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Flashcards in PD: Animal Models and Drug Development Deck (39)
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Describe features of toxin based models of PD?

Toxins are injected into nigrostriatal system/systemically to kill DA neurons

NB: route of delivery depends on if toxin can cross BBB


Examples of toxin-based models of PD?

- 6-OHDA


- Lactacystin


6-hydroxydopamine (6-OHDA) features and properties?

[oxidative product of dpoamine found in small amounts]

Can't cross BBB so must be administered as unilateral stereotaxic injection in anaesthetised animals

Dose responsive loss of nigrostriatal DA neurons

This is ideal to model different stages of cell loss (e.g. 60-70%)


Outcome of 6-hydroxydopamine (6-OHDA) injection into different regions of animal brain?

Injection into SNpc -> rapid cell loss (3-4 days)

Inject into medial forebrain bundle -> cell loss 7 days

Inject into striatum -> cell loss over 2 weeks


Compare features of 6-OHDA and PD?

- mitochondrial inhibition
- selective neuronal loss
- oxidative stress

(BUT no altered proteins)


How to assess outcomes using 6-OHDA model?

- behaviour
- immunohistochemistry (neuronal counts and glial activity)
- High Performance Liquid Chromatography (HPLC)]- detect neurotransmitters
- tyrosine hydroxylase immunopositive neurons (general neuron stain -> cell loss)]- compare loss of neurons in lesion vs control


Environmental mimics of PD

- Manganese -> Parkinson-like syndrome w/ fixed gaze, bradykinesia, postural difficulties, rigidity, dystonia]- from mining manganese ore

- Carbon disulphide (from rubber processing)

- Cycad seeds (from Guam) -> Parkinson-like syndrome w/ dementia


MPTP features and properties?

Lipophilic i.e. penetrates BBB]- can be given systematically


Compare features of MPTP and PD

- mitochondrial inhibition
- oxidative stress

(BUT no protein inclusions...but yes if given with probenicid)


Which species are susceptible to MPTP?

Humans, primates, mice (C57black)

Mice, rats, cats and dogs are relatively resistant to MPTP


MPTP in non-human primates?

3 doses of MPTP produces persisten behavioural syndrome: akinetic, flexed posture, increased limb rigidity, tremor, clumsy movement, freezing episodes


MPTP in primate brain?

MPTP rapidly converted to MPP+, which remains for several days

NB: in other species, both MPP+ and MPTP are rapidly removed from the brain


Outcome of MPTP administration?

Loss in SNpc but not VTA/NAc

Behavioural changes are reversed w/ L-DOPA + carbidopa (or DA agnoists)


What are Proteasome Inhibitor (PSI) Models?

Proteasome degrades altered proteins. Build up of altered proteins intracellularly -> oxidative stress + cell death


How to administer PSI?

Peripheral (systemic) administration

2 injections/week over 5 weeks


Disadvantages of PSI model for PD?

Not reproducible


Lactacystine features and properties?

Proteasome inhibitor

Doesn't cross BBB

(more stable model than PSI)


Lactacystin method of administration?

Stereotactic injection into SNpc/MFB


Lactacystin compared to 6-OHDA and MPTP?

Chronic progressive model and spread

(compared to rapid cell loss seen in 6-OHDA and MPTP


Compare features of Lactacystin and PD?

- selective neuronal loss
- oxidative stress
- altered proteins

(BUT no mitochondrial inhibition)


Outcome of a-syn in drosophiliae?

- Selective DA neuronal death
- Lewy body-like structures
- movement disorder (change in climbing behaviour)


Outcome of increased wild-type a-syn in transgenic mice?

- neuronal inclusions (hLB sunflower structure, rLB is disorganised)

- no neuronal loss


Outcome of expressing A30P/A53T double mutant

- age dependent decrease in SNpc TH cell number
- decreased motor function

- no inclusions


Disadvantages of using transgenic mice w/ a-syn to model PD?

- need to wait 18 months for pathology
- transgenic mice expensive
- mice require 2-3 mutations of a-syn, but no human has >1 a-syn mutation


Outcome of rAAV a-syn overexpression (viral vector delivers wild-type or mutated a-syn)?

- deficits in motor behaviour
- decreased DA striatal terminalis and cell bodies


Disadvantages of using rAAV a-syn overexpression?

Have to wait 6 months for pathology]- it is a progressive model


Mechanism of injecting pre-formed a-syn fibrils?

Braak hypothesis: injecting protofibrils in SNpc mirrors spread of altered proteins in similar pattern to PD

Taken up by striatal neurons -> Lewy bodies

- fibrils cause native a-syn to misfold

- inclusions spread across brain over time


Outcome of injecting pre-formed a-syn fibrils?

Small amount of nigrostriatal DA cell loss (30%) which doesn't translate to behavioural deficits


Outcome of using LRRK2 Transgenic mice?

Cell death in neuroblastoma cells and mouse cortical neurons


Compare LRRK2 model and PD

- movement dysfynction
- abnormal proteins

(BUT no neuronal loss in SNpc)

NB: you can add MPTP to induce stress or neurodegeneration