Verisimilitude (or "truthlikeness") as an alternative to pro and cons: migraine and cluster headache mechanisms

CGRP physiology, pharmacology, and therapeutic targets: migraine and beyond

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse physiological functions. Its two isoforms (α and β) are widely expressed throughout the body in sensory neurons as well as in other cell types, such as motor neurons and neuroendocrine cells. CGRP acts via at least two G protein-coupled receptors that form unusual complexes with receptor activity-modifying proteins. These are the CGRP receptor and the AMY1 receptor; in rodents, additional receptors come into play. Although CGRP is known to produce many effects, the precise molecular identity of the receptor(s) that mediates CGRP effects is seldom clear. Despite the many enigmas still in CGRP biology, therapeutics that target the CGRP axis to treat or prevent migraine are a bench-to-bedside success story. This review provides a contextual background on the regulation and sites of CGRP expression and CGRP receptor pharmacology. The physiological actions of CGRP in the nervous system are discussed, along with updates on CGRP actions in the cardiovascular, pulmonary, gastrointestinal, immune, hematopoietic, and reproductive systems and metabolic effects of CGRP in muscle and adipose tissues. We cover how CGRP in these systems is associated with disease states, most notably migraine. In this context, we discuss how CGRP actions in both the peripheral and central nervous systems provide a basis for therapeutic targeting of CGRP in migraine. Finally, we highlight potentially fertile ground for the development of additional therapeutics and combinatorial strategies that could be designed to modulate CGRP signaling for migraine and other diseases.

Primary headaches and trigeminal neuralgia: neuropathic pain yes or not? Evidences from neurophysiological procedures

Despite the fact that neurophysiological evaluation is not useful for primary headache diagnosis, the nociceptive system exploration through reflexes and evoked potentials procedures may give an aid in understanding the pathophysiological mechanism subtending pain. Neuropathic pain is caused by a lesion or disease of the somatosensory nervous system, which is supported by clinical evaluation and instrumental assessment by trigeminal and nociceptive reflexes and laser evoked potentials. The same methods, applied to migraine and cluster headache, together with evidences coming from structural and functional neuroimaging, excluded the neuropathic origin of pain, which is attaining to symptomatic and idiopathic trigeminal neuralgia, but confirmed a complex dysfunction of pain processing. Tension-type headache fits with a model of non-nociceptive and non-neuropathic pain, subtended by a complex interaction of peripheral muscular and central neuronal factors. The presence of altered modulation of pain concurs with migraine and tension-type headache, and should be taken into account for the choice of the best therapeutic approach.