ABSTRACT
BACKGROUND: Calcitonin gene-related peptide (CGRP) receptor antagonism is an approach to migraine therapy. The locus of action of antimigraine treatment is not resolved. The objective was to investigate CGRP receptors in the ventrolateral periaqueductal gray (vlPAG) involved in the modulation of trigeminovascular nociception by descending influences on neurotransmission. METHODS: The presence of calcitonin receptor-like receptor (CLR) and receptor activity modifying protein 1 (RAMP1), which form functional CGRP receptors, was investigated. CGRP and its receptor antagonists, olcegepant and CGRP (8-37), were microinjected into the vlPAG while changes of neural responses in the trigeminocervical complex (TCC) were monitored. RESULTS: Immunoreactivity indicated the presence of functional CGRP receptor components in the vlPAG and adjacent mesencephalic trigeminal nucleus. Inhibition of TCC responses to stimulation of dural afferents and ophthalmic cutaneous receptive fields after microinjection of bicuculline into vlPAG indicated a connection between the vlPAG and TCC neurons. CGRP facilitated these TCC responses, whereas olcegepant and CGRP (8-37) decreased them. CONCLUSIONS: CGRP and its receptor antagonists act on neurons in the region of vlPAG to influence nociceptive transmission in the TCC. This suggests CGRP receptor antagonists may act at loci outside of the TCC and reinforces the concept of migraine as a disorder of the brain.
Subject(s)
Calcitonin Gene-Related Peptide/administration & dosage , Neurons/physiology , Periaqueductal Gray/physiology , Receptors, Calcitonin Gene-Related Peptide/physiology , Trigeminal Nuclei/physiology , Animals , Calcitonin Gene-Related Peptide Receptor Antagonists , Male , Microinjections/methods , Neurons/drug effects , Peptide Fragments/administration & dosage , Periaqueductal Gray/drug effects , Rats , Rats, Sprague-Dawley , Receptors, Calcitonin Gene-Related Peptide/agonists , Trigeminal Nuclei/drug effectsABSTRACT
Migraine is a complex disorder of the brain whose mechanisms are only now being unraveled. It is common, disabling and economically costly. The pain suggests an important role of the nociceptive activation, or the perception of activation, of trigeminal cranial, particularly intracranial afferents. Moreover, the involvement of a multi-sensory disturbance that includes light, sound and smells, as well as nausea, suggests the problem may involve central modulation of afferent traffic more broadly. Brain imaging studies in migraine point to the importance of sub-cortical structures in the underlying pathophysiology of the disorder. Migraine may thus be considered an inherited dysfunction of sensory modulatory networks with the dominant disturbance affecting abnormal processing of essentially normal neural traffic.
