Steven L. McIntire

The mechanisms by which ethanol induces changes in behavior are not well understood. Here, we show that Caenorhabditis elegans loss‐of‐function mutations in the synaptic vesicle‐associated RAB‐3 protein and its guanosine triphosphate exchange factor AEX‐3 confer resistance to the acute locomotor effects of ethanol. Similarly, mice lacking one or both copies of Rab3A are resistant to the ataxic and sedative effects of ethanol, and Rab3A haploinsufficiency increases voluntary ethanol consumption. These data suggest a conserved role of RAB‐3‐/RAB3A‐regulated neurotransmitter release in ethanol‐related behaviors.

Memory and the expression of learned behaviors by an organism are often triggered by contextual cues that resemble those that were present when the initial learning occurred. In state‐dependent learning, the cue eliciting a learned behavior is a neuroactive drug; behaviors initially learned during exposure to centrally acting compounds such as ethanol are subsequently recalled better if the drug stimulus is again present during testing. Although state‐dependent learning is well documented in many vertebrate systems, the molecular mechanisms underlying state‐dependent learning and other forms of contextual learning are not understood. Here we demonstrate and present a genetic analysis of state‐ dependent adaptation in Caenorhabditis elegans. C. elegans normally exhibits adaptation, or reduced behavioral response, to an olfactory stimulus after prior exposure to the stimulus. If the adaptation to the olfactory stimulus is acquired during ethanol administration, the adaptation is subsequently displayed only if the ethanol stimulus is again present. cat‐1 and cat‐2 mutant animals are defective in dopaminergic neuron signaling and are impaired in state dependency, indicating that dopamine functions in state‐dependent adaptation in C. elegans.

Caenorhabditis elegans is an attractive model system for determining the targets of neuroactive compounds. Genetic screens in C. elegans provide a relatively unbiased approach to the identification of genes that are essential for behavioral effects of drugs and neuroactive compounds such as alcohol. Much work in vertebrate systems has identified multiple potential targets of ethanol but which, if any, of those candidates are responsible for the behavioral effects of alcohol is uncertain. Here we provide detailed methodology for a genetic screen for mutants of C. elegans that are resistant to the depressive effects of ethanol on locomotion and for the subsequent behavioral analysis of those mutants. The methods we describe should also be applicable for use in screening for mutants that are resistant or hypersensitive to many neuroactive compounds and for identifying the molecular targets or biochemical pathways mediating drug responses.