Melatonin increases reactive aggression in humans

Peripheral molecular and brain structural profile implicated stress activation and hyperoxidation in methamphetamine use disorder

AIM

Methamphetamine use disorders (MUDs) cause widespread disruptions in metabolomic and immunologic processes, highlighting the need for new therapeutic approaches. The purpose of this study was to find molecular and neuroimaging biomarkers for methamphetamine addiction.

METHODS

In this study, we recruited 231 patients with MUD at varying stages of withdrawal and 40 healthy controls to quantify the blood levels of 52 molecules using enzyme-linked immunosorbent assay.

RESULTS

The overall molecular disruption caused by methamphetamine was inversely related to withdrawal time (P = 0.0008), with partial recovery observed after 1 year of follow-up (P = 2.20 × 10-5). Molecules related to stress, immune activation, oxidative products, and cardiac injury were significantly elevated in all MUD groups, while antioxidation enzymes were downregulated. Additionally, the blood level of brain-derived neurotrophic factor was significantly correlated with gray matter volumes in nine brain regions (fusiform gyrus, orbitofrontal cortex, temporal pole, caudate, cerebellum crus, and vermis, adjusted P < 0.05) among patients with MUD.

CONCLUSION

These findings suggest that patients with MUD exhibit elevated levels of immune response, stress, and oxidative stress, which are associated with brain structural abnormalities.

Neurolipidomics in schizophrenia: A not so well-oiled machine

Most patients with schizophrenia (SCZ) do not exhibit violent behaviors and are more likely to be victims rather than perpetrators of violent acts. However, a subgroup of forensic detainees with SCZ exhibit tendencies to engage in criminal violations. Although numerous models have been proposed, ranging from substance use, serotonin transporter gene, and cognitive dysfunction, the molecular underpinnings of violence in SCZ patients remains elusive. Lithium and clozapine have established anti-aggression properties and recent studies have linked low cholesterol levels and ultraviolet (UV) radiation with human aggression, while vitamin D3 reduces violent behaviors. A recent study found that vitamin D3, omega-3 fatty acids, magnesium, and zinc lower aggression in forensic population. In this review article, we take a closer look at aryl hydrocarbon receptor (AhR) and the dysfunctional lipidome in neuronal membranes, with emphasis on cholesterol and vitamin D3 depletion, as sources of aggressive behavior. We also discuss modalities to increase the fluidity of neuronal double layer via membrane lipid replacement (MLR) and natural or synthetic compounds. This article is part of the Special Issue on "Personality Disorders".

Melatonin alters the excitability of mouse cerebellar granule neurons by inhibiting voltage-gated sodium, potassium, and calcium channels

Besides its role in the circadian rhythm, the pineal gland hormone melatonin (MLT) also possesses antiepileptogenic, antineoplastic, and cardioprotective properties, among others. The dosages necessary to elicit beneficial effects in these diseases often far surpass physiological concentrations. Although even high doses of MLT are considered to be largely harmless to humans, the possible side effects of pharmacological concentrations are so far not well investigated. In the present study, we report that pharmacological doses of MLT (3 mM) strongly altered the electrophysiological characteristics of cultured primary mouse cerebellar granule cells (CGCs). Using whole-cell patch clamp and ratiometric Ca2+ imaging, we observed that pharmacological concentrations of MLT inhibited several types of voltage-gated Na+ , K+ , and Ca2+ channels in CGCs independently of known MLT-receptors, altering the character and pattern of elicited action potentials (APs) significantly, quickly and reversibly. Specifically, MLT reduced AP frequency, afterhyperpolarization, and rheobase, whereas AP amplitude and threshold potential remained unchanged. The altered biophysical profile of the cells could constitute a possible mechanism underlying the proposed beneficial effects of MLT in brain-related disorders, such as epilepsy. On the other hand, it suggests potential adverse effects of pharmacological MLT concentrations on neurons, which should be considered when using MLT as a pharmacological compound.

