Anti-arthritic and anti-inflammatory activity of combined pioglitazone and prednisolone on adjuvant-induced arthritis.

The aim of the present study was to evaluate the effect of combined treatment of pioglitazone (PGZ) and prednisolone (PDL) on the progression of adjuvant-induced arthritis in rats. Adjuvant arthritis was induced by single intra-dermal injection of 0.1 ml Freund's complete adjuvant (0.05% w/v Mycobacterium butyricum in mineral oil) into foot pads of left hind paws of Wistar rats of either sex. There were six experimental groups: Group I was healthy animals as control, Group II was arthritic animals without drug treatment, Group III was arthritic animals treated with a standard non-steroidal anti-inflammatory drug aspirin (100 mg/kg), Group IV was arthritic animals received PGZ (10 mg/kg) alone, Group V was arthritic animals received PDL (10 mg/kg) alone, and Group VI was arthritic animals treated with a combined suspension of PGZ and PDL (20 mg/kg). Drugs were administered daily orally at day 0 and continued upto 28th day after induction of arthritis. Induction of arthritis significantly increased hind paw volume (HPV), loss of body weight (BW), enhanced tibiotarsal joint thickness (TJT), and increased plasma tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-6 levels. Treatment with aspirin or combined suspension of PGZ and PDL in the arthritic animals produced significant reductions in HPV and TJT, normalized BW, and significantly decreased plasma levels of TNF-α and IL-6. These observations suggest that the combined administration of PGZ and PDL was effective in modulating the inflammatory response and suppress arthritis progression in experimental animal model. These findings may help to improve the treatment of rheumatoid arthritis.

Evaluation of anticonvulsant and nootropic effect of ondansetron in mice.

The role of serotonin receptors have been implicated in various types of experimentally induced seizures. Ondansetron is a highly selective 5-hydroxytryptamine 3 (5-HT(3)) receptor antagonist used as antiemetic agent for chemotherapy-, and radiotherapy-induced nausea and vomiting. The present study was carried out to examine the effect of ondansetron on electroshock, pentylenetetrazole (PTZ)-induced seizures and cognitive functions in mice. Ondansetron was administered intraperitoneally (i.p.) at doses of 0.5, 1.0 and 2.0 mg/kg (single dose) to observe its effect on the increasing current electroshock seizure (ICES) test and PTZ-induced seizure test. In addition, a chronic study (21 days) was also performed to assess the effects of ondansetron on electroshock-induced convulsions and cognitive functions. The effect on cognition was assessed by elevated plus maze and passive avoidance paradigms. Phenytoin (25 mg/kg, i.p.) was used as a standard anticonvulsant drug and piracetam (200 mg/kg) was administered as a standard nootropic drug. The results were compared with an acute study, wherein it was found that the administration of ondansetron (1.0 and 2.0 mg/kg) significantly raised the seizure-threshold current as compared to control group in the ICES test. Similar results were observed after chronic administration of ondansetron. In PTZ test, ondansetron in all the three tested doses failed to show protective effect against PTZ-induced seizure test. Administration of ondansetron for 21 days significantly decreased the transfer latency (TL) and prolonged the step-down latency (SDL). The results of present study suggest the anticonvulsant and memory-enhancing effect of ondansetron in mice.

Protective role of curcumin on colchicine-induced cognitive dysfunction and oxidative stress in rats.

