Neuroprotective action of melatonin on neonatal rat motoneurons after sciatic nerve transection

Effect of mesenchymal stem cells and melatonin on experimentally induced peripheral nerve injury in rats

Injury of a peripheral nerve (PNI) leads to both ischemic and inflammatory alterations. Sciatic nerve injury (SNI) represents the most widely used model for PNI. Mesenchymal stem cell-based therapy (MSCs) has convenient properties on PNI by stimulating the nerve regeneration. Melatonin has cytoprotective activity. The neuroprotective characteristics of MSCs and melatonin separately or in combination remain a knowledge need. In the rats-challenged SNI, therapeutic roles of intralesional MSCs and intraperitoneal melatonin injections were evaluated by functional assessment of peripheral nerve regeneration by walking track analysis involving sciatic function index (SFI) and two electrophysiological tests, electromyography and nerve conduction velocity, as well as measurement of antioxidant markers in serum, total antioxidant capacity (TAC) and malondialdehyde, and mRNA expression of brain derived neurotrophic factor (BDNF) in nerve tissues in addition to the histopathological evaluation of nerve tissue. Both individual and combination therapy with MSCs and melatonin therapies could effectively ameliorate this SNI and promote its regeneration as evidenced by improving the SFI and two electrophysiological tests and remarkable elevation of TAC with decline in lipid peroxidation and upregulation of BDNF levels. All of these led to functional improvement of the damaged nerve tissues and good recovery of the histopathological sections of sciatic nerve tissues suggesting multifactorial synergistic approach of the concurrent usage of melatonin and MSCs in PNI. The combination regimen has the most synergistic neuro-beneficial effects in PNI that should be used as therapeutic option in patients with PNI to boost their quality of life.

The potential protective effects of melatonin and omega-3 on the male rat optic nerve exposed to 900 MHz electromagnetic radiation during the prenatal period

BACKGROUND

Due to children and adolescents' widespread use of electronic devices, researchers have focused on pre-and early postnatal electromagnetic field (EMF) exposure. However, little is known about the effects of EMF exposure on the optic nerve. The aim of study was to investigate the changes occurring in the optic nerve and the protective effects of melatonin (mel) and omega 3 (ω-3) in rats.

METHODS

Thirty-five pregnant rats were divided into seven groups, Cont, Sham, EMF, EMF + melatonin (EMF + Mel), EMF + ω3, Mel, and ω3. The EMF groups were exposed to 900 megahertz (MHz) EMF daily for two hours during pregnancy. After the experiment, the right optic nerve of each offspring rat was removed and fixed in glutaraldehyde. Thin and semi-thin sections were taken for electron microscopic and stereological analyses. Myelinated axon numbers, myelin sheath thicknesses, and axonal areas were estimated using stereological methods.

RESULTS

The groups had no significant differences regarding mean numbers of axons, mean axonal areas, or mean myelin sheath thicknesses (p > 0.05). Histological observations revealed impaired lamellae in the myelin sheath of most axons, and vacuolization was frequently observed between the myelin sheath and axon in the EMF-exposed group. The Mel and ω-3-treated EMF groups exhibited well-preserved myelinated nerve fibers and intact astrocytes and oligodendrocytes.

CONCLUSIONS

At the ultrastructural level, Mel and ω3 exhibits a neuroprotective effect on the optic nerve exposed to prenatal EMF. The protective effects of these antioxidants on oligodendrocytes, which play an essential role in myelin formation in the central nervous system, now require detailed investigation.

Neuroprotection by melatonin against acrylamide-induced brain damage in pinealectomized rats

The current study aimed to evaluate the neuroprotective effect of exogenous melatonin against acrylamide (ACR)-induced oxidative stress and inflammatory and apoptotic responses in the brain tissues in pinealectomized rats (PINX). ACR is a toxic chemical carcinogen that occurs owing to the preparation of carbohydrate-rich foods at high temperatures or other thermal processes. The rats who underwent pinealectomy and sham pinealectomy were exposed to ACR (25 mg/kg b.w., orally) alone or with exogenous melatonin (10 mg/kg b.w., i.p.) for 21 consecutive days. Alterations of brain oxidant/antioxidant status, dopamine (DA), Brain-Derived Neurotropic Factor (BDNF) inflammatory mediator and apoptosis during exposure to ACR in pinealectomized rats were more than without pinealectomized rats. Histopathological changes were more in brain tissue of pinealectomized rats after ACR administration. Exogenous melatonin treatment in ACR -exposed rats following pinealectomy increased the activities of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) and improved brain total antioxidant status (TAS) compared to PINX+ACR. Moreover, melatonin suppressed lipid peroxidation, inflammatory pathways and apoptosis in ACR-intoxicated brain tissues. In addition, after exposure to ACR on pinealectomized rats, melatonin treatment ameliorated BDNF and DA levels in brain tissues. Furthermore, exogenous melatonin intervention in ACR-intoxicated rats significantly rescued the architecture of neuronal tissues. In summary, the present study, for the first time, suggested that exogenous melatonin treatment could reduce oxidative damage by increasing the activities of antioxidant enzymes, inhibiting lipid peroxidation and inflammation, and improving histopathological alterations in the brain tissue of pinealectomized rats after ACR administration.

Electrophysiological, functional and histopathological assessments of high dose melatonin on regeneration after blunt sciatic nerve injury

The aim of this study was to determine the curative effects of high-dose (100 mg/kg) melatonin on peripheral nerve injury. Forty male Wistar albino rats were randomized into four groups as sham, vehicle, melatonin, and ischemia and their right sciatic nerves were exposed. The process was terminated in the sham group. In the other groups, nerve injury was induced by clip compression. The vehicle group was intraperitoneally administered ethanol 0.1 cc (melatonin solvent), while the melatonin group was intraperitoneally administered a single dose of melatonin (100 mg/kg). Following the surgery, sciatic nerve functional index (SFI) was measured using walking track analysis on days 7, 14, and 21, and latency, amplitude, and muscle action potentials (MAP) field values were measured using electroneuromyography (ENMG) on day 21. Histopathologically, edema, axonal degeneration, myelin damage, and inflammatory response were evaluated in all groups. SFI values were noted to be statistically significantly different among the vehicle, melatonin, and ischemia groups, and the melatonin group showed a faster recovery. In the ENMG evaluations, higher amplitude and field values in the melatonin group indicated that melatonin accelerated peripheral nerve recovery. Histopathologically, although fibers with loss of myelin were identified in the melatonin group, the myelin sheath was preserved in general and the axonal structure was noted to be normal. A single injection of high-dose melatonin was found to preserve myelin sheath, prevent axonal loss, and accelerate functional recovery during the nerve regeneration in peripheral nerve injury.

The Neuroprotective Effects of Melatonin: Possible Role in the Pathophysiology of Neuropsychiatric Disease

Melatonin is a hormone that is secreted by the pineal gland. To date, melatonin is known to regulate the sleep cycle by controlling the circadian rhythm. However, recent advances in neuroscience and molecular biology have led to the discovery of new actions and effects of melatonin. In recent studies, melatonin was shown to have antioxidant activity and, possibly, to affect the development of Alzheimer's disease (AD). In addition, melatonin has neuroprotective effects and affects neuroplasticity, thus indicating potential antidepressant properties. In the present review, the new functions of melatonin are summarized and a therapeutic target for the development of new drugs based on the mechanism of action of melatonin is proposed.

