Fig. 4.

Postsynaptic expression of PDE4D within dendritic spines in ERC layer II. (A-E) PDE4D immunolabeling was expressed in dendritic spines, directly in association with or near the SER spine apparatus (pseudocolored pink), the calcium-containing extension of the SER into the dendritic spine head, positioned to regulate cAMP-PKA-calcium signaling. (F) PDE4D immunolabeling was observed subjacent to the PSD near the synaptic active zone. (G) PDE4D was also observed in perisynaptic compartments near the plasma membrane flanking the excitatory synapse. All dendritic spines receive axospinous Type I asymmetric glutamatergic-like synapses; synapses are between black arrows. Color-coded arrowheads point to PDE4D (green) immunoreactivity. Profiles are pseudocolored for clarity. Ax, axon; Sp, dendritic spine; Mit, mitochondria. Scale bars, 200 nm.