Opiate-induced persistent pronociceptive trigeminal neural adaptations: potential relevance to opiate-induced medication overuse headache

Unsatisfactory response to acute medications does not affect the medication overuse headache development in pediatric chronic migraine

BACKGROUND

Chronic migraine (CM) negatively impacts the quality of life of 2 to 4% of pediatric patients. In adults, CM is frequently linked to medication overuse headache (MOH), but there is a much lower prevalence of MOH in children. A suboptimal response to acute therapies may lead to their reduced use, thus preventing MOH development in children and adolescents. The frequency of patients with CM who do not respond to acute therapies was examined in the present study. We investigated whether the prevalence of MOH was different between responders and non-responders. We also examined whether patients receiving prophylactic therapy had an improved response to acute therapy. Finally, we investigated if there was a difference in the frequency of psychiatric comorbidities between responders and non-responders.

METHODS

We retrospectively analysed clinical data of all chronic pediatric migraineurs under the age of 18 referred to the Headache Centre at Bambino Gesù Children Hospital in June 2021 and February 2023. ICHD3 criteria were used to diagnose CM and MOH. We collected demographic data, including the age at onset of migraine and the age of the CM course. At baseline and after 3 months of preventive treatment, we evaluated the response to acute medications. Neuropsychiatric comorbidities were referred by the children's parents during the first attendance evaluation.

RESULTS

Seventy patients with CM were assessed during the chosen period. Paracetamol was tried by 41 patients (58.5%), NSAIDs by 56 patients (80.0%), and triptans by 1 patient (1.4%). Fifty-one participants (73%) were non-responder to the abortive treatment. The presence of MOH was detected in 27.1% of the whole populations. Regarding our primary aim, MOH was diagnosed in 29% of non-responder patients and 22% of responders (p > 0.05). All patients received preventative treatment. After 3 months of preventive pharmacological therapy, 65.4% of patients who did not respond to acute medications achieved a response, while 34.6% of patients who were non-responder remain non-responder (p < 0.05). Prophylactic therapy was also effective in 69% of patients who responded to acute medication (p < 0.05). Psychiatric comorbidities were detected in 68.6% of patients, with no difference between responders and non-responders (72.2% vs. 67.3%; p = 0.05).

CONCLUSIONS

Despite the high prevalence of unresponsiveness to acute therapies in pediatric CM, it does not act as a protective factor for MOH. Moreover, responsiveness to acute drugs is improved by pharmacological preventive treatment and it is not affected by concomitant psychiatric comorbidities.

Morphine acts in vitro to directly prime nociceptors

Hyperalgesic priming is a preclinical model of the transition from acute to chronic pain characterized by a leftward shift in the dose-response curve for and marked prolongation of prostaglandin E2 (PGE2)-induced mechanical hyperalgesia, in vivo. In vitro, priming in nociceptors is characterized by a leftward shift in the concentration dependence for PGE2-induced nociceptor sensitization. In the present in vitro study we tested the hypothesis that a mu-opioid receptor (MOR) agonist opioid analgesic, morphine, can produce priming by its direct action on nociceptors. We report that treatment of nociceptors with morphine, in vitro, produces a leftward shift in the concentration dependence for PGE2-induced nociceptor sensitization. Our findings support the suggestion that opioids act directly on nociceptors to induce priming.

Risk factors for migraine disease progression: a narrative review for a patient-centered approach

BACKGROUND

In individuals with migraine, attacks may increase in frequency, severity, or both. Preventing migraine progression has emerged as a treatment goal in headache subspecialty practice, but there may be less awareness in general neurology or primary care settings where most people with migraine who seek treatment consult. Herein, we review the definition of and risk factors for migraine progression and consider strategies that could reduce its risk.

METHODS

A group of headache expert healthcare professionals, clinicians, and researchers reviewed published evidence documenting factors associated with increased or decreased rates of migraine progression and established expert opinions for disease management recommendations. Strength of evidence was rated as good, moderate, or based solely on expert opinion, using modified criteria for causation developed by AB Hill.

RESULTS

Migraine progression is commonly operationally defined as the transition from ≤ 15 to ≥ 15 monthly headache days among people with migraine; however, this does not necessarily constitute a fundamental change in migraine biology and other definitions should be considered. Established and theoretical key risk factors for migraine progression were categorized into five domains: migraine disease characteristics, treatment-related factors, comorbidities, lifestyle/exogenous factors, and demographic factors. Within these domains, good evidence supports the following risk factors: poorly optimized acute headache treatment, cutaneous allodynia, acute medication overuse, selected psychiatric symptoms, extra-cephalic chronic pain conditions, metabolism-related comorbidities, sleep disturbances, respiratory conditions, former/current high caffeine intake, physical inactivity, financial constraints, tobacco use, and personal triggers as risk factors. Protective actions that may mitigate migraine progression are sparsely investigated in published literature; our discussion of these factors is primarily based on expert opinion.

CONCLUSIONS

Recognizing risk factors for migraine progression will allow healthcare providers to suggest protective actions against migraine progression (Supplementary Fig. 1). Intervention studies are needed to weight the risk factors and test the clinical benefit of hypothesized mitigation strategies that emerge from epidemiological evidence.

Histone Deacetylase Inhibitors Counteract CGRP Signaling and Pronociceptive Sensitization in a Rat Model of Medication Overuse Headache

Chronic triptan exposurein rodents recapitulates medication overuse headache (MOH), causing cephalic pain sensitization and trigeminal ganglion overexpression of pronociceptive proteins including CGRP. Because of these transcriptional derangements, as well as the emerging role of epigenetics in chronic pain, in the present study, we evaluated the effects of the histone deacetylase inhibitors (HDACis) panobinostat and givinostat, in rats chronically exposed to eletriptan for one month. Both panobinostat and givinostat counteracted overexpression of genes coding for CGRP and its receptor subunit RAMP1, having no effects on CLR and RCP receptor subunits in the trigeminal ganglion (TG) of eletriptan-exposed rats. Within the trigeminal nucleus caudalis (TNc), transcripts for these genes were neither upregulated by eletriptan nor altered by concomitant treatment with panobinostat or givinostat. HDACis counteracted hypersensitivity to capsaicin-induced vasodilatation in the trigeminal territory, as well as photophobic behavior and cephalic allodyniain eletriptan-exposed rats. Eletriptan did not affect CGRP, CLR, and RAMP1 expression in cultured trigeminal ganglia, whereas both inhibitors reduced transcripts for CLR and RAMP-1. The drugs, however, increased luciferase expression driven by CGRP promoter in cultured cells. Our findings provide evidence for a key role of HDACs and epigenetics in MOH pathogenesis, highlighting the therapeutic potential of HDAC inhibition in the prevention of migraine chronification.

