Effects of binocular form deprivation on the excitatory post-synaptic currents mediated by N-methyl-D-aspartate receptors in rat visual cortex.

Abstract

To investigate the effects of binocular form deprivation (BFD) on the excitatory post-synaptic currents (EPSCs) mediated by the N-methyl-D-aspartate (NMDA) receptor (NMDA-EPSCs), and the proportion of NMDA-EPSCs relative to glutamate receptor currents (glutamate-EPSCs) in rat visual cortex. Binocular form deprivation was achieved by suturing the eyelids of Wistar rats at postnatal day (PD) 14, before eye-opening. Visual cortical slices (300 micro m) were prepared from normal and BFD Wistar rats aged PD 14, 21 and 28. Recordings were obtained in slices from layer II to IV using the whole-cell patch-clamp technique. Glutamate-EPSCs were isolated in the presence of bicuculline methiodide (20 micro mol/L) in the bathing medium, and NMDA-EPSCs were isolated with a combination of bicuculline methiodide (20 micro mol/L) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 20 micro mol/L). In addition, D,L-2-amino-5-phosphonovalerate (AP-5, 20 micro mol/L) was applied to study the NMDA-only mediated currents. For each cell, the ratio of peak NMDA to glutamate EPSCs was calculated. During visual development, the decay time constant of NMDA-EPSCs became shorter after eye-opening in normal rats (F = 5.949, P <0.05; PD 28 vs PD 14, P = 0.027), but not in rats with BFD (P > 0.05). The weighted time constant of NMDA-EPSCs in the visual cortex became shorter after the rats' eyes were opened in the normal group (F(2,37) = 4.727, P = 0.015; PD 28 vs PD 14, P = 0.035), but not in the BFD group (P > 0.05). However, the rise time constant and peak value of NMDA-EPSCs showed no significant changes in normal and BFD groups (P > 0.05). The ratio of NMDA-EPSCs to glutamate-EPSCs became gradually smaller with age in the normal rats (F = 4.661, P < 0.05; PD 28 vs PD 14, P = 0.025), but not in the BFD group (P > 0.05). These studies reveal that the proportion of NMDA-EPSCs relative to glutamate-EPSCs and the decay time constant of NMDA-EPSCs are influenced by BFD. These changes may reflect important experience-dependent modifications of neuronal synapses in visual cortex.