Abstract
Sex differences in spatial memory have long been observed in humans, non-human primates and rodents, but the underlying cellular and molecular mechanisms responsible for these differences remain obscure. In the present study we found that adolescent male rats outperformed female rats in 7 d and 28 d retention probes, but not in learning trials and immediate probes, in the Morris water maze task. Male rats also had larger long-term potentiation (LTP) at hippocampal temproammonic-CA1 (TA-CA1) synapses, which have been implicated to play a key role in place field and memory consolidation, when protocols designed to elicit late-stage LTP (LLTP) were used. Interestingly, the ratio of evoked AMPA/NMDA currents was found to be smaller at TA-CA1 synapses in male rats compared to female rats. Protein biotinylation experiments showed that male rats expressed more surface GluN1 receptors in hippocampal CA1 stratum lacunosum-moleculare (SLM) than female rats, although GluA1 expression was also slightly higher in male rats. Taken together, our results suggest that differences in the expression of AMPA and NMDA receptors may affect LTP expression at TA-CA1 synapses in adolescent male and female rats, and thus possibly contribute to the observed sex difference in spatial memory.
Highlights
Spatial navigation in familiar or new environments is an essential ability for many species in their daily life [1]
In the present study we found that adolescent male rats outperformed female rats in 7 d and 28 d retention probes, but not in learning trials and immediate probes, in the Morris water maze task
Our results suggest that differences in the expression of AMPA and NMDA receptors may affect long-term potentiation (LTP) expression at temporoammonic pathway (TA)-CA1 synapses in adolescent male and female rats, and possibly contribute to the observed sex difference in spatial memory
Summary
Spatial navigation in familiar or new environments is an essential ability for many species in their daily life [1]. Studies show that a significant improvement in the ability to process spatial and contextual information occurs in adolescence, the consequence of rapid structural and functional changes in the brain from childhood into adolescence [3]. Sex differences in performing spatial tasks have long been observed in humans, non-human primates and rodents [4,5,6,7,8,9], but the underlying mechanisms are not fully understood. Several studies have suggested that the brain regions that are associated with spatial cognitive processes could be different, or functioning differentially, in each sex [10,11,12,13,14]. The key neural circuits and biochemical signaling pathways responsible for these discrepancies are still largely unidentified
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