[Experimental study on developmental changes of synaptic currents in V1B cortical layer Ⅳ pyramidal neurons in...

Objective: To investigate the developmental changes of miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs) of layer Ⅳ pyramidal neurons in the primary visual cortex binocular zone (V1B) of C57BL/6J wild-type mice at different developmental stages. Methods: Sixteen male C57BL/6J mice of specific-pathogen-free grade were selected and divided into 4 groups according to their postnatal age: P14 group (before and after eye opening), P28 group (the peak of the critical period), P35 group (the end of the critical period), and P130 group (fully adult). Whole-cell patch-clamp technique was used to record the frequency and amplitude of mEPSCs and mIPSCs of layer Ⅳ pyramidal neurons in V1B of each group, and to analyze their differences and changes. Results: The frequency of mEPSCs of layer Ⅳ pyramidal neurons in V1B of mice in the four groups was statistically different (F=9.46, P<0.001), with the P35 group being higher than the P28 group [P28 and P35 groups were (8.72±1.34) and (13.28±4.05) Hz, t=3.39, P=0.012], and the P130 group being lower than the P35 group [P35 and P130 groups were (13.28±4.05) and (5.82±1.98) Hz, t=5.21, P<0.001]; the amplitude of mEPSCs of layer Ⅳ pyramidal neurons in V1B of mice in the four groups was not statistically different (F=2.84, P=0.055). The frequency of mIPSCs of layer Ⅳ pyramidal neurons in V1B of mice in the four groups was statistically different (F=8.14, P<0.001), with the P130 group being higher than the P14 group [P14 and P130 groups were (5.22±1.33) and (12.03±3.94) Hz, t=4.678, P<0.001]; the amplitude of mIPSCs of layer Ⅳ pyramidal neurons in V1B of mice in the four groups was statistically different (F=7.06, P=0.001), with the P35 group being higher than the P28 group [P28 and P35 groups were (20.07±3.56) and (28.47±5.98) pA, t=3.66, P=0.006], and the P130 group being lower than the P35 group [P35 and P130 groups were (28.47±5.98) and (20.32±3.55) pA, t=3.33, P=0.014]. Conclusions: The excitatory synaptic development of layer Ⅳ pyramidal neurons in V1B of mice is in a vigorous growth state during development and gradually weakens with age, while the inhibitory synaptic development gradually strengthens with increasing postnatal age, and both of them rapidly develop during the critical period.