Vasopressin V1b receptor (V1BR) also known as vasopressin 3 receptor (VPR3) or antidiuretic hormone receptor 1B is a protein that in humans is encoded by the AVPR1B (arginine vasopressin receptor 1B) gene. V1BR acts as a receptor for vasopressin. AVPR1B belongs to the subfamily of G protein-coupled receptors. Its activity is mediated by G proteins which stimulate a phosphatidylinositol-calcium second messenger system. It is a major contributor to homeostasis and the control of water, glucose, and salts in the blood. Arginine vasopressin has four receptors, each of which are located in different tissues and have specific functions. AVPR1b is a G protein-coupled pituitary receptor that has only recently been characterized because of its rarity. It has been found that the 420-amino-acid sequence of the AVPR1B receptor shared the most overall similarities with the AVP1A, AVP2 and oxytocin receptors. AVPR1B maps to chromosome region 1q32 and is a member of the vasopressin/oxytocin family subfamily. Tissue distribution AVPR1B was initially described as a novel vasopressin receptor located in the anterior pituitary, where it stimulates ACTH release. Subsequent studies have shown that it is also present in the brain and some peripheral tissues. Clinical significance Behavioral Inactivation of the Avpr1b gene in mice (knockout) produces mice with greatly reduced aggression and a reduced ability to recognize recently investigated mice. Defensive behaviour and predatory behaviours appear normal in these knockout mice, but there is evidence that social motivation or awareness is reduced. The AVPR1B antagonist, SSR149415, has been shown to have anti-aggressive actions in hamsters and anti-depressant- and anxiety (anxiolytic)-like behaviors in rats. A single nucleotide polymorphism (SNP) has been associated with susceptibility to depression in humans. Metabolic Various stress-induced elevations of ACTH are blunted in the Avpr1b knockout mouse. Oncology AVPR1B is expressed at high levels in ACTH-secreting pituitary adenomas as well as in bronchial carcinoids responsible for the ectopic ACTH syndrome. Ligands Nelivaptan (SSR149415) and D-[Leu4-Lys8]-vasopressin are a specific antagonist and agonist for the vasopressin 1b receptor, respectively. Function AVPR1B is found in different parts of the body and thus has several influences and regulatory actions. Arginine vasopressin influences several symptoms related to affective disorders including significant memory processes, pain sensitivity, synchronization of biological rhythms and the timing and quality of REM sleep. Studies have shown that AVPR1B deficiencies produce behavioral changes that can be reversed when the peptide is replaced. These effects are expressed through contact with specific plasma membrane receptors.