Re-innervation of rat skeleton muscle in the presence of alpha-bungarotoxin.
(49/389)
1. The possible role of acetylcholine (ACh) receptors in controlling neuromuscular synapse formation was studied by blocking the receptors with alpha-bungarotoxin during re-innervationf the rat diaphragm. Anaesthetized and artificially respirated rats were perfused with toxin throughout the 3-day period when most re-innervation was shown to take place (from day 4 to day 6 after a nerve crush). 2. The toxin treatment blocked about 99.9% of both junctional and extrajunctional ACh receptors, thereby eliminating virtually all end-plate potentials. However, a low level of ACh sensitivity returned to the muscle after several hours of washing, and small end-plate potentials were then recorded from the majority of fibres on the side that previously had been denervated. The degree of re-innervation was nearly as great as that seen in control denervated muscles that had not been treated with toxin. 3. The presence of bungarotoxin during re-innervation did not significantly affect either the appearance of newly formed synapses in the light microscope or the amount of transmitter they released during nerve stimulation. 4. Double innervation, which was not seen in normal muscles, was found in about 10-15% of re-innervated fibres in both the untreated and toxin-treated preparations. This suggests that some of the synapses formed during re-innervation may have been made over what previously had been extrajunctional membrane. 5. It is therefore unlikely that the ACh receptor, or at least that part of the receptor to which bungarotoxin binds, plays a direct role in controlling the process of synapse formation in mammalian skeletal muscle... (+info)
Lipoprotein lipase is expressed in rat sciatic nerve and regulated in response to crush injury.
(50/389)
Male adult Sprague-Dawley rats were subjected to unilateral crush injury, and expression of LPL protein and mRNA were assessed as a function of time post-crush. LPL activity increased in the distal portion of the injured nerve by Day 4 post-crush, after which LPL activity gradually returned to normal levels. Conversely, quantification of LPL mRNA by reverse transcription-polymerase chain reaction demonstrated unchanged or decreased LPL mRNA in the distal nerve. Immunohistochemical analysis of LPL protein expression using an anti-rat LPL antibody revealed that LPL protein is present throughout the endoneurium of the sciatic nerve and increases in abundance following crush injury. The possibility that infiltrating macrophages are responsible for the increase in LPL protein levels in the crush injured nerve was addressed by immunohistochemical staining for ED-1, a differentiated macrophage marker protein. ED-1 was minimally present in the uninjured nerve and was detected at Day 4 post-crush, suggesting that the increase in LPL protein and activity that occurs following crush injury is at least partly derived from macrophages. These data suggest a role for LPL in the response of peripheral nerves to crush injury, possibly in order to facilitate reutilization of lipids from degenerating myelin. (+info)
Quantification of histological changes after calibrated crush of the intraorbital optic nerve in rats.
(51/389)
BACKGROUND: Traumatic optic nerve lesions (TONL) are probable but unpredictable consequence after severe midface or skull base trauma. Based on a previously described rat model, the authors developed a new model in order to simulate optic nerve crush during trauma on the optic canal. METHODS: To achieve a calibrated TONL, a microinjuring device was designed that made it possible to assess the correlation between a defined trauma and the neuronal degeneration in the rat retinal ganglion cell (RGC) layer. This device is based on a small dynamometer mounted onto a conventional micromanipulator. The supraorbital approach was chosen to expose the extracranial optic nerve. RESULTS: In this rat model (n=100, Wistar strain) the parameters of "force" and "time" could be precisely monitored during the experiment. The decrease in the mean number of retinal neurons (N) according to the pressure exerted (2-30 cN x mm(-2)) on the optic nerve was linear for 1, 6, and 15 minutes of injuring time; the decrease in N for varying injuring forces also appears to be nearly linear. CONCLUSION: The results show that this model provides a reliable method for studying quantitatively the anatomical effects of TONL on the RGC layer and the optic nerve itself, and may allow the design of treatment strategies following TONL. (+info)
Repellent guidance of regenerating optic axons by chondroitin sulfate glycosaminoglycans in zebrafish.
(52/389)
We analyzed the role of chondroitin sulfate (CS) glycosaminoglycans, putative inhibitors of axonal regeneration in mammals, in the regenerating visual pathway of adult zebrafish. In the adult, CS immunoreactivity was not detectable before or after an optic nerve crush in the optic nerve and tract but was constitutively present in developing and adult nonretinorecipient pretectal brain nuclei, where CSs may form a boundary preventing regenerating optic fibers from growing into these inappropriate locations. Enzymatic removal of CSs by chondroitinase ABC after optic nerve crush significantly increased the number of animals showing erroneous growth of optic axons into the nonretinorecipient magnocellular superficial/posterior pretectal nucleus (83% vs 42% in controls). In vitro, a substrate border of CSs, but not heparan sulfates, strongly repelled regenerating retinal axons from adult zebrafish. We conclude that CSs contribute to repellent axon guidance during regeneration of the optic projection in zebrafish. (+info)
Small proline-rich repeat protein 1A is expressed by axotomized neurons and promotes axonal outgrowth.