Burden of increasing opioid use in the treatment of migraine: Results from the Migraine in America Symptoms and Treatment Study

OBJECTIVE

We sought to assess factors associated with the frequency of self-reported prescription opioid use in persons with migraine, including demographic variables, comorbidities, headache characteristics, and patterns of consultation.

BACKGROUND

Despite the dose-dependent effect of opioids on migraine progression and the association with negative outcomes, migraine treatment often includes opioids. The Migraine in America Symptoms and Treatment Study focuses on individuals with migraine who receive prescription acute medications, including those receiving and those not receiving opioids.

METHODS

This web-based panel survey identified people in the United States with migraine using a validated screener. This analysis stratified people with migraine into 4 groups based on days of monthly opioid use: non-opioid users, ≤3 days, 4-9 days, and ≥10 days per month.

RESULTS

Of 15,133 respondents with migraine, 4701 (31%) reported acute prescription medication use for headache/migraine in the previous 3 months (mean age 45 years, 71.6% [3367/4701] female), of whom 32.5% (1528/4701) reported opioid use. About one-third of respondents with primary care or neurology consults in the prior 6 months reported receiving an opioid, and more than half of respondents (209/391, 53.5%) with a pain clinic consultation did so. Models compared those using opioids ≤3 days/month (879/4701, 18.7%), 4-9 days/month (304/4701, 6.5%), ≥10 days/month (345/4701, 7.3%) to non-opioid users (3173/4701, 67.5%). Compared to non-opioid users, infrequent users (≤3 days/month) were more likely to be male and less likely to have chronic migraine or to screen positive for anxiety and depression; and frequent opioid users (the 4-9 days/month and the ≥10 days/month groups) were more likely to be male, to smoke, to be obese, to report greater pain interference, to have moderate to severe disability, to have symptoms of anxiety and depression, to use fewer triptans and nonsteroidal anti-inflammatory drugs, and to have poor acute treatment optimization.

CONCLUSION

Among prescription medication users, this cross-sectional analysis shows that increasing use of prescription opioids is associated with male gender, chronic migraine, more severe disability, anxiety and depression, poor acute treatment optimization, and treatment in a pain clinic.

Opioid-Induced Hyperalgesic Priming in Single Nociceptors

Clinical µ-opioid receptor (MOR) agonists produce hyperalgesic priming, a form of maladaptive nociceptor neuroplasticity, resulting in pain chronification. We have established an in vitro model of opioid-induced hyperalgesic priming (OIHP), in male rats, to identify nociceptor populations involved and its maintenance mechanisms. OIHP was induced in vivo by systemic administration of fentanyl and confirmed by prolongation of prostaglandin E₂ (PGE₂) hyperalgesia. Intrathecal cordycepin, which reverses Type I priming, or the combination of Src and mitogen-activated protein kinase (MAPK) inhibitors, which reverses Type II priming, both partially attenuated OIHP. Parallel in vitro experiments were performed on small-diameter (<30 µm) dorsal root ganglion (DRG) neurons, cultured from fentanyl-primed rats, and rats with OIHP treated with agents that reverse Type I or Type II priming. Enhancement of the sensitizing effect of a low concentration of PGE₂ (10 nm), another characteristic feature of priming, measured as reduction in action potential (AP) rheobase, was found in weakly isolectin B4 (IB4)-positive and IB4-negative (IB4-) neurons. In strongly IB4-positive (IB4+) neurons, only the response to a higher concentration of PGE₂ (100 nm) was enhanced. The sensitizing effect of 10 nm PGE₂ was attenuated in weakly IB4+ and IB4- neurons cultured from rats whose OIHP was reversed in vivo Thus, in vivo administration of fentanyl induces neuroplasticity in weakly IB4+ and IB4- nociceptors that persists in vitro and has properties of Type I and Type II priming. The mechanism underlying the enhanced sensitizing effect of 100 nm PGE₂ in strongly IB4+ nociceptors, not attenuated by inhibitors of Type I and Type II priming, remains to be elucidated.SIGNIFICANCE STATEMENT Commonly used clinical opioid analgesics, such as fentanyl and morphine, can produce hyperalgesia and chronification of pain. To uncover the nociceptor population mediating opioid-induced hyperalgesic priming (OIHP), a model of pain chronification, and elucidate its underlying mechanism, at the cellular level, we established an in vitro model of OIHP. In dorsal root ganglion (DRG) neurons cultured from rats primed with fentanyl, robust nociceptor population-specific changes in sensitization by prostaglandin E₂ (PGE₂) were observed, when compared with nociceptors from opioid naive rats. In DRG neurons cultured from rats with OIHP, enhanced PGE₂-induced sensitization was observed in vitro, with differences identified in non-peptidergic [strongly isolectin B4 (IB4)-positive] and peptidergic [weakly IB4-positive (IB4+) and IB4-negative (IB4-)] nociceptors.

Migraine and Two-Pore-Domain Potassium Channels

Migraine is a common, disabling neurological disorder with a genetic, environmental, and hormonal component with an annual prevalence estimated at ~15%. It is characterized by attacks of severe, usually unilateral and throbbing headache, and can be accompanied by nausea, vomiting, and photophobia. Migraine is clinically divided into two main subtypes: migraine with aura, when it is preceded by transient neurological disturbances due to cortical spreading depression (CSD), and migraine without aura. Activation and sensitization of trigeminal sensory neurons, leading to the release of pro-inflammatory peptides, is likely a key component in headache pain initiation and transmission in migraine. In the present review, we will focus on the function of two-pore-domain potassium (K_2P) channels, which control trigeminal sensory neuron excitability and their potential interest for developing new drugs to treat migraine.

Evaluation of LY573144 (lasmiditan) in a preclinical model of medication overuse headache

BACKGROUND

Medication overuse is a significant issue that complicates the treatment of headache disorders. The most effective medications for the acute treatment of migraine all have the capacity to induce medication overuse headache (MOH). Novel acute migraine-specific treatments are being developed. However, because the mechanism(s) underlying medication overuse headache are not well understood, it is difficult to predict whether any particular acute medication will induce MOH in susceptible individuals. LY573144 (lasmiditan), a 5-HT_1F receptor agonist, has recently been shown to be effective in the acute treatment of migraine in phase 3 trials. The aim of this study is to determine whether frequent administration of lasmiditan induces behaviors consistent with MOH in a pre-clinical rat model.

