Electrophysiological properties and synaptic activity of the mouse hippocampal CA1 neurons during postnatal development

Early postnatal development is a critical period for hippocampal circuit maturation. While postnatal hippocampal development has been mostly studied in rats, less is known about the developmental trajectory of electrophysiological properties in mice, despite the wide use of these animal models for molecular and genetic studies of nervous system. In this study, we investigated the postnatal maturation of hippocampal CA1 pyramidal neurons in male and female wild-type mice. Whole-cell patch-clamp recordings were performed in acute hippocampal slices to assess passive and active membrane properties as well as spontaneous excitatory synaptic activity. We found that maturation of neuronal firing properties was associated with faster responses to stimulation, higher-amplitude and shorter-duration action potentials, and more precise control of neuronal firing. Simultaneously, synaptic activity changed across development, with decreased sEPSC inter-event intervals and stable event amplitudes, suggesting enhanced functional connectivity without major changes in synaptic strength. Sex-dependent differences in electrophysiological properties were observed primarily during the first postnatal week, indicating that sex influences the early trajectory of neuronal maturation. Together, our findings provide a comprehensive electrophysiological baseline for mouse hippocampal CA1 pyramidal neurons during postnatal development.