Methamphetamine self-administration attenuates hippocampal serotonergic deficits: role of brain-derived neurotrophic factor

Regional-specific changes in rat brain BDNF in a model of methamphetamine abuse

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, plays key roles in neuronal protection and synaptic plasticity. Changes in BDNF are associated with various pathological conditions, including methamphetamine (meth) addiction, although the effects of meth on BDNF expression are not always consistent. We have previously demonstrated region-specific effects of a chronic meth regime on BDNF methylation and expression in the rat brain. This study aims to determine the effect of chronic meth administration on the expression of BDNF protein using immunohistochemistry in the rat frontal cortex and hippocampus. Novel object recognition (NOR) as a measure of cognitive function was also determined. Male Sprague Dawley rats were administered a chronic escalating dose (0.1-4 mg/kg over 14 days) (ED) of meth or vehicle; a subgroup of animals receiving meth were also given an acute "binge" (4x6mg) dose on the final day before NOR testing. The results showed that hippocampal CA1 BDNF protein was significantly increased by 72 % above control values in the ED-binge rats, while other hippocampal regions and frontal cortex were not significantly affected. Meth-administered animals also demonstrated deficits in NOR after 24 h delay. No significant effect of the additional binge dose on BDNF protein or NOR findings was apparent. This finding is consistent with our previous results of reduced DNA methylation and increased expression of the BDNF gene in this region. The hippocampal BDNF increase may reflect an initial increase in a protective factor produced in response to elevated glutamate release resulting in neurodegenerative excitotoxicity.

Epigenome-wide association study on methamphetamine dependence

Repeated abuse of methamphetamine (METH) can cause dependence, repeated relapse of psychotic symptoms, compulsive drug-seeking behaviour, and various neurological symptoms. These long-term biological changes may be associated with epigenetic mechanisms; however, the association between METH use and epigenetic mechanisms has been poorly investigated. Thus, we performed an epigenome-wide association study of METH dependence using genomic DNA extracted from the blood samples of 24 patients with METH dependence and 24 normal controls. All participants were of Japanese descent. We tested the association between METH dependence and DNA methylation using linear regression analysis. We found epigenome-wide significant associations at four CpG sites, one of which occurred in the CNOT1 gene and another in the PUM1 gene. We especially noted the CNOT1 and PUM1 genes as well as several other genes that indicated some degree of association with METH dependence. Among the relatively enriched Gene Ontology terms, we were interested in terms of mRNA metabolism, respirasome, and excitatory extracellular ligand-gated ion channel activity. Among the relatively enriched Kyoto Encyclopedia of Genes and Genome pathways, we noted pathways of several neurological diseases. Our results indicate that genetic changes akin to those in other psychiatric or neurodegenerative disorders may also occur via epigenetic mechanisms in patients with METH dependence.

Synaptic remodeling of GluA1 and GluA2 expression in the nucleus accumbens promotes susceptibility to cognitive deficits concomitant with downstream GSK3β mediated neurotoxicity in female mice during abstinence from voluntary oral methamphetamine

Stimulant-use disorders can present with long-term cognitive and mental health deficits. Little is known about the underlying molecular mechanisms perpetuating sex differences in cognitive and behavioral deficits in preclinical models of addiction to stimulants such as methamphetamine (MA). The current study investigated the neurochemical shifts underlying sex disparities in MA-induced working memory deficits and an addictive phenotype following abstinence from chronic MA abuse. We used our previously reported mouse model of voluntary oral methamphetamine administration (VOMA) consisting of an acquisition phase (days 1-14) characterized by escalating doses of MA and a binge phase (days 14-28) characterized by static doses. Female VOMA mice exhibited sustained MA consumption during the binge phase, demonstrating sex-specific vulnerabilities to the maintenance of MA addiction. The 8-arm radial maze was used to test spatial working memory performance following abstinence from VOMA. Results indicate working memory deficits correlated to higher MA consumption in females only. Hippocampal and accumbal tissue were collected and analyzed by immunoblotting. Female VOMA mice had decreased GluA1, but not GluA2, in the hippocampus, which may perpetuate synaptic destabilization and working memory deficits. Female-specific increases in GluA1 and p-GSK3β expression in accumbal tissue suggest vulnerability toward abstinence-induced drug craving and heightened downstream neurotoxicity. Our study reveals female-specific neurochemical shifts in hippocampal and accumbal AMPA receptor signaling following abstinence from chronic MA consumption that may perpetuate female susceptibility to MA-induced cognitive deficits. These data demonstrate a novel molecular pathway that would exacerbate memory deficits and perpetuate an addictive phenotype in female populations following MA abuse.