Pharmacological Effects of Melatonin as Neuroprotectant in Rodent Model: A Review on the Current Biological Evidence

The progressive loss of structure and functions of neurons, including neuronal death, is one of the main factors leading to poor quality of life. Promotion of functional recovery of neuron after injury is a great challenge in neuroregenerative studies. Melatonin, a hormone is secreted by pineal gland and has antioxidative, anti-inflammatory, and anti-apoptotic properties. Besides that, melatonin has high cell permeability and is able to cross the blood-brain barrier. Apart from that, there are no reported side effects associated with long-term usage of melatonin at both physiological and pharmacological doses. Thus, in this review article, we summarize the pharmacological effects of melatonin as neuroprotectant in central nervous system injury, ischemic-reperfusion injury, optic nerve injury, peripheral nerve injury, neurotmesis, axonotmesis, scar formation, cell degeneration, and apoptosis in rodent models.

Melatonin treatment in fetal and neonatal diseases

This literature review aims to address the main scientific findings on oxidative stress activity in different gestational disorders, as well as the function and application of melatonin in the treatment of fetal and neonatal changes. Oxidative stress has been associated with the etiopathogenesis of recurrent miscarriages, preeclampsia, intrauterine growth restriction, and stillbirth. Both, the exacerbated consumption of the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase, and the increased synthesis of reactive oxygen species, such as superoxide, peroxynitrite, and hydrogen peroxide, induce phospholipid peroxidation and endothelial dysfunction, impaired invasion and death of trophoblast cells, impaired decidualization, and remodeling of maternal spiral arteries. It has been postulated that melatonin induces specific biochemical responses that regulate cell proliferation in fetuses, and that its antioxidant action promotes bioavailability of nitric oxide and, thus, placental perfusion and also fetal nutrition and oxygenation. Therefore, the therapeutic action of melatonin has been the subject of major studies that aim to minimize or prevent different injuries affecting this pediatric age group, such as intrauterine growth restriction, encephalopathy, chronic lung diseases, retinopathy of prematurity Conclusion: the results antioxidant and indicate that melatonin is an important therapy for the clinical treatment of these diseases.

The multiple functions of melatonin in regenerative medicine

Melatonin research has been experiencing hyper growth in the last two decades; this relates to its numerous physiological functions including anti-inflammation, oncostasis, circadian and endocrine rhythm regulation, and its potent antioxidant activity. Recently, a large number of studies have focused on the role of melatonin in the regeneration of cells or tissues after their partial loss. In this review, we discuss the recent findings on the molecular involvement of melatonin in the regeneration of various tissues including the nervous system, liver, bone, kidney, bladder, skin, and muscle, among others.

Acute dose of melatonin via Nrf2 dependently prevents acute ethanol-induced neurotoxicity in the developing rodent brain

BACKGROUND

Melatonin is a well-known potent endogenous antioxidant pharmacological agent with significant neuroprotective actions. Here in the current study, we explored the nuclear factor erythroid 2-related factor 2 (Nrf2) gene-dependent antioxidant mechanism underlying the neuroprotective effects of the acute melatonin against acute ethanol-induced elevated reactive oxygen species (ROS)-mediated neuroinflammation and neurodegeneration in the developing rodent brain.

METHODS

In vivo rat pups were co-treated with a single dose of acute ethanol (5 g/kg, subcutaneous (S.C.)) and a single dose of acute melatonin (20 mg/kg, intraperitoneal (I.P.)). Four hours after a single S.C. and I.P. injections, all of the rat pups were sacrificed for further biochemical (Western blotting, ROS- assay, LPO-assay, and immunohistochemical) analyses. In order to corroborate the in vivo results, we used the in vitro murine-hippocampal HT22 and microglial BV2 cells, which were subjected to knockdown with small interfering RNA (siRNA) of Nrf2 genes and exposed with melatonin (100 μM) and ethanol (100 mM) and proceed for further biochemical analyses.

RESULTS

Our biochemical, immunohistochemical, and immunofluorescence results demonstrate that acute melatonin significantly upregulated the master endogenous antioxidant Nrf2 and heme oxygenase-1, consequently reversing the acute ethanol-induced elevated ROS and oxidative stress in the developing rodent brain, and in the murine-hippocampal HT22 and microglial BV2 cells. In addition, acute melatonin subsequently reduced the activated MAPK-p-P38-JNK pathways and attenuated neuroinflammation by decreasing the expression of activated gliosis and downregulated the p-NF-K-B/p-IKKβ pathway and decreased the expression levels of other inflammatory markers in the developing rodent brain and BV2 cells. Of note, melatonin acted through the Nrf2-dependent mechanism to attenuate neuronal apoptosis in the postnatal rodent brain and HT22 cells. Immunohistofluorescence results also showed that melatonin prevented ethanol-induced neurodegeneration in the developing rodent brain. The in vitro results indicated that melatonin induced neuroprotection via Nrf2-dependent manner and reduced ethanol-induced neurotoxicity.

CONCLUSIONS

The pleiotropic and potent neuroprotective antioxidant characteristics of melatonin, together with our in vivo and in vitro findings, suppose that acute melatonin could be beneficial to prevent and combat the acute ethanol-induced neurotoxic effects, such as elevated ROS, neuroinflammation, and neurodegeneration in the developing rodent brain.

Useful Effects of Melatonin in Peripheral Nerve Injury and Development of the Nervous System

This review summarizes the role of melatonin (MLT) in defense against toxic-free radicals and its novel effects in the development of the nervous system, and the effect of endogenously produced and exogenously administered MLT in reducing the degree of tissue and nerve injuries. MLT was recently reported to be an effective free radical scavenger and antioxidant. Since endogenous MLT levels fall significantly in senility, these findings imply that the loss of this antioxidant could contribute to the incidence or severity of some age-related neurodegenerative diseases. Considering the high efficacy of MLT in overcoming much of the injury not only to the peripheral nerve but also to other organs, clinical trials for this purpose should be seriously considered.

Prophylactic treatment with melatonin before recurrent neonatal seizures: Effects on long-term neurobehavioral changes and the underlying expression of metabolism-related genes in rat hippocampus and cerebral cortex

Although it has been suggested that the protective effect of melatonin against seizure-induced neurotoxicity involves inhibition of neuronal lipid peroxidation, current data concerning the exact molecular mechanism are still limited. This study was undertaken to investigate the changes in neurobehavioral, cognitive and lipid metabolism-related gene expressions in both hippocampus and cerebral cortex of rats subjected to recurrent neonatal seizures, and the effects of melatonin treatment before seizure (55mg/kg, 1mg/ml). 6-day-old (P6) SD rats were randomly divided into four groups of control (CONT, the same below), melatonin treated control (Mel), recurrent neonatal seizure (RS) and melatonin and RS combination treatment (Mel+RS). Neurological behavioral parameters of brain damage (plane righting reflex, negative geotaxis reaction reflex, Cliff avoidance reflex, forelimb suspension reflex) were observed on P31. Morris water maze test was performed during P29-P35. Then the protein levels of ACAT1, Cathepsin-E and Ca(2+)/calmodulin-dependent protein kinase II (CAMK II) in hippocampus and cerebral cortex were detected by western blot method. As expected, RS group showed a significant delay or reduce of the four reflexes, as well as bad performance in the Morris water maze test. Flurothyl-induced neurobehavioral toxicology was blocked by pre-treatment with melatonin. In parallel with these behavioral changes, gene expression by western blot method demonstrated that rats pretreated with melatonin (Mel+RS) showed a significant down-regulated expression of ACAT-1, Cathepsin-E and up-regulated CAMK II in hippocampus and cerebral cortex when compared with RS group. Our findings provide support for ACAT-1/Cathepsin-E as well as CaMK II being potential targets for the treatment of neonatal seizure-induced brain damage by melatonin.

