Androgen metabolism in the juvenile oscine forebrain: A cross-species analysis at neural sites implicated in memory function
✍ Scribed by Saldanha, Colin J. ;Clayton, Nicola S. ;Schlinger, Barney A.
- Book ID
- 101260185
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 185 KB
- Volume
- 40
- Category
- Article
- ISSN
- 0022-3034
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✦ Synopsis
Juvenile songbirds are useful models for studying the neural bases of memory. Memory-reliant behaviors demonstrated at this stage include song learning (most songbirds) and food caching (food-storing songbirds). Sex steroids are implicated in the modulation 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, respectively. To explore the role of local androgen metabolism on memory processes, we documented the activities of these enzymes in the anterior neostriatum (NAN), caudomedial neostriatum (NCM), and hippocampus (HP) of four species of juvenile songbird, two of which are food storers. Areas were dissected, homogenized, and provided with radiolabeled substrate; and formed estrogens, 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 perception. In the HP, both estrogens and 5␣ reduced androgens were formed, suggesting that HP function may be modulated by both estrogens and androgens. Finally, a derived measure of steroid-differential reveals that foodstoring 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 metabolites. This local conversion may play a role in the neuroendocrine modulation of memory in these birds.