Figure 6: Loss of Tbr1 in layer 6 somatosensory cortex results in an increase in hyperpolarization-activated cation currents (I_h).

Whole-cell patch clamp recordings from layer 6 SSCx at P56 (A-D) show that many intrinsic electrophysiological properties were unaffected by loss of Tbr1, including resting membrane potential (B), input resistance (C), and action potential half-width (data not shown). (E) Neurons were held in current clamp at −70mV. The resonant frequency was measured as the frequency at which the impedance profile reached its peak (arrows). Scale bar = 5 mV, 5 s. (F) ZD7288, an HCN channel blocker, decreased resonance frequency by over 50% in Tbr1^layer6 heterozygous (green), and Tbr1^layer6 homozygous mutants (blue). (G) Quantification of changes in resonant frequency of Tbr1^wildtype (red), Tbr1^layer6 heterozygous (green) and Tbr1^layer6 homozygous mutants (blue) after ZD7288 treatment. (**p< 0.01) (***p<0.001). See also Figure S6.