Improvement of the closed cranial window model in rats by intracarotid infusion of signalling molecules implicated in migraine

Intravital microscopy on a closed cranial window allows one to measure change in the diameter of cranial blood vessels after intravenous (i.v.) administration of pharmacodynamic substances. Putative targets being pursued in migraine are large vasodilating peptide molecules such as calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase polypeptide (PACAP)-38. High i.v. doses are required to study their craniovascular pharmacology. Unfortunately, this leads to a drop in blood pressure (BP) that subsequently causes blood vessels to dilate by autoregulation. Hence it is difficult to decipher what effect is caused by direct receptor agonist interaction or contributed by autoregulation. In the present study we infused substances with an ingenious indwelling catheter in the common carotid artery in rats. Intracarotidly seven-, 12- and 17-fold lower doses of CGRP, PACAP-38 and capsaicin were required, respectively, compared with i.v. infusion to induce the same dilation in dural artery. Dilating i...