Localization of the calcitonin gene-related peptide receptor complex at the vertebrate neuromuscular junction and its role in regulating acetylcholinesterase expression

Toxic effects of subacute exposure to acrylamide on motor endplates of the gastrocnemius in rats

Acrylamide (ACR) is a recognized toxin that is known to induce neurotoxicity in humans and experimental animals. This study aimed to investigate the toxic effects of subacute exposure of the motor endplate (MEP) of the gastrocnemius in rats to ACR. All rats were randomly divided into control, 9, 18, and 36 mg/kg ACR groups, and ACR was administered by gastric gavage for 21 days. The behavioral tests were performed weekly. On the 22nd day, the wet weight of the gastrocnemius was measured. The changes in muscle fiber structure, nerve endings, and MEP in the gastrocnemius were examined by hematoxylin-eosin (HE) and gold chloride staining. Acetylcholinesterase (AChE) content in the gastrocnemius was detected by AChE staining. The expression of AChE and calcitonin gene-related peptide was detected by immunohistochemistry and western blot. Rats exposed to ACR showed a significant increase in gait scores and hind limb splay distance compared with the control group, and the wet weight of the gastrocnemius was reduced, HE staining showed that the muscle fiber structure of the gastrocnemius became thin and the arrangement was dense with nuclear aggregation, gold chloride staining showed that nerve branches decreased and became thin, nerve fibers became short and light, the number of MEPs was decreased, the staining became light, and the structure was not clear. AChE staining showed that the number of MEPs was significantly reduced after exposure to ACR, the shape became small, and the AChE content decreased in a dose-dependent manner. Immunohistochemistry and western blot analysis results of the expression levels of AChE and CGRP showed a decreasing trend as compared to the control group with increasing ACR exposure dose. The reduction in protein levels may be the mechanism by which ACR has a toxic effect on the MEP in the gastrocnemius of rats.

High-flow oxygen and pro-serotonin agents for non-interventional treatment of post-dural-puncture headache

OBJECTIVE

Post dural puncture headache (PDPH) is a common complication in patients following diagnostic or therapeutic lumbar puncture, procedures requiring epidural access, and spinal surgery. Epidural blood patch (EBP), the gold standard for the treatment of this pathology requires training not provided to emergency physicians. In addition, the presence of concomitant pathology and abnormal laboratory values are contraindications to perform EBP. In presence of these limitations, we sought for a non-interventional management of PDPH utilizing high-flow oxygen and pro-serotonin agents. We reviewed the mechanism of action of this therapy METHODS: To illustrate our proposal, we report a series of twelve consecutive patients with PDPH treated with high-flow oxygen therapy at 12 L/min via a non-rebreathing mask and intravenous metoclopramide.

RESULTS

All patients were treated with this conservative therapy, no adverse reactions were observed. After the intervention, the headache resolved without further indications for PDPH.

CONCLUSION

Our series suggests that combining high-flow oxygen and pro-serotonin agents such metoclopramide in the ED might be a feasible option as effective as the invasive methods used in treating PDPH. This therapy appears to be efficient and to minimize risk, cost and side effects. It presents an easily accessible alternative that should be considered when PDPH is not a viable option.

Muscle gene expression of CGRP-α, CGRP receptor, nAchR-β, and GDNF in response to different endurance training protocols of Wistar rats

The neuromuscular junction underwent adaptations to meet the demands of muscles following increased muscle activity. This study aimed to investigate the effects of high-intensity interval training (HIIT), endurance training (END), and mixed interval training (MIX) on the gene expression of the calcitonin gene-related peptide-α (CGRP-α), CGRP receptor, nicotinic acetylcholine receptors (nAchR)-β and glial-derived neurotrophic factor (GDNF) among different muscle types. Male Wistar rats were randomly divided into four groups: Control (n = 8), END (n = 8), HIIT (n = 8), and MIX (n = 8). The animals run each training protocol for 8 weeks (five sessions/week). Forty-eight hours after the last training session, the muscles gastrocnemius and soleus were excised under the sterilized situation. After collection, the material was prepared for RNA extraction, Reverse Transcriptase reaction, and qPCR assay. The HIIT training up-regulated the CGRP-α (p < 0.01), CGRP-Rec (p < 0.01), and GDNF (p < 0.01) in soleus as well as the nAchR-β (p < 0.01) and GDNF (p < 0.01) in gastrocnemius muscles. END training down-regulated the gene expression of CGRP-α (p < 0.01), and nAchR-β (p < 0.01) in gastrocnemius but up-regulated nAchR-β (p = 0.037) in soleus and GDNF (p  < 0.01) in gastrocnemius muscles. MIX training did not show any significant up or down-regulation. The endurance performance of HIIT and MIX groups was higher than the END group (p < 0.01). All studied genes up-regulated by HIIT training in a muscle type-specific manner. It seems that the improvement of some synaptic indices induced by HIIT resulted in the improvement of endurance performance.

Serum Calcitonin Gene-Related Peptide and Receptor Protein Levels in Patients With Fibromyalgia Syndrome: A Cross-Sectional Study

Objectives

This study aims to compare the serum calcitonin gene-related peptide (CGRP) and CGRP receptor protein levels between patients with fibromyalgia syndrome (FM) and healthy control subjects.

Patients and methods

The study included 88 patients (7 males, 81 females; mean age 44.5±9.1 years; range, 20 to 72 years) newly-diagnosed with FM according to the 2010 American College of Rheumatology criteria and 88 healthy volunteers (6 males, 82 females; mean age 43.0±6.1 years; range, 20 to 57 years). Venous blood samples were collected from both groups for the measurement of the levels of serum CGRP and CGRP receptor proteins (receptor component protein [RCP], receptor activity modifying protein 1 [RAMP 1] and calcitonin receptor-like receptor [CLR]).

