Figure 5.

Hypothesized neural circuit and functions of α2 nAChRs. (A) Neural circuit with α2 nAChR in MC that projects to PC distal apical dendrite and interneuron (Int.) that, in turn, projects to PC. Nicotinic activation of MC will inhibit PC distal dendrite and disinhibit proximal dendrite. PC receives excitatory input from thalamocortical projections relaying CF information and horizontal projections relaying nonCF information. (B) Schematic current sinks (synaptic response) in layers 2/3 and 4 evoked by CF and nonCF stimuli. CF-evoked current sinks contain thalamocortical (TC) and local intracortical components, whereas nonCF-evoked sinks are entirely intracortical, mediated by horizontal inputs. Current sink components are differentially regulated by α2 and non-α2 (likely α4β2) nAChRs. (C) Hypothesized effect of systemic nicotine on RFs in layers 2/3 and 4 in WT and α2 KO mice. In WT mice nicotine sharpens RFs, i.e., increases gain and narrows RFs, in both layers. In KO mice, nicotine does not narrow RFs in either layer and only partly enhances gain in layer 4.