Cholinergic stimulation increases cortical spine formation via local inhibitory circuit

Basal forebrain (BF) cholinergic projections densely innervate the neocortex, releasing acetylcholine (ACh) to modulate neuronal excitability, thereby influencing sensory processing and cognitive functions. However, the synaptic basis of such ACh-induced effects in vivo remains elusive. To investigate how ACh release from BF regulates synaptic dynamics in the neocortex, we selectively stimulated BF cholinergic neurons in mice, and used two-photon microscopy to track structural changes of dendritic spines on cortical pyramidal neurons. We found that optogenetic and chemogenetic stimulation of BF cholinergic neurons rapidly induced spine formation in layer 5 pyramidal neurons in the auditory cortex and the posterior parietal cortex. Selective blockage of ACh receptors (AChRs) demonstrated that nicotinic AChRs are required for the ACh-induced spine formation. We also found that Ach-induced spine formation of pyramidal neurons requires the activity of cortical somatostatin-expressing inhibitory interneurons. Together, our study revealed ACh-induced synaptic plasticity in the cortical microcircuit in vivo, providing a synaptic mechanism for cortical neuronal plasticity and functional changes associated with BF ACh release.