| Keywords [eng] |
postnatal, development, electrophysiology, mice, hippocampus, pyramidal neurons, synapses, patch-clamp |
| Abstract [eng] |
In hippocampus, postnatal development is a critical period for neuronal maturation and for the organization of neural pathways. At this time, neonatal pyramidal neurons grow in size and transform extensively in terms of the composition and the kinetic properties of membrane ion channels, leading to a gradual maturation of coherent and cell-type specific neuronal activity. Simultaneously, neurons extend their arbors and form superfluous synapses that are sequentially removed, reorganized, or refined via activity-dependent mechanisms that in turn shape the characteristic hippocampal circuitry. Most data about the maturation of neuronal pathways has been obtained in anatomical and immunohistochemical studies; however, a number of the features, such as the development of intrinsic firing properties or functional synaptic activity, can only be evaluated by direct electrophysiological recordings in living neurons. Unfortunately, electrophysiological developmental research has evaluated these phenomena independently, without investigating how they shape one another to reach neuronal maturity. Additionally, electrophysiological developmental research is mainly based on experiments with rats. The emergence of genetically engineered mice comes together with modern toolkits for studying intricate molecular developmental mechanisms. Considering this phenomena, developmental electrophysiological profiles in mice will be necessary for further exploration of the developing brain. The aim of our study was to evaluate synaptic activity and intrinsic firing properties of postnatal hippocampal pyramidal CA1 neurons in mice. To achieve that, we utilized various patch-clamp techniques as well as implemented and optimized a method for preparation, maintenance, and robust electrophysiological recordings in acute mouse brain slices for different ages of postnatal development. We found substantial developmental changes in the maturation of synaptic activity: the frequency of the recorded synaptic events progressively increased and synaptic transmission was strengthened. Concurrently, hippocampal pyramidal neurons underwent substantial changes in intrinsic firing properties: while input resistance of neuronal membrane decreased, action potentials became higher and shorter, and demonstrated quicker depolarization and repolarization values. More mature pyramidal neurons were better adapted to sustain persistent firing activity. The distinct timelines of these processes indicate that intrinsic firing properties and synaptic activity might affect one another during postnatal development, and more research should be done to investigate this relationship. The present study described the developmental changes in electrophysiological profiles of hippocampal pyramidal neurons in mice, providing a useful baseline for research with transgenic mice in order to identify specific molecular mechanisms underlying healthy and faulty postnatal development of the brain. |