Ghrelin/GHS-R1A antagonism in memory test and its effects on central molecular signaling involved in addiction in rats

Central ghrelin signaling seems to play important role in addiction as well as memory processing. Antagonism of the growth hormone secretagogue receptor (GHS-R1A) has been recently proposed as a promising tool for the unsatisfactory drug addiction therapy. However, molecular aspects of GHS-R1A involvement in specific brain regions remain unclear. The present study demonstrated for the first time that acute as well as subchronic (4 days) administration of the experimental GHS-R1A antagonist JMV2959 in usual intraperitoneal doses including 3 mg/kg, had no influence on memory functions tested in the Morris Water Maze in rats as well as no significant effects on the molecular markers linked with memory processing in selected brain areas in rats, specifically on the β-actin, c-Fos, two forms of the calcium/calmodulin-dependent protein kinase II (CaMKII, p-CaMKII) and the cAMP-response element binding protein (CREB, p-CREB), within the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), dorsal striatum, and hippocampus (HIPP). Furthermore, following the methamphetamine intravenous self-administration in rats, the 3 mg/kg JMV2959 pretreatment significantly reduced or prevented the methamphetamine-induced significant decrease of hippocampal β-actin and c-Fos as well as it prevented the significant decrease of CREB in the NAC and mPFC. These results imply, that the GHS-R1A antagonist/JMV2959 might reduce/prevent some of the memory-linked molecular changes elicited by methamphetamine addiction within brain structures associated with memory (HIPP), reward (NAc), and motivation (mPFC), which may contribute to the previously observed significant JMV2959-induced reduction of the methamphetamine self-administration and drug-seeking behavior in the same animals. Further research is necessary to corroborate these results.

Aerobic exercise as a promising nonpharmacological therapy for the treatment of substance use disorders

Despite the prevalence and public health impact of substance use disorders (SUDs), effective long-term treatments remain elusive. Aerobic exercise is a promising, nonpharmacological treatment currently under investigation as a strategy for preventing drug relapse. Aerobic exercise could be incorporated into the comprehensive treatment regimens for people with substance abuse disorders. Preclinical studies of SUD with animal models have shown that aerobic exercise diminishes drug-seeking behavior, which leads to relapse, in both male and female rats. Nevertheless, little is known regarding the effects of substance abuse-induced cellular and physiological adaptations believed to be responsible for drug-seeking behavior. Accordingly, the overall goal of this review is to provide a summary and an assessment of findings to date, highlighting evidence of the molecular and neurological effects of exercise on adaptations associated with SUD.

Voluntary oral methamphetamine increases memory deficits and contextual sensitization during abstinence associated with decreased PKMζ and increased κOR in the hippocampus of female mice

BACKGROUND

Female populations exhibit vulnerabilities to psychostimulant addiction, as well as cognitive dysfunction following bouts of abuse.

AIMS

The goal for this study was to advance our understanding of the mechanisms that produce sex disparities in drug addiction.

METHODS

We used an animal model for voluntary oral methamphetamine administration (VOMA) and focused on male and female mice that consumed 7.6-8.2 mg/kg of methamphetamine (MA) per day during the last 18 days of the paradigm.

RESULTS

The VOMA-exposed female mice displayed increased locomotor activity in the drug-administration context compared to male mice, demonstrating sex-specific changes in contextual sensitization. During 2 weeks of forced abstinence, mice underwent further behavioral testing. We show that abstinence increased open-arm entries on the elevated plus maze in both sexes. There were no differences in immobility on the tail suspension test. In a hippocampal-dependent radial arm maze task, VOMA-treated female mice, but not male mice, showed working memory deficits. Hippocampal tissue was collected and analyzed using Western blotting. VOMA-exposed female mice exhibited increased kappa opioid receptor (κOR) expression in the hippocampus compared to male mice, suggesting a vulnerability toward abstinence-induced dysphoria. Female VOMA mice also exhibited a decrease in the memory protein marker, protein kinase M zeta (PKMζ), in the hippocampus.

