Experimental Epileptology- Dipper Wawra

Question 1

types of epilepsy

Answer 1

1. focal (onset in one hemispheres)

2. generalised (onset in both hemispheres)

Question 2

what is the definition of epileptogenesis?

Answer 2

the period during which a tissue besoms epileptic, after a traumatic insult

Question 3

what is the latency period of epileptogenesis of

a. TBI
b. stroke
c. cerebral vein thrombosis
d. CNS infection (meningitis/encephalitis)

Answer 3

a. TBI- latency period takes 5-15 years
b. storke- 5 years
c. cerebral vein thrombosis- 10 years
d. CNS infection (meningitis/encephalitis)- 20 years

Question 4

what mechanisms underlie epileptogenesis?

Answer 4

A. enhanced excitation:

• altered cell firing
• increased release probability
• altered connectivity

B. impaired inhibition:

• loss of interneurons
• altered GABA receptor distribution
• altered Cl- homeostasis

C. inflammatory processes
D. BBB disruption

Question 5

what is the clinical definition of epilepsy?

Answer 5

• more than two unprovoked and recurrent seizures with a break of min. 24h between them
  Or:
• 1 unprovoked seizure with a clear lesion connected to the seizure
  Or:
• clear epileptic syndrome (e.g. channelopathy)

Question 6

what types of animal models of epilepsy do you know?

Answer 6

A. in-vivo models:

• genetic animal models
• induction of seizures in WT animals (acute epilepsy)
• post status epilepticus models (chronic)

B. in-vitro:
induction of seizures in animal/human slices

Question 7

what genetic animal models of epilepsy are there?

Answer 7

• Darvet syndrome
• KCNQ2 - related epilepsy
• Myotonia congenita

Question 8

how can you induce acute epileptic seizures in animals?

Answer 8

• 6 Hz psychomotor seizure model

- PTZ model (GABA antagonist)

Question 9

how can you study chronic epilepsy in animal model?

Answer 9

post status epilepticus models-

• Kindling
• cheoconvulsants (with pilocarpine or electrical kindling)
• optokindling

Question 10

what is Darvet syndrome? why is it important for the study of epilepsy?

Answer 10

• Darvet syndrome is a condition caused by a mutation in SCN1A gene (coding foe NaV1.1 Na+ channel)
• childhood epileptic syndrome accompanied by mental disabilities

Darvet Syndrom is important for epilepsy studies, because it is used as a genetic model:
- heterozygot KO of NaV1.1 in PV/SST interneurons
results:
- WT: when applying current to depolarised cells –> cells respond with high frequency AP
- KO: amount of stimulus needs to be higher to induce a much smaller AP–> impaired inhibition

Question 11

what is KCNQ2 related epilepsy? why is it important for the study of epilepsy?

Answer 11

• missense mutation of KCNQ2 gene (codes for Ku7.2 subunit of M-channel)
• M-channel maintains membrane potential below threshold for Na+ current –> reduced M-current leads to hyper-excitability
• causes epileptic encephalitis, EEG abnormalities and seizures

This mutation is important for epilepsy studies, because it is used as a genetic model:

• application of depolarising current leads to strong depolarisation in WT.
• in heterozygous KO there is reduction of M-current
• -> good model for testing antiepileptic drugs

Question 12

what are acute seizure models good for? what are their limitations?

Answer 12

pros:

• induction of seizures (electrically or chemically) in healthy brain
• commonly used for screening of antiepileptic drugs
• less burden on the animal than chronic models

cons:

• cannot reflect ictogenesis in established epilepsy
• doesn’t assess efficacy in pharmacoresistant patients

Question 13

how can one induce epileptic seizures using the 6 Hz psychomotor seizure model? what is is used for?

Answer 13

• current application via corneal stimulation
• frequency of stimulation can’t be changed but intensity of stimulation can be adjusted
• corneal stimulation bc there is a direct connection between the eye and the brain via trigeminal nerve –> current goes directly to brain stem and and cortex

uses:

• used as an acute model for antiepileptic drugs (esp. selective discovery for drugs that block Na+ channel)
• -> score severity of seizure before and after drug application.

Question 14

PTZ model of acute seizures…(choose the WRONG answer)

a. induction of seizures using GABAR antagonist
b. acute seizures induced by applying acute dose of drug to rodents
c. leads to myoclonic jerks, tonic-clonic seizures
d. can be used as long term epilepsy model
e. no long term modification applied

Answer 14

d

Question 15

how is chronic epilepsy induced using kindling and why is it a good model?

Answer 15

• daily short (1 sec) stimulation of brain structures with unchanged stimulus
• initially- no clinical effect
• after weeks- brain is epileptic–> stimulation produces seizures

kindling is a reliable model because it alters brain function (as occurs in epilepsy):

• fully kindled rats show acute effects if AEDs are applied prior to stimulations
• possible to look for pharmacoresistance in fully kindled rats
• chronic AEDs delay kindling –> anti-epileptogenesis

Question 16

how is chronic epilepsy induced using chemoconvulsant (1 way) and why is it a good model?

Answer 16

pilocarpine-

• agonist for mAChR
• secondary release of glutamate
• 40-100% of animals develop epilepsy within weeks

procedure:

1. i.p. application of pilocarpine induces acute status epilepticus
2. post octal depression (latency period- epileptogenesis)
3. status epilepticus- seizure starts again (can go forever unless it’s stopped with benzos)

advantages:

• good and exact model tor temporal lobe epilepsy (TLE)
• allows for studying pathological changes in the limbic system and temporal lobe as a result of epilepsy

Question 17

how is chronic epilepsy induced using optokindling? what is the difference between test group and control? why is it a good model?

Answer 17

procedure:

1. bacterial injection of AAV CamKII-a-ChR2 in male P30-45 mice
2. light source used to activate CamKII-a
3. stimulation sub-threshold:
   - beginning- no severe epileptic discharges
   - after a few cycles- animals develops seizures

results:
EEG: 
- stimulate ChR2- very high seizure rate
- no stimulation of ChR2- no seizure 
- control: stimulation--> no seizure
- number of seizures grows over time
- behavioural scoring increases
- seizure induction is faster over time

pros:
cell specific epilepsy model