Neurotoxicity and persistent cognitive deficits induced by combined MDMA and alcohol exposure in adolescent rats

Striatal Iron Deposition in Recreational MDMA (Ecstasy) Users

BACKGROUND

The common club drug MDMA (also known as ecstasy) enhances mood, sensory perception, energy, sociability, and euphoria. While MDMA has been shown to produce neurotoxicity in animal models, research on its potential neurotoxic effects in humans is inconclusive and has focused primarily on the serotonin system.

METHODS

We investigated 34 regular, largely pure MDMA users for signs of premature neurodegenerative processes in the form of increased iron load in comparison to a group of 36 age-, sex-, and education-matched MDMA-naïve control subjects. We used quantitative susceptibility mapping, a novel tool able to detect even small tissue (nonheme) iron accumulations. Cortical and relevant subcortical gray matter structures were grouped into 8 regions of interest and analyzed.

RESULTS

Significantly increased iron deposition in the striatum was evident in the MDMA user group. The effect survived correction for multiple comparisons and remained after controlling for relevant confounding factors, including age, smoking, and stimulant co-use. Although no significant linear relationship between measurements of the amounts of MDMA intake (hair analysis and self-reports) and quantitative susceptibility mapping values was observed, increased striatal iron deposition might nevertheless point to MDMA-induced neurotoxic processes. Additional factors (hyperthermia and simultaneous co-use of other substances) that possibly amplify neurotoxic effects of MDMA during the state of acute intoxication are discussed.

CONCLUSIONS

The demonstrated increased striatal iron accumulation may indicate that regular MDMA users have an increased risk potential for neurodegenerative diseases with progressing age.

Combining ecstasy and ethanol: higher risk for toxicity? A review

Ecstasy use is commonly combined with ethanol consumption. While combination drug use in general is correlated with a higher risk for toxicity, the risk of the specific combination of ecstasy (3,4-methylenedioxymethamphetamine (MDMA)) and ethanol is largely unknown. Therefore, we have reviewed the literature on changes in MDMA pharmacokinetics and pharmacodynamics due to concurrent ethanol exposure in human, animal and in vitro studies. MDMA pharmacokinetics appear unaffected: the MDMA blood concentration after concurrent exposure to MDMA and ethanol was comparable to lone MDMA exposure in multiple human placebo-controlled studies. In contrast, MDMA pharmacodynamics were affected: locomotor activity increased and body temperature decreased after concurrent exposure to MDMA and ethanol compared to lone MDMA exposure. Importantly, these additional ethanol effects were consistently observed in multiple animal studies. Additional ethanol effects have also been reported on other pharmacodynamic aspects, but are inconclusive due to a low number of studies or due to inconsistent findings. These investigated pharmacodynamic aspects include monoamine brain concentrations, neurological (psychomotor function, memory, anxiety, reinforcing properties), cardiovascular, liver and endocrine effects. Although only a single or a few studies were available investigating these aspects, most studies indicated an aggravation of MDMA-induced effects upon concurrent ethanol exposure. In summary, concurrent ethanol exposure appears to increase the risk for MDMA toxicity. Increased toxicity is due to an aggravation of MDMA pharmacodynamics, while MDMA pharmacokinetics is largely unaffected. Although a significant attenuation of the MDMA-induced increase of body temperature was observed in animal studies, its relevance for human exposure remains unclear.

Withdrawal from Extended, Intermittent Access to A Highly Palatable Diet Impairs Hippocampal Memory Function and Neurogenesis: Effects of Memantine

Background: Compulsive eating can be promoted by intermittent access to palatable food and is often accompanied by cognitive deficits and reduction in hippocampal plasticity. Here, we investigated the effects of intermittent access to palatable food on hippocampal function and neurogenesis. Methods: Male Wistar rats were either fed chow for 7 days/week (Chow/Chow group), or fed chow intermittently for 5 days/week followed by a palatable diet for 2 days/week (Chow/Palatable group). Hippocampal function and neurogenesis were assessed either during withdrawal or following renewed access to palatable food. Furthermore, the ability of the uncompetitive N-methyl-d-aspartate receptor (NMDAR) antagonist memantine to prevent the diet-induced memory deficits and block the maladaptive feeding was tested. Results: Palatable food withdrawn Chow/Palatable rats showed both a weakened ability for contextual spatial processing and a bias in their preference for a “novel cue” over a “novel place,” compared to controls. They also showed reduced expression of immature neurons in the dentate gyrus of the hippocampus as well as a withdrawal-dependent decrease of proliferating cells. Memantine treatment was able both to reverse the memory deficits and to reduce the excessive intake of palatable diet and the withdrawal-induced hypophagia in food cycling rats. Conclusions: In summary, our results provide evidence that withdrawal from highly palatable food produces NMDAR-dependent deficits in hippocampal function and a reduction in hippocampal neurogenesis.

