Neurochemical effects of CGRP

A proteogenomic view of Parkinson's disease causality and heterogeneity

The pathogenesis and clinical heterogeneity of Parkinson's disease (PD) have been evaluated from molecular, pathophysiological, and clinical perspectives. High-throughput proteomic analysis of cerebrospinal fluid (CSF) opened new opportunities for scrutinizing this heterogeneity. To date, this is the most comprehensive CSF-based proteomics profiling study in PD with 569 patients (350 idiopathic patients, 65 GBA + mutation carriers and 154 LRRK2 + mutation carriers), 534 controls, and 4135 proteins analyzed. Combining CSF aptamer-based proteomics with genetics we determined protein quantitative trait loci (pQTLs). Analyses of pQTLs together with summary statistics from the largest PD genome wide association study (GWAS) identified 68 potential causal proteins by Mendelian randomization. The top causal protein, GPNMB, was previously reported to be upregulated in the substantia nigra of PD patients. We also compared the CSF proteomes of patients and controls. Proteome differences between GBA + patients and unaffected GBA + controls suggest degeneration of dopaminergic neurons, altered dopamine metabolism and increased brain inflammation. In the LRRK2 + subcohort we found dysregulated lysosomal degradation, altered alpha-synuclein processing, and neurotransmission. Proteome differences between idiopathic patients and controls suggest increased neuroinflammation, mitochondrial dysfunction/oxidative stress, altered iron metabolism and potential neuroprotection mediated by vasoactive substances. Finally, we used proteomic data to stratify idiopathic patients into "endotypes". The identified endotypes show differences in cognitive and motor disease progression based on previously reported protein-based risk scores.Our findings not only contribute to the identification of new therapeutic targets but also to shape personalized medicine in CNS neurodegeneration.

Neuropeptide Y and Calcitonin Gene-Related Peptide in Cerebrospinal Fluid in Parkinson's Disease with Comorbid Depression versus Patients with Major Depressive Disorder

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. The diagnosis of PD is based on movement dysfunctions. Many patients also suffer from comorbid depression in spite of adequate treatment with dopamine replacement, indicating that also other non-dopaminergic mechanisms are involved. Indeed, neuropeptides are critically implicated in the pathophysiology of major depressive disorder (MDD). To increase our understanding of the biochemical basis of depression in PD patients, we examined the levels of neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) in cerebrospinal fluid (CSF) from PD patients, with or without comorbid depression, and compared them to the levels in patients with MDD. We also compared the levels of NPY and CGRP with 5-hydroxyindoleacetic acid (5-HIAA), the major serotonin metabolite. Both NPY and CGRP were higher in PD patients with comorbid depression compared to MDD patients. No similar difference was found in 5-HIAA levels. Accordingly, there were no correlations between NPY and 5-HIAA or CGRP and 5-HIAA levels. The finding of higher NPY and CGRP CSF levels in PD patients with MDD raises the possibility that different pathophysiological processes may underlie depression in PD and MDD.

Comparison of beta-endorphin and CGRP levels before and after treatment for severe schizophrenia

OBJECTIVES

Links between endorphins and dopaminergic transmission have not been fully explored in schizophrenia. Both endorphins excess and deficiency were postulated. CGRP is probably involved in dopaminergic transmission. The aim of this study was the evaluation of beta-endorphin (BE) and CGRP blood concentrations before and after treatment of severe schizophrenia.

METHODS

Seventy patients treated with various antipsychotics, with severe symptoms of schizophrenia (51 with positive symptoms, 19 with negative symptoms), 15 first-degree relatives, and 44 healthy controls were included in the study. BE and CGRP blood concentrations were measured during patients severe schizophrenia and in their stable mental state after treatment. The results were compared with relatives and controls.

RESULTS

BE and CGRP concentrations in patients with negative symptoms were higher than in relatives and in controls. BE levels in patients with positive symptoms were lower than in patients with negative symptoms (P<0.0000) and controls (P<0.0006). No significant changes in CGRP concentration were found in patient samples. CGRP levels in these samples were independent of treatment, but they were significantly higher than in relatives and controls. After the treatment, BE level decreased in patients with negative symptoms (P<0.0001) and increased in patients with positive symptoms (P<0.0000). No differences in BE concentration between patients in stable mental state, their relatives, and controls were found.

