[Changes in electrophysiological properties of pyramidal neuron in motor cortex during the postnatal early development of mice].

Objective: To investigate the electrophysiological properties of pyramidal neurons in mouse motor cortex during the early postnatal development.
Methods: Thirty-six mice were randomly divided into postnatal 1-, 2-, 3-Week and 1-, 2-,3-Month groups ( n =6). Membrane properties, action potentials (AP) and spontaneous excitatory postsynaptic currents (sEPSCs) of motor cortex pyramidal neurons were recorded to evaluate the changes in the intrinsic electrophysilogical characteristics by using whole cell patch clamp. Pyramidal neurons and interneurons were distinguished according to the AP firing patterns.
Results: Comparing with interneurons, pyramidal neurons exhibited regular spiking (RS) with smaller frequency. During the period of postnatal 1 Week-3 Months, some of the intrinsic membrane properties of motor cortex pyramidal neurons changed. Compared to the 1-Week mice, the resting membrane potential (RMP) of 2-Week decreased significantly ( P ＜0.01), and the membrane input resistance (R _in ) of 1-Month got a hyperpolarization ( P ＜0.01), and they showed no significant change in the next period, while the membrane capacitance (Cm) showed no significant changes during the whole postnatal development. The AP dynamic properties changed significantly during this period. Compared to the 1-Week mice, the absolute value of the AP threshold and the AP amplitude of the 3-Week increased significantly ( P ＜0.01), while the spike half width of the 2-Week decreased substantially ( P ＜0.05), and they showed no significant change in the next period. The sEPSCs frequency and amplitude of 1- Month increased significantly compared to the 1-Week mice( P ＜0.01), while during the period of next 1 Month-3 Months, the amplitude and frequency showed no significant change.
Conclusion: These results suggest that the motor cortex pyramidal neurons have time-specific eletrophysilogical properties during the postnatal development. The electrophysiological properties can be used as a functional index to detect the degree of neurons maturity, and as a marker to distinguish the pyramidal neurons and interneurons.