Effect of axotomy on cholinergic enzyme activities in the spinal cord and sciatic nerve of the dog

Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity measured in the ventral and dorsal part of the dog spinal cord (L6-S2) and in the stumps of the sciatic nerve 5, 10, 15 and 21 days after its transection were compared with the corresponding activities in the intact contralateral nerve and in sham-operated animals. AChE was also examined histochemically. Changes in the enzyme activities in the central nerve stump were correlated with activity changes in the spinal cord. In the central nerve stump, a marked (25%) increase in AChE activity was found on the fifth day after transection, but by the 21st day it fell below control value levels; up to the 15th day it showed good correlation with AChE activity in the ventral spinal cord. Histochemically, pronounced reduction of enzymatic activity was found in the ipsilateral part of the spinal cord. On the 15th day, ChAT activity in the ventral spinal cord was also significantly decreased and the accumulation of the enzyme in the central nerve stump was negligible. On the contrary, at the last 21-day interval examined, a significant increase in ChAT activity and a nonsignificant increase in AChE activity was found in the spinal cord, but their activities in the central nerve stump were decreased. In the degenerated peripheral nerve stump ChAT activity dropped by an average of 99% and AChE activity by 48% during the first 15 days after transection but, on the 21st day, AChE activity was 22% higher than at the preceding interval.     

Distribution of choline acetyltransferase and acetylcholinesterase in the nervous system of the dog

Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity were determined in 23 selected parts of the dog CNS and 4 parts of the peripheral nervous system. Maximum ChAT activity was found in the caudate nucleus and the ventral roots of the spinal cord. High activity was also present in the thalamus, the pons, the cerebral cortex, the medulla oblongata, the ventral spinal horns and the sciatic nerve. The lowest activity was measured in the cerebellum, the dorsal cord roots and the spinal ganglia. Maximum AChE activity was found in the caudate nucleus and the cerebellum. Relatively high activity was also present in the thalamus, the pons, the medulla oblongata, the grey matter of the spinal cord and the spinal ganglia. The lowest AChE activity was measured in the ventral and dorsal spinal roots.     

Botulinum toxin's axonal transport from periphery to the spinal cord

Axonal transport of enzymatically active botulinum toxin A (BTX-A) from periphery to the CNS has been described in facial and trigeminal nerve, leading to cleavage of synaptosomal-associated protein 25 (SNAP-25) in central nuclei. Aim of present study was to examine the existence of axonal transport of peripherally applied BTX-A to spinal cord via sciatic nerve. We employed BTX-A-cleaved SNAP-25 immunohistochemistry of lumbar spinal cord after intramuscular and subcutaneous hind limb injections, and intraneural BTX-A sciatic nerve injections. Truncated SNAP-25 in ipsilateral spinal cord ventral horns and dorsal horns appeared after single peripheral BTX-A administrations, even at low intramuscular dose applied (5 U/kg). Cleaved SNAP-25 appearance in the spinal cord after BTX-A injection into the sciatic nerve was prevented by proximal intrasciatic injection of colchicine (5 mM, 2 μl). Cleaved SNAP-25 in ventral horn, using choline-acetyltransferase (ChAT) double labeling, was localized within cholinergic neurons. These results extend the recent findings on BTX-A retrograde axonal transport in facial and trigeminal nerve. Appearance of truncated SNAP-25 in spinal cord following low-dose peripheral BTX-A suggest that the axonal transport of BTX-A occurs commonly following peripheral application.     

