Calcitonin Gene-related Peptide-positive Nerve Research Articles

Development of a novel animal model of lumbar vertebral endplate lesion by intervertebral disk injection of monosodium iodoacetate in rats

PurposeVertebral endplate lesions (EPLs) caused by severe disk degeneration are associated with low back pain. However, its pathophysiology remains unclear. In this study, we aimed to develop a vertebral EPL rat model mimicking severe intervertebral disk (IVD) degeneration by injecting monosodium iodoacetate (MIA) into the IVDs and evaluating it by assessing pain-related behavior, micro-computed tomography (CT) findings, and histological changes.MethodsMIA was injected into the L4-5 and L5-6 IVDs of Sprague–Dawley rats. Their behavior was examined by measuring the total distance traveled and the total number of rearing in an open square arena. Bone alterations and volume around the vertebral endplate were assessed using micro-CT. Safranin-O staining, immunohistochemistry, and tartrate-resistant acid phosphatase (TRAP) staining were performed for histological assessment.ResultsThe total distance and number of rearing times in the open field were significantly reduced in a time-dependent manner. Micro-CT revealed intervertebral osteophytes and irregularities in the endplates at 12 weeks. The bone volume/tissue volume (BV/TV) around the endplates significantly increased from 6 weeks onward. Safranin-O staining revealed severe degeneration of IVDs and endplate disorders in a dose- and time-dependent manner. Calcitonin gene-related peptide-positive nerve fibers significantly increased from 6 weeks onward. However, the number of osteoclasts decreased over time.ConclusionOur rat EPL model showed progressive morphological vertebral endplate changes in a time- and concentration-dependent manner, similar to the degenerative changes in human IVDs. This model can be used as an animal model of severe IVD degeneration to better understand the pathophysiology of EPL.

Hyaluronic acid sheet transplantation attenuates infrapatellar fat pad fibrosis and pain in a rat arthritis model.

Fibrosis of the infrapatellar fat pad (IFP) occurs after knee joint surgery or during knee osteoarthritis (KOA) and causes persistent pain and limited mobility. Previous studies demonstrated that treating IFP fibrosis alleviated pain in animal models. In this study, we examined the effects of hyaluronic acid (HA) sheet transplantation on IFP fibrosis and articular cartilage degeneration in a monoiodoacetic acid (MIA) rat arthritis model (95 male rats). Rats received bilateral intra-articular MIA injections (1.0 mg/30 μL) and underwent surgery 4 days later. HA sheets were transplanted on the right knee of each rat (HA group), with the left knee receiving sham surgery (sham group). Incapacitance tests were performed at multiple time points up to 28 days after MIA injection. Macroscopic, histological, and immunohistochemical analyzes were performed 14 and 28 days after injection. The concentrations of HA and interleukin-1β (IL-1β) in the synovial fluid were measured using ELISA. Transplantation of HA sheets could alleviate persistent pain 10-28 days after injection. The HA sheets inhibited articular cartilage degeneration at 14 days. Fibrosis and the invasion of calcitonin gene-related peptide-positive nerve fiber endings in the IFP were inhibited at both 14 and 28 days. Moreover, the HA sheets remained histologically until 10 days after transplantation. The concentration of HA reached its peak on Day 10 after transplantation; the concentration of IL-1β in the sham group was significantly higher than that in the HA group on Day 7. Therefore, HA sheets could be a promising option to treat IFP fibrosis occurring in KOA and after knee joint surgery.

Therapeutic effect of C-type natriuretic peptide on persistent pain in a rat knee arthritis model.

