Restoring mitochondrial cardiolipin homeostasis reduces cell death and promotes recovery after spinal cord injury

Alterations in phospholipids have long been associated with spinal cord injury (SCI). However, their specific roles and signaling cascades in mediating cell death and tissue repair remain unclear. Here we investigated whether alterations of cardiolipin (CL), a family of mitochondrion-specific phospholipids, play a crucial role in mitochondrial dysfunction and neuronal death following SCI. Lipidomic analysis was used to determine the profile of CL alteration in the adult rat spinal cord following a moderate contusive SCI at the 10th thoracic (T10) level. Cellular, molecular, and genetic assessments were performed to determine whether CL alterations mediate mitochondrial dysfunction and neuronal death after SCI, and, if so, whether reversing CL alteration leads to neuroprotection after SCI. Using lipidomic analysis, we uncovered CL alterations at an early stage of SCI. Over 50 distinct CL species were identified, of which 50% showed significantly decreased abundance after SCI. The decreased CL species contained mainly polyunsaturated fatty acids that are highly susceptible to peroxidation. In parallel, 4-HNE, a lipid peroxidation marker, significantly increased after SCI. We found that mitochondrial oxidative stress not only induced CL oxidation, but also resulted in CL loss by activating cPLA₂ to hydrolyze CL. CL alterations induced mitochondrial dysfunction and neuronal death. Remarkably, pharmacologic inhibition of CL alterations with XJB-5-131, a novel mitochondria-targeted electron and reactive oxygen species scavenger, reduced cell death, tissue damage and ameliorated motor deficits after SCI in adult rats. These findings suggest that CL alteration could be a novel mechanism that mediates injury-induced neuronal death, and a potential therapeutic target for ameliorating secondary SCI.

Etomidate affects the anti-oxidant pathway to protect retinal ganglion cells after optic nerve transection

Our previous studies revealed that etomidate, a non-barbiturate intravenous anesthetic agent, has protective effects on retinal ganglion cells within 7 days after optic nerve transection. Whether this process is related to anti-oxidative stress is not clear. To reveal its mechanism, we established the optic nerve transection injury model by transecting 1 mm behind the left eyeball of adult male Sprague-Dawley rats. The rats received an intraperitoneal injection of etomidate (4 mg/kg) once per day for 7 days. The results showed that etomidate significantly enhanced the number of retinal ganglion cells retrogradely labeled with Fluorogold at 7 days after optic nerve transection. Etomidate also significantly reduced the levels of nitric oxide and malonaldehyde in the retina and increased the level of glutathione at 12 hours after optic nerve transection. Thus, etomidate can protect retinal ganglion cells after optic nerve transection in adult rats by activating an anti-oxidative stress response. The study was approved by the Animal Ethics Committee at Air Force Medical University, China (approval No. 20180305) on March 5, 2018.

Branched-Chain Amino Acids Enhance Retinal Ganglion Cell Survival and Axon Regeneration after Optic Nerve Transection in Rats

PURPOSE

This study's aim was to investigate the beneficial effects of branched-chain amino acids (BCAAs) on the neuronal survival and axon regeneration of retinal ganglion cells (RGCs) after optic nerve (ON) transection.

METHOD

The experimental rats received daily BCAA injections through the caudal vein after left intra-orbital ON transection. Neuroprotection was evaluated by counting Fluorogold-labeled RGCs. The role of mammalian target of rapamycin (mTOR) pathway activation in promoting RGC survival was studied after rapamycin administration. Moreover, a peripheral nerve (PN) graft was transplanted onto the transected ON to study the effects of BCAAs on axon regeneration of injured RGCs.

RESULTS

Our results showed that BCAAs alleviated the death of RGCs 7 and 14 days after ON transection, accompanied by an activation of mTOR pathway in RGCs. Blocking mTOR pathway with rapamycin eliminated such neuroprotective effects of BCAAs. Moreover, BCAAs also promoted axon regeneration of injured RGCs into a PN graft.

