Objective    To investigate the expression of synaptophysin (SYN) in rat retina following acute high intraocular pressure (HIOP).     Methods    The intraocular pressure of all left eyes was increased until b wave of flash electroretinogragh (fERG) disappeared and such pressure maintained for 60 min. All right eyes served as normal control. The animals

totally 60 SD rats

were sacrificed respectively on day 1

3

7

14 or 21 following operation

with 12 rats on each sacrifice day

half for immunohistochemistry and half for in situ hybridization to detect the expression of SYN.     Results    In normal condition

SYN was mainly located in the outer plexifo

rm layer (OPL) and the inner plexiform layer (IPL). SYN positive products were extended to the inner part of the outer nuclear layer (ONL) after HIOP. There was the widest distribution of SYN in the OPL and ONL on the 7

th

day after HIOP. On the 14

th

day

the distribution of SYN was similar to that of the normal control. By in situ hybridization

SYN positive neurons were mainly located in the inner nuclear layer (INL) and the ganglion cell layer (GCL). The number of SYN mRNA positive cells in the INL was increased following HIOP and reached its peak on the 7

th

day

then decreased to normal level at the 14

th

day.     Conclusion    In rat retina

SYN expression was first up-regulated

then down-regulated

accompanied with spatial redistribution following HIOP

indicating that instead of synaptic degeneration

the synaptic function is first enhanced at the early stage following HIOP.