Intra-articular injection of C-type natriuretic peptide (CNP) at the acute inflammatory stage suppressed fibrotic changes in the infrapatellar fat pad (IFP), articular cartilage degeneration, and persistent pain in a monoiodoacetic acid (MIA)-induced rat knee arthritis model. In this study, we administered CNP during the inflammation subsiding period to evaluate CNP effectiveness in knees with osteoarthritis (OA) pathology. 20male Wistar rats were randomly divided into two groups. The rats received an intra-articular injection of MIA solution in the right knee to induce inflammation-induced joint degeneration. One group subsequently received an intra-articular CNP injection for six consecutive days from day 8, whereas another group received vehicle solution. Pain avoidance behavior tests and histological analyses were conducted to examine the therapeutic effects of CNP. The incapacitance test indicated that the percent weight on the ipsilateral limb decreased after MIA injection by day 4 and continued to decrease until the end of the experiment in the vehicle group, suggesting persistent pain in the knee. Intra-articular injection of CNP reversed the weight-bearing ratio on day 19. Histological evaluation showed that the CNP group had more residual fat tissue in the IFP and fewer calcitonin gene-related peptide-positive nerve endings compared to the vehicle group. CNP could not reverse articular cartilage degeneration. Intra-articular injection of CNP after the IFP fibrosis onset had no significant effect on OA severity and extent. Nevertheless, CNP might be utilized therapeutically for OA treatment since it can alleviate persistent knee pain and inhibit structural changes in residual fat tissue.

413 Role of calcitonin gene-related peptide in atopic dermatitis

Atopic dermatitis (AD) is an often severely pruritic chronic inflammatory disease often worsened by psychological stress. Calcitonin gene-related peptide (CGRP) is a sensory neuropeptide, which may cause pruritus. Earlier studies indicate a special pathogenetic role for CGRP in AD. However, somewhat contradictory results regarding CGRP positive nerve fibers in AD skin, have been reported. We have studied skin biopsies from 26 patients with AD. The biopsies were taken from lesional and non-lesional skin, in addition, normal skin biopsies from 10 healthy individuals were investigated for expression of CGRP, using a biotinylated–streptavidine technique and fluorescence microscopy.

Effect of moxibustion on colonic mucosal injury and expression of CGRP positive nerve fibers of distal colonic mucosa in ulcerative colitis mice

To observe the effect of moxibustion at "Zusanli" (ST 36) on distal, middle and proximal colonic mucosal injury and expression of calcitonin gene-related peptide (CGRP) positive nerve fibers of distal colonic mucosa in ulcerative colitis (UC) mice at different time points. A total of 51 C57BL/6N mice were randomized into a 7-day control group (n=8), a 7-day model group (n=7), a 7-day moxibustion group (n=7), a 14-day control group (n=6), a 14-day model group (n=14) and a 14-day moxibustion group (n=9). In the model groups and the moxibustion groups, 2% dextran sulfate sodium (DSS) was given for 7-day free drinking to establish the UC model. Three days into modeling, moxibustion was applied at "Zusanli" (ST 36) in the 7-day moxibustion group and the 14-day moxibustion group, once a day, 10 min a time for 5 days and 12 days respectively. HE staining was used to observe the morphology of colonic tissue, the percentages of distal, middle and proximal colonic mucosal injury were calculated. Immunofluorescence staining was used to detected the expressions of positive nerve fibers of distal, middle and proximal colonic mucosa and CGRP positive nerve fibers of distal colonic mucosa. Mucosal injury can be observed in mice after modeling, displaying epithelial layer disappearance, abnormal crypt structure or crypt disappearance. Compared with the 7-day control group, colon length was shortened (P<0.001), percentages of overall, distal, middle colonic mucosal injury were increased (P<0.001), the expressions of positive nerve fibers of distal, middle and proximal colonic mucosa and CGRP positive nerve fibers of distal colonic mucosa were increased (P<0.001, P<0.05, P<0.01) in the 7-day model group. Compared with the 7-day model group, the expressions of positive nerve fibers of middle and distal colonic mucosa and CGRP positive nerve fibers of distal colonic mucosa were decreased in the 7-day moxibustion group (P<0.05). Compared with the 14-day control group, the colon length was shortened (P<0.01), percentage of overall colonic mucosal injury was increased (P<0.001) in the 14-day model group. Compared with the 14-day model group, colon length was lengthened (P<0.05), percentage of overall colonic mucosal injury was decreased (P<0.05) in the 14-day moxibustion group. Moxibustion at "Zusanli" (ST 36) can reduce the expressions of positive nerve fibers of colonic mucosa and CGRP positive nerve fibers of distal colonic mucosa, thus, improve the colonic mucosal injury.