CONCLUSION

Our results suggest a neuroprotection of BCAAs through the activation of mTOR pathway. BCAAs also have a beneficial effect on axon regeneration of injured RGCs. Therefore, BCAAs could be considered for the clinical treatment of ON injury.

Clinical Cell Therapy Guidelines for Neurorestoration (IANR/CANR 2017)

Cell therapy has been shown to be a key clinical therapeutic option for central nervous system diseases or damage. Standardization of clinical cell therapy procedures is an important task for professional associations devoted to cell therapy. The Chinese Branch of the International Association of Neurorestoratology (IANR) completed the first set of guidelines governing the clinical application of neurorestoration in 2011. The IANR and the Chinese Association of Neurorestoratology (CANR) collaborated to propose the current version "Clinical Cell Therapy Guidelines for Neurorestoration (IANR/CANR 2017)". The IANR council board members and CANR committee members approved this proposal on September 1, 2016, and recommend it to clinical practitioners of cellular therapy. These guidelines include items of cell type nomenclature, cell quality control, minimal suggested cell doses, patient-informed consent, indications for undergoing cell therapy, contraindications for undergoing cell therapy, documentation of procedure and therapy, safety evaluation, efficacy evaluation, policy of repeated treatments, do not charge patients for unproven therapies, basic principles of cell therapy, and publishing responsibility.

FTY720 enhances osteogenic differentiation of bone marrow mesenchymal stem cells in ovariectomized rats

Sphingosine-1-phosphate and its structural analog FTY720 (fingolimod) are important in the inhibition of osteoclast differentiation and bone resorption, however, it remains unknown whether they enhance osteogenic differentiation of the bone marrow mesenchymal stem cells (BM‑MSCs). The present study investigated the effect of FTY720 on the osteogenic differentiation of BM‑MSCs from the femurs of the ovariectomized (OVX) rats. Three different concentrations (1, 10 and 100 nM) of FTY720 were demonstrated to markedly upregulate mRNA expression levels of Runt‑related transcription factor 2 (Runx2) and Sp7 transcription factor (Sp7) at 2 weeks, and alkaline phosphatase (ALP) at 3 weeks. The osteocalcin (OCN) expression was similar at weeks 2 and 3. The protein expression levels of Runx2, Sp7, OCN and ALP induced by three different concentrations of FTY720 were higher than those in the control groups at 3 weeks in the OVX and sham groups. The findings of the current study suggested a beneficial effect of FTY720 on bone formation in OVX rats, and provided a potential therapeutic method of FTY720 to prevent alveolar bone resorption in patients with post‑menopausal osteoporosis.

Systemic injection of low-dose lipopolysaccharide fails to break down the blood-brain barrier or activate the TLR4-MyD88 pathway in neonatal rat brain

We aimed to investigate whether peripheral low-dose lipopolysaccharide (LPS) induces the breakdown of the blood–brain barrier (BBB) and/or the activation of toll-like receptor 4 (TLR4) in the neonatal rat brain. Neonatal rats received intraperitoneal injections of low-dose LPS (0.3 mg/kg∙bw), and the BBB compromise was detected by Evans Blue extravasation and electron microscopy. Meanwhile, TLR4, adaptin myeloid differentiation factor 88 (MyD88), nuclear transcription factor kappa-B (NF-κB) p50 and tumor necrosis factor alpha (TNFα) in the neonatal rat brain were determined by quantitative real-time polymerase chain reaction (PCR) and Western Blot. Immunohistochemistry was used to determine the distribution and activation of microglia in the brain after LPS administration. It was demonstrated that Evans Blue extravasation was not observed in the brain parenchyma, and that tight junctions of cerebral endothelial cells remained intact after systemic injections of LPS in neonatal rats. Although intracerebroventricular injections of LPS activated microglia and up-regulated the expression of TLR4, MyD88, NF-κB p50 and TNFα in the neonatal rat brain, systemic LPS did not induce these responses. These findings indicate that while the neonatal rat brain responds to the direct intra-cerebral administration of LPS through robust TLR4 activation, systemic low-dose LPS does not induce the innate immune reaction or compromise the BBB in neonatal rats.