METHODS

Sprague Dawley rats were administered six doses of lasmiditan (10 mg/kg), sumatriptan (10 mg/kg), or sterile water orally over 2 weeks and cutaneous allodynia was evaluated regularly in the periorbital and hindpaw regions using von Frey filaments. Testing continued until mechanosensitivity returned to baseline levels. Rats were then submitted to bright light stress (BLS) or nitric oxide (NO) donor administration and were again evaluated for cutaneous allodynia in the periorbital and hindpaw regions hourly for 5 hours.

RESULTS

Both lasmiditan and sumatriptan exhibited comparable levels of drug-induced cutaneous allodynia in both the periorbital and hindpaw regions, which resolved after cessation of drug administration. Both lasmiditan and sumatriptan pre-treatment resulted in cutaneous allodynia that was evoked by either BLS or NO donor.

CONCLUSIONS

In a pre-clinical rat model of MOH, oral lasmiditan, like sumatriptan, induced acute transient cutaneous allodynia in the periorbital and hindpaw regions that after resolution could be re-evoked by putative migraine triggers. These results suggest that lasmiditan has the capacity to induce MOH through persistent latent peripheral and central sensitization mechanisms.

Heroin-induced headache in female heroin addicts

Objective

To investigate the manifestations and incidence of headaches caused by heroin in Chinese women.

Methods

This was a survey study conducted from 29 June to 3 July 2015 with women attending the Shanxi Drug Rehabilitation Centre for Women (China). All study subjects were newly admitted and had not begun their drug rehabilitation. Demographic characteristics, heroin usage and headache episodes within the previous 3 months were surveyed, especially the presence of a headache within 2 hours of heroin use. Details of the severity, location, premonitory symptoms and characteristics of headaches were recorded.

Results

Of the 90 heroin-dependent patients, 74 experienced headache attacks within 2 hours of heroin use, and the headaches subsided within 72 hours of discontinuation of heroin use. Most heroin-induced headaches were similar to migraines and manifested as pulsating pain in 54 patients (51/74, 68.9%); bilateral pain was reported by 46 patients (46/74, 62.2%). Approximately half of the patients with heroin-induced headaches also reported accompanying symptoms of nausea, vomiting, and light and sound sensitivity.

Conclusions

Heroin-induced headache may eventually be listed as a new class of headache in the International Classification of Headache Disorders.

C-tactile touch perception in migraineurs – a case-control study

Background

Migraine is characterized by sensory hypersensitivity and habituation deficits. Slow brushing over the skin activates C-tactile nerve fibers, which mediate pleasant touch and analgesic effects in healthy subjects. As this function is altered in painful conditions, we aimed to examine whether the C-tactile processing is disrupted in migraines.

Methods

To psychophysically assess C-tactile function, we applied optimal and suboptimal C-tactile stroking stimuli on the dorsal forearm (body reference area) and the trigeminally innervated skin of 52 interictal migraineurs and 52 matched healthy controls. For habituation testing, 60 repeated C-tactile optimal stimuli were presented in both test areas. The participants rated each stimulus on a visual analogue scale by intensity, pleasantness, and painfulness.

Results

Regarding C-tactile function, migraineurs showed unphysiological rating patterns but no significantly different pleasantness ratings than controls. During repeated stimulation, controls showed stable pleasantness ratings while migraineurs’ ratings decreased, especially in those experiencing tactile allodynia during headaches. Migraineurs taking triptans responded like controls.

Conclusion

The C-tactile function of migraineurs is subclinically altered. Repeated C-tactile stimulation leads to altered habituation but differs from previous work by the direction of the changes. Although the pathophysiology remains unknown, causative mechanisms could include central and peripheral neuronal sensitization, tactile allodynia and hedonic stimulus attributions.

Impact of chronic migraine attacks and their severity on the endogenous μ-opioid neurotransmission in the limbic system

OBJECTIVE

To evaluate, in vivo, the impact of ongoing chronic migraine (CM) attacks on the endogenous μ-opioid neurotransmission.

BACKGROUND

CM is associated with cognitive-emotional dysfunction. CM is commonly associated with frequent acute medication use, including opioids.

METHODS

We scanned 15 migraine patients during the spontaneous headache attack (ictal phase): 7 individuals with CM and 8 with episodic migraine (EM), as well as 7 healthy controls (HC), using positron emission tomography (PET) with the selective μ-opioid receptor (μOR) radiotracer [11C]carfentanil. Migraineurs were scanned in two paradigms, one with thermal pain threshold challenge applied to the site of the headache, and one without thermal challenge. Multivariable analysis was performed between the μ-opioid receptor availability and the clinical data.

RESULTS

μOR availability, measured with [11C]carfentanil nondisplaceable binding potential (BPND), in the left thalamus (P-value = 0.005) and left caudate (P-value = 0.003) were decreased in CM patients with thermal pain threshold during the ictal phase relative to HC. Lower μOR BPND in the right parahippocampal region (P-value = 0.001) and right amygdala (P-value = 0.002) were seen in CM relative to EM patients. Lower μOR BPND values indicate either a decrease in μOR concentration or an increase in endogenous μ-opioid release in CM patients. In the right amygdala, 71% of the overall variance in μOR BPND levels was explained by the type of migraine (CM vs. EM: partial-R2 = 0.47, P-value<0.001, Cohen's effect size d = 2.6SD), the severity of the attack (pain area and intensity number summation [P.A.I.N.S.]: partial-R2 = 0.16, P-value = 0.031), and the thermal pain threshold (allodynia: partial-R2 = 0.08).

CONCLUSIONS

Increased endogenous μ-opioid receptor-mediated neurotransmission is seen in the limbic system of CM patients, especially in right amygdala, which is highly modulated by the attack frequency, pain severity, and sensitivity. This study demonstrates for the first time the negative impact of chronification and exacerbation of headache attacks on the endogenous μ-opioid mechanisms of migraine patients. ClinicalTrials.gov identifier: NCT03004313.

Diagnosing and managing migraine in children and young people

This article gives an overview of migraine in children. It outlines the epidemiology of the condition and describes presentation with headache and other symptoms and linked conditions. It aims to raise awareness of the diagnosis of migraine and its impact on children and young people, their families and school life. The author also describes methods of diagnosis and management, and the importance of recognising and of avoiding medication overuse.

