Thyroid hormone (t3)-induced up-regulation of voltage-activated sodium current in cultured postnatal hippocampal neurons requires secretion of soluble factors from glial cells

Abstract

We have previously shown that treatment with the thyroid hormone T 3 increases the voltage-gated Na+ current density (Nav-D) in hippocampal neurons from postnatal rats, leading to accelerated action potential upstrokes and increased firing frequencies. Here we show that the Na+ current regulation depends on the presence of glial cells, which secrete a heat-instable soluble factor upon stimulation with T3. The effect of conditioned medium from T3-treated glial cells was mimicked by basic fibroblast growth factor (bFGF), known to be released from cerebellar glial cells after T3 treatment. Neutralization assays of astrocyte-conditioned media with anti-bFGF antibody inhibited the regulation of the Nav-D by T3. This suggests that the up-regulation of the neuronal sodium current density by T3 is not a direct effect but involves bFGF release and satellite cells. Thus glial cells can modulate neuronal excitability via secretion of paracrinely acting factors. Copyright © 2009 by The Endocrine Society.