Results

A comparison of the serum CGRP, CLR and RCP levels of the FM and control groups revealed a statistically significant difference (p=0.001, p=0.005, p=0.001, respectively). The difference between the groups in respect of the serum RAMP 1 levels was not statistically significant (p=0.107).

Conclusion

The serum CGRP, CLR and RCP levels were found to be higher in the FM patients, but no difference was determined between the FM patients and the healthy control group in respect of the RAMP 1 level. These results can be of guidance for further clinical studies of the etiopathogenesis and treatment of FM.

Ryanodine- and CaMKII-dependent release of endogenous CGRP induces an increase in acetylcholine quantal size in neuromuscular junctions of mice

OBJECTIVE

The aim of this study was to identify the mechanism responsible for an increase in miniature endplate potentials (MEPPs) amplitude, induced by ryanodine as an agonist of ryanodine receptors in mouse motor nerve terminals.

METHODS

Using intracellular microelectrode recordings of MEPPs and evoked endplate potentials (EPPs), the changes in spontaneous and evoked acetylcholine release in motor synapses of mouse diaphragm neuromuscular preparations were studied.

RESULTS

Ryanodine (0.1 μM) increased both the amplitudes of MEPPs and EPPs to a similar extent (up to 130% compared to control). The ryanodine effect was prevented by blockage of receptors of calcitonin gene-related peptide (CGRP) by a truncated peptide CGRP_8-37 . Endogenous CGRP is stored in large dense-core vesicles in motor nerve terminals and may be released as a co-transmitter. The ryanodine-induced increase in MEPPs amplitude may be fully prevented by inhibition of vesicular acetylcholine transporter by vesamicol or by blocking the activity of protein kinase A with H-89, suggesting that endogenous CGRP is released in response to the activation of ryanodine receptors. Activation of CGRP receptors can, in turn, upregulate the loading of acetylcholine into synaptic vesicles, which will increase the quantal size. This new feature of endogenous CGRP activity looks similar to recently described action of exogenous CGRP in motor synapses of mice. The ryanodine effect was prevented by inhibitors of Ca/Calmodulin-dependent kinase II (CaMKII) KN-62 or KN-93. Inhibition of CaMKII did not prevent the increase in MEPPs amplitude, which was caused by exogenous CGRP.

CONCLUSIONS

We propose that the activity of presynaptic CaMKII is necessary for the ryanodine-stimulated release of endogenous CGRP from motor nerve terminals, but CaMKII does not participate in signaling downstream the activation of CGRP-receptors followed by quantal size increase.

Biochemical, Anatomical, and Pharmacological Characterization of Calcitonin-Type Neuropeptides in Starfish: Discovery of an Ancient Role as Muscle Relaxants

Calcitonin (CT) is a peptide hormone released by the thyroid gland that regulates blood Ca²⁺ levels in mammals. The CT gene is alternatively spliced, with one transcript encoding CT and another transcript encoding the CT-like neuropeptide calcitonin-gene related peptide (α-CGRP), which is a powerful vasodilator. Other CT-related peptides in vertebrates include adrenomedullin, amylin, and intermedin, which also act as smooth muscle relaxants. The evolutionary origin of CT-type peptides has been traced to the bilaterian common ancestor of protostomes and deuterostomes and a CT-like peptide (DH31) has been identified as a diuretic hormone in some insect species. However, little is known about the physiological roles of CT-type peptides in other invertebrates. Here we characterized a CT-type neuropeptide in a deuterostomian invertebrate—the starfish Asterias rubens (Phylum Echinodermata). A CT-type precursor cDNA (ArCTP) was sequenced and the predicted structure of the peptide (ArCT) derived from ArCTP was confirmed using mass spectrometry. The distribution of ArCTP mRNA and the ArCT peptide was investigated using in situ hybridization and immunohistochemistry, respectively, revealing stained cells/processes in the nervous system, digestive system, and muscular organs, including the apical muscle and tube feet. Investigation of the effects of synthetic ArCT on in vitro preparations of the apical muscle and tube feet revealed that it acts as a relaxant, causing dose-dependent reversal of acetylcholine-induced contraction. Furthermore, a muscle relaxant present in whole-animal extracts of another starfish species, Patiria pectinifera, was identified as an ortholog of ArCT and named PpCT. Consistent with the expression pattern of ArCTP in A. rubens, RT-qPCR revealed that in P. pectinifera the PpCT precursor transcript is more abundant in the radial nerve cords than in other tissues/organs analyzed. In conclusion, our findings indicate that the physiological action of CT-related peptides as muscle relaxants in vertebrates may reflect an evolutionarily ancient role of CT-type neuropeptides that can be traced back to the common ancestor of deuterostomes.

Comparison of the expression of neurotransmitter and muscular genesis markers in the postnatal male mouse masseter and trigeminal ganglion during development

Calcitonin gene-related peptide (CGRP) is released by motor neurons and affects skeletal muscle fiber and transient receptor potential cation channel subfamily V member 1 (TRPV1), an important marker of pain modulation. However, the expression of CGRP and TRPV1 in the trigeminal ganglion (TG) during changes and in feeding patterns has not been described. We used real-time reverse transcription polymerase chain reaction and in situ hybridization to investigate the mRNA expression levels of CGRP and TRPV1 in the TG. The expression of myosin heavy-chain (MyHC) isoforms was also investigated in the masseter muscle (MM) during the transition from sucking to mastication, an important functional trigger for muscle. The mRNA and protein levels of CGRP increased in the MM and TG from postnatal day 10 (P10) to P20 in male mice. The protein levels of TRPV1 were almost constant in the TG from P10 to P20, in contrast to increases in the MM. The mRNA abundance of TRPV1 in the TG and MM was increased from P10 to P20. The localization of an antisense probe was used to count CGRP cell numbers and found to differentiate the ophthalmic, maxillary, and mandibular nerve divisions of the TG. In particular, the number of CGRP⁺ cells per 10,000 μm² in the maxillary and mandibular divisions of the TG gradually changed from P10 to P20. The expression of CGRP and TRPV1 in the TG and MM and the patterns of expression of different MyHC isoforms were affected by changes in feeding during male mouse development.