Dementia is a syndrome of progressive nature, affects wide range of cognitive abilities like memory, language, calculation and so on, neuropsychiatric and social deficits to impair the routine social functions. The present study was designed to assess the effect of curcumin against colchicine-induced cognitive dysfunction and oxidative stress in rats and compare it with rivastigmine. Colchicine (15 µg/5µl) was administered to male Wistar rats intracerebroventricularly (i.c.v.) by stereotaxic apparatus to induce cognitive dysfunction. Administration of colchicine caused poor retention of memory in elevated plus maze, passive avoidance apparatus and Morris water maze paradigms. Chronic treatment with curcumin (100, 200 and 400 mg/kg, p.o.) twice daily and rivastigmine (2.5 mg/kg, p.o.) daily for a period of 28 days beginning 7 days prior to colchicine injection significantly improved colchicine-induced cognitive impairment. Biochemical assessment revealed that i.c.v. colchicine injection significantly increased lipid peroxidation, depleted reduced glutathione levels and decreased acetyl cholinesterase (AChE) activity in rat brains. Chronic administration of curcumin significantly reduced the elevated lipid peroxidation, restored the reduced glutathione levels and AChE activity; however, rivastigmine failed to prevent oxidative stress. The results of the current study indicate that curcumin (100, 200 and 400 mg/kg, p.o.) twice daily has a protective role against colchicine-induced cognitive impairment and associated oxidative stress.

Substitute of Animals in Drug Research: An Approach Towards Fulfillment of 4R's.

The preclinical studies for drug screening involve the use of animals which is very time consuming and expensive and at times leads to suffering of the used organism. Animal right activists around the world are increasingly opposing the use of animals. This has forced the researchers to find ways to not only decrease the time involved in drug screening procedures but also decrease the number of animals used and also increase the humane care of animals. To fulfill this goal a number of new in vitro techniques have been devised which are called 'Alternatives' or 'Substitutes' for use of animals in research involving drugs. These 'Alternatives' are defined as the adjuncts which help to decrease the use as well as the number of animals in biomedical research. Russell and Burch have defined these alternatives by three R's - Reduction, Refinement and Replacement. These alternative strategies include physico-chemical methods and techniques utilizing tissue culture, microbiological system, stem cells, DNA chips, micro fluidics, computer analysis models, epidemiological surveys and plant-tissue based materials. The advantages of these alternatives include the decrease in the number of animals used, ability to obtain the results quickly, reduction in the costs and flexibility to control the variables of the experiment. However these techniques are not glittering gold and have their own shortcomings. The disadvantages include the lack of an appropriate alternative to study the whole animal's metabolic response, inability to study transplant models and idiosyncratic responses and inability to study the body's handling of drugs and its subsequent metabolites. None-the-less these aalternative methods to certain extent help to reduce the number of animals required for research. But such alternatives cannot eliminate the need for animals in research completely. Even though no animal model is a complete set of replica for a process within a human body, the intact animal does provide a better model of the complex interaction of the physiological processes.

Propoxur-induced acetylcholine esterase inhibition and impairment of cognitive function: attenuation by Withania somnifera.

Propoxur (2-isopropoxyphenyl N-methylcarbamate) is widely used as an acaricide in agriculture and public health programs. Studies have shown that sub-chronic exposure to propoxur can cause oxidative stress and immuno-suppression in rats. Carbamates are also known to exhibit inhibitory effect on cholinesterase activity, which is directly related to their cholinergic effects. In the present study, the effect of Withania somnifera (Ashwagandha), a widely used herbal drug possessing anti-stress and immunomodulatory properties was studied on propoxur-induced acetylcholine esterase inhibition and impairment of cognitive function in rats. Male Wistar rats were divided into four groups. Group I was treated with olive oil and served as control. Group II was administered orally with propoxur (10 mg/kg b.wt.) in olive oil, group III received a combination of propoxur (10 mg/kg b.wt.) and W. somnifera (100 mg/kg b.wt.) suspension and group IV W. somnifera (100 mg/kg b.wt.) only. All animals were treated for 30 days. Cognitive behaviour was assessed by transfer latency using elevated plus maze. Blood and brain acetylcholine esterase (AChE) activity was also assessed. Oral administration of propoxur (10 mg/kg b.wt.) resulted in a significant reduction of brain and blood AChE activity. A significant prolongation of the acquisition as well as retention transfer latency was observed in propoxur-treated rats. Oral treatment of W. somnifera exerts protective effect and attenuates AChE inhibition and cognitive impairment caused by sub-chronic exposure to propoxur.

