Figure 9. Distribution and characterization of MOR-mcherry expression in the MHb-IPN pathway.

A. Scheme representing habenular nuclei at Bregma −1.58 mm and the interpeduncular nucleus at Bregma −3.80 mm. For nomenclature of sub-regions, see legends of Figure 2 and 3. B. MOR-mcherry red fluorescence is detectable with three different patterns. Intense fluorescence within cell bodies reveals MOR-mcherry expressing cells (red circles). MOR-positive cell bodies are seen in apical and basolateral parts of the MHb, as well as IPC and IPL. Few cells are also observed in the IPL and IPR. Fluorescence presenting a fibrous aspect reflects MOR-positive passing fibers (red lines). Fibers presenting MOR-mcherry expression are observed in the fr and IPR. Finally, diffuse fluorescence potentially arises from MOR expression at the level of afferent terminals (plain red areas) and is found in the apical part of MHb, and in both IPL and IPC. C. Representation of the MHb cholinergic (orange circles) and Substance P expressing neurons (blue circles) projecting to the IPN and colocalization with MOR-mcherry. Projection sites are symbolized with orange lines for cholinergic axons in the IPN and plain blue areas for substance P terminals. MOR-mcherry co-expression at the level of MHb neurons and IPN terminal sites is represented with red.