Neurogenesis Abstracts 3

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Thyroid hormone triggers the developmental loss of axonal regenerative capacity via thyroid hormone receptor alpha1 and kruppel-like factor 9 in Purkinje cells

         (Avci, Lebrun et al. 2012) Download

Neurons in the CNS of higher vertebrates lose their ability to regenerate their axons at a stage of development that coincides with peak circulating thyroid hormone (T(3)) levels. Here, we examined whether this peak in T(3) is involved in the loss of axonal regenerative capacity in Purkinje cells (PCs). This event occurs at the end of the first postnatal week in mice. Using organotypic culture, we found that the loss of axon regenerative capacity was triggered prematurely by early exposure of mouse PCs to T(3), whereas it was delayed in the absence of T(3). Analysis of mutant mice showed that this effect was mainly mediated by the T(3) receptor alpha1. Using gain- and loss-of-function approaches, we also showed that Kruppel-like factor 9 was a key mediator of this effect of T(3). These results indicate that the sudden physiological increase in T(3) during development is involved in the onset of the loss of axon regenerative capacity in PCs. This loss of regenerative capacity might be part of the general program triggered by T(3) throughout the body, which adapts the animal to its postnatal environment.

Thyrotropin-releasing hormone improves neurologic recovery after spinal trauma in cats

         (Faden, Jacobs et al. 1981) Download

Naloxone treatment improves neurologic outcome after experimentally induced spinal trauma, but this opiate-receptor antagonist may increase post-traumatic pain. In contrast, thyrotropin-releasing hormone appears to act in vivo as a partial physiologic opiate antagonist that spares analgesic systems; this activity prompted us to evaluate its effect in spinal injury. Cervical-spine trauma was produced in anesthetized cats by the Allen method. Six animals each received thyrotropin-releasing hormone, saline, or dexamethasone as an intravenous infusion over four hours, beginning one hour after injury. Neurologic recovery was significantly better after treatment with thyrotropin-releasing hormone than after saline or dexamethasone (P less than 0.01): at six weeks, the average animal given thyrotropin-releasing hormone was normal, whereas average control animals had marked spasticity. The beneficial effect of thyrotropin-releasing hormone in experimental spinal injury and its lack of effect on nociception indicate that it may have unique therapeutic potential in spinal trauma in human beings.

Thyrotropin-releasing hormone in experimental spinal injury: dose response and late treatment

         (Faden, Jacobs et al. 1984) Download

Early treatment with thyrotropin-releasing hormone (TRH) at high doses improves neurologic recovery from experimental spinal injury in cats. We have now compared the effects of TRH dose and time of treatment on neurologic outcome. TRH-treated animals showed better motor recovery than saline controls; effects were dose-related (between 0.02 mg/kg/hr and 2.0 mg/kg/hr), with significant effects even at the lowest dose. Cats treated at 24 hours after injury also improved significantly. These findings provide additional support for TRH trials in human spinal injury and suggest that even late treatment may be effective.

Enhancement of axonal regeneration in the brain of the rat by corticotrophin and triiodothyronine

         (Fertig, Kiernan et al. 1971) Download

Rats with simple incised wounds of the telencephalon were treated for either 7 or 50 days with either sunthetic corticotrophin (ACTH) or triiodothyronine (T3). Control animals received no treatment. Regenerating axons, which entered and sometimes crossed the lesions, were detected histologically in rats treated with both hormones. The effects of both ACTH and T3 were mediated during the first 7 days after placement of the lesion. We suggest that ACTH, in suitable dosage, acts by allowing the formation of a suitable type of loose connective tissue in the lesion, while T3 increases the rate of synthesis of axoplasmic structural protein.


Folate regulation of axonal regeneration in the rodent central nervous system through DNA methylation

         (Iskandar, Rizk et al. 2010) Download

The folate pathway plays a crucial role in the regeneration and repair of the adult CNS after injury. Here, we have shown in rodents that such repair occurs at least in part through DNA methylation. In animals with combined spinal cord and sciatic nerve injury, folate-mediated CNS axon regeneration was found to depend on injury-related induction of the high-affinity folate receptor 1 (Folr1). The activity of folate was dependent on its activation by the enzyme dihydrofolate reductase (Dhfr) and a functional methylation cycle. The effect of folate on the regeneration of afferent spinal neurons was biphasic and dose dependent and correlated closely over its dose range with global and gene-specific DNA methylation and with expression of both the folate receptor Folr1 and the de novo DNA methyltransferases. These data implicate an epigenetic mechanism in CNS repair. Folic acid and possibly other nontoxic dietary methyl donors may therefore be useful in clinical interventions to promote brain and spinal cord healing. If indeed the benefit of folate is mediated by epigenetic mechanisms that promote endogenous axonal regeneration, this provides possible avenues for new pharmacologic approaches to treating CNS injuries.

