Coexpression of the cannabinoid receptor type 1 with the corticotropin-releasing hormone receptor type 1 in distinct regions of the adult mouse forebrain.

The high abundance of the cannabinoid receptor type 1 (CB1) in the brain and the discovery of its endogenous ligands possessing neuromodulatory activities suggest an important potential of the endocannabinoid system to influence the functions of other receptor systems in the brain, including the corticotropin releasing hormone (CRH) system. Several studies evidenced a cross-talk between these two receptor systems. In trying to detail functional interactions between CB1 and the CRH receptor type 1 (CRHR1), we performed double-label-in situ hybridisation on mouse forebrain sections to localise the transcripts encoding the two receptors at a cellular level. Colocalisation of both receptor mRNAs was only detected in low CB1-expressing cells, which are mainly principal projecting neurons, whereas high CB1-expressing cells, which are considered to be mostly GABAergic did not contain mRNA encoding CRHR1. CB1 is differentially coexpressed with CRHR1 in olfactory regions, in several cortical and limbic structures, and in some hypothalamic and thalamic nuclei. These observations suggest a complex mechanism underlying the mutual interrelation and modulation of the two receptor systems. In particular, high levels of coexpressing cells in cortical and limbic areas may relate to cognitive functions, such as working memory, emotional and declarative learning. Colocalisation of CB1 and CRHR1 in hypothalamic regions strongly suggests functional interactions regarding the neuroendocrine homeostasis, including feeding behaviour.