Effects of age on binding sites for calcitonin gene-related peptide in the rat central nervous system

CGRP physiology, pharmacology, and therapeutic targets: migraine and beyond

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse physiological functions. Its two isoforms (α and β) are widely expressed throughout the body in sensory neurons as well as in other cell types, such as motor neurons and neuroendocrine cells. CGRP acts via at least two G protein-coupled receptors that form unusual complexes with receptor activity-modifying proteins. These are the CGRP receptor and the AMY1 receptor; in rodents, additional receptors come into play. Although CGRP is known to produce many effects, the precise molecular identity of the receptor(s) that mediates CGRP effects is seldom clear. Despite the many enigmas still in CGRP biology, therapeutics that target the CGRP axis to treat or prevent migraine are a bench-to-bedside success story. This review provides a contextual background on the regulation and sites of CGRP expression and CGRP receptor pharmacology. The physiological actions of CGRP in the nervous system are discussed, along with updates on CGRP actions in the cardiovascular, pulmonary, gastrointestinal, immune, hematopoietic, and reproductive systems and metabolic effects of CGRP in muscle and adipose tissues. We cover how CGRP in these systems is associated with disease states, most notably migraine. In this context, we discuss how CGRP actions in both the peripheral and central nervous systems provide a basis for therapeutic targeting of CGRP in migraine. Finally, we highlight potentially fertile ground for the development of additional therapeutics and combinatorial strategies that could be designed to modulate CGRP signaling for migraine and other diseases.

Amygdala, neuropeptides, and chronic pain-related affective behaviors

Neuropeptides play important modulatory roles throughout the nervous system, functioning as direct effectors or as interacting partners with other neuropeptide and neurotransmitter systems. Limbic brain areas involved in learning, memory and emotions are particularly rich in neuropeptides. This review will focus on the amygdala, a limbic region that plays a key role in emotional-affective behaviors and pain modulation. The amygdala is comprised of different nuclei; the basolateral (BLA) and central (CeA) nuclei and in between, the intercalated cells (ITC), have been linked to pain-related functions. A wide range of neuropeptides are found in the amygdala, particularly in the CeA, but this review will discuss those neuropeptides that have been explored for their role in pain modulation. Calcitonin gene-related peptide (CGRP) is a key peptide in the afferent nociceptive pathway from the parabrachial area and mediates excitatory drive of CeA neurons. CeA neurons containing corticotropin releasing factor (CRF) and/or somatostatin (SOM) are a source of long-range projections and serve major output functions, but CRF also acts locally to excite neurons in the CeA and BLA. Neuropeptide S (NPS) is associated with inhibitory ITC neurons that gate amygdala output. Oxytocin and vasopressin exert opposite (inhibitory and excitatory, respectively) effects on amygdala output. The opioid system of mu, delta and kappa receptors (MOR, DOR, KOR) and their peptide ligands (β-endorphin, enkephalin, dynorphin) have complex and partially opposing effects on amygdala function. Neuropeptides therefore serve as valuable targets to regulate amygdala function in pain conditions. This article is part of the special issue on Neuropeptides.

Expression of CGRP neurotransmitter and vascular genesis marker mRNA is age-dependent in superior cervical ganglia of senescence-accelerated prone mice

Calcitonin gene-related peptide (CGRP) is a neurotransmitter that is released from the superior cervical ganglion (SCG) and causes head and neck pain. The morphological properties of human SCG neurons, including neurotransmitter content, are altered during aging. However, morphological changes in CGRP in the SCG during aging are not known. Therefore, we investigated CGRP and other markers in the SCG during aging in an aging model of senescence-accelerated prone mouse (SAMP8) and senescence-accelerated resistant mice (SAMR1) using real-time RT-PCR mRNA analyses and in situ hybridization. The abundance of neurotransmitter (CGRP, NPY, TRPV1), vascular genesis marker (CD31, LYVE-1), and cytochrome C mRNA differed between 12-week-old and 24-week-old SAMP8 and SAMR1. Abundance of TRPV1, CD31 and cytochrome C mRNAs of SAMP8 decreased between 12- and 24-week-old. The ratio of CGRP mRNA positive cells and CGRP mRNA abundance levels of the SCG of aging mouse such as SAMP8 have already been also higher than that of SAMR1 at 12-week-old. The CGRP positive shrunken ganglion cells was increased from 12- to 24-weeks-old mouse in SAMR1 and SAMP8. The SCG primarily affected the internal and external carotid arteries, larynx thyroid gland, and pharyngeal muscle during aging.