CONCLUSION

Effective antipsychotic treatment results in "normalization" of BE level. Specific changes in BE concentration could be involved in dopaminergic transmission and related to some symptoms of schizophrenia.

Role of central calcitonin gene-related peptide (CGRP) in locomotor and anxiety- and depression-like behaviors in two mouse strains exhibiting a CGRP-dependent difference in thermal pain sensitivity

We have previously shown that, in AKR and C57BL/6 mice, a genetic polymorphism results in differential expression of the peptide, calcitonin gene-related polypeptide (CGRP), explaining a strain difference in thermal pain sensitivity. Although CGRP is widely distributed in the brain, little is known about the effects of supraspinal CGRP. We used AKR and C57BL/6 mice as a model to explore the effects of centrally (intracerebroventricular) injected CGRP and the CGRP receptor antagonists, CGRP(8-37) and BIBN4096BS, in a series of behavioral assays. Locomotor activity was significantly increased in C57BL/6 mice following the injection of BIBN4096BS and in both strains after the administration of CGRP(8-37) into the third ventricle. CGRP increased paw-withdrawal latencies in C57BL/6 mice only, while decreasing depression-like behaviors in both strains in the forced-swimming test. CGRP and CGRP receptor antagonists failed to modulate activity in the elevated plus maze, a model of anxiety. Taken together, these results suggest a complex role for supraspinal CGRP systems in the regulation of locomotion, nociception, and depression-like behaviors.

Differential effects of olanzapine, haloperidol and risperidone on calcitonin gene-related peptide in the rat brain

Calcitonin gene-related peptide (CGRP) is a 37 amino acid peptide which acts on central nervous system (CNS) neurons and is involved in activities related to dopamine. These effects of CGRP suggest that the peptide may have a role in pathophysiology and treatment of schizophrenia where dopaminergic system hypoactivity in the frontal cortex and hyperactivity in the subcortical structures have been demonstrated. In this study we measured by radioimmunoassay (RIA) the brain levels of CGRP-like immunoreactivity (CGRP-LI) in rats treated with either classical (haloperidol) or atypical (risperidone and olanzapine) antipsychotic drugs. Both haloperidol and risperidone decreased CGRP-LI in the striatum. Risperidone also decreased CGRP-LI in the occipital cortex. On the other hand, olanzapine increased CGRP-LI in the striatum, the frontal cortex and hypothalamus. The differential effects on CGRP could reflect a different profile of side effects and further suggest that CGRP is involved in CNS functions related to psychiatric disorders.

Effects of maternal separation on neuropeptide Y and calcitonin gene-related peptide in "depressed" Flinders Sensitive Line rats: a study of gene-environment interactions

Interactions between genetic vulnerability to stress/depression and early life experience may play a crucial role in the pathogenesis of mood disorders. Here we explore this hypothesis by superimposing early life trauma in the form of maternal deprivation for 180 min per day from postnatal day 2 to 14 onto a genetic model of depression/susceptibility to depression, Flinders Sensitive Line (FSL) and their controls, Flinders Resistant Line (FRL) rats. We investigate effects on neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) like immunoreactivity (LI) in 10 brain regions as these neuropeptides are affected by antidepressants and are altered in cerebrospinal fluid of depressed patients. NPY-LI was reduced while CGRP-LI was elevated in hippocampus and frontal cortex of "genetically depressed" FSL rats. The two peptides displayed a significant negative correlation in these regions that was strongest in the FSL strain. Maternal deprivation exacerbated the strain difference in hippocampal CGRP-LI, while it was without effect on NPY-LI. FSL rats had higher tissue concentration of both neuropeptides in periaqueductal grey and higher NPY-LI in caudate/putamen. Maternal deprivation selectively raised CGRP-LI in amygdala of the FRL control stain. Thus, in two brain regions implicated in the neurobiology of depression, hippocampus and frontal cortex, changes in CGRP-LI and NPY-LI were in opposite direction, and CGRP-LI appears to be more responsive to adverse experience. Our findings thus support the hypothesis that genetic disposition and developmental stress may contribute to the susceptibility to depression by exerting selective neuropeptide- and brain region-specific effects on adult neurobiology.