Different neuroprotection and therapeutic time windows by two specific diazepam regimens on retinal ganglion cells after optic nerve transection in adult rats

PURPOSE

To compare neuroprotection and therapeutic time windows of two diazepam regimens on retinal ganglion cells (RGCs) after rat optic nerve transection (ONT).

METHODS

Adult rats received initial intraperitoneal diazepam injections 30 minutes before left ONT, followed by daily diazepam (regimen-A) or every 8 hours for 3 days (regimen-B) until they were killed at day 7 or 14. Initial diazepam in regimen-A and regimen-B was delayed to 3, 6, 7, 9, 10, 12 and 6, 7, 8, 9, 10, 12 hours after ONT and these animals survived for 7 days. The effect of daily combinational uses of diazepam and bicuculline was assayed at 7 days.

RESULTS

Regimen-A induced higher RGC densities than those in control and regimen-B groups at day 7, but lower density than regimen-B did at day 14. When initial diazepam was delayed beyond 6 or 8 hours after ONT with regimen-A and regimen-B, the promoting effects of diazepam on RGC densities disappeared. Bicuculline completely inhibited the protection of diazepam.

CONCLUSIONS

Prolonged neuroprotection on RGCs at day 14 and extended therapeutic time window for 8 hours can be achieved by regimen-B, while regimen-A induces a stronger neuroprotection at day 7. Diazepam neuroprotection is mediated through GABAA receptor.

Glycomimetic improves recovery after femoral injury in a non-human primate

In adult mammals, restoration of function after peripheral nerve injury is often poor and effective therapies are not available. Previously we have shown in mice that a peptide which functionally mimics the human natural killer cell (HNK)-1 trisaccharide epitope significantly improves the outcome of femoral nerve injury. Here we evaluated the translational potential of this treatment using primates. We applied a linear HNK-1 mimetic or a functionally inactive control peptide in silicone cuffs used to reconstruct the cut femoral nerves of adult cynomolgus monkeys (Macaca fascicularis). Functional recovery was evaluated using video-based gait analysis over a 160-day observation period. The final outcome was further assessed using force measurements, H-reflex recordings, nerve histology, and ELISA to assess immunoreactivity to HNK-1 in the treated monkeys. Gait deficits were significantly reduced in HNK-1 mimetic-treated compared with control peptide-treated animals between 60 and 160 days after injury. Better outcome at 160 days after surgery in treated versus control animals was also confirmed by improved quadriceps muscle force, enhanced H-reflex amplitude, decreased H-reflex latency, and larger diameters of regenerated axons. No adverse reactions to the mimetic, in particular immune responses resulting in antibodies against the HNK-1 mimetic or immune cell infiltration into the damaged nerve, were observed. These results indicate the potential of the HNK-1 mimetic as an efficient, feasible, and safe adjunct treatment for nerve injuries requiring surgical repair in clinical settings.

Death of Axotomized Retinal Ganglion Cells Delayed after Intraoptic Nerve Transplantation of Olfactory Ensheathing Cells in Adult Rats