CALCB splice region pathogenic variants leading to plasma cell neurotropic enrichment in type 1 autoimmune pancreatitis

Recently, we have demonstrated that PRSS1 mutations cause ectopic trypsinogen activation and thereby result in type 1 autoimmune pancreatitis (AIP). However, the molecules involved in inducing obliterative vasculitis and perineural inflammation in the pancreas are not well-described. The present study applied whole-exome sequencing (WES) to determine the underlying etiology and revealed novel missense splice region variants, CALCB c.88T>C (p.Ser30Pro) and IR [1]-mutants, in 2 of the 3 families and 2 of 26 unrelated patients with type 1 AIP. In vitro, both of the mutants displayed decreased βCGRP, ERK1/2 phosphorylation, and co-localized with endoplasmic reticulum and Golgi apparatus. The novel pathogenic variant identified in this case should contribute to our understanding of the expanding spectrum of AIP.

Calcitonin gene-related peptide inhibits autophagic-lysosomal proteolysis through cAMP/PKA signaling in rat skeletal muscles

Calcitonin gene-related peptide (CGRP) is a neuropeptide released by motor neuron in skeletal muscle and modulates the neuromuscular transmission by induction of synthesis and insertion of acetylcholine receptor on postsynaptic muscle membrane; however, its role in skeletal muscle protein metabolism remains unclear. We examined the in vitro and in vivo effects of CGRP on protein breakdown and signaling pathways in control skeletal muscles and muscles following denervation (DEN) in rats. In isolated muscles, CGRP (10(-10) to 10(-6)M) reduced basal and DEN-induced activation of overall proteolysis in a concentration-dependent manner. The in vitro anti-proteolytic effect of CGRP was completely abolished by CGRP8-37, a CGRP receptor antagonist. CGRP down-regulated the lysosomal proteolysis, the mRNA levels of LC3b, Gabarapl1 and cathepsin L and the protein content of LC3-II in control and denervated muscles. In parallel, CGRP elevated cAMP levels, stimulated PKA/CREB signaling and increased Foxo1 phosphorylation in both conditions. In denervated muscles and starved C2C12 cells, Rp-8-Br-cAMPs or PKI, two PKA inhibitors, completely abolished the inhibitory effect of CGRP on Foxo1, 3 and 4 and LC3 lipidation. A single injection of CGRP (100 μg kg(-1)) in denervated rats increased the phosphorylation levels of CREB and Akt, inhibited Foxo transcriptional activity, the LC3 lipidation as well as the mRNA levels of LC3b and cathepsin L, two bona fide targets of Foxo. This study shows for the first time that CGRP exerts a direct inhibitory action on autophagic-lysosomal proteolysis in control and denervated skeletal muscle by recruiting cAMP/PKA signaling, effects that are related to inhibition of Foxo activity and LC3 lipidation.

Targeting CGRP: A New Era for Migraine Treatment

Migraine is a highly prevalent headache disease that typically affects patients during their most productive years. Despite significant progress in understanding the underlying pathophysiology of this disorder, its treatment so far continues to depend on drugs that, in their majority, were not specifically designed for this purpose. The neuropeptide calcitonin gene-related peptide (CGRP) has been indicated as playing a critical role in the central and peripheral pathways leading to a migraine attack. It is not surprising that drugs designed to specifically block its action are gaining remarkable attention from researchers in the field with, at least so far, a safe risk profile. In this article, we highlight the evolution from older traditional treatments to the innovative CGRP target drugs that are revolutionizing the way to approach this debilitating neurological disease. We provide a brief introduction on pathophysiology of migraine and details on the characteristic, function, and localization of CGRP to then focus on CGRP receptor antagonists (CGRP-RAs) and CGRP monoclonal antibodies (CGRP mAbs).

Calcitonin gene related peptide gene polymorphism in migraine patients

OBJECTIVE

Calcitonin gene related peptide (CGRP), which has a vasodilator effect, is held responsible for neurogenic inflammation and vasodilatation of the cranial vessels in migraine pathophysiology. In this study, we investigated the association between alpha CGRP gene polymorphism (CALCA T-692C) and migraine.

MATERIAL AND METHODS

One hundred and thirty-four female migraineurs and 96 healthy female cases were enrolled in the study. The patient group was further subdivided into migraine with and without aura groups. The CALCA T-692C gene polymorphism was identified using polymerase chain reaction (PCR) technique and restriction fragment length polymorphism (RFLP).

RESULTS

The genotype and allele frequencies of CALCA T-692C gene polymorphism did not differ between the migraine and control groups. Between the migraine with and without aura subgroups, there was no difference. No association was seen between the CALCA T-692C gene polymorphisms and migraine attack severity and frequency.

CONCLUSION

Our study did not show any association between CALCA T-692C gene polymorphism and migraine.