Calcitonin gene-related peptide and calcitonin in the CSF of patients with dementia and depression: possible disease markers

Cerebrospinal fluid (CSF) was obtained from 32 patients with dementia, 19 healthy controls that were age-matched with the dementia patients, and 29 DSM-IV major depression patients and calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) and calcitonin-like immunoreactivity (CT-LI) measured by RIA. CGRP-LI was lower in the dementia group compared to both the controls and depressed patients (P<.01) after covarying out sex and age. CT-LI was decreased in the dementia and depressed patients (P<.05) compared to the controls. A positive relationship between CGRP-LI and CT-LI was found in dementia. A logistic discriminant analysis with calcitonin gene-related peptide (CGRP) and log calcitonin (CT) predicting diagnosis (three classes) revealed a significant overall fit (chi2 = 18.08, P = .0011), with an effect test showing contributions of both independent variables: CGRP (chi2 = 10.03, P<.007), log CT (chi2 = 8.63, P = .013). In dementia, both CGRP-LI and CT-LI were decreased and their concentration ratio did not differ from that in controls, likely reflecting a general neuronal loss. Alternatively and more speculatively, but theoretically possible, expression of the alpha-CGRP/CT gene may be affected in dementia. In contrast, in depression, CT-LI but not CGRP-LI was decreased and the CGRP/CT concentration ratio was increased, which is consistent with a possibility of an altered splicing process favoring CGRP mRNA.

A pilot study of rat brain regional distribution of calcitonin, katacalcin and calcitonin gene-related peptide before and after antipsychotic treatment

In contrast to extensive determinations of calcitonin gene-related peptide (CGRP) in neural tissues, calcitonin and its carboxyl-terminal flanking peptide katacalcin (in human PDN-21) have not been systematically measured by radioimmunoassay (RIA) in discrete brain structures. Using microwave irradiation (MW), a procedure that increases the recovery of neuropeptides, we investigated by radioimmunoassay (RIA) the rat brain regional distribution of CGRP like- immunoreactivity (-LI), calcitonin-LI, and katacalcin-LI. Calcitonin-LI and katacalcin-LI were found in low concentrations in frontal cortex, occipital cortex, striatum and hippocampus. Moreover, a 4-week treatment with antipsychotic drugs altered the concentrations of the calcitonin-gene family peptides in the frontal cortex, occipital cortex, and hippocampus; the magnitude of these changes, however, was only moderate. Lastly, calcitonin-LI and katacalcin-LI baseline concentrations as well as after antipsychotic treatment were highly correlated in the frontal cortex, striatum, and hippocampus. The possible regulatory role of calcitonin gene family peptides in the central nervous system (CNS) needs to be further explored.

Dopamine receptor antagonists prevent the d-amphetamine-induced increase in calcitonin gene-related peptide levels in ventral striatum

Microdialysis in conjunction with radioimmunoassay (RIA) were used to study the effects of acute d-amphetamine or dopamine (DA) receptor antagonists administration on extracellular concentrations of calcitonin gene-related peptide (CGRP) in the ventral striatum of the rat. One hour after the subcutaneous (s.c.) injection of saline, the DA-D(1) receptor antagonist SCH 23390 (0.3 mg/kg) or the DA-D(2/3) receptor antagonist raclopride (1.0 mg/kg), one additional s.c. injection of saline or d-amphetamine (1.5 mg/kg) was given. The dialysates were collected at 60-min intervals; CGRP-like immunoreactivities (-LI) were determined by RIA. d-Amphetamine significantly increased extracellular CGRP-LI concentrations compared to the control animals. Administration of either SCH 23390 or raclopride did not significantly affect CGRP-LI concentrations. Pretreatment with either SCH 23390 or raclopride abolished the stimulatory effect of d-amphetamine on CGRP-LI levels. The results show that d-amphetamine administration results in an increase in extracellular concentrations of CGRP in the ventral striatum through a mechanism that appears to involve stimulation of either DA-D(1) or DA-D(2/3) receptors. The results also indicate that changes in dopaminergic neurotransmission affect CGRP outflow in the ventral striatum in a phasic but not tonic manner.

