Sex‐dependent effects of postweaning exposure to an enriched environment on novel objective recognition memory and anxiety‐like behaviors: The role of hippocampal BDNF level

Abstract

Exposure to enriched environment (EE) has been indicated to enhance cognitive functions, hippocampal neural plasticity, neurogenesis, long‐term potentiation, and levels of the brain‐derived neurotrophic factor (BDNF) in laboratory animals. Also, studies on the sex‐dependent effects of exposure to EE during adolescence on adult cognitive functions are less. This is important because the beneficial effects of EE may be predominant in the adolescence stage. Therefore, the present study was designed to compare the effects of EE during adolescence (PND21‐PND60) on novel objective recognition memory (NORM), anxiety‐like behaviors, and hippocampal BDNF mRNA level in the adult male and female rats. Assessment of NORM and anxiety‐like behaviors has been done by novel objective recognition task, open field (OF), and elevated plus maze (EPM), respectively. The expression of BDNF mRNA level was also evaluated by quantitative RT‐PCR. Our findings demonstrated that housing in the EE during adolescence improves NORM in adult male rats. Also, exposure to EE during adolescence had a different effect on anxiety‐like behaviors in both sexes. Additionally, our results indicated an augmented BDNF level in the hippocampus of male and female rats. In conclusion, adolescent exposure to EE has sex‐dependent effects on cognitive functions and anxiety‐like behaviors and increases BDNF mRNA expression in the hippocampus of both male and female rats; thus, BDNF is an important factor that can mediate the beneficial effects of EE and running exercise on cognitive functions and psychiatric traits.

Serotonin depletion during the postnatal developmental period causes behavioral and cognitive alterations and decreases BDNF level in the brain of rats

“…Fecal boli was calculated at the end of 5 min. Between each test, the open field device was cleaned with alcohol (Hakimeh & Vahid, 2017; Sakhaie et al., 2020; Sakhaie et al., 2020).…”

“…The elevated plus maze (EPM) test is one of the well‐known methods for testing anxiety‐like behaviors and motor activity as previously described (Sakhaie, Sadegzadeh, Dehghany, et al., 2020; Sakhaie, Sadegzadeh, Mohammadnia, et al., 2020). Briefly, the maze is made from wood and consists of two open arms (50 × 10 cm) and two enclosed arms (50× 10 × 40 cm) which are arranged opposite one another around a 10 cm square center.…”

“…The novel object recognition test is one of the explicit episodic memory consisted of three phases, habituation, training, and test, as described in previous studies (Sakhaie, Sadegzadeh, Dehghany, et al., 2020; Sakhaie, Sadegzadeh, Mohammadnia, et al., 2020). In the habituation phase, the animals were released in an empty Plexiglas box (60 × 60 × 50 cm) for 5 min.…”

“…Rats were killed by decapitation after anesthetizing with atmospheric carbon dioxide (CO 2 ) in a desiccator jar with a low‐pressure flow and brains were quickly removed. The hippocampi and prefrontal cortex (0.48 mm posterior relative to the optic chiasm and 2.0 mm anterior relative toward the olfactory bulbs) of the brain were dissected on an ice‐cold surface (Sadegzadeh, Sakhaie, Isazadehfar, et al., 2020; Sakhaie, Sadegzadeh, Mohammadnia, et al., 2020). Tissue samples were immediately frozen in liquid nitrogen and stored at −80°C until being ready for RT‐PCR evaluation.…”

Melamine disrupts spatial reversal learning and learning strategy via inhibiting hippocampal BDNF-mediated neural activity

“…To better understand the action of melamine on reversal performance, the action of melamine on learning strategy was assessed in cross-maze task. Previously, the hippocampal BDNF level was increased by exposure to a novel environment [32]. Learning-induced expression of BDNF in the HPC was implicated for effective solving of maze task by place strategy [33][34][35].…”