Reward and aversion processing in patients with post-traumatic stress disorder: functional neuroimaging with visual and thermal stimuli

In patients with post-traumatic stress disorder (PTSD), a decrease in the brain reward function was reported in behavioral- and in neuroimaging studies. While pathophysiological mechanisms underlying this response are unclear, there are several lines of evidence suggesting over-recruitment of the brain reward regions by aversive stimuli rendering them unavailable to respond to reward-related content. The purpose of this study was to juxtapose brain responses to functional neuroimaging probes that reliably produce rewarding and aversive experiences in PTSD subjects and in healthy controls. The stimuli used were pleasant, aversive and neutral images selected from the International Affective Picture System (IAPS) along with pain-inducing heat applied to the dorsum of the left hand; all were administered during 3 T functional magnetic resonance imaging. Analyses of IAPS responses for the pleasant images revealed significantly decreased subjective ratings and brain activations in PTSD subjects that included striatum and medial prefrontal-, parietal- and temporal cortices. For the aversive images, decreased activations were observed in the amygdala and in the thalamus. PTSD and healthy subjects provided similar subjective ratings of thermal sensory thresholds and each of the temperatures. When 46 °C (hot) and 42 °C (neutral) temperatures were contrasted, voxelwise between-group comparison revealed greater activations in the striatum, amygdala, hippocampus and medial prefrontal cortex in the PTSD subjects. These latter findings were for the most part mirrored by the 44 vs. 42 °C contrast. Our data suggest different brain alterations patterns in PTSD, namely relatively diminished corticolimbic response to pleasant and aversive psychosocial stimuli in the face of exaggerated response to heat-related pain. The present findings support the hypothesis that brain sensitization to pain in PTSD may interfere with the processing of psychosocial stimuli whether they are of rewarding or aversive valence.

Sustained exposure to acute migraine medications combined with repeated noxious stimulation dysregulates descending pain modulatory circuits: Relevance to medication overuse headache

Background

Loss of conditioned pain modulation/diffuse noxious inhibitory controls has been demonstrated in patients with migraine and medication overuse headache. We hypothesized that exposure to acute migraine medications may lead to dysregulation of central pain modulatory circuits that could be revealed by evaluating diffuse noxious inhibitory controls and that prior noxious stimulus is required for a loss of the diffuse noxious inhibitory control response in rats exposed to these medications.

Methods

Rats were “primed” by continuous infusion of morphine or one of two doses of sumatriptan. Diffuse noxious inhibitory control was evaluated at the end of drug-priming (day 7) and again after sensory thresholds returned to baseline (day 21). The Randall-Selitto hindpaw pressure test was used as the test stimulus and forepaw capsaicin injection served as the conditioning stimulus.

Results

Morphine-primed rats showed opioid-induced hyperalgesia accompanied by a loss of diffuse noxious inhibitory controls on day 7. Sumatriptan-primed rats did not develop hyperalgesia or loss of diffuse noxious inhibitory controls on day 7. Morphine-primed and high-dose sumatriptan-primed rats only had a loss of diffuse noxious inhibitory control on day 21 if they received a capsaicin injection on day 7.

Conclusions

Prolonged exposure to migraine treatments followed by an acute nociceptive stimulation caused long-lasting alterations in descending pain modulation, shown by a loss of diffuse noxious inhibitory controls. Morphine was more detrimental than sumatriptan, consistent with clinical observations of higher medication overuse headache risk with opioids. These data suggest a mechanism of medication overuse headache by which migraine medications combined with repeated episodes of pain may amplify the consequences of nociceptor activation and increase the probability of future migraine attacks as well as risk of medication overuse headache.

Kappa opioid receptor antagonists: A possible new class of therapeutics for migraine prevention

Background Stress is the most commonly reported migraine trigger. Dynorphin, an endogenous opioid peptide acting preferentially at kappa opioid receptors (KORs), is a key mediator of stress responses. The aim of this study was to use an injury-free rat model of functional cephalic pain with features of migraine and medication overuse headache (MOH) to test the possible preventive benefit of KOR blockade on stress-induced cephalic pain. Methods Following sumatriptan priming to model MOH, rats were hyper-responsive to environmental stress, demonstrating delayed cephalic and extracephalic allodynia and increased levels of CGRP in the jugular blood, consistent with commonly observed clinical outcomes during migraine. Nor-binaltorphimine (nor-BNI), a long-acting KOR antagonist or CYM51317, a novel short-acting KOR antagonist, were given systemically either during sumatriptan priming or immediately before environmental stress challenge. The effects of KOR blockade in the amygdala on stress-induced allodynia was determined by administration of nor-BNI into the right or left central nucleus of the amygdala (CeA). Results KOR blockade prevented both stress-induced allodynia and increased plasma CGRP. Stress increased dynorphin content and phosphorylated KOR in both the left and right CeA in sumatriptan-primed rats. However, KOR blockade only in the right CeA prevented stress-induced cephalic allodynia as well as extracephalic allodynia, measured in either the right or left hindpaws. U69,593, a KOR agonist, given into the right, but not the left, CeA, produced allodynia selectively in sumatriptan-primed rats. Both stress and U69,593-induced allodynia were prevented by right CeA U0126, a mitogen-activated protein kinase inhibitor, presumably acting downstream of KOR. Conclusions Our data reveal a novel lateralized KOR circuit that mediated stress-induced cutaneous allodynia and increased plasma CGRP in an injury-free model of functional cephalic pain with features of migraine and medication overuse headache. Selective, small molecule, orally available, and reversible KOR antagonists are currently in development and may represent a novel class of preventive therapeutics for migraine.

Neuropeptides and ATP signaling in the trigeminal ganglion

Peripheral nociceptive stimuli from orofacial structures are largely transmitted by the trigeminal nerve. According to the peripheral noxious stimuli, neurons in the trigeminal ganglion (TG) produce neuropeptides such as substance P, and calcitonin-gene-related peptide, etc. Beside the production of neuropeptides, there exists unique non-synaptic interaction system between maxillary and mandibular neurons in the TG. Neurons in the TG are surrounded by satellite glial cells (SGCs), which initially receive the signal from TG neurons. These activated SGCs secrete a transmitter to activate adjacent SGCs or TG neurons, thereby amplifying the signal, for example, from mandibular neurons to maxillary neurons in the TG. Similar to the dorsal root ganglion, in the TG, microglia/macrophage-like cells (MLCs) are activated by uptake of a transmitter from TG neurons or SGCs. This communication between neurons, SGCs, and MLCs results in responses such as ectopic pain, hyperesthesia, or allodynia. The focus of this review is the cooperative interaction of the maxillary and mandibular nerves in the TG by neuropeptides, and adenosine 3′-phosphate (ATP) signaling from neurons to SGCs and MLCs. Stimulated neurons either secrete ATP by means of vesicular nucleotide transporters, or secrete neuropeptides from the neuronal cell body to mediate signal transmission.

