A mutation affecting behavioral responses to nicotine and alcohol. a. rothenfluh , u. heberlein. anatomy, ucsf, san francisco, CA.

   Nicotine addiction is a problem associated with serious medical consequences. When flies are exposed to high doses of volatilized nicotine, they become strongly hyperactive and exhibit uncontrollable, seizure-like shaking, followed by death. At lower doses, after the initial hyperactivity, exposed flies show very little locomotor activity (hypolocomotion), and after 5-10 minutes they completely recover. We measure these behavioral responses in an assay where we test the flies ability to climb, and also measure their self-righting ability. We have used this assay to screen through 1200 homozygous viable P-element lines generated in our lab. ~15 lines were found with altered sensitivity to nicotine. Most lines show resistance to nicotines incapacitating effects, while some lines show altered kinetics of the behavioral response, marked by a prolonged period of hypolocomotion during the recovery phase. One mutant, 5-131, is strongly resistant to nicotine, and also shows an alcohol phenotype. Upon continuous exposure to a medium dose of ethanol, wild type flies initially exhibit a brief phase of increased locomotion, a startle response to the novel odor, followed by a quiescent phase. Flies then undergo a period of sustained hyperactivity, and later sedate as they become increasingly inebriated. 5-131 flies show two alterations in this response. First, both hyperactivity and sedation are delayed, indicating that this mutant is resistant to the behavioral effects of both nicotine and ethanol. Second, 5-131 flies show a strongly accentuated and prolonged startle response, suggesting that they are more sensitive to the sensory input of the alcohol smell, or more responsive to it. The 5-131 mutation is associated with a P-element insertion in a gene coding for a GTPase-activating protein of the Rho family (RhoGAP). The mutant phenotype is reversible upon P-element excision, and we will present our advances in the molecular characterisation of this gene.