Direct interactions between calcitonin-like receptor (CLR) and CGRP-receptor component protein (RCP) regulate CGRP receptor signaling

Calcitonin gene-related peptide (CGRP) is a neuropeptide with multiple neuroendocrine roles, including vasodilation, migraine, and pain. The receptor for CGRP is a G protein-coupled receptor (GPCR) that requires three proteins for function. CGRP binds to a heterodimer composed of the GPCR calcitonin-like receptor (CLR) and receptor activity-modifying protein (RAMP1), a single transmembrane protein required for pharmacological specificity and trafficking of the CLR/RAMP1 complex to the cell surface. In addition, the CLR/RAMP1 complex requires a third protein named CGRP-receptor component protein (RCP) for signaling. Previous studies have demonstrated that depletion of RCP from cells inhibits CLR signaling, and in vivo studies have demonstrated that expression of RCP correlates with CLR signaling and CGRP efficacy. It is not known whether RCP interacts directly with CLR to exert its effect. The current studies identified a direct interaction between RCP and an intracellular domain of CLR using yeast two-hybrid analysis and coimmunoprecipitation. When this interacting domain of CLR was expressed as a soluble fusion protein, it coimmunoprecipitated with RCP and inhibited signaling from endogenous CLR. Expression of this dominant-negative domain of CLR did not significantly inhibit trafficking of CLR to the cell surface, and thus RCP may not have a chaperone function for CLR. Instead, RCP may regulate CLR signaling in the cell membrane, and direct interaction between RCP and CLR is required for CLR activation. To date, RCP has been found to interact only with CLR and represents a novel neuroendocrine regulatory step in GPCR signaling.

The lumbrical muscle: a novel in situ system to evaluate adult skeletal muscle proteolysis and anticatabolic drugs for therapeutic purposes

The molecular regulation of skeletal muscle proteolysis and the pharmacological screening of anticatabolic drugs have been addressed by measuring tyrosine release from prepubertal rat skeletal muscles, which are thin enough to allow adequate in vitro diffusion of oxygen and substrates. However, the use of muscle at accelerated prepubertal growth has limited the analysis of adult muscle proteolysis or that associated with aging and neurodegenerative diseases. Here we established the adult rat lumbrical muscle (4/hindpaw; 8/rat) as a new in situ experimental model for dynamic measurement of skeletal muscle proteolysis. By incubating lumbrical muscles attached to their individual metatarsal bones in Tyrode solution, we showed that the muscle proteolysis rate of adult and aged rats (3-4 to 24 mo old) is 45-25% of that in prepubertal animals (1 mo old), which makes questionable the usual extrapolation of proteolysis from prepubertal to adult/senile muscles. While acute mechanical injury or 1- to 7-day denervation increased tyrosine release from adult lumbrical muscle by up to 60%, it was reduced by 20-28% after 2-h incubation with β-adrenoceptor agonists, forskolin or phosphodiesterase inhibitor IBMX. Using inhibitors of 26S-proteasome (MG132), lysosome (methylamine), or calpain (E64/leupeptin) systems, we showed that ubiquitin-proteasome is accountable for 40-50% of total lumbrical proteolysis of adult, middle-aged, and aged rats. In conclusion, the lumbrical model allows the analysis of muscle proteolysis rate from prepubertal to senile rats. By permitting eight simultaneous matched measurements per rat, the new model improves similar protocols performed in paired extensor digitorum longus (EDL) muscles from prepubertal rats, optimizing the pharmacological screening of drugs for anticatabolic purposes.

Differential roles of calcitonin family peptides in the dendrite formation and spinogenesis of the cerebral cortex in vitro

We examined roles of calcitonin family peptides in the initial stages of dendrite formation and the maturation of dendritic spines in the rat cerebral cortex in vitro. Embryonic day 18 cortical neurons were dissociated and cultured for 2-3days in the presence of calcitonin gene-related peptide (CGRP), calcitonin, amylin or adrenomedullin. The treatment of cortical neurons with CGRP promoted the formation of primary dendrites of non-GABAergic neurons. In contrast, the treatment with amylin and adrenomedullin for 3days inhibited the dendritic elongation of non-GABAergic neurons. Calcitonin had no effect on the initial dendrite formation. Next, we examined roles of the peptides in the spine formation. Embryonic day 16 cortical neurons were cultured for 14days and then treated acutely with CGRP, amylin or adrenomedullin for 24h. The density of filopodia, puncta/stubby spines and spines were increased by the CGRP treatment, whereas decreased by amylin. Therefore, CGRP and amylin showed opposite effects on the formation of dendritic filopodia, puncta and spines. Adrenomedullin had no effects on the spine formation. In conclusion, the present study showed that calcitonin family peptides have differential effects both in the dendrite formation during the initial stages and the spine formation of cortical neurons in vitro.

Characterization of the vagal motor neurons projecting to the Guinea pig airways and esophagus

Distinct parasympathetic postganglionic neurons mediate contractions and relaxations of the guinea pig airways. We set out to characterize the vagal inputs that regulate contractile and relaxant airway parasympathetic postganglionic neurons. Single and dual retrograde neuronal tracing from the airways and esophagus revealed that distinct, but intermingled, subsets of neurons in the compact formation of the nucleus ambiguus (nAmb) innervate these two tissues. Tracheal and esophageal neurons identified in the nAmb were cholinergic. Esophageal projecting neurons also preferentially (greater than 70%) expressed the neuropeptide CGRP, but could not otherwise be distinguished immunohistochemically from tracheal projecting preganglionic neurons. Few tracheal or esophageal neurons were located in the dorsal motor nucleus of the vagus. Electrical stimulation of the vagi in vitro elicited stimulus dependent tracheal and esophageal contractions and tracheal relaxations. The voltage required to evoke tracheal smooth muscle relaxation was significantly higher than that required for evoking either tracheal contractions or esophageal longitudinal striated muscle contractions. Together our data support the hypothesis that distinct vagal preganglionic pathways regulate airway contractile and relaxant postganglionic neurons. The relaxant preganglionic neurons can also be differentiated from the vagal motor neurons that innervate the esophageal striated muscle.