A seasonal switch hypothesis for the neuroendocrine control of aggression

Aggression is a well-studied social behavior that is universally exhibited by animals across a wide range of contexts. Prevailing knowledge suggests gonadal steroids primarily mediate aggression; however, this is based mainly on studies of male-male aggression in laboratory rodents. When males and females of other species, including humans, are examined, a positive relationship between gonadal steroids and aggression is less substantiated. For instance, hamsters housed in short 'winter-like' days show increased aggression compared with long-day housed hamsters, despite relatively low circulating gonadal steroids. These results suggest alternative, non-gonadal mechanisms controlling aggression. Here, we propose the seasonal switch hypothesis, which employs a multidisciplinary approach to describe how seasonal variation in extra-gonadal steroids, orchestrated by melatonin, drives context-specific changes in aggression.

Association between the plasma concentration of melatonin and behavioral temperament in horses

Aggression in horses may cause serious accidents during riding and non-riding activities. Hence, predicting the temperament of horses is essential for selecting suitable horses and ensuring safety during the activity. In certain animals, such as hamsters, plasma melatonin concentrations have been correlated with aggressive behavior. However, whether this relationship applies to horses remains unclear. To address this research gap, this study aimed to evaluate differences in the plasma melatonin concentrations among horses of different breeds, ages, and sexes and examine the correlation between plasma melatonin concentrations and the temperament of the horses, including docility, affinity, dominance, and trainability. Blood samples from 32 horses were collected from the Horse Industry Complex Center of Jeonju Kijeon College. The docility, affinity, dominance, and trainability of the horses were assessed by three professional trainers who were well-acquainted with the horses. Plasma melatonin concentrations were measured using an enzyme-linked immunosorbent assay. The consequent values were compared between the horses of different breeds, ages, and sexes using a three-way analysis of variance and least significant difference post hoc test. Linear regression analysis was employed to identify the relationship between plasma melatonin concentrations and docility, affinity, dominance, and trainability. The results showed that the plasma melatonin concentrations significantly differed with breeds in Thoroughbred and cold-blooded horses. However, there were no differences in the plasma melatonin concentrations between the horse ages and sexes. Furthermore, plasma melatonin concentrations did not exhibit a significant correlation with the ranking of docility, affinity, dominance, and trainability.

Winter madness: Melatonin as a neuroendocrine regulator of seasonal aggression

Individuals of virtually all vertebrate species are exposed to annual fluctuations in the deterioration and renewal of their environments. As such, organisms have evolved to restrict energetically expensive processes and activities to a specific time of the year. Thus, the precise timing of physiology and behavior is critical for individual reproductive success and subsequent fitness. Although the majority of research on seasonality has focused on seasonal reproduction, pronounced fluctuations in other non-reproductive social behaviors, including agonistic behaviors (e.g., aggression), also occur. To date, most studies that have investigated the neuroendocrine mechanisms underlying seasonal aggression have focused on the role of photoperiod (i.e., day length); prior findings have demonstrated that some seasonally breeding species housed in short "winter-like" photoperiods display increased aggression compared with those housed in long "summer-like" photoperiods, despite inhibited reproduction and low gonadal steroid levels. While fewer studies have examined how the hormonal correlates of environmental cues regulate seasonal aggression, our previous work suggests that the pineal hormone melatonin acts to increase non-breeding aggression in Siberian hamsters (Phodopus sungorus) by altering steroid hormone secretion. This review addresses the physiological and cellular mechanisms underlying seasonal plasticity in aggressive and non-aggressive social behaviors, including a key role for melatonin in facilitating a "neuroendocrine switch" to alternative physiological mechanisms of aggression across the annual cycle. Collectively, these studies highlight novel and important mechanisms by which melatonin regulates aggressive behavior in vertebrates and provide a more comprehensive understanding of the neuroendocrine bases of seasonal social behaviors broadly.

Melatonin and aggressive behavior: A systematic review of the literature on preclinical and clinical evidence

The melatonin system and circadian disruption have well-established links with aggressive behaviors; however, the biological underpinnings have not been thoroughly investigated. Here, we aimed at examining the current knowledge regarding the neurobiological and psychopharmacological involvement of the melatonin system in aggressive/violent behaviors. To this end, we performed a systematic review on Embase and Pubmed/MEDLINE of preclinical and clinical evidence linking the melatonin system, melatonin, and melatoninergic drugs with aggressive/violent behaviors. Two blinded raters performed an independent screening of the relevant literature. Overall, this review included 38 papers distributed between clinical and preclinical models. Eleven papers specifically addressed the existing evidence in rodent models, five in fish models, and 21 in humans. The data indicate that depending on the species, model, and timing of administration, melatonin may exert a complex influence on aggressive/violent behaviors. Particularly, the apparent contrasting findings on the link between the melatonin system and aggression/violence (with either increased, no, or decreased effect) shown in preclinical models underscore the need for further research to develop more accurate and fruitful translational models. Likewise, the significant heterogeneity found in the results of clinical studies does not allow yet to draw any firm conclusion on the efficacy of melatonin or melatonergic drugs on aggressive/violent behaviors. However, findings in children and in traits associated with aggressive/violent behavior, including irritability and anger, are emerging and deserve empirical attention given the low toxicity of melatonin and melatonergic drugs.

