In vivo microdialysis studies of striatal level of neurotransmitters after haloperidol and chlorpromazine administration.

Therapeutic success of atypical antipsychotics has focused the attention on the role of receptor systems other than dopaminergic system in the pathophysiology of neuroleptics-associated acute (Parkinson's like syndrome) and chronic (tardive dyskinesia) extrapyramidal side effects. This study was planned to investigate changes in striatal levels of norepinephrine, dopamine and serotonin after acute and chronic administration of classical neuroleptics (haloperidol and chlorpromazine). These changes were correlated with behavioural alterations in rats. In vivo microdialysis with HPLC/ECD system revealed that there was a marked decrease in striatal neurotransmitter contents (NE, DA and 5-HT), which was also correlated with severe cataleptic response in rats after acute administration of haloperidol (2 mg/kg) and chlorpromazine (20 mg/kg). Chronic administration of haloperidol (1 mg/kg for 21 days) and chlorpromazine (5 mg/kg for 21 days) resulted in time dependent increase in orofacial hyperkinetic movements. The microdialysis studies also showed a significant decrease in the striatal levels of all the neurotransmitters. The results provide evidence for the involvement of striatal adrenergic and serotonergic systems, besides dopaminergic system in neuroleptic-induced acute and chronic extrapyramidal symptoms.

Comparative behavioural profile of newer antianxiety drugs on different mazes.

Anxiety is associated with diverse range of psychiatric conditions. In the present study, antianxiety effect of fluoxetine, citalopram (SSRI's), gabapentin (antiepileptic drugs), venlafaxine (SNRI), clozapine and resperidone (atypical antipsychotics) and a herbal preparation ashwagandha on elevated zero maze and elevated plus maze paradigms was examined. Anti-anxiety potentials of these drugs were compared with diazepam. The drugs tested i.e. fluoxetine (10 mg/kg), citalopram (10 mg/kg), clozapine (0.25, 0.5, 1 mg/kg), resperidone.(0.5, 1 mg/kg), venlafaxine (4, 8, 16 mg/kg), citalopram (10 mg/kg), fluoxetine (10 mg/kg), gabapentin (10, 20 mg/kg) and ashwagandha (100, 200 mg/kg) significantly increased the number of open arm entries and time spent in open arm. These drugs also decreased the latency to enter in open arm as compared to control in both the paradigms. Present study confirms the antianxiety activity of different newer classes of drugs and found some of them comparable to diazepam in both the elevated zero maze and elevated plus maze paradigm.

Involvement of adenosinergic receptors in anxiety related behaviours.

In the present study, the effect of adenosine (A1 and A2 receptor agonist), caffeine (A2A receptor antagonist), theophylline (A2A receptor antagonist) and their combination was studied in anxiety related behaviours using elevated zero maze and elevated plus maze paradigms and compared their various behavioural profiles. Adenosine (10, 25, 50,100 mg/kg) significantly showed anxiolytic effect at all the doses, whereas caffeine (8, 15, 30, 60 mg/kg) and theophylline (30, 60 mg/kg) showed psychostimulatory action at lower doses and anxiogenic effect at higher doses. Pretreatment with caffeine (8, 15, 30 mg/kg) and theophylline (30 mg/kg) reversed the anxiolytic effect of adenosine. The study suggested the involvement of adenosinergic receptor system in anxiety related behaviours.

Comparative neurochemical changes associated with chronic administration of typical and atypical neuroleptics: implications in tardive dyskinesia.

An important goal of current neuroleptic research is to develop antipsychotic compounds with the low incidence of extrapyramidal side effects. The therapeutic success and less side-effect of atypical anti-psychotics such as clozapine and risperidone has focused the attention on the role of receptor systems other than dopaminergic system in the pathophysiology of neuroleptics-associated extrapyramidal side effects. The present study compares the effect of chronic administration of typical and atypical antipsychotics on neurochemical profile in rat forebrain. The study was planned to study changes in extracellular levels of norepinephrine, dopamine and serotonin in forebrain region of brain and tried to correlate them with hyperkinetic motor activities (vacuous chewing movements (VCM's), tongue protrusions and facial jerking) in rats, hall mark of chronic extrapyramidal side-effect of neuroleptic therapy tardive dyskinesia. Chronic administration of haloperidol (1 mg/kg) and chlorpromazine (5 mg/kg) resulted in significant increase in orofacial hyperkinetic movements where as clozapine and risperidone showed less significant increase in orofacial hyperkinetic movements as compared to control. There were also significant decrease in the extracellular levels of neurotransmitters dopamine, norepinephrine and serotonin in fore-brain as measured by HPLC/ED after chronic administration of haloperidol and chlorpromazine. Chronic administration of atypical neuroleptics clozapine and risperidone resulted in the decrease in extracellular concentration of dopamine and norepinephrine but the effect was less significant as compared to typical drugs. However, treatment with atypical neuroleptics resulted in 3 fold increase in serotonin levels as compared to forebrain of control rats. Typical and atypical neuroleptics showed varying effects on neurotransmitters, especially serotonin which may account for the difference in their profile of side effects (Tardive dyskinesia).

