Fig. 6.

Glutamatergic and GABAergic axon terminals innervating large mGlu1α+ ITC neurons contain mGlu7a receptors at their active zone. (A) Electron micrograph of a double pre-embedding immunoreaction in which a mGlu1α+ dendrite is revealed by horseradish peroxidase (HRP, diffuse electron dense reaction) whereas mGlu7a receptors are visualized by silver-intensified nanogold. Immunometal particles are clearly visible in the active zone of presynaptic terminals. (B–C) Electron micrographs of a triple pre-embedding immunoreaction in which the immunoreactivity for VGluT2 is shown by HRP, whereas immunometal particles on the postsynaptic membrane reveal mGlu1α receptors, and immunometal particles on the presynaptic membrane visualize mGlu7a receptors. Clear presynaptic labelling for mGlu7a receptors can be observed in the VGluT2+ (HRP) boutons forming asymmetric synapses (indicated by a solid arrowhead) with mGlu1α+ dendrites. (D) This electron micrograph shows the presence of mGlu7a receptors (immunometal particles) at the active zone of a VGluT1+ (HRP) axon terminal forming an asymmetric synapse (indicated by a solid arrowhead) with a mGlu1α+ dendrite. (E) In this electron micrograph the presence of mGlu7a receptors (immunometal particles) can be observed at the active zone of a VGAT+ (HRP) axon terminal forming a symmetric synapse (indicated by an empty arrowhead) with a mGlu1α+ dendrite. Scale bars: 200 nm.