Esophageal Mucosa Innervation in Children With Nonerosive Reflux Disease.

Esophageal mucosa innervation in adults with nonerosive reflux disease (NERD) is more superficial compared with healthy volunteers. We delineated the esophageal mucosal innervation in pediatric NERD and controls. Distal and proximal pediatric esophageal biopsies were immunohistochemically stained with calcitonin gene-related peptide and transient receptor potential cation channel subfamily V member 1. Mucosal innervation was assessed in 18 controls (9M:9F, median age: 9 years) and 11 NERD patients (6M:5F, median age: 5 years). Calcitonin gene-related peptide positive nerve fibers were lying deep in the mucosa in both groups, P > 0.05 and did not coexpress transient receptor potential cation channel subfamily V member 1. The pediatric esophageal mucosa in NERD displays deep lying nerve fibers, in contrast to adults.

Cutaneous neurogenic inflammation in the sensitized acupoints induced by gastric mucosal injury in rats

BackgroundIn acupuncture practice, the most important step is to confirm the location of a sensitized acupoint which reflects a diagnosis and can be stimulated with a specialized needle to treat the disease. Abnormal symptoms such as hyperalgesia or allodynia at the sensitized acupoints in patients with visceral disorders are considered to be in relation with referred pain and neurogenic inflammation. Yet, limited study has investigated the cutaneous neurochemical changes of the sensitized acuponits.MethodsThe resent study developed an animal model of gastric mucosal injury (GMI) by HCl administered into the stomach of the rats. Evans Blue (EB) dye was applied by injection of tail vein after mucosal damage to observe the neurogenic plasma extravasation dots in the skin of the rats. The EB dots extravagated in the skin were compared with locations of acupoints. Immnohistochemistry analysis was used to detect the expression of calcitonin gene-related peptide (CGRP)- or substance P (SP)-labeled nerve fibers, histamine (HA)-, serotonin (5-HT)-, and tryptase-labeled cells in EB dots. Images were recorded and analyzed by Confocal imaging system and Olympus Image Processing Software.ResultsThe results showed that GMI resulted in neurogenic plasma extravasation in the skin of the acupoints over the back and abdomen, which mostly occurred in the T9-11 dermatomere. The EB extravasation dots appeared after GMI and disappeared gradually during the natural self-recovery of the gastric mucosa. More SP and CGRP positive nerve fibers were distributed in EB dots than that in regions beside EB dots and in the control, mostly distributed in the nerve fibers around both the vessels and root of hair follicle. Mast cells also aggregated and degranulated to release algogenic substances of 5-HT and HA around the vessels in areas of the EB dots.ConclusionsOur results indicates that the mechanism of EB extravasation in the skin of the acupoints induced by GMI are closely related to neurogenic inflammation, and that the high expression of local allergic substances and nociceptive neuropeptides in the local skin including SP, CGRP, HA, 5-HT, and mast cell tryptase may be the underlying mechanism of the acupoint sensitization.

Pathogenesis of prurigo nodularis

Prurigo nodularis is a chronic reaction pattern associated with severe pruritus that markedly affects the quality of life in patients. The pathogenesis of prurigo nodularis is not completely clear. Patients have an increased number of substance P and calcitonin gene-related peptide positive nerves in the dermis. Eosinophils and mast cells are in close vicinity to peripheral nerves and increased in numbers in the inflammatory infiltrate in prurigo nodularis. Nerve growth factor (NGF) is increased in lesional skin of patients and can be released by mast cells and eosinophils. In addition, NGF modulates the functional activity of mast cells and eosinophils. Recently, higher levels of the novel pruritic cytokine IL-31 were found in the skin of patients with prurigo nodularis than other pruritic skin diseases. The pathogenesis of prurigo nodularis seems to be regulated by immunological and neuronal plasticity which will be highlighted in the current article.