Effect of cyclooxygenase-2 (COX-2) inhibitors in various animal models (bicuculline, picrotoxin, maximal electroshock-induced convulsions) of epilepsy with possible mechanism of action.

Enzyme cyclooxygenase (COX) is reported to play a significant role in neurodegeneration and may play a significant role in the pathogenesis of epilepsy. Bicuculline (4 mg/kg; ip), picrotoxin (8 mg/kg; ip) and electroshock (60 mA for 0.2 sec) significantly induced convulsions in male Laka mice. COX-inhibitors viz. nimesulide (2.5 mg/kg; ip) and rofecoxib (2 mg/kg, ip) administered 45 minutes prior to an epileptic challenge prolonged mean onset time of convulsions, decreased duration of clonus and decreased % mortality rate against bicuculline- and picrotoxin-induced convulsions in mice. COX-2 inhibitors were ineffective towards maximal electroshock-induced convulsions. Nimesulide (1 mg/kg) and rofecoxib (1 mg/kg) also enhanced the effect of subprotective dose of muscimol against picrotoxin-induced convulsions. The result of the present study strongly suggests for a possible role of cyclooxygenase isoenzymes particularly, COX-2 in the pathophysiology of epilepsy and its GABAergic modulation.

Potentiation of antinociceptive effect of NSAIDs by a specific lipooxygenase inhibitor, acetyl 11-keto-beta boswellic acid.

The present study was aimed to assess the combined effects of cyclooxygenase and 5-lipoxygenase (COX/5-LOX) inhibitors in different animal models of nociception. Naproxen, nimesulide and rofecoxib are well-established antinociceptive agents acting via COX inhibition. AKBA (acetyl-keto-beta-boswellic acid) is a 5-LOX inhibitor. AKBA (50-200 mg/kg) produced a dose dependent and significant antinociceptive effect in different animal models of nociception. Based on the earlier reports from our laboratory, sub effective doses of all the three COX Inhibitors were selected and they were administered (naproxen, 5 mg/kg; nimesulide, 1 mg/kg; and rofecoxib, 1 mg/kg) with AKBA (100 mg/kg). This produced a more significant antinociceptive effect as compared to per se effect observed in all the three models of nociception. However, the effect of combination of nimesulide with AKBA was more pronounced as compared to naproxen and rofecoxib and their combination with AKBA. The present finding provided an evidence for the potentiation of antinociceptive effect of NSAIDs with AKBA. Such a combination may help to reduce the therapeutic doses of conventional NSAIDs and also reduce side effects (gastric, cardiac and renal) that are popularly associated with the NSAIDs.

Effect of 5-lipoxygenase inhibitor against lipopolysaccharide-induced hypothermia in mice.

Bacterial endotoxin produces sepsis associated with alterations in body temperature (fever or hypothermia). The intraperitoneal administration of bacterial endotoxin, lipopolysaccharide (LPS; 50 microg/mouse) led to a decrease in colonic temperature starting 1 hr after the injection. The hypothermic effect was accompanied by a significant increase in hypothalamic leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) levels. 5-lipoxygenase inhibitor, zileuton (200 and 400 mg/kg, po) administered 30 min before LPS challenge significantly prevented hypothermia. However, non-selective cyclooxygenase inhibitor, indomethacin (10, 20 mg/kg, po) did not reverse the hypothermic response. Further, pretreatment of mice with zileuton prevented LPS-stimulated increase in hypothalamic LTB4 levels and caused a relatively small increase in PGE2 levels. Indomethacin had no effect on LTB4 levels but it reduced PGE2 levels. These results suggest a possible involvement of leukotrienes in LPS-induced hypothermia and the potential protective role of 5-lipoxygenase inhibitors in endotoxemia.

