Immunohistochemical studies have also revealed the presence of CB1 receptor immunoreactivity within the rodent amygdala. The first detailed description by Tsou and co-workers, using an antibody directed against the N-terminal of the CB1 receptor, revealed CB1-immunoreactive (CB1-ir) neurons within both the centromedial nuclei and the BLA (Tsou et al., 1998a). Using this antibody, McDonald and Mascagni found light staining in principal neurons of the BLA, other cortical-like amygdaloid nuclei, CeAL, and anteroventral division of the MeA. In addition, lightly CB1-ir dendrites of pyramidal cells were also observed in all BLA nuclei. Double-labeling studies revealed that between 60–81% of high-CB1 expressing neurons within the BLA co-expressed CCK. Furthermore, all medium to large sized CCK neurons (type L) co-expresses CB1 (100% co-expression of CB1 and CCK in L-type CCK-positive neurons), whereas only a small population of the small CCK-expressing neurons (type S) co-expresses CB1 (10–14% co-localization depending on anatomical subregion) (McDonald and Mascagni, 2001).
