Effect of preferential cyclooxygenase-2 (COX-2) inhibitor against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced striatal lesions in rats: Behavioral, biochemical and histological evidences.

Cyclooxygenase (COX) isoenzyme is known to play an important role in the pathophysiology of Parkinson’s disease. The present study evaluated the neuroprotective effect of nimesulide, a preferential COX-2-inhibitor against 1-methyl-4-phenyl-1,2,3,6-tertahydropyridine (MPTP)-model of Parkinson’s disease. Intrastriatal administration of MPTP (32 μmol in 2 μl) produced a significant decrease in the locomotor activity. Biochemical investigation of striatal region revealed a significant enhancement in the oxidative stress as evidenced by increased lipid peroxidation levels, nitrite levels and myeloperoxidase activity along with depleted antioxidant pool (reduced glutathione and superoxide dismutase levels) and reduced redox (GSH/GSSG) ratio. MPTP administration also showed significant mitochondrial complex-I inhibition and reduction in the mitochondrial viability. Histological examination of the MPTP-treated brain sections revealed alteration in the histo-architecture as well as undifferentiated bodies of varying contour and lesions. Chronic administration of nimesulide (5 or 10 mg/kg, po) for 12 days, significantly reversed the behavioral, biochemical, mitochondrial and histological alterations induced by MPTP. In conclusion, the findings of the present study implicate the possible neuroprotective potential of nimesulide in MPTP-treated rats and thus highlight the therapeutic potential of COX-inhibitors in treatment of Parkinson’s disease.

Effect of Convolvulus pluricaulis Choisy. and Asparagus racemosus Willd on learning and memory in young and old mice: A comparative evaluation.

A dose dependent enhancement of memory was observed with A. racemosus and C. pluricaulis treatment as compared to control group when tested on second day. A. racemosus and C. pluricaulis at the dose of 200 mg/kg, po showed significantly higher percent retentions, than piracetam. Multiple treatment with A. racemosus and C. pluricaulis for three days also demonstrated significant dose dependent increase in percent retentions as compared to control group. The effect was more prominent with C. pluricaulis as compared with piracetam and A. racemosus. A significantly lower percent retention in aged mice was observed as compared to young mice. Aged mice (18-20 months) showed higher transfer latency (TL) values on first and second day (after 24 h) as compared to young mice, indicating impairment in learning and memory. Pretreatment with A. racemosus and C. pluricaulis for 7 days enhanced memory in aged mice, as significant increase in percent retention was observed. Significantly higher retention was observed with C. pluricaulis (200 mg/kg; po) as compared with piracetam (10 mg/kg/; po). Post-trial administration of C.pluricaulis and A. racemosus extract demonstrated significant decrease in latency time during retention trials. Hippocampal regions associated with the learning and memory functions showed dose dependent increase in AChE activity in CA 1 with A. reacemosus and CA3 area with C. pluracaulis treatment. The underlying mechanism of these actions of A. racemosus and C. pluricaulis may be attributed to their antioxidant, neuroprotective and cholinergic properties.

Effect of Withania somnifera Dunal root extract against pentylenetetrazol seizure threshold in mice: possible involvement of GABAergic system.

Withania somnifera (ashwagandha) is a widely used herb in the Ayurvedic system of medicine. The objective of the present study was to elucidate the effect of W. somnifera root extract (Ws) alone or in combination with exogenous gamma-amino butyric acid (GABA), a GABA receptor agonist or with diazepam, a GABA receptor modulator against pentylenetetrazol (PTZ, iv) seizure threshold in mice. Minimal dose of PTZ (iv, mg/kg) needed to induce different phases (myoclonic jerks, generalized clonus and tonic extension) of convulsions were recorded as an index of seizure threshold. Ws (100 or 200 mg/kg, po) increased the PTZ seizure threshold for the onset of tonic extension phase whereas a lower dose (50 mg/kg, po) did not show any effect on the seizure threshold. Co-administration of a sub-effective dose of Ws (50 mg/kg, po) with a sub-protective dose of either GABA (25 mg/kg, ip) or diazepam (0.5 mg/kg, ip) increased the seizure threshold. The results suggested that the anticonvulsant effect of W. somnifera against PTZ seizure threshold paradigm involved the GABAAergic modulation.