Reactive vs proactive aggression: A differential psychobiological profile? Conclusions derived from a systematic review

INTRODUCTION

Scholars have established subcategories of aggressive behavior in order to better understand this construct. Specifically, a classification based on motivational underpinnings makes it possible to differentiate between reactive and proactive aggression. Whereas reactive aggression is characterized by emotional lability, which means it is prone to impulsive reactions after provocation, proactive aggression is driven by low emotionality and high levels of instrumentality to obtain benefits. Some authors have conceived these two types as having a dichotomous nature, but others argue against this conceptualization, considering a complementary model more suitable. Hence, neuroscientific research might help to clarify discussions about their nature because biological markers do not present the same biases as psychological instruments.

AIM

The main objective of this study was to carry out a systematic review of studies that assess underlying biological markers (e.g., genes, brain, psychophysiological, and hormonal) of reactive and proactive aggression.

METHODS

To carry out this review, we followed PRISMA quality criteria for reviews, using five digital databases complemented by hand-searching.

RESULTS

The reading of 3993 abstracts led to the final inclusion of 157 papers that met all the inclusion criteria. The studies included allow us to conclude that heritability accounted for approximately 45% of the explained variance in both types of aggression, with 60% shared by both, especially, for overt and physical expression forms, and 10% specific to each type. Regarding allelic risk factors, whereas low functioning variants affecting serotonin transport and monoaminoxidase increased the risk of reactive aggression, high functioning variants were associated with proactive aggression. Furthermore, brain analysis revealed an overlap between the two types of aggression and alterations in the volume of the amygdala and temporal cortex. Moreover, high activation of the medial prefrontal cortex (PFC) facilitated proneness to both types of aggression equally. Whereas stimulation of the right ventrolateral (VLPFC) and dorsolateral (DLPFC) reduced proneness to aggression, inhibition of the left DLPFC increased it. Finally, psychophysiological and hormonal correlates in general did not clearly differentiate between the two types because they were equally related to each type (e.g., low basal cortisol and vagal variability in response to acute stress) CONCLUSIONS: This study reinforces the complementary model of both types of aggression instead of a dichotomous model. Additionally, this review also offers background about several treatments (i.e., pharmacological, non-invasive brain techniques…) to reduce aggression proneness.

Translational relevance of forward genetic screens in animal models for the study of psychiatric disease

Psychiatric disorders represent a significant burden in our societies. Despite the convincing evidence pointing at gene and gene-environment interaction contributions, the role of genetics in the etiology of psychiatric disease is still poorly understood. Forward genetic screens in animal models have helped elucidate causal links. Here we discuss the application of mutagenesis-based forward genetic approaches in common animal model species: two invertebrates, nematodes (Caenorhabditis elegans) and fruit flies (Drosophila sp.); and two vertebrates, zebrafish (Danio rerio) and mice (Mus musculus), in relation to psychiatric disease. We also discuss the use of large scale genomic studies in human populations. Despite the advances using data from human populations, animal models coupled with next-generation sequencing strategies are still needed. Although with its own limitations, zebrafish possess characteristics that make them especially well-suited to forward genetic studies exploring the etiology of psychiatric disorders.

Effects of exercise on sleep, melatonin level, and behavioral functioning in children with autism

LAY ABSTRACT

This study examined the impact of physical exercise on sleep and behavioral functioning in children (aged 8-12 years) with autism spectrum disorders. It also investigated whether exercise would alter endogenous melatonin level among the population. Participants were divided into two groups: exercise group (12-week, 30-min morning jogging intervention) and a control group (i.e. did not receive any physical exercise intervention during the study period). Significant improvements on sleep and behavioral functioning were found in the exercise group, but not in the control group Moreover, a significant increase in melatonin level was also shown in the exercise group. Findings of this study reconfirmed the sleep and behavioral benefits of exercise in children with autism spectrum disorder. Melatonin-mediated mechanism should be further explored to develop an effective treatment intervention.

