The cholinomimetic agent carbachol induces headache in healthy subjects

Radial artery diameter: a comprehensive systematic review of anatomy

AIMS

The objective of this systematic review is to determine with the highest accuracy the average radial artery (RA) diameter overall and in certain subgroups. The aim of this study is to provide assistance in the development of fitting transradial devices, an increasingly popular intervention.

METHODS

Several databases were used to extract appropriate studies highlighting RA diameter. Databases used in the generation of this study were Ovid EBM Reviews, Ovid Embase, Ovid Medline, Scopus and Web of Science Core Collection. RA diameter was determined overall, in males versus females, adults only, adults+children, in the presence of comorbidities, and finally RA diameter in the context of various vasodilators.

RESULTS

A total of 71 studies were included. The average RA diameter overall was determined to be 2.62±0.15 mm in children+adults and 2.70±0.15 mm in adults only. In comparison to an RA diameter of 2.68±0.24 mm in adult males, the diameter was found to be 2.27±0.27 mm in adult females (p=0.028). As for comorbidities, the mean RA diameter in adult patients with hypertension and congestive heart failure was 2.72±0.37 mm and 2.80±0.25 mm, respectively. Finally, the mean RA diameter with nitrate and angiotensin-converting enzyme (ACE) inhibitor use was 2.97±0.53 mm and 2.82±0.29 mm respectively. For comparison, the average outer diameter of a 5 French introducer sheath is 2.29 mm and a 6 French introducer sheath is 2.62 mm.

CONCLUSIONS

The findings presented in this study will help determine the most appropriate transradial device to use in several different populations in the context of vasodilator usage or the absence thereof.

Nocebo response in human models of migraine: A systematic review and meta-analysis of randomized, double-blind, placebo-controlled, two-way crossover trials in migraine without aura and healthy volunteers

BACKGROUND

Human models of migraine have been used for the past 30 years to test putative 'trigger' molecules and ascertain whether they induce migraine attacks in humans. However, nocebo effects using this model have never been systematically explored.

OBJECTIVE

To assess the nocebo response rate in randomised clinical trials conducted at the Danish Headache Center, and in which human models of migraine were used.

METHODS

In this systematic review and meta-analysis, we searched PubMed for studies of human models of migraine with a randomised, double-blind, placebo-controlled, two-way crossover design that included data on the incidence of migraine attacks or headache after infusion of placebo. A total of 943 articles were screened by title and abstract. Of these, 27 studies met the inclusion criteria (published between 1994 and 2020) and were included in the qualitative and quantitative analysis. We performed a random effects meta-analysis for the incidence of migraine attacks or delayed headache after placebo infusion.

RESULTS

Twenty-seven studies were eligible for inclusion: 12 studies reported data for adults with migraine (n = 182), whereas 16 studies reported data on healthy volunteers (n = 210). For adults with migraine, the incidence of migraine attacks after placebo was 8.1% (95% CI = 2.5-15.5%, I² = 50.8%). The incidence of delayed headache was 25.9% (95% CI = 18.5-34.1%, I² = 18.9%). For healthy volunteers, the incidence of migraine attacks after placebo was 0.5% (95% CI = 0.0-3.6%, I² = 0.0%) while the incidence of delayed headache was 10.5% (95% CI = 4.8-17.6%, I² = 45.2%).

CONCLUSION

The nocebo response in randomised, placebo-controlled two-way crossover trials with intravenous infusions of placebo in migraine is negligible. Future studies using human models of migraine can be conducted by assuming a nocebo response rate of 15.5%.

Cholinergic modulation inhibits cortical spreading depression in mouse neocortex through activation of muscarinic receptors and decreased excitatory/inhibitory drive