4991W93 inhibits release of calcitonin gene-related peptide in the cat but only at doses with 5HT(1B/1D) receptor agonist activity?

Calcitonin gene-related peptide (CGRP) is a marker for trigeminovascular activation and is released during the headache phase of migraine and cluster headache. CGRP may have a role in migraine through its potent cranial vasodilator effects, or by an action on trigeminal nerve activity, both of which are targeted by 5HT(1B/1D) agonist drugs. CP122,288, a conformationally restricted analogue of sumatriptan that is a potent inhibitor of neurogenic plasma protein extravasation (PPE), was ineffective at inhibiting CGRP release at a single low dose; and is also ineffective as an acute anti-migraine compound. However, it remained unclear as to whether, as a class, the conformationally-restricted triptan analogues could have inhibitory effects on CGRP in higher doses. 4991W93, a conformationally restricted analogue of zolmitriptan, is also a potent inhibitor of PPE at doses without 5HT(1B/1D)-mediated effects, that was developed as an anti-migraine drug, and thus was suitable to test whether higher doses of such conformationally restricted triptan analogues could inhibit trigeminal-evoked CGRP release. The superior sagittal sinus (SSS) was stimulated in 14 anaesthetised cats and external jugular vein blood samples were analysed by radioimmunoassay for CGRP levels before, 1 min after SSS stimulation, and 1 min after SSS stimulation in the presence of 4991W93. Stimulation of the SSS resulted in release of CGRP from the external jugular vein. 4991W93 at a dose of 0.1 and 10 microg/kg, selected for maximal PPE blocking effects in rodents, was ineffective at inhibiting CGRP release, with an SSS stimulation level of 78+/-4 pmol/l compared to a post-4991W93 level of 79+/-3 pmol/l (n=4). In comparison CGRP release was inhibited after a dose of 100 microg/kg 4991W93 from 64+/-6 to 36+/-3 pmol/l (n=5). Given that 4991W93 is inactive clinically at non-vascular doses, it seems clear that the 5HT(1B/1D) agonist effects of the compound are necessary for blockade of CGRP release and thus any anti-migraine action. Taken with the clinical results, these data emphasise the importance of CGRP release in migraine, and suggest that other non-5HT-based pharmacological targets may account for PPE blockade in animal studies.

Inhibitory effect of central dopamine on basal pancreatic secretion in conscious rats

We examined the role and the peripheral mechanism of action of central dopamine on basal pancreatic exocrine secretion in conscious rats. Rats were fitted with bile and pancreatic catheters to collect bile and pancreatic juice separately and also with a left lateral brain ventricle and external jugular vein catheters. After 90-min basal collection, the D1- and D2-receptor antagonists (Sch-23390 and eticlopride, respectively) and dopamine were administered into the lateral brain ventricle. Sch-23390 (30, 100, and 300 nmol/rat), but not eticlopride (300 nmol/rat), stimulated pancreatic fluid and protein secretion. Dopamine (30, 100, and 300 nmol/rat) inhibited pancreatic secretion lose dependently. Pretreatment with Sch-23390 prevented the inhibitory effect of dopamine. Intravenously injected Sch-23390 or dopamine had no effect on pancreatic secretion. The inhibitory effect of dopamine was blocked by bretylium, an inhibitor of norepinephrine release, and phentolamine, an alpha-blocker, but not by vagotomy. The beta-antagonist propranolol alone significantly inhibited basal pancreatic secretion, and dopamine did not modify the inhibitory effect of propranolol. The proton pump inhibitor omeprazole partially but not completely reduced the inhibition by dopamine. These results suggest that central dopamine inhibits pancreatic exocrine secretion via D1-like receptors and that the inhibitory effect is mediated via sympathetic nerves, especially alpha-adrenoceptors.

