ACh and NE depolarize thalamocortical neurons
The application of ACh or NE results in the depolarization of thalamocortical neurons through the reduction of a "leak" potassium current. This depolarization results in the abolition of low threshold Ca2+ spikes and, if large enough, the occurrence of single spike activity.
see McCormick, D.A. and Prince, D.A. Noradrenergic modulation of firing pattern in guinea pig and cat thalamic neurons, in vitro. Journal of Neurophysiology (1988) 59 978-996.
McCormick, D.A., and Prince, D.A. Actions of acetylcholine in the guinea-pig and cat medial and lateral geniculate nuclei, in vitro. Journal of Physiology, (1987) 392 147-165.
McCormick, D.A. Cellular mechanisms underlying cholinergic and noradrenergic modulation of neuronal firing mode in cat and guinea pig dorsal lateral geniculate nucleus. Journal of Neuroscience (1992) 12: 278-289.