Electrical Excitability of Early Neurons in the Human Cerebral Cortex during the Second Trimester of Gestation

Abstract

Information about development of the human cerebral cortex (proliferation, migration, and differentiation of neurons) is largely based on postmortem histology. Physiological properties of developing human cortical neurons are difficult to access experimentally and therefore remain largely unexplored. Animal studies have shown that information about the arousal of electrical activity in individual cells within fundamental cortical zones (subventricular zone [SVZ], intermediate zone, subplate [SP], and cortical plate [CP]) is necessary for understanding normal brain development. Here we ask where, in what cortical zone, and when, in what gestational week (gw), human neurons acquire the ability to generate nerve impulses (action potentials [APs]). We performed electrical recordings from individual cells in acute brain slices harvested postmortem from the human fetal cerebral cortex (16-22 gw). Tetrodotoxin-sensitive Na(+) current occurs more frequently among CP cells and with significantly greater peak amplitudes than in SVZ. As early as 16 gw, a relatively small population of CP neurons (27%) was able to generate sodium APs upon direct current injection. Neurons located in the SP exhibited the highest level of cellular differentiation, as judged by their ability to fire repetitive APs. At 19 gw, a fraction of human CP and SP neurons possess beta IV spectrin-positive axon initial segments populated with voltage-gated sodium channels (PanNav). These results yield the first physiological characterization of developing human fetal cortical neurons with preserved morphologies in intact surrounding brain tissue.

Neuronal medium that supports basic synaptic functions and activity of human neurons in vitro

“…We report that classic media, which we and others have used to differentiate and culture human neurons, are suboptimal to support electrical activity and, therefore, provide very different conditions than those observed in the living brain (53,56). Most neurological disorders are chronic and progressive and are very closely related to neuronal activity and synaptic function; thus, when modeling human neurological and psychiatric disorders in vitro, the lack of accurate physiological conditions may mask the real mechanisms of the pathologies.…”

Induced pluripotent stem cell models of the genomic imprinting disorders Angelman and Prader–Willi syndromes

“…This is not surprising because only 14% of human cortical plate neurons sampled at 16 wk of gestation fire repetitive action potentials (21).…”

Dopamine Receptors in Human Embryonic Stem Cell Neurodifferentiation

“…Whole cell patch clamp recordings were performed as previously described [28]. Briefly, cells grown on 12-mm round coverslips were transferred to an Olympus BX51WI upright microscope (equipped with infrared video microscopy) and perfused in aerated (95% O 2 /5% CO 2 ) artificial cerebrospinal fluid (ACSF) at 30°C.…”

“…Our working hypothesis stated that facilitated neuroproliferation and en masse commitment to dopaminergic neuron type leaves neurons with less time and resources to build fully excitable membranes capable of AP generation. In the human fetus (16)(17)(18)(19)(20)(21), the postmitotic neurons mature gradually by inserting voltage-gated sodium channels into the plasmalemma, by decreasing their electrical input resistance, and by making their resting membrane potential more and more negative as neural maturation progresses [28]. The insertion of sodium channels in developing human neurons is manifested in electrophysiological recordings by an increase in peak amplitude of the fast inactivating sodium current paralleled by neuronal ability to generate APs [28].…”

“…In the human fetus (16)(17)(18)(19)(20)(21), the postmitotic neurons mature gradually by inserting voltage-gated sodium channels into the plasmalemma, by decreasing their electrical input resistance, and by making their resting membrane potential more and more negative as neural maturation progresses [28]. The insertion of sodium channels in developing human neurons is manifested in electrophysiological recordings by an increase in peak amplitude of the fast inactivating sodium current paralleled by neuronal ability to generate APs [28]. In the current project, whole cell recordings were performed on differentiated cells at Stage 5 (days [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38], after at least 2 weeks of chronic DA exposure.…”