Aspects of early postnatal development of cortical neurons that proceed independently of normally present extrinsic influences

Abstract

To examine the contribution of local versus extrinsic influences on postnatal development of cortical neurons, we compared the maturation of deep (infragranular) layer neurons in isolated slices of neocortex grown in organotypic culture to a similar population of neurons developing in vivo. All slice cultures were prepared from sensorimotor cortices of newborn mice (P0) and neurons in these cultures were examined at daily intervals during the first 9 days in vitro (DIV). The maturational state of neurons developing in vivo over this same time period was assessed in acute slices prepared from animals of equivalent postnatal age, P1-P9. Electrophysiological recordings were obtained from neurons in both cultured and acute slices, using Lucifer yellow filled whole-cell recording electrodes, enabling subsequent morphometric analysis of the labeled cells. We report significant changes in both cellular morphology and electrical membrane properties of these deep layer cortical neurons during the first week in culture. Morphological maturation over this time period was characterized by a two- to three-fold increase in cell body size and total process length, and an increase in dendritic complexity. In this same population of cells a three-fold decrease in input resistance and changes in the action potential waveform, including a two-fold decrease in the AP duration, also occur. The degree of morphological and electrophysiological differentiation of individual neurons was highly correlated across developmental ages, suggesting that the maturational state of a cell is reflected in both cellular morphology and intrinsic membrane properties. A remarkably similar pattern of neuronal maturation was observed in neurons in layers V, VI/SP examined in acute slices prepared from animals between P1-P9. Because our culture system preserves many aspects of the local cortical environment while eliminating normal extrinsic influences (including thalamic, brainstem, and callosal connections), our findings argue that this early phase of neuronal differentiation, including the rate and extent of dendritic growth and development of AP waveform, results from instructive and/or permissive local influences, and appears to proceed independently of the many normally present extrinsic factors.

Activity Dependence of Cortical Axon Branch Formation: A Morphological and Electrophysiological Study Using Organotypic Slice Cultures

“…Previous studies have shown that neuronal migration, layer formation, cellular morphology, and physiology develop normally in cultured cortical explants (Yamamoto et al, 1989(Yamamoto et al, , 1992Bolz et al, 1990Molnar and Blakemore, 1991;Gotz and Bolz, 1992;Annis et al, 1993;Dantzker and Callaway, 1998). Similarly, individually YFP-labeled cells in our slice cultures exhibited a projection pattern and branch formation that is typical for layer 2/3 cells in rodents (Lohmann and Rorig, 1994;van Brederode et al, 2000).…”

Development and Plasticity of Spontaneous Activity and Up States in Cortical Organotypic Slices

“…Although not specifically addressed in this study, the increase in excitation is mostly likely produced by a number of different mechanisms acting in parallel. Indeed, increases in excitatory synaptic strength, spine density, and dendritic and axonal branching have all been reported in organotypic slices as a function of age (Caeser et al, 1989;Annis et al, 1993;Yamada et al, 2000;De Simoni et al, 2003;Uesaka et al, 2005). All or a subset of these mechanisms could underlie the increase in evoked activity reported here.…”

Critical Roles of Voltage-Dependent Sodium Channels in the Process of Synaptogenesis During the Postnatal Cortical Development of Rats

“…The postnatal neurons gain the capacity to fire repetitive trains of AP (Annis et al 1993;Heidi et al 2003). But in our results, most of the neurons in P B 6 group (n = 8) were not able to emit a typical action potential waveform which was in accordance with that in embryonic 13 (E13) of rat spinal motoneuron reported by Gao and ZIiskind-Conhaim (1998) (Fig.…”