peroneal fascicle) above the neurotomy was cut and tied off. In this way only functional regeneration of misrouted axons was tested in the LPN (or the fSPN). In regenerated animals the glabrous skin area had no functional fSPN-related low-threshold mechanoreceptive axons. However, the hairy fSPN skin area showed function of misrouted LPN-related low-threshold mechanoreceptive axons. In both the glabrous skin domain innervated by the LPN and the hairy skin area supplied by the fSPN, functional regeneration of misrouted polymodal nociceptor C-fibers was found. We conclude that functional regeneration of misrouted axons related to polymodal nociceptive units and low-threshold mechanoreceptive units is more efficient in hairy skin of the rat foot whereas only misrouted polymodal nociceptor C-fibers recover function in glabrous skin.

Invasion of the rat ventral root L5 by putative sympathetic C-fibers after neonatal sciatic nerve crush

The present study examines the occurrence of C-fibers in lumbar ventral roots after sciatic nerve crush in neonatal and adult rats. Electron microscopic analysis showed that the number of C-fibers in the ventral root L5 increased significantly on the lesion side after neonatal but not adult sciatic nerve crush and that the number of C-fibers was higher in the ventral root L5 on the unoperated side compared to this root in normal control rats. In order to determine whether the new C-fibers in the L5 root on the lesion side are sensory or sympathetic we made immunohistochemical studies on roots from neonatally crushed rats. We found that there was no obvious lesion side/contralateral side or operated rat/control rat difference with respect to the occurrence and general configuration of axons with substance P-, calcitonin gene-related peptide- or vasoactive intestinal polypeptide-like immunoreactivity. However, the occurrence of axons with tyrosine hydroxylase-like immunoreactivity appeared clearly higher in the ventral root L5 on the lesion side compared to the unoperated side in neonatally crushed rats. Moreover, these axons seemed to be more numerous also in the ventral root L5 on the unoperated side compared to normal control rats. No lesion side/contralateral side or operated rat/control rat differences were seen in the ventral root L4. We propose that the ventral root L5 is invaded by putative sympathetic C-fibers after sciatic nerve crush lesions in newborn rats.

A new fibrin seal: functional evaluation of sensory regeneration following primary repair of peripheral nerves

A new fibrin seal has recently been evaluated in terms of axonal regeneration; however morphological examination of the fibre composition of regenerated nerves may not necessarily provide functionally relevant information. This study therefore aims to evaluate the functional regenerated sensation, following peripheral nerve transection treated with fibrin seal (Tisseel-Duo, Immuno; Austria). The sural nerve-innervated skin of the rat hindfoot served as the target organ. Previously published results from animals following transection and suture served as controls. Ten 3-month-old female Sprague-Dawley rats were used. The sciatic nerve was divided and rejoined with fibrin seal. The rats were allowed unrestricted movement directly after surgery and allowed to survive for 3 months. Our observations show that the functional results of regenerated polymodal nociceptors and low-threshold mechanoreceptors show no statistical difference when compared with microsuture. This strengthens the early positive morphological impression of this new product. Further prospective studies in man are anticipated.