The Nature of 3, 4-Methylenedioxymethamphetamine (MDMA)-Induced Serotonergic Dysfunction: Evidence for and Against the Neurodegeneration Hypothesis

High doses of the recreational drug 3,4-methylenedioxymethamphetamine (MDMA, “Ecstasy”) have been well-documented to reduce the expression of serotonergic markers in several forebrain regions of rats and nonhuman primates. Neuroimaging studies further suggest that at least one of these markers, the plasma membrane serotonin transporter (SERT), may also be reduced in heavy Ecstasy users. Such effects, particularly when observed in experimental animal models, have generally been interpreted as reflecting a loss of serotonergic fibers and terminals following MDMA exposure. This view has been challenged, however, based on the finding that MDMA usually does not elicit glial cell reactions known to occur in response to central nervous system (CNS) damage. The aim of this review is to address both sides of the MDMA-neurotoxicity controversy, including recent findings from our laboratory regarding the potential of MDMA to induce serotonergic damage in a rat binge model. Our data add to the growing literature implicating neuroregulatory mechanisms underlying MDMA-induced serotonergic dysfunction and questioning the need to invoke a degenerative response to explain such dysfunction

Investigations into the Potential for 3,4-methylenedioxymethamphetamine to Induce Neurotoxic Terminal Damage to Serotonergic Neurons

High doses of 3,4-methylenedioxymethamphetamine (MDMA; Ecstasy ) are known to reduce levels of various serotonergic markers outside of the raphe nuclei. To test the hypothesis that these deficits reflect a degeneration of distal axons/terminals, we investigated the effects of an MDMA binge (10mg/kg x 4) on the relative protein and genetic expression of several serotonergic markers in rats, as well as the effects of this compound on the quantity of serotonergic terminals in these animals. In experiment I, we examined whether MDMA alters serotonin transporter (SERT) levels as determined by lysate binding and immunoblotting analyses. Both methods of analysis revealed MDMA-induced reductions in regional SERT content. Experiment II investigated MDMA-induced changes in terminal-specific levels of SERT and the vesicular monoamine transporter 2 (VMAT-2) in the hippocampus, a region with sparse dopaminergic innervation, after lesioning noradrenergic input with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4). Animals were administered 100 mg/kg DSP-4 or saline 1 week prior to MDMA (or saline). As determined by immunoblotting of synaptosomal tissue, the DSP-4/MDMA group showed little change in hippocampal VMAT-2 protein expression compared to DSP-4/Saline controls, despite large reductions in SERT levels in all regions examined in the MDMA-treated animals. Experiment III examined whether MDMA alters genetic expression of SERT and VMAT-2. When compared to saline-treated controls, animals given MDMA showed a striking decrease in SERT gene expression (and a lesser effect on VMAT-2) in dorsal/median raphe as assessed by quantitative RT-PCR. Experiment IV(a) investigated the effects of MDMA on gene and protein expression of tryptophan hydroxylase (TPH) in the hippocampus. Levels of TPH protein were unchanged between treatment groups, while transcript levels were decreased 15-fold in the dorsal/median raphe. In experiment IV(b), flow cytometry was used to measure whether MDMA alters the quantity of serotonergic terminals in the hippocampus. MDMA-treated animals showed an increase in the number of serotonergic synaptosomes identified by co-labeling for synaptosome-associated protein of 25 kDa (SNAP-25) and TPH. These results demonstrate that MDMA causes substantial regulatory changes in the expression of serotonergic markers with no evidence for synaptic loss, questioning the need to invoke distal axotomy as an explanation of MDMA-related serotonergic deficits

Evidence against dopamine D1/D2 receptor heteromers

Hetero-oligomers of G-protein-coupled receptors have become the subject of intense investigation because their purported potential to manifest signaling and pharmacological properties that differ from the component receptors makes them highly attractive for the development of more selective pharmacological treatments. In particular, dopamine D1 and D2 receptors have been proposed to form hetero-oligomers that couple to Gαq proteins, and SKF83959 has been proposed to act as a biased agonist that selectively engages these receptor complexes to activate Gαq and thus phospholipase C. D1/D2 heteromers have been proposed as relevant to the pathophysiology and treatment of depression and schizophrenia. We used in vitro bioluminescence resonance energy transfer (BRET), ex vivo analyses of receptor localization and proximity in brain slices, and behavioral assays in mice to characterize signaling from these putative dimers/oligomers. We were unable to detect Gαq or Gα11 protein coupling to homomers or heteromers of D1 or D2 receptors using a variety of biosensors. SKF83959-induced locomotor and grooming behaviors were eliminated in D1 receptor knockout mice, verifying a key role for D1-like receptor activation. In contrast, SKF83959-induced motor responses were intact in D2 receptor and Gαq knockout mice, as well as in knock-in mice expressing a mutant Ala286-CaMKIIα, that cannot autophosphorylate to become active. Moreover, we found that in the shell of the nucleus accumbens, even in neurons in which D1 and D2 receptor promoters are both active, the receptor proteins are segregated and do not form complexes. These data are not compatible with SKF83959 signaling through Gαq or through a D1–D2 heteromer and challenge the existence of such a signaling complex in the adult animals that we used for our studies

Family Environment, Neurodevelopmental Risk, and the Environmental Influences on Child Health Outcomes (ECHO) Initiative: Looking Back and Moving Forward.

The family environment, with all its complexity and diverse components, plays a critical role in shaping neurodevelopmental outcomes in children. Herein we review several domains of the family environment (family socioeconomic status, family composition and home environment, parenting behaviors and interaction styles, parental mental health and functioning, and parental substance use) and discuss how these domains influence neurodevelopment, with particular emphasis on mental health outcomes. We also highlight a new initiative launched by the National Institutes of Health, the Environmental influences on Child Health Outcomes (ECHO) program. We discuss the role that ECHO will play in advancing our understanding of the impact of the family environment on children's risk for psychiatric outcomes. Lastly, we conclude with important unanswered questions and controversies in this area of research, highlighting how ECHO will contribute to resolving these gaps in our understanding, clarifying relationships between the family environment and children's mental health

Family Environment, Neurodevelopmental Risk, and the Environmental Influences on Child Health Outcomes (ECHO) Initiative: Looking Back and Moving Forward.

The family environment, with all its complexity and diverse components, plays a critical role in shaping neurodevelopmental outcomes in children. Herein we review several domains of the family environment (family socioeconomic status, family composition and home environment, parenting behaviors and interaction styles, parental mental health and functioning, and parental substance use) and discuss how these domains influence neurodevelopment, with particular emphasis on mental health outcomes. We also highlight a new initiative launched by the National Institutes of Health, the Environmental influences on Child Health Outcomes (ECHO) program. We discuss the role that ECHO will play in advancing our understanding of the impact of the family environment on children's risk for psychiatric outcomes. Lastly, we conclude with important unanswered questions and controversies in this area of research, highlighting how ECHO will contribute to resolving these gaps in our understanding, clarifying relationships between the family environment and children's mental health