Cognitive Effects of MDMA in Laboratory Animals: A Systematic Review Focusing on Dose

±3,4-Methylenedioxymethamphetamine (MDMA) is a synthetic, psychoactive drug that is primarily used recreationally but also may have some therapeutic value. At low doses, MDMA produces feelings of relaxation, empathy, emotional closeness, and euphoria. Higher doses can produce unpleasant psychostimulant- and hallucinogen-like adverse effects and therefore are usually not taken intentionally. There is considerable evidence that MDMA produces neurotoxicity and cognitive deficits at high doses; however, these findings may not generalize to typical recreational or therapeutic use of low-dose MDMA. Here, we systematically review 25 years of research on the cognitive effects of MDMA in animals, with a critical focus on dose. We found no evidence that doses of less than 3 mg/kg MDMA-the dose range that users typically take-produce cognitive deficits in animals. Doses of 3 mg/kg or greater, which were administered most often and frequently ranged from 5 to 20 times greater than an average dose, also did not produce cognitive deficits in a slight majority of experiments. Overall, the preclinical evidence of MDMA-induced cognitive deficits is weak and, if anything, may be the result of unrealistically high dosing. While factors associated with recreational use such as polydrug use, adulterants, hyperthermia, and hyponatremia can increase the potential for neurotoxicity, the short-term, infrequent, therapeutic use of ultra low-dose MDMA is unlikely to pose significant cognitive risks. Future studies must examine any adverse cognitive effects of MDMA using clinically relevant doses to reliably assess its potential as a psychotherapeutic.

The acute toxic and neurotoxic effects of 3,4-methylenedioxymethamphetamine are more pronounced in adolescent than adult mice

3,4-methylenedioxymethamphetamine (MDMA) recently achieved breakthrough status from the Food and Drug Administration (FDA) for post-traumatic stress disorder (PTSD). However, evidence indicates that exposure to toxic doses of MDMA can lead to long-lasting dysregulation of brain monoaminergic neurotransmitters, primarily from studies conducted in young adult rodents. To date, there is a paucity of data on whether toxic doses of MDMA can differentially affect neurotransmitter systems in adolescents and mature adults, which is an important question as adolescents and adults may be differentially vulnerable to MDMA abuse. In the current study, adolescent (6-7 weeks of age) and mature adult (16-18 weeks of age) male, Swiss-Webster mice were exposed to MDMA (20 mg/kg) using a binge-like dosing regimen (4 administrations spaced every 2 h). Acute lethality, acute hyperthermia, and acute decreases in body weight following MDMA administration were more pronounced in adolescent than adult mice. Likewise, acute loss of striatal dopamine neurochemistry was also exacerbated in adolescents, as determined by high-pressure liquid chromatography coupled to electrochemical detection. Exposure to MDMA induced greater turnover of dopamine into its major metabolite dihydroxyphenylacetic acid (DOPAC) in adolescents, but not in adults, suggesting a novel mechanism through which adolescents may show increased vulnerability to the acute toxic and neurotoxic effects of MDMA, or conversely that mature adults show greater protection. These data caution that MDMA exposure in adolescence may be particularly dangerous and that the therapeutic window for MDMA may differ between adolescents and mature adults.

Resveratrol alleviates ethanol-induced neuroinflammation in vivo and in vitro: Involvement of TLR2-MyD88-NF-κB pathway

Excessive ethanol (EtOH) intake affects cognitive function and leads to permanent learning and memory deficits. EtOH-induced neuroinflammation plays an important role in EtOH neurotoxicity. Studies have shown that EtOH activates microglia and induces an inflammatory response. Resveratrol (Rsv) is a natural polyphenol found in a wide variety of plants and fruits, and produces the neuroprotective and anti-inflammatory effects in the central nervous system. However, effect of Rsv on EtOH-induced neuroinflammation is still unknown. We investigated the anti-inflammatory effect of Rsv in the context of EtOH-induced neurotoxicity and the molecular mechanisms potentially involved in the effect. The results showed that treatment of rats with Rsv prevented the deficits of spatial reference memory induced by EtOH and mitigated EtOH-induced neuroinflammation by inhibiting microglial activation and decreasing the levels of inflammatory cytokines including interleukin-1β, interleukin-6 and tumor necrosis factor α. The further studies indicated that Rsv reduced TLR2 expression in vivo and in vitro, and downregulated expression of myeloid differentiation primary response 88 (MyD88) and phosphorylation of nuclear factor κB (NF-κB). These data demonstrate that Rsv alleviates the ethanol-induced neuroinflammation via inhibition of TLR2-MyD88-NF-κB signal pathway.

Alcohol aggravates ketamine-induced behavioral, morphological and neurochemical alterations in adolescent rats: The involvement of CREB-related pathways

Currently, an increasing proportion of adolescent ketamine users simultaneously consume alcohol. However, the potential behavioural and neurological alterations induced by such a drug combination and the underlying mechanisms have not been systematically examined. Therefore, in the present study, the behavioural and morphological changes and the underlying mechanisms were studied in adolescent rats after repeated alcohol and/or ketamine treatment. This study provided the first evidence that co-administration of alcohol (2 and 4 g/kg, i.g.) in adolescent rats significantly potentiated the neurotoxic properties of repeated ketamine (30 mg/kg, i.p.) treatments over 14 days, manifesting as increased locomotor activity, stereotypic behaviour, ataxia and morphological changes. This potentiation was associated with the enhancement by alcohol of ketamine-induced glutamate (Glu) and dopamine (DA) release in the cortex and hippocampus. Further mechanistic study demonstrated that alcohol potentiated ketamine-induced neurotoxicity through down-regulation of Akt (a serine/threonine kinase or protein kinase, PKB), protein kinase A (PKA), calmodulin-dependent kinase IV (CaMK-IV)-mediated cyclic AMP-responsive element binding protein (CREB) pathways and induction of neuronal apoptosis in the cortex and hippocampus of the adolescent rats. As this study provides strong evidence that repeated alcohol and ketamine co-exposure may cause serious neurotoxicity, attention needs to be drawn to the potential risk of this consumption behaviour, especially for adolescents.

