Fig. 1.

Anatomy of the C bouton synpase. (A) An electron micrograph (adapted from Conradi, 1969) showing a C bouton (C) contacting a motor neuron (MN). Note the elongated subsurface cisternae (arrowheads) located postsynaptically. (B) A single motor neuron, labelled via injection of CTB into the gastrocnemius muscle, with numerous C boutons (vAChT-immunolabelled terminals) contacting the soma and proximal dendrites. (C,D) Immunolabelling reveals postsynaptic clusters of Kv2.1 channels (C) and m2 (D) receptors aligned with vAChT-labelled C boutons. (E) Schematic representation of a C bouton synapse. Nicotonic acetylcholine (NACh) and ATP (P2X7) receptors are thought to be located presynaptically. Muscarinic acetylcholine receptors (m2), Ca²⁺-dependent K⁺ channels (SK), voltage-activated Ca²⁺ channels (N-type) and delayed rectifier K⁺ channels (Kv2.1) are clustered postsynaptically. Sigma-1 receptors (σ1R) appear to be located beneath the postsynaptic plasma membrane, on subsurface cisternae (SSC).