Figure 2.

Neurotransmitters/neuropeptides influence bone homeostasis via their receptors. Norepinephrine (NE), vasoactive intestinal peptide (VIP), substance P (SP), and calcitonin gene-related peptide (CGRP) affect bone formation and bone resorption by modulating osteogenesis and osteoclastogenesis in different, partly opposing ways. The effects are mediated through neurokinin 1 (NK1) receptor and CGRP receptor (CLR) and both α- and β2-adrenoceptors, depending on catecholamine concentration. A line with an arrow at the end indicates stimulation, and a line with a bar at the end 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; BMM, bone marrow-derived macrophages; M-CSF, granulocyte/macrophage colony-stimulating factor; OPG, osteoprotegerin; RANK, receptor activator of nuclear factor kappa-B; RANKL, receptor activator of nuclear factor kappa-B ligand; TRAP, tartrate-resistant alkaline phosphatase.