CONCLUSIONS

Our study reveals sex-specific effects following abstinence from chronic MA consumption on hippocampal κOR and PKMζ expression, suggesting that these neural changes in female mice may underlie spatial memory deficits and identify an increased susceptibility to dysregulated neural mechanisms. These data validate VOMA as a model sensitive to sex differences in behavior and hippocampal neurochemistry following chronic MA exposure.

Impairment of cost-benefit decision making in morphine-dependent rats is partly mediated via the alteration of BDNF and p-CREB levels in the nucleus accumbens

The ability to choose goals based on decision usefulness or the time required to reach the goals chosen are important aspects of decision making. There is considerable evidence in the literature indicating the fact that drug abuse affects different aspects of cognition. In the current study, we assessed the effects of morphine dependence and its withdrawal on cost-benefit decision making and furthermore the involvement of BDNF and p-CREB in the nucleus accumbens, a key brain area involved in decision making was measured. Different groups of male Wistar rats were trained in an effort-based and/or delay-based form of cost-benefit T-maze decision-making task. Thereafter, the animals were morphine dependent and the percentage of the high reward preference was evaluated. After behavioral tests, the BDNF level, and p-CREB/CREB ratio were measured by Western blot analysis. The results showed that during effort-based but not delay-based decision making, BDNF and p-CREB levels increased. During effort-based decision making in morphine dependent rats, BDNF decreased but there was no significant change in p-CREB. Besides, during delay-based decision making in the morphine dependent group, both BDNF and p-CREB did not show any significant change. These findings revealed that BDNF and p-CREB/CREB ratio in the NAc are essential factors for effort-based but not delay-based decision making. In addition, impairment of effort-based decision making in morphine dependent rats is related to the decrease of BDNF level but not p-CREB/CREB ratio in the NAc. However, delay-based decision making defects in morphine dependent rats did not associate with the change in BDNF and p-CREB levels in the NAc.

Alteration level of hippocampus BDNF expression and long-term potentiation upon microinjection of BRL15572 hydrochloride in a rat model of methamphetamine relapse

Methamphetamine (METH) relapse affects the function of the serotonergic system, which this system important for synaptic plasticity and brain-derived neurotrophic factor (BDNF) level. While there is a clear distribution of serotonin receptors in the reward and memory areas but the function of 5-HT_1D receptor isn't known. This article assessed effects of BRL15572 hydrochloride (5-HT_1D receptor antagonist) on behavior, long-term potentiation (LTP), and BDNF level in reinstated METH-rats. Conditioned place preference was induced by injecting METH (5 mg/kg; i.p.) or saline on the conditioning days. On the last day of extinction, they received priming METH [simultaneously with BRL (2 μg/5 μl; i.c.v.) or vehicle] or saline or saline + vehicle. Preference scores, LTP components and expression of BDNF were measured on the following day. The preference score of METH treatment increased dramatically more than the sham group and co-administration of BRL + METH couldn't decrease the preference score than the METH group. Also, METH treatment increased the population spike relative to the sham group, whereas the treatment METH + BRL attenuated this parameter than METH group. Furthermore, BDNF expression significantly increased in the METH group although it decreased markedly upon treatment with BRL. These results suggest that future studies should evaluate the potential of 5-HT_1D antagonist for METH-reinstatement behaviors.

Effects of lithium on inflammatory and neurotrophic factors after an immune challenge in a lisdexamfetamine animal model of mania

Objective:

To evaluate whether an animal model of mania induced by lisdexamfetamine dimesylate (LDX) has an inflammatory profile and whether immune activation by lipopolysaccharides (LPS) has a cumulative effect on subsequent stimuli in this model. We also evaluated the action of lithium (Li) on inflammatory and neurotrophic factors.

