Increased expression of Gem after rat sciatic nerve injury

Gem belongs to the Rad/Gem/Kir subfamily of Ras-related GTPases, whose expression is induced in several cell types upon activation by extracellular stimuli. Two functions of Gem have been demonstrated, including regulation of voltage-gated calcium channel activity and inhibition of Rho kinase-mediated cytoskeletal reorganization, such as stress fiber formation and neurite retraction. Because of the essential relationship between actin reorganization and peripheral nerve regeneration, we investigated the spatiotemporal expression of Gem in a rat sciatic nerve crush (SNC) model. After never injury, we observed that Gem had a significant up-regulation from 1 day, peaked at day 5 and then gradually decreased to the normal level. At its peak expression, Gem expressed mainly in Schwann cells (SCs) and macrophages of the distal sciatic nerve segment, but had few colocalization in axons. In addition, the peak expression of Gem was in parallel with PCNA, and numerous SCs expressing Gem were PCNA positive. Thus, all of our findings suggested that Gem may be involved in the pathophysiology of sciatic nerve after SNC.     

Acceleration of axonal outgrowth in rat sciatic nerve at one week after axotomy

Following injury of sciatic motor axons in the rat, the rate of axonal outgrowth is faster if there has been a prior “conditioning” axotomy. The acceleration of outgrowth is due to an acceleration of SCb, the rate [slow (SC)] component of axonal transport that carries cytomatrix proteins; this occurs throughout the axon by 7 days after the conditioning axotomy (Jacob and McQuarrie, 1991a, J. Neurobiol. 22:570–583). To further characterize the conditioning lesion effect (CLE), it is important to know (1) the minimum effective conditioning interval (time between conditioning and testing lesions), (2) whether the cell body reaction is required, and (3) whether outgrowth accelerates after a single axotomy. Outgrowth distances were measured by radiolabeling all newly synthesized neuronal proteins and detecting those carried to growth cones by fast axonal transport. When the conditioning and testing lesions were made simultaneously (0 day conditioning interval), there was no CLE. With a conditioning interval of 3 days, there was a shortening of the initial delay (before the onset of outgrowth) without a change in outgrowth rate. With conditioning intervals of 7, 14, and 21 days, the rates of outgrowth were increased by 8%, 22%, and 11%, respectively. To determine whether the cell body reaction to axotomy is necessary for the CLE, a nonaxotomizing stimulus to axonal growth (partial denervation) was used in place of a conditioning axotomy. This had no effect on the rate of outgrowth from a testing lesion made 14 days later. Finally, we examined the possibility that outgrowth accelerates after a single lesion. Outgrowth was faster at 6–9 days after axotomy than at 3–6 days (p < 0.001), and accelerated further at 9–12 days (p < 0.001). We conclude that (1) the shortest effective conditioning interval is 3 days; (2) the cell body reaction is necessary for the CLE; (3) axonal outgrowth from a single axotomy accelerates in concert with the anabolic phase of the cell body reaction. The SCb motor is, in turn, upregulated by this reaction. This suggests that the SCb motor responds to a fast-transported signal that is a product of the cell body reaction. © 1993 John Wiley & Sons, Inc.     

Evoked activity of spinal neurons in the early period after sciatic nerve division

The character of dorsal horn motoneurons and interneurons evoked by stimulation of the dorsal root, and activity of Renshaw cells in response to stimulation of the ventral root were studied in albino rats in the lower lumbar segments of the spinal cord 5 days after sciatic nerve division. A significant increase in the mean amplitude of excitatory postsynaptic potentials of motoneurons was observed on the side of division of the nerve. No significant change in membrane potential and in the threshold of appearance of the action potential of these motoneurons took place. The mean number of action potentials and the duration of discharge of the Renshaw cells and dorsal horn interneurons likewise were not significantly changed.Dnepropetrovsk Medical Institute, Ukrainian Ministry of Health. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 306–314, May–June, 1992.     

Changes in contralateral protein metabolism following unilateral sciatic nerve section

Changes in nerve biochemistry, anatomy, and function following injuries to the contralateral nerve have been repeatedly reported, though their significance is unknown. The most likely mechanisms for their development are either substances carried by axoplasmic flow or electrically transmitted signals. This study analyzes which mechanism underlies the development of a contralateral change in protein metabolism. The incorporation of labelled amino acids (AA) into proteins of both sciatic nerves was assessed by liquid scintillation after an unilateral section. AA were offered locally for 30 min to the distal stump of the sectioned nerves and at homologous levels of the intact contralateral nerves. At various times, from 1 to 24 h, both sciatic nerves were removed and the proteins extracted with trichloroacetic acid (TCA). An increase in incorporation was found in both nerves 14–24 h after section. No difference existed between sectioned and intact nerves, which is consistent with the contralateral effect. Lidocaine, but not colchicine, when applied previously to the nerves midway between the sectioning site and the spinal cord, inhibited the contralateral increase in AA incorporation. It is concluded that electrical signals, crossing through the spinal cord, are responsible for the development of the contralateral effect. Both the nature of the proteins and the significance of the contralateral effect are matters for speculation.     

