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Background & Objective: In addition to pyramidal neurons and interneurons, the hippocampus contains Astrocytes that play important roles in regulating ion flux currents, energy production, neurotransmitter release and memory. Learning needs some instrument for information storage and information maintenances mechanisms resemble to memory. The aim of this study was determination of spatial memory effect on the number of astrocytes in rat’s hippocampus. Materials & Methods: In this experimental study, with usage of Morris Water Maze and Reference memory technique, we used 10 male albino wistar rats. 5 rats were in control group and 5 rats in Reference memory group. After histological preparation, the slides were stained with PTAH staining for showing the Astrocytes. Results: The findings of this study showed significant difference in astrocytes number in CA1, CA2 and CA3 area of hippocampus between control and reference memory group. The mean and SD of astrocytes in CA1, CA2 and CA3 of reference memory group were 118.57±25.29, 58.91±23.59 and 116.6±31.14, that they are more than control group with 49±17.29 in CA1, 48.8±25.21 in CA2 and 41.95±11.22 in CA3. Conclusion: We concluded that the number of astrocytes increased due to spatial learning (e.g. reference memory method).

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Background and Objective: Dentate gyrus is a part of hippocampal formation that plays an important role in memory and learning. Astrocytes are one of the important glial cells in nervous tissue that play a more active role in neuronal activity, including regulating ion flux currents, energy production, neurotransmitter release, and synaptogenesis. The aim of this study was to determine the spatial memory effect on the number of astrocytes in Rat’s dentate gyrus. Materials and Methods: This experimental study, was done on 18 male Wistar Rats with using Morris water maze and Reference and Working memory methods. After spatial learning the Rat's brains was carried out and histological preparation was carried out, the slices were with PTAH method. The data analyzed, using T-test and One-way ANOVA. Results: The results showed significant difference in astrocytes number in dentate gyrus area between Reference memory (300.57±5.98) and control (73.73±22.61) groups (P<0.05). The difference between working memory (375.77±4.11) and control groups was significant. Comparing two groups there was a significant difference of number of astrocytes cell between the working memory and Reference memory group (P<0.05). Conclusion: This study showed that spatial learning such as Reference memory and Working memory increase the number of astrocytes in dentate gyrus and this increase can be due to duration of learning.

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Background and Objective: Morphological alterations of hippocampus and dentate gyrus due to opium were reported in humans and animals. Also other evidences have shown that astrocytes actively participate in synaptic plasticity. This study was done to determine the conditioning place preference (CPP) on astrocytes number of Rat dentate gyrus by immunohistochemical technique.

Materials and Methods: In this experimental study, 48 male Wistar Rat weighted average 220-250 g were used. For behavioural tests, Rats divided into eight experimental groups. The Rats were received morphine at different doses (2.5, 5, 7.5 mg/kg) for three days by subcutaneous injection and sham groups, received saline dose (1 mg/kg) and then CPP test in them were investigated. 48 hours after behavioural testing animals were decapitated under chloroform anesthesia and their brains fixed and after tissue processing, slices stained with immunohistochemistery techniques. For morphometric study PTAH staining of astrocytes was used.

Results: The most dose responses of morphine was observed in 7.5mg/kg. The number of astrocytes in the controls (20.627±6.129) was similar to control-saline group (17.339±4.71). This difference was not significant, while the difference in the number of astrocytes in control group with morphine-treated experimental groups was significant (P<0.05).

Conclusion: We concluded that the phenomenon of conditioned place preference induced by morphine can cause a significant increase in the number of astrocytes of sham and experimental groups compared to controls.

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Background and Objective: Diabetes mellitus is one of the most common serious metabolic disorders characterized by hyperglycemia, altered metabolism of lipids, carbohydrates and proteins. Gestational diabetes mellitus (GDM), affects 3.5–5% of all human pregnancy. Therefore, this study was done to evaluate the effect of gestational diabetes on astrocyte density in CA1 and CA3 subfields of hippocampus in rat male offspring.