Differential effects of MDMA and cocaine on inhibitory avoidance and object recognition tests in rodents

INTRODUCTION

Drug addiction continues being a major public problem faced by modern societies with different social, health and legal consequences for the consumers. Consumption of psychostimulants, like cocaine or MDMA (known as ecstasy) are highly prevalent and cognitive and memory impairments have been related with the abuse of these drugs.

AIM

The aim of this work was to review the most important data of the literature in the last 10 years about the effects of cocaine and MDMA on inhibitory avoidance and object recognition tests in rodents.

DEVELOPMENT

The object recognition and the inhibitory avoidance tests are popular procedures used to assess different types of memory. We compare the effects of cocaine and MDMA administration in these tests, taking in consideration different factors such as the period of life development of the animals (prenatal, adolescence and adult age), the presence of polydrug consumption or the role of environmental variables. Brain structures involved in the effects of cocaine and MDMA on memory are also described.

CONCLUSIONS

Cocaine and MDMA induced similar impairing effects on the object recognition test during critical periods of lifetime or after abstinence of prolonged consumption in adulthood. Deficits of inhibitory avoidance memory are observed only in adult rodents exposed to MDMA. Psychostimulant abuse is a potential factor to induce memory impairments and could facilitate the development of future neurodegenerative disorders.

A proof-of-concept investigation into ketamine as a pharmacological treatment for alcohol dependence: study protocol for a randomised controlled trial

Background

Worldwide, alcohol abuse is a burgeoning problem. Abstinence is key to allow recovery of physical and mental health as well as quality of life, but treatment for alcohol dependence is associated with high relapse rates. Preliminary data have suggested that a combined repeated ketamine and psychological therapy programme may be effective in reducing relapse in severe alcohol use disorder. This non-commercial proof-of-concept trial is aimed at making a preliminary assessment of the effectiveness of this combined treatment in this patient group.

Methods/design

This is a phase II, randomised, double-blind, placebo-controlled, parallel-group clinical trial taking place in two sites in the UK: the South West of England and London. Ninety-six recently detoxified alcoholics, with comorbid depressive symptoms, will be randomised to one of four treatment arms. Patients will receive either three sessions of ketamine (0.8 mg/kg administered intravenously (IV) over 40 minutes) or placebo (50 ml saline 0.9% IV over 40 minutes) plus either seven sessions of manualised psychological therapy or an alcohol education control. Patients will be assessed at 3 and 6 months on a range of psychological and biological variables. The primary endpoints are (1) relapse rates at 6 months and (2) percentage days abstinent at 6 months. Secondary endpoints include 3 and 6 month percentage days abstinence, tolerability (indicated by dropout), adverse events, depressive symptoms, craving and quality of life.

Discussion

This study will provide important information on a new combined psychological and pharmacological intervention aimed at reducing relapse rates in alcoholics. The findings would have broad application given the worldwide prevalence of alcoholism and its associated medical, psychological and social problems.

Trial registration

ClinicalTrials.gov, NCT02649231. Registered on 5 January 2016.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-1895-6) contains supplementary material, which is available to authorized users.

Long-term cognitive, emotional and neurogenic alterations induced by alcohol and methamphetamine exposure in adolescent rats

A high proportion of young methamphetamine (MA) users simultaneously consume alcohol. However, the potential neurological and behavioural alterations induced by such a drug combination have not been systematically examined. We studied in adolescent rats the long-term effects of alcohol, MA, and alcohol and MA combined on anxiety-like behaviour, memory, and neurogenesis in the adult hippocampus. Rats received saline, ethanol (ETOH, 1.5g/kg), MA (MA, 2mg/kg), or ethanol and MA combined (ETHOH-MA, 1.5g/kg ethanol plus 2mg/kg MA) via oral gavage, once daily for 5 consecutive days. Open field (OF), elevated plus maze (EPM) and radial arm maze (RAM) tests were conducted following a 15-day withdrawal period. The results showed alterations in exploratory behaviour in the OF in the MA and ETOH-MA groups, and anxiety-like effects in the EPM in all three drug treatment groups. All three drug groups exhibited reference memory deficits in the RAM, but only the combination treatment group displayed alterations in working memory. Both MA and ETOH-MA treatments increased the length of doublecortin (DCX)-void gaps in the dentate gyrus but only ETOH-MA treatment increased the number of such gaps. An increased number and length of DCX-void gaps correlated with decreased exploratory activity in the OF, and impaired working memory in the RAM was associated with an augmented number of gaps. These findings suggest that alterations in adult hippocampal neurogenesis are linked to the persistent cognitive and behavioural deficits produced by alcohol and MA exposure.

