Expression Of Glutamate And GABA In Synaptic Plasticity Of Rat Retina Following Acute High Intraocular Pressure

Objective:To investigate the relationship between the synaptic plasticity and neurotransmitters, glutamate(Glu) and y-aminobutyric acid (GABA) which are the major excitatory and inhibitory neurotransmitters in retina, following acute high intraocular pressure (HIOP).Methods:The intraocular pressure of all left eyes was increased to110mmHg and such pressure maintained for60min. All right eyes served as normal control. The SD rats were sacrificed respectively on hour2,6,12or day1,3,7,14following operation. Immunofluorescent staining was used to detect the expression of synaptophysin (SYN), Glu and GABA.Results:1. In the normal condition, SYN immunoreactivity was mainly located in the outer plexiform layer (OPL) and the inner plexiform layer (IPL). The expression and distribution of SYN was kept nearly stable in the OPL within1d after acute HIOP. But in the IPL, SYN immunoreactivity was a little bit stronger than normal. From3d to7d, SYN positive products in the OPL were widened and extended into the inner part of the outer nuclear layer (ONL) where there was no SYN immunostaining under normal condition and reached the maximum distribution at the seventh day after acute HIOP. At the fourteenth day, distribution of SYN in the OPL and ONL gradually returned to normal. In this period, SYN immunoreactivity in the IPL was still seen in the whole layer, but the thickness of the IPL became thinner and thinner. In a word, SYN positive products were upregulated in the IPL and then increased in the OPL, ultimatelly returned to the normal in the different survival time.2. A few number of Glu-positive cells were located in the inner nuclear layer (INL), the ONL and the ganglion cell layer (GCL) in normal retina. Glu-positive cells were activated from the inner part to the outer part of the retina after acute HIOP which was the same as the pattern of SYN expression. Glu-positive cells in the GCL were obviously increased at six hours after acute HIOP, then disappeared with the death of retina ganglion cells. The expression and distribution of Glu in the INL was upregulated from the first day to the third day after acute HIOP and reached the maximum level at the third day, with some processes extending to the IPL and OPL, while decreased at the seventh and fourteenth day. Glu-positive cells in the ONL obviously upregulated in the third day to the fourteen day after acute HIOP.3. GABA immunoreactivity was mainly located in the outer part of IPL and the inner part of OPL in normal condition. There were a few GABA positive neurons in the INL. After acute HIOP, the expression of GABA in retina was similar to the normal. Conclusion There was synaptic plasticity in rat retina following acute HIOP. Glutamatergic neurons might participate in this process, and there was no evidence showed that GABAergic neurons participated in the synaptic plasticity.