Reversal of propoxur-induced impairment of step-down passive avoidance, transfer latency and oxidative stress by piracetam and ascorbic acid in rats.

Propoxur, a carbamate pesticide has been shown to adversely affect memory and induce oxidative stress. The present study was designed to correlate the effect of propoxur, piracetam (a nootropic drug) and ascorbic acid (an antioxidant) on oxidative stress and cognitive function. Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus and transfer latency (TL) on elevated plus maze. Oxidative stress was assessed by examining brain malondialdehyde (MDA) and non-protein thiol (NP-SH) levels. A significant reduction in SDL and prolongation of TL was found for the propoxur-treated group at weeks 6 and 7 as compared with control (p<0.001). One week treatment by piracetam (400mg/kg/d, i.p.) or ascorbic acid (120mg/kg/d, i.p.) antagonized the effect of propoxur on SDL as well as TL. Both piracetam and ascorbic acid attenuated the propoxur-induced increase in brain MDA levels and decrease in brain NP-SH levels. Results of the present study show that ascorbic acid and piracetam have the potential to reverse cognitive dysfunction and oxidative stress induced by propoxur in the brain.

Role of kappa- and delta-opioid receptors in the antinociceptive effect of oxytocin in formalin-induced pain response in mice.

Oxytocin has been implicated in the modulation of somatosensory transmission such as nociception and pain. The present study investigates the effect of oxytocin on formalin-induced pain response, a model of tonic continuous pain. The animals were injected with 0.1 ml of 1% formalin in the right hindpaw and the left hindpaw was injected with an equal volume of normal saline. The time spent by the animals licking or biting the injected paw during 0-5 min (early phase) and 20-25 min (late phase) was recorded separately. Oxytocin (25, 50, 100 microg/kg, i.p.) dose dependently decreased the licking/biting response, both in the early as well as the late phases. The antinociceptive effect of oxytocin (100 microg/kg, i.p.) was significantly attenuated in both the phases by a higher dose of the non-selective opioid receptor antagonist naloxone (5 mg/kg, i.p.), MR 2266 (0.1 mg/kg, i.p.), a selective kappa-opioid receptor antagonist and naltrindole (0.5 mg/kg, i.p.), a selective delta-opioid receptor antagonist but not by a lower dose of naloxone (1 mg/kg, i.p.) or beta-funaltrexamine (2.5 microg/mouse, i.c.v.), a selective mu-opioid receptor antagonist. Nimodipine, a calcium channel blocker (1 and 5 mg/kg, i.p.) produced a dose-dependent analgesic effect. The antinociceptive effect of oxytocin was significantly enhanced by the lower dose of nimodipine (1 mg/kg, i.p.) in both the phases. Chronic treatment with oxytocin (100 microg/kg/day, i.p. daily for 7 days) did not produce tolerance in both the phases of formalin-induced pain response. The results thus indicate that oxytocin displays an important analgesic response in formalin test; both kappa- and delta-opioid receptors as well as voltage-gated calcium channels seem to be involved in the oxytocin-induced antinociception.

Protective effect of melatonin against propoxur-induced oxidative stress and suppression of humoral immune response in rats.

Effect of melatonin in attenuation of propoxur induced oxidative stress and suppression of humoral immune response was studied in rats. Oral administration of propoxur (10 mg/kg) increased lipid peroxidation in serum after 28 days treatment. Superoxide dismutase, catalase and glutathione were also altered following propoxur exposure. In addition propoxur exposure markedly suppressed humoral immune response as assessed by antibody titre and plaque forming cell assay. Simultaneous treatment with melatonin (5 mg/kg, ip) markedly attenuated the effect of propoxur on (a) lipid peroxidation, (b) oxidative stress parameters and (c) immunotoxicity. Results have been discussed in the light of possible immunopotentiating and antioxidant effects of melatonin to understand the influence of oxidative stress on propoxur induced immunomodulation.

Receptor mechanisms involved in the anticonvulsant effect of melatonin in maximal electroshock seizures.