Possible involvement of nitric oxide (NO) signaling pathway in the antidepressant-like effect of MK-801(dizocilpine), a NMDA receptor antagonist in mouse forced swim test.

L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) is an important signaling pathway involved in depression. With this information, the present study aimed to study the involvement of this signaling pathway in the antidepressant-like action of MK-801 (dizocilpine; N-methyl-d-aspartate receptor antagonist) in the mouse forced-swim test. Total immobility period was recorded in mouse forced swim test for 6 min. MK-801 (5-25 microg/kg., ip) produced a U-shaped curve in reducing the immobility period. The antidepressant-like effect of MK-801 (10 microg/kg, ip) was prevented by pretreatment with L-arginine (750 mg/kg, ip) [substrate for nitric oxide synthase (NOS)]. Pretreatment of mice with 7-nitroindazole (7-NI) (25 mg/kg, ip) [a specific neuronal nitric oxide synthase inhibitor] produced potentiation of the action of subeffective dose of MK-801 (5 microg/kg, ip). In addition, treatment of mice with methylene blue (10 mg/kg, ip) [direct inhibitor of both nitric oxide synthase and soluble guanylate cyclase] potentiated the effect of MK-801 (5 microg/kg, ip) in the forced-swim test. Further, the reduction in the immobility period elicited by MK-801 (10 microg/kg, ip) was also inhibited by pretreatment with sildenafil (5 mg/kg, ip) [phosphodiesterase 5 inhibitor]. The various modulators used in the study and their combination did not produce any changes in locomotor activity per se and in combination with MK-801. MK-801 however, at higher doses (25 microg/kg, ip) produced hyperlocomotion. The results demonstrated the involvement of nitric oxide signaling pathway in the antidepressant-like effect of MK-801 in mouse forced-swim test.

Pro-convulsant effect of cefazolin sodium against pentylenetetrazol- or picrotoxin-induced convulsions in mice.

Cefazolin injection (3000 mg/kg, i.v.) in mice showed several behavioral excitations such as wild running, jumping, rolling, and finally undergoing severe convulsions followed by death. It's lower doses (500-2000 mg/kg, i.v.) were unable to produce any convulsions or behavioral excitations in mice. However, cefazolin (500 or 1000 mg/kg, i.v.) when administered before different doses of pentylenetetrazol (PTZ; 40 or 60 mg/kg, i.p.) or picrotoxin (PTX; 4 or 8 mg/kg, i.p.), it produced severe tonic-clonic convulsions in mice. The convulsions or behavioral excitations produced by 3000 mg/kg, i.v. cefazolin was also reversed by different doses of diazepam (0.5-2 mg/kg, i.p.) further proving the GABAergic modulatory effect of cefazolin. The results conclude the pro-convulsant action of cefazolin on PTZ- or PTX-induced convulsions, and further confirm the clinical reports.

Effect of withdrawal of diazepam or morphine treatment on gastric motility (charcoal meal test) in mice: possible role of different central and peripheral receptors.

Increased gastrointestinal motility in mice as one of the withdrawal symptoms of commonly abused drugs like diazepam or morphine and its possible mechanism of action was studied. Male Laka mice (20-25 g) were made addict to either diazepam (20 mg/kg, ip for 7 days) or morphine (10 mg/kg, sc for 9 days). Withdrawal symptoms were noted 24 hr after the last injection of diazepam or morphine. The animals were injected with Ro 15-1788 (flumazenil) (1 mg/kg, ip) or naloxone (2 mg/kg, ip) in the respective group to precipitate the withdrawal symptoms. Gastrointestinal motility was assessed by charcoal-meal test. Animals developed tolerance to acute sedative effect of diazepam, and similarly to the acute nociceptive action of morphine. On abrupt cessation of these drugs after chronic treatment the animals showed hyperlocomotion and hyperreactivity in diazepam withdrawal group and hyperalgesia on hot plate in morphine withdrawal groups, respectively. Increase in gastrointestinal motility was observed in all the drug withdrawal groups. Treatment with respective antagonists, Ro 15-1788 (flumazenil) and naloxone precipitated the withdrawal symptoms. The results suggest the involvement of both central and peripheral receptors of benzodiazepines and opioid (mu) receptors in the withdrawal symptoms of the benzodiazepines and morphine, respectively.

