Transforming growth factor alpha attenuates the functional expression of AMPA receptors in cortical GABAergic neurons

In the developing neocortex, brain-derived neurotrophic factor (BDNF) exerts a trophic activity to increase the expression and channel activity of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor subunits. Here, we demonstrate that the epidermal growth factor (EGF) receptor (ErbB1) ligands exert the opposite biological activity in cultured neocortical neurons. Subchronic stimulation of ErbB1 with transforming growth factor alpha (TGF alpha) EGF, or heparin-binding EGF (HB-EGF) down-regulated protein expression of the GluR1 AMPA receptor subunit in cultured neocortical neurons. In agreement, TGF alpha treatment decreased the B-max of [H-3] AMPA binding and GluR1 mRNA levels. Immunocytochemistry revealed that the decrease in GluR1 was most pronounced in multipolar GABAergic neurons. To examine the physiological consequences, we recorded AMPA-evoked currents as well as miniature excitatory postsynaptic currents in morphologically identified putative GABAergic neurons in culture. Suhchronic TGF alpha treatment decreased AMPA-triggered currents as well as the amplitude and frequency of miniature excitatory postsynaptic currents. An ErbB1 tyrosine kinase inhibitor, PD153035, inhibited the TGF alpha effect. Moreover, TGF alpha counteracted the neurotrophic activity of BDNF on AMPA receptor expression. Co-application of TGF alpha with BDNF blocked the BDNF-triggered up-regulation of AMPA receptor expression and currents. These observations reveal a negative regulatory activity of the ErbB1 ligand, TGF alpha, which reduces the input sensitivity of cortical GABAergic neurons to attenuate their inhibitory function. (c) 2005 Elsevier Inc. All rights reserved.