Calcitonin receptor-like receptor expression in rat skeletal muscle fibers

The calcitonin gene related peptide (CGRP) pathway is important in many processes including several in the central and peripheral nervous systems. CGRP is present in motor neurons and in sensory tracts, with its expression likely regulated by its use. This is supported by the fact that axotomy results in increased CGRP production in the nerve cell body. The target CGRP receptor, produced in part from the calcitonin receptor-like receptor (Calcrl) gene, has been thought to be present in multiple forms based on kinetic studies; however, understanding of the regulation of the expression of the Calcrl gene remains incomplete. CALCRL is an important factor in aging and associated disorders. This study focused on the neuromuscular system where it has been unclear whether different proteins are initially translated and whether higher levels of CALCRL are localized to the endplate regions. Rat gracilis muscle neuromuscular junctions were examined by isolating endplate enriched and non-endplate regions identified by staining for acetylcholine esterase or conjugated α-bungarotoxin binding. The CALCRL protein was detected at approximately 60kDa by Western immunoblotting and, in the isolated extracts, we found that the Calcrl mRNA level was elevated 6 fold in the muscle endplate regions and that there were two distinct Calcrl messages present. Sequence analysis showed that the two different Calcrl forms were due to alternative splicing but in a non-coding region of the transcript such that only one translation product would be generated. This indicates that previously identified pharmacologic heterogeneity is most likely due to post-translational modifications and interactions.

CGRP receptor antagonism and migraine

Calcitonin gene-related peptide (CGRP) is expressed throughout the central and peripheral nervous systems, consistent with control of vasodilatation, nociception, motor function, secretion, and olfaction. alphaCGRP is prominently localized in primary spinal afferent C and ADelta fibers of sensory ganglia, and betaCGRP is the main isoform in the enteric nervous system. In the CNS there is a wide distribution of CGRP-containing neurons, with the highest levels occurring in striatum, amygdala, colliculi, and cerebellum. The peripheral projections are involved in neurogenic vasodilatation and inflammation, and central release induces hyperalgesia. CGRP is released from trigeminal nerves in migraine. Trigeminal nerve activation results in antidromic release of CGRP to cause non-endothelium-mediated vasodilatation. At the central synapses in the trigeminal nucleus caudalis, CGRP acts postjunctionally on second-order neurons to transmit pain signals centrally via the brainstem and midbrain to the thalamus and higher cortical pain regions. Recently developed CGRP receptor antagonists are effective at aborting acute migraine attacks. They may act both centrally and peripherally to attenuate signaling within the trigeminovascular pathway.

Myosin Va cooperates with PKA RIalpha to mediate maintenance of the endplate in vivo

Myosin V motor proteins facilitate recycling of synaptic receptors, including AMPA and acetylcholine receptors, in central and peripheral synapses, respectively. To shed light on the regulation of receptor recycling, we employed in vivo imaging of mouse neuromuscular synapses. We found that myosin Va cooperates with PKA on the postsynapse to maintain size and integrity of the synapse; this cooperation also regulated the lifetime of acetylcholine receptors. Myosin Va and PKA colocalized in subsynaptic enrichments. These accumulations were crucial for synaptic integrity and proper cAMP signaling, and were dependent on AKAP function, myosin Va, and an intact actin cytoskeleton. The neuropeptide and cAMP agonist, calcitonin-gene related peptide, rescued fragmentation of synapses upon denervation. We hypothesize that neuronal ligands trigger local activation of PKA, which in turn controls synaptic integrity and turnover of receptors. To this end, myosin Va mediates correct positioning of PKA in a postsynaptic microdomain, presumably by tethering PKA to the actin cytoskeleton.

Myocyte enhancer factor 2 mediates acetylcholine-induced expression of acetylcholinesterase-associated collagen ColQ in cultured myotubes

The collagenous protein (ColQ) characterizes the collagen-tailed forms of acetylcholinesterase (AChE) in vertebrate muscles. Two ColQ transcripts, ColQ-1 and ColQ-1a, driven by two distinct promoters are expressed differentially in mammalian slow- and fast-twitch muscles, respectively. Such expression patterns are determined by the contractile activity in different muscle fiber types. To reveal the regulatory role of muscular activity on ColQ expression, acetylcholine and nicotine were applied onto C2C12 muscle cells: the challenge increased the expression of ColQ-1/ColQ-1a mRNAs. The agonist challenge induced the phosphorylation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). In parallel, over expression of an active mutant of CaMKII enhanced both ColQ-1/ColQ-1a mRNA levels in cultured C2C12 myotubes. Moreover, the over expression of myocyte enhancer factor 2 (MEF2), a downstream mediator of CaMKII, in the myotubes potentiated the CaMKII-induced ColQ expression. The current results reveal a signaling cascade that drives the expression profiles of ColQ in responding to activity challenge in cultured myotubes.

Excitotoxic motoneuron disease in chick embryo evolves with autophagic neurodegeneration and deregulation of neuromuscular innervation

In the chick embryo, in ovo application of NMDA from embryonic day (E) 5 to E9 results in selective damage to spinal cord motoneurons (MNs) that undergo a long-lasting degenerative process without immediate cell death. This contrasts with a single application of NMDA on E8, or later, which induces massive necrosis of the whole spinal cord. Chronic MN degeneration after NMDA implies transient incompetence to develop programmed cell death, altered protein processing within secretory pathways, and late activation of autophagy. Chronic NMDA treatment also results in an enlargement of thapsigargin-sensitive Ca(2+) stores. In particular MN pools, such as sartorius-innervating MNs, the neuropeptide CGRP is accumulated in somas, peripheral axons and neuromuscular junctions after chronic NMDA treatment, but not in embryos paralyzed by chronic administration of curare. Intramuscular axonal branching is also altered severely after NMDA: it usually increases, but in some cases a marked reduction can also be observed. Moreover, innervated muscle postsynaptic sites increase by NMDA, but to a lesser extent than by curare. Because some of these results show interesting homologies with MN pathology in human sporadic ALS, the model presented here provides a valuable tool for advancing in the understanding of some cellular and molecular processes particularly involved in this disease.