大鼠坐骨神经切断后外源性bcl-2对脊髓运动神经元的保护作用

采用大鼠坐骨神经切断损伤模型,行神经外膜端端对线缝合,术中依不同组别,动物于神经缝合处远端0．5cm处分别注射人的正义和反义bcl-2重组腺病毒(Ad／s-bcl-2、Ad／as-bcl-2),报道基因重组腺病毒(Ad／lacZ)和生理盐水。术后48h,7d,15d和30d常规灌注固定大鼠,取L4-L6脊髓节段,应用X-gal染色、bel-2原位杂交和免疫组化染色、TUNEL染色以及乙酰胆碱酯酶(AChE)组织化学染色方法,观察到外源基因能在脊髓中表达,同时外源性Ad／s-bcl-2能显著减少L4到L6节段脊髓前角运动神经元凋亡的数目,减少脊髓前角运动神经元中因坐骨神经切断导致的AChE活性的降低幅度,并加快其恢复。而Ad／as-bcl-2可显著增加坐骨神经切断诱导的脊髓前角运动神经元凋亡数目以及AChE活性降低幅度,并延缓其恢复。这些观察结果表明,外源性bcl-2能保护周围神经切断后引起的脊髓运动神经元损伤。     

Moderately Different NADPH-Diaphorase Positivity in the Selected Peripheral Nerves after Ischemia/ Reperfusion Injury of the Spinal Cord in Rabbit

1. To vicariously investigate the nitric oxide synthase (NOS) production after spinal cord injury, NADPH-d histochemistry was performed on the selected peripheral nerves of adult rabbits 7 days after ischemia. The effect of transient spinal cord ischemia (15 min) on possible degenerative changes in the motor and mixed peripheral nerves of Chinchilla rabbits was evaluated.2. The NADPH-diaphorase histochemistry was used to determine NADPH-diaphorase activity after ischemia/reperfusion injury in radial nerve and mediane nerve isolated from the fore-limb and femoral nerve, saphenous nerve and sciatic nerve separated from the hind-limb of rabbits. The qualitative analysis of the optical density of NADPH-diaphorase in selected peripheral nerves demonstrated different frequency of staining intensity (attained by UTHSCSA Image Tool 2 analysis for each determined nerve).3. On the seventh postsurgery day, the ischemic spinal cord injury resulted in an extensive increase of NADPH-d positivity in isolated nerves. The transient ischemia caused neurological disorders related to the neurological injury—a partial paraplegia. The sciatic, femoral, and saphenous nerves of paraplegic animals presented the noticeable increase of NADPH-d activity. The mean of NADPH-diaphorase intensity staining per unit area ranged from 134.87 (±32.81) pixels to 141.65 (±35.06) pixels (using a 256-unit gray scale where 0 denotes black, 256 denotes white) depending on the determined nerve as the consequence of spinal cord ischemia. The obtained data were compared to the mean values of staining intensity in the same nerves in the limbs of control animals (163.69 (±25.66) pixels/unit area in the femoral nerve, 173.00 (±32.93) pixels/unit area in saphenous nerve, 186.01 (±29.65) pixels/unit area in sciatic nerve). Based on the statistical analysis of the data (two-way unpaired Mann–Whitney test), a significant increase (p≤0.05) of NADPH-d activity in femoral and saphenous nerve, and also in sciatic nerve (p≤0.001) has been found. On the other hand, there was no significant difference between the histochemically stained nerves of fore-limbs after ischemia/reperfusion injury and the same histochemically stained nerves of fore-limbs in control animals.4. The neurodegenerative changes of the hind-limbs, characterized by damage of their motor function exhibiting a partial paraplegia after 15 min spinal cord ischemia and subsequent 7 days of reperfusions resulted in the different sensitivity of peripheral nerves to transient ischemia. Finally, we suppose that activation of NOS indirectly demonstrable through the NADPH-d study may contribute to the explanation of neurodegenerative processes and the production of nitric oxide could be involved in the pathophysiology of spinal cord injury by transient ischemia.     

