Evidence for a new subclass of calcitonin/ calcitonin gene-related peptide binding site in rat brain

doi:10.1016/0197-0186(88)90171-4

Neurochemistry International

Volume 12, Issue 3, 1988, Pages 323-335

https://doi.org/10.1016/0197-0186(88)90171-4 Get rights and content

Abstract

Binding sites for calcitonin and calcitonin gene-related peptide are widely distributed in the central nervous system. In this study, binding of [¹²⁵I]-alpha-rat calcitonin gene-related peptide and [¹²⁵I]-salmon calcitonin in adjacent sections of rat brain revealed clearly distinct patterns of binding in most regions although in some restricted areas such as parts of the ventral striatum, including the nucleus accumbens, there was some overlap in the patterns of binding. In the primary olfactory cortex, which bound only calcitonin gene-related peptide, salmon calcitonin was very weak in inhibiting the binding of calcitonin gene-related peptide. In the nucleus accumbens, high affinity binding of calcitonin and calcitonin gene-related peptide at their homologous receptors was observed, with affinity constants for calcitonin and calcitonin gene-related peptide of 1.4 × 10⁹ M⁻¹ and 1.2 × 10⁹ M⁻¹ respectively. Cross competition studies in this nucleus demonstrated that salmon calcitonin was able to compete for [¹²⁵I]-rat calcitonin gene-related peptide labelled sites with high affinity, with an affinity constant of 0.8 × 10⁹ M⁻¹. However, rat calcitonin gene-related peptide was less potent in inhibiting the binding of [¹²⁵I]-salmon calcitonin labelled sites with only 28% inhibition at 10⁻⁶M. Further characterization of the calcitonin sensitive calcitonin gene-related peptide labelled sites demonstrated that a range of calcitonin analogs inhibited the binding of [¹²⁵I]-rat calcitonin gene-related peptide with the same order of potency as the analogs competed for [¹²⁵I]-salmon calcitonin labelled sites. Digital substraction mapping revealed calcitonin-sensitive calcitonin gene-related peptide binding sites over parts of the ventral striatum, including mid-caudal nucleus accumbens and fundus striati; over the lateral border of the lateral bed nucleus of the stria terminalis; part of the central amygdaloid nucleus; the organum vasculosum of the lamina terminalis and area postrema and over the wings of the dorsal raphe.

These results demonstrate the existence of a new subtype of calcitonin/calcitonin gene-related peptide binding site, which has high affinity for the two otherwise biochemically distinct peptides.

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Citation Excerpt :
It is presently not known whether RAMPs are more general modulators of receptor function, dynamically modifying responsivity with time or across other receptor classes. The distribution of sites corresponding to amylin receptors was first identified by Sexton et al. in 1988 (Sexton et al., 1988). They were first termed C3 binding sites, characterized as calcitonin binding sites that also had high affinity to both sCT and CGRP (Sexton et al., 1988).
Despite a clear evidence for a distinct amylin pharmacology and the localization of such pharmacology to sites such as the nucleus accumbens, efforts to clone an amylin receptor were fruitless for over a decade. This enigma led many to doubt the status of amylin as a bona fide hormone. The enigma of the amylin receptor was solved following the identification of receptor activity modifying proteins (RAMPs). These single transmembrane spanning molecules, when associated with a calcitonin receptor, altered its pharmacology from calcitonin-preferring to amylin-preferring. The newly designated amylinomimetic drug class has been defined on the basis of its unique pharmacology prior to the molecular characterization of amylin receptors. Currently, the class includes any agent that acts as an agonist at characterized amylin receptors. Several peptides, typically analogs of truncated salmon calcitonin, have been developed as potent and selective amylin antagonists and have been useful in identifying amylinergic responses.
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Calcitonin (CT) and amylin are related peptides with potent central actions, including suppression of appetite and gastric acid secretion. Little is known about the distribution and binding characteristics of amylin receptors in species other than rat; therefore, in this study, by using in vitro autoradiography, we have mapped the distribution of ¹²⁵I-rat amylin binding sites in the monkey brain and compared this distribution to that of binding sites for ¹²⁵I-salmon CT (¹²⁵I-sCT). Highest densities of ¹²⁵I-amylin binding were in the hypothalamus, including the arcuate nucleus and parts of the ventromedial hypothalamic nuclei, and the solitary nucleus. Rostrally, moderate to high density binding was present in parts of the preoptic area, bed nucleus of the stria terminalis, amygdala and accumbens nucleus (Acb). Caudally, binding of amylin was more restricted, with moderate to high density binding present only in dorsal raphe, and area postrema. The primary visual cortex displayed strong and periodic CT binding in layer 4. The subcortical pattern of distribution of amylin and CT receptors in the monkey was similar to that seen previously in the rat, although the relative densities of binding to different brain structures were not always conserved. As with rat, monkey amylin receptors were a subset of the sites labeled with ¹²⁵I-sCT. Analysis of receptor specificity indicated a greater relative potency of CT peptides in competing for ¹²⁵I-amylin binding in monkey, when compared to rat, while, there was a decrease in the relative potency of CT gene-related peptides, potentially due to differences the level of receptor activity modifying proteins (RAMPs) in monkey versus rat brain. Amylin receptors in primates are likely to perform a similar role to those in rats; however, the interaction of the receptors with related peptides may differ.

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Evidence for a new subclass of calcitonin/ calcitonin gene-related peptide binding site in rat brain

Abstract

Brain Res.

Brain Res.

Brains Res.

Peptides

Biochem. Biophys. Res. Commun.

Brain Res.

Neuroscience

Kidney Int.

Peptides

Life Sci.

Peptides

Expression in brain of a messenger RNA encoding a novel neuropeptide homologous to calcitonin gene-related peptide

Science

Hypoprolactinemic action of calcitonin and the tuberoinfundibular dopaminergic system

J. Neurochem.