Minocycline alleviated scopolamine-induced amnesia by regulating antioxidant and cholinergic function.

Background and aim: Minocycline, a tetracycline derivative, has been found to exert neuroprotective properties. The current project aimed to assess the antioxidant status and cholinergic function in the amnesia induced by scopolamine. Methods: We evaluated the passive avoidance performance, acetylcholine esterase (AChE) enzyme activity, and the oxidative stress indicators in the following groups: Normal control, scopolamine, and the treatment groups (the animals were given minocycline (10-30 mg/kg)). Results: Scopolamine (intraperitoneal) injection was associated with impairment of passive avoidance performance and neurotoxicity. Minocycline pronouncedly ameliorated scopolamine injury as presented by the increased latency time to darkness and stay time in lightness along with the decreased darkness entry. Moreover, minocycline decreased lipid peroxidation, while it elevated the levels of superoxide dismutase, AChE enzymes, and thiol groups in both the cortex and hippocampus. Conclusion: Our data suggested that minocycline modulated the antioxidant status and AChE in the brains, which may contribute to its protective effects against scopolamine-induced amnesia.

Targeting Caveolin-1 and Claudin-5 with AY9944, Improve Blood-Brain Barrier Permeability; Computational Simulation and Experimental Study.

The current study aimed to determine the protective effect of AY9944 related to Caveolin-1 and Claudin-5 role in lipid raft, which can rescue the blood-brain barrier from enhanced permeability. Therefore, in vivo analyses were performed following ischemia in normal, ischemic, and AY9944-treated animal groups. The results revealed that AY9944 reduced the infarct size, edema, and brain water content. The extravasation of Alb-Alexa 594 and biocytin-TMR was minimum in the AY9944-treated animals. The results showed a significant decrease in the expression level of Caveolin-1 over 8 h and 48 h and a remarkable increase in the level of Claudin-5 over 48 h following ischemia in AY9944-treated animals. Molecular docking simulation demonstrated that AY9944 exerts a possible protective role via attenuating the interaction of the Caveolin-1 and cholesterol in lipid raft. These findings point out that AY9944 plays a protective role in stroke by means of blood-brain barrier preservation. Proper neural function essentially needs a constant homeostatic brain environment which is provided by the blood-brain barrier. Rescuing blood-brain barrier from enhanced permeability via inducing the protective effect of AY9944 related to caveolin-1 and claudin-5 role in lipid raft was the aim of the current study.

Anti-LINGO-1 improved remyelination and neurobehavioral deficit in cuprizone-induced demyelination.

OBJECTIVES: Central nervous system demyelination is the main feature of multiple sclerosis (MS). The most important unmet need in MS is use of treatments that delay the progression of the disease. Leucine-rich repeat and Immunoglobulin-like domain containing NOGO receptor-interacting protein 1(LINGO-1) have been known as inhibitors of oligodendrocyte differentiation and myelination. MATERIALS AND METHODS: We investigated LINGO-1 antibody effects on remyelination and neurobehavioral deficit using cuprizone-induced demyelination. Animals were randomly divided into three groups (n = 10): (1) Control group; received the regular diet, (2) CPZ group; normal saline was injected intraperitoneally, and (3) Treatment group; LINGO-1 antibody (10 mg/kg) was injected IP once every six days for 3 weeks. We assessed the level of myelin basic protein (MBP), neurofilament heavy chain (NF200), and Brain-derived neuroprotective factor (BDNF) in the corpus callosum (CC) by immunostaining against MBP, NF200, and BDNF. RESULTS: We found decreased levels of MBP, NF200, and BDNF in demyelinated CC, and anti-LINGO-1 treatment improved demyelinated structures. Furthermore, motor impairment was measured by Open-field (OFT) and Balance beam tests. In the treatment group, motor impairment was significantly improved. CONCLUSION: These results provide evidence that LINGO-1 antibody can improve remyelination and neurobehavioral deficit.

Evaluation of the Effect of (S)-3,4-Dicarboxyphenylglycine as a Metabotropic Glutamate Receptors Subtype 8 Agonist on Thermal Nociception Following Central Neuropathic Pain.