Effect of licofelone against NSAIDs-induced gastrointestinal ulceration and inflammation.

The present study was aimed to evaluate the effect of licofelone, a dual inhibitor of cycloxygenase1/2-5-lipoxygenase against indomethacin-induced gastric damage in rats and mice in order to assess the role of leukotrienes if any, in non-steroidal anti-inflammatory drugs (NSAIDs)-induced gastrointestinal inflammation. Acute pretreatment with licofelone reversed the indomethacin-induced gastric ulceration, neutrophil adhesion in mesentery venules, neutrophil count in blood, lipid peroxides and vascularity in the stomachs of mice and rats. Further, chronic pretreatment of licofelone also prevented indomethacin-induced gastric morphological changes and cellular infiltration in mesentery venules. Moreover, acute administration of indomethacin elevated leukotriene B4 levels in gastric mucosa, which was reversed by pretreatment with licofelone The results suggest that licofelone offered gastroprotection against NSAIDs-induced gastropathy through its effect on leukotrienes and by inhibiting extravasation of neutrophils.

Inhibitory effect of sildenafil on gastrointestinal smooth muscle: role of NO-cGMP transduction pathway.

Nitric oxide (NO) is an important neurotransmitter in the gut and has been demonstrated to be a key physiological mediator of non-adrenergic non-cholinergic (NANC) relaxation of gastrointestinal smooth muscle. In the present study the effect of PDE 5 inhibitor sildenafil on the gastrointestinal function (gastric emptying and intestinal transit) has been demonstrated in mice. Sildenafil (0.5-2 mg/kg, po) did not alter the percent gastric emptying however, in higher doses (5, 10 and 30 mg/kg, po) it inhibited the gastric emptying. On acute administration (0.5-5 mg/kg, po) it did not alter the intestinal transit but in higher doses (10 and 30 mg/kg, p.o.) delayed the intestinal transit. Further, the inhibitory effect of sildenafil was significantly blocked by L-NAME (10 mg/kg, ip), a non-selective NOS inhibitor and methylene blue (1 mg/kg, ip), a guanylate cyclase inhibitor. These findings suggest the participation of NO-cGMP transduction pathway in the inhibitory effect of sildenafil (higher doses) on the gastrointestinal smooth muscles and its potential application in patients with nutcracker oesophagus, hypertensive lower oesophageal sphincter (LOS), achalsia and diabetic gastroparesis or colitis where there is a loss of nNOS.

Role of cyclooxygenase-2 in lipopolysaccharide-induced hyperalgesia in formalin test.

Lipopolysaccharide (LPS)-induced hyperalgesia and the role of cyclooxygenase (COX) isoforms in acute and chronic nociceptive assays have been well established. However, the role of COX isoforms in LPS-induced hyperalgesia in the formalin test is not clear. Thus, the present study was undertaken to characterize the time course of formalin-induced nociceptive response in LPS-pretreated mice and to investigate possible effects of COX inhibitors to address the potential role of COX isoforms in LPS-induced hyperalgesia in the formalin test. All the animals showed typical biphasic response to formalin challenge. At 0 hr (immediately) and 4 hr after LPS pretreatment, animals did not show any alteration in formalin-induced tonic pain. However, 12 and 16 hr after LPS pretreatment, there was a significant increase in the late phase of formalin-induced nocifensive response as compared to control mice. Treatment with intravenously administered ketorolac (a nonselective COX inhibitor) significantly and dose-dependently inhibited the late phase of formalin-induced nociceptive behaviour in saline and LPS-pretreated mice. In contrast, parecoxib (prodrug of valdecoxib, a selective COX-2 inhibitor) or dexamethasone (COX-2 transcription inhibitor), when administered intravenously or intraperitoneally, respectively, did not show antinociceptive effect in the formalin test in saline-pretreated mice. However, both the agents significantly and dose-dependently decreased the late phase nociceptive behaviour of the formalin test in LPS-pretreated mice to the level of the animals that received saline pretreatment. These results suggest that induction of COX-2 by proinflammatory mediators and subsequent release of prostaglandins could be responsible for LPS enhancement of formalin-induced nocifensive behaviour and supports an important role of COX-2 in LPS-induced hyperalgesia in the formalin test.

