The distribution of calcitonin (CT) binding sites in serial sections of the rat brain
and spinal cord has been examined by an 'in vitro' autoradiographic technique using
a radioisotope-sensitive sheet film and salmon CT. Autoradiograms of the diencephalic
region had the highest grain density throughout the entire hypothalamus, with the
exception of the nuclei ventromedialis, posterior and mammillaris, which were not
labeled at all. In the brainstem, large amounts of grains were found in the ventrolateral
division of the periaqueductal gray, in the locus coeruleus, in the nucleus tractus
spinalis nervi trigemini and in the raphe obscurus, pallidus and magnus, while a widespread
and lower grain density was observed in the reticular formation. In the spinal cord
the labeling was discretely localized in laminae IV, V and VI of the dorsal horn.
The observed distribution of CT binding sites is closely related to the neuroendocrine
and analgesic effects of exogenous CT and reinforces the concept of a possible neuromodulatory
role proposed for the peptide at brain level.