Fig. 4.

EMs revealing the differential localization of (β-ARs in astrocytes and neurons of adult visual cortex by SIG and their relation to GABA-immunoreactivity. (A) The dendrite from layer 5/6a of adult rat visual cortex exhibits numerous SIG particles (e.g., arrows), reflecting the presence of cytosolic (β-ARs. Within a neighboring astrocytic process (A), the SIG particles are close to the plasma membrane. Asterisks point to the irregular contours of the astrocyte. The same dendrite exhibits numerous lO-nm colloidal gold particles, resulting from EM-ICC detection of GABA, using PEG as label (e.g., Circled particles). A terminal, GT, contacting the dendrite exhibits high densitY of PEG labeling, indicating that it is a GABAergic terminal. (B) At a higher magnification, the neuropil from layer 2/3 of rat visual cortex exhibits five astrocytic processes (A1–A5). A1–A4 are immediately adjacent to asymmetric synaptic junctions (probably excitatory). A1, A3, and A5 exhibit robust (β-AR immunoreactivity (small arrows) primarily along the plasma membrane, but A2 and A4 exhibit much lower levels of (β-AR immunoreactivity and at sites away from the plasma membrane. Note that A4 is GABA-immunoreactive. In contrast, a dendritic process exhibits robust immunoreactivity for (β-ARs at sites away from the plasma membrane (e.g., arrow in (βD). A1 contacts an unlabeled terminal, UT, and also envelopes a dendrite, GD, identified to be GABAergic by the prevalence of PEG labels (circle), and synaptically associated with UT (curved arrow points to the postsynaptic density). Calibration bar = 500 nm.