Reducing Peripheral Inflammation with Infliximab Reduces Neuroinflammation and Improves Cognition in Rats with Hepatic Encephalopathy

Inflammation contributes to cognitive impairment in patients with hepatic encephalopathy (HE). However, the process by which peripheral inflammation results in cognitive impairment remains unclear. In animal models, neuroinflammation and altered neurotransmission mediate cognitive impairment. Taking into account these data, we hypothesized that in rats with HE: (1) peripheral inflammation is a main contributor to neuroinflammation; (2) neuroinflammation in hippocampus impairs spatial learning by altering AMPA and/or NMDA receptors membrane expression; (3) reducing peripheral inflammation with infliximab (anti-TNF-a) would improve spatial learning; (4) this would be associated with reduced neuroinflammation and normalization of the membrane expression of glutamate receptors. The aims of this work were to assess these hypotheses. We analyzed in rats with portacaval shunt (PCS) and control rats, treated or not with infliximab: (a) peripheral inflammation by measuring prostaglandin E2, IL10, IL-17, and IL-6; (b) neuroinflammation in hippocampus by analyzing microglial activation and the content of TNF-a and IL-1b; (c) AMPA and NMDA receptors membrane expression in hippocampus; and (d) spatial learning in the Radial and Morris water mazes. We assessed the effects of treatment with infliximab on peripheral inflammation, on neuroinflammation and AMPA and NMDA receptors membrane expression in hippocampus and on spatial learning and memory. PCS rats show increased serum prostaglandin E2, IL-17, and IL-6 and reduced IL-10 levels, indicating increased peripheral inflammation. PCS rats also show microglial activation and increased nuclear NF-kB and expression of TNF-a and IL-1b in hippocampus. This was associated with altered AMPA and NMDA receptors membrane expression in hippocampus and impaired spatial learning and memory in the radial and Morris water maze. Treatment with infliximab reduces peripheral inflammation in PCS rats, normalizing prostaglandin E2, IL-17, IL-6, and IL-10 levels in serum. Infliximab also prevents neuroinflammation, reduces microglial activation, translocates NF-kB into nucleoli and normalizes TNF-a and IL-1b content in hippocampus. This was associated with normalization of AMPA receptors membrane expression in hippocampus and of spatial learning and memory. The results suggest that peripheral inflammation contributes to spatial learning impairment in PCS rats. Treatment with anti-TNF-a could be a new therapeutic approach to improve cognitive function in patients with HE.

Adult Neurogenesis and Psychiatric Disorders

Psychiatric disorders continue to be among the most challenging disorders to diagnose and treat because there is no single genetic or anatomical locus that is causative for the disease. Current treatments are often blunt tools used to ameliorate the most severe symptoms, at the risk of disrupting functional neural systems. There is a critical need to develop new therapeutic strategies that can target circumscribed functional or anatomical domains of pathology. Adult hippocampal neurogenesis may be one such domain. Here, we review the evidence suggesting that adult hippocampal neurogenesis plays a role in emotional regulation and forms of learning and memory that include temporal and spatial memory encoding and context discrimination, and that its dysregulation is associated with psychiatric disorders, such as affective disorders, schizophrenia, and drug addiction. Further, adult neurogenesis has proven to be an effective model to investigate basic processes of neuronal development and converging evidence suggests that aberrant neural development may be an etiological factor, even in late-onset diseases. Constitutive neurogenesis in the hippocampus of the mature brain reflects large-scale plasticity unique to this region and could be a potential hub for modulation of a subset of cognitive and affective behaviors that are affected by multiple psychiatric disorders.

Hyperammonemia induces glial activation, neuroinflammation and alters neurotransmitter receptors in hippocampus, impairing spatial learning: reversal by sulforaphane

Background

Patients with liver cirrhosis and minimal hepatic encephalopathy (MHE) show mild cognitive impairment and spatial learning dysfunction. Hyperammonemia acts synergistically with inflammation to induce cognitive impairment in MHE. Hyperammonemia-induced neuroinflammation in hippocampus could contribute to spatial learning impairment in MHE. Two main aims of this work were: (1) to assess whether chronic hyperammonemia increases inflammatory factors in the hippocampus and if this is associated with microglia and/or astrocytes activation and (2) to assess whether hyperammonemia-induced neuroinflammation in the hippocampus is associated with altered membrane expression of glutamate and GABA receptors and spatial learning impairment. There are no specific treatments for cognitive alterations in patients with MHE. A third aim was to assess whether treatment with sulforaphane enhances endogenous the anti-inflammatory system, reduces neuroinflammation in the hippocampus of hyperammonemic rats, and restores spatial learning and if normalization of receptor membrane expression is associated with learning improvement.

Methods

We analyzed the following in control and hyperammonemic rats, treated or not with sulforaphane: (1) microglia and astrocytes activation by immunohistochemistry, (2) markers of pro-inflammatory (M1) (IL-1β, IL-6) and anti-inflammatory (M2) microglia (Arg1, YM-1) by Western blot, (3) membrane expression of GABA, AMPA, and NMDA receptors using the BS3 cross-linker, and (4) spatial learning using the radial maze.