神经生长因子对兔坐骨神经损伤后脊髓前角运动神经元乙酰胆碱酯酶的影响

钳夹损伤兔右坐骨神经,于损伤处注射蛇毒ＮＧＦ４００Ｂｕ／ｋｇ／日,损伤术后１,３,７天和２,３,４,６,８周动态观察脊髓腰段伤侧第Ⅸ板层外侧群的大型运动神经元的ＡＣｈＥ活性改变。结果表明术后１,３天实验组（指损伤给药组）和对照组（指损伤对照组）ＡＣｈＥ活性均下降（Ｐ＞００５）;术后１,２,３周对照组ＡＣｈＥ活性明显下降,而实验组ＡＣｈＥ活性逐渐趋于恢复（Ｐ＜００１）;术后６周实验组ＡＣｈＥ活性恢复至正常水平（Ｐ＜００１）。本研究显示蛇毒ＮＧＦ对坐骨神经损伤后脊髓前角运动神经元ＡＣｈＥ活性恢复有促进作用,从而对运动神经元可起一定的保护作用和促进恢复的作用     

Permanent alterations of spinal cord reflexes following nerve lesion in newborn rats

Sciatic nerve lesion in newborn rats is known to cause degeneration of a large number of axotomized motoneurones and spinal ganglion cells. Some of the surviving motoneurones exhibit abnormal firing properties and the projection pattern of central terminals of sensory neurones is altered. We report here on long-term changes in spinal cord reflexes in adult rats following neonatal nerve crush. In acutely spinalized and anaesthetized adult rats 4-6 months old in which the sciatic nerve had been crushed on one side at birth, the tibial nerve, common peroneal nerve or sural nerve were stimulated on the reinnervated and control side and reflex responses were recorded from the L5 ventral spinal roots. Ventral root responses (VRRs) to tibial and peroneal nerve stimulation on the side of the nerve lesion were significantly smaller in amplitude representing only about 15% of the mean amplitude of VRRs on the control side. The calculated central delay of the first, presumably monosynaptic component of the VRR potential was 1.6 ms on the control side while the earliest VRR wave on the side of the nerve lesion appeared after a mean central latency of 4.0 ms that seems too long to be of monosynaptic origin. These results suggest that neonatal sciatic nerve injury markedly alters the physiological properties and synaptic connectivity in spinal cord neurones and causes a marked depression of spinal cord responses to peripheral nerve stimulation.     

Genetic evidence for an essential role of neuronally expressed IL-6 signal transducer gp130 in the induction and maintenance of experimentally induced mechanical hypersensitivity in vivo and in vitro

Background

A preconditioning stimulus can trigger a neuroprotective phenotype in the nervous system - a preconditioning nerve lesion causes a significant increase in axonal regeneration, and cerebral preconditioning protects against subsequent ischemia. We hypothesized that a preconditioning nerve lesion induces gene/protein modifications, neuronal changes, and immune activation that may affect pain sensation following subsequent nerve injury. We examined whether a preconditioning lesion affects neuropathic pain and neuroinflammation after peripheral nerve injury.

Results

We found that a preconditioning crush injury to a terminal branch of the sciatic nerve seven days before partial ligation of the sciatic nerve (PSNL; a model of neuropathic pain) induced a significant attenuation of pain hypersensitivity, particularly mechanical allodynia. A preconditioning lesion of the tibial nerve induced a long-term significant increase in paw-withdrawal threshold to mechanical stimuli and paw-withdrawal latency to thermal stimuli, after PSNL. A preconditioning lesion of the common peroneal induced a smaller but significant short-term increase in paw-withdrawal threshold to mechanical stimuli, after PSNL. There was no difference between preconditioned and unconditioned animals in neuronal damage and macrophage and T-cell infiltration into the dorsal root ganglia (DRGs) or in astrocyte and microglia activation in the spinal dorsal and ventral horns.

Conclusions

These results suggest that prior exposure to a mild nerve lesion protects against adverse effects of subsequent neuropathic injury, and that this conditioning-induced inhibition of pain hypersensitivity is not dependent on neuroinflammation in DRGs and spinal cord. Identifying the underlying mechanisms may have important implications for the understanding of neuropathic pain due to nerve injury.     