Cortical spreading depression (CSD) is a wave of transient network hyperexcitability leading to long lasting depolarization and block of firing, which initiates focally and slowly propagates in the cerebral cortex. It causes migraine aura and it has been implicated in the generation of migraine headache. Cortical excitability can be modulated by cholinergic actions, leading in neocortical slices to the generation of rhythmic synchronous activities (UP/DOWN states). We investigated the effect of cholinergic activation with the cholinomimetic agonist carbachol on CSD triggered with 130 mM KCl pulse injections in acute mouse neocortical brain slices, hypothesizing that the cholinergic-induced increase of cortical network excitability during UP states could facilitate CSD. We observed instead an inhibitory effect of cholinergic activation on both initiation and propagation of CSD, through the action of muscarinic receptors. In fact, carbachol-induced CSD inhibition was blocked by atropine or by the preferential M1 muscarinic antagonist telenzepine; the preferential M1 muscarinic agonist McN-A-343 inhibited CSD similarly to carbachol, and its effect was blocked by telenzepine. Recordings of spontaneous excitatory and inhibitory post-synaptic currents in pyramidal neurons showed that McN-A-343 induced overall a decrease of the excitatory/inhibitory ratio. This inhibitory action may be targeted for novel pharmacological approaches in the treatment of migraine with muscarinic agonists.

Prolonged and localized sweat stimulation by iontophoretic delivery of the slowly-metabolized cholinergic agent carbachol

BACKGROUND

Continuous non-invasive sampling and sensing of multiple classes of analytes could revolutionize medical diagnostics and wearable technologies, but also remains highly elusive because of the many confounding factors for candidate biofluids such as interstitial fluid, tears, saliva, and sweat. Eccrine sweat biosensing has seen a recent surge in demonstrations of wearable sampling and sensing devices. However, for subjects at rest, access to eccrine sweat is highly limited and unpredictable compared to saliva and tears.

OBJECTIVE

Reported here is a prolonged and localized sweat stimulation by iontophoretic delivery of the slowly-metabolized nicotinic cholinergic agonist carbachol.

METHODS

Presented here are detailed measurements of natural baseline sweat rates across multiple days, confirming a clear need for localized sweat stimulation. Iontophoresis was performed with either carbachol or pilocarpine in order to stimulate sweat in subjects at rest. Furthermore, improved methods of quantifying sweat generation rates (nL/min/gland) are demonstrated.

RESULTS

In-vivo testing reveals that carbachol stimulation can surpass a major goal of 24-h sweat access, in some cases providing more than an order of magnitude longer duration than stimulation with commonly-used pilocarpine. Also demonstrated is reduction of the traditional iontophoretic dosage for sweat stimulation (<5.25-42mC/cm²). This increases the viability of repeated dosing as demonstrated herein, and for carbachol is as much as 100-1000X less than used for other applications.

CONCLUSION

This work is not only significant for wearable sweat biosensing technology, but could also have broader impact for those studying topical skin products, antiperspirants, textiles and medical adhesives, nerve disorders, the effects of perspiration on skin-health, skin related diseases such as idiopathic pure sudomotor failure and hyperhidrosis, and other skin- and perspiration-related applications.

Mamontov O, A. Kamshilin A, Giniatullin R. Parasympathetic Cholinergic and Neuropeptide Mechanisms of Migraine

Context

Migraine mechanisms remain largely uncovered for various reasons including a very high complexity of the neurophysiological mechanisms implicated in this disorder and a plethora of endogenous biologically active compounds involved in the pathological process. The functional role of parasympathetic innervation of meninges and cholinergic mechanisms of migraine are among little explored issues despite multiple evidence indirectly indicating the role of acetylcholine (ACh) and its analogues in migraine and other types of headache. In the current short review, we discuss morphological, functional, and clinical issues related to the role of ACh and its analogues such as carbachol and nicotine in this most common neurological disorder.

Evidence Acquisition

In the present work, studies published from 1953 to 2016 were investigated. Literature was searched with following keywords: acetylcholine (ACh), carbachol, nicotine, parasympathetic, mast cells, vasoactive intestinal polypeptide (VIP), and pituitary adenylate cyclase-activating polypeptide (PACAP).

Results

Parasympathetic fibers originated from SPG and trigeminal nerves can interact at the level of meninges which is considered to be the origin site of migraine pain. Here, in dura mater, ACh, VIP, and PACAP released by parasympathetic afferents can both affect mast cells provoking its degranulation and additional release of neurotransmitters, or they can directly affect trigeminal nerves inducing nociception.

Conclusions

In summary, cholinergic mechanisms in migraine and other types of headache remain little elucidated and future studies should clarify the role of parasympathetic nerves and molecular mechanisms of cholinergic modulation within the nociceptive system.

