[
West Coast Worm Meeting,
2002]
Amphetamine as well as other psychostimulants such as cocaine and methylphenidate have a high potential for abuse. Their primary mechanism of action is the inhibition of the clearance of dopamine from the synapse via the dopamine plasma membrane transporter (DAT). The CeDAT has been cloned and shown in vitro to bind both amphetamine and cocaine (LD Jayanthi et al., Mol Pharm 54:601-9, 1998). There is also evidence that even a single exposure to psychostimulants can produce long term potentiation on the mesolimbic dopamine system (Ungless et al., Nature 411:583-587, 2001) which is part of the reward pathway activated by drugs of abuse. These synaptic changes may be important for the subsequent addiction to these types of drugs. We are interested in characterizing further the mechanisms that contribute to the effects of amphetamine modulation on dopaminergic pathways. To examine the effects of amphetamine on synaptic transmission in C. elegans we pretreated worms with amphetamine in liquid culture prior to transferring animals to agar plates for behavioral analysis. We found that amphetamine pretreatment resulted in suppression of locomotion, egg laying, and pharyngeal pumping in a dose dependent manner. These behavioral effects are similar to those produced by exposing animals to exogenous dopamine, suggesting amphetamine is acting on dopaminergic pathways. We then initiated a genetic screen to identify mutants that showed reduced sensitivity to the effects of amphetamine on locomotion. We have identified eight candidate mutants and are in the process of mapping and cloning the genes responsible for their resistance. Most of these mutants are visibly wild type with the exception of two of the mutants which appeared hyperactive for locomotion. This hyperactivity was confirmed by assaying for aldicarb sensitivity. The other mutants were found to be either wild-type or resistant to the effect of aldicarb on movement. One of these mutants also displayed reduced sensitivity to the effects of amphetamine on pharyngeal pumping and two other mutants displayed reduced sensitivity to the effects of amphetamine on egg laying. We are characterizing the mutants from our screen for defects in dopamine mediated behaviors. Preliminary results indicate that two of these mutants are defective in the dopamine dependent basal slowing response on bacteria (Sawin et al., Neuron 26:619-631, 2000).