Role of sensory and sympathetic neurotransmitters and their receptors in chondrogenic differentiation. Sensory - substance P (SP) and calcitonin gene-related peptide (CGRP) - and sympathetic (norepinephrine; NE) neurotransmitters and antagonists/agonists (isoproterenol and propranolol) affect chondrogenic differentiation and metabolism of chondroprogenitor cells and bone marrow-derived stem cells (BMSCs). These neurotropic effects are mediated through specific receptors for sensory neuropeptides, neurokinin 1 (NK1) receptor and CGRP receptor (CLR) and mainly the sympathetic β2-adrenoceptor. A line with an arrow indicates stimulation, and a line with a bar indicates inhibition. The red (green) nerve ending represent sensory (sympathetic) nerve fibers. Numbers indicate references according to bibliography at the end of this review. β2, β2-adrenoceptor; Iso, isoproterenol; Pro, propranolol.