Results

The results reported show that hyperammonemia induces astrocytes and microglia activation in the hippocampus, increasing pro-inflammatory cytokines IL-1β and IL-6. This is associated with altered membrane expression of AMPA, NMDA, and GABA receptors which would be responsible for altered neurotransmission and impairment of spatial learning in the radial maze. Treatment with sulforaphane promotes microglia differentiation from pro-inflammatory M1 to anti-inflammatory M2 phenotype and reduces activation of astrocytes in hyperammonemic rats. This reduces neuroinflammation, normalizes membrane expression of glutamate and GABA receptors, and restores spatial learning in hyperammonemic rats.

Conclusions

Hyperammonemia-induced neuroinflammation impairs glutamatergic and GABAergic neurotransmission by altering membrane expression of glutamate and GABA receptors, resulting in impaired spatial learning. Sulforaphane reverses all these effects. Treatment with sulforaphane could be useful to improve cognitive function in cirrhotic patients with minimal or clinical hepatic encephalopathy.

The combination of ethanol with mephedrone increases the signs of neurotoxicity and impairs neurogenesis and learning in adolescent CD-1 mice

A new family of psychostimulants, under the name of cathinones, has broken into the market in the last decade. In light of the fact that around 95% of cathinone consumers have been reported to combine them with alcoholic drinks, we sought to study the consequences of the concomitant administration of ethanol on mephedrone -induced neurotoxicity. Adolescent male Swiss-CD1 mice were administered four times in one day, every 2h, with saline, mephedrone (25mg/kg), ethanol (2; 1.5; 1.5; 1g/kg) and their combination at a room temperature of 26±2°C. The combination with ethanol impaired mephedrone-induced decreases in dopamine transporter and tyrosine hydroxylase in the frontal cortex; and in serotonin transporter and tryptophan hydroxylase in the hippocampus by approximately 2-fold, 7days post-treatment. Furthermore, these decreases correlated with a 2-fold increase in lipid peroxidation, measured as concentration of malondialdehyde (MDA), 24h post-treatment, and were accompanied by changes in oxidative stress-related enzymes. Ethanol also notably potentiated mephedrone-induced negative effects on learning and memory, as well as hippocampal neurogenesis, measured through the Morris water maze (MWM) and 5-bromo-2'-deoxyuridine staining, respectively. These results are of special significance, since alcohol is widely co-abused with amphetamine derivatives such as mephedrone, especially during adolescence, a crucial stage in brain maturation. Given that the hippocampus is greatly involved in learning and memory processes, normal brain development in young adults could be affected with permanent behavioral consequences after this type of drug co-abuse.

Sildenafil reduces neuroinflammation and restores spatial learning in rats with hepatic encephalopathy: underlying mechanisms

Background

There are no specific treatments for the neurological alterations of cirrhotic patients with minimal hepatic encephalopathy (MHE). Rats with MHE due to portacaval shunt (PCS) show impaired spatial learning. The underlying mechanisms remain unknown. The aims of this work were to assess: (a) whether PCS rats show neuroinflammation in hippocampus, (b) whether treatment with sildenafil reduces neuroinflammation and restores spatial learning in PCS rats, and (c) analyze the underlying mechanisms.

Methods

Neuroinflammation was assessed by determining inflammatory markers by Western blot. Phosphorylation of MAP-kinase p38 was assessed by immunohistochemistry. Membrane expression of GABA and glutamate receptors was analyzed using BS3 cross-linker. Spatial learning was analyzed using the radial and Morris water mazes. To assess if sildenafil reverses the alterations, rats were treated with sildenafil in the drinking water.

Results

PCS rats show increased IL-1β and TNF-α levels and phosphorylation (activity) of p38 in hippocampus. Membrane expression of subunits α1 of GABA_A receptor and GluR2 of AMPA receptor are increased in PCS rats, while subunits GluR1 of AMPA receptors and NR1 and NR2a of NMDA receptors are reduced. PCS rats show reduced spatial learning in the radial and Morris water mazes. Sildenafil treatment normalizes IL-1β and TNF-α levels, p38 phosphorylation, and membrane expression of GABA_A, AMPA, and NMDA receptors and restores spatial learning.

Conclusions

Increased IL-1β alters GABAergic and glutamatergic neurotransmission in hippocampus and impairs spatial learning in rats with MHE. Sildenafil reduces neuroinflammation and restores learning. Phosphodiesterase-5 inhibitors may be useful to improve cognitive function in patients with MHE.

Effects of addictive drugs on adult neural stem/progenitor cells

Neural stem/progenitor cells (NSPCs) undergo a series of developmental processes before giving rise to newborn neurons, astrocytes and oligodendrocytes in adult neurogenesis. During the past decade, the role of NSPCs has been highlighted by studies on adult neurogenesis modulated by addictive drugs. It has been proven that these drugs regulate the proliferation, differentiation and survival of adult NSPCs in different manners, which results in the varying consequences of adult neurogenesis. The effects of addictive drugs on NSPCs are exerted via a variety of different mechanisms and pathways, which interact with one another and contribute to the complexity of NSPC regulation. Here, we review the effects of different addictive drugs on NSPCs, and the related experimental methods and paradigms. We also discuss the current understanding of major signaling molecules, especially the putative common mechanisms, underlying such effects. Finally, we review the future directions of research in this area.

