Hippocampus remodeling by chronic stress accompanied by GR, proteasome and caspase-3 overexpression.

Chronic stress is a threat to homeostasis for many brain regions. While hippocampal formation is one of the most stress-sensitive areas of the cortex, molecular changes occurring as a result of increased glucocorticoid neurotoxicity in hippocampus are largely unknown. The aim of these studies was to investigate mRNA expression of mineralocorticoid and glucocorticoid receptors (MR, GR), proteasome subunits ß5 (constitutive subunit) and ß1i (inducible immunoproteasome subunit), mTOR (mammalian target of rapamycin), bcl-2; as well as caspase-3 immunoreactivity (confocal microscopy) in adult Wistar rat hippocampus following 10-day restraint stress (plastic restrainers, 6h daily). Chronic restraint led to a significant reduction in number of neuronal and astroglial cells in hippocampal regions CA1-3. This reaction was combined with substantial increase in GR and decrease in MR mRNA levels with the greatest response - 1.5-fold amplitude increase - observed in dentate gyrus and CA3 correspondingly. Stress did not change the expression of constitutive ß5 subunit but dramatically enhanced expression of inducible ß1i subunit and increased mTOR, and bcl-2 mRNA expression. Multiple scattered cells demonstrating caspase-3(+) profile were found in hippocampus of stressed animals. The study demonstrates that hippocampal remodeling induced by chronic restraint stress is associated with GR, immunoproteasome, mTOR, caspase-3 and bcl-2 overexpression in hippocampus.

Remodeling of ammon's horn during the first two weeks of experimental diabetes development.

It is known that long-term diabetes mellitus causes hippocampal dysfunction, however, early events leading to diabetes-related impairments of hippocampal tissue remain obscure. The present study was performed to examine temporal and spatial patterns of neuronal damage and astrogliosis in hippocampal CA1-C3 areas during the early stage of streptozotocin-induced diabetes in rats. NeuN and GFAP immunohistochemistry was used to visualize neurons and glial cells. Immunopositive cells were counted in hippocampal CA1-CA3 areas at days 3, 7 and 14 of diabetes development using confocal Olympus FV1000 microscope. Significant decrease in the number of neurons in CA2 area was observed in diabetic rats at day 3. In contrast, in CA1 and CA3 areas NeuN-positive cell count started to decrease later being at day 7, correspondingly, by 7 and 9 % lower than that in the control. This trend developed further till day 14, when the number of neurons in CA1 and CA3 areas was, respectively, 20.3 and 18.1% smaller as compared with the control. These changes were accompanied by astrogliosis: the number of astrocytes in pyramidal cell layer was increased significantly in all examined time-points. Thus, our study demonstrates that streptozotocin-induced diabetes is associated with early neurodegeneration in Ammon's horn. It suggests that clinically relevant cognitive deficits development in diabetic patients starting from the early stage of the disease.