Pharmacotherapy of Primary Impulsive Aggression in Violent Criminal Offenders

Primary impulsive aggression (PIA) can be implicated as a common factor that results in an arrest, disciplinary, and restraint measures during confinement, and criminal recidivism after release. Evidence suggests that anti-impulsive aggression agents (AIAAs) can diminish or prevent impulsive aggression even when occurring with personality pathology such as borderline or antisocial personality disorder (ASPD), common conditions in offender populations. A previous review identified agents that have been subjected to controlled drug trials of sufficient quality, and subsequently, a decisional algorithm was developed for selecting an AIAA for individuals with IA. This selection process began with the five agents that showed efficacy in two or more quality studies from the earlier review. Today, 8 years after the quality review study, the present authors undertook this follow-up literature review. The aims of the present review were to survey the literature to identify and assess: (1) drug trials of comparable quality published since the 2013 review, including trials of the previously identified AIAAs as well as trials of agents not included in the earlier review; (2) severity of aggressive outbursts; (3) the materiality of risks or side-effects that are associated with individual AIAAs as well as antipsychotic agents commonly used to control clinical aggression; (4) efficacy of these agents in special populations (e.g., females); and (5) cost and convenience of each agent. Improved pharmacotherapy of PIA by addressing risks, side effects and practicality as well as the efficacy of AIAAs, should promote the rehabilitation and reintegration of some pathologically aggressive offenders back into the community.

Pharmacological and philosophical considerations for the around-the-clock use of scheduled melatonin to promote sedation and reduce aggression in individuals with serious mental illness: a case report

Melatonin, the endogenous hormone that helps maintain circadian rhythm, has been used exogenously for both primary and secondary sleep disorders. While the effects of melatonin given prior to planned sleep and to restore normal circadian sleep phases have been well studied, there is little information on the use of melatonin as a pharmacotherapeutic intervention for around-the-clock sedation to prevent agitation and aggressive patient behaviors. This is the first case report to our knowledge of melatonin used throughout the day, as a scheduled dose for prolonged treatment duration, to reduce aggression in a patient with severe mental illness.

Melatonin-dependent changes in neurosteroids are associated with increased aggression in a seasonally breeding rodent

Aggression is a complex social behaviour that allows individuals to compete for access to limited resources (eg, mates, food and territories). Excessive or inappropriate aggression, however, has become problematic in modern societies, and current treatments are largely ineffective. Although previous work in mammals suggests that aggressive behaviour varies seasonally, seasonality is largely overlooked when developing clinical treatments for inappropriate aggression. Here, we investigated how the hormone melatonin regulates seasonal changes in neurosteroid levels and aggressive behaviour in Siberian hamsters, a rodent model of seasonal aggression. Specifically, we housed males in long-day (LD) or short-day (SD) photoperiods, administered timed s.c. melatonin injections (which mimic a SD-like signal) or control injections, and measured aggression using a resident-intruder paradigm after 9 weeks of treatment. Moreover, we quantified five steroid hormones in circulation and in brain regions associated with aggressive behaviour (lateral septum, anterior hypothalamus, medial amygdala and periaqueductal gray) using liquid chromatography-tandem mass spectrometry. SD hamsters and LD hamsters administered timed melatonin injections (LD-M) displayed increased aggression and exhibited region-specific decreases in neural dehydroepiandrosterone, testosterone and oestradiol, but showed no changes in progesterone or cortisol. Male hamsters also showed distinct associations between neurosteroids and aggressive behaviour, in which neural progesterone and dehydroepiandrosterone were positively correlated with aggression in all treatment groups, whereas neural testosterone, oestradiol and cortisol were negatively correlated with aggression only in LD-M and SD hamsters. Collectively, these results provide insight into a novel neuroendocrine mechanism of mammalian aggression, in which melatonin reduces neurosteroid levels and elevates aggressive behaviour.

Commentary regarding "neuroactive compounds in foods: Occurrence, mechanism and potential health effects"

A letter to the Editor focusing on some safety concerns about melatonin, provoked by the article "Neuroactive compounds in foods: Occurrence, mechanism and potential health effects" published in Journal of Food Research International.

