Abstract
Achieving the distinctive complex behaviors of adult mammals requires the development of a great variety of specialized neural circuits. Although the development of these circuits begins during the embryonic stage, they remain immature at birth, requiring a postnatal maturation process to achieve these complex tasks. Understanding how the neuronal membrane properties and circuits change during development is the first step to understand their transition into efficient ones. Thus, using whole cell patch clamp recordings, we have studied the changes in the electrophysiological properties of layer V pyramidal neurons of the rat primary motor cortex during postnatal development. Among all the parameters studied, only the voltage threshold was established at birth and, although some of the changes occurred mainly during the second postnatal week, other properties such as membrane potential, capacitance, duration of the post-hyperpolarization phase or the maximum firing rate were not defined until the beginning of adulthood. Those modifications lead to a decrease in neuronal excitability and to an increase in the working range in young adult neurons, allowing more sensitive and accurate responses. This maturation process, that involves an increase in neuronal size and changes in ionic conductances, seems to be influenced by the neuronal type and by the task that neurons perform as inferred from the comparison with other pyramidal and motor neuron populations.
Highlights
The development of a large variety of specialized neuronal circuits is needed to achieve all the complex behaviors found in adult mammals
In this work we hypothesize that layer V pyramidal neurons from the primary motor cortex are tuned during postnatal development, and we wonder whether the temporal course of such changes is similar to that of other pyramidal neurons or on the contrary each population of pyramidal neurons evolves with a different temporal course dependent on their final tasks and inputs
Pyramidal neurons from the motor cortex exhibited a stable membrane potential that progressively hyperpolarized during postnatal development
Summary
The development of a large variety of specialized neuronal circuits is needed to achieve all the complex behaviors found in adult mammals. Neocortical neurons undergo an extensive change in their dendritic morphology during postnatal development (Petit et al, 1988; Kasper et al, 1994) and few studies in layer V pyramidal neurons from neocortex demonstrate postnatal changes in its electrophysiological properties during the first 4 postnatal weeks (Zhu, 2000; Zhang, 2004; Christophe et al, 2005; Etherington and Williams, 2011; Elston and Fujita, 2014). These studies are mainly focused in prefrontal and visual cortex or somatosensorial cortex. It has been reported in detail the electrophysiological postnatal maturation of cervical and lumbar motor neurons showing great changes (Smith and Brownstone, 2020)
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