Skeletal muscle expresses the extracellular cyclic AMP-adenosine pathway

BACKGROUND AND PURPOSE

cAMP is a key intracellular signalling molecule that regulates multiple processes of the vertebrate skeletal muscle. We have shown that cAMP can be actively pumped out from the skeletal muscle cell. Since in other tissues, cAMP efflux had been associated with extracellular generation of adenosine, in the present study we have assessed the fate of interstitial cAMP and the existence of an extracellular cAMP-adenosine signalling pathway in skeletal muscle.

EXPERIMENTAL APPROACH

cAMP efflux and/or its extracellular degradation were analysed by incubating rat cultured skeletal muscle with exogenous cAMP, forskolin or isoprenaline. cAMP and its metabolites were quantified by radioassay or HPLC, respectively.

KEY RESULTS

Incubation of cells with exogenous cAMP was followed by interstitial accumulation of 5'-AMP and adenosine, a phenomenon inhibited by selective inhibitors of ecto-phosphodiesterase (DPSPX) and ecto-nucleotidase (AMPCP). Activation of adenylyl cyclase (AC) in cultured cells with forskolin or isoprenaline increased cAMP efflux and extracellular generation of 5'-AMP and adenosine. Extracellular cAMP-adenosine pathway was also observed after direct and receptor-dependent stimulation of AC in rat extensor muscle ex vivo. These events were attenuated by probenecid, an inhibitor of ATP binding cassette family transporters.

CONCLUSIONS AND IMPLICATIONS

Our results show the existence of an extracellular biochemical cascade that converts cAMP into adenosine. The functional relevance of this extracellular signalling system may involve a feedback modulation of cellular response initiated by several G protein-coupled receptor ligands, amplifying cAMP influence to a paracrine mode, through its metabolite, adenosine.

Calcitonin gene-related peptide induces the expression of acetylcholinesterase-associated collagen ColQ in muscle: a distinction in driving two different promoters between fast- and slow-twitch muscle fibers

The presence of a collagenous protein (ColQ) characterizes the collagen-tailed forms of acetylcholinesterase at vertebrate neuromuscular junctions (nmjs). Two ColQ transcripts as ColQ-1 and ColQ-1a, driven by two promoters: pColQ-1 and pColQ-1a, were found in mammalian slow- and fast-twitch muscles, respectively, which have distinct expression pattern in different muscle fibers. In this study, we show the differential expression of CoQ in different muscles is triggered by calcitonin gene-related peptide (CGRP), a known motor neuron-derived factor. Application of CGRP, or dibutyryl-cAMP (Bt(2)-cAMP), in cultured myotubes induced the expression of ColQ-1a transcript and promoter activity; however, the expression of ColQ-1 transcript did not respond to CGRP or Bt(2)-cAMP. The CGRP-induced gene activation was blocked by an adenylyl cyclase inhibitor or a dominant negative mutant of cAMP-responsive element (CRE) binding protein (CREB). Two CRE sites were mapped within the ColQ-1a promoter, and mutations of the CRE sites abolished the response of CGRP or Bt(2)-cAMP. In parallel, CGRP receptor complex was dominantly expressed at the nmjs of fast muscle but not of slow muscle. These results suggested that the expression of ColQ-1a at the nmjs of fast-twitch muscle was governed by a CGRP-mediated cAMP signaling mechanism.

Sustained CGRP1 receptor stimulation modulates development of EC coupling by cAMP/PKA signalling pathway in mouse skeletal myotubes

We investigated modulation of excitation-contraction (EC) coupling by calcitonin gene-related peptide (CGRP), which is released by motorneurons during neuromuscular transmission. Mouse skeletal myotubes were cultured either under control conditions or in the presence of 100 nm CGRP ( approximately 4-72 h). T- and L-type Ca(2+) currents, immobilization resistant charge movement, and intracellular Ca(2+) transients were characterized in whole-cell patch-clamp experiments. CGRP treatment increased the amplitude of voltage-gated Ca(2+) release ((DeltaF/F)(max)) approximately 75-350% and moderately increased both maximal L-current conductance (G(max)) and charge movement (Q(max)). In contrast, CGRP treatment did not affect their corresponding voltage dependence of activation (V(1/2) and k) or T-current density. CGRP treatment enhanced voltage-gated Ca(2+) release in approximately 4 h, whereas the effect on L-channel magnitude took longer to develop ( approximately 24 h), suggesting that short-term potentiation of EC coupling may lead to subsequent long-term up-regulation of DHPR expression. CGRP treatment also drastically increased caffeine-induced Ca(2+) release in approximately 4 h ( approximately 400%). Thus, short-term potentiation of EC coupling is due to an increase in sarcoplasmic reticulum Ca(2+) content. Both application of a phosphodiesterase inhibitor (papaverine) and a membrane-permeant cAMP analogue (Db-cAMP) produced a similar potentiation of EC coupling. Conversely, this potentiation was prevented by pretreatment with either CGRP1 receptor antagonist (CGRP(8-37)) or a PKA inhibitor (H-89). Thus, CGRP acts through CGRP1 receptors and the cAMP/PKA signalling pathway to enhance voltage-gated Ca(2+) release. Effects of CGRP on both EC coupling and L-channels were attenuated at later times during myotube differentiation. Therefore, we conclude that CGRP accelerates maturation of EC coupling.