Recovery of Corneal Sensitivity, Calcitonin Gene-Related Peptide–Positive Nerves, and Increased Wound Healing Induced by Pigment Epithelial–Derived Factor Plus Docosahexaenoic Acid After Experimental Surgery

To assess function of regenerated corneal nerves in correlation with epithelial wound healing after experimental nerve damage in rabbits treated with pigment epithelial-derived factor (PEDF) plus docosahexaenoic acid (DHA). An 8-mm stromal dissection was performed in the right eyes of adult New Zealand rabbits. Treatment with PEDF+DHA was for 6 weeks. Corneal sensation was measured weekly by Cochet-Bonnet esthesiometer. After 8 weeks, immunofluorescence with βIII-tubulin, calcitonin gene-related peptide, and substance P antibodies was performed to quantify nerves. Also, rabbits were treated with PEDF+DHA for 4 weeks after lamellar keratectomy, followed by 8-mm epithelial debridement and epithelial defect assessment. One week after surgery, corneas were stained with anti-Ki67 antibody to assess cell proliferation. Eight weeks after surgery, calcitonin gene-related peptide-positive nerve fibers in the PEDF+DHA group were similar to normal rabbit corneas but were decreased in the vehicle. Substance P was localized in the subepithelial plexus but appeared in epithelial cells after nerve injury regardless of treatment. Five weeks after surgery, an increase in corneal sensitivity occurred in the PEDF+DHA group and reached normal values by 8 weeks. Pigment epithelial-derived factor plus DHA increased epithelial wound healing after lamellar keratectomy. One week after epithelial injury, Ki67-positive cells increased in the limbal area. Pigment epithelial-derived factor plus DHA promotes regeneration of calcitonin gene-related peptide-positive corneal nerves, accelerating wound healing and return of corneal sensitivity. Pigment epithelial-derived factor plus DHA represents a new approach to regenerate nerves and a potential treatment for prevention of severe dry eye after surgery or diseases of the ocular surface.

Neuroimmune mechanisms in patients with atopic dermatitis during chronic stress

ObjectiveTo identify pathoaetiological neuroimmune mechanisms in patients with atopic dermatitis (AD) and chronic stress, focusing at nerve density, sensory neuropeptides, and the serotonergic system.MethodsEleven patients with AD with histories of stress worsening were included. Biopsies from involved and non-involved skin were processed for immunohistochemistry. Salivary cortisol test was done as a marker for chronic stress.ResultsThere were more acanthosis and fewer nerve fibres in epidermis and papillary dermis of involved compared with non-involved skin. Whereas there was no significant change in the number of substance P and calcitonin gene-related peptide–positive nerve fibres between the involved and non-involved skin, there was an increase in the epidermal fraction of 5-hydroxtrytamine 1A (5-HT1A) receptor and serotonin transporter protein (SERT) immunoreactivity in the involved skin. The number of 5-HT2AR, CD3-positive cells, and SERT-positive cells, most of them being CD3 positive, was increased in involved skin. There was an increase in mast cells in the involved skin, and these cells were often located close to the basement membrane. There was a strong tendency to a correlation between 5-HT2AR positive cells in the papillary dermis of involved skin and low cortisol ratios, being an indicator of chronic stress.ConclusionA changed innervation and modulation of the serotonergic system are indicated in chronic atopic eczema also during chronic stress.

