Figure 7.

Electron microscopy immunogold-labeling demonstrates the presence of GABA within the lumen of the endoplasmic reticulum of glutamatergic cortical neurons. (A) Postembedding immunogold-labeling of GABA in slices of mouse primary motor cortex neurons shows GABA present within the lumen of the rough endoplasmic reticulum (RER) in a neuron of unidentified phenotype. Intraluminal and outer RER membrane associated GABA labeling are indicated by arrow. Inset is a higher magnification of a cluster of GABA immunogold-labeling within the RER lumen. Mitochondria (M) displaying dense GABA labeling. (B) Identification of a glutamatergic neuron of the motor cortex (hand-drawn outline) by retrograde tracing with biotinylated dextran amine (BDA) injected into the dorsolateral striatum. (C) Representative BDA-labeled glutamatergic neuron showing postembedding immunogold GABA labeling of the RER in the cell soma (D) Representative BDA-labeled glutamatergic neuron showing postembedding immunogold GABA labeling of mitochondria (M) in the cell soma. (E) Replicate data from multiple tissue sections from BDA-labeled glutamate neurons analyzed for the density of immunogold GABA labeling of various subcellular compartments (average ± SEM, n ≥ 31). Gold particle densities in the RER and mitochondria were each significantly greater than that in cytoplasm (*Tukey-Kramer HSD, p ≤ 0.0001).