Materials and Methods: In this experimental study, 12 Wistar Dams rats were randomly allocated in control and diabetic groups. Gestational diabetes induced by 40 mg/kg/body weight of streptozotocin at the first day of gestation (GD) in experimental group and controls were received an equivalent volume normal saline injection intraperitoneally (IP). Six male offspring of cases and controls dams, at the 7, 21 postnatal day (P7, P21) were randomly selected. Animals were scarified using chloroform anesthesia. The coronal sections of brain by 6 micrometer serially were prepared. The sections were stained with PTAH. The number of astrocytes was evaluated in 100000 μm² area of CA1 and CA3 in 1000X magnification. Data was analyzed by SPSS-11.5 and t-test.

Results: In CA1 subfield of hippocampus in offspring, the number of astrocytes  significantly reduced by 36.25% and 36.37% in diabetic group in compare to controls in the P7 and P21, respectively (P<0.05). In CA3, astrocytes density significantly reduced 36.35% and 26.5% in GD in comparison with controls in the P7 and P21, respectively (P<0.05).

Conclusion: This study showed that the uncontrol gestational diabetes significantly reduces astrocytes density in CA1 and CA3 subfields of hippocampus in rat offspring.

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Background and Objective: Adult neurogenesis occurs in most mammalian species in two main areas of brain: 1- subventricular zone 2- the dentate gyrus of the hippocampus. Many factors such as 17-B estradiol affect neurogenesis in the hippocampus. The aim of this study was to investigate the effect of exogenous 17-B estradiol on neurogenesis and astrocyte functions in the ovariectomized mice.
Methods: In this experimental study; NMRI mice were allocated into five experimental groups including Sham, Control, Treatment with single dose of 17-B estradiol two weeks after ovariectomy (OVX) and were sacrificed 24 hours later, Treatment with single dose of 17-B estradiol two weeks after Ovx and were sacrificed 48 hours later and   Treatment with single dose of Seasame Oil 2 weeks after OVX and were sacrificed after 24 hours. Animals were transcardially perfused with paraformaldehyde. Brains were removed and its sections for cresyl fast violet staining and GFAP immunohistochemistry were prepared. Cells were counted and investigated.
Results: Neuronal density and Proliferation of hippocampal progenitor cells in the CA1 region of 17-B estradiol treated mice significantly increased up to 24 hours (P<0.05). Density of glia and particularly astrocytes in different regions of the hippocampus significantly reduced after treatment with 17-B estradiol (P<0.05).
Conclusion: Density of hippocampal CA1 neurons are influenced by 17-B estradiol. Also, density and morphology of glia cells, especially astrocytes in different regions of the hippocampus are affected by 17-B estradiol.

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Background and Objective: Neurogenesis is the process through which neurons are generated from neural stem cells. This process has been shown to occur in special zones of the adult brain including the subventricular zone (SVZ) of the lateral ventricles and the dentate gyrus of the hippocampus. Gonadal steroids affect different steps of neurogenesis, and cell proliferation seems to be increased by estrogens. This study aimed to investigate the neurogenic changes in the SVZ at different phases of the estrous cycle.
Methods: In this experimental study, 26 NMRI mice were used. The mice were identified by vaginal smear and then divided into 4 groups including proestrus (n=5), estrous (n=7), metestrus (n=7) and diestrous (n=7). Different stages of the estrous cycle were determined by staining vaginal smears. Also, the qualitative assessment of cell proliferation in the SVZ was performed by cresyl fast violet staining and glial fibrillary acidic protein (GFAP) immunohistochemistry at different stages of the estrous cycle.
Results: In microscopic sections stained with cresyl violet, it was observed that cell density in the proestrus stage of the estrous cycle was greater than in any other stages of the estrous cycle. A comparison of sections stained with anti-GFAP showed that the density of astrocytes in proestrus was significantly higher than in other groups.
Conclusion: Proestrus stage of the estrous cycle is associated with increased cell proliferation and density of astrocytes in the SVZ of mice. Neurogenesis is correlated to changes in sex hormonal levels at different phases of the estrus cycle.