Introduction to seizure and epilepsy 1
Epilepsy : disorder of brain function characterized by a periodic and unpredictable occurrence of seizures. Seizure : abnormal increased electrical activity in the brain. Convulsion : major motor manifestations of a seizure (rhythmic jerking of the limbs). 2
Causes of epilepsy : Neurological diseases stroke Infection Head injury Neoplasm of brain hereditary 3
Classification of Seizures Primary Genralised Partial Seizure Unclassified Seizure Tonic Clonic seizure Absence seizure Atonic seizure Myoclonic seizure Simple Partial Seizure Complex Partial Seizure Partial Seizures Secondarily generalized. Infantile Spasms Status Epilepticus 4
Generalised seizure Whole brain is involved Characterised by immediate loss of consciousness Major Types 1. Tonic Clonic Seizure (Grand Mal Epilepsy): Cry Unconsciousness- Strong (Tonic) contraction of all body muscles Clonic Jerking Prolonged sleep & Depression. 1-2 min 2. Absence Seizure (Petit Mal Epilepsy): Prevalant in Children. Momemtary loss of consciousnees Patient freezes & stares in one direction No muscular movement & jerking. ½ mins 3. Atonic Seizure: Due to excessive inhibitory dischagre Relaxation & Patient may fall. 5
Partial seizure Discharge begins locally, remains localized. Symptoms depend on the brain region involved. Also known as Psychomotor Epilepsy. 1. Simple partial seizures (Cortical Focal Epilepsy): Involvement of area of cortex causes convulsions. No loss of consciousness. ½ to 1 min. 2. Complex partial Seizures (Temporal lobe epilepsy) Attacks of bizarre, purposeless movement. Impairment of consciousness. 1 2 min. 3. Partial Seizures Secondarily generalized. Partial seizures occurs first & evolves into generalized tonic-clonic seizure. 6
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Selection Of Anti-epileptic Drug Primary GTC Secondarily GTC Partial Absence Atypical, Myoclonic, Atonic Carbamazepine Carbamazepine Carbamazepine Carbamazepine Carbamazepine Carbamazepine Carbamazepine Carbamazepine Ethosuximide Ethosuximide Ethosuximide Ethosuximide Carbamazepine Carbamazepine Carbamazepine Carbamazepine Oxcarbazepine Oxcarbazepine Oxcarbazepine Oxcarbazepine Oxcarbazepine Oxcarbazepine Oxcarbazepine Oxcarbazepine Clonazepam Clonazepam Clonazepam Clonazepam Topiramate Topiramate Topiramate Topiramate Topiramate Topiramate Topiramate Topiramate Phenytoin Phenytoin Phenytoin Phenytoin phenobarbital phenobarbital phenobarbital phenobarbital phenobarbital phenobarbital phenobarbital phenobarbital phenobarbital phenobarbital phenobarbital phenobarbital Phenytoin Phenytoin Phenytoin Phenytoin Phenytoin Phenytoin Phenytoin Phenytoin 8
PRECLINICAL EVALUATION of Anti-Epileptic Drugs 9
Animal Models of Seizure The usual approach to anticonvulsant drug testing in animals is to observe the effect of prior drug administration on seizures produced by 1. Electrical stimulation of brain 2. Systemic administration of a convulsant drug 3. Animal strains with spontaneous or sensory-evoked convulsions 10
Measurement of drug effects: 1. Change in the seizure threshold (or latency) 2. Change in incidence of seizures or deaths 3. Changes in the EEG pattern 11
Models for Epilepsy Induction of Seizure in normal animal Genetic animal Model Electrically induced Seizure Chemically induced Seizure Acute induced Seizure MES PTZ Chronic induced Seizure Electrical or Chemical Kindling Post Status Epilepticus model with spontaneous recurrent seizures 12 Electrical SE Induction (Perforanth path) Chemical SE Induction ( Pilocarpine)
Methods 1. Electroshock seizures i. Thresholod model ii. MES (Maximal Electro Shock) 2. Chemical-induced seizures : i. Pentylenetetrazol(PTZ)-induced seizures ii. iii. iv. Strychnine-induced convulsions. Picrotoxin-induced convulsions. Isoniazid-induced convulsions. v. Bicuculline tests in rats. vi. 4-Aminopyridine induced seizures in mice. 3. Epilepsy induced by Focal Seizures 4. Kindled rat seizure model 5. Genetic animal model of epilepsy 13
Electroshock Seizures In Mice & Rats PHASES: 1. Phase of tonic limb flexion (1.5 sec) 2. Full extension of hind limbs (10 sec) 3. Clonic interval (Variable) 4. Death/Recovery (in some animals) 14
Electro convulsiometer 15
Maximal Electroshock Convulsion Threshold Test (MEST) Principle: To determine the ability of the drug to alter the threshold for tonic limb extension * Effective drugs increases the threshold * Good test for generalized tonic-clonic seizures (grand mal) Animals: Mice or Rat An electro-convulsiometer with Corneal or Ear electrodes CC 50 : Current for inducing hind limb extension 50% of animal 16