Rapamycin could increase the effects of melatonin against age-dependent bone loss

Previous studies have demonstrated the beneficial effect of melatonin (MEL) on bone tissue and bone metabolism. Rapamycin (RAP) promotes osteoblast proliferation and inhibits osteoclast proliferation, and positively affects bone regeneration; however, reports about effects of RAP on bone loss for aged female rats with MEL administration are limited. This study investigated the impact of treatment with RAP on bone loss for aged female rats with MEL administration. Female Sprague-Dawley rats weighing approximately 520 g were randomly divided into 3 groups of 10: group CON, group MEL and group MEL + RAP and received saline, MEL, RAP plus MEL treatment until death at 12 weeks, respectively. The results of maintaining bone mass and bone strength with RAP plus MEL administration were evaluated by histology, microcomputerized tomography (Micro-CT), gene expression analysis and biomechanical testing. Results from this study indicated that MEL + RAP had stronger effects on the prevention and treatment of osteoporosis than MEL administration. Administration of MEL + RAP produced the strongest effects on bone parameters and strength for distal femurs and regulation of OPG/RANKL signalling pathway-related gene expression. These results seemed to indicate that RAP could increase the effects of MEL on age-dependent bone loss.

Melatonin improves the osseointegration of hydroxyapatite-coated titanium implants in senile female rats

The aim of this study was to confirm the effect of the systemic administration of melatonin on hydroxyapatite-coated titanium (HA-Ti) implants in senile osteopenic rats. For this study 24-month-old female Sprague-Dawley rats were used. The animals were randomly divided into two groups: a control group and a melatonin group and the bilateral femurs of all the rats received HA-Ti implants. Animals in the melatonin group received treatment with melatonin (30 mg/kg day). After a 12-week healing period, rats in the melatonin group revealed improved osseointegration compared to the control group, with the bone area ratio (BAR) and bone to implant contact (BIC) increased by 1.87-fold and 1.65-fold in histomorphometry, the quantitative results of implant osseointegration and peri-implant trabeculae, such as a higher bone volume per total volume (BV/TV), trabecular number (Tb.N), the mean connective density (Conn.D), trabecular thickness (Tb.Th), and a lower trabecular spacing (Tb.Sp) in micro-computed tomography (CT) evaluation and the maximum push-out force by 1.75-fold in push out tests. Additionally, compared with the control group, melatonin could significantly up-regulate the expression of the runt-related transcription factor 2 (Runx2), osteocalcin (OC) and osteoprotegerin (OPG) genes and down-regulate the expression of the RANKL gene. These findings suggest that systemic administration with melatonin is useful to improve the fixation of HA-coated implants even in osteopenic rats through promoting Runx2, OC and OPG gene expression and inhibiting RANKL gene expression.

Melatonin pretreatment attenuates acute methamphetamine-induced aggression in male ICR mice

Aggression is one of the symptoms of methamphetamine (MA) use and withdrawal, which can exacerbate MA addiction and relapse. Many studies have demonstrated that poor sleep is significantly associated with aggression. Melatonin has been indicated to be effective in treating sleep disorders induced by MA, and it can also protect neuronal cells against MA-induced neurotoxicity. However, the underlying effects of melatonin on MA-reduced aggression remain unclarified. This study was designed to evaluate the effects of melatonin on acute MA-induced aggressive behavior in male ICR mice and the effects on neurotransmitters related to aggression. Fifty male ICR mice were randomly assigned to control and treatment groups pretreated with MA (3 mg/kg) or melatonin (2.5, 5, 10 mg/kg) plus MA. Aggressive behaviors were observed through isolation-induced aggression in the resident-intruder model. High-performance liquid chromatography combined with electrochemical detection (HPLC-ECD) was used to anatomize the levels of dopamine (DA) and its metabolites, 3,4-dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA), and the concentrations of serotonin (5-HT) and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), in the hippocampus involved in behavior processing. The results showed that acute MA administration decreased latency to initial attacks and thereby increased the number and total duration of attacks. Furthermore, HVA level as well as 5-HIAA and 5-HT turnover estimated by 5-HIAA/5-HT ratios declined compared to those in the vehicle group. The medium melatonin pretreatment dose (5 mg/kg) could significantly reverse acute MA-induced aggressive behavior in the form of prolonging latency to initial attacks and thereby attenuating the number of attacks and total duration of attacks. HVA and 5-HIAA levels, 5-HT turnover estimated by 5-HIAA/5-HT ratios, and DA turnover estimated by HVA/DA ratios and (DOPAC + HVA)/DA ratios were elevated compared to those in the MA group. These results indicate that the DA and 5-HT systems are involved in the processes of MA-induced aggressive behaviors and that melatonin has the capacity to reverse MA-induced aggressive behaviors.

