Fig. 1.

ISH staining of CB₁ (a–c, g–i) and CB₂ (d–f, j–l) mRNA in the colon of healthy mice. CB₁ mRNA is strongly detected in neurons of the myenteric (a brown, DAB, arrowheads; i FastRed) and the submucosal plexus (h FastRed). CB₁ gene expression is also found in the longitudinal muscle layer (a, g, iarrows), in lymph follicles (b arrows) and to a lesser degree in epithelial cells (c arrows) as well as some cells of the lamina propria (c, arrowhead). In contrast, CB₂ gene expression is scarcely found in the myenteric plexus (d arrows). Highest expression of the CB₂ gene occurs in lymph follicles (e arrows), whereas low expression is seen in epithelial cells (fep) and the lamina propria (flp). CB₁ mRNA fluorescence staining (FastRed) shows modest co-localization (yellow) with synaptophysin (green) in the myenteric plexus (g plexus denoted by asterisks). CB₁ mRNA (FastRed) shows clear co-localization with neurofilament H (brown, VIP) in the submucosal (h) as well as in the myenteric (i) plexus. CB₁ mRNA is also found in the longitudinal muscular layer where it does not co-localize with either of the neuronal markers (arrows in g and i). CB₂ mRNA (brown, DAB) is predominantly detected in B220⁺ cells (purple, VIP) of lymph follicles (j) and only marginally in F4/80⁺ (k) or CD3⁺ (l) cells. Calibration bars: a–f, h–l 10 µm, g 200 µm; cm circular muscle layer, ep epithelium, lp lamina propria, lm longitudinal muscle layer, cl crypt lumen; *, myenteric ganglion; arrows point at representative cells expressing CB₁ or CB₂ genes