The present study investigates the mechanisms involved in the anticonvulsant effect of melatonin in maximum electroshock (MES) seizures. Melatonin (25-100 mg/kg) dose-dependently decreased the duration of tonic hindlimb extension (THLE). The anticonvulsant effect of melatonin was blocked by bicuculline, a GABA(A) receptor antagonist, and luzindole, an ML(1) receptor antagonist, while prazosin, an ML(2) receptor antagonist, enhanced the anticonvulsant actions of melatonin in this seizure model. Administration of serotonergic agents, mianserin and ondansetron, along with melatonin, increased the antiseizurogenic activity of melatonin, while buspirone had no effect. Pretreating the animals with diazepam, carbamazepine or lamotrigine enhanced the anticonvulsant effect of melatonin. Melatonin thus appears to be an effective anticonvulsant, and melatonin ML(1) receptors, GABAergic and serotonergic mechanisms may play an important role in mediating the anticonvulsant activity of melatonin in electroshock seizures.

Evaluation of the role of melatonin in formalin-induced pain response in mice.

BACKGROUND: Melatonin, the major secretory product of pineal gland has been suggested to play a regulatory role in the circadian rhythm of body activities including the pain sensitivity. Three subtypes of melatonin receptors, i.e. ML1, ML2 and ML3 have been identified. AIM: To investigate the antinociceptive activity of melatonin and to unravel the underlying receptor mechanisms involved in this action. MATERIAL AND METHODS: Effect of melatonin (25-100 mg/kg, ip) and its interaction with putative melatonin receptor antagonists and opioidergic and serotoninergic agents have been studied in formalin test, a model of tonic continuous pain. Formalin (0.1 ml of 1% solution) was injected under the plantar surface of right hind paw of mice and the time an animal spent in licking the injected paw was measured. STATISTICAL ANALYSIS: The data were analysed by one-way ANOVA followed by Tukey's test for multiple comparisons. RESULTS: Injection of formalin produced two phases of intense licking, an early phase (0-5 min) and a late phase (20-25 min). Melatonin dose-dependently decreased the licking response in both the phases, effect being more marked in the late phase. Luzindole, a ML1 receptor antagonist did not block but rather enhanced the antinociceptive activity of melatonin. However, prazosin, a ML2 receptor antagonist in the low dose (0.5 mg/kg) significantly attenuated but in higher dose (1 mg/kg) enhanced the analgesic effect of melatonin. Naloxone, an opioid receptor antagonist did not reverse but morphine, an opioid agonist enhanced the antinociceptive activity of melatonin. Both mianserin and ondansetron the 5HT2 and 5HT3 receptor antagonists, respectively increased the analgesic effect of melatonin. CONCLUSION: The present results suggest the involvement of ML2 receptors in mediating the antinociceptive activity of melatonin in formalin-induced pain response. Further an interplay between melatonin, alpha-1 adrenergic and 5HT2 and 5HT3 serotoninergic receptors may also be participating in this action.

Effect of L-arginine on restraint stress induced modulation of immune responses in rats and mice.