Neuritic regeneration and synaptic reconstruction induced by withanolide A

         (Kuboyama, Tohda et al. 2005) Download

We investigated whether withanolide A (WL-A), isolated from the Indian herbal drug Ashwagandha (root of Withania somnifera), could regenerate neurites and reconstruct synapses in severely damaged neurons. We also investigated the effect of WL-A on memory-deficient mice showing neuronal atrophy and synaptic loss in the brain. Axons, dendrites, presynapses, and postsynapses were visualized by immunostaining for phosphorylated neurofilament-H (NF-H), microtubule-associated protein 2 (MAP2), synaptophysin, and postsynaptic density-95 (PSD-95), respectively. Treatment with A beta(25-35) (10 microM) induced axonal and dendritic atrophy, and pre- and postsynaptic loss in cultured rat cortical neurons. Subsequent treatment with WL-A (1 microM) induced significant regeneration of both axons and dendrites, in addition to the reconstruction of pre- and postsynapses in the neurons. WL-A (10 micromol kg(-1) day(-1), for 13 days, p.o.) recovered A beta(25-35)-induced memory deficit in mice. At that time, the decline of axons, dendrites, and synapses in the cerebral cortex and hippocampus was almost recovered. WL-A is therefore an important candidate for the therapeutic treatment of neurodegenerative diseases, as it is able to reconstruct neuronal networks.

Thyroid hormone enhances transected axonal regeneration and muscle reinnervation following rat sciatic nerve injury

         (Panaite and Barakat-Walter 2010) Download

Improvement of nerve regeneration and functional recovery following nerve injury is a challenging problem in clinical research. We have already shown that following rat sciatic nerve transection, the local administration of triiodothyronine (T3) significantly increased the number and the myelination of regenerated axons. Functional recovery is a sum of the number of regenerated axons and reinnervation of denervated peripheral targets. In the present study, we investigated whether the increased number of regenerated axons by T3-treatment is linked to improved reinnervation of hind limb muscles. After transection of rat sciatic nerves, silicone or biodegradable nerve guides were implanted and filled with either T3 or phosphate buffer solution (PBS). Neuromuscular junctions (NMJs) were analyzed on gastrocnemius and plantar muscle sections stained with rhodamine alpha-bungarotoxin and neurofilament antibody. Four weeks after surgery, most end-plates (EPs) of operated limbs were still denervated and no effect of T3 on muscle reinnervation was detected at this stage of nerve repair. In contrast, after 14 weeks of nerve regeneration, T3 clearly enhanced the reinnervation of gastrocnemius and plantar EPs, demonstrated by significantly higher recovery of size and shape complexity of reinnervated EPs and also by increased acetylcholine receptor (AChRs) density on post synaptic membranes compared to PBS-treated EPs. The stimulating effect of T3 on EP reinnervation is confirmed by a higher index of compound muscle action potentials recorded in gastrocnemius muscles. In conclusion, our results provide for the first time strong evidence that T3 enhances the restoration of NMJ structure and improves synaptic transmission.


A ginkgo biloba extract promotes proliferation of endogenous neural stem cells in vascular dementia rats

         (Wang, Chen et al. 2013) Download

The ginkgo biloba extract EGb761 improves memory loss and cognitive impairments in patients with senile dementia. It also promotes proliferation of neural stem cells in the subventricular zone in Parkinson’s disease model mice and in the hippocampal zone of young epileptic rats. However, it remains unclear whether EGb761 enhances proliferation of endogenous neural stem cells in the brain of rats with vascular dementia. In this study, a vascular dementia model was established by repeatedly clipping and reperfusing the bilateral common carotid arteries of rats in combination with an intraperitoneal injection of a sodium nitroprusside solution. Seven days after establishing the model, rats were intragastrically given EGb761 at 50 mg/kg per day. Learning and memory abilities were assessed using the Morris water maze and proliferation of endogenous neural stem cells in the subventricular zone and dentate gyrus were labeled by 5-bromo-2-deoxyuridine immunofluorescence in all rats at 15 days, and 1, 2, and 4 months after model establishment. The escape latencies in Morris water maze tests of rats with vascular dementia after EGb761 treatment were significantly shorter than the model group. Immunofluorescence staining showed that the number and proliferation of 5-bromo-2-deoxyuridine-positive cells in the subventricular zone and dentate gyrus of the EGb761-treated group were significantly higher than in the model group. These experimental findings suggest that EGb761 enhances proliferation of neural stem cells in the subventricular zone and dentate gyrus, and significantly improves learning and memory in rats with vascular dementia.

