125I-calcitonin gene-related peptide (CGRP) binding sites were mapped in the human
brain and rat brains by in vitro macroautoradiography, and compared to each other.
Binding experiments were made to characterize 125I-CGRP binding on the human and rat
brains. Scatchard analysis of saturation experiments from slide-mounted sections of
the human and rat cerebellum displayed 125I-CGRP binding sites with a dissociation
constant (Kd) of 0.17 nM and 0.11 nM, respectively, and a maximal number of binding
sites (Bmax) of 96.8 fmol/mg and 23.0 fmol/mg protein. 125I-CGRP binding was time-dependent,
reversible and saturable with high affinity in the brains. Autoradiograms showed a
discrete distribution of 125I-CGRP binding sites throughout the brains of human and
rat with patterns similar to each other. In the human brain, the highest binding was
seen in the cerebellum, inferior olivary nuclear complex, certain parts of the central
gray matter, arcuate nuclei of the medulla oblongata and dorsal motor nucleus of the
vagus, and densities of CGRP-binding sites were high in the nucleus accumbens, amygdala,
tail of the nucleus caudatus, substantia nigra, ventral tegmental area, medial portion
of the inferior colliculus, medial pontine nuclei, locus coeruleus, inferior vestibular
nucleus, substantia gelatinosa of the spinal trigeminal nucleus, nucleus of the solitary
tract and nucleus cuneatus lateralis. In the rat, high densities were found in the
hippocampus pars anterior, nucleus accumbens, ventral and caudal portions of the nucleus
caudatus-putamen, central and basolateral nuclei of the amygdala, caudal portion of
the insular cortex, medial geniculate body, superior and inferior colliculi, certain
portions of the central gray matter, locus coeruleus, inferior olivary nuclei, vagal
complex, nucleus cuneatus lateralis and cerebellum. In contrast, in both species,
most of the cortical areas including the hippocampus, most of the thalamus, and hypothalamus
exhibited few binding sites. In addition, high quantities of the binding sites were
seen on the pia mater and on walls of blood vessels in the brain and subarachnoidea.
These results revealed essentially homologous locations of CGRP binding sites in the
human and rat central nervous systems and well corresponding distributions of binding
sites and endogenous CGRP-like immunoreactivity.