Ex vivo stimulation of the trigeminal nucleus caudalis induces peripheral CGRP release in the trigeminal ganglion and reveals a distinct dopamine-endocannabinoid mechanism relevant to migraine

BACKGROUND: Calcitonin gene-related peptide (CGRP) release from trigeminal structures is central to migraine pathophysiology. This study employed an ex vivo model preserving anatomical continuity between the trigeminal nucleus caudalis (TNC) and trigeminal ganglion (TG) to investigate (1) whether TNC stimulation induces peripheral CGRP release from the TG and (2) the potential involvement of a distinct dopamine-endocannabinoid mechanism.

METHODS: Tissues were dissected as a single unit and placed in custom 3D-printed chambers, allowing targeted stimulation of either the TNC or the TG while measuring CGRP in both compartments. Pharmacological tools, including capsaicin (TRPV1 agonist), KCl (depolarizing agent), dopamine, and selective enzyme inhibitors or receptor antagonists, were used to elucidate underlying signalling pathways. CGRP levels were quantified via enzyme-linked immunosorbent assay.

RESULTS: Stimulation of the TNC elicited a significant rise in CGRP release locally and in the TG compartment, whereas directly stimulating the TG did not trigger CGRP release in the TNC. Subsequent experiments showed that applying dopamine to the TNC further enhanced CGRP release. TRPV1 blockade or pharmacological inhibition of N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD), an enzyme important for anandamide biosynthesis, markedly attenuated dopamine-induced CGRP release, indicating that an endocannabinoid-driven mechanism is involved.

CONCLUSION: Activating the TNC alone was sufficient to evoke CGRP release in the peripheral trigeminal compartment, underscoring a potential central-to-peripheral mechanism that may be relevant to migraine. Moreover, a dopamine-endocannabinoid-TRPV1 axis appears to modulate CGRP signalling in this system, indicating additional complexity and providing potential new strategies for migraine therapy.