Cardiac arrhythmias are of different types based on their mechanism and origin. The information gathered from animal studies has been instrumental in devising diagnostic and therapeutic strategies; so different animal models are needed for different types of arrhythmias. The origin and mechanism underlying clinical arrhythmias are of considerable significance, since knowledge of these processes may provide a basis for successful therapy. Various animal models that encompass different types of arrhythmias are reviewed. This review classifies various experimental models according to their origin, which are mainly supraventricular and ventricular. Also included are various transgenic animal models for arrhythmias.

Probiotics are nonpathogenic microbes used to confer health benefits to the recipient. The derangement of normal body flora has been held responsible for causation of various disorders. Probiotics have been tried in a number of infective and noninfective disorders and found useful, primarily because of their ability to supplement the normal body flora. Their use offers various advantages over-existing antimicrobial agents in being relatively cheap and safe. However, there are few reports of systemic fungemia associated with their use especially, in immunocompromised and severely debilitated patients. They also carry a risk of transferring resistance to other microbes including pathogens. In conclusion, more studies are required to establish their definite place in therapeutics.

OBJECTIVE: To investigate the role of reactive oxygen species (ROS) on cholinergic receptor function. MATERIALS AND METHODS : Rectus abdominis and isolated heart preparations of frog ( Rana tigirina ) were used to assess nicotinic and muscarinic receptor activity, respectively. Thirty percent hydrogen peroxide (H2O2) solution and Fenton mixture (Fm, 13.9 mg, 50 µM of FeSO4, 75 mg of sodium EDTA and 50 µL of 30% H2O2 were added to 10 ml of 0.1 M K2HPO4) were used to generate 1 mM H2O2 and hydroxyl free radicals. The responses were recorded with acetylcholine at different phases of exposure of tissues to ROS. Normal frog Ringer was used as a physiological solution. Responses of acetylcholine were also recorded in the presence of ROS before and after exposure of the tissue to an antioxidant (ascorbic acid). RESULTS : Free-radical-mediated receptor damage was dose (1-100 mM H2O2) and time (10-30 min) dependent when responses were taken with 30 µg and 30 ng of ACh for nicotinic and muscarinic receptors, respectively. There was no effect of ROS on prior exposure of tissue to ascorbic acid (antioxidant) at a concentration of 300 µg/ml. The antioxidant has not shown any beneficial effect on sulfhydryl groups of G-protein-coupled muscarinic receptors, which are more susceptible and sensitive to ROS than ion-channel nicotinic receptors where there is 96% protection with the antioxidant. Reactive oxygen species has shown different effects on receptor function. CONCLUSION: Free radicals continuously cause considerable damage to the receptors. G-protein-coupled muscarinic receptors are more susceptible than ion-channel-linked nicotinic receptors. Antioxidants are shown to play a major role in protecting free-radical-mediated receptor damage.

OBJECTIVE : To demonstrate the mechanism of action mediating the acute and chronic antiinflammatory activity of leafy exudate of Aloe vera (AVL) in animal models of inflammation. MATERIALS AND METHODS : The acute antiinflammatory activity of AVL was evaluated using carrageenan and dextran as phlogistic agents while its chronic antiinflammatory effect was investigated in a complete Freund's adjuvant-induced model of arthritis. The degree of inflammation in all models was measured plethysmographically. The effect of AVL on nitric oxide production in mouse peritoneal macrophages was measured by the Griess reagent. RESULTS : AVL (25 mg/kg) significantly reduced carrageenan and dextran-induced pedal edema in rats by 61.9% and 61.7%, respectively. In the Freund's adjuvant-induced model of chronic inflammation, AVL showed chronic antiinflammatory activity but failed to decrease the arthritic index indicating the absence of antiarthritic activity. AVL (10 µg/ml) caused a decrease in NO production in macrophages without causing toxicity. CONCLUSION : AVL possesses acute and chronic antiinflammatory activity, which is partly mediated by reduced production of NO, which in turn prevents the release of inflammatory mediators.

OBJECTIVE: To study the efficacy of Asparagus racemosus in reducing the cholesterol levels and as an antioxidant in hypercholesteremic rats. MATERIALS AND METHODS: Hypercholesteremia was induced in normal rats by including 0.75 g% cholesterol and 1.5 g% bile salt in normal diet and were used for the experiments. Dried root powder of Asparagus racemosus was administered as feed supplement at 5 g% and 10 gm% dose levels to the hypercholesteremic rats. Plasma and liver lipid profiles, hepatic HMG-CoA reductase, bile acid, malondialdehyde, ascorbic acid, catalase and SOD, fecal bile acid, cholesterol and neutral sterols were estimated using standard methods. RESULTS: Feed supplementation with 5 g% and 10 g% Asparagus racemosus resulted in a significant decline in plasma and hepatic lipid profiles. The feed supplementation increased the HMG-CoA reductase activity and bile acid production in both groups (5 and 10 g% supplemented groups) with concomitant increase in fecal bile acid and fecal cholesterol excretion. The activities of catalase, SOD and ascorbic acid content increased significantly in both the experimental groups (5 and 10 g% supplemented groups). On the other hand, the concentration of malondialdehyde in these groups (5 and 10 g% supplemented groups) decreased significantly, indicating decreased lipid peroxidation. CONCLUSION: The present study demonstrates that addition of Asparagus racemosus root powder at 5 g% and 10 g% level as feed supplement reduces the plasma and hepatic lipid (cholesterol) levels and also decreases lipid peroxidation.