Methods:

Adult male Wistar rats were subjected to an animal model of mania. After the open-field test, they were given LPS to induce systemic immune activation. Subsequently, the animals’ blood was collected, and their serum levels of brain-derived neurotrophic factor and inflammatory markers (tumor necrosis factor [TNF]-α, interleukin [IL]-6, IL-1β, IL-10, and inducible nitric oxide synthase [iNOS]) were measured.

Results:

LDX induced hyperactivity in the animals, but no inflammatory marker levels increased except brain-derived neurotrophic factor (BDNF). Li had no effect on serum BDNF levels but prevented iNOS levels from increasing in animals subjected to immune activation.

Conclusion:

Although Li prevented an LPS-induced increase in serum iNOS levels, its potential anti-inflammatory effects in this animal model of mania were conflicting.

Methamphetamine binge administration during late adolescence induced enduring hippocampal cell damage following prolonged withdrawal in rats

A recent study from our laboratory demonstrated that binge methamphetamine induced hippocampal cell damage (i.e., impaired cell genesis) in rats when administered specifically during late adolescence (postnatal day, PND 54-57) and evaluated 24 h later (PND 58). The results also suggested a possible role for brain-derived neurotrophic factor (BDNF) regulating cell genesis and survival. This subsequent study evaluated whether these effects persisted in time as measured following prolonged withdrawal. Male Sprague-Dawley rats were treated (i.p.) with BrdU (2 × 50 mg/kg, 3 days, PND 48-50) followed by a binge paradigm (3 pulses/day, every 3 h, 4 days, PND 54-57) of methamphetamine (5 mg/kg, n = 14, M) or saline (0.9% NaCl, 1 ml/kg, n = 12, C). Following 34 days of forced withdrawal (PND 91), rats were killed 45 min after a challenge dose of saline (Sal: C-Sal, n = 6; M-Sal, n = 7) or methamphetamine (Meth: C-Meth, n = 6; M-Meth, n = 7). Neurogenesis markers (Ki-67: cell proliferation; NeuroD: early neuronal survival; BrdU: prolonged cell survival, 41-43 days old cells) were evaluated by immunohistochemistry while neuroplasticity markers (BDNF and Fos forms) were evaluated by Western blot. The main results showed that a history of methamphetamine administration (PND 54-57) induced enduring hippocampal cell damage (i.e., observed on PND 91) by decreasing cell survival (BrdU + cells) and mature-BDNF (m-BDNF) protein content, associated with neuronal survival, growth and differentiation. Interestingly, m-BDNF regulation paralleled hippocampal c-Fos protein content, indicating decreased neuronal activity, and thus reinforcing the persisting negative effects induced by methamphetamine in rat hippocampus following prolonged withdrawal.

The neurochemical consequences of methamphetamine self-administration in male and female rats

BACKGROUND

Methamphetamine (METH) is an addictive substance that is used in both males and females. Few preclinical studies have focused on understanding sex-differences in the neurochemical consequences of contingent METH. The purpose of the current study was to investigate potential sex-differences in the neurochemical consequences of METH self-administration.

METHODS

Male and female adult rats were given extended access to METH or saline self-administration for 7d. Following self-administration, hippocampal brain-derived neurotrophic factor (BDNF) and striatal dopamine transporter (DAT) were assessed via western blotting.

RESULTS

Male and female rats had similar METH intake. METH self-administration reduced striatal DAT in both sexes, but only males that self-administered METH had elevated hippocampal BDNF levels.

CONCLUSIONS

Sex-differences exist in the neurochemical consequences of METH self-administration. These differences may lead to sex-specific vulnerability to the toxic effects of METH.

Methamphetamine addiction: involvement of CREB and neuroinflammatory signaling pathways

RATIONALE AND OBJECTIVES

Addiction to psychostimulant methamphetamine (METH) remains a major public health problem in the world. Animal models that use METH self-administration incorporate many features of human drug-taking behavior and are very helpful in elucidating mechanisms underlying METH addiction. These models are also helping to decipher the neurobiological substrates of associated neuropsychiatric complications. This review summarizes our work on the influence of METH self-administration on dopamine systems, transcription and immune responses in the brain.

