Role of ATP P2Y1 receptor in the rat dentate gyrus after a severe ischemic insult

P2Y1 receptors (P2Y1R) are widely expressed in the brain, including the dentate gyrus (DG), on both neurons and glial cells. Multipotent neural stem cells are present in the subgranular zone (SGZ) of the DG. They are able to proliferate and differentiate into neurons, astrocytes and oligodendrocytes in response to hypoxic-ischemic injury. The purpose of our research was to study the contribution of P2Y1R to the recovery of neurotransmission and to the modulation of proliferative and maturational responses in the DG, in acutely isolated hippocampal slices. Extracellular field excitatory post-synaptic potentials (fEPSPs) in granule cells of the DG were recorded from rat hippocampal slices by using electrophysiological technique. For immunohistochemical analysis, proliferating cells in the SGZ were detected by using the DNA replication marker 5-Bromo-2′-deoxyuridine (BrdU), a thymidine analog which incorporates into the DNA of all cells during the S-phase. To determine the phenotype of the newly born cells, doublecortin (DCX), an immature neuronal marker, was used. A severe period of oxygen and glucose deprivation (OGD, 9 min duration) in acute rat hippocampal slices induced the appearance of anoxic depolarization (AD), a clear sign of tissue damage, and the irreversible block of synaptic activity in all the slices (n=26) examined. The selective P2Y1R antagonist MRS2179 (10 μM, n=23) prevented the appearance of AD, allowing an almost complete fEPSP recovery (96.0±12.5%, calculated 50 min from the end of OGD versus 4.0±4.5%, n=26, found in OGD-untreated slices). Data indicate that P2Y1R contribute to the early damage induced by OGD in the DG likely contributing to glutamate-induced excitotoxic effects that causes irreversible synaptic failure after severe OGD. In hippocampal slices prepared from BrdU-treated rats and incubated with the immature neuronal marker DCX, the number of BrdU+ cells of the SGZ was significantly decreased 6 hours after OGD, but returned to control values 24 hours thereafter, when a significant increase of DCX immunofluorescence was also observed. MRS2179 significantly decreased the number of BrdU+ cells 24 hours after OGD. Since it has been demonstrated that P2Y1R stimulation promotes cell proliferation in the SGZ niche, it is likely that the antagonism of P2Y1R in the DG, at times later from OGD, reduces cell proliferation.