Resveratrol, a polyphenolic phytoalexin attenuates thermal hyperalgesia and cold allodynia in STZ-induced diabetic rats.

The effects of resveratrol, a polyphenolic phytoalexin present in red wine have been investigated on hyperalgesia and cold allodynia in streptozotocin (STZ) induced diabetic rats. Diabetes was induced by a single intraperitoneal injection of streptozotocin (65mg/kg). After 4-weeks of STZ injection, diabetic rats exhibited a significant thermal hyperalgesia and cold allodynia along with increased plasma glucose and decreased body weights as compared with controls rats. Chronic treatment with resveratrol (10mg/kg orally) from week 4 to week 6 significantly attenuated the cold allodynia and thermal hyperalgesia. The results emphasize the role of oxidative stress in development of hyperalgesia and cold allodynia in diabetic animals and point towards the potential of resveratrol as an adjuvant therapy for the prevention and treatment of diabetic neuropathy.

Effect of BR-16A (Mentat), a polyherbal formulation on drug-induced catalepsy in mice.

Parkinson's disease (PD) is a neurodegenerative disease characterized by the selective loss of dopamine (DA) neurons of the substantia nigra pars compacta (SNc). The events, which trigger and/or mediate the loss of nigral DA neurons, however, remain unclear. Neuroleptic-induced catalepsy has long been used as an animal model for screening drugs for Parkinsonism. Administration of haloperidol (1 mg/kg, ip) or reserpine (2 mg/kg, ip) significantly induced catalepsy in mice. BR-16A (50 and 100 mg/kg, po), a polyherbal formulation or ashwagandha (50 and 100 mg/kg, po), significantly reversed the haloperidol or reserpine-induced catalepsy. The results indicate that BR-16A or ashwagandha has protective effect against haloperidol or reserpine-induced catalepsy and provide hope that BR-16A could be used in preventing the drug-induced extrapyramidal side effects and may offer a new therapeutic approach to the treatment of Parkinson's disease.

Possible analgesic and anti-inflammatory interactions of aspartame with opioids and NSAIDs.

The purpose of the present study was to investigate analgesic and anti-inflammatory properties of aspartame, an artificial sweetner and its combination with various opioids and NSAIDs for a possible synergistic response. The oral administration of aspartame (2-16mg/kg, po) significantly increased the pain threshold against acetic acid-induced writhes in mice. Co-administration of aspartame (2mg/kg, po) with nimesulide (2 mg/kg, po) and naproxen (5 mg/kg, po) significantly reduced acetic acid-induced writhes as compared to effects per se of individual drugs. Similarly when morphine (1 mg/kg, po) or pentazocine (1 mg/kg, po) was co-administered with aspartame it reduced the number of writhes as compared to their effects per se. Aspartame (4,8,16 mg/kg, po) significantly decreased carrageenan-induced increase in paw volume and also reversed the hyperalgesic effects in rats in combination with nimesulide (2 mg/kg, po).The study indicated that aspartame exerted analgesic and anti-inflammatory effects on its own and have a synergistic analgesic response with conventional analgesics of opioid and non-opioid type, respectively.

On the sleep promoting effects of BR-16A: interaction with GABAergic modulators.

