| Summary: | 碩士 === 國立臺灣大學 === 生理學研究所 === 94 === Learning and memory is critical for the survival of organisms during development. Female rodents have been used for a long time as subjects for investigating the relationship between ovarian hormones and cognitive performance. However, it remains unclear what role of ovarian hormones may play in the process of learning and memory in male rats. The aim of this study is to reveal the influence of estradiol (E2) and progesterone (P) on male rats in different mnemonic tasks.
In part one, the investigation was designed to examine if different doses of E2 have the opposite effects on spatial learning tasks in young male rats. Long-Evans hooded rats were gonadectomized and pre-trained in a water maze with a visible platform. Following pre-training, high dose (120 μg/kg body weight, SC) or low dose E2 (30μg/kg body weight, SC) or oil was administered every single day since 48 h prior to testing and P (500 μg, SC) 4 h prior to testing. Rats were tested in a water maze with a submerged platform for 15 trials with randomed start locations for 4 days.The E2 treatment in both doses showed significantly impairments in the beginning of the testing days but only the high dose E2 treated group showed longer latency to the platform on the third and forth testing days. Interestingly, none of the E2 plus P treated animals showed significantly impaired performance relative to the control groups. In the high dose E2 treated group, levels of the epinephrine and 5-HT were elevated but 5-HIAA was decreased in hippocampus, the level of NE was elevated but DA decreased in the amygdala. In high dose E2-P treated group, DOPAC was elevated in hippocampus but decreased in amygdala. In the low dose E2 treated group, level of 5-HIAA in the hippocampus and DA in the amygdala were decreased, however, levels of 5-HT and 5-HIAA were increased in the amygdalar region. In the low dose E2-P treated group, levels of NE, DOPAC and 5-HIAA were elevated in the amygdala.
In part two, the experiment was mainly designed to determine if similar procedures and treatments of steroidal hormones would have the same effect on the acquisition of conditioned taste aversion in young male rats. Sixty gonadectomized male rats received multiple doses of E2 (30μg/kg body weight, SC) or oil and P (500 μg, SC) before and during acquisition of LiCl-induced conditioned taste aversion. During acquisition, 30-min access to novel saccharin solution was given to rats and injected with either 0.15M LiCl or normal saline (4 ml/kg body weight). The results showed that E2 and E2-P treated groups enhance the acquisition of conditioned taste aversion compared to the oil-treated one. Besides, the well-established suppressive intake effect of E2 was reflected in reduction of both the total fluid intake and the body weight. However, significant aversion toward sucrose solution was mainly due to the effect of sucrose-LiCl conditioning reflected in results of comparison between LiCl and saline as an unconditioned stimulus. In the granular insular cortex, level of NE was elevated in E2-P-LiCl treated group. In the lateral hypothalamus, level of epinephrine was increased in E2-LiCl treated group and levels of NE in E2-saline treated group was higher than oil-saline treated group, E2-P-saline treated group and E2-LiCl treated group. Taken together, similar procedures and treatments of ovarian hormones had different effects with regard to different types of learning and memory in male rats.
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