Neurochemical and Immunocytochemical Studies on the Distribution of N-Acetyl-Aspartylglutamate and N-Acetyl-Aspartate in Rat Spinal Cord and Some Peripheral Nervous Tissues

HPLC analysis of rat spinal cord revealed a uniform distribution of N-acetyl-aspartate (NAA) across both longitudinal and dorsoventral axes. In contrast, ventral cord N-acetyl-aspartylglutamate (NAAG) levels were significantly higher than those measured in dorsal halves of cervical, thoracic, and lumbar segments. Immunocytochemical studies using an affinity-purified antiserum raised against NAAG-bovine serum albumin revealed an intense staining of motoneurons within rat spinal cord. Along with the considerable NAAG content in ventral roots, these results suggest that NAAG may be concentrated in motoneurons and play a role in motor pathways. NAAG was also present in other peripheral neural tissues, including dorsal roots, dorsal root ganglia, superior cervical ganglia, and sciatic nerve. It is interesting that NAA levels in peripheral nervous tissues were lower than those in CNS structures and that NAA levels in ventral roots and sciatic nerve were lower than NAAG levels. These findings further document a lack of correlation between NAAG and NAA levels in both central and peripheral nervous tissues. Taken together, these data demonstrate the presence of NAAG in nonglutamatergic neuronal systems and suggest a more complex role of NAAG in neuronal physiology than previously postulated.     

Effect of Treadmill Exercise on Serotonin Immunoreactivity in Medullary Raphe Nuclei and Spinal Cord Following Sciatic Nerve Transection in Rats

The serotoninergic system modulates nociceptive and locomotor spinal cord circuits. Exercise improves motor function and changes dopaminergic, noradrenergic, and serotonergic central systems. However, the direct relationship between serotonin, peripheral nerve lesion and aerobic treadmill exercise has not been studied. Using immunohistochemistry and optic densitometry, this study showed that the sciatic nerve transection increased the serotoninergic immunoreactivity in neuronal cytoplasm of the magnus raphe nuclei of trained and sedentary rats. In the dorsal raphe nucleus the increase only occurred in sedentary-sham-operated rats. In the spinal cord of trained, transected rats, the ventral horn showed significant changes, while the change in dorsal horn was insignificant. Von Frey’s test indicated analgesia in all exercise-trained rats. The sciatic nerve functional index indicated recovery in the trained group. Thus, both the aerobic treadmill exercise training and the nervous lesion appear to contribute to changes in serotonin immunoreactivity.     

FK506 Protects Neurons Following Peripheral Nerve Injury Via Immunosuppression

In this study, we have evaluated neuroprotective effect of an immunosuppressant immunophilin ligand, FK506, in the sciatic nerve injury model in rats. FK506 was injected to the sciatic nerve transected 3-month-old female Wistar rats (2 mg/kg/day starting 1 day prior to sciatic nerve injury up to 7 day post operation). Equal number of sciatic nerve transected animals served as injured untreated controls. The contralateral side served as respective control. L4-L5 region of the spinal cord was removed on day 1, 3, 7, 14, 21, and 28, post operation and then processed for cryo-sectioning and paraffin sectioning. The cryocut sections were used for immunohistochemistry for localizing all microglia (using anti-Iba-1) and MHC-II expressing microglia (with OX-6). The physical dissector method was applied on Nissl stained paraffin sections for absolute motor neuron counting in the L4-L5 region of spinal cord. FK506 treated animals presented 88.7% neuronal survival while the injured alone had 79.12%, which is significantly less than the treated animals. FK506 caused early proliferation of microglia at 1 and 3 days post operation. FK506 also significantly restricted transformation of these cells in to phagocytes. Colocalization of activated microglia by anti-Iba-1 and OX-6 antibodies, confirms that the MHC-II expressing cells in injured spinal cord are none other than microglial cells and MHC-II expressing cells are significantly less in treated as compared to untreated injured animals. We propose that immunosuppression is one of the main mechanisms by which FK506 protects the central neurons following peripheral injury.     