Pentobarbitone-induced hypnosis test was used as an animal model to explore the role of BR-16A, a polyherbal formulation in sleep. Pentobarbitone produces quick sleep latency (onset) and prolongation of total sleep time (duration). Sleep latency and total sleep time were used as a parameters for the evaluation. BR-16A potentiated the effect of triazolam (0.1 mg/kg, ip) and alprazolam (0.25 mg/kg, ip). Melatonin (5.0 mg/kg, ip) and zolpidem (0.5 mg/kg, ip) did not produce any significant effect on sleep parameters. However, alprazolam (0.25mg/kg, ip) potentiated the effect of BR-16A (100 mg/ kg, po) in higher dose only. Sleep promoting effect of BR-16A in combination with GABAergic drugs (triazolam and alprazolam,) suggested that these drugs have common mechanism in sleep promoting effect of pentobarbitone and could be used along with other GABAergic hypnotics for the treatment of insomnia. This may reduce the dose of the latter drug(s). BR-16A can be used for the treatment of sleep and sleep-related disorders.

Role of adenosine in drug-induced catatonia in mice.

Parkinson's disease is one of the most common neurodegenerative disorders affecting large majority of population who are older than age of 65. Apart from dopamine, acetylcholine and glutamate, adenosinc has also been identified in the basal ganglia. Adenosine modulates the release of a variety of neurotransmitters including dopamine. In order to establish adenosine-dopamine interactions in drug-induced catatonia we studied the effect of adenosine in drug-induced catatonia in mice. In the present study adenosine dose dependently produced catatonia when assessed on rota-rod and bar tests in mice. Adenosine also potentiated the catatonic effect of perphenazine. L-dopa plus carbidopa or OR-486 (a potent centrally acting COMT inhibitor) completely reversed adenosine-induced catatonia. Since reversal by scopolamine of adenosine-induced catatonia was not to the same extent as with l-dopa and OR-486 it appears that catecholamines particularly dopamine rather than cholinergic modulation is more important in adenosine induced catatonia. The motor dysfunction (catatonia) could be easily assessed using rota-rod test apparatus in mice.

Differential effect of polyherbal, antiobesity preparation, OB-200G in male and female mice and monosodium glutamate-treated rats.

Effect of administration of different doses (0.25, 0.5, 1 and 2 g/kg, twice daily, po) of a polyherbal preparation, OB-200G and fluoxetine (10 mg/kg, ip) for 21 days was studied on food intake and body weight in male and female Laka mice. The study further investigated the effect of administration of 0.5 g/kg dose of OB-200G for 40 days on body weight, fat pad weights, locomotor activity and biochemical parameters in monosodium glutamate (MSG)-treated male and female Wistar rat pups. Administration of OB-200G produced dose dependent decrease in body weight in both male and female mice. On the other hand, fluoxetine decreased body weight only in female mice. The food intake was significantly (P < 0.05) increased in both fasted male and female mice after treatment with the lower dose (0.25 g/kg, po) of OB-200G. However, significant (P < 0.05) decrease in food intake was recorded with the administration of higher doses (0.5, 1 and 2 g/kg, po) of OB-200G and fluoxetine in fasted female mice on day 1, 7, 14 and 21. But in male mice differential effect on food intake was recorded at different doses on day 1, 7, 14 and 21. Further, OB-200G administration significantly (P < 0.05) decreased body weight and fat pad weights, increased serum glucose levels and ambulatory activity in MSG-treated female rats but not in MSG-treated male rats. The results suggest that OB-200G involves gender differences in mediating its antiobesity effect and may supplement the current armamentarium for the treatment of obesity.

Animal models of tardive dyskinesia--a review.

Tardive dyskinesia is a serious motor side effect of long term neuroleptic therapy, with an unknown pathophysiological basis. The leading hypothesis of the pathophysiology of tardive dyskinesia includes dopamine receptor supersensitivity, GABAergic hypofunction, excitotoxicity and oxidative stress. Many preclinical models have been developed to identify the underlying pathological processes of tardive dyskinesia, but none has yet produced a parsimonious results. A wide range of animal models, viz. Homologous, analogous and correlational models have been developed to explore the pathophysiology of tardive dyskinesia. Vacuous chewing movements in rodents induced by chronic neuroleptic treatment is the most frequently employed model. As the existing models suffer from several phenomenological and methodological problems, development of new models, highly predictive of pathological basis of tardive dyskinesia can accelerate tardive dyskinesia research for the better understanding of the pathophysiological processes underlying the syndrome and for the discovery of new therapeutic targets for the treatment of tardive dyskinesia.

