The presynaptic terminal bouton is filled with vesicles containing acetylcholine and a neuropeptide called Calcitonin gene-related peptide (CGRP).
It is worth noting that unlike the classical one ligand-one receptor notion of receptor signalling, the interaction of both Calcitonin receptor-like (CALCRL) and RAMP ( Receptor activity-modifying protein) at the membrane, is required for AM to mediate its action.
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At present AM is believed to function through combinations of the calcitonin receptor like receptor (CALCRL) and receptor activity-modifying proteins (RAMP2) complexes, as well as CGRP receptors.
The parafollicular cells of the thyroid produce calcitonin in response to high calcium levels, but its significance is much smaller than that of PTH.