Normal aging is associated with deficits in certain aspects of cognition, such as attention, learning, and memory. Specifically, a decline is observed in episodic (declarative) memory, working memory, and spatial learning (Driscoll and Sutherland, 2005; Kausler, 1994).

Navigating to a target location and recognizing it from different perspectives are crucial for daily functioning (Chersi and Burgess, 2015; Segen et al., 2021). Normal aging leads to declines in spatial orientation and navigation abilities (Hartley et al., 2007; Montefinese et al., 2015; Muffato et al., 2019; Segen et al., 2021), largely due to deficits in spatial information processing (Kirasic and Allen, 1985; Perlmutter et al., 1981), which leads to avoidance of unfamiliar routes in older individuals (Burns, 1999). Furthermore, elderly people exhibit impairments in both real-world (Wilkniss et al., 1997) and virtual spatial navigation tasks, including the Morris water maze task, transverse pattern discrimination task, and mental rotation test (Driscoll et al., 2003; Driscoll et al., 2005; Iaria et al., 2009; Laurance et al., 2002; Moffat et al., 2001; Moffat and Resnick, 2002; Newman and Kaszniak, 2000; Rodgers et al., 2012). Older individuals make more errors, acquire spatial information more slowly, require more time to form a cognitive map, are less efficient in using it, and take longer to complete routes than young individuals. Animal studies have further indicated age-related differences in cognition. Deficits in memory and spatial learning are commonly observed in older animals (Barnes et al., 1997; Driscoll et al., 2006), as they perform poorly on various navigational tasks, such as the Morris water maze, T-maze, Barnes maze, radial maze, and object location memory tasks (Barnes, 1979; Barnes et al., 1980; Ingram, 1988; Jaeger et al., 2020; Jiménez-Rubio et al., 2020; McLay et al., 1999; Shukitt-Hale et al., 2004).

Age-related declines in testosterone levels have been linked to cognitive changes in men (Cherrier et al., 2001). The testes secrete testosterone into the circulation, allowing it to reach the brain structures involved in modulating cognition. This hormone decreases steadily with age (Bremner et al., 1983; Gray et al., 1991; Harman et al., 2001; Vermeulen, 1991), with an average reduction of 100 ng/dl per decade (Morley et al., 1997), resulting in 35 % lower plasma testosterone levels in men over 75 years of age compared to younger men (Harman et al., 2001). Total testosterone decreases by 1 % annually (Bardin et al., 1991), whereas free testosterone declines by 2–3 % per year as sex hormone-binding globulin increases with age (Feldman et al., 2002). Testosterone levels are positively correlated with spatial ability in men (Driscoll et al., 2005), and testosterone supplementation has been shown to enhance cognitive function in healthy elderly men (Cherrier, 1999; Cherrier et al., 2001; Janowsky et al., 1994; Kenny et al., 2002; Yaffe et al., 2002). Similarly, older rats exhibited improved memory in the 8-arm radial maze as a result of testosterone supplementation (Bimonte-Nelson et al., 2003; Jaeger et al., 2020; Onaolapo et al., 2016).

Testosterone exerts neurophysiological effects by being metabolized into estradiol and dihydrotestosterone, which bind to the estrogen and androgen receptors, respectively, in the hippocampus, prefrontal cortex, and striatum (Bimonte-Nelson et al., 2003; Salimi et al., 2021). In addition to being secreted by the testes, testosterone is also synthesized and converted into its active metabolites in brain structures involved in cognition (Hojo et al., 2009; Hojo and Kawato, 2018). Interestingly, the activity of testosterone and dihydrotestosterone (but not estrogen) in the brain decreases with aging (Munetomo et al., 2015), suggesting that circulating and brain levels of androgens may collaboratively modulate cognitive function in males. Furthermore, high-density androgen receptors are expressed in key learning and memory centers, including the hippocampus and cortex (Dart et al., 2024; Kerr et al., 1995). Low et al. suggested that decreased testosterone levels, particularly with aging, may be linked to reduced androgen receptor levels. Research has demonstrated that androgen receptors decline with age in the mice brain cortex (Thakur et al., 2000) and the rat prefrontal cortex (Low et al., 2020), regions associated with working memory. Additionally, reduced androgen receptor mRNA levels in the CA1 area of the hippocampus in individuals over 65 years of age have been linked to cognitive decline (Tohgi et al., 1995). Taken together, this evidence supports the notion that testosterone and androgen receptor signaling play critical roles in cognitive performance in males.

Antiandrogens block androgen receptor signaling in androgen-dependent prostate cancer (Gao et al., 2006). Flutamide, a selective non-steroidal competitive androgen receptor antagonist, causes fatigue, irritability, and cognitive impairments in men (Cherrier et al., 2009). Its use may also impair spatial performance and cognitive abilities in patients with prostate cancer (Cherrier et al., 2003; Cherrier et al., 2009).

In preclinical research, direct administration of flutamide to the hippocampus of young rats impaired their performance on tasks such as the Morris water maze, inhibitory avoidance, and object recognition and placement tasks (Edinger and Frye, 2007; Koss and Frick, 2019; Naghdi et al., 2001). Systemic administration of flutamide causes memory deficits in male rodents during passive avoidance tests (Nayebi et al., 2014) and contextual fear conditioning (Ramzan et al., 2018). These findings indicate that androgen receptors may modulate hippocampus-mediated memory processes in males.

Research on spatial memory in animals often involves mazes that use strong stressors, which can obscure treatment effects, particularly in older males, due to their increased stress sensitivity (Lamberts et al., 1997; Smith et al., 2005). The Barnes maze, which relies on hippocampal function (Bartus et al., 1983; Woodruff-Pak, 1990), employs mild stressors, such as white noise and bright light, to motivate rats to locate the goal box. This method avoids food deprivation and enhances the performance of older rodents.

In a previous study using this paradigm (Jiménez-Rubio et al., 2020), we observed that older male rats exhibited significant deficits in memory acquisition compared to young adult males and showed lower serum levels of total testosterone. Castration impaired the performance of young adult males across acquisition days but only resulted in a marginal deficit in the performance of older animals. Testosterone treatment induced a small improvement in spatial memory acquisition in castrated old rats and enhanced the retention of spatial memory in young adult males. These findings suggest that the decline in total testosterone levels cannot fully account for age-related deficits in spatial memory in the Barnes maze. Given the importance of circulating and brain levels of sex steroids in cognitive performance, other ligands of androgen receptors with actions on the central nervous system (Spritzer and Galea, 2007) may also influence the performance of old and young adult males on the Barnes maze.

This study aimed to investigate the role of androgen receptors in age-related spatial memory deficits using the Barnes maze in male rats. To achieve this, we utilized the androgen receptor antagonist flutamide. Additionally, since age-related motor deficits could affect the rats' performance in the Barnes maze, we also assessed their general motor activity using the open-field test (OFT).