Rapid and reversible formation of spine head filopodia in response to muscarinic receptor activation in CA1 pyramidal cells

Non-technical summary Changes in the shape and number of spines on neuronal dendrites modify synaptic transmission and circuit properties, processes considered important for learning and memory. We show, in hippocampal pyramidal neurons, that brief activation of acetylcholine receptors of the muscarinic subtype induces the emergence of fine filopodia from spine heads in all CA1 pyramidal neurons examined. Experiments to test whether changes in the cytoskeleton play a role in the emergence of filopodia revealed that the extension of microtubules, but not actin polymerization, was necessary. These findings reveal a new form of structural plasticity at the subspine level where the heads of mature dendritic spines can modulate the degree of interaction with their presynaptic partners. Knowledge of how the cholinergic system in the brain affects spine morphology and physiology is important for understanding memory formation.