An in vitro analysis of neuronal survival in response to hormones and photoperiod in the HVc of the songbird Junco hyemalis

Abstract

The ability of songbirds to sing is essential for their survival, proper reproductive behavior, and territorial establishment. Male and female juvenile passerine songbirds learn their song through the formation of a song template in their earliest days of life, first by listening to their parents, and then followed by auditory feedback against their own templates to crystallize their individual songs. However, in most passerine species, only the adult males actually sing on a seasonal basis with little to no singing during winter, followed by a phase of song production in the spring in correlation with increased plasma testosterone concentration and extended photoperiods. While the production of new neurons in the song system of adult males is continuous throughout the year, a counterbalancing turnover of these neurons must exist until the spring, when a three- to four-fold decrease in dying HVc (hyperstriatum pars ventralis caudale or higher vocal center) neurons in males initiates song production. We hypothesized that testosterone, under the influence of increased photoperiod, attenuates the rate of programmed cell death (apoptosis) of newly generated neurons migrating into the HVc song nucleus in the wild arctic songbird Junco hyemalis. Using an organotypic culture system, we examined the effect of testosterone and [beta]-estradiol on the degree of apoptosis in the HVc obtained from photo stimulated and non-photo stimulated male and female juncos. We employed a TUNEL assay and BrdU-labeling to detect and quantify apoptosis. We found that hormonal treatment with testosterone, and [beta]-estradiol in photostimulated birds only, extends the lifespan of cells within the HVc compared to controls, as shown by BrdU labeling, and decreasing apoptosis, as shown by TUNEL assay.