OBJECTIVE: To evaluate the immunomodulatory and antioxidant properties, if any, of S elaginella involvens, S. delicatula and S. wightii . MATERIALS AND METHODS: Immunomodulatory activity of the whole plants (water suspension) was studied in mice immunized with sheep RBC. The plant extracts were tested for their effect on lipid peroxidation ( in vitro and in vivo in mice), and for in vitro hydroxyl radical scavenging activity. The most promising extract (water extract of S. involvens ) was evaluated for its short-term toxicity in mice. RESULTS: The dried suspension (500 mg/kg) of the three plants did not influence humoral antibody titre and the number of antibody secreting cells in the mouse spleen. However, the plant suspensions as well as the water extracts (and not the other extracts) of the plants remarkably increased the weight of thymus in adult mice, and not in suckling mice. This effect was very marked in the case of S. involvens compared to the other two species. Although the water extract of all the three plants showed varying degrees of antioxidant activity, the antilipid peroxidation activity of S. involvens (water extract) was remarkable [EC50: 2 µg/ml]. This extract did not exhibit any conspicuous toxicity in mice in general, short-term toxicity evaluation. At high dose, serum cholesterol level was significantly reduced. CONCLUSION: Out of the three Selaginella species studied, the water extract of S. involvens has promising thymus growth stimulatory activity in adult mice and remarkable antilipid peroxidation property; these observations are of interest in view of tribal and folklore belief that this plant prolongs life span.

OBJECTIVE: To study the antifungal activity of 10 different extracts of seed kernels of Azadirachta indica A. Juss (Meliaceae) on Candida sps. isolated from immunocompromised patients. MATERIALS AND METHODS: The extractants used were hexane, methanol, chloroform, water, petroleum ether, dichloromethane, acetone and absolute alcohol. The products of a successive extraction procedure involving hexane, chloroform and methanol were also tested for anticandidal activity. The minimum inhibitory concentration was tested by broth dilution method at concentrations ranging from 1 to 0.0625 mg/ml. RESULTS: The ethanol extract of commercial neem seed oil, ethanol extract of neem seed kernels and the hexane extract showed best results. All strains were resistant to methanol: chloroform: water extracts and chloroform extracts of the successive extraction procedure. CONCLUSION: The hexane and alcoholic extracts of neem seed seem to be promising anticandidal agents.

OBJECTIVE: To investigate the antidepressant-like effect of glycyrrhizin (glycyrrhizic acid ammonium) in mice. MATERIALS AND METHODS: Glycyrrhizin (1.5, 3.0 and 6.0 mg/kg, i.p.) was administered once daily for seven successive days to separate groups of young male Swiss albino mice. The immobility periods of control and treated mice were recorded in forced swim test (FST) and tail suspension test (TST). Effect of sulpiride (50 mg/kg, i.p.; a selective D2 receptor antagonist), prazosin (62.5 µg/kg, i.p.; an a1-adrenoceptor antagonist) and p-chlorophenylalanine (100 mg/kg, i.p.; an inhibitor of serotonin synthesis) on antidepressant-like effect of glycyrrhizin in TST was also studied. The antidepressant-like effect of glycyrrhizin was compared to that of imipramine (15 mg/kg, i.p.) and fluoxetine (20 mg/kg, i.p.) administered for seven successive days. RESULTS: Glycyrrhizin produced significant antidepressant-like effect at a dose of 3.0 mg/kg administered for seven successive days, as indicated by reduction in the immobility times of mice in both FST and TST. Glycyrrhizin did not show significant effect on locomotor activity of mice. The efficacy of glycyrrhizin was found to be comparable to that of imipramine and fluoxetine. Sulpiride and prazosin significantly attenuated the glycyrrhizin-induced antidepressant-like effect in TST. On the other hand, p-chlorophenylalanine did not reverse antidepressant-like effect of glycyrrhizin. This suggests that the antidepressant-like effect of glycyrrhizin seems to be mediated by an increase in brain norepinephrine and dopamine, but not by an increase in serotonin. CONCLUSION: The results of the present study indicate the involvement of adrenergic and dopaminergic systems in the antidepressant-like effect of glycyrrhizin.