STUDY DESIGN: In this study, we decided to change the activity of periaqueductal gray (PAG)'s metabotropic glutamate receptors subtype 8 (mGluR8) by means of its specific agonist, (S)-3,4-dicarboxyphenylglycine (DCPG), and by knock downing it with mGluR8 siRNA. We then evaluated the changes in animal pain threshold levels in the face of painful thermal stimuli (thermal hyperalgesia). PURPOSE: Although several mechanisms have been examined for central neuropathic pain, researchers have so far failed to find the precise mechanism for the development and progression of this type of pain. Hyperalgesia is one of the most important complications of central neuropathic pain and there is not a consensus among researchers about the exact cause of this complication. In this study, we investigated the effect of activation of the PAG region mGluR8 on the threshold of pain response to thermal noxious stimulus in rats and measured mGluR8 expression. OVERVIEW OF LITERATURE: Spinal cord injury (SCI) produces an decrease in mGluR2/3 expression in the injured and vehicle-treated groups compared to normal levels, APDC and L-AP4 treated groups had higher expression levels of mGluR2/3. These findings suggesting that the level of mGluR expression after SCI may modulate nociceptive responses. METHODS: Male Wistar rats were randomly assigned to five groups (n=10 per group). The clip compression injury model was used to induce chronic central neuropathic pain. Three weeks after SCI, DCPG, siRNA, or normal saline were administered to the intra-ventrolateral PAG region. Withdrawal threshold to the noxious thermal stimulus (e.g., heat hyperalgesia) was assessed through the tail-flick test. In order to assure involvement of this receptor, pain responses were compared with mice that received GRM8 siRNA. RESULTS: We found that the mGluR8 agonist DCPG increased lead to an increased expression of mGluR8 in the PAG region. We also found that SCI can decrease the threshold of response to painful thermal stimuli; however, activation of mGluR8 with DCPG agonist did not significantly improve the tail-flick response. CONCLUSIONS: The results revealed that activation of mGluR8 in PAG is not capable of improving the thermal hyperalgesia threshold. Based on the decreased expression of mGluR8 after SCI induced by clip compression injury and its significant increase after treatment of siRNA against mGluR8, this method might still hold promise as an effective treatment of neuropathic pain. It can be concluded that increased expression of mGluR8 is due to the fact that DCPG prevents the death of neurons that express these receptors.

Netrin-1 protects the SH-SY5Y cells against amyloid beta neurotoxicity through NF-κB/Nrf2 dependent mechanism.

Many evidence confirms that amyloid beta 1-42 fragment (Aß1-42) causes neuroinflammation, oxidative stress, and cell death, which are related to progressive memory loss, cognitive impairments and mental disorders that will lead to Alzheimer's disease (AD) progression. Netrin-1, as a member of the laminins, has been proved to inhibit apoptosis and inflammation outside of nervous system, in addition to having a vital role in morphogenesis and neurogenesis of neural system. This study was designed to assess the protective effects of netrin-1 in SH-SY5Y human neuroblastoma cell line exposed to Aß1-42 and to explore some mechanisms that underlie netrin-1 effects. Cultured SH-SY5Y neuroblast-like cells were treated with netrin-1 prior to Aß1-42 exposure and the effects were assessed by MTT and ELISA assay kits. Netrin- 1 pretreatment of Aß1-42-exposed SH-SY5Y human neuroblastoma cells attenuated Aß1-42 induced toxic effects, increased cell viability and partially restored levels of 3 inflammatory and oxidative stress biomarkers including: nuclear factor erythroid 2-like 2 (Nrf2), tumor necrosis factor alpha (TNFα) and nuclear factor kappa-light chain-enhancer of activated B cells (NF-κB). Based on the findings of this study, netrin-1 represents a promising therapeutic bio agent to abrogate cellular inflammation and reactive oxygen species (ROS) activation induced by Aß1-42 in the SH-SY5Y cell model of AD.

The effect of periaqueductal gray's metabotropic glutamate receptor subtype 8 activation on locomotor function following spinal cord injury.

