ACh also modulates synaptic transmission in cortical circuits (Figure 3). Activation of α4β2 nAChRs on thalamocortical terminals enhances glutamate release in both sensory and association cortex (Gil et al., 1997; Lambe et al., 2003; Oldford and Castro-Alamancos, 2003), whereas activation of mAChRs on terminals of parvalbumin-expressing interneurons decreases the probability of GABA release onto the perisynaptic compartment of pyramidal neurons, and therefore reduces post-synaptic inhibition of pyramidal neurons (Kruglikov and Rudy, 2008). These interneurons normally decrease the response of cortical neurons to feed-forward excitation (Gabernet et al., 2005; Higley and Contreras, 2006), and the reduction of GABA release from these interneurons by ACh therefore enhances the ability of thalamocortical inputs to stimulate pyramidal neuron firing (Kruglikov and Rudy, 2008).
