Stereological study of Hippocampus Role of D2 receptors on learning memory

Background: Some of the studies showed that related to memory and Hippocampusdependent learning, relation after take Bromocriptine (as D2 agonist) and Haloperidol (as D2 antagonist), there is no investigation concerning the effects of these two drugs on Hippocampus size and number of Asterocyt’s cell . The aim of this study is to investigation the probable effects of Bromocriptine and Haloperidol on learning activities and Hippocampal size and number of Asterocyte in male Rats. Materials and Methods: 45 male Rats of Sprague-Dawley race with the body weight of 220±20 gr have been selected randomly and divided to 5 groups (each one consists of 9 rats). The studied groups have been received 5 and 10 mg/kg/day and 2.5 and 5 mg/kg/day Bromocriptine and Haloperidol respectively and as daily Intra peritunial injections for one month. At the end of this period, spatial memory of different groups has been tested by Morris water maze. Then, the rats were anesthetized, and their brains have been fixed by intra cardiac fixator injection and then the brain was removed. The hippocampus serial sections of 7μm have been prepared. 10 samples have been chosen systematically from 100 and were evaluated. Volume estamination was done by Cavalier principle method. Results: for the groups which received maximal dose of Haloperidol and Bromocriptine, it took long time and high distances to reach Morris water maze which indicated of week learning ability of these two groups. Furthermore, comparing to control, these two groups had small sized right Hippocampus. It took short time and low distances for the groups which received low dose of Haloperidol and Bromocriptine which indicated bether learning ability of these two groups and comparing to control one, these two groups had large sized Hippocampus. At the other hand, consumption of Haloperidol and Bromocritine with low and high dose in comparison with control group had increase and reduces in asterocytes cell respectivly Conclusion: This study demonstrated that the low dose consumption of Haloperidol & Bromocriptine not only affects the learning positively, but also increases the Hippocampus volume and the number of