Evaluation of neuroprotection by melatonin against adverse effects of prenatal exposure to a nonsteroidal anti-inflammatory drug during peripheral nerve development

The potential ability of melatonin to protect against impairment of the fetal peripheral nerve system due to maternal consumption of diclofenac sodium (DS) was investigated. Eighty-four pregnant rats were divided into seven groups: control (CONT), saline administered (PS), DS administered (DS), DS with low-dose melatonin administered (DS+MLT10), DS with high-dose melatonin administered (DS+MLT50), low-dose melatonin administered (MLT10), and high-dose melatonin administered (MLT50). After the pregnancy, six male newborn rats from each group were sacrificed at 4 and 20 weeks of age. Their right sciatic nerves were harvested, and nerve fibers were evaluated using stereological techniques. Mean numbers of myelinated axons, axon cross-section areas and the mean thickness of the myelin sheet were estimated. Four-week-old prenatally DS-exposed rats had significantly fewer axons, a smaller myelinated axonal area, and a thinner myelin sheath compared to CONT group (p<0.05). Although melatonin at both doses significantly increased axon numbers, only a high dose of melatonin increased the diameter of those axons (p<0.05). At 20-weeks of age, myelinated axon number in the DS group was not only significantly lower than all other groups (p<0.05) but also the cross-sectional area of these axons was smaller than all other groups (p<0.05). There were no differences between the groups regarding the mean thickness of the myelin sheet. The current study indicates that prenatal exposure to DS decreases the number and the diameter of sciatic nerve axons and that melatonin prophylaxis can prevent these effects.

Application of topical pharmacological agents at the site of peripheral nerve injury and methods used for evaluating the success of the regenerative process

Traumatic injuries of the peripheral nerves are very common. Surgical repair of the damaged nerve is often complicated by scar tissue formation around the damaged nerve itself. The main objective of this study is to present the recent data from animal experimental studies where pharmacological topical agents are used at the site of peripheral nerve repair. Some of the most commonly topical agents used are tacrolimus (FK506), hyaluronic acid and its derivatives, and melatonin, whereas methylprednisolone and vitamin B12 have been used less. These studies have shown that the abovementioned substances have neuroprotective and neuroregenerative properties though different mechanisms. The successes of the regenerative process of the nerve repair in experimental research, using topical agents, can be evaluated using variety of methods such as morphological, electrophysiologic, and functional evaluation. However, most authors agree that despite good microsurgical repair and topical application of these substances, full regeneration and functional recovery of the nerve injured are almost never achieved.

Neuroprotective effect of tempol (4 hydroxy-tempo) on neuronal death induced by sciatic nerve transection in neonatal rats

Peripheral nerve injury in newborn rats triggers extensive neuronal death within the spinal cord. Because most neurodegeneration is related to oxidative stress and apoptosis, the use of antioxidants may be of therapeutic interest. Tempol is promising because of its ability to chelate reactive oxygen species and to minimize or even prevent tissue damage. Here, we evaluated neuroprotective effects of tempol following neonatal sciatic nerve transection. Two-day-old pups underwent sciatic nerve axotomy followed by tempol (12, 24 and 48 mg/kg) treatment (i.p.) at 10 min, 6 h, and every 24 h up to 1 week after injury. The rats were then killed for lumbar intumescence analysis. Nissl staining, TUNEL, synaptophysin immunolabeling and qRT-PCR (Caspase 3, Bax and Bcl2) were carried out. The results indicated that tempol treatment, at 24 mg/kg, increased up to 21% spinal cord motoneuron survival (p<0.001), also preserving pre-synaptic terminals in the neuropile. Likewise, the TUNEL-positive cell number decreased in tempol-treated animals. qRT-PCR results indicated differential increase in Caspase 3 (3-fold), Bax (13-fold) and Bcl2 (28-fold) gene expression, after 12 h following axotomy and tempol treatment. In conclusion, tempol administration has proven to be neuroprotective after neonatal nerve injury, leading to improved motoneuron survival, synapse preservation and minimizing apoptosis.

Does circadian rhythm disruption induced by light-at-night has beneficial effect of melatonin on sciatic nerve injury?

Melatonin stimulates peripheral nerve regeneration. However, the precise effect of Melatonin on nerve repair in dark period have not been clarified. The aim of the present study was to investigate the effect of melatonin on sciatic nerve injury after melatonin was given to rats in the morning or evening by means of combined analysis. This is the first study to investigate the influence of melatonin on sciatic nerve in cut injury two different times of the day. 60 adult female Wistar rats were divided into 4 groups: control (Group 1), sham-operated (Group 2), sciatic nerve cut+melatonin treatment in light (Group 3), sciatic nerve cut+melatonin treatment in dark (Group 4). Melatonin was administered intraperitoneally at dose of 50 mg/kg/day for six weeks. Recovery of function was analyzed by structural (biochemical properties of the antioxidant levels and ultrastructural analysis) and functional analyses (Sciatic function index, pinch test). The data demonstrated beneficial effect of melatonin in light period. However significant beneficial effect of melatonin was detected on the recovery of the cut sciatic nerve in dark period. Melatonin treatment was unable to influence on the recovery of the cut sciatic nerve in dark period. This means that the effect of melatonin the recovery of the cut injured sciatic nerve depends on the time of treatment may be attributed to its circadian rhythm.

Effect of melatonin on the functional recovery from experimental traumatic compression of the spinal cord

Spinal cord injury is an extremely severe condition with no available effective therapies. We examined the effect of melatonin on traumatic compression of the spinal cord. Sixty male adult Wistar rats were divided into three groups: sham-operated animals and animals with 35 and 50% spinal cord compression with a polycarbonate rod spacer. Each group was divided into two subgroups, each receiving an injection of vehicle or melatonin (2.5 mg/kg, intraperitoneal) 5 min prior to and 1, 2, 3, and 4 h after injury. Functional recovery was monitored weekly by the open-field test, the Basso, Beattie and Bresnahan locomotor scale and the inclined plane test. Histological changes of the spinal cord were examined 35 days after injury. Motor scores were progressively lower as spacer size increased according to the motor scale and inclined plane test evaluation at all times of assessment. The results of the two tests were correlated. The open-field test presented similar results with a less pronounced difference between the 35 and 50% compression groups. The injured groups presented functional recovery that was more evident in the first and second weeks. Animals receiving melatonin treatment presented more pronounced functional recovery than vehicle-treated animals as measured by the motor scale or inclined plane. NADPH-d histochemistry revealed integrity of the spinal cord thoracic segment in sham-operated animals and confirmed the severity of the lesion after spinal cord narrowing. The results obtained after experimental compression of the spinal cord support the hypothesis that melatonin may be considered for use in clinical practice because of its protective effect on the secondary wave of neuronal death following the primary wave after spinal cord injury.