Amphetamine-related drugs neurotoxicity in humans and in experimental animals: Main mechanisms

Amphetamine-related drugs, such as 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (METH), are popular recreational psychostimulants. Several preclinical studies have demonstrated that, besides having the potential for abuse, amphetamine-related drugs may also elicit neurotoxic and neuroinflammatory effects. The neurotoxic potentials of MDMA and METH to dopaminergic and serotonergic neurons have been clearly demonstrated in both rodents and non-human primates. This review summarizes the species-specific cellular and molecular mechanisms involved in MDMA and METH-mediated neurotoxic and neuroinflammatory effects, along with the most important behavioral changes elicited by these substances in experimental animals and humans. Emphasis is placed on the neuropsychological and neurological consequences associated with the neuronal damage. Moreover, we point out the gap in our knowledge and the need for developing appropriate therapeutic strategies to manage the neurological problems associated with amphetamine-related drug abuse.

GR3027 antagonizes GABAA receptor-potentiating neurosteroids and restores spatial learning and motor coordination in rats with chronic hyperammonemia and hepatic encephalopathy

Hepatic encephalopathy (HE) is one of the primary complications of liver cirrhosis. Current treatments for HE, mainly directed to reduction of ammonia levels, are not effective enough because they cannot completely eliminate hyperammonemia and inflammation, which induce the neurological alterations. Studies in animal models show that overactivation of GABAA receptors is involved in cognitive and motor impairment in HE and that reducing this activation restores these functions. We have developed a new compound, GR3027, that selectively antagonizes the enhanced activation of GABAA receptors by neurosteroids such as allopregnanolone and 3α,21-dihydroxy-5α-pregnan-20-one (THDOC). This work aimed to assess whether GR3027 improves motor incoordination, spatial learning, and circadian rhythms of activity in rats with HE. GR3027 was administered subcutaneously to two main models of HE: rats with chronic hyperammonemia due to ammonia feeding and rats with portacaval shunts (PCS). Motor coordination was assessed in beam walking and spatial learning and memory in the Morris water maze and the radial maze. Circadian rhythms of ambulatory and vertical activity were also assessed. In both hyperammonemic and PCS rats, GR3027 restores motor coordination, spatial memory in the Morris water maze, and spatial learning in the radial maze. GR3027 also partially restores circadian rhythms of ambulatory and vertical activity in PCS rats. GR3027 is a novel approach to treatment of HE that would normalize neurological functions altered because of enhanced GABAergic tone, affording more complete normalization of cognitive and motor function than current treatments for HE.

Gender differences in spatial learning, synaptic activity, and long-term potentiation in the hippocampus in rats: molecular mechanisms

In tests of spatial ability, males outperform females both in rats and in humans. The mechanism underlying this gender differential learning ability and memory in spatial tasks remains unknown. Long-term potentiation (LTP) in the hippocampus is considered the basis for spatial learning and memory. The aims of this work were (a) to assess spatial learning and memory in male and female rats in the radial and Morris mazes; (b) to assess whether basal synaptic activity and LTP in the hippocampus are different in male and female rats; and (c) to identify the molecular mechanisms responsible for the gender differences in LTP. We analyzed in young male and female rats (a) performance in spatial tasks in the radial and Morris water mazes; (b) basal synaptic activity in hippocampal slices; and (c) LTP and some mechanisms modulating its magnitude. The results reported allow us to conclude that female rats show larger AMPA receptor-mediate synaptic responses under basal conditions, likely due to enhanced phosphorylation of GluR2 in Ser880 and increased amounts of GluR2-containing AMPA receptors in postsynaptic densities. In contrast, the magnitude of tetanus-induced LTP was lower in females than in males. This is due to reduced activation of soluble guanylate cyclase and the formation of cGMP, leading to lower activation of cGMP-dependent protein kinase and phosphorylation of GluR1 in Ser845, which results in lower insertion of AMPA receptors in the synaptic membrane and a lower magnitude of LTP. These mechanisms may contribute to the reduced performance of females in the radial and Morris water mazes.

MDMA administration during adolescence exacerbates MPTP-induced cognitive impairment and neuroinflammation in the hippocampus and prefrontal cortex

RATIONALE

We have recently shown that chronic exposure to 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") of adolescent mice exacerbates dopamine neurotoxicity and neuroinflammatory effects elicited by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the substantia nigra and striatum at adulthood.

OBJECTIVES

The present study investigated whether the amplification of MPTP effects by previous treatment with MDMA extends to the limbic and cortical regions and consequently affects cognitive performance.

METHODS

Mice received MDMA (10 mg/kg, twice a day/twice a week) for 9 weeks, followed by MPTP (20 mg/kg × 4 administrations), starting 2 weeks after MDMA discontinuation. Complement type 3 receptor (CD11b) and glial fibrillary acidic protein (GFAP) were evaluated by immunohistochemistry in both the hippocampus and the medial prefrontal cortex (mPFC) to measure microglia and astroglia activation. These neurochemical evaluations were paired with an assessment of cognitive performance by means of the novel object recognition (NOR) and spontaneous alternation tasks.

RESULTS

MPTP administration to MDMA-pretreated mice elicited a stronger activation of CD11b and GFAP in both the hippocampus and the mPFC compared with either substance administered alone. Furthermore, NOR performance was lower in MDMA-pretreated mice administered MPTP compared with mice that received either substance alone.

CONCLUSIONS

These results demonstrate that MDMA-MPTP negative interactions extend to the limbic and cortical regions and may result in cognitive impairment, providing further evidence that exposure to MDMA may amplify the effects of later neurotoxic insults.

