Figure 4.

Example functional connectivity of a subgroup of CNS cholinergic neurons. Striatal cholinergic neurons (TANs) receive glutamatergic inputs from both cortex and intralaminar thalamus, as well as dopaminergic modulation from the substantia nigra pars compacta (SNc). Medium spiny neurons (MSNs), projection neurons in the striatum, express either type 1 or type 2 dopamine receptors (D1 or D2, respectively). Following thalamic stimulation, TANs generate a burst-pause pattern of activity that transiently and presynaptically inhibits thalamic and cortical excitation of D1 and D2 striatal MSNs through muscarinic receptor subtype M2 signaling. It also initiates a sustained, muscarinic receptor subtype M1-mediated facilitation of dendritic responsiveness in D2 MSNs: resulting in a bias of cortical and thalamic excitation toward D2 expressing, striatopallidal MSNs for the duration of the pause in TAN activity. The pause is dependent on dopaminergic signaling onto TANs. Functionally, thalamic excitation of TANs is thought to provide a window in which excitation of D2-expressing MSNs is enhanced, allowing for preferential recruitment of the striatopallidal pathway. Such wiring diagrams may serve as useful models to study subep-ChAT neuron connectivity. Distinct neuronal cell types and projection patterns are represented in different colors for clarity.