Chronic Opioid Therapy and Central Sensitization in Sickle Cell Disease

Chronic opioid therapy (COT) for chronic non-cancer pain is frequently debated, and its effectiveness is unproven in sickle cell disease (SCD). The authors conducted a descriptive study among 83 adult SCD patients and compared the severity of disease and pain symptoms among those who were prescribed COT (n=29) with those who were not using COT. All patients completed baseline laboratory pain assessment and questionnaires between January 2010 and June 2014. Thereafter, participants recorded daily pain, crises, function, and healthcare utilization for 90 days using electronic diaries. Analyses were conducted shortly after the final diary data collection period. Patients on COT did not differ on age, sex, or measures of disease severity. However, patients on COT exhibited greater levels of clinical pain (particularly non-crisis); central sensitization; and depression and increased diary measures of pain severity, function, and healthcare utilization on crisis and non-crisis diary days, as well as a greater proportion of days in crisis. Including depressive symptoms in multivariate models did not change the associations between COT and pain, interference, central sensitization, or utilization. Additionally, participants not on COT displayed the expected positive relationship between central sensitization and clinical pain, whereas those on COT demonstrated no such relationship, despite having both higher central sensitization and higher clinical pain. Overall, the results point out a high symptom burden in SCD patients on COT, including those on high-dose COT, and suggest that nociceptive processing in SCD patients on COT differs from those who are not.

Prevention of stress- or nitric oxide donor-induced medication overuse headache by a calcitonin gene-related peptide antibody in rodents

Objective The objective of this study was the determination of the role of calcitonin gene-related peptide (CGRP) in the induction of medication overuse headache (MOH)-related migraine in an injury-free preclinical model. Methods Rats were primed by a 7-day period of exposure to acute migraine therapies including sumatriptan and morphine. After an additional 14-day drug-free period, rats were exposed to putative migraine triggers including bright light stress (BLS) or nitric oxide (NO) donor in the presence or absence of TEV48125, a fully humanized CGRP antibody. Cutaneous allodynia (CA) was used as an outcome measure and CGRP blood and cerebrospinal fluid (CSF) levels were measured. Results BLS and NO donor challenge evoked delayed, long-lasting CA selectively in rats that were previously treated with sumatriptan or morphine. BLS produced a significant increase in CGRP in the plasma, but not CSF, in animals that were previously exposed to sumatriptan compared to saline controls. TEV48125 did not modify baseline tactile thresholds or produce behavioral side effects, but significantly inhibited both BLS- and NO donor-induced CA in animals that were previously primed with sumatriptan or morphine; an isotype control protein that does not bind CGRP had no effect. Interpretation These data suggest that acute migraine medications may promote MOH in susceptible individuals through CGRP-dependent mechanisms and that anti-CGRP antibodies may be a useful clinical strategy for the treatment of MOH.

Activation of dura-sensitive trigeminal neurons and increased c-Fos protein induced by morphine withdrawal in the rostral ventromedial medulla

Aims

Overuse of medications used to treat migraine headache can increase the frequency of headaches. Sudden abstinence from migraine medication can also lead to a period of withdrawal-induced headaches. The aim of this study was to examine the effect of morphine withdrawal localized to the rostral ventromedial medulla (RVM) on the activity of dura-sensitive spinal trigeminal nucleus caudalis (Vc) neurons.

Methods

Rats were implanted with either morphine or placebo pellets for six to seven days before the microinjection of naloxone methiodide or phosphate-buffered saline into the RVM in urethane-anesthetized animals. Dura-sensitive neurons were recorded in the Vc and the production of c-Fos-like immunoreactivity was quantified.

Results

In chronic morphine-treated animals, naloxone methiodide microinjections produced a significant increase both in ongoing and facial heat-evoked activity and an increase in Fos-positive neurons in the Vc and in the nucleus reticularis dorsalis, a brainstem region involved in diffuse noxious inhibitory controls.

Conclusions

These results indicate that activation of pronociceptive neurons in the RVM under conditions of morphine withdrawal can increase the activity of neurons that transmit headache pain. Modulation of the subnucleus reticularis dorsalis by the RVM may explain the attenuation of conditioned pain modulation in patients with chronic headache.

Pharmacological and biochemical studies on the protective effects of melatonin during stress-induced behavioral and immunological changes in relation to oxidative stress in rats

Stress is known to precipitate neuropsychiatric diseases, and depending upon its nature and intensity it can also influence the functioning of the immune system. Melatonin (N-acetyl-5-methoxy tryptamine) a pineal gland hormone and potent antioxidant is known to protect against many diseases. Effect of melatonin in stress-induced neuro-immunomodulation is not well elucidated. Therefore in the present study, the protective effects of melatonin were evaluated in restraint stress (RS)-induced behavioral and immunological changes in rats. RS for 1 h significantly reduces (i) percentage of open-arm entries and (ii) percentage of time spent on open-arm in elevated plus maze (EPM) test parameters (p < 0.01) and significant increase in MDA levels in brain homogenate when compared to non-RS control groups (p < 0.05). In immunological studies, both humoral and cell-mediated immune responses to antigen were significantly suppressed by RS for 1 h for 5 consecutive days, as evidenced by significant reduction in (i) anti-SRBC antibody titre, (ii) PFC counts, (iii) percentage change in paw volume, and (iv) Th1 (IFN-γ) and Th2 (IL-4) cytokine levels (p < 0.001 in all parameters). These RS-induced immunological changes were associated with significantly increased lipid peroxidation (MDA) levels in serum and significantly decreased activity of (i) SOD, (ii) CAT, and (iii) GSH levels in RS (X5)-exposed group (p < 0.02). Pretreatment with melatonin (10, 50, and 100 mg/kg) significantly reversed these RS-induced changes in EPM test parameters and humoral and cell-mediated immunological parameters, as well as oxidative stress markers in a dose-dependent manner by differential degrees (p < 0.001). Results are strongly suggestive of the involvement of free radicals during stress-induced neurobehavioral and immunological changes. These changes were significantly restored by melatonin pretreatment. We can conclude that melatonin may have a protective role during such stress-induced neuro-immunomodulation.

