putative biology of highrisk behavior, including certain sexual behaviors and drug use, requires an expanded basic knowledge base. With respect to sexuality, characterization of sexual dimorphism at the genomic, molecular, cellular, and behavioral levels is still in its early stages. Whether and how it may relate to the drive to engage in specific, highrisk sexual behavior is not known, but it should at least be explored. Similarly, although much has been learned about the biology of substance abuse, further elucidation of molecular and cellular mechanisms underlying addictive behavior may assist in the development of new therapeutic approaches to addiction, which in turn may profoundly alter the AIDS epidemic.
Recent neuroscience investigations have contributed to knowledge about the biology of sexuality. However, to date most research has focused on the sexually dimorphic nature of the brain (e.g., how aspects of synaptic architecture differ in males and females) (Raisman and Field, 1971) and on potential neuroanatomical correlates of homosexuality in men (Gorski et al., 1978; LeVay, 1991). Extensive studies using experimental animals have identified specific pathways and centers in the brain and spinal cord involved in sexual responses among both males and females (Gorski, 1988; Gorski et al., 1978; Johnson, Coirini, Ball, et al., 1989; Johnson, Coirini, McEwen, et al., 1989; McEwen, Luine, and Fischette, 1988; Meisel and Pfaff, 1985; Parsons et al., 1982; Pfaff and Reiner, 1973; Pfaff and Sakuma, 1979; Pfaff and Schwartz-Giblin, 1988; Sar and Stumpf, 1975). Experimental animal studies have provided a rather detailed account of the neural and hormonal bases of a spectrum of sexual behaviors. However, it remains unknown if and how neuroanatomical and genetic factors in sexuality translate into sexual risk behavior.
Indeed, the biology of sexual risk taking is a missing element in basic biomedical and neurobiological AIDS research. Some outstanding issues include: identifying the neurochemical molecular substrates, if any, associated with sexual risk taking; determining how insights from the studies of the neurobiology of sexuality would relate to highrisk sexual behavior and to sexually transmitted diseases, including AIDS; and determining how society might best integrate the study of the biology of sexuality and sexual risk taking into the broader context of sexuality, sexual behavior, and sexually transmitted diseases.