It seems that astrocytes or Microglia are positive for this protein.

Is this specific?

Given that this antibody reagent is positive for Fibroblasts/cytes, I assume it is specific.

Comments are welcome.

Region of anterior olfactory nucleus, I think. What is the clump of positive cells to the right of the image?

Olfactory bulb glomeruli.

Black arrowheads indicate positivity due to endogenous IgG immunoglobulins ( in blood vessels) as the primary Ab is a goat anti nnos.

Positive stellate cells in the cerebellum.