Spinogenesis in spinal cord motor neurons following pharmacological lesions to the rat motor cortex

INTRODUCTION

Motor function is impaired in multiple neurological diseases associated with corticospinal tract degeneration. Motor impairment has been linked to plastic changes at both the presynaptic and postsynaptic levels. However, there is no evidence of changes in information transmission from the cortex to spinal motor neurons.

METHODS

We used kainic acid to induce stereotactic lesions to the primary motor cortex of female adult rats. Fifteen days later, we evaluated motor function with the BBB scale and the rotarod and determined the density of thin, stubby, and mushroom spines of motor neurons from a thoracolumbar segment of the spinal cord. Spinophilin, synaptophysin, and β iii-tubulin expression was also measured.

RESULTS

Pharmacological lesions resulted in poor motor performance. Spine density and the proportion of thin and stubby spines were greater. We also observed increased expression of the 3 proteins analysed.

CONCLUSION

The clinical symptoms of neurological damage secondary to Wallerian degeneration of the corticospinal tract are associated with spontaneous, compensatory plastic changes at the synaptic level. Based on these findings, spontaneous plasticity is a factor to consider when designing more efficient strategies in the early phase of rehabilitation.

Neuroprotection of completely lacerated spinal cord of adult rats by homotopic and heterotopic transplantation

To evaluate the neuroprotective effect of transplants placed in the lesion zone after a complete spinal cord (SC) laceration, two independent series of experiments were carried out. In the first, allogeneic or xenogeneic fetal SC was transplanted into the gaps of the damaged lower thoracic SC of adult rats. In the transplanted rats the incidence of life-threatening complications was reduced, and the survival rate was increased compared with the control group (lesion, without implant). Histological examination showed less damage to the neighboring SC parenchyma in the transplanted rats. The measurement of this neuroprotective effect was made in a second series of experiments. Using the same model of SC injury, allogeneic fetal SC, autologous peripheral nerve and/or adipose tissue were implanted. Rats with implants of Gelfoam and damaged rats without implants were the controls. The implanted rats of all groups, including the Gelfoam group, showed a better survival rate than the nonimplanted rats. Significantly less damage to the neighboring SC parenchyma was measured in implanted rats with any of the live tissues tested compared with non-implanted rats, although no significant differences were observed between the Gelfoam group and the nonimplanted rats. Histological evidence of tissue implant survival was observed in all corresponding groups. It is concluded that the transplanted tissues tested here have a neuroprotective effect, possibly by acting as a buffer to neurotoxic substance(s) released by the stumps, and/or by exerting trophic effect(s) on the host.

Deleterious versus neuroprotective effect of metabolic inhibition after traumatic spinal cord injury

STUDY DESIGN

This work is an experimental and prospective study in adult, female, Long-Evans rats.

OBJECTIVES

The aim of this study was to probe the effect of metabolic inhibition after an acute traumatic spinal cord injury (TSCI) using a standardized contusion model (NYU impactor) to know whether the metabolic inhibition is a 'secondary mechanism of injury' or a mechanism of protection.

SETTING

All experimental procedures were carried out in the Mexico City.

METHODS

Animals were divided into five groups: one sham and four with TSCI, including no treatment, rotenone (inhibitor of mitochondrial complex I), sodium azide (inhibitor of mitochondrial complex IV) and pyrophosphate of thiamine or non-degradable cocarboxylase as a metabolic reactivator.

RESULTS

After TSCI, the metabolic inhibition with sodium azide treatment diminished the lipid peroxidation process (malondialdehyde levels by spectrophotometric procedures) and the damage to the spinal cord tissue (morphometric analysis), and increased the activity of creatine kinase and lactate dehydrogenase enzymes (P<0.05) (measured by spectrophotometric procedures 24 h after TSCI as well as after the functional recovery of the hind limb (evaluated weekly for 2 months by the BBB (Basso, Beattie and Bresnahan) scale)) when compared with the TSCI group without treatment.

CONCLUSION

The results show that the partial and transitory inhibition of the aerobic metabolism after an acute TSCI could be a self-protection mechanism instead of being a 'secondary mechanism of injury'.

Spontaneous long-term remyelination after traumatic spinal cord injury in rats

The capability of the central nervous system to remyelinate axons after a lesion has been well documented, even though it had been described as an abortive and incomplete process. At present there are no long-term morphometric studies to assess the spinal cord (S.C.) remyelinative capability. With the purpose to understand this phenomenon better, the S.C. of seven lesionless rats and the S.C. of 21 rats subjected to a severe weight-drop contusion injury were evaluated at 1, 2, 4, 6, and 12 months after injury. The axonal diameter and the myelination index (MI = axolemmal perimeter divided by myelinated fiber perimeter) were registered in the outer rim of the cord at T9 SC level using a transmission electron microscope and a digitizing computer system. The average myelinated fiber loss was 95.1%. One month after the SC, 64% of the surviving fibers were demyelinated while 12 months later, only 30% of the fibers had no myelin sheath. The MI in the control group was 0.72 +/- 0.07 (X +/- S.D.). In the experimental groups, the greatest demyelination was observed two months after the lesion (MI = 0.90 +/- 0.03), while the greatest myelination was observed 12 months after the injury (MI = 0.83 +/- 0.02). There was a statistical difference (p < 0.02) in MI between 2 and 12 months which means that remyelination had taken place. Remyelination was mainly achieved because of Schwann cells. The proportion of small fibers (diameter = 0.5 micron or less) considered as axon collaterals, increased from 18.45% at 1 month to 27.66% a year after the contusion. Results suggest that remyelination is not an abortive phenomenon but in fact a slow process occurring parallel to other tissue plastic phenomena, such as the emission of axon collaterals.

Alteration of cyclosporin-A pharmacokinetics after experimental spinal cord injury

The pharmacokinetics of the immunosuppressive agent cyclosporin-A (CsA) were studied in rats submitted to spinal cord (SC) injury. A single CsA 10 mg/kg dose was given either intraperitoneally (i.p.) or orally to rats submitted to experimental SC injury at the T8 level. Twenty four hours after lesion (acute stage of SC injury) i.p. CsA bioavailability was increased, while t1/2 was prolonged. However, oral bioavailability was reduced. Seven weeks after lesion (chronic stage of SC injury) CsA bioavailability, by either route, was not significantly different from control values. Results indicate that parenteral CsA bioavailability is increased during the acute stage of SC lesion, probably due to an impaired elimination. Oral bioavailability, however, is decreased, since there is also an important reduction in gastrointestinal CsA absorption that overrides the effect of impaired elimination. Alterations in CsA pharmacokinetics appear to revert during the chronic stage of SC injury. Changes in CsA bioavailability, depending on the route of administration and on time, must be considered to design an adequate immunosuppressive treatment in SC injury.