To identify genetic contributions to alcoholism vulnerability, we focus on serotonergic behaviors, since a subtype of alcoholism is associated with decreased serotonin turnover. Serotonin biosynthesis is governed by tryptophan hydroxylase (TPH), which is rate-limiting. Levels of tryptophan, a precursor in serotonin biosynthesis, are modulated by tryptophan 2,3-dioxygenase (TDO). Serotonergic neurotransmission is influenced pre- and postsynaptically by the 5-HT1A receptor. We hypothesize that genetic variants of TPH, TDO and 5-HT1A and factors controlling their gene expression are determinants of alcoholism vulnerability and related behaviors. TDO gene expression was detected for the first time in brain. Polymorphic variants of the human, mouse and macaque TPH and the human and macaque 5-HT1A receptor alleles were identified by SSCP analysis. The human TPH gene was mapped to chromosome 11p15.5. The human TPH polymorphism associated with CSF 5-HIAA concentration in alcoholic, impulsive, violent Finns. The TPH polymorphism associated with suicidal behavior in alcoholic violent Finns. Polymorphic TPH and 5HT-1A alleles are being sequenced. The factors and sequences controlling the expression of TPH and 5-HT1A are being identified. DNA constructions are being assayed to delineate regions controlling tissue- specific and regulated TPH expression. The mouse TPH promoter is being analyzed by mobility shift assay and DNase I footprint analysis to identify transcription factors which regulate TPH gene expression and their cognate binding sites.