Comparison of the beneficial effect of melatonin on recovery after cut and crush sciatic nerve injury: a combined study using functional, electrophysiological, biochemical, and electron microscopic analyses

PURPOSE

Following tissue injury, melatonin is known to reduce detrimental effects of free radicals by stimulating antioxidant enzymes and also to inhibit posttraumatic polymorphonuclear infiltration. Beneficial effects after peripheral nerve injury have been suggested, but not studied in detail. Therefore, we aimed to elucidate the effects of melatonin on the recovery of the lesioned rat sciatic nerve by means of combined analysis.

METHODS

A total number of 90 rats were randomly distributed into six groups: control (group 1), sham-operated (group 2), sciatic nerve cut (group 3), sciatic nerve cut + melatonin treatment (group 4), sciatic nerve crush (group 5), and sciatic nerve crush + melatonin treatment (group 6). Melatonin was administered intraperitoneally at a dose of 50 mg/kg/day for 6 weeks. Recovery of function was analyzed by assessment of the sciatic functional index based on walking track analysis, somatosensory evoked potentials, biochemical quantification of malondialdehyde, antioxidant enzymes levels, and ultrastructural analysis.

RESULTS

Our data showed the beneficial effect of melatonin on sciatic nerve recovery. Rats treated with melatonin demonstrated better structural preservation of the myelin sheaths compared to the nontreated group. The biochemical analysis confirmed the beneficial effects of melatonin displaying lower lipid peroxidation and higher superoxide dismutase, catalase, and glutathione peroxidase activities in sciatic nerve samples in comparison to nontreated groups.

CONCLUSIONS

The beneficial effects of melatonin administration on the recovery of the cut and crush injured sciatic nerve may be attributed to its antioxidant properties. Based on these investigations, we think that our data would be helpful for clinicians who deal with peripheral nerve injuries.

JAK2 inhibition is neuroprotective and reduces astrogliosis after quinolinic acid striatal lesion in adult mice

Quinolinic acid (QA) striatal lesion in rodents induces neuronal death, astrogliosis and migration of neuroblasts from subventricular zone to damaged striatum. These phenomena occur in some human neurodegenerative illnesses, but the underlying mechanisms are unknown. We investigated the effect of AG490, a Janus-kinase 2 (JAK2) inhibitor, on astrogliosis, neuronal loss and neurogenesis in the striatum of adult mice after unilateral infusion of QA (30 nmol). Animals were given subcutaneous injections of AG490 (10 mg/kg) or vehicle immediately after lesion and then once daily for six days. Brain sections were used for neuronal stereological quantification, immunohistochemical and Western Blotting analyses for GFAP and doublecortin, markers of astrocytes and neuroblasts, respectively. The total area of doublecortin-positive cells (ADPC) and the number of neurons (NN) in the lesioned (L) and contralateral (CL) sides were evaluated. Neurogenesis index (NI=ADPC(L)/ADPC(CL)) and neuronal ratio (NR=NN(L)/NN(CL)) were calculated. After QA administration, blotting for GFAP showed an ipsilateral decrease of 19% in AG490- vs vehicle-treated animals. NR was 25% higher in mice given AG490 vs controls given vehicle. NI showed a decrease of 21% in AG490- vs vehicle-treated mice. Our results indicate that JAK2 inhibition reduces QA lesion and suggest that astrogliosis may impair neuronal survival in this model.

Comparison of melatonin and oxytocin in the prevention of critical illness polyneuropathy in rats with experimentally induced sepsis

BACKGROUND

Critical illness polyneuropathy is an acute neuromuscular disorder of critically ill patients and is characterized by limb and respiratory muscle weakness. The purpose of the study was to evaluate the neuroprotective effects of melatonin (MEL) and oxytocin (OT) on the early stage of sepsis by recording compound muscle action potentials and measuring plasma tumor necrosis factor (TNF)-α levels, lipid peroxidation (malondialdehyde; MDA), and total antioxidant capacity.

MATERIALS AND METHODS

One hundred adult male Sprague-Dawley rats were included in the study. The cecal ligation and puncture (CLP) procedure was performed to induce the sepsis model. MEL (10, 20, and 40 mg/kg), OT (0.4, 0.8, and 1.6 mg/kg), and a combination of MEL (20 mg/kg) and OT (0.8 mg/kg) were administered intraperitoneally in the first hour of surgery. Electromyography (EMG) studies were achieved 24 h after CLP surgery and then blood samples were collected for biochemical measurements.

RESULTS

EMG findings revealed that compound muscle action potential amplitude was significantly decreased and distal latency was prolonged in the CLP group compared with the sham group (P < 0.05 and P < 0.0005). Moreover, the animals that received CLP surgery showed significantly higher TNF-α and MDA levels and lower total antioxidant capacity values than the sham group. The administration of MEL and OT to rats significantly abolished the EMG alterations and suppressed oxidative stress and TNF-α release in CLP-induced rats.

CONCLUSIONS

The inflammatory processes and imbalance in oxidative/antioxidative status play important roles in the pathogenesis of critical illness polyneuropathy. We suggest that both oxytocin and melatonin may have beneficial effects against sepsis-induced polyneuropathy in critical illness.

Neonatal exposure to antiepileptic drugs disrupts striatal synaptic development

OBJECTIVE

Drug exposure during critical periods of brain development may adversely affect nervous system function, posing a challenge for treating infants. This is of particular concern for treating neonatal seizures, as early life exposure to drugs such as phenobarbital is associated with adverse neurological outcomes in patients and induction of neuronal apoptosis in animal models. The functional significance of the preclinical neurotoxicity has been questioned due to the absence of evidence for functional impairment associated with drug-induced developmental apoptosis.

METHODS

We used patch-clamp recordings to examine functional synaptic maturation in striatal medium spiny neurons from neonatal rats exposed to antiepileptic drugs with proapoptotic action (phenobarbital, phenytoin, lamotrigine) and without proapoptotic action (levetiracetam). Phenobarbital-exposed rats were also assessed for reversal learning at weaning.

RESULTS

Recordings from control animals revealed increased inhibitory and excitatory synaptic connectivity between postnatal day (P)10 and P18. This maturation was absent in rats exposed at P7 to a single dose of phenobarbital, phenytoin, or lamotrigine. Additionally, phenobarbital exposure impaired striatal-mediated behavior on P25. Neuroprotective pretreatment with melatonin, which prevents drug-induced neurodevelopmental apoptosis, prevented the drug-induced disruption in maturation. Levetiracetam was found not to disrupt synaptic development.

INTERPRETATION

Our results provide the first evidence that exposure to antiepileptic drugs during a sensitive postnatal period impairs physiological maturation of synapses in neurons that survive the initial drug insult. These findings suggest a mechanism by which early life exposure to antiepileptic drugs can impact cognitive and behavioral outcomes, underscoring the need to identify therapies that control seizures without compromising synaptic maturation.

Evaluating motor neuron death in neonatal rats subjected to sciatic nerve lesion

Neonatal sciatic nerve lesion is a useful experimental model for the study of neuronal cell death. Sciatic nerve transection or crush is the most frequently used approach to evaluate motoneuron loss in the lumbar enlargement of the spinal cord. Here we describe and illustrate the surgical procedures performed in our laboratory to assess motoneuron cell death and the related cellular mechanisms.

Protective effect of GCSB-5, an herbal preparation, against peripheral nerve injury in rats

AIM OF THE STUDY

GCSB-5 (traditional name: Chungpa-Juhn), an herbal medicine composed of 6 crude herbs (Saposhnikovia divaricata Schiskin, Achyranthis bidentata Blume, Acanthopanax sessiliflorum Seem, Cibotium baromets J. Smith, Glycine max Meriill, and Eucommia ulmoides Oliver), has been widely used in Asia for treatment of neuropathic and inflammatory diseases. This study investigated the protective effect of GCSB-5 against peripheral nerve injury in vitro and in vivo.