Intraorbital transection of the optic nerve (ON) always induces ultimate apoptosis of retinal ganglion cells (RGCs) and consequently irreversible defects of vision function. It was demonstrated that transplanted olfactory ensheathing cells (OECs) in partially injured spinal cord have a distant in vivo neuroprotective effect on descending cortical and brain stem neurons. However, this study gave no answers to the question whether OECs can protect the central sensitive neurons with a closer axonal injury because different neurons respond variously to similar axonal injury and the distance between the neuronal soma and axonal injury site has a definite effect on the severity of neuronal response and apoptosis. In the present study, we investigated the effect of transplanted OECs on RGCs after intraorbital ON transection in adult rats. Green fluorescent protein (GFP)-OECs were injected into the ocular stumps of transected ON and a significantly higher number of surviving RGCs was found together with a consistent marked increase in the mRNA and protein levels of BDNF in the ON stump and retina in the OEC-treated group at 7 days, but not 2 and 14 days, time point when compared to the control group. Our findings suggest that OEC transplantation induces the expression of BDNF in the ocular ON stump and retina and delays the death of axotomized RGCs at a certain survival period.

Evidence for heterogeneity of astrocyte de-differentiation in vitro: astrocytes transform into intermediate precursor cells following induction of ACM from scratch-insulted astrocytes

Our previous study definitely demonstrated that the mature astrocytes could undergo a de-differentiation process and further transform into pluripotential neural stem cells (NSCs), which might well arise from the effect of diffusible factors released from scratch-insulted astrocytes. However, these neurospheres passaged from one neurosphere-derived from de-differentiated astrocytes possessed a completely distinct characteristic in the differentiation behavior, namely heterogeneity of differentiation. The heterogeneity in cell differentiation has become a crucial but elusive issue. In this study, we show that purified astrocytes could de-differentiate into intermediate precursor cells (IPCs) with addition of scratch-insulted astrocyte-conditioned medium (ACM) to the culture, which can express NG2 and A2B5, the IPCs markers. Apart from the number of NG2(+) and A2B5(+) cells, the percentage of proliferative cells as labeled with BrdU progressively increased with prolonged culture period ranging from 1 to 10 days. Meanwhile, the protein level of A2B5 in cells also increased significantly. These results revealed that not all astrocytes could de-differentiate fully into NSCs directly when induced by ACM, rather they generated intermediate or more restricted precursor cells that might undergo progressive de-differentiation to generate NSCs.

Nogo-66 receptor at the gap junctions between pituicytes of the rat

Nogo-66 receptor was first identified in neurons. Recently, it was demonstrated in glial cells as well. Our previous study on the expression of Nogo-66 receptor in the cerebellum of the rat surprisingly found its location at the glial gap junctions. Here, we present our study on Nogo-66 receptor in the rat posterior pituitary, which is densely packed with pituicytes, a special type of astrocyte, and is known to be rich in gap junctions. We were able to demonstrate with immunohistochemistry and immuno-electron microscopy abundant Nogo-66 receptor immunoreactive gap junctions between pituicytes. This study, together with our prior one, strongly suggests that the Nogo-66 receptor may play a role in regulating the function of the gap junctions.

Nano neuro knitting: peptide nanofiber scaffold for brain repair and axon regeneration with functional return of vision

Nanotechnology is often associated with materials fabrication, microelectronics, and microfluidics. Until now, the use of nanotechnology and molecular self assembly in biomedicine to repair injured brain structures has not been explored. To achieve axonal regeneration after injury in the CNS, several formidable barriers must be overcome, such as scar tissue formation after tissue injury, gaps in nervous tissue formed during phagocytosis of dying cells after injury, and the failure of many adult neurons to initiate axonal extension. Using the mammalian visual system as a model, we report that a designed self-assembling peptide nanofiber scaffold creates a permissive environment for axons not only to regenerate through the site of an acute injury but also to knit the brain tissue together. In experiments using a severed optic tract in the hamster, we show that regenerated axons reconnect to target tissues with sufficient density to promote functional return of vision, as evidenced by visually elicited orienting behavior. The peptide nanofiber scaffold not only represents a previously undiscovered nanobiomedical technology for tissue repair and restoration but also raises the possibility of effective treatment of CNS and other tissue or organ trauma.