Effects of electroconvulsive stimuli and MK-801 on neuropeptide Y, neurokinin A, and calcitonin gene-related peptide in rat brain

Rats were pretreated with 0.9% NaCl, or 0.1 or 1.0 mg/kg MK-801, an anticonvulsant and a psychotomimetic drug, and 60 minutes later given ECS or sham ECS. After six sessions the animals were sacrificed and neuropeptide Y (NPY-), neurokinin A (NKA-), and calcitonin gene-related peptide (CGRP-) like immunoreactivity (-LI) measured with radioimmunoassays. ECS increased NPY-LI in frontal cortex, striatum, occipital cortex and hippocampus, and NKA-LI in occipital cortex and hippocampus. MK-801 increased CGRP in a dose-response manner in frontal cortex, and NKA-LI in occipital cortex. Although the higher MK-801 dose reduced seizure duration by 50%, the ECS induced NPY-LI increase in striatum, occipital cortex and hippocampus, and NKA-LI in occipital cortex was not diminished. In contrast, there was a parallel decrease in seizures and NPY-LI and NKA-LI changes in frontal cortex and hippocampus, respectively. Investigation of neuropeptides in brain may contribute to understanding of the mechanisms of action of antidepressive and antipsychotic treatments and of psychotomimetic drugs.

The psychotomimetic drugs D-amphetamine and phencyclidine release calcitonin gene-related peptide in the limbic forebrain of the rat

Calcitonin gene-related peptide (CGRP) is the major product of the calcitonin gene in brain and exerts a number of actions in the central nervous system (CNS). In particular the finding that CGRP affects dopamine (DA) release and metabolism has raised the possibility that it may play a role in several neuropsychiatric disorders. Consequently, we have here studied the effects of two psychotomimetic drugs, namely, d-amphetamine (AMPH) and phencyclidine (PCP), on CGRP concentrations in brain microdialysates from freely moving rats. The animals were stereotaxically implanted with vertical concentric probes in the medial prefrontal cortex (mPFC), the ventral striatum (vSTR), or the hippocampus; and the experiments were performed 48 hr after surgery. The dialysis probes were perfused with a modified Ringer's solution at the rate of 5 microliters/min. AMPH 1.5 mg/kg, PCP 2.5 mg/kg, or NaCl 0.9% were injected s.c.; and the perfusates were collected at 60 min intervals before and after the injections and used for CGRP-like immunoreactivity (-LI) determination by radioimmunoassay (RIA). In separate experiment, KCl (100 mM), veratridine (50 microM), or tetrodotoxin (2 microM), were added to the perfusate and infused in the vSTR. Baseline levels of CGRP-LI were detected in dialysates from all three regions. Both AMPH and PCP caused a significant and sustained increase (maximum about 300%) in CGRP-LI concentrations, in particular from the mPFC and vSTR, while saline had no effect. KCl and veratridine also increased CGRP-LI in dialysates during the first posttreatment period, while tetrodotoxin induced a significant but delayed decrease in CGRP-LI levels. Finally, cervical dislocation also elevated CGRP-LI in dialysates from the mPFC and the vSTR. Our findings demonstrate that 1) CGRP-LI can be measured in vivo in microdialysates from mPFC, vSTR, and hippocampus; 2) the release in vSTR is action potential-dependent; and 3) systemic administration of AMPH or PCP results in a long-lasting release of CGRP-LI in the mPFC and vSTR, thus demonstrating a novel action of these drugs in the brain. Since other studies have shown that major antipsychotic drugs appear to reduce CGRP release in brain, our study provides, in principle, support for a role of CGRP in psychotic disorders.