MATERIALS AND METHODS

After left sciatic nerve transection, rats received oral administration of GCSB-5 (30, 100, 300, and 600 mg/kg), or saline (vehicle), respectively, once daily for 8 weeks. Motor functional recovery and axonal nerve regeneration were evaluated by measurement of sciatic functional index (SFI), sensory regeneration distance, and gastrocnemius muscle mass ratio. The myelinated axon number was counted by morphometric analysis. In the in vitro study, the effects of GCSB-5 on H(2)O(2)-induced oxidative damage in SH-SY5Y cells were investigated by measurement of cell viability, production of reactive oxygen species (ROS), lipid peroxidation, release of lactate dehydrogenease (LDH), and cellular glutathione contents. Neurite outgrowth was also determined.

RESULTS

After 8 weeks of nerve transection, SFI, regeneration distance, and gastrocnemius muscle mass ratio and myelinated axon number showed a significant decrease and these decreases were attenuated by GCSB-5. GCSB-5 significantly inhibited H(2)O(2)-induced cell death and oxidative stress, as evidenced by decreases in production of ROS and lipid peroxidation and release of LDH, and by increase in total GSH content.

CONCLUSIONS

The neuroprotective effect afforded by GCSB-5 is due in part to reduced oxidative stress.

Electrophysiological and theoretical analysis of melatonin in peripheral nerve crush injury

Electrophysiological and theoretical studies have been performed to investigate peripheral nerve injuries and nerve regeneration. The aim of this work is to evaluate the effect of melatonin functionally and electrophysiologically on peripheral nerve crush injury. Adult male Wistar rats (n=32, 200+/-50 g) were randomly allocated into four groups. Sciatic crush was constituted on left sciatic nerves. Treatment groups received intraperitoneal melatonin at doses of 5 and 20mg/kg for 21 days. Functional nerve recovery was evaluated using sciatic functional index (SFI) every week during the experiment. In vivo electrophysiological measurements were performed at the end of the treatment. The electrophysiological data were also analyzed by wavelet analysis. Melatonin treatments increased the SFI values in the injured sciatic nerves. In vivo electrophysiological measurements showed that melatonin increased the conduction velocities and also decreased the latency values. The wavelet analysis showed that melatonin treatment reduced the densities of high frequency components of compound muscle action potential (CMAP). These results suggest that melatonin application is a promising strategy for the treatment of peripheral nerve crush injuries. Furthermore, analysis of EMG data with wavelet methods seems to give more reliable results to evaluate the nerve recovery.

Stereological analysis of sciatic nerve in chickens following neonatal pinealectomy: an experimental study

Background

Although the injury to the peripheral nervous system is a common clinical problem, understanding of the role of melatonin in nerve degeneration and regeneration is incomplete.

Methods

The current study investigated the effects of neonatal pinealectomy on the sciatic nerve microarchitecture in the chicken. The chickens were divided into two equal groups: unpinealectomized controls and pinealectomized chickens. At the end of the study, biochemical examination of 10 sciatic nerve samples from both groups was performed and a quantitative stereological evaluation of 10 animals in each group was performed. The results were compared using Mann-Whitney test.

Results

In this study, the results of axon number and thickness of the myelin sheath of a nerve fiber in newly hatched pinealectomy group were higher than those in control group. Similarly, surgical pinealectomy group had significantly larger axonal cross-sectional area than the control group (p < 0.05). In addition, the average hydroxyproline content of the nerve tissue in neonatal pinealectomy group was higher than those found in control group. Our results suggest that melatonin may play a role on the morphologic features of the peripheral nerve tissue and that melatonin deficiency might be a pathophysiological mechanism in some degenerative diseases of peripheral nerves. The changes demonstrated by quantitative morphometric methods and biochemical analysis has been interpreted as a reflection of the effects of melatonin upon nerve tissue.

Conclusion

In the light of these results from present animal study, changes in sciatic nerve morphometry may be indicative of neuroprotective feature of melatonin, but this suggestion need to be validated in the human setting.

Effects of systemic administration of ciliary neurotrophic factor on Bax and Bcl-2 proteins in the lumbar spinal cord of neonatal rats after sciatic nerve transection

Ciliary neurotrophic factor (CNTF) is a cytokine that plays a neuroprotective role in relation to axotomized motoneurons. We determined the effect of daily subcutaneous doses of CNTF (1.2 microg/g for 5 days; N = 13) or PBS (N = 13) on the levels of mRNA for Bcl-2 and Bax, as well as the expression and inter-association of Bcl-2 and Bax proteins, and the survival of motoneurons in the spinal cord lumbar enlargement of 2-day-old Wistar rats after sciatic nerve transection. Five days after transection, the effects were evaluated on histological and molecular levels using Nissl staining, immunoprecipitation, Western blot analysis, and reverse transcriptase-polymerase chain reaction. The motoneuron survival ratio, defined as the ratio between the number of motoneurons counted on the lesioned side vs those on the unlesioned side, was calculated. This ratio was 0.77 +/- 0.02 for CNTF-treated rats vs 0.53 +/- 0.02 for the PBS-treated controls (P < 0.001). Treatment with CNTF modified the level of mRNA, with the expression of Bax RNA decreasing 18% (with a consequent decrease in the level of Bax protein), while the expression of Bcl-2 RNA was increased 87%, although the level of Bcl-2 protein was unchanged. The amount of Bcl-2/Bax heterodimer increased 91% over that found in the PBS-treated controls. These data show, for the first time, that the neuroprotective effect of CNTF on neonatal rat axotomized motoneurons is associated with a reduction in free Bax, due to the inhibition of Bax expression, as well as increased Bcl-2/Bax heterodimerization. Thus, the neuroprotective action of the CNTF on axotomized motoneurons can be related to the inhibition of this apoptotic pathway.

Neuroprotective effects of high-dose vs low-dose melatonin after blunt sciatic nerve injury

INTRODUCTION

Melatonin, the secretory product of the pineal gland, has potent antioxidant properties. The aim of this study was to compare the effects of low-dose (10 mg/kg) vs high-dose (50 mg/kg) melatonin on early lipid peroxidation levels and ultrastructural changes in experimental blunt sciatic nerve injury (SNI). We believe this to be the first study to assess the dose-dependent neuroprotective effects of melatonin after a blunt peripheral nerve injury.

MATERIALS AND METHODS

Rats were randomly allocated into 5 groups of 10 animals each. The SNI only rats underwent a nerve injury procedure. The SNI plus vehicle group received SNI and intraperitoneal injection of vehicle (diluted ethanol) as a placebo. The SNI plus low-dose or high-dose melatonin groups received intraperitoneal melatonin at doses of 10 mg/kg or 50 mg/kg, respectively. Controls had no operation, melatonin or vehicle injection. SNI was induced by clamping the sciatic nerve at the upper border of the quadratus femoris for 2 min.

RESULTS

Sciatic nerve samples were harvested 6 h after nerve injury and processed for biochemical and ultrastructural analysis. Trauma increased the lipid peroxidation of the sciatic nerve by 3.6-fold (153.85 +/- 18.73 in SNI only vs 41.73 +/- 2.23 in control rats, P < 0.01). Low (P = 0.02) and high (P < 0.01) doses of melatonin attenuated the nerve lipid peroxidation by 25% and 57.25%, respectively (65.76 +/- 2.47 in high-dose vs 115.08 +/- 7.03 in low-dose melatonin groups).