Acetyl-l-carnitine increases nerve regeneration and target organ reinnervation - a morphological study

         (Wilson, Hart et al. 2010) Download

Peripheral nerve injury frequently results in functional morbidity since standard management fails to adequately address many of the neurobiological hurdles to optimal regeneration. Neuronal survival and regeneration are neurotrophin dependent and require increased aerobic capacity. Acetyl-l-carnitine (ALCAR) facilitates this need and prevents neuronal loss. ALCAR is clinically safe and is shown here to significantly improve nerve regeneration and target organ reinnervation. Two groups of five rats underwent sciatic nerve division followed by immediate repair. One group received parenteral ALCAR (50mg/kg/day) from time of operation until termination at 12 weeks. A 'sham treatment' group received normal saline. A third group was left unoperated and did not receive any treatment. A segment of nerve was harvested between 5mm proximal and 10mm distal to the repair in operated groups, and at the corresponding level in the unoperated group. Mean axonal count in normal, non-axotomised nerve was 14,720 (SD 2378). That of the saline group (17,217 SD 1808) was not significantly different from normal nerve (P=0.0985). Mean number of myelinated axons in the ALCAR group (24,460 SD 3750) was significantly greater than both sham group (P<0.01) and normal nerve (P=0.0012). Mean myelin thickness in the saline treated group (0.408 microm SD 0.067 microm) was less than normal nerve (0.770 microm SD 0.143 microm) (P<0.001). Mean myelin thickness in the ALCAR group (0.627 microm SD 0.052 microm) was greater than the sham (saline) group (P<0.01) and not statistically different from normal nerve (P=0.07). ALCAR increased dermal PGP9.5 staining by 210% compared to sham treatment (P<0.0001) and significantly reduced the mean percentage weight loss in gastrocnemius muscle (ALCAR group 0.203% vs. 0.312% in sham group P=0.015). ALCAR not only increases the number of regenerating nerve fibres but also morphologically improves the quality of regeneration and target organ reinnervation. Adjuvant ALCAR treatment may improve both sensory and motor outcomes and merits further investigation.


References

Avci, H. X., C. Lebrun, et al. (2012). "Thyroid hormone triggers the developmental loss of axonal regenerative capacity via thyroid hormone receptor alpha1 and kruppel-like factor 9 in Purkinje cells." Proc Natl Acad Sci U S A 109(35): 14206-11. [PMID: 22891348]

Faden, A. I., T. P. Jacobs, et al. (1981). "Thyrotropin-releasing hormone improves neurologic recovery after spinal trauma in cats." N Engl J Med 305(18): 1063-7. [PMID: 6792542]

Faden, A. I., T. P. Jacobs, et al. (1984). "Thyrotropin-releasing hormone in experimental spinal injury: dose response and late treatment." Neurology 34(10): 1280-4. [PMID: 6435011]

Fertig, A., J. A. Kiernan, et al. (1971). "Enhancement of axonal regeneration in the brain of the rat by corticotrophin and triiodothyronine." Exp Neurol 33(2): 372-85. [PMID: 4330990]

Iskandar, B. J., E. Rizk, et al. (2010). "Folate regulation of axonal regeneration in the rodent central nervous system through DNA methylation." J Clin Invest 120(5): 1603-16. [PMID: 20424322]

Kuboyama, T., C. Tohda, et al. (2005). "Neuritic regeneration and synaptic reconstruction induced by withanolide A." Br J Pharmacol 144(7): 961-71. [PMID: 15711595]

Panaite, P. A. and I. Barakat-Walter (2010). "Thyroid hormone enhances transected axonal regeneration and muscle reinnervation following rat sciatic nerve injury." J Neurosci Res 88(8): 1751-63. [PMID: 20127814]

Wang, J., W. Chen, et al. (2013). "A ginkgo biloba extract promotes proliferation of endogenous neural stem cells in vascular dementia rats." Neural Regen Res 8(18). [PMID:

Wilson, A. D., A. Hart, et al. (2010). "Acetyl-l-carnitine increases nerve regeneration and target organ reinnervation - a morphological study." J Plast Reconstr Aesthet Surg 63(7): 1186-95. [PMID: 19664977]