Neuropeptides as mediators of vascular function and pain in tendon. Nerve fibres in normal and pathological tendons include sympathetic (NA: noradrenaline / adrenaline; NPY: neuropeptide Y), parasympathetic (Ach: acetylcholine), and sensory (SP: substance P; CGRP: calcitonin gene related peptide) nerve fibres, as well as free nerve endings expressing delta opioid receptors (δ OR). Tenocytes have been identified as both source and target of neuropeptide signals. Vascular regulation may occur via both direct and mast cell- or tenocyte-mediated mechanisms. Reproduced from Scott (BJSM, in press), with permission.