CNTF and BDNF have similar effects on retinal ganglion cell survival but differential effects on nitric oxide synthase expression soon after optic nerve injury

PURPOSE

To investigate the effect of ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) on retinal ganglion cell (RGC) survival and nitric oxide synthase (NOS) expression in the retina during the early phase of optic nerve (ON) injury, and to examine whether intraperitoneal application of the NOS scavenger nitro-l-arginine (l-NA) could protect the injured RGCs.

METHODS

RGCs were retrogradely labeled with granular blue 3 days before the ON was intraorbitally transected. RGC survival was examined 1 week after ON transection and intraocular injection of CNTF and/or BDNF, or 1 to 2 weeks after daily intraperitoneal injection of the NOS inhibitor l-NA. NOS expression was examined by NADPH-diaphorase histochemistry and neuronal NOS (nNOS) immunohistochemistry, and nNOS-positive cells were identified by various staining approaches.

RESULTS

Both CNTF and BDNF significantly increased RGC survival 1 week after ON injury. In the ganglion cell layer (GCL), CNTF did not increase the number of NADPH-diaphorase positive ((+)) cells but appeared to reduce the intensity of NADPH-diaphorase staining, whereas BDNF increased the number of NADPH-diaphorase(+) cells and also appeared to enhance the intensity of NADPH-diaphorase staining. In the GCL, amacrine cells but not RGCs were nNOS(+). Some macrophages were also nNOS(+). In contrast, no amacrine cells were nNOS(+) in the inner nuclear layer. Daily intraperitoneal injection of l-NA at appropriate concentrations promoted RGC survival for 1 or 2 weeks after ON injury.

CONCLUSIONS

Both CNTF and BDNF protected RGCs after ON injury. CNTF and BDNF acted differently on NOS expression in the GCL. Intraperitoneal injections of l-NA at appropriate dosages enhance RGC survival.

Neuroprotective Effect of Inosine on Axotomized Retinal Ganglion Cells in Adult Rats

PURPOSE

To explore the potential survival-promoting effect of inosine on axotomized retinal ganglion cells (RGCs) of adult rats in vivo.

METHODS

The left optic nerves (ON) in the subject rats were transected at 1.5 mm from the optic disc. Repeated intraperitoneal injections or single intraocular injection of inosine were administered. The RGCs were retrogradely labeled with a gold fluorescent dye and the density of surviving RGCs in number per square millimeter of retina was calculated in wholemounted retinas. The functional integrity of the blood-retinal barrier (BRB) after ON transection was evaluated with an intravenous injection of Evans blue.

RESULTS

In control animals, the mean density of surviving RGCs (number per square millimeter) of the whole retina was 2007 +/- 68 at 2 days (taken as the normal value), 927 +/- 156 at 7 days, and 384 +/- 33 at 14 days after surgery. Repeated intraperitoneal injections (75 mg/kg for each injection) of inosine significantly enhanced RGC survival at 14 days after ON transection (500 +/- 38), whereas no significant difference in the densities was detected at 7 days (974 +/- 101), even when the dosage of inosine was doubled (1039 +/- 61). At this time point, however, a single intraocular injection of inosine significantly increased the density of surviving RGCs (1184 +/- 156). Moreover, more RGCs around the optic disc were rescued when inosine, administered either intraperitoneally or intraocularly, showed a beneficial effect on RGC survival. No breakdown of the BRB after ON transection was detected with the method used in the study.

CONCLUSIONS

These findings demonstrate that inosine could protect axotomized RGCs in vivo after ON transection.

