Immunolocalization of cannabinoid receptor 1 (CB1), monoglyceride lipase (MGL) and fatty-acid amide hydrolase 1 (FAAH) in the pig claustrum

The claustrum (Cl) is a subcortical nucleus present in all mammalian species examined so far, whose function is still a puzzling problem. There is a wealth of data on its general anatomy, cytoarchitecture, and chemoarchitecture including the connectivity with both cortical and subcortical structures; instead, much less is known about the presence of the endocannabinoid system (ECs) an important neuromodulatory complex in this brain area. In an attempt to better understand the role of the ECs within the Cl circuitry, we undertook an immunohistochemical analysis to describe the distribution of the CB1 and of the endogenous cannabinoids degrading enzymes MGL and FAAH in the pig Cl as well as their relationship with both the catecholaminergic system and with parvalbumin (PV) expressing neurons. CB1, FAAH and MGL were expressed throughout the entire Cl. CB1 was expressed by fibers and puncta, while FAAH and MGL were mainly localized in the neuropil. FAAH also showed a faint cell body localization that colocalized with PV. Tyrosine hydroxylase positive fibers (catecholaminergic system), did not demonstrate the presence of CB1. Taken together, the results described herein provide evidence for an anatomical distribution of a CB1/PV signaling system in the pig Cl suggesting that PV cells may play a role within the ECs.