CB1 Expression Levels Vary Widely in the Mouse Hippocampal Formation.

<p>In cortex, CB1 mRNA is highly expressed in a very restricted set of interneurons and more moderately expressed in a broader population of principal neurons. A representative coronal section through the hippocampal formation of mouse brain is shown. Nonradioactive in situ hybridization was used to identify CB1 mRNA-containing cells. The very highest levels (darkest red) are found in a restricted subset of cells (arrowheads) that are distributed throughout the hippocampal formation. Other studies have shown these to be CCK-containing GABAergic interneurons. Intermediate levels (light pink) are found in the principal neurons of CA1 (arrows) and CA3. Dentate granule cells (asterisks) do not express CB1 mRNA and provide a measure of the background inherent in this technique. Nuclei are identified by toluidine blue counterstaining. This general pattern of expression is recapitulated throughout the neocortex and amygdala. mo, molecular layer; po, polymorphic layer; sg, granule cell layer; slm, stratum lacunosum; so, stratum oriens; sp, stratum pyramidale; sr, stratum radiatum. (Original image provided by Martin Häring.)