The present study investigates the role of nitric oxide (NO) on restraint stress (RS)-induced modulation of humoral and cell-mediated immune responses in rats and mice. RS produced suppression of humoral immune response, i.e., anti-SRBC antibody titre ( 7.38 +/- 0.32 versus 4.13 +/- 0.30; mean +/- S.E.M., P < 0.001). In case of cell-mediated immunity, in delayed type hypersensitivity (DTH) response the change in paw volume decreased from 0.069 +/- 0.003 mm (mean +/- S.E.M.) in control non-stressed group to 0.038 +/- 0.002 mm in the stressed group (P < 0.001) while percentage leucocyte migration inhibition (% LMI) decreased from 39.7 +/- 1.95 in control non-stressed animals to 15.2 +/- 1.07 in animals subjected to stress (P < 0.01). Pretreating the animals with an NO precursor, L-arginine (1000 mg kg-1, i.p.) antagonized the effect of RS on humoral (anti-SRBC antibody titre 6.50 +/- 0.27 versus 4.13 +/- 0.30, P < 0.001 ) and cell-mediated (DTH response 0.066 +/- 0.002 mm versus 0.038 +/- 0.002 mm, P < 0.001; % LMI 41.5 +/- 1.46 versus 15.2 +/- 1.07, P < 0.01) immune responses. Administration of 7-nitroindazole (7-NI, 50 mg kg-1, i.p.), an inhibitor of neuronal NO synthase, alone further enhanced the immunosuppressive effect of RS (anti-SRBC antibody titre 2.75 +/- 0.25 versus 4.13 +/- 0.30, P < 0.001; DTH response 0.019 +/- 0.002 mm versus 0.038 +/- 0.002 mm, P < 0.001; % LMI 5.0 +/- 1.08 versus 15.2 +/- 1.07, P < 0.01). However, when given before L-arginine treatment, 7-NI reversed the effect of the latter drug on stress-induced immunomodulation (anti-SRBC antibody titre 3.00 +/- 0.27 versus 6.5 +/- 0.27, P < 0.001; DTH response 0.043 +/- 0.003 mm versus 0.066 +/- 0.002 mm, P < 0.001; % LMI 12.0 +/- 0.93 versus 41.5 +/- 1.46, P < 0.01). Unlike its effect on RS-induced immune responsiveness, L-arginine (250, 500, 1000 mg kg-1) when given for 5-7 days to naive non-stressed animals produced dose dependent suppression of both humoral (anti-SRBC antibody titre 6.4 +/- 0.32 versus 5.4 +/- 0.32, 4.0 +/- 0.27, 3.1 +/- 0.30, respectively) and cell-mediated (DTH 0.065 +/- 0.003 mm versus 0.064 +/- 0.004 mm, 0.039 +/- 0.003 mm, 0.020 +/- 0.002 mm, respectively and % LMI 37.52 +/- 1.58 versus 30.48 +/- 1.07, 28.18 +/- 1.22, 19.76 +/- 0.83, respectively) immune responses. 7-NI significantly blocked these immunosuppressive effects of L-arginine (anti-SRBC antibody titre 6.0 +/- 0.38 versus 3.1 +/- 0.030, P < 0.01; DTH response 0.056 +/- 0.004 mm versus 0.020 +/- 0.002 mm, P < 0.001; % LMI 34.76 +/- 1.31 versus 19.76 +/- 0.83, P < 0.01). However, 7-NI when given to non-stressed animals failed to modulate immune responsiveness. Thus, NO appears to play an important role in RS-induced immunomodulation and these effects are different from its effect on immune responsiveness in non-stressed animals.

Attenuation of the effect of progesterone and 4'-chlordiazepam on stress-induced immune responses by bicuculline.

The present study investigates the effect of progesterone, a pregnane precursor of neurosteroids, and 4'-chlordiazepam (4'-CD), a specific ligand for mitochondrial diazepam binding inhibitor receptor (MDR) involved in neurosteroidogenesis, on restraint stress (RS)-induced modulation of humoral and cell-mediated immune responses. RS produced a significant reduction in anti-sheep red blood cells (SRBC) antibody titre, a measure of humoral immune response, and % leucocyte migration inhibition (LMI) and foot-pad thickness test, measures of cell-mediated immune responses. These effects of RS on immune responses were effectively blocked by pretreating the animals with progesterone (10 mg/kg, sc) or 4'-CD (0.5 mg/kg, sc) administered just before subjecting the animal to RS. The effect of both progesterone and 4'-CD on RS-induced immune modulation was significantly attenuated by bicuculline (2 mg/kg, ip) but not by flumazenil (10 mg/kg, ip). Unlike its effect on RS-induced immune responsiveness, progesterone (5, 10 mg/kg, sc) when administered to non-stressed animals produced a significant suppression of both humoral and cell-mediated immune responses which was not reversed by bicuculline. However, 4'-CD failed to modulate immune response in naive non-stressed animals. These results suggest that progesterone and 4'-CD affect stress-induced immune responses by modulating GABA-ergic mechanism. However, GABA-A receptor system does not appear to be involved in progesterone-induced immunosuppression in nonstressed animals.