Cardiac Nociception

Cardiac Nociception

Upregulation of the Axonal Growth and the Expression of Substance P and its NK1 Receptor in Human Allergic Contact Dermatitis

Nerve fibers and sensory neuropeptides substance P and calcitonin gene-related peptide (CGRP) have been reported to be involved in allergic contact dermatitis (ACD). In the present study, we investigated the general innervation (using antibody against protein gene product 9.5, PGP 9.5), axonal growth (using antibody against growth associated protein, GAP-43), CGRP, and substance P with its receptor neurokinin 1 (NK1), in positive epicutaneous reactions to nickel sulphate from nickel-allergic patients, at the peak of inflammation, 72 hr after challenge with the antigen. There was an increased (p < 0.01) number of GAP-43 positive fibers in the eczematous compared with control skin, indicating an increased axonal growth already at 72 hr postchallenge. Double staining revealed a coexpression of CGRP and GAP-43 on dermal nerve fibers. There was no difference in the number of substance P and CGRP positive nerve fibers between eczematous and control skin. However, semiquantification analyses showed an increased expression of substance P positive inflammatory cells, being CD3, CD4, or CD8 positive, and NK1R positive inflammatory cells, being tryptase or CD3 positive. These results indicate a contribution of regenerating nerve fibers and substance P to the contact allergic reaction.

Increase in sensory neuropeptides surrounding the Achilles tendon in rats with adjuvant arthritis

The Achilles tendon in rats with adjuvant arthritis was analyzed by radioimmunoassay (RIA) and semi-quantitative immunohistochemistry for the occurrence of two sensory neuropeptides, substance P (SP) and calcitonin gene related peptide (CGRP), and a sensory modulating peptide, galanin (GAL). The tissue concentration of SP and CGRP in the Achilles tendon and its envelope, i.e. the paratenon and bony insertion, as assessed by RIA was increased by 22% and 71%, respectively, compared to normal controls, whereas the level of GAL was unchanged. Semi-quantitative immunohistochemistry applied to different regions of the tendon in arthritic rats disclosed an increased occurrence of SP and CGRP positive nerve fibers in the paratenon and bone tendinous junction, whereas GAL fibers were only increased at the bone tendinous junction. Notably, neither neuropeptides nor inflammatory cells were seen in the tendon proper. The increased occurrence of SP and CGRP in the tendon envelope presumably reflects inflammatory actions, whereas that of GAL implies an endogenous anti-inflammatory response. The observed SP and CGRP upregulation in the paratenon and bony insertion suggests a pathophysiological role in paratenonitis and enthesitis often seen in patients with rheumatoid arthritis. Presumably Achillodynia originates in the tendon envelope rather than the tendon proper. The observations could be used to define new pharmacological targets for mitigating symptoms from tendons in rheumatoid arthritis and possibly also in other disorders. Whether a neuronal pathogenic mechanism underlies tendon overuse disorders in non-arthritic tendinopathies and the development of degeneration, i.e. tendinosis, remains to be studied.

Sensory hypoinnervation in club foot

We have compared the density of nerve fibres in the synovium in club foot with that of specimens obtained from the synovium of the hip at operations for developmental dysplasia. The study focused on the sensory neuropeptides substance P; calcitonin gene-related peptide; protein gene product 9.5, a general marker for mature peripheral nerve fibres; and growth associated protein 43, a neuronal marker for new or regenerating nerve fibres. In order to establish whether there might be any inherent difference we analysed the density of calcitonin gene-related peptide-positive nerve fibres in the hip and ankle joints in young rats. Semi-quantitative analysis showed a significant reduction in the number of sensory and mature nerve fibres in the synovium in club foot compared with the control hips. Calcitonin gene-related peptide (CGRP) positive fibres were reduced by 28%, substance P-positive fibres by 36% and protein gene product 9.5-positive fibres by 52% in club foot. The growth associated protein 43-positive fibres also seemed to be less in six samples of club foot. No difference in the density of CGRP-positive nerve fibres was observed in the synovium between ankle and hip joints in rats. The lack of sensory input may be responsible for the fibrosis and soft-tissue contractures associated with idiopathic club foot.

Sensory innervation of normal and hypospadiac prepuce: possible implications in hypospadiology.

