Sex differences in passive avoidance learning

• Main Authors: Yi-Ya Fang, 方怡雅
• Other Authors: Yuan-Feen Tsai
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/64825154943945144775

碩士 === 國立臺灣大學 === 生理學研究所 === 98 === First part: Passive avoidance learning is a one-trial fear-motivated avoidance task in which the animal learns to refrain from stepping through a door to an apparently safer but previously punished dark compartment. Male rats have been observed to be more efficient than females in a passive avoidance situation once the duration of the interval exceeds 15 min. According to previous studies on spontaneous behavior, reproductive behavior and conditioned learning, it appears that differences in the rat strains may influence exploratory behavior, sexual behavior, and learning behavior. To address this question, passive avoidance tasks were given to rats of two strains, albono (Wistar) and pigmented (Long-Evans) strains. During passive avoidance learning, rats had to learn from the training procedures that paired the dark compartment with a mild footshock. Step-through latencies were measured to infer the animal’s memory for the fearful experience. The passive avoidance behavior of Wistar male rats were superior to that of Wistar female rats, but there was no significant difference in this behavior between the retenion of Long-Evans male and female rats. In conclusion, our data demonstrate that sex differences in passive avoidance learning exist in Wistar rats, but not in Long-Evans rats. Thus, choice of animal strains for studies on sex differences may be an important variable. Second part: Although there is extensive literature demonstrating that male and female rats differ in many behavioral patterns related to reproductive behavior, sex differences in non-reproductive behaviors have been investigated less. Female rats show more response suppression in aversively motivated learning when the effect of presentation of an aversive stimulus upon subsequent responding is measured immediately, whereas males show more suppression in procedures in which the effect of an aversive stimulus is measured after longer intervals. In the present study, we used both male and female Wistar rats aged 8 weeks which have been through passive avoidance learning to examine whether sexual divergence can indeed be attributed to temporal parameters. The step-through latencies were studied using various intervals between footshock and retention interval. During training, male and female rats received a footshock in the dark section of a conditioning chamber while control rats received the same training procedures but without the footshock. Female rats were superior to males in the retention of a step-through type passive avoidance response immediately after training. However, males performed better in the acquisition of a passive avoidance response 30 min after training. Males and females showed no sex differences in behavioral performance when they were tested 120 min after training. In order to examine whether the sex difference in the performance of passive avoidance conditioning is associated with a change in the activation of extracellular signal-regulated kinase (ERK), animals were decapitated immediately after testing, and we used western blot analysis to examine the activation of ERK in the dorsal hippocampus, ventral hippocampus, central nucleus of amygdale (CeA), and basolateral nucleus of amygdala (BLA). Our data demonstrated that phosphorylated ERK levels in the BLA and CeA, but not dorsal hippocampus, or ventral hippocampus, were higher in males than in females, relative to same sex controls, immediately after training. In both males and females, phosphorylation of ERK was not found in any brain regions at 30 min after training. When a shock-retest interval was 120 min, ERK activation in the BLA was observed only in males, but not in females. In summary, sex differences in passive avoidance learning depend on the time intervals between training and retention trial. ERK would be activated in the BLA only in males, immediately after training. Together, these findings suggest that there may be the existence of sexual dimorphism in memory process.