Pharmacological Acute Migraine Treatment Strategies: Choosing the Right Drug for a Specific Patient

Background:

In our targeted review (Section 2), 12 acute medications received a strong recommendation for use in acute migraine therapy while four received a weak recommendation for use. Strong recommendations were made to avoid use of two other medications, except for exceptional circumstances. Two anti-emetics received strong recommendations for use as needed.

Objective:

To organize the available acute migraine medications into acute migraine treatment strategies in order to assist the practitioner in choosing a specific medication(s) for an individual patient.

Methods:

Acute migraine treatment strategies were developed based on the targeted literature review used for the development of this guideline (Section 2), and a general literature review. Expert consensus groups were used to refine and validate these strategies.

Results:

Based on evidence for drug efficacy, drug side effects, migraine severity, and coexistent medical disorders, our analysis resulted in the formulation of eight general acute migraine treatment strategies. These could be grouped into four categories: 1) two mild-moderate attack strategies, 2) two moderate-severe attack or NSAID failure strategies, 3) three refractory migraine strategies, and 4) a vasoconstrictor unresponsive-contraindicated strategy. In addition, strategies were developed for menstrual migraine, migraine during pregnancy, and migraine during lactation. The eight general treatment strategies were coordinated with a “combined acute medication approach” to therapy which used features of both the “stratified” and the “step care across attacks” approaches to acute migraine management.

Conclusions:

The available medications for acute migraine treatment can be organized into a series of strategies based on patient clinical features. These strategies may help practitioners make appropriate acute medication choices for patients with migraine.

Up-regulation of calcitonin gene-related peptide in trigeminal ganglion following chronic exposure to paracetamol in a CSD migraine animal model

Previously, our group has demonstrated that chronic paracetamol (APAP) treatment induces alterations to the trigeminovascular nociceptive system in the cortical spreading depression (CSD) migraine animal model. The calcitonin gene related peptide (CGRP) is a key neuropeptide involved in the activation of the trigeminovascular nociceptive system. Therefore, this study examined the expression levels of CGRP in the trigeminal ganglion (TG) after chronic APAP exposure (0, 15, and 30 days) using a CSD model. Rats were divided into control, CSD only, APAP only and APAP treatment with CSD groups. A single injection (i.p.) of APAP (200 mg/kg body weight) was given to the 0-day APAP-treated groups, while the other APAP-treated groups received daily injections for 15 and 30 days. CSD was induced by the topical application of KCl to the parietal cortex. The protein expression of CGRP in the TG was evaluated by immunohistochemistry, and the CGRP mRNA level was investigated by real-time quantitative reverse transcription polymerase chain reaction. The results revealed that the induction of CSD significantly increased the level of CGRP protein but had no effect on CGRP mRNA level. Pretreatment with APAP 1 hour before CSD activation significantly reduced CGRP expression induced by CSD. In contrast, chronic treatment with APAP (15 and 30 days) significantly enhanced CGRP expression in both protein and mRNA levels when compared with the control groups. In combination with CSD, the expression of CGRP further increased in the animal with 30 day treatment. These findings indicate that chronic treatment with APAP induces an increase of CGRP expression in the TG. This alteration may be associated with the increased trigeminovascular nociception observed in our previous studies.

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).

Medication overuse headache - An under-diagnosed problem in shunted idiopathic intracranial hypertension patients

PURPOSE

Management of headache in a subgroup of shunted idiopathic intracranial hypertension (IIH) patients is a well- described and difficult task. We present our series of shunted IIH patients with medication overuse headache (MOH) and discuss the role of careful pain management in this group of patients.

MATERIALS AND METHODS

A retrospective review of shunted IIH patients with headache, who had their shunt function assessed by monitoring their intracranial pressure and were subsequently diagnosed with MOH.

RESULTS

A total of 15 patients were identified. The mean time between the diagnosis of IIH and the diagnosis of medication overuse headache was 6 years (standard deviation 4.9, range 2-18 years). The majority of patients in this group (12/15) had undergone multiple shunt revisions.

CONCLUSIONS

Medication overuse headache in shunted IIH patients can lead to the requirement of hospital admission, investigations and procedures. We suggest that opiates and non-steroidal anti-inflammatory analgesics (NSAIDs) are used for a specified duration post-operatively and reviewed regularly. We suggest that patients are counselled regarding medication overuse headache in a multidisciplinary setting.

Medication overuse headache

BACKGROUND

Medication overuse headache (MOH) affects between 1% and 2% of the general population but is present in up to 50% of patients seen in headache centers. There are currently no internationally accepted guidelines for treatment of MOH.

METHODS

A review of the current literature on MOH treatment and pathophysiology.

RESULTS

We conclude that headache frequency can be reduced to episodic headache in more than 50% of the patients by simple detoxification and information. Approximately half the patients will not have need for prophylactic medication after withdrawal. Pain perception is altered in patients with MOH but can be restored to a baseline pattern, indicating a reversible mechanism in the central sensitization leading to chronic pain. The great comorbidity with depression and anxiety could be a consequence of the altered serotonin metabolism indicating a reversible and potentially treatable condition.

CONCLUSION

Increased focus on MOH is extremely important, as MOH both can and should be treated and prevented. MOH is thus a diagnosis that should be considered in all chronic headache patients as the very first step in their management strategy. In the general population, prevention campaigns against MOH are essential to minimize chronic pain disability.

μ-Opioid activation in the midbrain during migraine allodynia - brief report II

We investigated in vivo the allodynic response of the central μ-opioid system during spontaneous migraine headaches, following a sustained pain threshold challenge on the trigeminal ophthalmic region. Six migraineurs were scanned during the ictal and interictal phases using positron emission tomography (PET) with the selective μ-opioid receptor (μOR) radiotracer [11C]carfentanil. Females were scanned during the mid-late follicular phase of two separate cycles. Patients showed ictal trigeminal allodynia during the thermal challenge that was concurrent and positively correlated with μOR activation in the midbrain, extending from red nucleus to ventrolateral periaqueductal gray matter. These findings demonstrate for the first time in vivo the high μOR activation in the migraineurs' brains in response to their allodynic experience.