DISCUSSION

Although low-dose melatonin reduced trauma-induced myelin breakdown and axonal changes in the sciatic nerve, high-dose melatonin almost entirely neutralized any ultrastructural changes.

CONCLUSION

Our results suggest that melatonin, especially at a dose of 50 mg/kg, has a potent neuroprotective effect and can preserve peripheral neural fibers from lipid peroxidative damage after blunt trauma. With further investigations, we hope that these data may prove useful to clinicians who treat patients with nerve injuries.

mRNA and protein expression and activities of nitric oxide synthases in the lumbar spinal cord of neonatal rats after sciatic nerve transection and melatonin administration

Sciatic axotomy in 2-day-old rats (P2) causes lumbar motoneuron loss, which could be associated with nitric oxide (NO) production. NO may be produced by three isoforms of synthase (NOS): neuronal (nNOS), endothelial (eNOS) and inducible (iNOS). We investigated NOS expression and NO synthesis in the lumbar enlargement of rats after sciatic nerve transection at P2 and treatment with the antioxidant melatonin (sc; 1 mg/kg). At time points ranging from P2 to P7, expression of each isoform was assessed by RT-PCR and immunohistochemistry; catalytic rates of calcium-dependent (nNOS, eNOS) and independent (iNOS) NOS were measured by the conversion of [3H]L-arginine to [3H]L-citrulline. All NOS isoforms were expressed and active in unlesioned animals. nNOS and iNOS were detected in some small cells in the parenchyma. Only endothelial cells were positive for eNOS. No NOS isoform was detected in motoneurons. Axotomy did not change these immunohistochemical findings, nNOS and iNOS mRNA expression and calcium-independent activity at all survival times. However, sciatic nerve transection reduced eNOS mRNA levels at P7 and increased calcium-dependent activity at 1 and 6 h. Melatonin did not alter NOS expression. Despite having no action on NOS activity in unlesioned controls the neurohormone enhanced calcium-dependent activity at 1 and 72 h and reduced calcium-independent catalysis at 72 h in lesioned rats. These results suggest that NOS isoforms are constitutive in the neonatal lumbar enlargement and are not overexpressed after sciatic axotomy. Changes in NO synthesis induced by axotomy and melatonin administration in the current model are discussed considering some beneficial and deleterious effects that NO may have.

Bax and Bcl-2 expression and TUNEL labeling in lumbar enlargement of neonatal rats after sciatic axotomy and melatonin treatment

Peripheral axotomy in neonatal rats induces neuronal death. We studied the anti-apoptotic protein Bcl-2 and cell death promoter Bax in spinal cord of neonatal rats after sciatic transection and treatment with melatonin, a neuroprotective substance. Pups were unilaterally axotomized at P2 and received melatonin (1 mg/kg; sc) or vehicle 1 h prior to lesion, immediately after, at 1 h, 2 h and then once daily. Rats were sacrificed at 3 h, 6 h, 24 h, 72 h and 5 days postaxotomy. Intact animals were used as controls. Lumbar enlargement was processed for Nissl staining, immunohistochemistry and RT-PCR for Bax or Bcl-2 and TUNEL reaction. Motoneurons (MN) of lesioned (L) and normal (N) sides were counted, and MN survival ratio (MSR=L/N) was calculated. Bax and Bcl-2 showed cytoplasmic immunoreactivity (IR). Bax IR was noticeable in small cells but less evident in MN. In unlesioned pups, some Bax-positive small cells (B+) and TUNEL-positive nuclei (T+) were mainly seen in the dorsal horn. In lesioned animals given vehicle, Bax mRNA levels and numbers of B+ and T+ were increased in comparison with intact controls at 24 h postaxotomy. The basal IR for Bax in MN was not changed by axotomy. Bcl-2 IR was noted in all cells and, like Bcl-2 mRNA, was unaltered after lesion. Melatonin reduced MN loss at 24 h, 72 h and 5 days and T+ at 24 h after lesion but did not interfere with Bax or Bcl-2 expression. These results suggest that (1) sciatic transection at P2 increases Bax mRNA and the amount of B+ and T+ in the lumbar enlargement, (2) Bax IR in immature MN is not altered by axotomy and (3) melatonin protects MN and dorsal horn cells through a mechanism independent of Bax and Bcl-2.

Effects of Constant Lightness, Darkness and Parachlorophenylalanine Treatment on Tail Regeneration in the Lizard Ophisops elegans macrodactylus: Macroscopic, Biochemical and Histological Changes

A better understanding of regenerative growth is very important for the development of new potential strategies. Recently, the pineal secretory product melatonin was shown to stimulate the regeneration process. In this study, we carried out an experimental investigation of tail regeneration in young adult lizards, Ophisops elegans macrodactylus Berthold, 1842, addressing the role of melatonin on the regeneration process. Lizards were divided into three groups: constant light-exposed control group (n = 13), constant dark-exposed group (n = 15) and parachlorophenylalanine (p-CPA) treatment group exposed to constant light (n = 15). Using a tail autotomy procedure, the effects of p-CPA treatment on connective tissue together with neural tissue and vascular tissue in regenerating tail in lizards were investigated. p-CPA (400 microg/kg body mass) was injected from day 0 to 30 days after autotomy. p-CPA treatment produced a significant increase in the length of the regenerated tail compared with light-exposed control and dark-exposed lizards. Total collagen content was found to be higher in p-CPA-treated animals in comparison with other groups. Histologically, a higher percentage of connective tissue and vascular tissue and a lower percentage of neural tissue were found in the regenerated tails of the p-CPA-treated lizards. Importantly, the percentage of neural tissue in lizards in the dark-exposed animals was higher than that in animals of both light-exposed and p-CPA treatment groups. Thus, it is clear that p-CPA has a stimulatory influence on fibroblast collagen production and vascularization of the regenerated tail in the lizards. Furthermore, it seems that the neural regeneration process was markedly enhanced in lizards exposed to continuous darkness. Based on the results of our study, it is suggested that melatonin may be an active factor that speeds up the rate of tail regeneration in lacertilians.

Melatonin in Alzheimer's disease and other neurodegenerative disorders

Increased oxidative stress and mitochondrial dysfunction have been identified as common pathophysiological phenomena associated with neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). As the age-related decline in the production of melatonin may contribute to increased levels of oxidative stress in the elderly, the role of this neuroprotective agent is attracting increasing attention. Melatonin has multiple actions as a regulator of antioxidant and prooxidant enzymes, radical scavenger and antagonist of mitochondrial radical formation. The ability of melatonin and its kynuramine metabolites to interact directly with the electron transport chain by increasing the electron flow and reducing electron leakage are unique features by which melatonin is able to increase the survival of neurons under enhanced oxidative stress. Moreover, antifibrillogenic actions have been demonstrated in vitro, also in the presence of profibrillogenic apoE4 or apoE3, and in vivo, in a transgenic mouse model. Amyloid-β toxicity is antagonized by melatonin and one of its kynuramine metabolites. Cytoskeletal disorganization and protein hyperphosphorylation, as induced in several cell-line models, have been attenuated by melatonin, effects comprising stress kinase downregulation and extending to neurotrophin expression. Various experimental models of AD, PD and HD indicate the usefulness of melatonin in antagonizing disease progression and/or mitigating some of the symptoms. Melatonin secretion has been found to be altered in AD and PD. Attempts to compensate for age- and disease-dependent melatonin deficiency have shown that administration of this compound can improve sleep efficiency in AD and PD and, to some extent, cognitive function in AD patients. Exogenous melatonin has also been reported to alleviate behavioral symptoms such as sundowning. Taken together, these findings suggest that melatonin, its analogues and kynuric metabolites may have potential value in prevention and treatment of AD and other neurodegenerative disorders.

