Effects of suppressing gonadal hormones on response to novel objects in adolescent rats

Abstract

Human adolescents exhibit higher levels of novelty-seeking behaviour than younger or older individuals, and novelty-seeking is higher in males than females from adolescence onwards. Gonadal hormones, such as testosterone and estradiol, have been suggested to underlie age and sex difference in response to novelty; however, empirical evidence in support of this hypothesis is limited. Here, we investigated whether suppressing gonadal hormone levels during adolescence affects response to novelty in laboratory rats. Previously, we have shown that male adolescent Lister-hooded rats (postnatal day, pnd, 40) exhibit a stronger preference than same-aged females for a novel object compared to a familiar object. In the current study, 24 male and 24 female Lister-hooded rats were administered with Antide (a gonadotrophin-releasing hormone antagonist), or with a control vehicle solution, at pnd 28. Antide provided long-term suppression of gonadal hormone production, as confirmed by ELISA assays and measurement of internal organs. Response to novel objects was tested at pnd 40 in Antide-treated and control subjects using a ‘novel object recognition’ task with a short (2-minute) inter-trial interval. In support of previous findings, control males exhibited a stronger preference than control females for novelty when presented with a choice of objects. Antide-treated males exhibited a significantly lower preference for novel objects compared to control males, whilst Antide-treated females did not differ significantly from control females in their preference for novelty. Antide treatment did not affect total time spent interacting with objects. We discuss how gonadal hormones might influence sex differences in preference for novelty during adolescence.

Sex-specific enhanced behavioral toxicity induced by maternal exposure to a mixture of low dose endocrine-disrupting chemicals

“…The current findings add further support to those assertions that developmental exposure to EDCs creates sex-specific alterations in exploratory behavior (Patisaul, Sullivan, 2012). In this study, vehicle males showed significantly increased overall exploration time with objects compared to vehicle females, findings consistent with prior reports (Cummings et al, 2013, Cyrenne and Brown, 2011, Frick and Gresack, 2003, Wilson and Daly, 1985). In contrast, mice developmentally exposed to the mixture of EDCs showed the opposite relationship, as MIX exposed males showed significantly decreased exploration times compared to MIX exposed females.…”

“…There is experimental evidence that such behavioral differences can be hormonally mediated, as rats exposed to a long-acting gonadotrophin-releasing hormone antagonist, Antide, demonstrated a similar behavioral reversal. Antide treated males showed reduced serum testosterone and diminished preference for novelty compared to females (Cyrenne and Brown, 2011). Additionally, gonadectomized males showed diminished exploratory behavior compared to control males, while gonadectomized males given testosterone increased novel object exploration (Aubele et al, 2008b).…”

“…Male preference for novelty has been suggested to have adaptive functions (Wilson and Daly, 1985), with support from rodent studies indicating that males spend more time exploring novel objects than females (Cyrenne and Brown, 2011, Frick and Gresack, 2003). Even when females show increased exploratory behavior, developmental exposure to EDCs eliminates any sex specific differences in exploratory behavior and alters sex-specific neurochemistry (Gioiosa, Fissore, 2007, Rubin et al, 2006).…”

The effects of gonadectomy on sex- and age-typical responses to novelty and ethanol-induced social inhibition in adult male and female Sprague-Dawley rats

“…While no sex differences in novelty-seeking were observed at any age in this [38] and similar studies examining response to novelty [36], other studies have reported adult male mice [39] and adolescent and adult male rats [40] to show greater preferences for novel objects than adult females. Indeed, increases in gonadal hormones associated with puberty have been suggested to underlie age- and sex-typical responses to novelty, a suggestion supported by data showing that long-term suppression of gonadal hormone production via prepubertal administration of Antide eliminated sex differences in novelty preference during late adolescence [41]. Yet, groups of similarly treated adults were not included in this study, and thus it is unclear whether the observed effects were related to activational or organizational effects of gonadal hormones.…”

Androgens Increase Persistence But Do Not Affect Neophobia in a Problem-Solving Context in a Songbird

“…Avoidance or fear of novelty (i.e., neophobia) is also suggested to be influenced by gonadal hormone levels in mammals (Cornwell-Jones & Kovanic 1981). For example, novelty-seeking behavior was reduced by suppressing gonadal hormone levels in rats (Cyrenne & Brown 2011). By contrast, the approach taken in many avian studies has mainly focused on the long-term effects of maternal steroids in behavioral responses to novelty.…”