Activation of mu opioid receptors sensitizes transient receptor potential vanilloid type 1 (TRPV1) via β-arrestin-2-mediated cross-talk

The transient receptor potential family V1 channel (TRPV1) is activated by multiple stimuli, including capsaicin, acid, endovanilloids, and heat (>42C). Post-translational modifications to TRPV1 result in dynamic changes to the sensitivity of receptor activation. We have previously demonstrated that β-arrestin2 actively participates in a scaffolding mechanism to inhibit TRPV1 phosphorylation, thereby reducing TRPV1 sensitivity. In this study, we evaluated the effect of β-arrestin2 sequestration by G-protein coupled receptors (GPCRs) on thermal and chemical activation of TRPV1. Here we report that activation of mu opioid receptor by either morphine or DAMGO results in β-arrestin2 recruitment to mu opioid receptor in sensory neurons, while activation by herkinorin does not. Furthermore, treatment of sensory neurons with morphine or DAMGO stimulates β-arrestin2 dissociation from TRPV1 and increased sensitivity of the receptor. Conversely, herkinorin treatment has no effect on TRPV1 sensitivity. Additional behavioral studies indicate that GPCR-driven β-arrestin2 sequestration plays an important peripheral role in the development of thermal sensitivity. Taken together, the reported data identify a novel cross-talk mechanism between GPCRs and TRPV1 that may contribute to multiple clinical conditions.

Increased susceptibility to cortical spreading depression in an animal model of medication-overuse headache

OBJECTIVE

The objective of this article is to evaluate electrically evoked thresholds for cortical spreading depression (CSD) and stress-induced activation of trigeminal afferents in a rat model of medication-overuse headache (MOH).

METHODS

Sumatriptan or saline was delivered subcutaneously by osmotic minipump for six days to Sprague-Dawley rats. Two weeks after pump removal, animals were anesthetized and recording/stimulating electrodes implanted. The animals were pretreated with vehicle or topiramate followed by graded electrical stimulation within the visual cortex. CSD events were identified by decreased EEG amplitude and DC potential shift. Additional unanesthetized sumatriptan or saline-pretreated rats were exposed to bright light environmental stress and periorbital and hindpaw withdrawal thresholds were measured. Following CSD stimulation or environmental stress, immunohistochemical staining for Fos in the trigeminal nucleus caudalis (TNC) was performed.

RESULTS

Sumatriptan pre-exposure significantly decreased electrical stimulation threshold to generate a CSD event. Topiramate normalized the decreased CSD threshold as well as stress-induced behavioral withdrawal thresholds in sumatriptan-treated rats compared to saline-treated animals. Moreover, CSD and environmental stress increased Fos expression in the TNC of sumatriptan-treated rats, and these effects were blocked by topiramate. Environmental stress did not elicit cutaneous allodynia or elevate TNC Fos expression in saline-treated rats.

CONCLUSIONS

A previous period of sumatriptan exposure produced long-lasting increased susceptibility to evoked CSD and environmental stress-induced activation of the TNC that was prevented by topiramate. Lowered CSD threshold, and enhanced consequences of CSD events (increased activation of TNC), may represent an underlying biological mechanism of MOH related to triptans.

Medication-overuse headache

PURPOSE OF REVIEW

Medication-overuse headache (MOH) is a well described clinical entity. There is a growing body of knowledge on the epidemiology of MOH, risk factors, and treatment strategies.

RECENT FINDINGS

The International Headache Society updated the classification criteria for MOH. Population-based studies provided an insight into the prevalence and peculiarities of MOH patients in eastern Europe and Asia. Large-scaled population-based longitudinal studies made it possible to analyze risk factors leading to the development of MOH. Imaging studies helped to better understand the pathophysiology of headache chronicity. New treatment strategies have been suggested.

SUMMARY

MOH is a common headache disorder and a serious public health problem all over the world. Although the treatment regimen for MOH patients is straightforward and the outcomes are favorable, it is time now to move forward and establish a predictive model for early recognition of patients at high risk, to intervene early and avoid development of chronic headache.

Medication overuse headache: history, features, prevention and management strategies

Medication overuse headache (MOH) is a daily, or almost daily, headache form that arises from overuse of one or more classes of migraine-abortive or analgesic medication. The main classes of drugs that cause MOH are opioids, butalbital-containing mixed analgesics, triptans, ergotamine tartrate derivatives, simple analgesics (except for plain aspirin), and perhaps non-steroidal anti-inflammatory drugs. MOH can be debilitating and results from biochemical and functional brain changes induced by certain medications taken too frequently. At this time, migraine and other primary headache disorders in which migraine or migraine-like elements occur seem exclusively vulnerable to the development of MOH. Other primary headache disorders are not currently believed to be vulnerable. The treatment of MOH consists of discontinuation of the offending drug(s), acute treatment of the withdrawal symptoms and escalating pain, establishing a preventive treatment when necessary, and the implementation of educational and behavioral programs to prevent recidivism. In most patients, MOH can be treated in the outpatient setting but, for the most difficult cases, including those with opioid or butalbital overuse, or in patients with serious medical or behavioral disturbances, effective treatment requires a multidisciplinary, comprehensive headache program, either day-hospital with infusion or an inpatient hospital setting.

Pathophysiology of medication overuse headache--an update

The pathogenesis of medication overuse headache is unclear. Clinical and preclinical studies have consistently demonstrated increased excitability of neurons in the cerebral cortex and trigeminal system after medication overuse. Cortical hyperexcitability may facilitate the development of cortical spreading depression, while increased excitability of trigeminal neurons may facilitate the process of peripheral and central sensitization. These changes may be secondary to the derangement of central, probably serotonin (5-HT)-, and perhaps endocannabinoid-dependent or other, modulating systems. Increased expression of excitatory cortical 5-HT2A receptors may increase the susceptibility to developing cortical spreading depression, an analog of migraine aura. A reduction of diffuse noxious inhibitory controls may facilitate the process of central sensitization, activate the nociceptive facilitating system, or promote similar molecular mechanisms to those involved in kindling. Low 5-HT levels also increase the expression and release of calcitonin gene-related peptide from the trigeminal ganglion and sensitize trigeminal nociceptors. Thus, derangement of central modulation of the trigeminal system as a result of chronic medication use may increase sensitivity to pain perception and foster or reinforce medication overuse headache.

