2. THE CGRP SYSTEM and MIGRAINE.
CGRP and its receptor are extensively expressed in two separate neuron populations in the TGV system (Eftekhari, Salvatore, Calamari, Kane, Tajti & Edvinsson, 2010). CGRP is released from the TGV system in conjunction of acute attacks of migraine and cluster headache (Ho, Edvinsson & Goadsby, 2010). The trigeminal C-fibres and ganglia are the main source of stimulus-induced CGRP found in the jugular vein as shown in man and cat (Goadsby, Edvinsson & Ekman, 1988) and rat (Hoffmann, Wecker, Neeb, Dirnagl & Reuter, 2012). The C-fibres have both afferent and efferent aspects; perivascular fibres release CGRP onto the vascular smooth muscle cells to induce dilatation and on dural mast cells to participate in induction of neurogenic inflammation (Pietrobon & Moskowitz, 2013). Many outstanding questions remain, particularly regarding the other members of the CGRP family. This group of signalling peptides include calcitonin (CT), adrenomedullin (AM) and amylin (AMY) and their receptors (Table 1). A fair question is often asked: Can other peptides be released in the TGV and will CGRP acting drugs have effects that include other related receptor targets?