Human brain calcitonin gene-related peptide (CGRP) is concentrated in the locus caeruleus

A quantitative survey of calcitonin gene-related peptide (CGRP) in brain, peripheral nerve and cerebrospinal fluid (CSF) was performed using radioimmunoassay (RIA) with antiserum against synthetic hCGRP. High levels (approximately 2000-15,000 fmol/mg protein) were found in the dorsal spinal cord, dorsal nerve and trigeminal nerve. Relatively large amounts (500-2000) were found in parts of the hypothalamic-pituitary axis, peripheral nerve and, for the first time, in the locus caeruleus. Low levels of CGRP (less than 500) were detected in the cerebrum, subcortical nuclei and cerebellum. CGRP, not previously reported in CSF, was detectable in all of 27 CSF specimens with mean values of 30 +/- 4.5 pmol/L (SE). Simultaneous plasma CGRP levels were higher and, when elevated by antihypertensive treatment were not increased in CSF, just as astronomical plasma levels of calcitonin in medullary carcinoma of the thyroid are not reflected in CSF. Our data confirm and extend the results of previous human and animal studies with evidence of species variation: humans have low CGRP levels in subcortical nuclei whereas high levels have been found in rat caudate-putamen and amygdala. The high level of CGRP in the locus caeruleus, the major source of noradrenergic neurotransmission in the CNS, is in harmony with the presumed functions of the LC and the very potent hemodynamic activity of CGRP.