Preferential Localization of Muscarinic M₁Receptor on Dendritic Shaft and Spine of Cortical Pyramidal Cells and Its Anatomical Evidence for Volume Transmission

Abstract

Acetylcholine (ACh) plays important roles for higher brain functions, including arousal, attention, and cognition. These effects are mediated largely by muscarinic acetylcholine receptors (mAChRs). However, it remains inconclusive whether the mode of ACh-mAChR signaling is synaptic, so-called "wired," transmission mediated by ACh released into the synaptic cleft, or nonsynaptic, so-called "volume," transmission by ambient ACh. To address this issue, we examined cellular and subcellular distribution of M 1 , the most predominant mAChR subtype in the cerebral cortex and hippocampus, and pursued its anatomical relationship with cholinergic varicosities in these regions of adult mice. M 1 was highly expressed in glutamatergic pyramidal neurons, whereas it was low or undetectable in various GABAergic interneuron subtypes. M 1 was preferentially distributed on the extrasynaptic membrane of pyramidal cell dendrites and spines. Cholinergic varicosities often made direct contact to pyramidal cell dendrites and synapses. At such contact sites, however, synapse-like specialization was infrequent, and no particular accumulation was found at around contact sites for both M 1 and presynpatic active zone protein Bassoon. These features contrasted with those of the glutamatergic system, in which AMPA receptor GluA2 and metabotropic receptor mGluR5 were recruited to the synaptic or perisynaptic membrane, respectively, and Bassoon was highly accumulated in the presynaptic terminals. These results suggest that M 1 is so positioned to sense ambient ACh released from cholinergic varicosities at variable distances, and to enhance the synaptic efficacy and excitability of pyramidal cells. These molecular-anatomical arrangements will provide the evidence for volume transmission, at least in M 1 -mediated cortical cholinergic signaling.

α4* Nicotinic Acetylcholine Receptors Modulate Experience-Based Cortical Depression in the Adult Mouse Somatosensory Cortex

“…This finding is supported by electron microscopy studies showing that ␣4* nAChRs are detected near the plasma membrane of neuronal cell bodies and apical dendritic shafts, but not typically at postsynaptic densities (Nakayama et al, 1995;Commons, 2008). Whether ␣4* nAChR are directly apposed by cholinergic terminals is not entirely clear, however our immunofluorescence data suggest a loose spatial relationship between ␣4* nAChRs and cholinergic terminals, similar to that described for ␣7 nAChRs and muscarinic receptors (Jones and Wonnacott, 2004;Yamasaki et al, 2010).…”

Cellular and subcellular localization of cholecystokinin (CCK)-1 receptors in the pancreas, gallbladder, and stomach of mice

“…Mouse cDNA fragments of the CCK1 receptor (nucleotides 348-1658bp; GenBank accession number, NM_009827), pepsinogen C (1-1352bp; NM_025973.3), and c-Kit (37-1320bp; BC052457.1) were subcloned into the pBluescript II plasmid vector. Digoxigenin (DIG)-or fluorescein-labeled cRNA probes were transcribed in vitro for FISH analysis (Yamasaki et al 2010). The fragmentation of riboprobes by alkaline digestion was omitted in order to increase the sensitivity and specificity.…”

Electrophysiological evidence showing muscarinic agonist–antagonist activities of N-desmethylclozapine using hippocampal excitatory and inhibitory neurons

“…Yamasaki et al examined cellular and subcellular distribution of M 1 receptors in the cerebral cortex and hippocampus, and demonstrated that M 1 receptors are expressed preferentially in glutamatergic pyramidal neurons, and scarce or undetectable in various GABAergic interneuron subtypes (Yamasaki et al, 2010). Instead of M 1 receptors, M 3 receptors were detectable in interneurons (Yamasaki et al, 2010).…”

“…Instead of M 1 receptors, M 3 receptors were detectable in interneurons (Yamasaki et al, 2010). Using mice genetically lacking specific muscarinic receptor subtypes, receptor subtypes responsible for cholinergic modulation of ion channels have been identified in hippocampal pyramidal neurons (Dasari and Gulledge, 2011;Rouse et al, 2000).…”