Animal Models

what are the 3 aspects of study

• levels

• models

• measures

Molecular level

• structure and function of molecular aspects of biological pathways 

  • genes and proteins

• uses PCR, gel electrophoresis, blotting and microscopy 

• most common area of research 

Cellular level

• investigates structure, function and behaviour of cells

• uses cell culture, microscopy and electrophysiology 

whole organism level

• investigates structure and function of systems using the entire organism

• uses behavioural tests and imaging 

4 models

• In Vivo

• Ex vivo

• In vitro

• In silico

In vitro

• within the glass

• uses cells from a repository (cell line) - Cell culture

• use microscopy and electrophysiology

Ex vivo

• Outside the living

• cells and tissues from an organism (eg. brain slices)

• uses PCR, microscopy and electrophysiology 

In vivo

• within the living

• uses living organisms

• uses animal models, microscopy, imaging and electrophysiology

In silico

• computational models

• simulations based on data collected from other models

two types of measurement

static and functional

static measurements

• measurements at a point in time

• examine the morphology, density and expression of genes

• techniques: microscopy, PCR, gel electrophoresis, blotting, immunohistochemistry and imaging

functional measurements

• measurements that are changing over time

• activity

• techniques: microscopy, electrophysiology, behavioural testing, imaging

define animal models

• non-human species used in biomedical research to mimic aspects of a biological process or disease found in humans

• anatomy, physiology or response to a pathogen are similar enough to that of a human that their results can be extrapolated to improve human understanding

• allow the performing of experiments that would be impractical or ethically prohibited with humans 

Naive animal

an animal with no changes made to it, used to understand normal function

animal model

has been idealised or modified to represent something (eg. disease) 

reasons to use drosophila, c.elegans and zebra fish

• less complex nervous system than mammals (easier to understand but harder to translate to mammals)

• cheaper and faster to breed

• good for fundamental questions about genetics

• highly conserved genetics (homologues)

• can do behavioural studies (drosophila in mazes)

reasons to use mice and rats in animal research

• mammalian nervous system so more translatable to humans

• mice are most common for genetic models

• rats are best when size or easy training is important

• cheaper and faster than large animals

reasons to use larger animals in animal research 

• brain structure needs to be more similar to humans 

• sheep have folded cortex and solid tentorium (dura mater) —> good for stroke research 

UK legislation on selecting animals for research

must use lowest sentient being to address the question

what are the three criteria for animal models?

1. predictive validity

2. face validity

3. constructive validity 

Predictive validity

• behaviour

• do outcome measures from the animal correlate with the condition

face validity

• neurobiology

• does the animal model correspond ecologically, biochemically and pathologically to the condition?

constructive validity

• mechanisms

• does the model hold up the theoretical rational regarding mechanisms? 

types of animal models

different ways to genetically modify animals

• knock in

• knock out

• altering DNA to express characteristics

how might surgery be used on animal models?

• causing lesions

• causing pain

R6/2 model of Huntington’s disease genetic modification in animal models

• first and most understood model of Huntingtons

• take exon-1 CAG repeats from human and insert into chromosome 4 of mice to cause huntingtons

• causes smaller straital volume and decline in motor function when compared to wildtype mice

MPTP model of Parkinson’s Disease in mice

• MPTP drug can cross the BBB and is then taken up by glial cells

  • MPTP → MPP+ by MAO-B in the glia

  • MPP+ is then taken up by dopaminergic neurones via DAT (dopamine transporter)

    • MPP+ inhibits the electron transport chain in mitochondria

      • causes cell death

• Is administered to the abdomen of mice via injection

• administered gradually throughout the day to mimic human Parkinson’s

  • more frequent MPTP injection causes more striatal dopamine depletion → substantia nigra

    • stain for dopaminergic neurones with tyrosine hydroxylase

  • MPTP mice show anti-anxiety symptoms by spending more time in arm of maize with glass floor (open arm)

Ischemic stroke

• most common (80-90% of cases)

• obstruction of blood flow and so limited oxygen supply to brain

• two types

  • global cerebral

  • focal cerebral

    • requiring craniectomy or not (remove part of skull to relieve pressure )

• different models

haemorrhagic stroke

• less common (10-20% of cases)

• weakened blood vessel in the brain ruptures and bleeds into surrounding tissues

• cam be modelled

MCAO model of stroke

• surgical animal model

• Middle cerebral artery occlusion model (MCAO)

• filament inserted into carotid artery in the neck and up to the circle of Willis

  • this blocks the cerebral artery which feeds the medial section of the brain causing ischemia

    • cell death in the oxygen deprived areas

• removal of filament causes reperfusion

• done in controlled conditions, animals still undergo surgical conditions and anaesthetic which could have effects

• stroke mice show difficulty seeing what is in front of them and MRI shows areas where cells have died

Lesion animal models

• combine pharmacological and surgical models

• canula inserted into brain so that drugs can be infused into particular brain areas causing cell death or damage

• Parkinson’s model infuses 6-OHDA at the substantia nigra

• Huntington’s model infuses ibotenic and quinolinc acids at the striatum

Brain surgery in mice

• steriotaxic surgery uses 3D technique to locate neural locations with coordinates

  • uses the skull structure

  • Bregma is 0,0,0

• done using a animal steriotaxic frame

label the steriotaxic frame