Phosphorylation of extracellular signal-regulated kinases 1/2 is predominantly enhanced in the microglia of the rat spinal cord following dorsal root transection

The present study was initiated to investigate the role of extracellular signal-regulated kinases (ERK) 1/2 signaling pathway in the early response of spinal cord and associated dorsal root ganglion (DRG) to rhizotomy by using Western blotting and immunohistochemical techniques in a rat model of L3 and L4 dorsal root transection. The results showed that there were a considerable amount of total and phosphorylated ERK 1/2 protein in both spinal cord and DRG in normal animals killed under pentobarbital anesthesia. The total ERK 1/2 distributed in both glia and neurons, while phosphorylated ERK 1/2 dominantly existed in the latter in the gray matter of spinal cord, as demonstrated with double immunofluorescent staining. Twenty-four and forty-eight hours after axotomy, the phosphorylation level of ERK 1/2 in the operation side of dorsal spinal cord was much higher than that in the contralateral side, while the total ERK 1/2 level seemed unchanged. The increased expression of Fos protein was also seen in the dorsal spinal cord at lesion side twelve and twenty-four hours after axotomy. Double fluorescent staining proved that the phosphorylated ERK 1/2 positive cells in the ipsilateral dorsal spinal cord after axotomy predominantly were microglia and small portion was oligodendrocytes, whereas the Fos expression was mainly in neurons. In normal DRG, most neurons, especially the medium and small-sized ones, and the satellite cells contained total ERK 1/2-like immunoreactivity, whereas only a small portion of neurons and satellite cells contained phosphorylated ERK 1/2. After unilateral dorsal rhizotomy, there were no detectable changes for the phosphorylation of ERK 1/2 in either neurons or satellite cells in DRG.Collectively, the present results suggest that both ERK and Fos signal pathways involve the cellular activation in the spinal cord following dorsal rhizotomy, with ERK mainly in microglia and Fos in neurons. The increase of phosphorylation of ERK 1/2 in microglia of spinal cord after rhizotomy implicates that ERK signaling pathway involves intracellular activity of microglia responding to the experimental injury.

Significance of fixation of the vertebral column for spinal cord injury experiments

STUDY DESIGN

Thoracic spinal cord transections were performed in adult rats. The animals were divided into two groups, with or without internal fixation of the involved vertebral column. Histologic and immunohistochemical studies were performed to compare the effect of internal fixation of the vertebral column.

OBJECTIVES

To find out the aspects and extent of beneficial effects of vertebral column fixation for spinal cord repair.

SUMMARY OF BACKGROUND DATA

Vertebral column fixation is a routine procedure in clinical spinal cord surgery. Paradoxically, most, if not all, animal spinal cord experiments seem to have ignored the importance of vertebral column fixation. During trunk movements, the vertebral column flexes to different directions, accompanied by bending of the spinal cord. Following spinal cord lesions, with frequent bending of the cord there will be repeated bleeding, inflammation, and other pathologic processes at the lesion site. Thus, the healing process will be hampered. The severity of the damages that will be brought about by bending of the cord is, to a certain degree, unpredictable. There will be rather big individual variations in injury and repair among the same type of experiments, rendering quantification and conclusion difficult.

METHODS

Adult Sprague-Dawley rats were used. The thoracic spinal cord was transected. Strong stainless steel wires were used for internal fixation of the vertebral column. The histology of the horizontal sections of the spinal cord segment, which included the lesion site, was examined at the 14th postoperative day. The volumes of the secondary degeneration and meningeal scar, the gap between the borders of the proximal and distal stumps of the transected spinal cord, the thickness of the meningeal scar, the astrocytic reaction, and the abundance of regenerating nerve fibers at the lesion site were compared between the vertebral column fixed and nonfixed groups. Whenever possible, the results were evaluated quantitatively.

RESULTS

In all these aspects, the internally fixed group was consistently far better than the unfixed group. The quantitative analyses were as follows (fixed/unfixed): 1)volume of secondary degeneration: 1.07 +/- 0.20/1.81 +/- 0.43 mm3 (P < 0.01); 2) volume of meningeal scar: 2.38 +/- 0.55/4.34 +/- 1.40 mm3 (P < 0.05); 3) distance between cord stumps: 1.38 +/- 0.34/2.35 +/- 0.79 mm (P < 0.05); 4) the mean thinnest dimension of the meningeal scar: 0.90 +/- 0.43/1.98 +/- 0.85 mm (P < 0.05).