Effects of ischemia on cholinergic neurotransmission and electrolyte content in newborn pig lumbar spinal cord

The biochemical changes of the elements of cholinergic neurotransmission (choline acetyltransferase, ChAT; acetylcholinesterase, AChE; butyrylcholinesterase, BuChE; and muscarinic cholinergic receptors, mAChR) as well as the electrolyte content were studied in ischemic lumbar spinal cord segments of newborn pigs. Ischemia was elicited by ligating the aorta for 30 min. Although no significant changes were observed in the sodium, potassium and calcium content of ischemic spinal cords, the calcium content was slightly elevated, to 119.3% of the control value. Whereas significant depletions were observed in both AChE and ChAT activities (to 69.1 and 87.7% of the control value, respectively), there was no significant change in BuChE activity as compared to the control value. The mAChR were also decreased, from 33.25 +/- 2.2 to 27.18 +/- 1.9 fmol/mg protein, while the Kd value was not significantly altered. It is concluded that even a relatively brief interruption of the oxygen supply can cause severe damage in the lumbar spinal cord of the newborn pig, affecting the cholinergic neurotransmission elements. This animal model might be suitable for studying the effects of hypoxia in newborns and children during chest operations involving the descending aorta.     

Somatostatin-, calcitonin gene-related peptide, and gamma-aminobutyric acid-like immunoreactivitity in the frog lumbosacral spinal cord: distribution and effects of sciatic nerve transection

Using immunohistochemistry and optical densitometry, somatostatin (SOM), calcitonin gene-related peptide (CGRP), and gamma-aminobutyric acid (GABA) were investigated in the lumbosacral spinal cord of the frog Rana catesbeiana after sciatic nerve transection. In control animals, the densest network of the SOM-, CGRP- and GABA-like immunoreactive fibers was located in the dorsal part of the lateral funiculus. SOM and GABA-like fibers were found in the dorsal terminal field and in the mediolateral band. The latter region showed CGRP and SOM-like immunoreactive cell bodies. SOM- and GABA-like immunoreactive neurons also occurred around the cavity of the central canal, and other GABA-like fibers were found in the ventral terminal field. While the ventral horn showed scarce somatostatin-like fibers, the putative motoneurons were immunoreactive for the two peptides investigated and GABA, but only a few SOM- and GABA-like fibers occurred in the ventral funiculus. After axotomy, GABA-like immunoreactivity decreased in the dorsal part of the lateral funiculus on the same side of the lesion. The other regions remained labeled. These changes were observed at 3 days following axonal injury and persisted at 5, 8 and 15 days. There was no significant difference in the pattern of CGRP- and SOM- immunoreactivity between the axotomized and the control sides. These results are discussed in relation to the effects of the peripheral axotomy on GABA, SOM, and CGRP expression in vertebrates, emphasizing the use of frogs as a model to study the effects of peripheral nerve injury.     

Modulation of Matrix Metalloproteinases Activity in the Ventral Horn of the Spinal Cord Re-stores Neuroglial Synaptic Homeostasis and Neurotrophic Support following Peripheral Nerve Injury

Modulation of extracellular matrix (ECM) remodeling after peripheral nerve injury (PNI) could represent a valid therapeutic strategy to prevent maladaptive synaptic plasticity in central nervous system (CNS). Inhibition of matrix metalloproteinases (MMPs) and maintaining a neurotrophic support could represent two approaches to prevent or reduce the maladaptive plastic changes in the ventral horn of spinal cord following PNI. The purpose of our study was to analyze changes in the ventral horn produced by gliopathy determined by the suffering of motor neurons following spared nerve injury (SNI) of the sciatic nerve and how the intrathecal (i.t.) administration of GM6001 (a MMPs inhibitor) or the NGF mimetic peptide BB14 modulate these events. Immunohistochemical analysis of spinal cord sections revealed that motor neuron disease following SNI was associated with increased microglial (Iba1) and astrocytic (GFAP) response in the ventral horn of the spinal cord, indicative of reactive gliosis. These changes were paralleled by decreased glial aminoacid transporters (glutamate GLT1 and glycine GlyT1), increased levels of the neuronal glutamate transporter EAAC1, and a net increase of the Glutamate/GABA ratio, as measured by HPLC analysis. These molecular changes correlated to a significant reduction of mature NGF levels in the ventral horn. Continuous i.t. infusion of both GM6001 and BB14 reduced reactive astrogliosis, recovered the expression of neuronal and glial transporters, lowering the Glutamate/GABA ratio. Inhibition of MMPs by GM6001 significantly increased mature NGF levels, but it was absolutely ineffective in modifying the reactivity of microglia cells. Therefore, MMPs inhibition, although supplies neurotrophic support to ECM components and restores neuro-glial transporters expression, differently modulates astrocytic and microglial response after PNI.     