Regulation of a transcript encoding the proline-rich membrane anchor of globular muscle acetylcholinesterase. The suppressive roles of myogenesis and innervating nerves

The transcriptional regulation of proline-rich membrane anchor (PRiMA), an anchoring protein of tetrameric globular form acetylcholinesterase (G(4) AChE), was revealed in muscle during myogenic differentiation under the influence of innervation. During myotube formation of C2C12 cells, the expression of AChE(T) protein and the enzymatic activity were dramatically increased, but the level of G(4) AChE was relatively decreased. This G(4) AChE in C2C12 cells was specifically recognized by anti-PRiMA antibody, suggesting the association of this enzyme with PRiMA. Reverse transcription-PCR analysis revealed that the level of PRiMA mRNA was reduced during the myogenic differentiation of C2C12 cells. Overexpression of PRiMA in C2C12 myotubes significantly increased the production of G(4) AChE. The oligomerization of G(4) AChE, however, did not require the intracellular cytoplasmic tail of PRiMA. After overexpressing the muscle regulatory factors, myogenin and MyoD, the expressions of PRiMA and G(4) AChE in cultured myotubes were markedly reduced. In addition, calcitonin gene-related peptide, a known motor neuron-derived factor, and muscular activity were able to suppress PRiMA expression in muscle; the suppression was mediated by the phosphorylation of a cAMP-responsive element-binding protein. In accordance with the in vitro results, sciatic nerve denervation transiently increased the expression of PRiMA mRNA and decreased the phosphorylation of cAMP-responsive element-binding protein as well as its activator calcium/calmodulin-dependent protein kinase II in muscles. Our results suggest that the expression of PRiMA, as well as PRiMA-associated G(4) AChE, in muscle is suppressed by muscle regulatory factors, muscular activity, and nerve-derived trophic factor(s).

The role of muscle activation pattern and calcineurin in acetylcholinesterase regulation in rat skeletal muscles

Acetylcholinesterase (AChE) expression in fast rat muscles is approximately fourfold higher than in slow muscles. We examined whether different muscle activation patterns are responsible for this difference and whether the calcineurin signaling pathway is involved in AChE regulation. The slow soleus and fast extensor digitorum longus (EDL) muscles were directly or indirectly stimulated by a tonic low-frequency or a phasic high-frequency pattern of electric impulses. The phasic, but not tonic, stimulation increased the AChE mRNA levels in denervated soleus muscles to those in the normal EDL and maintained high levels of AChE mRNA in denervated EDL muscles. Therefore, muscle activation pattern is the predominant regulator of extrajunctional AChE expression in rat muscles. Indirect phasic stimulation of innervated muscles, imposed on their natural pattern of neural activation, did not increase the AChE transcript levels in the soleus, whereas a 30% reduction was observed in the EDL muscles. A low number of impulses per day is therefore prerequisite for high AChE expression. Treatment by tacrolimus and cyclosporin A, two inhibitors of calcineurin (but not by a related substance rapamycin, which does not inhibit calcineurin), increased the levels of AChE transcripts in the control soleus muscles and in tonically electrically stimulated soleus and EDL muscles, even to reach those in the control EDL muscles. Therefore, tonic muscle activation reduces the extrajunctional levels of AChE transcripts by activating the calcineurin signaling pathway. In denervated soleus and EDL muscles, tacrolimus did not prevent the reduction of AChE mRNA levels, indicating that a calcineurin-independent suppressive mechanism was involved.

Termination and beyond: acetylcholinesterase as a modulator of synaptic transmission

Termination of synaptic transmission by neurotransmitter hydrolysis is a substantial characteristic of cholinergic synapses. This unique termination mechanism makes acetylcholinesterase (AChE), the enzyme in charge of executing acetylcholine breakdown, a key component of cholinergic signaling. AChE is now known to exist not as a single entity, but rather as a combinatorial complex of protein products. The diverse AChE molecular forms are generated by a single gene that produces over ten different transcripts by alternative splicing and alternative promoter choices. These transcripts are translated into six different protein subunits. Mature AChE proteins are found as soluble monomers, amphipatic dimers, or tetramers of these subunits and become associated to the cellular membrane by specialized anchoring molecules or members of other heteromeric structural components. A substantial increasing body of research indicates that AChE functions in the central nervous system go far beyond the termination of synaptic transmission. The non-enzymatic neuromodulatory functions of AChE affect neurite outgrowth and synaptogenesis and play a major role in memory formation and stress responses. The structural homology between AChE and cell adhesion proteins, together with the recently discovered protein partners of AChE, predict the future unraveling of the molecular pathways underlying these multileveled functions.

Progression of vascular and neural dysfunction in sciatic nerves of Zucker diabetic fatty and Zucker rats

We have examined the progression of vascular and neural deficits in Zucker rats, Zucker diabetic fatty (ZDF) diabetic rats, and age-matched lean ZDF rats from 8 to 40 wk of age. Both the ZDF diabetic and Zucker rats were glucose intolerant at 8 wk of age. The Zucker rats did not become hyperglycemic but were hyperinsulinemic through 32 wk of age. All ZDF diabetic rats became hyperglycemic by 8 wk of age. Through their life span, serum free fatty acids and triglycerides levels were significantly higher in Zucker and ZDF diabetic rats compared with age-matched lean ZDF rats. After 24 and 28 wk of age, endoneurial blood flow was significantly decreased in ZDF diabetic and Zucker rats. Motor nerve conduction velocity was significantly decreased after 12-14 wk of age in ZDF diabetic rats and at 32 wk of age in Zucker rats. ACh-mediated vascular relaxation of epineurial arterioles of the sciatic nerve was impaired after 8-10 wk of age in ZDF diabetic rats and after approximately 16 wk of age in Zucker rats. In contrast, vascular relaxation mediated by calcitonin gene-related peptide was impaired significantly after 28 wk of age in ZDF diabetic rats but not impaired in Zucker rats up to 40 wk of age. Markers of oxidative stress were differentially elevated in ZDF diabetic rats and Zucker rats. These data indicate that vascular and neural dysfunction develops in both Zucker and ZDF diabetic rats but at different rates, which may be the result of hyperglycemia.

