Figure 6.

Demonstration of COUP-TFII immunoreactivity in a double bouquet cell. (A) Reconstruction of the dendritic (black) and axonal (gray) arborizations of the cell with the boundary between layers I and II indicated. Note the descending axonal bundle identifying the cell as a double bouquet cell. Most dendritic and axonal branches are truncated by the slice preparation. (B) The biocytin-labeled cell (arrow) next to 2 sequentially recorded pyramidal cells (P), which were tested for connectivity, but there was no detectable synaptic interaction between the interneuron and either of the pyramidal cells. (C) The double bouquet cells (arrow), but not the pyramidal cells, are immunopositive for calretinin. (D) The nucleus of the cell (arrow) is positive for COUP-TFII, as are the nuclei of 2 other calretinin-positive interneurons (top). (E and F) Electron micrographs of representative serial sections of a double bouquet cell bouton making a type II synaptic junction (between bars) with a small dendritic shaft that also receives another synapse (arrow) from a bouton of unknown origin. Scale bars: A, 50 µm; B–D, 25 µm; E and F, 0.5 µm.