On the basis of the distribution of the nuclei that are known to be activated by GTN and involved in migraine pain, the following discrete brain areas were dissected out 4 h after GTN or vehicle administration and used for analysis: medulla-pons, containing nucleus trigeminalis caudalis (NTC), nucleus tractus solitarius and area postrema; mesencephalon, containing ventrolateral column of the periaqueductal grey and parabrachial nucleus, and hypothalamus, containing the paraventricular and supraoptic nuclei of the hypothalamus.