Immunocytochemical study of the relations of acetylcholinesterase,enkephalin-, substance P-, choline acetyltransferase- and calcitonin gene-related peptide-immunoreactive structures in the ventral horn of rat spinal cord

Summary Calcitonin gene-related peptide (CGRP)-like immunoreactivity was localized immunocytochemically in the large motoneurons in the ventral horn of rat spinal cord. Using fluorescence double-labelling substance P (SP)-immunoreactive nerve fibres were found to surround both the CGRP-positive and negative motoneurons, whereas enkephalin (ENK)-immunoreactive fibres surrounded mainly CGRP-negative cells. All CGRP-like immunoreactive motoneurons were also choline acetyltransferase (ChAT)- and acetylcholinesterase (AChE)-positive. On the other hand a large population of ChAT- and AChE-positive motoneurons were devoid of CGRP-immunoreactivity. It is probable that CGRP/ChAT/AChE-positive cells surrounded by SP-positive fibres have different functions in motoric nervous system than the CGRP-negative ChAT/AChE-positive cells, which are surrounded by ENK-immunoreactive fibres.     

Transport of Muscarinic Cholinergic Marker Protein Activities in Regenerating Sciatic Nerve of Rat

The transport characteristics of choline acetyltransferase (ChAT; EC 2.3.1.6), acetylcholinesterase (AChE; EC 3.1.1.7), and the muscarinic acetylcholine receptors (mAChR) were studied in perineurally sutured, regenerating rat sciatic nerve. At different times after repair, the sciatic nerve was ligated for 24 h, and the activities of the cholinergic marker proteins, as well as the binding capacity, were measured proximally and distally from the ligature. The number of bidirectionally transported receptors increased linearly up to 5 months postoperatively (6.1-33.6% and 5.6-25.6% of the control level proximal and distal to the ligature, respectively). The quantity of anterogradely transported ChAT reached a plateau 3 months postoperatively (74.9% of the control level), whereas the retrogradely transported enzyme was then only 34.7% of the control value. The activity of AChE increased linearly during nerve regeneration, and exceeded the control level after 4 months (121.0% and 63.7% proximally and distally, respectively). The data indicate that the altered bidirectional transport of cholinergic marker proteins may be monitored quantitatively during nerve regeneration. This method might be suitable for studies of the nerve regeneration process.     

Protein composition and synthesis in the adult mouse spinal cord

Propepties of spinal cord proteins were studied in adult mice subjected to unilateral crush or electrical stimulation of sciatic nerve. The protein composition of spinal tissue was determined using SDS-polyacrylamide gel electrophoresis coupled with subcellular fractionation. Comparisons of mouse spinal cord and brain revealed similarities in the types but differences in the concentrations of myelin associated proteins, nuclear histones and other proteins. Comparisons with sciatic nerve proteins demonstrated differences in types of proteins but similarities in the concentration of myelin proteins and nuclear histones. The short term (<2 hrs.) incorporation of radioactive amino acids into spinal cord proteins revealed heterogeneous rates of incorporation. Neither nerve crush six days prior to testing nor sciatic nerve stimulation had a significant effect on the protein composition or amino acid incorporation rates of spinal cord tissue. These observations suggest that known differences in spinal cord function following alterations in nerve input may be dependent upon different mechanisms than have been found in the brain.     