Modulation of motor functions involving central dopaminergic system by L-histidine.

There exists a possibility of interactions of histaminergic system with other neurotransmitters and their receptors in the central nervous system. Experimental evidences suggest a possible inhibitory influence of histaminergic system on the dopaminergic system. To elucidate the possible interaction between the histaminergic and dopaminergic pathways, we devised a strategy to study their effects on locomotor function and stereotypy behaviour. We investigated the effect of L-histidine, the precursor of histamine, on apomorphine-induced stereotypy and perphenazine-induced catalepsy. Histidine antagonised apomorphine-induced stereotypy. This inhibitory effect of histidine was abolished by both H1- and H2-receptor antagonists, chlorpheniramine and cimetidine, respectively. Perphenazine-induced catalepsy was potentiated by histidine and this effect was inhibited by chlorpheniramine alone but not by cimetidine. These results confirm a possible histamine-dopamine interaction in the modulation of motor functions by the central nervous system.

Differential effect of a polyherbal formulation-OB-200G in male and female mice subjected to forced swim stress.

The antistress effect of a polyherbal formulation-OB-200G (500 mg/kg. p.o.) was studied in both male and female mice subjected to forced swim stress. Fluoxetine (10 mg/kg, i.p.) was chosen as standard drug for comparison. Exposure of mice to chronic stress regime resulted in decreased body weight in both male and female mice, increased sweetened food intake, anxiety, depression and locomotor activity in stressed female mice as compared to unstressed control (normal) mice. Treatment with OB-200G resulted in a further decrease in body weight, increased food intake and locomotor activity in both stressed male and female mice. It also reduced immobility time, decreased latency to enter and increased number of entries and time spent in mirror chamber in stressed female mice. Administration of fluoxetine (10 mg/kg, i.p.) decreased body weight and food intake in both stressed male and female mice. Fluoxetine treatment also increased time spent in mirror chamber and decreased immobility time in stressed female mice. Thus, like fluoxetine, OB-200G decreased body weight and produced antianxiety and antidepressant effects in stressed female mice and may prove beneficial in obese patients reported to be more susceptible to stress-related psychological disorders.

Studies on anticonvulsant actions of L-deprenyl.

L-Deprenyl (Selegeline) introduced for use in parkinson's disease, is implicated to show beneficial effects in epilepsy, alzheimer's disease, cognition, depression and other age related neurological diseases. In this study, we investigated the CNS effects of L-deprenyl with special reference to epilepsy, anxiety and cognition and memory in mice. L-deprenyl (10, 20 and 40 mg/kg) showed a significant anticonvulsant activity against pentylenetetrazole (PTZ)-induced convulsions. Combination of L-deprenyl (10 mg/kg) with the sub-protective dose of diazepam (1 mg/kg) showed potentiation of the anticonvulsant effect. In the maximal-electroshock (MES)-induced convulsions, L-deprenyl (10 mg/kg) significantly delayed the onset and decreased the duration of extensor phase. Its combination with the lower dose of phenytoin (10 mg/kg) showed potentiation in response compared to the per se effect of both the drugs. However, L-deprenyl did not show any protective effect in lithium-pilocarpine induced status epilepticus. Acute treatment with L-deprenyl had no effect on learning and memory. In chronic treatment, L-deprenyl per se showed no effect on learning and memory but did improve the condition in mice with scopolamine induced memory deficit. L-Deprenyl per se was anxiogenic though in combination with diazepam (1 mg/kg) it potentiated the antianxiety effect of the latter. The above observations suggest that in epilepsy, L-deprenyl might be acting partially by influencing the GABAA/benzodiazepine mechanism in the brain (similar to diazepam and phenytoin), and in cognition enhancing effect, the cholinergic system might be playing a role. Thus, L-deprenyl could prove to be an adjuvant in the antiepileptic therapy and beneficial in dementia associated with epilepsy.

