Intravital microscope studies on the effects of neurokinin agonists and calcitonin gene-related peptide on dural vessel diameter in the anaesthetized rat.

This study describes a novel intravital microscope technique for direct measurement of dural blood vessel diameter through a closed cranial window in anaesthetized rats. This technique avoids removal of the skull, which can lead to problems of altered vessel reactivity and brain swelling that are encountered with open cranial window techniques. Substance P and calcitonin gene-related (CGRP) evoked increases in dural vessel diameter, which were abolished by the NK1 receptor antagonist, RP67580 and the CGRP receptor antagonist, human-alpha CGRP(8-37) respectively. Neurokinin A produced increases in dural vessel diameter which were unaffected by the NK2 receptor antagonist SR 48968 but were blocked by RP67580, suggesting that neurokinin A can act through NK1 receptors to produce dural vasodilation in rats. The NK3 receptor agonist, senktide, had no effects on dural vessel diameter. All drugs were administered intravenously. In humans, vasodilation within the meningeal vasculature has been implicated in the pathogenesis of migraine, the present experiments indicate that substance P or neurokinin A (both acting through NK1 receptors) or CGRP may be responsible.