Sources of variability of resting cerebral blood flow in healthy subjects: a study using ¹³³Xe SPECT measurements

Measurements of cerebral blood flow (CBF) show large variability among healthy subjects. The aim of the present study was to investigate the relative effect of established factors influencing CBF on the variability of resting CBF. We retrospectively analyzed spontaneous variability in 430 CBF measurements acquired in 152 healthy, young subjects using (133)Xe single-photon emission computed tomography. Cerebral blood flow was correlated positively with both end-tidal expiratory PCO₂ (PETCO₂) and female gender and inversely with hematocrit (Hct). Between- and within-subject CO₂ reactivity was not significantly different. Including PETCO₂, Hct and gender in the model reduced between-subject and within-subject variance by 14% and 13.5%, respectively. Within-subject variability was mainly influenced by PETCO₂ and between-subject variability mostly by Hct, whereas gender appeared to be of little added value when Hct was also accounted for. The present study confirms large between-subject variability in CBF measurements and that gender, Hct, and PETCO₂ explain only a small part of this variability. This implies that a large fraction of CBF variability may be due to unknown factors such as differences in neuron density or metabolism that could be subject for further studies.

Prostaglandin E(2) induces immediate migraine-like attack in migraine patients without aura

BACKGROUND

Prostaglandin E(2) (PGE(2)) has been suggested to play an important role in the pathogenesis of migraine. In the present experiment we investigated if an intravenous infusion of PGE(2) would induce migraine-like attacks in patients with migraine.

METHODS

Twelve patients with migraine without aura were randomly allocated to receive 0.4 µg/kg/min PGE(2) (Prostin(®)E2, dinoprostone) or placebo over 25 minutes in a two-way, crossover study. Headache intensity was recorded on a verbal rating scale, middle cerebral artery blood flow velocity (V(MCA)) was measured by transcranial Doppler (TCD) and diameter of the superficial temporal artery (STA) was obtained by c-series scan (Dermascan C).

RESULTS

In total, nine migraine patients (75%) experienced migraine-like attacks after PGE(2) compared to none after placebo (p = 0.004). Seven out of 9 (58%) patients reported the migraine-like attacks during the immediate phase (0-90 min) (p = 0.016). Only two patients experienced the delayed migraine-like attacks several hours after the PGE(2) infusion stop (p = 0.500). The V(MCA) decreased during the PGE(2) infusion (p = 0.005) but there was no significant dilatation of the STA (p = 0.850).

CONCLUSION

The migraine-like attacks during, and immediately after, the PGE(2) infusion contrast with those found in previous provocation studies, in which the other pharmacological compounds triggered the delayed migraine-like attacks several hours after the infusion. We suggest that PGE(2) may be one of the important final products involved in the generation of migraine attacks.

The role of the neurovascular scalp structures in migraine

AIM

To review reports suggesting a role for neurovascular scalp structures in migraine.

MAIN DATA REPORTED

(A) Scalp periarterial nervous fibres contain all the main peptides and receptors involved in pain. (B) It is possible to interrupt or alleviate migraine pain with a prolonged compression of the main scalp arteries, which decreases blood flow through the pain-sensitized vessels and probably induces a temporary conduction block of periarterial nociceptive fibres. (C) Painful points are present on the scalp arteries of a considerable percentage of migraine sufferers. (D) It is possible to stop or alleviate pain by intervening on nociceptive periarterial fibres, as for example with the injection of lidocaine or 3-5 ml saline, and with percutaneous application of a capsaicin cream.

CONCLUSION

The data reported suggest a role for neurovascular scalp structures in at least some patients with migraine. It would be of interest to find a clinical distinction between patients according to the prevalence of an intracranial or extracranial peripheral pain mechanism. This could lead to more efficacious treatments.

Emerging migraine treatments and drug targets

Migraine has a 1-year prevalence of 10% and high socioeconomic costs. Despite recent drug developments, there is a huge unmet need for better pharmacotherapy. In this review we discuss promising anti-migraine strategies such as calcitonin gene-related peptide (CGRP) receptor antagonists and 5-hydroxytrypamine (5-HT)(1F) receptor agonists, which are in late-stage development. Nitric oxide antagonists are also in development. New forms of administration of sumatriptan might improve efficacy and reduce side effects. Botulinum toxin A has recently been approved for the prophylaxis of chronic migraine. Tonabersat, a cortical spreading depression inhibitor, has shown efficacy in the prophylaxis of migraine with aura. Several new drug targets such as nitric oxide synthase, the 5-HT(1D) receptor, the prostanoid receptors EP(2) and EP(4), and the pituitary adenylate cyclase receptor PAC1 await development. The greatest need is for new prophylactic drugs, and it seems likely that such compounds will be developed in the coming decade.

