*Dissertation Defense Announcement To: The George Mason University Community* *Candidate: Laura L. Locklear Program: PhD Biosciences * *Date: Monday April 25, 2011 Time: 1:00 p.m. Place: George Mason University ** David King Hall, Room 3006 Fairfax campus <http://www.gmu.edu/resources/visitors/findex.html> Dissertation Chair: Dr. Karl J. Fryxell Committee members: Dr. Daniel N. Cox, Dr. Alan Christensen, Dr. Robert F. Smith* *Title: **"Nicotine Preference and Gene Expression: the Role of /Cd81"/** * The dissertation is on reserve in the Johnson Center Library, Fairfax campus. The doctoral project will not be read at the meeting, but should be read in advance. /**/All members of the George Mason University community are invited to attend. *ABSTRACT: * Smoking is a leading preventable cause of death worldwide. Variation in smoking behavior arises in large part from individual perception of nicotine's rewarding effects, and the propensity for nicotine dependence. Attempts to elucidate molecular mechanisms underlying these factors have so far been insufficient for developing effective treatments for, or reliable predictors of dependence. Thus, identifying genetic determinants of nicotine addiction is of vital importance. This can most readily be accomplished using laboratory mice. We used two-bottle choice nicotine self-selection to assess differences in nicotine consumption between the C57BL/6J and A/J inbred strains, and in a separate experiment, C57BL/6J /Cd81/ knockout mouse strains. We quantified the relative motivation to seek nicotine. Our unique set of experimental design parameters allowed unprecedented success in distinguishing between the strains and sexes through voluntary nicotine consumption. The cohorts exhibited distinct nicotine consumption levels. Most showed increasing consumption with time, indicating tolerance effects. We measured signs of nicotine withdrawal in the C57BL/6J mice, and found without exception, each cohort became nicotine dependent. Our nicotine self-selection paradigm satisfies all accepted criteria for animal models of alcoholism. On this basis, we regard our design as being a valid model for nicotine dependence. During self-selection, we determined that /Cd81/ loss-of-function significantly increased nicotine preference. However, previous studies had indicated /Cd81/ loss-of-function produced a reduction in cocaine preference. Thus, we investigated further by comparing gene expression in wild-type and /Cd81/ knockout mice at baseline and after nicotine treatments. We measured the expression of genes for dopamine receptors (/Drd1, Drd2_S , Drd2_L , Drd3/), the dopamine transporter (DAT), phosphodiesterases (/Pde4b, Pde4d/), and the tetraspanin /Cd81/, in the mesocorticolimbic pathway. Our results indicated the following: (i) CD81 function was essential for normal transcriptional response to nicotine, (ii) baseline expression of /Pde4b/ and DAT were each influenced by /Cd81/ genotype in key brain areas and (iii) the baseline expression of /Pde4b/ and DAT correlated with nicotine consumption behaviors. Finally, we speculate that /Cd81/, /Pde4b/ and DAT work in concert to modulate nicotine preference and that this /Cd81/-associated pathway may function in a drug-specific manner. In conclusion, our results support the use of laboratory mice in nicotine self-selection for assessing nicotine preference. We found that CD81 influences nicotine consumption and transcriptional activity of dopamine signaling-associated components. Our hypothesis that CD81, PDE4B and DAT participate in a single pathway, working in concert to modulate drug consumption will be tested in future experiments. ###