In vivo modulation of sigma receptor sites by calcitonin gene-related peptide in the mouse and rat hippocampal formation: radioligand binding and electrophysiological studies

Possible interactions between sigma (sigma) receptor sites and calcitonin gene-related peptides (CGRP) were investigated using receptor subtype-related analogues and fragment in in vivo [3H](+)SKF 10 047/sigma binding in the hippocampus, and electrophysiological recording of the N-methyl-D-aspartate (NMDA)-induced activation of CA3 pyramidal neurons, two well-established sigma assays. In both paradigms, CGRP and the agonist [Cys(ACM)2,7]hCGRPalpha modulated sigma systems. In vivo binding experiments demonstrated that CGRP and [Cys(ACM)2,7]hCGRPalpha inhibited 25-40% of specific [3H](+)SKF 10 047 labelling in the mouse hippocampal formation while the purported antagonist hCGRP8-37 was inactive. The specificity of this modulation was demonstrated further by the lack of effect of other vasoactive peptides, including the atrial natriuretic peptide, substance P, and its N-terminal fragment, substance P1-7. In the CA3 subfield of the rat dorsal hippocampus, hCGRP alpha decreased (up to 61%) the NMDA-induced activation of the pyramidal neurons. Conversely, the linear analogue [Cys(ACM)2,7]hCGRP alpha enhanced (by 85%) the NMDA-induced activation of CA3 pyramidal neurons, while the antagonistic fragment hCGRP8-37 had no effect. Haloperidol, a high-affinity sigma receptor ligand, inhibited by 90% the in vivo [3H](+)SKF 10 047 labelling, and prevented the modulation of the NMDA-induced activation by hCGRP alpha and [Cys(ACM)2,7]hCGRP alpha. It thus appears that CGRP can modulate sigma-related systems in the hippocampal formation.

The role of 5-HT3 receptors in the anti-ulcer effect of calcitonin

1. The aim of the present study was to determine the role of 5-HT3 receptors of the gastroprotective effect of salmon calcitonin (sCT) and sCT-induced changes in gastric, hepatic, brain and brainstem glutathione (GSH) and lipid-peroxidation (LP) levels in rats subjected to cold-immobilization stress. 2. Stress exposure resulted in ulcer formation and a decrease in GSH levels of the liver, brain and brainstem and an increase in gastric and hepatic LP (P < 0.05). 3. sCT prevented stress-induced gastric ulcer development (P < 0.01) and reversed the decrease in hepatic and brain GSH levels (P < 0.05). 4. In the present study, a 5-HT3 receptor antagonist, ICS 205,930 was used. Interestingly, the effect of the blocker on GSH and LP levels of the tissues studied was similar to those of sCT. 5. ICS 205,930 dose dependently reversed the anti-ulcer effect of sCT although it did not antagonize the effect of sCT on GSH and LP levels, but it seemed to show an additive interaction for brain and brainstem GSH and gastric LP levels with sCT.

Effects of calcitonin gene-related peptide on the rabbit electroretinogram

In order to better understand the role of Calcitonin gene-related peptide (CGRP) in mammalian retina, the dose related effects of human CGRP (hCGRP) on rabbit electroretinogram (ERG) were examined in the present study. CGRP was administered intraocularly in doses of 0.1, 1.0 and 10.0 micrograms. ERG A- and B-wave as well as oscillatory potentials (P1, P2, P3 and P4) were recorded. The highest dose of CGRP (10.0 micrograms) significantly increased the amplitudes of the A-wave and OP components (P1, P2, P3 and P4) produced by relatively high stimulus intensity. The same dose of the peptide also enhanced B-wave amplitude at all intensities studied. The effects of the intermediate dose of CGRP (1.0 microgram) on the B-wave amplitudes were dependent on stimulus intensities. B-wave amplitudes at high stimulus intensities were not affected by 1.0 microgram of CGRP but were significantly increased with relatively lower stimulus intensities. The amplitudes of P3, one of OP components, were significantly increased. However, amplitudes of A-wave and other OP components (P1, P2 and P4) were not affected by 1.0 microgram CGRP. The lowest dose of the peptide (0.1 microgram) did not affect any amplitudes of ERG components. Implicit times of A-wave, B-wave and OP components were not significantly affected by the different doses of CGRP. Taken together, these results indicate that CGRP may play a functional role in modulating retinal responses to photic stimulation.