METHODS

We used the rat model of METH self-administration with extended access (15 h/day for eight consecutive days) to investigate the effects of voluntary METH intake on the markers of dopamine system integrity and changes in gene expression observed in the brain at 2 h-1 month after cessation of drug exposure.

RESULTS

Extended access to METH self-administration caused changes in the rat brain that are consistent with clinical findings reported in neuroimaging and postmortem studies of human METH addicts. In addition, gene expression studies using striatal tissues from METH self-administering rats revealed increased expression of genes involved in cAMP response element binding protein (CREB) signaling pathway and in the activation of neuroinflammatory response in the brain.

CONCLUSION

These data show an association of METH exposure with activation of neuroplastic and neuroinflammatory cascades in the brain. The neuroplastic changes may be involved in promoting METH addiction. Neuroinflammatory processes in the striatum may underlie cognitive deficits, depression, and parkinsonism reported in METH addicts. Therapeutic approaches that include suppression of neuroinflammation may be beneficial to addicted patients.

Epigenetic landscape of amphetamine and methamphetamine addiction in rodents

Amphetamine and methamphetamine addiction is described by specific behavioral alterations, suggesting long-lasting changes in gene and protein expression within specific brain subregions involved in the reward circuitry. Given the persistence of the addiction phenotype at both behavioral and transcriptional levels, several studies have been conducted to elucidate the epigenetic landscape associated with persistent effects of drug use on the mammalian brain. This review discusses recent advances in our comprehension of epigenetic mechanisms underlying amphetamine- or methamphetamine-induced behavioral, transcriptional, and synaptic plasticity. Accumulating evidence demonstrated that drug exposure induces major epigenetic modifications-histone acetylation and methylation, DNA methylation-in a very complex manner. In rare instances, however, the regulation of a specific target gene can be correlated to both epigenetic alterations and behavioral abnormalities. Work is now needed to clarify and validate an epigenetic model of addiction to amphetamines. Investigations that include genome-wide approaches will accelerate the speed of discovery in the field of addiction.

Time-Dependent Serum Brain-Derived Neurotrophic Factor Decline During Methamphetamine Withdrawal

Methamphetamine (METH) is a widely abused illegal psychostimulant, which is confirmed to be neurotoxic and of great damage to human. Studies on the role of brain-derived neurotrophic factor (BDNF) in human METH addicts are limited and inconsistent. The purposes of this study are to compare the serum BDNF levels between METH addicts and healthy controls during early withdrawal, and explore the changes of serum BDNF levels during the first month after METH withdrawal.179 METH addicts and 90 age- and gender-matched healthy controls were recruited in this study. We measured serum BDNF levels at baseline (both METH addicts and healthy controls) and at 1 month after abstinence of METH (METH addicts only).Serum BDNF levels of METH addicts at baseline were significantly higher than controls (1460.28  ±  490.69 vs 1241.27  ±  335.52  pg/mL; F = 14.51, P < 0.001). The serum BDNF levels of 40 METH addicts were re-examined after 1 month of METH abstinence, which were significantly lower than that at baseline (1363.70  ±  580.59 vs 1621.41  ±  591.07  pg/mL; t = 2.26, P = .03), but showed no differences to the controls (1363.70  ±  580.59 vs 1241.27  ±  335.52  pg/mL; F = 2.29, P = 0.13).Our study demonstrated that serum BDNF levels were higher in METH addicts than controls during early withdrawal, and were time dependent decreased during the first month of abstinence. These findings may provide further evidence that increased serum BDNF levels may be associated with the pathophysiology of METH addiction and withdrawal and may be a protective response against the subsequent METH-induced neurotoxicity. Besides, these findings may also promote the development of medicine in the treatment of METH addiction and withdrawal.