CONCLUSION

Vertebral column fixation is a crucial procedure for spinal cord animal experiments.

Spontaneous recovery of locomotion induced by remaining fibers after spinal cord transection in adult rats

PURPOSE

A major issue in analysis of experimental results after spinal cord injury is spontaneous functional recovery induced by remaining nerve fibers. The authors investigated the relationship between the degree of locomotor recovery and the percentage and location of the fibers that spared spinal cord transection.

METHODS

The spinal cords of 12 adult rats were transected at T9 with a razor blade, which often resulted in sparing of nerve fibers in the ventral spinal cord. The incompletely-transected animals were used to study the degree of spontaneous recovery of hindlimb locomotion, evaluated with the BBB rating scale, in correlation to the extent and location of the remaining fibers.

RESULTS

Incomplete transection was found in the ventral spinal cord in 42% of the animals. The degree of locomotor recovery was highly correlated with the percentage of the remaining fibers in the ventral and ventrolateral funiculi. In one of the rats, 4.82% of remaining fibers in unilateral ventrolateral funiculus were able to sustain a certain recovery of locomotion.

CONCLUSIONS

Less than 5% of remaining ventrolateral white matter is sufficient for an unequivocal motor recovery after incomplete spinal cord injury. Therefore, for studies with spinal cord transection, the completeness of sectioning should be carefully checked before any conclusion can be reached. The fact that the degree of locomotor recovery is correlated with the percentage of remaining fibers in the ventrolateral spinal cord, exclusive of most of the descending motor tracts, may imply an essential role of propriospinal connections in the initiation of spontaneous locomotor recovery.

Effects of inosine on axonal regeneration of axotomized retinal ganglion cells in adult rats

Damage to the central nervous system (CNS) is always followed by an irreversible axon degeneration of injured neurons. The purine nucleoside inosine has been shown to induce neurons to regenerate axons in culture and in vivo. In the present study, we investigated the in vivo effects of inosine on the axon regeneration of axotomized retinal ganglion cells (RGCs) in adult rats, using the model of peripheral nerve (PN) grafting onto the ocular stump of the transected optic nerve. Animals were allowed to survive for 4 weeks after surgery with repeated intraperitoneal injections of inosine 1 day before PN grafting till they were killed. Treatment with inosine induced a significant increase (62%) in the number of FluroGold -labeled RGCs regrowing their axons into the PN graft, when compared with the control animals. The axon outgrowth-promoting effect of inosine in adult rodents may represent a potential clinical treatment for injured or degenerated CNS.

Axonal regeneration of retinal ganglion cells after optic nerve pre-lesions and attachment of normal or pre-degenerated peripheral nerve grafts

Axonal regeneration of retinal ganglion cells (RGCs) into a normal or pre-degenerated peripheral nerve graft after an optic nerve pre-lesion was investigated. A pre-lesion performed 1-2 weeks before a second lesion has been shown to enhance axonal regeneration in peripheral nerves (PN) but not in optic nerves (ON) in mammals. The lack of such a beneficial pre-lesion effect may be due to the long delay (1-6 weeks) between the two lesions since RGCs and their axons degenerate rapidly 1-2 weeks following axotomy in adult rodents. The present study examined the effects of the proximal and distal ON pre-lesions with a shortened delay (0-8 days) on axonal regeneration of RGCs through a normal or pre-degenerated PN graft. The ON of adult hamsters was transected intraorbitally at 2 mm (proximal lesion) or intracranially at 7 mm (distal lesion) from the optic disc. The pre-lesioned ON was re-transected at 0.5 mm from the disc after 0, 1, 2, 4, or 8 days and a normal or a pre-degenerated PN graft was attached onto the ocular stump. The number of RGCs regenerating their injured axons into the PN graft was estimated by retrograde labeling with FluoroGold 4 weeks after grafting. The number of regenerating RGCs decreased significantly when the delay-time increased in animals with both the ON pre-lesions (proximal or distal) compared to control animals without an ON pre-lesion. The proximal ON pre-lesion significantly reduced the number of regenerating RGCs after a delay of 8 days in comparison with the distal lesion. However, this adverse effect can be overcome, to some degree, by a pre-degenerated PN graft applied 2, 4, or 8 days after the distal ON pre-lesion enhanced more RGCs to regenerate than the normal PN graft. Thus, in order to obtain the highest number of regenerating RGCs, a pre-degenerated PN should be grafted immediately after an ON lesion.

