CNR1 (CB1, cannabinoid receptor type 1) is a G protein-coupled cannabinoid receptor that binds endocannabinoid neurotransmitters and their analogs in the brain. CNR1 functions include regulating cardiac blood supply, inhibiting neuronal excitability in the brain, regulating motor control, and reinforcing drug-seeking behavior in addiction. CNR1 is also an important modulator of anxiety and arousal in response to novel situations; loss of CNR1 has been found to lead to increased object exploration, social interaction and aggression in mice. In immunohistochemistry, CNR1 has membranous positivity in the peripheral and central nervous systems. It is also found on cells in the pituitary, thyroid and adrenal glands, on fat and muscle cells, and in the liver, retina, digestive tract, lungs and kidney. References: Abood, Mary et al. Cannabinoid receptors: CB1 receptor. IUPHAR/BPS Guide to PHARMACOLOGY. 2019, URL: www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=56; Endocrine Reviews. 27 (1): 73–100, PMID: 16306385; PLOS ONE. 6 (11): e26617, PMID: 22069458.