Antioxidative protection by melatonin: multiplicity of mechanisms from radical detoxification to radical avoidance

Melatonin has been shown to protect against oxidative stress in various, highly divergent experimental systems. There are many reasons for its remarkable protective potential. Signaling effects comprise the upregulation of antioxidant enzymes, such as superoxide dismutases, peroxidases, and enzymes of glutathione supply, down-regulation of prooxidant enzymes, such as nitric oxide synthases and lipoxygenases, and presumably also the control of quinone reductase 2. Other mechanisms are based on direct interactions with several reactive oxygen and nitrogen species. Among these reactions, the capacity of easily undergoing single-electron transfer reactions is of particular importance. Electron donation by melatonin is not only an aspect of direct radical scavenging, but additionally represents the basis for formation of the protective metabolites AFMK (N1-ace-tyl-N2-formyl-5-methoxykynuramine) and AMK (N1-acetyl-5-methoxykynuramine). Recent investigations on mitochondrial metabolism indicate that melatonin as well as AMK are capable of supporting the electron flux through the respiratory chain, of preventing the breakdown of the mitochondrial membrane potential, and of decreasing electron leakage, thereby reducing the formation of superoxide anions. Radical avoidance is a new line of investigation, which exceeds mitochondrial actions and also comprises antiexcitatory effects and contributions to the maintenance of internal circadian phase relationships.

Melatonin, a potent agent in antioxidative defense: actions as a natural food constituent, gastrointestinal factor, drug and prodrug

Melatonin, originally discovered as a hormone of the pineal gland, is also produced in other organs and represents, additionally, a normal food constituent found in yeast and plant material, which can influence the level in the circulation. Compared to the pineal, the gastrointestinal tract contains several hundred times more melatonin, which can be released into the blood in response to food intake and stimuli by nutrients, especially tryptophan. Apart from its use as a commercial food additive, supraphysiological doses have been applied in medical trials and pure preparations are well tolerated by patients. Owing to its amphiphilicity, melatonin can enter any body fluid, cell or cell compartment. Its properties as an antioxidant agent are based on several, highly diverse effects. Apart from direct radical scavenging, it plays a role in upregulation of antioxidant and downregulation of prooxidant enzymes, and damage by free radicals can be reduced by its antiexcitatory actions, and presumably by contributions to appropriate internal circadian phasing, and by its improvement of mitochondrial metabolism, in terms of avoiding electron leakage and enhancing complex I and complex IV activities. Melatonin was shown to potentiate effects of other antioxidants, such as ascorbate and Trolox. Under physiological conditions, direct radical scavenging may only contribute to a minor extent to overall radical detoxification, although melatonin can eliminate several of them in scavenger cascades and potentiates the efficacy of antioxidant vitamins. Melatonin oxidation seems rather important for the production of other biologically active metabolites such as N¹-acetyl-N²-formyl-5-methoxykynuramine (AFMK) and N¹-acetyl-5-methoxykynuramine (AMK), which have been shown to also dispose of protective properties. Thus, melatonin may be regarded as a prodrug, too. AMK interacts with reactive oxygen and nitrogen species, conveys protection to mitochondria, inhibits and downregulates cyclooxygenase 2.

Superoxide dismutase isoforms 1 and 2 in lumbar spinal cord of neonatal rats after sciatic nerve transection and melatonin treatment

Oxidative stress has been implicated in motoneuron death secondary to axotomy in the neonatal period. We studied the effect of sciatic transection at P2 on the motoneuron population in the lumbar enlargement of newborn rats looking for a protective role of daily doses of the antioxidant melatonin. The animals were allowed to survive from P2 to P7, and the spinal cords were processed for immunohistochemistry for superoxide dismutase (SOD) isoforms 1 and 2 and nitric oxide synthase (nNOS) (at 2, 3, 5, and 7 days post-natum), histological neuron counting and immunoblotting for the SOD isoforms (both at 2, 3, and 7 days post-natum). Melatonin reduced by 75% motoneuron loss due to axotomy at P3 and P7. Neither sciatic transection nor melatonin induced any detectable changes in the immunoreactivity patterns of the enzymes. SOD1 was expressed diffusely in the cytoplasm of neurons and ependyma and in the nuclei of presumed glial cells from P2 to P7. SOD2 was detected in neurons and ependyma and its expression was similar to SOD1 at P2 but decreased later to a spotty cytoplasmic pattern in motoneurons. nNOS was localized to the cytoplasm of a few small cells in the ventral and dorsal horns and around the central canal. Immunoblotting at 1 day postaxotomy detected a significant increase in SOD1 expression in melatonin-treated axotomized rats and a decrease in controls after axotomy and vehicle. Blotting for SOD2 did not show significant changes between groups at any time. This study provides the first evidence that SOD2 immunostaining pattern varies during motoneuron postnatal development and that melatonin alters the expression of SOD1 in the present model of peripheral nerve injury.

Beneficial effects of melatonin on reperfusion injury in rat sciatic nerve

Studies have shown that ischemia-reperfusion (I/R) produces free radicals leading to lipid peroxidation and to damage of the nervous tissue. Melatonin, a main secretory product of the pineal gland, has free radical scavenging and antioxidant properties and has been shown to diminish I/R injury in many tissues. There are a limited number of studies related to the effects of melatonin on I/R injury in the peripheral nervous system. Therefore, in the present study, the protective effect of melatonin was investigated in rats subjected to 2 hr of sciatic nerve ischemia followed by 3 hr of reperfusion. Following reperfusion, nerve tissue samples were collected for quantitative assessment of malondialdehyde (MDA), an oxidative stress marker, and superoxide dismutase (SOD), a principal antioxidant enzyme. Samples were further evaluated at electron microscopic level to examine the neuropathological changes. I/R elevated the concentration of MDA significantly while there was a reduction at SOD levels. Melatonin treatment reversed the I/R-induced increase and decrease in MDA and SOD levels, respectively. Furthermore, melatonin salvaged the nerve fibers from ischemic degeneration. Histopathologic findings in the samples of melatonin-treated animals indicated less edema and less damage to the myelin sheaths and axons than those observed in the control samples. Our results suggest that administration of melatonin protects the sciatic nerve from I/R injury, which may be attributed to its antioxidant property.

