Genetics and the Organization of the Basal Ganglia

This chapter reviews the evidence for genetic factors contributing to variability in the functional, neurochemical, and neuroanatomical organization of the basal ganglia. Most of the citations reviewed in the chapter involve comparisons amongst inbred strains of mice or rats. The purpose of many inbred strain studies is not only to establish the existence of genetic differences, but also to test hypotheses about relationships between traits, for example, apomorphine-induced stereotypy and D2 receptor density. Strain similarities on multiple traits suggest a common genetic influence. The chapter reviews the phenotypes (for example, receptor density, drug responses, dopamine neuron number), which are quite complex. When such complex phenotypes are characterized in a large panel of inbred stains or in genetically segregating population, the phenotypic values are usually continuously distributed. To explain this observation, quantitative genetic theory argues that multiple genes, each with a modest effect, combine to produce the phenotypic variance.