The monoamine neurotransmitter dopamine (DA) regulates a wide variety of complex behaviors across phylogeny. The presynaptic DA transporter (DAT) is critical for restricting DA actions in space and time by limiting DA availability at synaptic and extra-synaptic DA receptors. Mutations impacting DAT protein expression or structure have been identified in subjects with multiple brain disorders in humans, including attention-deficit hyperactivity disorder (ADHD), juvenile Parkinsonism/dystonia, bipolar disorder and autism. In the nematode C. elegans, loss of function mutations in
dat-1 gene result in a hyperdopaminergic state that causes animals to paralyze in water, a phenotype termed Swimming-induced paralysis (Swip). This phenotype can be rescued by either treatment of animals with the vesicular monoamine transporter (CAT-1) inhibitor reserpine or through mutation of the TH ortholog CAT-2, or the D2-type DA receptor DOP-3. We have implemented a forward genetic screen to identify novel
dat-1 alleles as well as novel determinants of DA signaling. Here we describe our efforts to characterize two mutant lines that express DA-dependent Swip,
vt39 and
vt44, using genetic and pharmacological approaches. Evaluation of sensitivity to osmotic tone and the DAT-1 antagonist nisoxetine, as well as genetic reversal experiments, are consistent with the genes mutated in these lines as DA signaling dependent. SNP mapping and genome sequencing analyses have revealed multiple candidates as the site of the molecular lesion responsible for the Swip phenotype. Further studies related to the identity of the genes encoding these mutations and their functional analyses will be presented. Supported by NIH Award MH095044 (RDB, PF) and MH093102 (JAH).