The catecholamine dopamine (DA) functions as a modulatory neurotransmitter in vertebrate and invertebrate nervous systems. In vertebrates, DA mediates behavioral processes such as cognition, reward, and locomotion, and is implicated in the pathophysiology of neuropsychiatric diseases such as Parkinson''s Disease, Attention Deficit Hyperactivity Disorder (ADHD), Schizophrenia, and drug addiction. In C. elegans, DA influences behaviors including egg-laying, defecation, response to food, habituation to touch, and basal locomotor activity. For DA to function as an effective neurotransmitter in the CNS, its magnitude and duration of action at the synapse must be precisely regulated. Various macromolecules, including biosynthetic enzymes, secretory proteins, ion channels, and receptors contribute to this regulation, but reuptake through the presynaptic DA transporter (DAT) is the primary mechanism by which DA signaling at the synapse is terminated. DAT is therefore the major determinant of synaptic DA inactivation and DA homeostasis in the brain. The general goals of our research are to determine how DAT supports chemical neurotransmission in the nervous system, how DAT synaptic localization and function is regulated, and whether altered signaling in disease states is caused by genetic variations in transporter structure. The technical challenges presented by the mammalian nervous system have encouraged our laboratory to pursue the study of DAT-associated phenotypes and regulatory genes in C. elegans. The C. elegans DAT (DAT-1) is 43% identical to mammalian DA transporters, preferentially transports DA, and is expressed in all known DA neurons in the nematode. Worms lacking a functional
dat-1 gene display no overt locomotor phenotype under normal conditions, but when placed in a liquid environment exhibit swimming-induced paralysis (SWIP), a DA-dependent phenotype that we have identified and characterized. SWIP is dependent on endogenous DA release, synaptic DAT-1 expression, and post-synaptic signaling through the DA receptor DOP-3. Using the SWIP phenotype as a behavioral reporter of altered DAT-1 localization or activity, we are employing a forward genetic screen to identify DAT-associated proteins. Many proteins have been previously implicated in the synaptic localization and regulation of DAT-1, but their functional relevance has not been demonstrated in vivo. Preliminary results have yielded several mutants specific to an excess in DA signaling.