" Maximal Electroshock ( MES ) Induced Convulsions "- A Model for Evaluate Anti Epileptic Activity.
Meritt and Putnam developed the MES test and discovered the anticonvulsive effect of Diphenyl hydantoin using this test in 1938. Phenytoins subsequent success in the clinical management of generalized tonic clonic seizures provided the validation necessary to consider the MES test as a reasonable model of human generalized tonic clonic seizure. MES produce the spread of seizure similar to grandmal epilepsy. In MES method brief high intensity shock is applied to the head through corneal or ear electrodes with a stimulator that either delivers constant current on constant voltage as a frequency of 50-60/sec. The electrodes are moistened with saline solution before application for better conductance. All animals are stimulated with the constant current stimulator typical stimulation parameters include 50 mA in mice and 150 mA in rats, 50-60/Sec current delivered via corneal/ear electrodes for 0.2 Sec. The MES convulsions are divided into five phases such as Phase of tonic limb flexion, Phase of tonic limb extension, Phase of clonic convulsions, Stupor and Recovery or death. A substance is known to possess anticonvulsant property it reduces or abolishes the extensor phase of MES convulsion. Drugs effective against generalized tonic clonic seizure such as Phenytoin, Carbamazepine, Phenobarbitone and Primidone are effective while Ethosuximide is in effective in this test
Healthy young 8 to 12 weeks old Albino Wistar rats of laboratory strains of either sex weighing 200 -250 g should be employed. Females should be nulliparous and non-pregnant. The temperature in the experimental animal room was should be at 22°C (± 3°C) with the relative humidity was at 50 % to 60 %. Lighting should be provided artificial, the sequence being 12 hours light and 12 hours dark. The animals should be housed individually. For feeding conventional rodent laboratory diets should be used with an unlimited supply of drinking water. The animals should be kept in their cages for at least 5 days prior to dosing to allow for acclimatization to the laboratory conditions and should be fasted overnight ad libitum prier to dosing extract/ standard drug/ vehicle.
Selection of doses of drug/ extract (As per OECD Guidelines 425):
For the assessment of Antidepressant activity, three dose levels should be chosen in such a way that, middle dose was approximately one tenth of the maximum dose during acute toxicity studies, and a high dose which was twice that of one tenth dose and a low dose which was 50% of one tenth dose
Divide overnight fasted animals in to five groups comprising of six animals each. Administer the drug / extract at different doses for Group III, IV and V orally (2 mL/100g body weight, extract should be suspended in 0.6% Sodium Carboxy Methyl Cellulose) 60 min prier to induction of MES. Inject Group II with the standard drug (Phenytoin, 25 mg/Kg body weight, i.p) 30 min before induction of MES, administer vehicle (2mL/100g body weight, 0.6% Sodium Carboxy Methyl Cellulose) for Group I and serve as control. Apply A supramaximal electrical stimulus of 150 mA to the animals for 0.2 seconds through ear clip electrodes. Observe the animals for various phases of MES seizures viz. tonic hind limb flexion, tonic hind limb extensor and tonic-clonic phase. Abolition or decrease in the duration of extensor phase should be taken as an index of anti epileptic activity.
The data should be presented as mean ± SEM. Analyse the data by one-way analysis of variance (ANOVA) followed by Dunnett’s test.