Abstract
Purpose :
Hypoxia is the main factor in the pathogenesis of numerous retinal and optic nerve diseases. The retinocollicular projections are part of a fundamental set of structures in visual attention. We have previously reported that hypoxia-induced pathological long-term potentiation (LTP) of NMDA retinocollicular transmission is associated with a decrease of the current decay time. Such a decrease reflects an increase in NR2A/NR2B ratio and subsequent decrease of calcium influx and is a protective cellular mechanism in response to hypoxic injury. In this study, we tested the hypothesis that the protein kinase C (PKC) pathway is involved in hypoxia-induced LTP of NMDA retinocollicular transmission as well as in changes in NMDAR subunits ratio.
Methods :
We developed the in vitro model of the visual retinocollicular pathway - a coculture of dissociated retinal cells and superficial superior colliculus (SSC) neurons. Using paired patch-clamp technique, we recorded pharmacologically isolated evoked NMDA postsynaptic currents in SSC neurons by generation action potentials in presynaptic retinal ganglion cells. Spontaneous postsynaptic currents we recorded in absence of presynaptic stimulation. The method of fast local superfusion was used for the application of hypoxic solutions on the pairs of neurons. We tested effect of chelerythrine chloride (ChC, 5 µM) - an inhibitor of PKC. The decay time constants were determined from a single exponential fit of the decay phase of currents.
Results :
The presence of ChC completely blocked LTP of NMDA transmission induced by hypoxia. The ChC also abolished the hypoxia-induced increase of spontaneous NMDA currents amplitudes but did not affect the increased occurrence frequency. Moreover, we observed that ChC blocked the decrease of the decay time of evoked and spontaneous currents (for example control 48.2 ± 4.6ms; hypoxia 13.5 ± 5.4ms; hypoxia in presence of ChC 45.8 ± 5.5 ms; reoxygenation in presence of ChC 46.2± 4.8ms; reoxygenation 43.8 ± 5.6ms).
Conclusions :
The results obtained are consistent with our hypothesis. Inhibition of PKC pathway completely blocked LTP of NMDA retinocollicular transmission and lead to the offset of associated changes in NMDA receptor subunits. The revealed electrophysiological basis of plasticity and protective mechanism in response to hypoxic injury might be targeted to prevent lesions of the retinocollicular pathway.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.