Calcitonin: brainstem microinjection but not systemic administration inhibits spinal nociceptive transmission in the cat

In anaesthetized cats, nociceptive responses of lumbar dorsal horn neurons were studied during administration of salmon calcitonin (sCT). Systemic sCT administration (4–95IU/kg i.v.) produced no change in neuronal responses produced by noxious skin heating or by impulses evoked electrically in afferent C-fibres. Responses to skin heating were reduced during electrical stimulation in the brainstem, but the efficacy of this descending inhibition was not altered by systemic sCT administration. In contrast, noxious heat responses were clearly reduced by microinjection of sCT into the mesencephalic periaqueductal grey or the medullary raphe regions. These results suggest that calcitonin or a related peptide could act at specific brainstem sites to inhibit the spinal transmission of nociceptive information.