[Effect of melatonin on the daytime sleepiness side-effect of gabapentin in adults patients with neuropathic pain]

BACKGROUND AND OBJECTIVES

Gabapentin is an antiepileptic drug. Widely used for the management of neuropathic pain. Although it is known to be well tolerated, somnolence and dizziness are the most frequent adverse effects. In this study, we aimed to evaluate the effect of melatonin on daytime sleepiness side effect of gabapentin, sleep quality and pain intensity of patients with neuropathic pain.

METHODS

Patients suffering from "neuropathic pain" and planed to receive gabapentin therapy were randomly divided into two groups. Group 1 received melatonin 3mg and gabapentin 900mg orally, group 2 received matching placebo capsule and gabapentin 900mg. The Epworth Sleepiness Scale, the Pittsburgh sleep quality index for assessment of sleep quality and Verbal Rating Scale were completed at the 0th, 10th and 30th days of treatment. Additive analgesic drug requirements were recorded.

RESULTS

Eighty patients were enrolled to the study; age, gender, ratio of additive analgesic consumption, baseline Epworth Sleepiness Scale, Pittsburg Sleep Quality index and Verbal Rating Scale scores were similar between the groups. Epworth Sleepiness Scale scores, Pittsburgh sleep quality index scores and Verbal Rating Scale scores in Group 1 were significantly lower than group 2 at the 10th day of treatment (p=0.002, p=0.003, p=0.002 respectively). At the 30th day of treatment, Epworth Sleepiness Scale scores and Verbal Rating Scale scores were significantly lower in Group 1 (p=0.002, p=0.008 respectively). However, Pittsburgh sleep quality index scores did not significantly differ between the groups (p=0.0566).

CONCLUSIONS

Melatonin supplementation rapidly and significantly improved daytime sleepiness side-effect of gabapentin, however sleep quality of the patients with neuropathic pain was similar between groups.

Effect of melatonin on the daytime sleepiness side-effect of gabapentin in adults patients with neuropathic pain

Background and objectives

Gabapentin is an antiepileptic drug. Widely used for the management of neuropathic pain. Although it is known to be well tolerated, somnolence and dizziness are the most frequent adverse effects. In this study, we aimed to evaluate the effect of melatonin on daytime sleepiness side effect of gabapentin, sleep quality and pain intensity of patients with neuropathic pain.

Methods

Patients suffering from “neuropathic pain” and planed to receive gabapentin therapy were randomly divided into two groups. Group 1 received melatonin 3 mg and gabapentin 900 mg orally, group 2 received matching placebo capsule and gabapentin 900 mg. The Epworth Sleepiness Scale, the Pittsburgh sleep quality index for assessment of sleep quality and Verbal Rating Scale were completed at the 0th, 10th and 30th days of treatment. Additive analgesic drug requirements were recorded.

Results

Eighty patients were enrolled to the study; age, gender, ratio of additive analgesic consumption, baseline Epworth Sleepiness Scale, Pittsburg Sleep Quality index and Verbal Rating Scale scores were similar between the groups. Epworth Sleepiness Scale scores, Pittsburgh sleep quality index scores and Verbal Rating Scale scores in Group 1 were significantly lower than group 2 at the 10th day of treatment (p = 0.002, p = 0.003, p = 0.002 respectively). At the 30th day of treatment, Epworth Sleepiness Scale scores and Verbal Rating Scale scores were significantly lower in Group 1 (p = 0.002, p = 0.008 respectively). However, Pittsburgh sleep quality index scores did not significantly differ between the groups (p = 0.0566).

Conclusions

Melatonin supplementation rapidly and significantly improved daytime sleepiness side-effect of gabapentin, however sleep quality of the patients with neuropathic pain was similar between groups.