Zebrafish behavioural assays to identify genetic mechanisms underlying drug seeking and addiction.

Human studies demonstrate that genetic factors contribute to an individual?s vulnerability to drug dependence but few genetic markers that predict vulnerability have been identified. Nonetheless, recent evidence suggests that tailoring treatment to individual characteristics based on assessment of the small number of available genetic markers improves treatment outcomes. Increasing understanding of genetic contributions to drug seeking behaviour will aid development of new therapies to improve treatment outcomes. Impulsivity and novelty seeking are risk factors for drug dependence; novelty seeking predicts propensity to initiate drug taking, impulsivity is associated with progression to compulsive drug taking and return to drug taking following abstinence (relapse). These are key characteristics of drug addiction with relapse presenting the greatest challenge for treatment. Here we aim to develop assays of impulsivity and novelty seeking in zebrafish and use these to selectively-breed zebrafish lines to identify variations in gene sequence that may contribute to vulnerability to drug addiction. We have previously demonstrated that zebrafish show reward responses to drugs of abuse and we have developed tests of compulsive drug seeking and relapse in zebrafish. Here we use modifications of rodent tests to relate novelty seeking and impulsivity in zebrafish to drug seeking behaviour. Once tests predictive of drug seeking in zebrafish have been developed we will use these to establish fish lines that show altered drug seeking behaviour. As the neurochemical pathways involved in drug seeking are evolutionarily conserved and there is a high degree of sequence and functional homology between zebrafish and mammalian genes, results found in zebrafish can inform human studies.
Use of zebrafish for neurobehavioural research represents a great opportunity for reduction of the use of higher order vertebrate species thereby reducing animal suffering. Given the proposed EU directive to include tests for addictive potential in all new drug development programmes, the development of zebrafish lines with heightened sensitivity to drugs of abuse and establishment of suitable assays has the potential to minimise costs, both material and ethical, in drug development programmes.

Human studies demonstrate that genetic factors contribute to an individual?s vulnerability to drug dependence but few genetic markers have been identified. Nonetheless, recent evidence suggests that tailoring treatment to individual characteristics based on the small number of available genetic markers improves treatment outcomes. Impulsivity and novelty seeking are risk factors for vulnerability to drug dependence; novelty seeking predicts propensity to initiate drug taking, impulsivity is associated with progression to compulsive drug taking and return to drug taking following abstinence (relapse). These latter aspects are key characteristics of drug addiction with relapse presenting the greatest challenge for treatment. Increasing understanding of the genetic contributions to drug seeking behaviour will aid development of new therapies to improve treatment outcomes. Here we develop assays of impulsivity and novelty seeking in zebrafish and use these to selectively-breed lines to identify genetic mechanisms contributing to drug addiction. We have shown previously that zebrafish have a conserved reward response to drugs of abuse and have developed assays of compulsive drug seeking and relapse in zebrafish [1]. Here we use modifications of the novel object, open field assay and delayed reward tasks used in rodents to relate novelty seeking and impulsivity in zebrafish to drug seeking behaviour. Once assays predictive of drug seeking in zebrafish are developed we will use these to screen adults from families of ENU-mutagenised fish to establish lines that show altered drug seeking behaviour. ENU-mutagenesis introduces single nucleotide variations in the genome that may alter drug seeking behaviour and act as markers for genome association studies. The existence of ENU-mutagenised zebrafish lines is an enormous resource facilitating the identification of linked alleles in zebrafish not available in other vertebrate species. In order to obtain a similar resource in rodents expensive, ethically and technically challenging mutagenesis programmes would be required. As the neurochemical pathways involved in drug seeking are evolutionarily conserved and there is a high degree of sequence and functional homology between zebrafish and mammalian genes, results found in zebrafish have translational relevance.
Use of zebrafish for neurobehavioural research represents a great opportunity for reduction of the use of higher order vertebrate species thereby reducing animal suffering. The development of zebrafish lines with heightened sensitivity to drugs of abuse and establishment of suitable assays has the potential to minimise costs, both material and ethical, in drug development programmes.