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Maximal Electroshock Seizure (MES) Test A model for screening drugs for Generalized tonic clonic seizures 18 Electric stimuli evoke tonic hind limb extensions
ANIMALS: Groups of 6-10 male Swiss mice (20-32g) or Wistar rats (100-150g) are used. ROUTE OF DRUG ADMINISTRATION: i. Intraperitoneal ii. Oral 30 min after i.p. injection and 60 min after oral administration the animals are subjected to electroshock. An electro-convulsiometer with Corneal or Ear electrodes is used to deliver the shock. Current used: o Rat : 150mA / 750 V Freq- 50-60/sec o Mice : 50 ma/ 250 V 0.2 second duration 19
END POINT for Electroshock Tests : The effect of drugs will be observed in terms of Presence/absence of tonic phase or death Increase latency to tonic phase Decrease in the duration of tonic phase 20
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PTZ-induced Seizure Principle : GABA antagonist causes direct depolarization of central neurons. PTZ-induced seizure is an screening model for absence seizure. Procedure: Groups of 10 Albino Swiss mice of either sex (20-25 g) Animals are injected with vehicle, test drug(s) or Diazepam 4mg/kg (i.p.) 30 min after treatment, inject with 75 mg/kg of PTZ by (i.p. or s.c.) Each animal is observed for 30 min in a plastic cage 22
Observations: PTZ-induced Seizure 1. One/more jerks (twists or myoclonus) 2. Clonic seizure 3. Loss of righting reflexes 4. Maximal tonic-clonic seizure and possible death At least 80% of animals in control have to show convulsion. Clonic seizure with loss of righting reflex end point Evaluation: The number of protected animal in treated group is calculated as percentage of affected animal in control group. Latency to myoclonic and clonic seizures ED50 for myoclonic and clonic protection 23
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Kindled Rat Seizure Model The kindled seizure model in rats offer a method to study the anticonvulsant activity on the basis of pathophysiological model. Principle: Repetitive admn of subconvulsive electrical stimulation of certain areas of brain progressive stimulus induced seizure. On continued stimulation electrical activity spreads and generalized convulsions occur. The animals are given stimulation through an electrode implanted within right amygdala. Kindling model Epilepsy induced Epilepsy 25
Other brain areas like Neocortex, hippocampus in rats Electrical stimulus: 400-500 µa, 20 msec. 50-60/sec frequency 26
Seizure severity is graded into 5 stages. Rats are considered to be kindled causing all stages of seizure 27
Evaluation Test animals are tested on the day before and after the test compound is given orally or i.p. Seizure scores Afterdischarge duration 28
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Rat: 3o mg/kg of PTZ i.p. 3 dose/week for 9 weeks Scoring : 0 - no response 1 ear and facial twitching 2 one to 20 myoclonic jerck 3 more than 20 body jerck 4 clonic forelimb convulsion 5 generalized convulsions with rearing and falling down episodes 6 generelized convulsions with tonic extension episodes and status epilepticus At the end of the 9 th week 90% animals are kindled Test drug should be administered before each PTZ Efficacy preventing seizure development 30
EPILEPSY INDUCED BY FOCAL SEIZURES Topical or intracerebral application of metal and chemical can lead to simple partial seizures Cortical imlanted metals: Alumina cream, cobalt, tungstic acid Appliead onto or into the cerebral cortex Injection of iron in brain cortex Aluminium Hydroxide gel model 4% aluminium hydroxide is injected into surgically exposed monkey neocortex One or two month after injection spontaneous and recurrent seizures begins Model for focal epilepsy Chemical Intrahippocampal kainic acid, tetanus toxin Topical application penicillin, picrotoxin, bicuculline 31
Genetic animal model for epilepsy Totterer Mice: Homozygous (tg/tg) strain. totterer mice are prone to spontaneous seizure. Develop both partial & absent seizure Two seizure type in one model 32
Lethargic mice: Homozygous(lh/lh) Model for absent seizure DBA/2J Mice: Audiogenic seizure susceptible mice 33
Photosensitive baboons: Intermittent light stimulation leads to seizure. Model for tonic clonic seizure. 34
Mongolian gerbils: Seizure can be provoked by Placing animal in new environment Bright light Vigorous shaking of cage Model for petitmal/myoclonous 35
Conclusion : Ideal model of epilepsy should show the following characteristics Development of spontaneously occurring seizures Type of seizure similar to that seen in human epilepsy EEG correlates of epileptic like activity 36
At present no models follows all criteria Only genetic models come close to call ideal& resemble epilepsy in humans more closely than any other experimental model. 37