Effect of 5-lipoxygenase inhibition on events associated with inflammatory bowel disease in rats.

Leukotrienes play a part in inflammatory response. The unique role of the enzyme 5-lipoxygenase (5-LOX) in the production of leukotrienes makes it a likely therapeutic target for inflammatory conditions like asthma, rheumatoid arthritis, psoriasis, and inflammatory bowel disease (IBD). The aim of the present study was to evaluate the effect of zileuton, an orally active selective 5-LOX inhibitor against the events associated with dextran sodium sulphate-induced colitis in a rat model of IBD. The animals were administered simultaneously zileuton (100mg/kg) or sulphasalazine (100mg/kg) orally for 7 days. On day eight, rats were sacrificed, and distal colon isolated to determine myeloperoxidase activity, in vivo superoxide dismutase activity, prostaglandin E2 levels and histological examination. Both zileuton and sulphasalazine significantly prevented the development of inflammatory events associated with colitis. The effect of zileuton was more pronounced towards reducing myeloperoxidase activity and increasing PGE2 levels in distal colon. The results show that chemotactic leukotrienes are responsible for inflammatory surge in damaged colon and, zileuton, significantly improved healing by inhibition of neutrophil recruitment and indirectly through increase in prostaglandins at the site of inflammation. It is suggested that inhibitors of 5-LOX enzyme may have useful therapeutic role in the treatment of chronic intestinal inflammation.

Modulatory effect of diclofenac on antispasmodic effect of pitofenone in cholinergic spasm.

Biliary, ureteric and intestinal colic are extremely common clinical conditions associated with smooth muscle spasm. In the present study, antispasmodic activity was carried out against acetylcholine (10-640 ng/ml)-induced contractions on guinea pig ileum. Acetylcholine (10-640 ng/ml) induced concentration-dependent contraction of smooth muscle. Diclofenac, in varying concentration (9.4 x 10(-5) mol/l and 14.1 x 10(-5) mol/l) shifted the concentration response curve of acetylcholine to the right without suppressing the maximal response. However, in higher concentration diclofenac (18.9 x 10(-5) mol/l) blocked the response in an unsurmountable fashion. Further, analgin (11.09 x 10(-5), 16.63 x 10(-5) and 22.18 x 10(-5) mol/l) in equimolar concentrations did not alter the concentration response curve of acetylcholine, but in higher concentration analgin (44.36 x 10(-5) mol/l) also blocked the response in an unsurmountable fashion. Pitofenone (2.5 x 10(-6) mol/l) also, shifted the concentration response curve of acetylcholine to right in a parallel fashion with no change in maximal response. The present study confirms the potent antispasmodic activity of diclofenac-pitofenone combination in comparison to analgin-pitofenone in molar equivalent concentration (in comparison to diclofenac) against acetylcholine-induced contractions of guinea pig ileum.

Cholinergic-NO-cGMP mediation of sildenafil-induced antinociception.

Acetylcholine and cholinomimetic agents with predominant muscarinic action are known to increase the concentration of cGMP by activation of nitric oxide signaling pathway in the nociceptive conditions. The present study was aimed to investigate the NO-cGMP-PDE5 pathway in nociceptive conditions in the experimental animals. Nociceptive threshold was assessed by acetic acid-induced writhing assay (chemonociception) or carrageenan-induced hyperalgesia. Sildenafil [1-5 mg/kg, ip, 50-200 microg/paw, intraplantar (ipl)] produced dose dependent antinociception in both the tested models. Coadministration of acetylcholine (50 mcg/paw, ipl) or cholinomimetic agent, neostigmine (0.1 mcg/kg, ip and 25 ng/paw, ipl) augmented the peripheral antinociceptive effect of sildenafil. This effect was sensitive to blockade by L-NAME (20 mg/kg, ip, 100 microg/paw, ipl), a non-selective NOS inhibitor and methylene blue (1 mg/kg, ip), a guanylate cyclase inhibitor, which per se had little or no effect in both the models of nociception. Further, the per se analgesic effect of acetylcholine and neostigmine was blocked by both L-NAME and methylene blue in the models of nociception, suggesting the activation of NO-cGMP pathway. Also, both L-NAME and methylene blue blocked the per se analgesic effect of sildenafil. These results indicate the peripheral accumulation of cGMP may be responsible for antinociceptive effect, and a possible interaction between cholinergic agents and PDE5 system in models of nociception.

