Abstract
Previous research has shown that exposure to testicular hormones during the peri-pubertal period of life has long-term, organizational effects on adult sexual behaviour and underlying neural mechanisms in laboratory rodents. However, the organizational effects of peri-pubertal testicular hormones on other aspects of behaviour and brain function are less well understood. Here, we investigated the effects of manipulating peri-pubertal testicular hormone exposure on later behavioural responses to novel environments and on hormone receptors in various brain regions that are involved in response to novelty. Male rodents generally spend less time in the exposed areas of novel environments than females, and this sex difference emerges during the peri-pubertal period. Male Lister-hooded rats (Rattus norvegicus) were castrated either before puberty or after puberty, then tested in three novel environments (elevated plus-maze, light–dark box, open field) and in an object/social novelty task in adulthood. Androgen receptor (AR), oestrogen receptor (ER1) and corticotropin-releasing factor receptor (CRF-R2) mRNA expression were quantified in the hypothalamus, hippocampus and medial amygdala. The results showed that pre-pubertally castrated males spent more time in the exposed areas of the elevated-plus maze and light–dark box than post-pubertally castrated males, and also confirmed that peri-pubertal hormone exposure influences later response to an opposite-sex conspecific. Hormone receptor gene expression levels did not differ between pre-pubertally and post-pubertally castrated males in any of the brain regions examined. This study therefore demonstrates that testicular hormone exposure during the peri-pubertal period masculinizes later response to novel environments, although the neural mechanisms remain to be fully elucidated.
Highlights
Puberty is characterised by increased circulating levels of gonadal hormones, such as testosterone and estradiol, and is accompanied by a suite of physical and behavioural changes in both human beings and non-human animals (Blakemore, 2008; Spear, 2000)
elevated plus-maze (EPM) Males that had been castrated before puberty spent more time on the open arms of the EPM (F1,18 = 5.86, p = 0.03,ηp2 = 0.25; Fig. 2a), and entered the open arms more frequently (F1,18 = 4.80, p = 0.04,ηp2 = 0.21; Fig. 2b), than males that had been castrated after puberty
The main finding was that male rats that had been castrated before puberty spent more time on the open arms of the EPM, and in the light section of the LD box, than males that had been castrated after puberty
Summary
Puberty is characterised by increased circulating levels of gonadal hormones, such as testosterone and estradiol, and is accompanied by a suite of physical and behavioural changes in both human beings and non-human animals (Blakemore, 2008; Spear, 2000). Recent studies of laboratory rodents have shown that gonadal hormones can direct brain development during the peripubertal period by influencing neurodevelopmental processes, such as cell proliferation and axon myelination, with long-term implications for brain structure and function (e.g., Ahmed et al, 2008; De Lorme et al, 2012a; Yates and Juraska, 2008). Experimental studies on rodents have shown that exposure to gonadal hormones during the peri-pubertal period has long-term effects on behaviour; for example,. The developing brain, and its behavioural outputs, can be described as being sensitive to the long-term, ‘organizational’ effects of gonadal hormones during the peri-pubertal period (Schulz et al, 2009; Sisk and Zehr, 2005; Juraska et al, 2013). Brown et al / Hormones and Behavior 73 (2015) 135–141
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