Influence of sex steroid hormones on spatial memory in a songbird

Abstract

In mammals, sex steroid hormones influence spatial learning and memory abilities but there are few data regarding such effects in birds. We investigated whether non-invasive sex steroid hormone treatment would affect spatial memory task performance of great tits (Parus major). For five consecutive days, birds were fed wax moth larvae injected with either 80 microg testosterone or 80 microg estradiol carried in peanut oil immediately prior to behavioral testing. During the 5 days prior to and the 5 days following hormone treatment, birds were fed vehicle-injected larvae. Both hormone manipulations resulted in an elevation of circulating hormone levels within 5 min of larva ingestion. This elevation was sustained for at least 30 min but had no short-term (<1 day) effect on spatial memory performance. However, performance tended to increase during the first 5 days of vehicle treatment and during both sex steroid treatments whereas it decreased during the 5 days of vehicle treatment following either hormone treatment. These results suggest that both hormones led to some improvement in spatial memory that declined once treatment ended. The great tit hippocampus was found to express androgen and estrogen receptors which would provide a direct site of sex steroid action.

Sex Differences in Spatial Memory in Brown-Headed Cowbirds: Males Outperform Females on a Touchscreen Task

“…In a task similar to ours, exogenous androgens improved performance on a delayed-non-matching-to-sample touchscreen task in great tits [35]. In situ hybridization shows expression of androgen and estrogen receptor genes in the hippocampus of tits and testosterone and estrogen could influence spatial memory by binding to these receptors [35]. The songbird hippocampus expresses high levels of aromatase, resulting in high levels of local estrogen synthesis from testosterone and enhanced spatial memory acquisition and performance [34, 36, 52].…”

“…Male deer mice show better acquisition of spatial maze performance than females in breeding condition only, when their testosterone levels are highest [12]. In a task similar to ours, exogenous androgens improved performance on a delayed-non-matching-to-sample touchscreen task in great tits [35]. In situ hybridization shows expression of androgen and estrogen receptor genes in the hippocampus of tits and testosterone and estrogen could influence spatial memory by binding to these receptors [35].…”

“…Changes in breeding condition influence hormone levels in both female and male brown-headed cowbirds [21] and both testosterone and estradiol can influence acquisition and performance of spatial tasks [34, 35, 36]. …”

The importance of neural aromatization in the acquisition, recall, and integration of song and spatial memories in passerines

“…While not directly testing the role of neural aromatization in the hippocampus on spatial memory function, a few studies have examined the short-and long-term effects of E 2 treatment. Testosterone and E 2 fed to great tits (Parus major) did not affect spatial memory performance shortly after ingestion but led to gradual improvements over the 5 days of treatment, an effect that subsided when hormone delivery ceased (Hodgson et al, 2008).…”

Effects of testosterone on the spatial ecology, coloration, and brain regions in western fence lizards, Sceloporus occidentalis

“…However, exogenous T and estradiol increased spatial memory performance equally in great tits (Parus major; Hodgson et al, 2008). In U. stansburiana, males with higher T levels had larger home range sizes (DeNardo and Sinervo, 1994;Sinervo et al, 2000).…”