Vascular extracellular signal-regulated kinase mediates migraine-related sensitization of meningeal nociceptors

OBJECTIVE

To examine changes in the response properties of meningeal nociceptors that might lead to migraine pain and examine endogenous processes that could play a role in mediating them using a clinically relevant model of migraine triggering, namely infusion of the nitric oxide (NO) donor nitroglycerin (NTG).

METHODS

Single-unit recordings made in the trigeminal ganglion of rats were used to test changes in the activity and mechanosensitivity of meningeal nociceptors in response to administration of the migraine trigger NTG or another NO donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) at doses relevant to the human model of migraine headache. Immunohistochemistry and pharmacological manipulations were used to investigate the possible role of meningeal vascular signaling in mediating the responses of meningeal nociceptors to NO.

RESULTS

Infusion of NTG promoted a delayed and robust increase in the mechanosensitivity of meningeal nociceptors, with a time course resembling the development of the delayed migraine headache. A similar sensitization was elicited by dural application of NTG and SNAP. NTG-evoked delayed meningeal nociceptor sensitization was associated with a robust extracellular signal-regulated kinase (ERK) phosphorylation in meningeal arteries. Pharmacological blockade of meningeal ERK phosphorylation inhibited the development of NTG-evoked delayed meningeal nociceptor sensitization.

INTERPRETATION

The development of delayed mechanical sensitization evoked by the migraine trigger NTG is potentially of great importance as the first finding of a neurophysiological correlate of migraine headache in meningeal nociceptors. The arterial ERK phosphorylation and its involvement in mediating the NTG-evoked delayed sensitization points to an important, yet unappreciated, role of the meningeal vasculature in the genesis of migraine pain.

Brain imaging in migraine research

Understanding the pathophysiology and pharmacology of migraine has been driven by astute clinical observations, elegant experimental medicine studies, and importantly by studying highly effective anti-migraine agents in the laboratory and the clinic. Significant progress has been made in the use of functional brain imaging to compliment observational studies of migraine phenotypes by highlighting pathways within the brain that may be involved in predisposition to migraine, modulating migraine pain or that could be sensitive to pharmacological or behavioral therapeutic intervention. In drug discovery, molecular imaging approaches compliment functional neuroimaging by visualizing migraine drug targets within the brain. Molecular imaging enables the selection and evaluation of drug candidates by confirming that they engage their targets sufficiently at well tolerated doses to test our therapeutic hypotheses. Migraine is a progressive disorder. Developing our knowledge of where drugs act in the brain and of how the brain is altered in both episodic migraine (interictal state and ictal state) and chronic migraine are important steps to understanding why there is such differential responsiveness to therapeutics among migraine patients and to improving how they are evaluated and treated.

Medication-overuse headache

PURPOSE OF REVIEW

Medication-overuse headache (MOH) is a chronic daily headache in which acute medications used at high frequency cause transformation to headache occurring 15 or more days per month for 4 or more hours per day if left untreated. MOH is a form of US Food and Drug Administration-defined chronic migraine. This review will describe (1) MOH clinical features and diagnosis, (2) pathophysiology and structural and functional MOH brain changes, and (3) prevention and treatment of MOH.

RECENT FINDINGS

MOH causes structural and functional brain changes. Any butalbital or opioid use increases the risk of transforming episodic into chronic migraine (sometimes referred to as chronification). The American Migraine Prevalence and Prevention Study demonstrated that transformation is most likely to occur with 5 days of butalbital use per month, 8 days of opioid use per month, 10 days of triptan or combination analgesic use per month, and 10 to 15 days of nonsteroidal anti-inflammatory use per month. Acute migraine treatment should be limited to 2 or fewer days per week, and opioids and butalbital should be avoided.Treatment of MOH consists of combining prophylaxis, 100% wean of overused acute medications, and provision of new acute medications, strictly limiting use to 2 or fewer days per week. Wean can be done slowly in an outpatient setting or it can be done abruptly, sometimes requiring hospitalization with medicine bridges.

SUMMARY

MOH development is linked to baseline frequency of headache days per month, acute medication class ingested, frequency of acute medications ingested, and other risk factors. Using less effective or nonspecific medication for severe migraine results in inadequate treatment response, with redosing and attack prolongation, frequently leading to chronification. Use of any barbiturates or opioids increases the transformation likelihood.Patients with MOH can usually be effectively treated. The first step is 100% wean, followed by establishing preventive medications such as onabotulinumtoxinA or daily prophylaxis and providing acute treatment for severe migraine 2 or fewer days per week. Slow wean or quick termination of rebound medications can be accomplished for most patients on an outpatient basis, but some more difficult problems may need referral for multidisciplinary day hospital or inpatient treatments.

Detailed mechanistic investigation into the S-nitrosation of cysteamine

The nitrosation of cysteamine (H₂NCH₂CH₂SH) to produce cysteamine-S-nitrosothiol (CANO) was studied in slightly acidic medium by using nitrous acid prepared in situ. The stoichiometry of the reaction was H₂NCH₂CH₂SH + HNO₂ → H₂NCH₂CH₂SNO + H₂O. On prolonged standing, the nitrosothiol decomposed quantitatively to yield the disulfide, cystamine: 2H₂NCH₂CH₂SNO → H₂NCH₂CH₂S-SCH₂CH₂NH₂ + 2NO. NO₂ and N₂O₃ are not the primary nitrosating agents, since their precursor (NO) was not detected during the nitrosation process. The reaction is first order in nitrous acid, thus implicating it as the major nitrosating agent in mildly acidic pH conditions. Acid catalyzes nitrosation after nitrous acid has saturated, implicating the protonated nitrous acid species, the nitrosonium cation (NO⁺) as a contributing nitrosating species in highly acidic environments. The acid catalysis at constant nitrous acid concentrations suggests that the nitrosonium cation nitrosates at a much higher rate than nitrous acid. Bimolecular rate constants for the nitrosation of cysteamine by nitrous acid and by the nitrosonium cation were deduced to be 17.9 ± 1.5 (mol/L)^-1 s^-1 and 6.7 × 10⁴ (mol/L)^-1 s^-1, respectively. Both Cu(I) and Cu(II) ions were effective catalysts for the formation and decomposition of the cysteamine nitrosothiol. Cu(II) ions could catalyze the nitrosation of cysteamine in neutral conditions, whereas Cu(I) could only catalyze in acidic conditions. Transnitrosation kinetics of CANO with glutathione showed the formation of cystamine and the mixed disulfide with no formation of oxidized glutathione (GSSG). The nitrosation reaction was satisfactorily simulated by a simple reaction scheme involving eight reactions.