Partial cloning and expression of mRNA coding choline acetyltransferase in the spinal cord of the goldfish, Carassius auratus

Choline acetyltransferase (ChAT, EC 2.3.1.6) synthesizes a neurotransmitter, acetylcholine in cholinergic neurons. ChAT is considered to be the most specific marker for cholinergic neurons. To obtain a better marker of the neurons, as the first step, we isolated a partial ChAT cDNA from the goldfish (Carassius auratus) brain by RT-PCR methods. The partial cDNA of the goldfish ChAT was composed of 718 nucleotides. The amino acid sequence of the goldfish ChAT is approximately 70% identical to those of mammalian and chicken ChAT. Northern blot analysis demonstrated that ChAT mRNA was expressed in the brain and the spinal cord of the goldfish, and much abundant in the spinal cord. In the spinal cord of the goldfish, ChAT-positive neurons were detected mainly in the ventral horn by in situ hybridization. In addition, fluorescence in situ hybridization combined with a retrograde labeling by using True Blue demonstrated ChAT mRNA positive neurons were exactly motoneurons. In the cord, putative presynaptic sympathetic neurons were also labeled.     

Sciatic Nerve Transection Modulates Oxidative Parameters in Spinal and Supraspinal Regions

Neuropathic pain is a very common dysfunction caused by several types of nerve injury. This condition leads to a variety of pathological changes in central nervous system regions related to pain transmission. It has been demonstrated that nociception is modulated by reactive oxidative species and treatments with antioxidant compounds produce antinociceptive effects. Thus, the aim of the present study was to investigate oxidative parameters in spinal and supraspinal regions following sciatic nerve transection (SNT). In behavioral assessments, animals showed mechanical allodynia and a significant functional impairment following SNT, measured by von Frey hairs test and sciatic functional index, respectively. Superoxide dismutase activity was increased 3 and 7 days following SNT in cerebral cortex and brainstem. Catalase activity was also increased in cerebral cortex 3 days after SNT. Ascorbic acid levels were decreased 7 days in the spinal cord only in SNT group. We also showed an increase in lipid peroxidation in cerebral cortex and brainstem 3 days after surgery in SNT and sham groups. These results showed that supraspinal regions also exhibit changes in antioxidant activity after SNT and demonstrate an intricate relationship among antioxidant defenses in different regions of the neuro axis related to pain transmission.     

MYELIN SYNTHESIS IN VITRO: A COMPARATIVE STUDY OF CENTRAL AND PERIPHERAL NERVOUS TISSUE

Abstract— Brain, spinal cord and sciatic nerve from rats at different ages were incubated for 2 h in a medium containing [¹⁴C]acetate and [¹⁴C]leucine as the precursors for synthesis of lipids and proteins. Myelin was purified from the incubated tissues and the specific and total radioactivites of myelin lipids and protein were determined. The uptake of radioactive precursors decreased with increasing age up to 6 months of postnatal age, the decrease following the same pattern for the three types of myelin. After age 6 months the uptake of the protein and lipid precursors reached a plateau that persisted up to 18 months, the oldest postnatal age studied. The amount of myelin isolated and the total myelin lipids extracted from both the central and peripheral nervous systems increased continuously from age 25 days to 18 months after birth. Consequently we suggest that myelination is a process that continues during the whole life of the rat.
The metabolic activity of peripheral nerve myelin was higher than myelin from the CNS at all ages studied. Although myelination in the sciatic nerve begins before that in brain and spinal cord, the three types of myelin apparently reach maturity at the same age. Lecithin exhibited the highest metabolic activity of the individual myelin lipids at all ages in both the central and peripheral nervous system. The metabolic activity of cholesterol in myelin from the 25-day-old rats was similar to that of lecithin but decreased to very low levels in myelin from the 18-month-old rats.