Methamphetamine blocks exercise effects on Bdnf and Drd2 gene expression in frontal cortex and striatum

Exposure to drugs of abuse can produce many neurobiological changes which may lead to increased valuation of rewards and decreased sensitivity to their costs. Many of these behavioral alterations are associated with activity of D2-expressing medium spiny neurons in the striatum. Additionally, Bdnf in the striatum has been shown to play a role in flexible reward-seeking behavior. Given that voluntary aerobic exercise can affect the expression of these proteins in healthy subjects, and that exercise has shown promise as an anti-addictive therapy, we set out to quantify changes in D2 and Bdnf expression in methamphetamine-exposed rats given access to running wheels. Sixty-four rats were treated for two weeks with an escalating dose of methamphetamine or saline, then either sacrificed, housed in standard cages, or given free access to a running wheel for 6 weeks prior to sacrifice. Rats treated with methamphetamine ran significantly greater distances than saline-treated rats, suggesting an augmentation in the reinforcement value of voluntary wheel running. Transcription of Drd2 and Bdnf was assessed via RT-qPCR. Protein expression levels of D2 and phosphorylation of the TrkB receptor were measured via western blot. Drd2 and Bdnf mRNA levels were impacted independently by exercise and methamphetamine, but exposure to methamphetamine prior to the initiation of exercise blocked the exercise-induced changes seen in rats treated with saline. Expression levels of both proteins were elevated immediately after methamphetamine, but returned to baseline after six weeks, regardless of exercise status.

Temporal regulation of peripheral BDNF levels during cocaine and morphine withdrawal: comparison with a natural reward

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that has long been studied in the field of addiction and its importance in regulating drug addiction-related behavior has been widely demonstrated. The aim of our study was to analyze the consequences of a repeated exposure to drugs of abuse or natural reward on plasma BDNF levels during withdrawal.

METHODS

Rats were chronically injected with morphine (subcutaneously, 5mg/kg) or cocaine (intraperitoneally, 20mg/kg) or fed with a butter biscuit (per os, 4g) once per day for 14 days. Blood collection was performed on the 1st (withdrawal day 1 or WD1) or on (WD14), either at the same time point rats had been exposed to drugs or natural reward or at a different time point (used to quantify basal brain-derived neurotrophic factor levels).

RESULTS

Cocaine treatment led to a rapid (WD1) and persistent (WD14) decrease of basal BDNF levels compared with saline-treated animals, whereas morphine induced an increase on WD14 without any alteration on WD1. On the contrary, the natural reward induced a significant increase of basal brain-derived neurotrophic factor levels only on WD1. The analysis of BDNF levels at the usual time point at which animals had been exposed showed that both drugs, but not the natural reward, increased BDNF levels compared with basal levels.

CONCLUSION

Our data highlight that only drugs of abuse are able to persistently alter BDNF levels and to induce specific variations of this neurotrophic factor at the usual hour of injection.

Transcriptional and epigenetic substrates of methamphetamine addiction and withdrawal: evidence from a long-access self-administration model in the rat

Methamphetamine use disorder is a chronic neuropsychiatric disorder characterized by recurrent binge episodes, intervals of abstinence, and relapses to drug use. Humans addicted to methamphetamine experience various degrees of cognitive deficits and other neurological abnormalities that complicate their activities of daily living and their participation in treatment programs. Importantly, models of methamphetamine addiction in rodents have shown that animals will readily learn to give themselves methamphetamine. Rats also accelerate their intake over time. Microarray studies have also shown that methamphetamine taking is associated with major transcriptional changes in the striatum measured within a short or longer time after cessation of drug taking. After a 2-h withdrawal time, there was increased expression of genes that participate in transcription regulation. These included cyclic AMP response element binding (CREB), ETS domain-containing protein (ELK1), and members of the FOS family of transcription factors. Other genes of interest include brain-derived neurotrophic factor (BDNF), tyrosine kinase receptor, type 2 (TrkB), and synaptophysin. Methamphetamine-induced transcription was found to be regulated via phosphorylated CREB-dependent events. After a 30-day withdrawal from methamphetamine self-administration, however, there was mostly decreased expression of transcription factors including junD. There was also downregulation of genes whose protein products are constituents of chromatin-remodeling complexes. Altogether, these genome-wide results show that methamphetamine abuse might be associated with altered regulation of a diversity of gene networks that impact cellular and synaptic functions. These transcriptional changes might serve as triggers for the neuropsychiatric presentations of humans who abuse this drug. Better understanding of the way that gene products interact to cause methamphetamine addiction will help to develop better pharmacological treatment of methamphetamine addicts.