Antinociceptive action of FK506 in mice.

Immunophilins are abundantly present in the brain as compared to the immune system. Immunophilin-binding agents like FK506 are known to inactivate neuronal nitric oxide synthase (nNOS) by inhibiting calcineurin and decrease the production of nitric oxide. Nitric oxide is involved in the mediation of nociception at the spinal level. In the present study, the effect of FK506 on the tail flick response in mice and the possible involvement of NO-L-arginine pathway in this paradigm was evaluated. FK506 (0.5, 1 and 3 mg/kg, ip) produced a significant antinociception in the tail flick test. Nitric oxide synthase (NOS) inhibitor L-NAME significantly and dose dependently (10-40 mg/kg, ip) potentiated the FK506 (0.5 mg/kg)-induced antinociception. On the other hand, NOS substrate L-arginine (100, 200 and 400 mg/kg) inhibited the FK506-induced antinociception in a dose-dependent manner. Concomitant administration of L-NAME (20 and 40 mg/kg) with L-arginine (200 mg/kg) blocked the inhibition exerted by L-arginine on the FK506-induced antinociception. Thus, it was concluded that NO- L-arginine pathway may be involved in the FK506-induced antinociception in tail flick test.

D2-dopamine receptor and alpha2-adrenoreceptor-mediated analgesic response of quercetin.

Quercetin, a bioflavonoid (100-300 mg/kg) produced dose dependent increase in tail-flick latency, the analgesic effect being sensitive to reversal by naloxone (1 mg/kg). Prior treatment with haloperidol (1 mg/kg), D1/D2 receptor antagonist haloperidol, sulpiride (50 mg/kg), a selective D2 receptor antagonist, yohimbine (5 mg/kg), a alpha2-adrenoreceptor antagonist but not by SCH 23390 a, selective D1 receptor antagonist blocked this response. Apomorphine (1 mg/kg) a mixed D1/D2 dopamine receptor agonist, and quinpirole (0.5 mg/kg), a selective D2 receptor agonist also produced antinociception, that was reversed by haloperidol (1 mg/kg), sulpiride (50 mg/kg), but not by yohimbine (5 mg/kg). The antinociceptive action of quercetin (200 mg/kg) was potentiated by D2 agonist quinpirole (0.2 mg/kg). Dopamine D1 receptor agonist SKF38393 (10 and 15 mg/kg) failed to alter the antinociceptive effect of quercetin (200 mg/kg). Quercetin (200 mg/kg) reversed reserpine (2 mg/kg-4 hr) induced hyperalgesia, which was reversed by sulpiride but not by yohimbine. Thus, a role of dopamine D2 and alpha2-adrenoreceptors is postulated in the antinociceptive action of quercetin.

FK506 as effective adjunct to L-dopa in reserpine-induced catalepsy in rats.

Reserpine-induced catalepsy is a widely accepted animal model of Parkinson's disease. In the present study reserpine (2.5 mg/kg, ip) 20 hr and alpha-mehyl-para-tyrosine (AMPT; 200 mg/kg, ip), one hour before the experiment induced significant catalepsy in rats as assessed by bar test. There was a significant increase in the time spent on the bar in bar test as compared to the control untreated rats. L-dopa (100 mg/kg, ip) and carbidopa (10 mg/kg, ip) combination, a conventional therapy was less effective in reversing reserpine-induced catalepsy. Pretreatment with FK506, a neuroprotectant (0.5-2 mg/kg, po) not only dose dependently reduced the catalepsy in reserpine-treated rats but a lower dose (1 mg/kg) potentiated the motor stimulant actions of sub threshold dose of L-dopa (100 mg/kg, ip) and carbidopa (10 mg/kg, ip) combination. Anticataleptic effect of FK506 was blocked dose dependently by specific D2 receptor blocker sulpiride (25-100 mg/kg, ip). In conclusion, the findings of the present study suggest that FK506 has an indirect modulatory action on the dopamine D2 receptors. FK506 being a neuroprotectant, could be used as an effective adjunct to L-dopa for the treatment of neuroleptic-induced extrapyramidal side effects.