Animal Models/Experimental Design Flashcards
3 questions for neurological disorders:
What is the site of the lesion/what neurological populations are affected?
What is the likely pathology - does it cause LOF or GOF?
Does the pattern fit in with a recognisable disease?
Diseases of the CNS
Is it a basic pathological process that occurs in any organ or tissue?
ie. Ischaemia, haemorrhage, infarction, trauma, neoplasm (tumours)
Is it a condition unique to the nervous system?
ie. Degeneration of neurones, loss or alteration of myelin
Focal diseases in the CNS
Suppresion of function/destruction of neurones and surrounding structures
Synchronous discharge of neurones due to irritative lesions causing partial seizures that may become generalised
Displacement of the intracranial contents or spinal cord
Experimental = amyloid plaques/hyperphosphorylated fibrillary tau tangles
Mutations
Must have thioflavin positive staining!!!!
Mutations:
ADAM10/17
BACE-1
Presenellin 1/2
MAPT ie. P301L - hyperphosphorylation; frontotemporal dementia
AD animal models
Over-express APP with mutations in secretase cleavage sites (early-onset AD)
ADAM10/17, BACE1, presenellin (y-secretase adaptor)
BUT: early-onset AD only represents ~ 1-2% dementias therefore not representative - could this contribute to lack of efficacy at phase III clinical trials?
MAPT = ie. P301L
Could use ADDLs (amyloid-derived diffusible ligands)
Cell line, transfect to over-express APP with mutations in secretaries, secretes AB40/42 into medium, apply medium onto hippocampal slices (acute not organotypic)
Good controls:
- Thioflavin positive staining
- Add gamma-secretase blocker = should see no effect; show effects are due to increased AB40/42 and not simply increased APP
PD/HD In vitro
Direct = D1, dynorphin, substance P Indirect = D2, A2, enkephalin
PD/HD in vivo
Optogenetics:
Fusion protein:
Expressed Cre recombinase down-stream:
D1-Cre of D2-Cre
Injected AAV1 containing a fusion protein: ChR2-YFP into the dorsal striatum of transgenic mice
ChR2-YFP expressed in neurones expressing Cre (D1 or D2)
Controls:
- confirmed that ChR2-YFP expression did not alter electrophysiological properties of MSNs = performed whole-cell recordings in brain slices - not sig. different from control
Parkinson’s Disease Animal Models
Reserpine = reversibly inhibits VMAT2 (decrease RRP of DAergic vesicles)
- Reversed by L-DOPA treatment = good predictive validity
- Quick + easy to induce
- Good face validity
- Drug-induced, transient + reversible
- Do not see signs of neurodegeneration
6-ODHA unilateral lesion
MPP-model
Depression Animal Models
Forced swim test - rats do not like swimming, therefore they keep swimming and try to find the platform; keep repeating until they realise that there is no escape = give up + develop depression-like behavioural pattern
Learned helplessness model/”foot shock” - rats receive a gently but unpleasant shock; they learn that they cannot avoid the shock + give up
Social defeat - rat placed with an unpleasant companion (locked together); develop depressive-like symptoms
Social isolation
Intracranial self-stimulation - rats press a button to deliver drugs for pleasure; due to anti-depressant drugs, rats had a reduced urge to press the button
Used to test drugs = good predictive validity
Stroke Animal Models
Embolic stroke model
Middle cerebral artery occlusion
Epilepsy Models
Generalised
Induce seizure = used to test new AEDs
TONIC CLONIC
MES = Maximal Electroshock Seizure - transcorneal (through the eyes)
Acute
Add AED - good predictive validity
ABSENCE/NON-CONVULSANT
PTZ Seizure test - subcutaneous injections = blocks GABAa
Acute
Parameters to look at when given AED following MED/PTZ:
- Latency to twitch
- Latency to tonic-clonic
- Latency to tonic
- Seizure rank
Epilepsy Models
Focal status epilepticus
Status epilepticus - have epilepsy for life - have spontaneous epileptic seizures
CHEMICAL
Kainate/pilocarpine injection model
ELECTRICAL
Repetitive electrical stimulation of the perforant pathway (entorhinal cortex –> hippocampus)
MRI/fMRI/PET/CT
MRI = uses strong magnetic fields and radio waves to produced detailed images of the inside of the body
ie. Demyelinated plaques
- Can record signals from all brain regions – unlike EEG/MEG which are based towards the cortical surfaces
- High spatial resolution
- Poor temporal resolution
fMRI = Indirectly measures the brain activity – measures the blood flow; BOLD response (Blood Oxygenation Level Dependent activity)
PET = measuring the metabolic activity of cells in the human body
ie. PET tracers for amyloid + beta (not a-synuclein)
- Machine detects energy emitted during the decay of positively-charged particles – injected into the body on a biologically active molecule
- Allows evaluation of body function
CT = multiple x-rays which produces a 3D image
- Good detail compared to ultrasound
- Quick compared to MRI
- Requires breath holding
MS Animal Model
EAE = Experimental autoimmune encephalomyelitis
SZ Models
Developmental
Gestational MAM = pregnant mother given MAM (intraperitoneal injection); targets neuroblast proliferation + affects brain development
Face + construct validity
BUT = complicated procedure
