11. Animal Models

11. Animal Models

1. Commonly used models

   • Fruit Fly
     • only 4 pairs of chromosomes to study with translocation and transcirption
     • genome easily manipulated
     • used as a model for neurogeneitive disorders
     • morphology is easily identifiable
     • examine learning, memory and sensory behaviours
   • Rodent models
     • Mice = genome readily manipulated and readily used
     • rats = not as easily manipulated as mouse
     • range of behaviours to study, e.g. motor abilities, anxiety, mating, courtship, cogntiion and executive
     • high degree and physiological homology with humans
   • Worm
     • simple animal, with a nervous system
     • exhibits many behaviours, learning mating and learning like humans
     • can be used to study complex processes
     • well-defined fate for cells
     • 1st animal to have its genome sequenced
     • many strains with genetic mutations to study
   • Zebra-fish
     • genome is easily and readily manipulated
     • expression and splicing of genes can be altered
     • well-characterised easily observable behaviours, e.g. sleep, social interactions
     • Parker et al (2012) showed zebrafish were able to learn which hole LED lights were coming from

2. Genetic Rodents

   • Selective Breeding
     • Recominant inbred = crosses phenotypically-distinct inbred strains for several generation to identify regions of genome affecting behaviour
     • Inbreeding = select members of founder strain, inbred over generations to ensure homogenity. Less phenotypic variability (dissociate genetic vs environment). But inbred strains can differ in appearance and behaviour (polymorphisms)
     • Outbreeding = Members of founder strain bred to unrelated individuals (more like humans) to ensure genetic heterogeneity. More phnotypic variability
   • Transgenesis
     • Insert extra DNA into genome
     • Knock in studies
     • pronucelar injection of DNA of interest
     • rodent genome modified to assess behaviour
     • unction to insert sequence or have more copies of DNA
   • Mategenesis
     • randomly mutate genome with chemicals and radiation
     • Selectively breed animals with phenotype
     • can suggest genes you wouldnt suggest to be involved in behaviours
     • genome sequencing
   • Gene Knockout
     • ger rid of targeted genes
     • Mutate gene of interest in embryonic stem cells from mice, insert that into blastocyst of other mice and impact embryo into surrogate mother = mouse born mix of genetic mutation and normal cells, genetic mutation carries into sperm/ egg cells = bred with other mouse to create HZ mice, which bred with another HZ mouse will create MZ mouse only with mutated gen
     • Consider effects of lack of a gene on behaviour, or specific effects on brain regions
     • Genetic insert can be designed so that ‘knockout’ only occurs at certain developmental stages or in certain tissues → ‘conditional knockout’
   • Selective breeding, gene knockout, transgenesis, mutagenesis and chromosomal mutations

3. Animal Models

   • Living Non-human animals used to understand biological basis of healthy and pathological phenotypes
   • Disadvantages
     • Different evolutionary pressure
     • Limited rnage of genetic modifications we can do
     • Genetic and physiological divergence from humans
     • Relevance of complex human behaviours, influenced by many combined factors
     • Inability to model-specific phnotypes, e.g. language
     • models rarely have face, construct and predictive validity
     • Ethical issues with possible effects
   • Advantages
     • Genomes responsive to genetic manipulation
     • Genomes similar to human genome
     • Strong environmental control = regulate background
     • Good breeders with short generation times
     • can be maintained in large colonies
     • exhibit many sophisticated behaviours , e.g. motor control
     • acessibility to tissue and procedures not ethical in humans
   • Should have good face validity = resemble human phenotypes/behaviours, construct validity = share biological underpinnings and predictive validity = drugs have same effect in humans/animals for treatments

4. New approaches

   • Designer receptor exclusivity activated by designer drugs (DREDD's)
     • Ferguson et al (2013) = DNA encoding designer G-protein coupled receptors that do not respond to endogenous chemicals inserted into specific neurons/circuits. Drugs binding to these receptors introduced into the animal to modulate circuit activity = look at behaviour
   • Optogenetics
     • provide range of experiemental paradigms
     • high spatial and temporal precision
     • light-based control of neural elements, prove neural circuit physiology
     • Allows us to suggest basic neural mechanisms of social behaviours and disease relevant to social cognitive dysfunction
       • Subcortical = hypothalamus linked to aggresion, amygdala linked to socal and progression in encounter
       • neocortical regions = cortical modulation of higher cognitive processes, e.g. amygdala plays a role on autism and SCZ

5. Acute administration of molecules

   • Zhang et al (2013) = X-linked disability protein PHF6 associted with PAF1 regulates brain
   • poor permeability and difficult in adult brain
   • molecules introduced into brain to inhibit translocation of genes
   • transient gene knockout = characterise function of poorly-annotated gene
   • anti-sense = remove the need for animal models, direclty delievered to the brain to induce enhibition of expression

6. New Technologies

   • Chromosomal mutations
     • Davis et al mice learned were a flash of light was coming from over a number of trials
     • Spontaneous mutations sometimes occur
     • Mouse model of down syndrome due to mutation of extra chromosome (O'Doherty et al, 2005)
     • Trent et al (2012) mice with STS gene mutation have ADHD
   • Clustered regularly interspaced short-panlindromic repeats
     • Cas9
     • RNA guided genome editing tool
     • used for gene knockout and knock in mutations
     • delivering it to the brain is difficult