Motor and electrographic response of refractory experimental status epilepticus in rats and effect of calcium channel blockers.

Effects of various calcium channel inhibitors have been studied in lithium-pilocarpine model of status epilepticus. Status epilepticus was induced by administration of lithium chloride (3 meq/kg) followed 21 hr later by pilocarpine (30 mg/kg). Diltiazem (5 and 10 mg/kg) was not effective in delaying onset of convulsions. Verapamil (20 mg/kg) showed protection against lithium-pilocarpine-induced convulsions. The dihydropyridine nifidepine (2.5 and 5 mg/kg) did not show any protection in this model. Amlodipine (5 and 10 mg/kg) as partially protective. Flunarizine (10 and 20 mg/kg) delayed the onset of forelimb clonus and rearing and only 60% of the rats underwent status in the 20 mg/kg group. Pre-treatment of MK-801 led to a potentiation of the antiseizure activity of calcium channel inhibitors. The percent increase in amplitude at various time points with amlodipine pretreatment was significant only at the 30th min recording, and at the rest of the time frames was practically similar as the controls. It can be concluded that the anticonvulsant action of MK-801 can be enhanced by centrally acting calcium channel inhibitors.

Analgesic and anti-inflammatory effects of phosphodiesterase inhibitors.

The aim of the present study was to investigate the role of phosphodiesterase (PDE) enzyme inhibitors namely rolipram and theophylline in pain and inflammation in experimental animals. Rolipram, a selective PDE IV inhibitor and theophylline a nonspecific PDE inhibitor exerted dose dependent analgesic and anti-inflammatory effect against acetic acid-induced writhing in mice and carrageenan-induced paw edema in rats, respectively. Nimesulide (1, 2 mg/kg) produced significant anti-inflammatory effect. Further, nimesulide (0.5 mg/kg) potentiated analgesic effect of rolipram but it failed to modulate the anti-inflammatory effect of PDE inhibitors. Present study suggests that PDE enzymes might be playing a role in nociceptive and inflammatory responses in animals.

Involvement of dopamine D2 and 5-HT1A receptors in roxindole-induced antinociception.

Roxindole, a DA D2 receptor agonist (2-16 mg/kg) produced dose-dependent increase in percentage antinociception. The effect which was blocked by DA D2 antagonist (-)sulpiride (50 mg/kg) and 5-HT1A receptor antagonist (-) pindolol (5 mg/kg). Roxindole (4 and 8 mg/kg) reversed both naloxone (20 mg/kg)-induced hyperalgesia and reserpine (2 mg/kg)-induced hyperalgesia. This reversal was sensitive to blockade by both (-)sulpiride (50 mg/kg) and (-) pindolol (5 mg/kg). The present study suggests that roxindole-induced antinociception is mediated by postsynaptic DA D2 and 5-HT1A receptors.

Antinociceptive effect of sumatriptan in mice.

Antinociceptive effect of the antimigraine drug sumatriptan (5-HT1A agonist) was studied against acetic acid-induced writhing in mice. Sumatriptan produced the effect in a dose-dependent manner (1, 5, 10 and 20 mg/kg, s.c.). Naloxone (1 mg/kg i.p.) an opiate antagonist failed to reverse sumatriptan-induced antinociception. Cholinomimetic physostigmine (0.05 mg/kg, i.p.) potentiated and the muscarinic antagonist atropine (5 mg/kg, i.p.) blocked the antinociceptive effect of sumatriptan, respectively. The antinociceptive effect of sumatriptan was compared with an another 5-HT agonist (5-HT1A) buspirone which also produced antinociception. Like sumatriptan-analgesia, the buspirone response was also potentiated by physostigmine in atropine sensitive way. Further, buspirone potentiated the analgesic effect of sumatriptan. These observations suggest that 5-HT1A agonists produce antinociception possibly by modulating central cholinergic activity.