Calcitonin gene-related peptide and its role in migraine pathophysiology

Migraine is a common neurological disorder that is associated with an increase in plasma calcitonin gene-related peptide (CGRP) levels. CGRP, a neuropeptide released from activated trigeminal sensory nerves, dilates intracranial blood vessels and transmits vascular nociception. Therefore, it is propounded that: (i) CGRP may have an important role in migraine pathophysiology, and (ii) inhibition of trigeminal CGRP release or CGRP-induced cranial vasodilatation may abort migraine. In this regard, triptans ameliorate migraine headache primarily by constricting the dilated cranial blood vessels and by inhibiting the trigeminal CGRP release. In order to explore the potential role of CGRP in migraine pathophysiology, the advent of a selective CGRP receptor antagonist was obligatory. The introduction of di-peptide CGRP receptor antagonists, namely BIBN4096BS (1-piperidinecarboxamide, N-[2-[[5-amino-1-[[4-(4-pyridinyl)-1-piperazinyl]carbonyl] pentyl] amino]-1-[(3,5-dibromo-4-hydroxyphenyl) methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl)-, [R-(R*,S*)]-), is a breakthrough in CGRP receptor pharmacology and can be used as a tool to investigate the role of CGRP in migraine headaches. Preclinical investigations in established migraine models that are predictive of antimigraine activity have shown that BIBN4096BS is a potent CGRP receptor antagonist and that it has antimigraine potential. Indeed, a recently published clinical study has reported that BIBN409BS is effective in treating acute migraine attacks without significant side effects. The present review will discuss mainly the potential role of CGRP in the pathophysiology of migraine and the various treatment modalities that are currently available to target this neuropeptide.

An expansion of Simons' integrated hypothesis of trigger point formation

Simons' integrated hypothesis proposed a model of trigger point (TrP) activation to explain known TrP phenomena, particularly endplate noise. We propose an expansion of this hypothesis to account for new experimental data and established muscle pathophysiology.

Endophyte-infected tall fescue diet alters gene expression in heifer luteal tissue as revealed by interspecies microarray analysis

Cattle consuming endophyte-infected tall fescue grass have an associated reduction in circulating progesterone and reduced reproductive rates. In this study, commercially available rat microarrays were used to analyze the gene expression in luteal tissues from heifers fed endophyte-free fescue, endophyte-infected fescue, or endophyte-infected fescue supplemented with the dopamine (DA) antagonist, domperidone. The number of hybridized spots represented approximately 40% of the total 10,000 rat genes/ESTs evaluated. Each luteal sample was analyzed in triplicate, resulting in within treatment correlation coefficients of >/=0.98. Median values of mRNA abundance from luteal tissue taken from the endophyte-infected fed heifers revealed 598 genes and ESTs that were down regulated and 56 genes and ESTs that were upregulated compared with luteal mRNA values from the endophyte-free treatment. There were fewer comparative differences between median values from luteal mRNA from the endophyte-free versus feeding endophyte-infected plus domperidone treated heifers. Only 19 genes and ESTs were upregulated and two were down-regulated.

Diabetes mellitus influences the degree of colocalization of calcitonin gene-related peptide with insulin and somatostatin in the rat pancreas

OBJECTIVES

Although calcitonin-gene related peptide (CGRP) (C162H262N50O50S2) has been shown to be present in pancreatic islet cells, no data have been reported on the pattern of its distribution in the islets of Langerhans of diabetic rats.

METHODS

The present study used immunohistochemical and immunofluorescence techniques to examine the pattern of distribution of CGRP-like immunoreactive (CGRP-LIR) cells and nerves in the pancreata of rats with streptozotocin-induced diabetes. The effect of CGRP on insulin secretion from rat pancreatic tissue fragments was also investigated using a radioimmunoassay technique.

RESULTS

Numerous CGRP-LIR cells were observed in both the peripheral and central regions of the islets of Langerhans of normal pancreata where they colocalized with large and small subsets of insulin-LIR and somatostatin-LIR cells, respectively. By contrast, the islets of diabetic rat pancreata contained significantly (P < 0.0001) fewer CGRP-LIR cells compared with normal rats. In diabetic rat pancreata, CGRP was colocalized with larger and smaller subsets of somatostatin-LIR and insulin-LIR cells, respectively. CGRP-LIR nerve fibers were discerned in the perivascular and periacinar regions of the pancreata of both normal and diabetic rats. CGRP (10 M) induced a significant (P < 0.02) increase in insulin secretion from the pancreas of normal rat.

CONCLUSION

CGRP is colocalized with insulin and somatostatin in the pancreata of normal and diabetic rats and may play an important role in the humoral and neural regulation of the endocrine pancreas.

Muscle induces neuronal expression of acetylcholinesterase in neuron-muscle co-culture: transcriptional regulation mediated by cAMP-dependent signaling

Presynaptic motor neuron synthesizes and secretes acetylcholinesterase (AChE) at vertebrate neuromuscular junctions. In order to determine the retrograde role of muscle in regulating the expression of AChE in motor neuron, a chimeric co-culture of NG108-15 cell, a cholinergic cell line that resembles motor neuron, with chick myotube was established to mimic the neuromuscular contact in vitro. A DNA construct of human AChE promoter tagged with luciferase (pAChE-Luc) was stably transfected into NG108-15 cells. The co-culture with myotubes robustly stimulated the promoter activity as well as the endogenous expression of AChE in pAChE-Luc stably transfected NG108-15 cells. Muscle extract derived from chick embryos when applied onto pAChE-Luc-expressing NG108-15 cells induced expressions of AChE promoter and endogenous AChE. The cAMP-responsive element mutation on human AChE promoter blocked the muscle-induced AChE transcriptional activity in cultured NG108-15 cells either in co-culturing with myotube or in applying muscle extract. The accumulation of intracellular cAMP and the phosphorylation of cAMP-responsive element-binding protein in cultured NG108-15 cells were stimulated by applied muscle extract. Part of the muscle-induced signaling was mimicked by application of calcitonin gene-related peptide in cultured NG108-15 cells. These results suggest the muscle-induced neuronal AChE expression in the co-culture is mediated by a cAMP-dependent signaling.