Sensory innervation of the skin influences wound healing through the release of neuropeptides from the nerve endings. The purpose of this study was to investigate the differences in the sensory innervation of the normal and the hypospadiac prepuce. The prepuce from 10 healthy children undergoing routine circumcision and 10 age-matched children undergoing hypospadias repair were submitted for immunohistochemistry, using antibodies against protein gene product (PGP) 9.5, calcitonin gene-related peptide (CGRP), and substance P (SP). The hypospadiac prepuce was found to be hypo-innervated for PGP 9.5 and CGRP positive nerves when compared with the normal prepuce ( p<0.05). The number of SP-positive nerves were increased in the hypospadiac prepuce, but not to statistical significance ( p=0.06, confidence interval >95%). There may be differences in the sensory innervation of the normal and hypospadiac prepuce. These differences in tissue environment may partly explain the postoperative edema, poor wound healing leading to urethrocutaneous fistula (UF), and increased analgesia requirements in patients undergoing hypospadias surgery.

Normal perivascular sensory dilator nerve function in arteries of Zucker diabetic fatty rats

Background Type II diabetes in humans is associated with pathology of both the cardiovascular and peripheral sensory nervous systems. Because abnormal vasodilator responses have been reported in animals of type II diabetes and perivascular sensory nerves are a source of vasodilator substances, we tested the hypothesis that sensory nerve-dependent relaxation is abnormal in arteries of the Zucker diabetic fatty (ZDF) rat model of type II diabetes. Methods The ZDF rats and genetic controls were studied at 26 weeks of age. Tail-cuff systolic blood pressure (BP) was measured, serum was obtained for chemical determinations, and mesenteric branch arteries were isolated for wire myograph analysis and confocal-based measurement of calcitonin gene-related peptide (CGRP) positive nerve density. Results No differences in BP were detected. Serum glucose, triglycerides, and cholesterol were significantly elevated in ZDF. Sensory nerve-dependent vasodilation was assessed by measuring relaxation of phenylephrine preconstricted arterial segments to cumulative addition of divalent calcium ion (Ca 2+) or capsaicin. Neither Ca 2+- nor capsaicin-induced relaxation were different in ZDF versus control (maximal ZDF response to Ca 2+ = 64% ± 2% v 59% ± 4%; ED 50 for Ca 2+ = 3.7 ± 0.5 mmol/L v 3.2 ± 0.5 mmol/L; n = 5, P = not significant [NS]; maximal ZDF response to capsaicin = 68% ± 9% v 74% ± 4%; ZDF ED 50 = 3.8 ± 0.5 nmol/L v 9.8 ± 7 nmol/L; n = 5, P = NS). In contrast, the maximal relaxation response to acetylcholine was impaired in ZDF (maximal ZDF response = 83% ± 5% v 94% ± 2%, n = 4, P = .039; ED 50 for acetylcholine = 8.1 ± 2.9 nmol/L for ZDF v 33.5 ± 18.2; n = 4 per group, P = .086). The CGRP positive nerve density was not different between groups. Conclusions Blood pressure, perivascular sensory nerve CGRP content, and dilator function is normal in the ZDF model of type II diabetes, whereas endothelium-dependent relaxation is impaired.

Combinatorial expression patterns of the connexins 26, 32, and 43 during development, homeostasis, and regeneration of rat teeth.

Gap junctions permit the exchange of regulatory molecules between cells and play important roles during organogenesis. The expression pattern of the gap junction proteins connexin 26, 32, and 43 was studied by immunohistochemistry in the developing, adult, and injured rat teeth. Connexins 32 and 43, but not the connexin 26, were detected during the late stages of embryonic tooth development (bell stage). Expression of connexin 32 was predominant in epithelial cells, whereas connexin 43 was more widely distributed and found in both epithelial and mesenchymal cells. During cytodifferentiation (early postnatal stages), both connexin 32 and 43 were expressed in the epithelial-derived ameloblasts, synthesizing and secreting the enamel matrix proteins. In mesenchyme, connexin 32 was observed only in differentiating odontoblasts, while connexin 43 was expressed in both differentiating and functional odontoblasts, which secrete the dentin matrix. In adult rat teeth, connexin 26 and 43 were expressed in the odontoblastic layer at low and high levels, respectively, while connexin 32 was absent from odontoblasts. Electron microscopy showed that connexin 43 was distributed exclusively at sites of contacts between odontoblasts. However, double immunostaining combined with confocal microscopy suggested an occasional overlap between odontoblasts and calcitonin gene-related peptide-positive nerve fibers. Denervation experiments showed that the expression of connexins in dental pulp was independent of innervation, whereas in injured teeth connexin 43 was upregulated in pulpal fibroblasts. Finally, cultured dental epithelial cells expressed both connexin 32 and 43, and connexin 43 was detected in cultured pulp fibroblasts in vitro, thus mimicking the in vivo distribution pattern of connexins. These results demonstrate that connexins are involved in tooth development and suggest that a given connexin may have distinct roles during odontogenesis and tooth homeostasis.