Altered neuronatin expression in the rat dorsal root ganglion after sciatic nerve transection

Background  

Several molecular changes occur following axotomy, such as gene up-regulation and down-regulation. In our previous study using Affymetrix arrays, it was found that after the axotomy of sciatic nerve, there were many novel genes with significant expression changes. Among them, neuronatin (Nnat) was the one which expression was significantly up-regulated. Nnat was identified as a gene selectively expressed in neonatal brains and markedly reduced in adult brains. The present study investigated whether the expression of Nnat correlates with symptoms of neuropathic pain in adult rats with transected sciatic nerve.     

Effects of dexamethasone on the electrical activity of spinal neurons in rats with the transected sciatic nerve

Effects of the glucocorticoid hormone dexamethasone on the reflex discharges in the lumbar ventral roots and background activity (BA) of single neurons in the dorsal laminae of spinal grey were studied in rats after transection of the sciatic nerve. Administration of the hormone during early post-traumatic period (up to seven days) evoked no significant changes in the amplitude of increased (due to the postdenervation hyperreflexia) monosynaptic discharges on the side of nerve transection. At the same time, the monosynaptic discharges grew by 150–170% on the intact side. During later post-transection periods (up to 35 days), when ventral root reflex discharges were suppressed, dexamethasone facilitated reflex transmission via the polysynaptic segmental pathways on both the operated and intact sides. Nonetheless, the monosynaptic component of reflex discharges on the injured side did not recover. Dexamethasone treatment resulted in an increase in the number of BA-generating interneurons within the superficial dorsal horn laminae, and in a decrease in the proportion of units generating bursting activity (possibly of pathological nature).Neirofiziologiya/Neurophysiology, Vol. 27, No. 1, pp. 26–31, January–February, 1995.     

Tonic sympathetic activity in the rabbit sciatic nerve

Tonic activity of sympathetic nerve fibers of the tibial and peroneal nerves was investigated in rabbits anesthetized with urethane by the multichannel coherent recording technique. Activity of stochastic character was shown to predominate in the tonic activity of these fibers. A component of activity with the frequency of the heart beat also is frequently observed, but the power of this component is never more than half the total power of activity. Activity with a frequency of 10 Hz, observed by other workers, and also modulation of tonic activity in the rhythm of respiration were not recorded in these experiments. Slow changes in the power of activity from zero to a level several times above average were observed when the blood pressure was stable.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 351–358, May–June, 1985.     

Changes in contralateral protein metabolism following unilateral sciatic nerve section.

Changes in nerve biochemistry, anatomy, and function following injuries to the contralateral nerve have been repeatedly reported, though their significance is unknown. The most likely mechanisms for their development are either substances carried by axoplasmic flow or electrically transmitted signals. This study analyzes which mechanism underlies the development of a contralateral change in protein metabolism. The incorporation of labelled amino acids (AA) into proteins of both sciatic nerves was assessed by liquid scintillation after an unilateral section. AA were offered locally for 30 min to the distal stump of the sectioned nerves and at homologous levels of the intact contralateral nerves. At various times, from 1 to 24 h, both sciatic nerves were removed and the proteins extracted with trichloroacetic acid (TCA). An increase in incorporation was found in both nerves 14-24 h after section. No difference existed between sectioned and intact nerves, which is consistent with the contralateral effect. Lidocaine, but not colchicine, when applied previously to the nerves midway between the sectioning site and the spinal cord, inhibited the contralateral increase in AA incorporation. It is concluded that electrical signals, crossing through the spinal cord, are responsible for the development of the contralateral effect. Both the nature of the proteins and the significance of the contralateral effect are matters for speculation.     

Effect of electromagnetic radiation of millimeter range on restoration of motor activity after impairment of the sciatic nerve in the rat

The effect of low-intensity (10–12 mW/cm²) amplitude-modulated electromagnetic radiation (EMR) with a wavelength of 8.1 mm on restoration of motor activity of hindlimb after the sciatic nerve had been crushed was studied in rats (only the injured area was radiated). The recovery was found to be significantly accelerated by EMR: after a seven-week-long treatment by EMR, the mean amplitude of the extensor force developed by the hindlimb of the EMR-treated animals reached 62.3% of its initial value (recorded before the nerve had been crushed), while in the control group of animals it was equal to near 40%.Neirofiziologiya/Neurophysiology, Vol. 28, No. 1, pp. 3–6, January–February, 1996.