Background and aims The pathophysiology of spinal cord injury is very complex. One of the debilitating aspects of spinal cord injury in addition to pain is a defect in motor function below the lesion surface. In this study, we tried to assess the modulatory effect of (S)-3,4-Dicarboxyphenylglycine (DCPG), a metabotropic glutamate receptor subtype 8 (mGluR8) agonist, on animal's locomotor functions in a model of compression spinal cord injury. Methods We used a contusion method (T6-T8) for induction of spinal cord injury. Male Wistar rats were randomly assigned to five equal groups (n = 10 per group). Clips compression injury model was used to induce spinal cord injury. Three weeks post injury DCPG, siRNA (small interfering Ribonucleic Acid) and normal saline (vehicle) were administered intra-ventrolaterally to the periaqueductal gray (PAG) region. Motor function, were assessed through BBB (Basso, Beattie, and Bresnahan Locomotor Rating Scale) and ladder walking test. In addition, the effects of DCPG on axonal regeneration in corticospinal tract were evaluated. Results We found that DCPG could improve motor function and axonal regeneration in corticospinal tract when compared to siRNA group. Conclusions The results revealed that activation of mGluR8 in PAG is capable to improve motor function and of axonal regeneration due to the inhibitory effect on glutamate transmission on the spinal cord surface and also the elimination of the deleterious effect of glutamate on the regeneration of the injured area as an excitatory neurotransmitter. Implications Our findings in this study showed that, more attention should be paid to glutamate and its receptors in spinal cord injury studies, whether at the spinal or cerebral level, especially in the field of motor function after spinal cord injury.

The inhibiting role of periaqueductal gray metabotropic glutamate receptor subtype 8 in a rat model of central neuropathic pain.

The pathophysiology of neuropathic pain is very complex. It involves several environmental and central mechanisms. In this study, we tried to assess the modulatory effect of (S)-3,4-Dicarboxyphenylglycine (DCPG), a metabotropic glutamate receptor subtype 8 (mGluR8) agonist, in a model of chronic central neuropathic pain in male rats. We used a spinal cord contusion method (T6-T8) for the induction of chronic central neuropathic pain.Male Wistar rats were randomly assigned to 5 equal groups (n = 10 per group). Clips compression injury model was used to induce chronic central neuropathic pain. Three weeks after spinal cord injury DCPG, siRNA and normal saline were administered intra-ventrolaterally to the periaqueductal gray (PAG) region. Paw withdrawal response to acetone (cold allodynia) was assessed through acetone test. In addition, the effects of DCPG on rostral ventromedial medulla (RVM) off-cells activity were evaluated with immunohistochemistry. mGluR8 expressions were also measured.We found that treatment with DCPG increased pain threshold in acetone test. In addition, immunohistochemical evaluation of RVM off-cells showed that DCPG increased the suppressive function of these cells.The results revealed that activation of mGluR8 in PAG is capable to improve pain threshold via modulation of RVM off-cells activity.Abbreviations SCI: spinal cord injury; DCPG: (S)-3,4-dicarboxyphenylglycine; PAG: periaqueductal gray; siRNA: small interfering ribonucleic acid; RVM: rostral ventromedial medulla; mGluR: metabotropic glutamate receptor.

Key mechanisms underlying netrin-1 prevention of impaired spatial and object memory in Aß1-42 CA1-injected rats.

Alzheimer's disease (AD) is a neurodegenerative disorder with an incompletely defined aetiology that is associated with memory and cognitive impairment. Currently available therapeutics only provide temporary assistance with symptoms. In spite of plentiful research in the field and the generation of thousands of studies, much is still to be clarified on precise mechanisms of pathobiology, prevention modalities, disease course and cure. Netrin-1, a laminin family protein, is said to have anti-inflammatory and anti-apoptotic effects and has a key role in neurogenesis and morphogenesis of neural structures. Accordingly, this study was designed to investigate protective effects of bilateral intrahippocampal fissure microinjections of netrin-1 on memory impairment in rat model of AD. Concomitant administration of netrin-1 with amyloid beta 1-42 (Aß1-42 ) improved cognitive dysfunction in novel object recognition task (NOR), ameliorated impaired spatial memory in Morris water maze (MWM) setting, increased neuronal density and reduced amyloid aggregation in rat AD model. Netrin-1 was also seen to prevent Aß1-42 -induced caspase-3, caspase-7 and NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activation. Therefore, based on the data reported here, netrin-1 may be a promising biologic therapeutic that addresses the memory and neuronal loss associated with AD.

Perspectives of Medieval Persian Medicine on Multiple Sclerosis.

