Figure 4.

Electron micrographs of the immunolocalization of the α2 and α3 subunits in Imp synapses. (A) A symmetric synapse (indicated by the open arrowhead) on an Imp dendrite shows electron dense peroxidase reaction end product for α3 enriched at the plasma membrane of the postsynaptic specialization. Because the antibody recognizes an extracellular epitope, also the presynaptic active zone and some intracellular organelles located immediately underneath the postsynaptic membrane appear labeled due to the diffusion of the HRP-immunoreaction product. Nearby an immunonegative excitatory synapse (closed arrowhead) made with a small spine(s) can be observed. (B) Immunometal particles visualizing α3 subunits can be seen directly located at the postsynaptic membrane of an inhibitory synapse in the Imp. (C and D) Numerous immunometal particles identifying the GABA_A α2 subunit can be observed leaning on the cytoplasmic portion of the postsynaptic plasma membrane of a symmetrical inhibitory synapse (open arrowheads) in the Imp. Abbreviations: at, axon terminal; d, dendrite; s, spine. Scale bars: A, 500 nm; B, 200 nm; C, 250 nm; D, 200 nm.