(53/389)
The ability of neurons to regenerate an axon after injury is determined by both the surrounding environment and factors intrinsic to the damaged neuron. We have used cDNA microarrays to survey those genes induced during successful sciatic nerve regeneration. The small proline-rich repeat protein 1A (SPRR1A) is not detectable in uninjured neurons but is induced by >60-fold after peripheral axonal damage. The protein is localized to injured neurons and axons. sprr1a is one of a group of epithelial differentiation genes, including s100c and p21/waf, that are coinduced in neurons by axotomy. Overexpressed SPRR1A colocalizes with F-actin in membrane ruffles and augments axonal outgrowth on a range of substrates. In axotomized sensory neurons, reduction of SPRR1A function restricts axonal outgrowth. Neuronal SPRR1A may be a significant contributor to successful nerve regeneration. (+info)
Selective and non-selective reinnervation of fast-twitch and slow-twitch rat skeletal muscle.
(54/389)
1. The problem of selectivity during reinnervation of skeletal muscle fibres was investigated in the rat using the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus muscles and their nerves. 2. After an operation on these nerves permitting them to compete for reinnervation of one or the other muscle (hereafter called Y-union), virtually the total isometric tetanic tension of EDL muscle could be elicited by stimulating the EDL nerve, while stimulating the soleus nerve yielded little or no tension. In the case of the soleus muscle, stimulation of either nerve elicited about half of the total isometric tetanic tension. 3. During the course of reinnervation of these muscles in non-competitive situations, the time course of increase in the ratio of tension elicited by nerve stimulation to that by direct stimulation was slower in the case of soleus nerve reinnervating EDL muscle, compared with cross-reinnervation in the reverse direction or reinnervation of each muscle by its own nerve. 4. Crushing the common peroneal nerve 12 days after a Y-union in an attempt to retard the EDL nerve did not favour reinnervation of the EDL by soleus nerve, but crushing the nerve again or just once at 1 month after the original operation produced substantial partial reinnervation of the EDL by the soleus nerve. 5. It is concluded that soleus nerve fibres form functioning neuromuscular synapses on EDL muscle fibres only with difficulty. The pattern of reinnervation reveals characteristic differences between fast-twitch and slow-twitch muscles on the one hand and between their respective nerves on the other. (+info)
Spontaneous retinal activity is tonic and does not drive tectal activity during activity-dependent refinement in regeneration.
(55/389)
During development, waves of activity periodically spread across retina to produce correlated activity that is thought to drive activity-dependent ordering in optic fibers. We asked whether similar waves of activity are produced in the retina of adult goldfish during activity-dependent refinement by regenerating optic fibers. Dual-electrode recordings of spontaneous activity were made at different distances across retina but revealed no evidence of retinal waves in normal retina or during regeneration. Retinal activity was tonic and lacked the episodic bursting associated with waves. Cross-correlation analysis showed that the correlated activity that was normally restricted to near neighbors (typically seen across 100-200 microm and absent at >500 microm) was not altered during regeneration. The only change associated with regeneration was a twofold reduction in ganglion cell firing rates. Because spontaneous retinal activity is known to be sufficient to generate refinement during regeneration in goldfish, we examined its effect on tectal activity. In normal fish, acutely eliminating retinal activity with TTX rapidly reduced tectal unit activity by >90%. Surprisingly, during refinement at 4-6 weeks, eliminating retinal activity had no detectable effect on tectal activity. Similar results were obtained in recordings from torus longitudinalis. After refinement at 3 months, tectal activity was again highly dependent on ongoing retinal activity. We conclude that spontaneous retinal activity drives tectal cells in normal fish and after regeneration but not during activity-dependent refinement. The implications of these results for the role of presynaptic activity in refinement are considered. (+info)
Changes in crossed spinal reflexes after peripheral nerve injury and repair.
(56/389)
We investigated the changes induced in crossed extensor reflex responses after peripheral nerve injury and repair in the rat. Adults rats were submitted to non repaired sciatic nerve crush (CRH, n = 9), section repaired by either aligned epineurial suture (CS, n = 11) or silicone tube (SIL4, n = 13), and 8 mm resection repaired by tubulization (SIL8, n = 12). To assess reinnervation, the sciatic nerve was stimulated proximal to the injury site, and the evoked compound muscle action potential (M and H waves) from tibialis anterior and plantar muscles and nerve action potential (CNAP) from the tibial nerve and the 4th digital nerve were recorded at monthly intervals for 3 mo postoperation. Nociceptive reinnervation to the hindpaw was also assessed by plantar algesimetry. Crossed extensor reflexes were evoked by stimulation of the tibial nerve at the ankle and recorded from the contralateral tibialis anterior muscle. Reinnervation of the hindpaw increased progressively with time during the 3 mo after lesion. The degree of muscle and sensory target reinnervation was dependent on the severity of the injury and the nerve gap created. The crossed extensor reflex consisted of three bursts of activity (C1, C2, and C3) of gradually longer latency, lower amplitude, and higher threshold in control rats. During follow-up after sciatic nerve injury, all animals in the operated groups showed recovery of components C1 and C2 and of the reflex H wave, whereas component C3 was detected in a significantly lower proportion of animals in groups with tube repair. The maximal amplitude of components C1 and C2 recovered to values higher than preoperative values, reaching final levels between 150 and 245% at the end of the follow-up in groups CRH, CS, and SIL4. When reflex amplitude was normalized by the CNAP amplitude of the regenerated tibial nerve, components C1 (300-400%) and C2 (150-350%) showed highly increased responses, while C3 was similar to baseline levels. In conclusion, reflexes mediated by myelinated sensory afferents showed, after nerve injuries, a higher degree of facilitation than those mediated by unmyelinated fibers. These changes tended to decline toward baseline values with progressive reinnervation but still remained significant 3 mo after injury. (+info)