INTRODUCTION: Traditional Persian Medicine (TPM) was the prevailing practice of medicine in the Eurasia region up through the 18th century, a practice of medicine stemming back to Hippocrates and to the 5000 year old civilization of the region. It is a school of medicine which touches on many a delicate points which may seem unimaginable within the realm of modern allopathic medicine. This practice of ancient medicine besides shedding light on various possible theoretical modern day disorders serves as a vast resource for therapeutics. In this paper, we present study of the manuscripts of this ancient medical practice in search of symptom presentations coinciding with presentation of multiple sclerosis (MS). MATERIAL & METHOD: This paper represents a comprehensive search through TPM texts and manuscripts with the intention to seek possible clues on MS from potentially valuable age-old resources. We predominantly focused our search on the works of five eminent physicians of Medieval Persia: Avicenna (980-1037 AD), Haly Abbas (949-982 AD), Rhazes (865-925 AD), Averroes (1126-1198 AD) and Jorjani (1042-1137 AD). RESULTS: In this paper, the authors attempt a theory and conclude with high probability that a conjunction of a series of signs, symptoms found in TPM texts under the terms khadar, isterkha and falej form the symptoms and the disease pattern of modern day MS. This theory draws upon existent similarities in terms of disease pathology, disease patterns and predisposing factors seen between MS and the related morbidities within Persian Medicine. CONCLUSION: We recommend further examinations of such potentially valuable long-standing resources, examining the diagnoses and treatments as set forth by Persian Medicine through international collaboration within the global scientific community.

Protective effect of magnesium on renal function in STZ-induced diabetic rats.

BACKGROUND: Diabetic nephropathy is a serious complication of T1D (type one diabetes mellitus). Persistent hyperglycemia and subsequent hypomagnesemia is believed to develop kidney damage by activation of oxidative stress. We conducted this study to investigate the renoprotective effect of magnesium sulfate (MgSO4) on renal histopathology and oxidative stress in diabetic rats. METHODS: The study included 70 male rats. The animals were divided into seven groups: control (CRL), control receiving MgSO4 (CRL + Mg1 & CRL + Mg8), diabetic (DM1 & DM8) and diabetic receiving MgSO4 (DM + Mg1 & DM + Mg8). Rats were given 20 mg/kg (i.p) Streptozocin (STZ) for 5 consecutive days in (MLD) multiple low doses to induce T1D. At day 10 treatment groups were received MgSO4 (10 g/l) in drinking water, for 1 or 8 weeks. The blood glucose, BUN and creatinine levels were measured. Renal tissue levels of malondialdehyde (MDA) were measured by thiobarbituric acid (TBA) method to evaluate the oxidative stress. Renal histopathology was done using H & E staining method. RESULTS: Treatment with MgSO4 significantly decreased the blood glucose in DM + Mg1 and DM + Mg8 groups as compared with DM1 and DM8. Magnesium treatment also decreased serum BUN and tissue level of MDA significantly in both short and long term treatment. The body weight loss and kidney weight to body weight ratio was improved by MgSO4. Histological results showed there were no differences between DM and DM + Mg groups. CONCLUSION: Our findings showed that diabetic nephropathy is associated with high blood glucose level and oxidative stress (significant increase in MDA level). The renal dysfunction and oxidative stress can be improved by magnesium sulfate administration. It is suggested that protection against development of diabetic nephropathy by MgSO4 treatment involves changes in the blood glucose and oxidative stress.

Role of GABAA receptor in modulation of acute thermal pain using a rat model of cholestasis.

Increased activity of the endogenous opioid system in cholestasis results in analgesia. GABAA receptors have been ascribed both pronociceptive and antinociceptive roles in pain modulation. Considering the elevated endogenous opioid tone in cholestasis and the existence of close interaction between the GABAergic and opioidergic systems in pain control, the involvement of GABAA receptors in modulation of nociception in a model of elevated endogenous opioid tone, cholestasis, was investigated using muscimol and bicuculline as selective GABAA receptor agonist and antagonist respectively. Cholestasis was induced by ligation of the main bile duct using two ligatures and transsection of the duct between them. Cholestatic rats had increased tail-flick latencies (TFLs) compared to non-cholestatic rats. Administration of muscimol (0.2 and 0.4 mg/kg, s.c.) and bicuculline (0.5 and 1mg/kg, s.c.) to the cholestatic groups significantly increased and decreased respectively TFLs compared to the saline treated cholestatic group. Muscimol antinociception in cholestatic animals was attenuated by co-administration of naloxone or bicuculline. Furthermore, the combination of bicuculline and naloxone completely reversed the increased TFLs of cholestatic rats back to the level of unoperated animals. Muscimol and bicuculline injections into non-cholestatic animals did not alter TFLs. At the doses used here, none of the drugs impaired motor coordination, as revealed by the rotarod test. This study shows the involvement of GABAA receptors in pain modulation during cholestasis in rats.

