Postnatal neocortical development: maturational changes in the intrinsic properties of pyramidal neurons and their possible significance for epileptogenesis

During early postnatal life neocortical neurons undergo significant maturational changes in passive membrane properties and active mechanisms, relevant to cell excitability. In rats the most significant changes occur during the first postnatal month. With respect to adults, immature pyramidal neurons have physiological properties supporting an increased excitability: less negative resting potential, higher input resistance, shorter electrotonic length, slower action potential repolarization, and lower efficiency in spike frequency adaptation. On the other hand, the inability to sustain long-lasting discharges, the less steep rising phase of the action potentials and the absence of intrinsically generated burst discharges may significantly affect the expression of cortical hyperexcitability, thus explaining the fragmentary and asynchronous characteristics of epileptic discharges in the immature brain