Evaluation of immunomodulatory potential of Ocimum sanctum seed oil and its possible mechanism of action.

The present study investigates the effect of Ocimum sanctum seed oil (OSSO) on some immunological parameters in both non-stressed and stressed animals. An attempt has also been made to explore the possible mechanism of immunomodulatory activity. OSSO (3 ml/kg, ip) produced a significant increase in anti-sheep red blood cells (SRBC) antibody titre and a decrease in percentage histamine release from peritoneal mast cells of sensitized rats (humoral immune responses), and decrease in footpad thickness and percentage leucocyte migration inhibition (LMI) (cell-mediated immune responses). Restraint stress (RS) produced a significant reduction in the anti-SRBC antibody titre, foot pad thickness and percentage LMI (% LMI). The effects of RS on humoral as well as cell-mediated immune responses were effectively attenuated by pretreating the animals with OSSO. Co-administration of diazepam (1 mg/kg, sc), a benzodiazepine (BZD), with OSSO (1 ml/kg, ip) enhanced the effect of OSSO on RS-induced changes in both humoral and cell-mediated immune responses. Further, flumazenil (5 mg/kg, ip), a central BZD receptor antagonist inhibited the immunomodulatory action of OSSO on RS-induced immune responsiveness. Thus, OSSO appears to modulate both humoral and cell-mediated immune responsiveness and these immunomodulatory effects may be mediated by GABAergic pathways.

Effect of minocycline and tetracycline on immunological responses in experimental animals.

In recent years, there has been an increase in the use of antibiotics, primarily tetracycline anlogues, like minocy cline to treat rheumatoid arthritis. However, the mechanism of action of these analogues is not clearly defined. The present study investigates the effects of minocycline and tetracycline on some immunological parameters in Wistar rats and Swiss albino mice. Haemagglutination (HA) titre was employed as parameter of humoral immune response and % leukocyte migration inhibition (% LMI) and footpad thickness tests were used as measures of cell mediated immune response. Both minocycline and tetracycline significantly improved humoral immune response in rats as indicated by an increase in anti-SRBC antibody titre. In the LMI test, depending on the time period of drug administration, there was an increase or a decrease in the % LMI. When drugs were administered on days 1-7 after sensitization, both the compounds caused a significant increase in % LMI. However, the % LMI was significantly decreased when the drugs were administered on days 7-13 of sensitization, indicating variable effects of these agents on the Immune mechanism depending on the time of administration in relation to the development of immune responsiveness. Both minocycline as well as tetracycline produced a significant decrease in the paw volume in the footpad-thickness test which indicates a decrease in lymphokine production/release. The present study thus shows that minocycline and tetracycline exhibit immunomodulatory properties, which may contribute significantly to their beneficial effects in rheumatoid arthritis.

Differential effects of benzodiazepines on immune responses in non-stressed and stressed animals.

Benzodiazepines (BZDs) used extensively as antianxiety agents are known for their low toxicity. However, a long lasting depression of mitogen stimulated secretion of macrophage-derived cytokines has been shown in offsprings of rats that were exposed to diazepam during pregnancy. The Present study investigates the effects of long term administration of diazepam and alprazolam on humoral and cell-mediated immune responses in adult male Wistar rats and Swiss albino mice. Administration of diazepam (5 mg/kg/day x 7-14 d) and alprazolam (1 mg/kg/day x 7-14 d) produced a significant reduction of anti-SRBC antibody titre, a measure of humoral immune response, and foot pad thickness and % leucocyte migration inhibition (% LMI), measures of cell-mediated immune responses. Administration of diazepam (5 mg/kg, i.p.) or alprazolam (1 mg/kg, i.p.) before subjecting the animals to restraint stress (RS) reversed the immunosuppressive effects of RS. Both per se immunosuppressive effects and attenuation of RS-induced immunosuppression of BZDs was antagonized by flumazenil (10 mg/kg, i.p.), a central BZD receptor antagonist. Thus, BZDs appear to modulate the immune system in non-stressed and stressed adult animals in a differential manner and these effects are mediated via central benzodiazepine receptors.