The ontogeny of [125I]rat-alpha-CGRP binding sites in the spinal cord of sheep: a prenatal and postnatal study

In this study we describe the ontogeny of [125I]rat-alpha-calcitonin gene-related peptide binding sites in the spinal cord of fetal and postnatal sheep. The density and distribution of binding sites has been compared with the localization of calcitonin gene-related peptide like-immunoreactivity at corresponding stages of development [Nitsos I. and Rees S. (1993) Neuroscience 54, 239-252]. At 68 days of gestation (term = 146 days), the earliest fetal tissue examined, there was no evidence of binding sites in lamina I or the outer regions of lamina II (lamina IIo), although there was a sparse distribution of binding sites in the inner region of lamina II (lamina IIi). By comparison, binding appeared to be more marked in laminae III-V and more concentrated again in laminae VI-X. This distribution essentially remained constant until 124 days, when there appeared to be a marked increase in the density of binding sites throughout the gray matter, particularly in the dorsal horn in the lateral extent of both lamina IIo and IIi as well as in laminae III, V and VI. This increase was also observed in the intermediate zone (lamina VII) and in lamina X. Binding in the ventral horn, which was diffuse until this stage, now became particularly dense in the medial and lateral regions of the horn. From 124 days to one month postnatal, there was no marked change in the density or distribution of binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

On the effect of ageing on the distribution of vasoactive intestinal polypeptide and calcitonin gene-related peptide in the rat brain

The distribution of calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) was investigated by the use of immunohistochemical techniques in the brain of young and aged rats. CGRP-like immunoreactivity (CGRP-LI) showed a significant decrease only in the amygdala, whereas a substantial age-dependent decrease in VIP-like immunoreactivity (VIP-LI) was observed in the cortex, amygdala, substantia nigra, hippocampus and suprachiasmatic nucleus.

Age-related changes in tissue contents of immunoreactive calcitonin gene-related peptide

Age-related changes in calcitonin gene-related peptide (CGRP) content were found in a number of rat tissues, and most can be explained by the physiological and pathological changes associated with advancing age. In some specific areas of the brain, and some cardiovascular tissues such as atria and arteries, the CGRP content declined with age (p < 0.01), while the contents were increased in the thyroid gland, plasma and in veins (p < 0.01). In the substantia nigra and striatum, the immunoreactive-CGRP (i-CGRP) levels found in older rats were about 50% of those found in adolescent rats (p < 0.01). The i-CGRP levels found in the penis, bladder, kidney, testis and adrenal gland gradually increased up to maturity, and then rapidly declined in the aging rats. However, in the lungs and sensory ganglia (dorsal root and trigeminal), the highest content of i-CGRP was found in immature 3-week-old rats, and then declined with age. Changes of i-CGRP observed with age may support multiple physiological roles for CGRP at various stages of development. The changes described here, particularly in the lungs, substantia nigra, striatum and the cardiovascular system, should help in further understanding the physiological and pathophysiological role of CGRP in health and in age-related disorders.

Central nervous system binding sites for calcitonin and calcitonin gene-related peptide

Alternative splicing of the primary RNA transcript of the calcitonin gene leads to the generation of two distinct peptides, calcitonin (CT) and calcitonin gene-related peptide (CGRP). These peptides share only limited sequence homology and generally subserve different biological functions through their own distinct binding sites, which differ in specificity and distribution. Additionally, a binding site with high-affinity binding for both peptides that has a restricted pattern of distribution has been identified. The present article reviews the biochemical and morphological characteristics of centra CT and CGRP binding sites.

Local cerebral glucose utilization in the brain of old, learning impaired rats

The local cerebral glucose utilization (LCGU) was measured in 63 different cortical areas and nuclei of the telencephalon, diencephalon and rhombencephalon of young adult (3 to 4-month-old) rats and of 27-month-old Wistar rats, in which learning impairments had been proven by a water maze test. The LCGU was determined by [14C]2-deoxyglucose autoradiography. In the old rats the mean LCGU of all brain regions was significantly reduced by about 10% compared with the young control group; the mean LCGU was 74.2 mumol glucose/(100 g x min) in the young and 66.7 in the old rats. Different degrees of LCGU decrease were found in the different regions. Most of the brain regions with significantly reduced LCGU values in the aged, learning impaired rats were associated with auditory and visual functions, the dopaminergic system, and structures known to be involved in learning and memory processes. Therefore, the regional pattern of LCGU reduction found in the aged, learning impaired rats did not resemble any known pattern found after lesions of a single transmitter system or systemic administration of transmitter agonists or antagonists.