GABAA receptors are involved in the analgesic effects of morphine microinjected into the central nucleus of the amygdala.

The central nucleus of the amygdala (CeA) has an important role in pain perception and analgesia. Opioid and GABAA receptors, which are both involved in pain modulation, are found in high concentration in the CeA. The present study was designed to examine the interaction of opioidergic and GABAergic systems in the CeA during modulation of acute thermal pain. In the present study, different doses of morphine (25, 50 and 100 µg/rat), either alone or after 5 min pretreatment with the selective GABAA receptor agonist muscimol (60 ng/rat) or the selective GABAA receptor antagonist bicuculline (50 ng/rat), were injected bilaterally into the CeA of each rat. Tail-flick latencies (TFL) were measured every 5 min for 60 min. The results revealed that microinjection of morphine into the CeA significantly increased TFL in a dose-dependent manner. Microinjection of bicuculline or muscimol in combination with morphine into the CeA increased and decreased TFL, respectively. It seems that morphine in the CeA facilitates the function of descending inhibitory systems by interacting with the activity of local GABAA receptors.

Systemic hyperthermia masks the neuroprotective effects of MK-801, but not rosiglitazone in brain ischaemia.

The use of neuroprotective agents has been under investigation for the treatment of ischaemic brain stroke. In this study, we examined the effects of rosiglitazone and MK-801, two potential neuroprotectants, on thromboembloic focal stroke in hyperthermic rats. The animals were assigned into groups of rosiglitazone, MK-801 and control, all under both normothermic and hyperthermic conditions. A focal ischaemia was induced by injection of preformed clot into the origin of the middle cerebral artery. The animals were assessed by measuring infarct size and brain oedema and also evaluating neurological deficit and seizure activity. Rosiglitazone improved infarct volume and neurological deficit in both normo- (36%) and hyperthermic (63%) animals; but MK-801 only improved normothermic animals. Our results do not support the use of MK-801 in hyperthermic conditions of brain stroke but suggest that rosiglitazone may preserve its efficiency even in hyperthermia.

URB597, an inhibitor of fatty acid amide hydrolase, reduces hyperalgesia in diabetic rats.

Diabetic rats display increased pain responses after injection of formalin into the paw or thermal stimulation of the tail, suggesting the presence of hyperalgesia. In this study, we investigated the efficacy of URB597 (0.1, 0.3, and 0.5 mg/kg, i.p.), an inhibitor of endocannabinoids metabolism, on 2 models of experimental hyperalgesia in streptozotocin (STZ)-induced diabetic rats. Animals were divided into control, URB597-treated control (0.1, 0.3, and 0.5 mg/kg), diabetic, and URB597-treated diabetic (0.1, 0.3, and 0.5 mg/kg) groups. Formalin and tail-flick tests were performed 4 and 8 weeks after the onset of hyperglycemia, respectively. Diabetes caused significant hyperalgesia during these tests. URB597 (0.3 and 0.5 mg/kg) reversed chemical and thermal hyperalgesia in diabetic rats. Administration of URB597 at a dose of 0.1 mg/kg did not alter pain-related behaviors in control and diabetic groups compared with those of the respective control groups. URB597 treatment did not affect body weight or plasma glucose level of treated animals compared with nontreated animals. This study shows that increasing endocannabinoid neurotransmission with URB597 displays efficacy in chemical and thermal models of diabetic hyperalgesia. It also suggests that URB597 is a promising tool for treatment of painful diabetic neuropathy.

Cardiovascular response to renin substrate microinjection into the central nucleus of the amygdala of rats.

Central nucleus of the amygdala is involved in cardiovascular regulation. Although most components of the renin-angiotensin system have been found to be distributed in amygdala, renin expression in brain has remained controversial. This work was undertaken to elucidate the extent of renin presence in this nucleus. A cannula was implanted bilaterally into the central nucleus of the amygdala. Mean arterial pressure and heart rate were directly measured via indwelling femoral artery cannula post bilateral intra central nucleus of the amygdala microinjection of renin substrate. Renin substrate microinjection dose-dependently increased mean arterial pressure and heart rate, whereas captopril, saralasin and losartan pretreatment inhibited these effects. The results suggest the presence of local renin or similar proteases in this nucleus.

CB1 receptor activation in the basolateral amygdala produces antinociception in animal models of acute and tonic nociception.