Development of differential tolerance to the sedative and anti-stress effects of benzodiazepines.

Differential degree of tolerance has been reported to develop for anticonvulsant, sedative and skeletal muscle relaxant effects of benzodiazepines (BZDs). Acute treatment with BZDs reportedly reduces the formation of gastric stress ulcers and attenuates stress-induced immunosuppression. The present study investigates whether tolerance develops to these antistress effects of BZDs by using diazepam and chlordiazepoxide as representative drugs. A single dose of diazepam (5 mg/kg, i.p.) or chlordiazepoxide (20 mg/kg, i.p.) produced a significant reduction in locomotor activity, a measure of sedative effect and antagonized the effect of restraint stress (RS) on gastric mucosal lesions and anti-sheep red blood cell (SRBC) antibody titre. With chronic treatment (X 7 d), there was a marked tolerance to the sedative effect of both the studied BZD drugs, while much less tolerance developed to their ulcer protective action. However, no tolerance was observed to the attenuating effect of diazepam and chlordiazepoxide on RS-induced immunosuppression. Thus, the results of the present study indicate that different mechanisms may be involved in the development of tolerance to the sedative, antiulcer and immunomodulatory effects of BZDs.

Antinociceptive activity of a neurosteroid tetrahydrodeoxycorticosterone (5alpha-pregnan-3alpha-21-diol-20-one) and its possible mechanism(s) of action.

The present study investigates the effects of a neurosteroid tetrahydrodeoxycorticosterone (5alpha-pregnan-3alpha-21-diol-20-one) in two experimental models of pain sensitivity in mice. Tetrahydrodeoxycorticosterone (2.5, 5 mg/kg, i.p.) dose dependently decreased the licking response in formalin test and increased the tail flick latency (TFL) in tail flick test. Bicuculline (2 mg/kg, i.p.), a GABA(A) receptor antagonist blocked the antinociceptive effect of tetrahydrodeoxycorticosterone in TFL test but failed to modulate licking response in formalin test. Naloxone (1 mg/kg, i.p.), an opioid antagonist effectively attenuated the analgesic effect of tetrahydrodeoxycorticosterone in both the models. Tetrahydrodeoxycorticosterone pretreatment potentiated the antinociceptive response of morphine, an opioid compound and nimodipine, a calcium channel blocker in formalin as well as TFL test. Thus, tetrahydrodeoxycorticosterone exerts an analgesic effect, which may be mediated by modulating GABA-ergic and/or opioid-ergic mechanisms and voltage-gated calcium channels.

Potentiation of analgesia and reversal of tolerance to morphine by calcium channel blockers.

Effect of four calcium channel blockers (CCBs) belonging to different chemical classes, alone and in combination with morphine was investigated on two models of pain sensitivity, i.e. formalin and tail flick tests in mice. All the studied CCBs, i.e. diltiazem, flunarizine, nimodipine and verapamil inhibited formalin-induced pain responses; however, with verapamil, though there was a trend towards a reduction of paw-licking response to formalin, it was not found to be statistically significant. In contrast, none of the CCBs affected the tail flick latency at any of the doses studied. Morphine, a mu-receptor agonist exerted a significant analgesic effect in formalin as well in tail flick tests. Pretreatment with all CCBs significantly enhanced the analgesic effect of morphine in both tests of nociception. Further, concomitant administration of one of the CCBs, diltiazem with morphine prevented the development of tolerance to the latter. However, combination of diltiazem with morphine, like morphine alone was found to be ineffective in morphine tolerant animals. Results, thus, show that CCBs produced an analgesic effect of their own in formalin-induced tonic pain and potentiated the analgesic activity of morphine. They also modulated opioid-induced tolerance.