Androgen Metabolism in the Juvenile Oscine Forebrain: A Cross-Species Analysis at Neural Sites Implicated in Memory Function Colin J. Saldanha, 1,2 Nicola S. Clayton, 3 Barney A. Schlinger 1,2 1 Department of Physiological Science, University of California Los Angeles, 621 Charles E. Young Drive South, Los Angeles, California 90095 2 Laboratory of Neuroendocrinology of the Brain Research Institute, University of California Los Angeles, Los Angeles, California 90095 3 Section of Neurophysiology and Behavior, University of California Davis, Davis, California 95616 Received 14 August 1998; accepted 19 March 1999 ABSTRACT: Juvenile songbirds are useful models for studying the neural bases of memory. Memory-reli- ant behaviors demonstrated at this stage include song learning (most songbirds) and food caching (food-stor- ing songbirds). Sex steroids are implicated in the mod- ulation of memory processes in several vertebrates. The songbird forebrain expresses aromatase, 5-reductase and 5-reductase, enzymes which convert testosterone to estradiol, 5-, and 5-dihydrotestosterone, respec- tively. To explore the role of local androgen metabolism on memory processes, we documented the activities of these enzymes in the anterior neostriatum (NAN), cau- domedial neostriatum (NCM), and hippocampus (HP) of four species of juvenile songbird, two of which are food storers. Areas were dissected, homogenized, and pro- vided with radiolabeled substrate; and formed estro- gens, and 5- and 5-reduced androgens were mea- sured. In the NAN, 5-reductase was the predominant enzyme, suggesting that local inactivation of testosterone may preserve the sensitive period of song acquisition. In the NCM, estrogens were formed in abundance despite high 5-reductase, suggesting that locally high estrogen synthesis may play a role in processes of song percep- tion. In the HP, both estrogens and 5 reduced andro- gens were formed, suggesting that HP function may be modulated by both estrogens and androgens. Finally, a derived measure of steroid-differential reveals that food- storing songbirds differ from nonstorers in the steroidal milleiu within the HP, but not in the NAN or NCM. Thus, distinct loci within the juvenile songbird forebrain are exposed to different patterns of androgen metabo- lites. This local conversion may play a role in the neu- roendocrine modulation of memory in these birds. © 1999 John Wiley & Sons, Inc. J Neurobiol 40: 397– 406, 1999 Gonadal steroids have been implicated in aspects of memory function in several vertebrates (McEwen et al., 1995). In humans, testosterone (T) (Janowsky et al., 1994) and estrogen (E) (Sherwin, 1988; Kampen and Sherwin, 1996) are associated with increased memory performance. In rodents, a corresponding enhancement is seen in response to T (Gouchie and Kimura, 1991; Roof and Havens, 1992), or E admin- istration (Singh et al., 1994; O’Neal et al., 1996). The data suggest the involvement of T or its aromatized metabolite E in aspects of vertebrate memory. Several oscine passerines (hereafter: songbirds) in- cluding the zebra finch (Taenopygia guttata) (Vockel et al., 1990; Schlinger and Arnold, 1991), white- crowned sparrow (Zonotrichia leucophrys) (Schlinger Correspondence to: C. J. Saldanha Contract grant sponsor: JD French Alzheimer’s Foundation Contract grant sponsor: NIH NS 35465 Contract grant sponsor: Whitehall Foundation Contract grant sponsor: NSF; contract grant number: IBN 9120776 © 1999 John Wiley & Sons, Inc. CCC 0022-3034/99/030397-10 397