Demonstration of Functional Neuronal β3-Adrenoceptors Within the Enteric Nervous System

Background & Aims: Although the β 3 -adrenoceptor (AR) has been suggested to be involved in regulation of gut motility and visceral algesia, the precise mechanisms have been unknown. β 3 -AR has been postulated to have a nonneuronal expression, being initially characterized in adipocytes and subsequently in the smooth muscle. We aimed to investigate the expression of β 3 -AR in human enteric nervous system and its role in motility and visceral algesia. Methods: The expression of β 3 -AR in human colon myenteric and submucosal plexus was investigated using immunohistochemistry. The effects of a β 3 -AR agonist on nerve-evoked and carbachol-induced contractions as well as somatostatin release were investigated in strips of human colon. The effect of an agonist on diarrhea and visceral pain was investigated in vivo in rat models. Results: β 3 -AR is expressed in cholinergic neurons in the myenteric plexus and submucosal plexus of human colon. Activation of β 3 -AR causes the release of somatostatin from human isolated colon. In a rat model of visceral pain, β 3 -AR agonist elicits somatostatin-dependent visceral analgesia. β 3 -AR agonists inhibit cholinergically mediated muscle contraction of the human colon, as well as chemically induced diarrhea in vivo in a rat model. Conclusions: This is the first demonstration of expression of β 3 -AR in the enteric nervous system. Activation of these receptors results in inhibition of cholinergic contractions and enhanced release of somatostatin, which may lead to visceral analgesia and inhibition of diarrhea. Therefore, β 3 -AR could be a novel therapeutic target for functional gastrointestinal disorders.