Lack of correlation between vasodilatation and pharmacologically induced immediate headache in healthy subjects

BACKGROUND

The causal relationship between experimental headache and vasodilatation has not been fully clarified. In the present study, we combined headache and vascular data from eight experimental studies and conducted detailed statistical analyses. Given that substances used in all these experiments were vasodilators we examined a possible correlation between headache scores and increases in arterial diameter.

METHODS

We identified nine studies and retrieved raw data in 89 healthy subjects (46 females, 43 males), mean age 27 years (range 18-59 years). The following variables were collected: maximal median headache intensity scores on a verbal rating scale (VRS) during immediate headache (0-120 minutes); the mean velocity of blood flow in the middle cerebral artery (V(meanMCA)); and the diameter of the frontal branch of the superficial temporal artery (STA) during the maximal median headache intensity.

RESULTS

The scatter plots show no relationship between maximal headache score and the relative changes in V(meanMCA) and diameter of the STA. The main analyses of covariance showed a significant effect only of heart rate on headache (p = .014). The interaction tests were insignificant for all variables.

CONCLUSIONS

The major outcome is a finding of no linear relationship between experimental immediate headache and dilatation of the MCA or STA.

What have we learnt from triggering migraine?

PURPOSE OF REVIEW

This review presents what we have learnt from triggering migraine.

RECENT FINDINGS

Experimental studies have shown that glyceryl trinitrate (GTN), calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase activating polypeptide-38 (PACAP38) and prostaglandin I2 (PGI2) induce migraine-like attacks in migraine suffers indistinguishable from their spontaneous attacks. These studies point to two key pathways to play an important role in migraine pathophysiology: cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP). At present, no valid experimental model exists to reproduce aura episodes in migraine with aura patients. Familiar hemiplegic migraine patients seem to be less sensitive to GTN and CGRP provocation compared with common types of migraine. Advances in recent imaging studies suggest neuronal mechanisms to be behind migraine attacks. The experimental headache models have resulted in development and an ongoing search of new migraine targets.

SUMMARY

Human models of migraine offer unique possibilities to study mechanisms responsible for different migraine subtypes and to explore the mechanisms of action of existing and future antimigraine drugs. Adding advanced imaging techniques to the models may lead to a better understanding of the complex events that constitutes a migraine attack and thereby more targeted ways of intervention.

Carbachol induces headache, but not migraine-like attacks, in patients with migraine without aura

Carbachol induces headache in healthy subjects, but the migraine eliciting effect of carbachol has not previously been studied. We hypothesized that the cholinomimetic agonist carbachol would induce headache and migraine-like attacks in migraineurs. Carbachol (3 µg/kg) or placebo was randomly infused into 18 patients with migraine without aura in a double-blind crossover study. Headache was scored on a verbal rating scale from 0 to 10. Velocity in the middle cerebral artery (VMCA) and diameter of the superficial temporal artery (STA) were recorded. Fifteen patients experienced headache after carbachol compared with eight after placebo ( P = 0.039). There was no difference in incidence of migraine-like attacks after carbachol ( n = 8) compared with placebo ( n = 6) ( P = 0.687). Carbachol caused a decrease in VMCA ( P = 0.044), but no change in STA ( P = 0.089) compared with placebo. The study demonstrated that carbachol provocation is not a good model for experimental migraine.

Migraine pain: reflections against vasodilatation

The original Wolff’s vascular theory of migraine was supported by the discovery of a class of drugs, the triptans, developed as a selective cephalic vasoconstrictor agents. Even in the neurovascular hypothesis of Moskowitz, that is the neurogenic inflammation of meningeal vessels provoked by peptides released from trigeminal sensory neurons, the vasodilatation provoked by calcitonin gene-related peptide (CGRP) is considered today much more important than oedema. The role of cephalic vasodilatation as a cause of migraine pain was recently sustained by studies showing the therapeutic effect of CGRP receptor antagonists. We discuss the evidence against vasodilatation as migraine pain generator and some findings which we suggest in support of a central (brain) origin of pain.