1. Recent studies have suggested that the basolateral nucleus of the amygdala (BLA) participates in the processing of pain information, especially noxious somatic information. Cannabinoid receptors or CB1 mRNA are expressed more in the BLA than in other nuclei of the amygdala. Thus, the aim of the present study was to examine whether CB1 receptors in the BLA may be involved in modulating acute and/or tonic nociceptive processing. 2. Adult rats were exposed to intra-BLA microinjection of the cannabinoid receptor agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo [1,2,3,-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate [WIN 55,212-2 (1, 2.5, 5 or 10 microg/side)] and subjected to the tail flick and formalin tests. 3. The rats demonstrated a dose-dependent increase in latency to withdraw from a thermal noxious stimulus in the tail flick test and a decrease in formalin-induced pain behaviours. The antinociceptive effects of the CB1 receptor agonist WIN 55,212-2 (10 microg/side) in both tests were attenuated in the presence of the selective CB1 receptor antagonist, N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3- carboxamide (AM251; 0.55 ng/side). Administration of the CB1 receptor antagonist AM251 (0.55, 5.5, or 55.5 ng/side) alone did not alter the nociceptive thresholds in either test. Bilateral microinjection of the selective CB2 receptor antagonist N-[(1S)-endo-1,3,3-trimethyl bicyclo [2.2.1] heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528; 1 microg/side) had no effect on the antinociception produced by WIN 55,212-2, suggesting that the antinociceptive actions of WIN 55,212-2 are mediated by CB1 receptors. 4. The findings suggest the existence of a CB1-mediated inhibitory system in the BLA that, when activated, can diminish responsivity to acute and tonic noxious stimuli, but that normally has no tonic effect on the response threshold of these stimuli.

Modeling force-velocity relation in skeletal muscle isotonic contraction using an artificial neural network.

The aim of this study is to design an artificial neural network (ANN) to model force-velocity relation in skeletal muscle isotonic contraction. We obtained the data set, including physiological and morphometric parameters, by myography and morphometric measurements on frog gastrocnemius muscle. Then, we designed a multilayer perceptron ANN, the inputs of which are muscle volume, muscle optimum length, tendon length, preload, and afterload. The output of the ANN is contraction velocity. The experimental data were divided randomly into two parts. The first part was used to train the ANN. In order to validate the model, the second part of experimental data, which was not used in training, was employed to the ANN and then, its output was compared with Hill model and the experimental data. The behavior of ANN in high forces was more similar to experimental data, but in low forces the Hill model had better results. Furthermore, extrapolation of ANN performance showed that our model is more or less able to simulate eccentric contraction. Our results indicate that ANNs represent a powerful tool to capture some essential features of muscle isotonic contraction.

Modulation of cholestasis-induced antinociception in rats by two NMDA receptor antagonists: MK-801 and magnesium sulfate.

Acute cholestasis is associated with increased activity of the endogenous opioid system that results to changes including analgesia. N-methyl-d-aspartate (NMDA) receptors are involved in the nociceptive pathway and play a major role in the development of morphine induced analgesia. The magnesium acts as a non-competitive NMDA receptor antagonist by blocking the NMDA receptor channel. Considering the reported antinociceptive effect of magnesium sulfate as a NMDA receptor antagonist and the existence of close functional links between NMDA receptor antagonists and magnesium with the opioid system, we studied the effect of acute and chronic administration of MK-801 as a NMDA antagonist and magnesium sulfate on modulation of nociception in an experimental model of elevated endogenous opioid tone, acute cholestasis, using the tail-flick paradigm. Cholestasis was induced by ligation of the main bile duct using two ligatures and then transsection of the duct at the midpoint between them. A significant increase (P<0.001) in nociception threshold was observed in bile duct ligated rats compared to unoperated and sham-operated animals. In acute treatment, MK-801 (0.1 mg/kg, b.i.d), but not magnesium (150 mg/kg magnesium sulfate, i.e. 30 mg/kg of Mg(+2), i.p., b.i.d.) increased antinociception in cholestatic rats compared to saline treated cholestatics (P<0.05). In chronic treatment, administration of MK-801 or magnesium sulfate for 7 consecutive days, increased tail-flick latency (P<0.05, P<0.01) in cholestatic animals compared to saline treated cholestatics. These data showed that NMDA receptor pathway is involved in modulation of cholestasis-induced antinociception in rats and that repeated dosages of magnesium sulfate similar to MK-801 is able to modulate nociception in cholestasis.