We have identified an insertional mutant, during the course of making transgenic mice in our laboratory, which exhibits an abnormal circling behavior as the overt phenotype. This transgenic insertional mutant, which we call the chakragati mouse, displays excessive lateralized circling behavior and locomotor hyperactivity by postnatal days 14-16, which persists unattenuated through adolescence and adulthood. the insertional mutation is characterized as autosomal and recessive and is stably transmitted. We hypothesize that integration of the transgene sequences has caused the loss of at least one endogenous gene function resulting in asymmetry and imbalances in the dopaminergic system and the circling phenotype. In the mutants, dopamine D2 receptors are asymmetrically upregulated contralaterally to the preferred direction of circling. Moreover, the potent D2 receptor agonist, quinpirole, was found to potentiate their rate of circling. We have mapped the DNA sequences in the host genome flanking the integration site of the transgene sequences to mouse chromosome 16 and to the homologous region of human chromosome 3. We propose, here, to identify the genetic lesion(s) that resulted in the abnormal circling behavior and asymmetrical D2 receptor upregulation. As part of a general approach, we will carry out a physical characterization of the integration site, then isolate clones across the integration site from the normal genome using the flanking markers as hybridization probes and look for gene coding sequences in these clones. We will also pursue a candidate locus approach as one of our flanking DNA markers appears, in the light of some very recent genetic mapping data, potentially coincident with the dopamine D3 receptor locus. Given that these DNA markers are known to be unlinked to the D2 receptor gene locus and that quinpirole has been reported to have a similarly high affinity for the D3 receptor gene was in fact disrupted during the integration of the transgene sequences and that its expression profile in the insertional mutant is aberrant. We believe that bringing the tools of molecular biology to bear on this insertional mouse mutant will provide novel and specific insights into nigrostriatal systems mediating motor function. This will be important as perturbations in the nigrostriatal pathways of the central dopaminergic system have been implicated to be the basis of several neurobehavioral disorders including Parkinsonism, schizophrenia, and possibly others.