Physiology of meningeal innervation: Aspects and consequences of chemosensitivity of meningeal nociceptors

Up to now, the cause of most types of headaches is unknown. Why headache st arts or why it fades away during hours or a few days is still a mystery. Th is phenomenon makes headache unique compared to other pain states. For long it has been known that during headache sensory structures in the meninges are activated. But it was not until the last two decades that scientists in vestigated the physiology of the sensory innervation of the meninges. Anima l models and in vitro preparations have been developed to get access to the meninges and to determine the response properties of meningeal afferents. Although animals hardly can tell their pain, blood pressure measurements an d observations of behaviour in two models of headache suggest that such ani mal models are valid and may add remarkable information to our understandin g of human headache. Since chemicals and endogenous inflammatory mediators may alter sensory thresholds and responsiveness of neurons, they are putati ve key molecules in triggering pathophysiological sensory processing. This review briefly summarizes what is known about the chemosensitivity of menin geal innervation. (C) 2001 Wiley-Liss, Inc.