Peptidergic innervation of the human prostate, seminal vesicle and vas deferens.

Neuropeptidergic innervation of the human prostate, seminal vesicle and vas deferens was investigated by immunohistochemical methods. The innervation pattern of all organs was very dense. Neuropeptide Y- and tyrosine hydroxylase-positive nerve fibers were most abundant and localized mainly in the smooth muscle layer. On the contrary, vasoactive intestinal polypeptide-positive nerve fibers were mainly found beneath the epithelium. Also leu-enkephaline-, peptide histidine isoleusine- and calcitonin gene-related peptide-positive nerve fibers could be observed in all organs, but somatostatin-positive nerves only in the prostate and seminal vesicle and met-enkephalin- and substance P-positive nerves only in the prostate.

The Role of Calcitonin Gene-Related Peptide in the Mouse Thymus Revisited

Calcitonin gene-related peptide has been identified by immunocytochemistry within the thymus of fetal through aged adult mice. Calcitonin gene-related peptide positive nerves are observed from embryonic day 17 throughout the lifespan of the mouse. A sparse cell population positive for CGRP is first observed during the late embryonic period at the corticomedullary boundary and the medulla, and it becomes more densely distributed in this region in the adult. In the thymus of the aged mouse the number of CGRP-positive cells diminishes. Pharmacologic studies demonstrated that fresh thymocytes display a receptor Kd for CGRP of 1.17 +/- 0.06 x 10(-10)M and a Bmax of 12.7 +/- 4.7 fmol/mg protein. Functional studies indicate that CGRP is a potent inhibitor of mitogen and antigen-stimulated proliferation of T cells and that it inhibits IL-2 production in cloned splenic T cells. Recent studies suggest that endogenous CGRP may serve as a natural inhibitor of inappropriate induction of mature, antigen-sensitive cells in the thymus as well as play a role in thymocyte education. These findings are discussed in terms of the distribution of CGRP cells and nerve terminals within the thymus and their relationship to positive and negative selection of the T-cell repertoire.

The role of calcitonin gene-related peptide in the mouse thymus revisited.

Calcitonin gene-related peptide has been identified by immunocytochemistry within the thymus of fetal through aged adult mice. Calcitonin gene-related peptide positive nerves are observed from embryonic day 17 throughout the lifespan of the mouse. A sparse cell population positive for CGRP is first observed during the late embryonic period at the corticomedullary boundary and the medulla, and it becomes more densely distributed in this region in the adult. In the thymus of the aged mouse the number of CGRP-positive cells diminishes. Pharmacologic studies demonstrated that fresh thymocytes display a receptor Kd for CGRP of 1.17 +/- 0.06 x 10(-10)M and a Bmax of 12.7 +/- 4.7 fmol/mg protein. Functional studies indicate that CGRP is a potent inhibitor of mitogen and antigen-stimulated proliferation of T cells and that it inhibits IL-2 production in cloned splenic T cells. Recent studies suggest that endogenous CGRP may serve as a natural inhibitor of inappropriate induction of mature, antigen-sensitive cells in the thymus as well as play a role in thymocyte education. These findings are discussed in terms of the distribution of CGRP cells and nerve terminals within the thymus and their relationship to positive and negative selection of the T-cell repertoire.