Monoamine Metabolism and Behavioral Responses to Ethanol in Mitochondrial Aldehyde Dehydrogenase Knockout Mice Elizabeth Fernandez, Wouter Koek, Qitao Ran, Greg A. Gerhardt, Charles P. France, and Randy Strong Background: It is widely accepted that, in addition to removing acetaldehyde produced during the metabolism of ethanol, mitochondrial aldehyde dehydrogenase (ALDH2) functions in the pathway by which aldehyde metabolites of the monoamines dopamine (DA) and serotonin (5-HT) are converted to their acidic metabolites. Moreover, studies of ALDH2 inhibitors used for treating alcoholism suggest that their antidipsotropic effects may be related to inhibition of monoamine metabolism. Therefore, we examined the hypothesis that altered brain monoamine metabolism is related to the influence of ALDH2 on behavioral responses to ethanol. Methods: Mice were generated with a gene-trap mutation of the ALDH2 gene. ALDH2 mRNA was absent in ALDH2 /  mice. Western blot analysis of liver mitochondria confirmed the absence of ALDH2 protein in the ALDH2 /  mice. Wild-type and ALDH2-deficient mice were tested for the effects of different doses of ethanol on locomotor activity, ataxia, and a 2-bottle ethanol–water preference test. Results: Wild-type and ALDH21 /  mice preferred ethanol to water. However, ALDH2 /  mice drank significantly less ethanol than wild-type or ALDH21 /  mice. Locomotor activity and ataxia were significantly more affected by ethanol in ALDH2 /  mice than in wild-type or ALDH21 /  mice. There was no effect of genotype on levels of 5-HT, DA, or their precursors or metabolites in several brain regions, as measured by HPLCec. Conclusions: The results indicate that: (1) the effect of the mutant genotype on behavioral responses to ethanol is unrelated to altered brain monoamine metabolism and (2) ALDH2 is not required for the metabolism of brain monoamines in vivo. Key Words: Mitochondrial Aldehyde Dehydrogenase, ALDH2, Monoamines, Ethanol. E THANOL IS OXIDIZED in the liver by cytosolic alcohol dehydrogenase 2 (ADH2) to acetaldehyde and is then further oxidized by mitochondrial aldehyde dehydrogenase (ALDH2) to produce acetic acid. Alcohol sensitivity in Asian populations is associated with a deficiency of ALDH2 activity, caused by a point mutation G ! A transition at nt 1,510 on the ALDH2 gene, which translates to Glu ! Lys at protein position 487 (Yoshida, 1992). The ALDH2 Glu487Lys polymorphism is associated with a markedly reduced risk of alcoholism and alcoholic liver disease (Yoshida, 1992). Moreover, differ- ences among rodent strains in preference for ethanol over water have been reported to be related to differences in ALDH2 activity in the liver and the brain (Messiha, 1985). The mechanism underlying this genetic effect on beha- vioral responses to ethanol is unclear. Several studies have linked differences in the function of monoamines, dopamine (DA), and serotonin (5-HT), to differences in behavioral responses to ethanol. For example, 5-HT1a receptor agonists increase preference for ethanol, while 5-HT1a receptor antagonists or targeted deletion of the 5-HT transporter reduce preference for ethanol (Kelai et al., 2003; Svensson et al., 1993; Tomkins et al., 1994). Furthermore, mice with targeted deletions of the DA transporter (DAT) had increased sensitivity to, and decreased preference for, ethanol (Savelieva et al., 2002). Moreover, targeted deletion of the DA D2 receptor reduced both ethanol preference and ethanol sensitivity From the Research Service and Geriatric Research, Education and Clinical Center, South Texas Veterans Health Care System, San Antonio, Texas (RS); the Departments of Pharmacology (EF, WK, CPF, RS); Psychiatry and Cellular & Structural Biology (WK, CPF), University of Texas Health Science Center, San Antonio, Texas (QR); and the Departments of Anatomy and Neurobiology, Neurology and Psychiatry, University of Kentucky, Chandler Medical Center, Lexing- ton, Kentucky (GAG). Received for publication January 27, 2006; accepted June 29, 2006. This work was supported by a grant from the Department of Veterans Affairs Office of Research and Development (RS); Grants AG022307 (RS), DA17198 (CPF), AG022014 (QR), and NS039787 (GAG) from the United States Public Health Service; and a grant from the Peter F. McManus Charitable Trust (WK). Reprint requests: Randy Strong, Department of Pharmacology, Uni- versity of Texas Health Science Center, 1355 Lambda Drive, MSC 7755, San Antonio, TX 78245-3207; E-mail: strong@uthscsa.edu Copyright r 2006 by the Research Society on Alcoholism. No claim to original US government works. DOI: 10.1111/j.1530-0277.2006.00200.x Alcohol Clin Exp Res, Vol 30, No 10, 2006: pp 1650–1658 1650 ALCOHOLISM:CLINICAL AND EXPERIMENTAL RESEARCH Vol. 30, No. 10 October 2006