Zebra fish as a model for translational neurobiology: Implications for drug discovery and development

PhDDiseases which affect the central nervous system present a huge burden to sufferers and caregivers. In tandem with longevity, prevalences of age-related neurodegenerative diseases are increasing. However, despite the evident necessity for pharmaceutical interventions, there has been a distinct lack of drug development to combat these disorders. This is largely attributed to high financial costs of using rodent models. Thus the validation of a more cost-effective in vivo system would facilitate pharmaceutical screening. The work presented in this thesis addresses this issue by assessing the utility of zebra fish in two costly areas of translational neurobiology { lead identi cation and safety pharmacology. An aversive classical conditioning assay was developed and automated as a behavioural screening method. This robust assay allows fast assessment of cognition and cognitive decline. The effect of neurotoxin treatment on aversive learning was then assessed using this assay, demonstrating its efficacy as a screening tool for neurodegeneration research. Subsequently, a transgenic zebra fish line - expressing a mutated form of the Alzheimer's-associated human amyloid precursor protein - was assessed, demonstrating an age-related cognitive impairment. Additionally new genetic zebra fish lines were generated, which over-express genes (both endogenous and transgenic) related to Alzheimer's-like pathologies. Whilst these were not assessed within this thesis, they present promising tools for possible future investigations. Regarding safety pharmacology, regulatory bodies require all CNS-penetrant drugs be assessed for abuse potential. Zebra fish display reward responses to several common drugs of abuse (e.g. amphetamine, cocaine, morphine). Thus, the latter sections of this thesis evaluated the utility of zebra fish for assessing human abuse potential. A CPP paradigm was utilised to test a range of drugs, with the sensitivity and specificity of zebra fish compared to previous reports using rodent. Additionally, the development of a zebra fish drug discrimination assay was attempted. However the paradigms utilised failed to develop an efficacious assay.EPSRC and P zer Inc., grant number EP/K50290X/

Developmental role of acetylcholinesterase in impulse control in zebrafish

Cellular and molecular processes that mediate individual variability in impulsivity, a key behavioural component of many neuropsychiatric disorders, are poorly understood. Zebrafish heterozygous for a nonsense mutation in Ache (achesb55/+) showed lower levels of impulsivity in a 5-choice serial reaction time task (5-CSRTT) than wild type and ache+/+. Assessment of expression of cholinergic (nAChR), serotonergic (5-HT) and dopamine (DR) receptor mRNA in both adult and larval (9dpf) achesb55/+ revealed significant downregulation of Chrna2, Chrna5 and Drd2 mRNA in achesb55/+ larvae, but no differences in adults. Acute exposure to cholinergic agonist/antagonists had no effect on impulsivity, supporting the hypothesis that behavioural effects observed in adults were due to lasting impact of developmental alterations in cholinergic and dopaminergic signalling. This shows the cross-species role of cholinergic signalling during brain development in impulsivity, and suggests zebrafish may be a useful model for the role of cholinergic pathways as a target for therapeutic advances in addiction medicine