Circadian rhythms, oxidative stress, and antioxidative defense mechanisms

Endogenous circadian and exogenously driven daily rhythms of antioxidative enzyme activities and of low molecular weight antioxidants (LMWAs) are described in various phylogenetically distant organisms. Substantial amplitudes are detected in several cases, suggesting the significance of rhythmicity in avoiding excessive oxidative stress. Mammalian and/or avian glutathione peroxidase and, as a consequence, glutathione reductase activities follow the rhythm of melatonin. Another hint for an involvement of melatonin in the control of redox processes is seen in its high-affinity binding to cytosolic quinone reductase 2, previously believed to be a melatonin receptor. Although antioxidative protection by pharmacological doses of melatonin is repeatedly reported, explanations of these findings are still insufficient and their physiological and chronobiological relevance is not yet settled. Recent data indicate a role of melatonin in the avoidance of mitochondrial radical formation, a function which may prevail over direct scavenging. Rhythmic changes in oxidative damage of protein and lipid molecules are also reported. Enhanced oxidative protein modification accompanied by a marked increase in the circadian amplitude of this parameter is detected in the Drosophila mutant rosy, which is deficient in the LMWA urate. Preliminary evidence for the significance of circadian rhythmicity in diminishing oxidative stress comes from clock mutants. In Drosophila, moderately enhanced protein damage is described for the arrhythmic and melatonin null mutant per0, but even more elevated, periodic damage is found in the short-period mutant per(s), synchronized to LD 12:12. Remarkably large increases in oxidative protein damage, along with impairment of tissue integrity and--obviously insufficient--compensatory elevations in protective enzymes are observed in a particularly vulnerable organ, the Harderian gland, of another short-period mutant tau, in the Syrian hamster. Mice deficient in the per2 gene homolog are reported to be cancer-prone, a finding which might also relate to oxidative stress. In the dinoflagellate Lingulodinium polyedrum [Gonyaulax polyedra], various treatments that cause oxidative stress result in strong suppressions of melatonin and its metabolite 5-methoxytryptamine (5-MT) and to secondary effects on overt rhythmicity. The glow maximum, depending on the presence of elevated 5-MT at the end of subjective night, decreases in a dose-dependent manner already under moderate, non-lethal oxidative stress, but is restored by replenishing melatonin. Therefore, a general effect of oxidative stress may consist in declines of easily oxidizable signaling molecules such as melatonin, and this can have consequences on the circadian intraorganismal organization and expression of overt rhythms. Recent findings on a redox-sensitive input into the core oscillator via modulation of NPAS2/BMAL1 or CLK/BMAL1 heterodimer binding to DNA indicate a direct influence of cellular redox balance, including oxidative stress, on the circadian clock.

Evaluation of topiramate as an anti-hyperalgesic and neuroprotective agent in the peripheral nervous system

Abstract Topiramate (TPM), a novel anti-convulsant currently approved for the treatment of epileptic disorders, has been shown to possess neuroprotective effects in models of cerebral ischemia, status epilepticus, and facial nerve lesion. Furthermore, pilot studies showed an effect of TPM in neuropathic pain models. Here, we studied the anti-hyperalgesic and neuroprotective efficacy of TPM in rat models of peripheral nerve lesions. Rats with a unilateral chronic constrictive injury (CCI) or a crush lesion of the sciatic nerve were treated with a twice-daily dose of 20 mg/kg of TPM. Behavioral and neurophysiological tests were used to measure pain-related behavior, motor, and sensory function. Morphometry was performed to evaluate sciatic nerves. In CCI, treatment with TPM attenuated mechanical hyperalgesia and cold allodynia. In sciatic nerve crush, TPM reduced cold allodynia and attenuated thermal hyperalgesia at the early and late phase of the observation. There was no difference in the numbers of surviving or regenerating nerve fibers between saline- and TPM-treated rats in either model. Electrophysiological studies carried out over a period of 3 months after sciatic nerve crush did not show major differences between TPM- and saline-treated rats. In conclusion, we could show moderate anti-hyperalgesic effects but could not prove a neuroprotective effect of TPM in these two rat nerve injury models using electrophysiological and morphometric methods.

T-588 protects motor neuron death following axotomy

R(-)-1-(benzo [b] thiophen-5-yl)-2-[2-(N,N-diethylamino)ethoxy] ethanol hydrochloride) (T-588) enhances acetylcholine release. This compound slows the motor deterioration of wobbler mouse motor neuron disease and enhances neurite outgrowth and choline acetyltransferase activity in cultured rat spinal motor neurons. We examined the ability of T-588 on axotomized spinal motor neuron death in the rat spinal cord. After the postnatal unilateral section of sciatic nerve, there was approximately a 50% survival of motor neurons in the fourth lumbar segment. In comparison with vehicle, intraperitoneal injection of T-588 for 14 consecutive days rescued spinal motor neuron death. Our results showing in vivo neurotrophic activity of T-588 for motor neurons support the applicability of T-588 for the treatment of motor neuron diseases, such as amyotrophic lateral sclerosis and motor neuropathies.

Neuronal NOS deficiency promotes apoptotic cell death of spinal cord neurons after peripheral nerve transection

To study the role of endogenous NO in survival and recovery of spinal cord neurons after nerve lesions, wild type mice were compared to knock-out mice lacking neuronal, endothelial or inducible NO synthase (NOS) after sciatic nerve transection. The NO-generating capacities were assessed by NOS immunohistochemistry and NADPH-diaphorase staining. The feature of affected neurons was evaluated following Nissl- and TUNEL-staining, by immunocytochemical demonstration of cytochrome c-translocation, and by ultrastructural examination. Time point of cell loss was found to be independent of the mice type and occurred only at later post-axotomy states. The extent of neuronal degeneration, however, depended on the NO supply. Whereas a lack of endothelial or inducible NOS was well tolerated, deficiency of neuronal NOS enhanced the competence-to-die and led to a substantial apoptotic cell death of spinal cord neurons. Thus, NO supply turned out to be essential for cell survival and recovery with reference to the neuronal NOS isoform.

Protective effect of melatonin against fractionated irradiation-induced epiphyseal injury in a weanling rat model

The effects of melatonin, a free-radical scavenger and a general antioxidant, on radiation-induced growth plate injury have not been studied previously. The purpose of this study was to determine the potential benefits of sparing longitudinal bone growth by fractionated radiotherapy alone compared with pretreatment with melatonin that provides differential radioprotection of normal cells. Weanling 4-wk-old (75-100 g) male Sprague-Dawley rats were randomly assigned to one of three groups: Group R received fractionated radiation alone (n = 8); groups M5 (n = 8) and M15 (n = 7) received 5 or 15 mg/kg melatonin prior to fractionated radiation, respectively. The distal femur and proximal tibia in the right leg of each animal were exposed to a therapeutic X-irradiation dose (25 Gy total in three fractions) with the contralateral left leg as the non-irradiated control. Melatonin was administered intraperitoneally to the animals 30 min before radiation exposure. Six weeks after treatment, the rats were killed and the lower limbs disarticulated, skeletonized, radiographed, and bone growth was calculated based on measurement of the bone lengths. Fractionated radiation resulted in a mean percent overall limb growth loss of 41.2 +/- 9.5 and a mean percent overall limb discrepancy of 11.2 +/- 2.2. The administration of 5 or 15 mg/kg melatonin before each of the three fractions of radiotherapy reduced the mean percent overall limb growth loss to 33.9 +/- 5.8 and 32.2 +/- 4.5, respectively, and the mean percent overall limb discrepancy to 9.4 +/- 1.6 and 8.9 +/- 1.1, respectively; these values were significantly different compared with irradiation alone (range: P = 0.01-0.04). When compared with Group R, the growth arrest recovered by 5 or 15 mg/kg melatonin was 19.7 and 24.1% for the tibia, 7 and 18.6% for the femur, and 17.7 and 21.8% for the total limb, respectively. These results support further investigation of melatonin in combination with fractionation for potential use in growing children requiring radiotherapy to the extremity for malignant tumors.