Direct protection of inosine on PC12 cells against zinc-induced injury

It has been reported that inosine has no direct neuroprotection against respiratory inhibitors due to the absence of purine nucleoside phosphorylase in neurons. Recent evidence, however, has shown that inosine has direct neurotrophic effects. Thus, lack of direct neuroprotection, as reported before, may not be a general conclusion, but is related to special types of injury. We used PC12 cells to explore direct neuroprotection of inosine against high concentration of zinc sulfate, an injury different from the previous one and found that inosine reduced the mortality of PC12 cells significantly in a dose dependent manner. The results indicate that inosine can directly protect neurons from zinc-induced injury, and such effect might be mediated via mechanism(s) other than purine nucleoside phosphorylase.

Increase in cytochrome oxidase activity in regenerating nerve fibers of hemitransected spinal cord in the rat

We explored the possibility of cytochrome oxidase (CO) involvement in spinal cord regeneration in adult rats. The spinal cord was hemitransected at T9. After one month's survival, the animals were deeply anesthetized and perfused. The spinal cord segments including the lesion site were removed and sectioned horizontally for CO histochemistry. Under light microscope, a substantial number of CO-reactive nerve fibers and boutons were identified in the lateral funiculus adjacent to the lesion site. Under electron microscope, moderately to highly CO-reactive mitochondria could be seen within nerve fibers and boutons. Synaptic contacts were identified among them. The increase in CO activity in nerve fibers and boutons may indicate their high-energy demand for synaptic and spontaneous activity following spinal cord hemisection.

[Transplantation of peripheral nerves and their tissue constituents to repair axotomized retinal ganglion cells in adult mammals]

We focus on how peripheral nerves or their tissue constituents including Schwann cells, fibroblasts and neurotrophic factors are used to overcome the unfavorable extrinsic CNS environment and upregulate the intrinsic growth potential of injured neurons for the enhancement of neuronal survival and axonal regeneration of axotomized retinal ganglion cells in adult mammals.

Axonal regeneration of retinal ganglion cells depending on the distance of axotomy in adult hamsters

PURPOSE

To examine the relationship between the distance of axotomy and axonal regeneration of injured retinal ganglion cells (RGCs) systematically and the effect of a predegenerated (pretransected or precrushed) peripheral nerve (PN) graft on axonal regeneration of RGCs axotomized at a definite distance (0.5 mm from the optic disc) in comparison with a normal PN graft.

METHODS

The optic nerve (ON) was transected intraorbitally at 0.5, 1, 1.5, 2, or 3 mm or intracranially at 6 to 8 mm from the optic disc, and a PN graft was transplanted onto the ocular ON stump in adult hamsters. Four weeks after grafting, the number of RGCs regenerating their injured axons into the PN graft was investigated in all animals.

RESULTS

The number of regenerating RGCs decreased significantly when the distance of axotomy increased from 0.5 to 7 mm. A precrushed PN graft was shown to enhance more injured RGCs to regenerate axons than a normal or pretransected PN graft.

CONCLUSIONS

The distance of axotomy on the ON of adult hamsters is critical in determining the number of regenerating RGCs. Thus, experimental strategies to repair the damaged ON by PN transplantation is to attach a precrushed PN graft as close to the optic disc as possible to obtain optimal axonal regeneration of the axotomized RGCs.