Depression, impulsiveness, sleep, and memory in past and present polydrug users of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy)

RATIONALE

Ecstasy (3,4-methylenedioxymethamphetamine, MDMA) is a worldwide recreational drug of abuse. Unfortunately, the results from human research investigating its psychological effects have been inconsistent.

OBJECTIVES

The present study aimed to be the largest to date in sample size and 5HT-related behaviors; the first to compare present ecstasy users with past users after an abstinence of 4 or more years, and the first to include robust controls for other recreational substances.

METHODS

A sample of 997 participants (52 % male) was recruited to four control groups (non-drug (ND), alcohol/nicotine (AN), cannabis/alcohol/nicotine (CAN), non-ecstasy polydrug (PD)), and two ecstasy polydrug groups (present (MDMA) and past users (EX-MDMA). Participants completed a drug history questionnaire, Beck Depression Inventory, Barratt Impulsiveness Scale, Pittsburgh Sleep Quality Index, and Wechsler Memory Scale-Revised which, in total, provided 13 psychometric measures.

RESULTS

While the CAN and PD groups tended to record greater deficits than the non-drug controls, the MDMA and EX-MDMA groups recorded greater deficits than all the control groups on ten of the 13 psychometric measures. Strikingly, despite prolonged abstinence (mean, 4.98; range, 4-9 years), past ecstasy users showed few signs of recovery. Compared with present ecstasy users, the past users showed no change for ten measures, increased impairment for two measures, and improvement on just one measure.

CONCLUSIONS

Given this record of impaired memory and clinically significant levels of depression, impulsiveness, and sleep disturbance, the prognosis for the current generation of ecstasy users is a major cause for concern.

Effects of ethanol on hippocampal neurogenesis depend on the conditioned appetitive response

Neurogenesis in the subgranular layer of the dentate gyrus (DG) has been suggested to underlie some forms of associative learning. The present study was undertaken to determine whether there was also a role of neurogenesis in the ethanol (EtOH)-induced conditioned place preference (CPP). Outbreed Swiss mice were conditioned with EtOH (2.0 g/kg) in one compartment of a non-biased place preference chamber and saline in the other compartment. This procedure produced three groups of mice: some developed a conditioned preference (EtOH_Cpp), others developed a conditioned avoidance (EtOH_Cpa) and still others demonstrated indifference to the context previously paired with ethanol (EtOH_Ind). BrdU (40 mg/kg, i.p.) was administered 4 hours after each session comprising the conditioning phase. When measured 24 hours following the CPP test, there was no effect of EtOH on doublecortin (DCX) expression or Fluoro Jade B staining. However, there were decreases in the number of BrdU+ and Ki-67+ cells in the EtOH_Cpa and EtOH_Ind groups, but not in the EtOH_Cpp group. Most of BrdU+ cells were co-labeled with DCX. Similarly, in another experiment, in that the perfusion was done 28 days after CPP test, most BrdU+ cells were co-localized with NeuN. These results suggest that conditioned appetitive response is able to maintain normal levels of neurogenesis in DG and might counteract ethanol-produced decreased cell proliferation/survival rate.

Adult hippocampal neurogenesis in the pathogenesis of addiction and dual diagnosis disorders

BACKGROUND

As knowledge deepens about how new neurons are born, differentiate, and wire into the adult mammalian brain, growing evidence depicts hippocampal neurogenesis as a special form of neuroplasticity that may be impaired across psychiatric disorders. This review provides an integrated-evidence based framework describing a neurogenic basis for addictions and addiction vulnerability in mental illness.

METHODS

Basic studies conducted over the last decade examining the effects of addictive drugs on adult neurogenesis and the impact of neurogenic activity on addictive behavior were compiled and integrated with relevant neurocomputational and human studies.

RESULTS

While suppression of hippocampal neurogenic proliferation appears to be a universal property of addictive drugs, the pathophysiology of addictions involves neuroadaptative processes within frontal-cortical-striatal motivation circuits that the neurogenic hippocampus regulates via direct projections. States of suppressed neurogenic activity may simultaneously underlie psychiatric and cognitive symptoms, but also confer or signify hippocampal dysfunction that heightens addiction vulnerability in mental illness as a basis for dual diagnosis disorders.

CONCLUSIONS

Research on pharmacological, behavioral and experiential strategies that enhance adaptive regulation of hippocampal neurogenesis holds potential in advancing preventative and integrative treatment strategies for addictions and dual diagnosis disorders.

The effects of abused drugs on adolescent development of corticolimbic circuitry and behavior

Adolescence is a period of significant neurobiological change that occurs as individuals transition from childhood to adulthood. Because the nervous system is in a relatively labile state during this stage of development, it may be especially sensitive to experience-induced plasticity. One such experience that is relatively common to adolescents is the exposure to drugs of abuse, particularly alcohol and psychostimulants. In this review, we highlight recent findings on the long-lasting effects of exposure to these drugs during adolescence in humans as well as in animal models. Whenever possible, our focus is on studies that use comparison groups of adolescent- and adult-exposed subjects as this is a more direct test of the hypothesis that adolescence represents a period of enhanced vulnerability to the effects of drug-induced plasticity. Lastly, we suggest areas of future investigation that are needed and methodological concerns that should be addressed.

Effect of intermittent exposure to ethanol and MDMA during adolescence on learning and memory in adult mice

Background

Heavy binge drinking is increasingly frequent among adolescents, and consumption of 3,4-methylenedioxymethamphetamine (MDMA) is often combined with ethanol (EtOH). The long-lasting effects of intermittent exposure to EtOH and MDMA during adolescence on learning and memory were evaluated in adult mice using the Hebb-Williams maze.

Methods

Adolescent OF1 mice were exposed to EtOH (1.25 g/kg) on two consecutive days at 48-h intervals over a 14-day period (from PD 29 to 42). MDMA (10 or 20 mg/kg) was injected twice daily at 4-h intervals over two consecutive days, and this schedule was repeated six days later (PD 33, 34, 41 and 42), resulting in a total of eight injections. Animals were initiated in the Hebb-Williams maze on PND 64. The concentration of brain monoamines in the striatum and hippocampus was then measured.

Results

At the doses employed, both EtOH and MDMA, administered alone or together, impaired learning in the Hebb-Williams maze, as treated animals required more time to reach the goal than their saline-treated counterparts. The groups treated during adolescence with EtOH, alone or plus MDMA, also presented longer latency scores and needed more trials to reach the acquisition criterion score. MDMA induced a decrease in striatal DA concentration, an effect that was augmented by the co-administration of EtOH. All the treatment groups displayed an imbalance in the interaction DA/serotonin.

Conclusions

The present findings indicate that the developing brain is highly vulnerable to the damaging effects of EtOH and/or MDMA, since mice receiving these drugs in a binge pattern during adolescence exhibit impaired learning and memory in adulthood.

Microglia in the developing brain: a potential target with lifetime effects

Microglia are a heterogenous group of monocyte-derived cells serving multiple roles within the brain, many of which are associated with immune and macrophage like properties. These cells are known to serve a critical role during brain injury and to maintain homeostasis; yet, their defined roles during development have yet to be elucidated. Microglial actions appear to influence events associated with neuronal proliferation and differentiation during development, as well as, contribute to processes associated with the removal of dying neurons or cellular debris and management of synaptic connections. These long-lived cells display changes during injury and with aging that are critical to the maintenance of the neuronal environment over the lifespan of the organism. These processes may be altered by changes in the colonization of the brain or by inflammatory events during development. This review addresses the role of microglia during brain development, both structurally and functionally, as well as the inherent vulnerability of the developing nervous system. A framework is presented considering microglia as a critical nervous system-specific cell that can influence multiple aspects of brain development (e.g., vascularization, synaptogenesis, and myelination) and have a long term impact on the functional vulnerability of the nervous system to a subsequent insult, whether environmental, physical, age-related, or disease-related.

Deficient plasticity in the hippocampus and the spiral of addiction: focus on adult neurogenesis

Addiction is a complex neuropsychiatric disorder which causes disruption at multiple levels, including cognitive, emotional, and behavioral domains. Traditional biological theories of addiction have focused on the mesolimbic dopamine pathway and the nucleus accumbens as anatomical substrates mediating addictive-like behaviors. More recently, we have begun to recognize the engagement and dynamic influence of a much broader circuitry which encompasses the frontal cortex, the amygdala, and the hippocampus. In particular, neurogenesis in the adult hippocampus has become a major focus of attention due to its ability to influence memory, motivation, and affect, all of which are disrupted in addiction. First, I summarize toxicological data that reveal strongly suppressive effects of drug exposure on adult hippocampal neurogenesis. Then, I discuss the impact of deficient neurogenesis on learning and memory function, stress responsiveness and affective behavior, as they relate to addiction. Finally, I examine recent behavioral observations that implicate neurogenesis in the adult hippocampus in the emergence and maintenance of addictive behavior. The evidence reviewed here suggests that deficient neurogenesis is associated with several components of the downward spiraling loop that characterizes addiction, including elevated sensitivity to drug-induced reward and reinforcement, enhanced neurohormonal responsiveness, emergence of a negative affective state, memory impairment, and inflexible behavior.

Cocaine and MDMA Induce Cellular and Molecular Changes in Adult Neurogenic Systems: Functional Implications

The capacity of the brain to generate new adult neurons is a recent discovery that challenges the old theory of an immutable adult brain. A new and fascinating field of research now focuses on this regenerative process. The two brain systems that constantly produce new adult neurons, known as the adult neurogenic systems, are the dentate gyrus (DG) of the hippocampus and the lateral ventricules/olfactory bulb system. Both systems are involved in memory and learning processes. Different drugs of abuse, such as cocaine and MDMA, have been shown to produce cellular and molecular changes that affect adult neurogenesis. This review summarizes the effects that these drugs have on the adult neurogenic systems. The functional relevance of adult neurogenesis is obscured by the functions of the systems that integrate adult neurons. Therefore, we explore the effects that cocaine and MDMA produce not only on adult neurogenesis, but also on the DG and olfactory bulbs. Finally, we discuss the possible role of new adult neurons in cocaine- and MDMA-induced impairments. We conclude that, although harmful drug effects are produced at multiple physiological and anatomical levels, the specific consequences of reduced hippocampus neurogenesis are unclear and require further exploration.