Potentiation of N-methyl-D-aspartate receptor-mediated neuronal injury during methamphetamine withdrawal in vitro requires co-activation of IP3 receptors

Transcriptome profiling of whisker follicles in methamphetamine self-administered rats

Methamphetamine (MA) is a highly addictive psychostimulant that disturbs the central nervous system; therefore, diagnosis of MA addiction is important in clinical and forensic toxicology. In this study, a MA self-administration rat model was used to illustrate the gene expression profiling of the rewarding effect caused by MA. RNA-sequencing was performed to examine changes in gene expression in rat whisker follicles collected before self-administration, after MA self-administration, and after withdrawal sessions. We identified six distinct groups of genes, with statistically significant expression patterns. By constructing the functional association network of these genes and performing the subsequent topological analysis, we identified 43 genes, which have the potential to regulate MA reward and addiction. The gene pathways were then analysed using the Reactome and Knowledgebase for Addiction-Related Gene database, and it was found that genes and pathways associated with Alzheimer's disease and the heparan sulfate biosynthesis were enriched in MA self-administration rats. The findings suggest that changes of the genes identified in rat whisker follicles may be useful indicators of the rewarding effect of MA. Further studies are needed to provide a comprehensive understanding of MA addiction.

Neurotoxic Doses of Chronic Methamphetamine Trigger Retrotransposition of the Identifier Element in Rat Dorsal Dentate Gyrus

Short interspersed elements (SINEs) are typically silenced by DNA hypermethylation in somatic cells, but can retrotranspose in proliferating cells during adult neurogenesis. Hypomethylation caused by disease pathology or genotoxic stress leads to genomic instability of SINEs. The goal of the present investigation was to determine whether neurotoxic doses of binge or chronic methamphetamine (METH) trigger retrotransposition of the identifier (ID) element, a member of the rat SINE family, in the dentate gyrus genomic DNA. Adult male Sprague-Dawley rats were treated with saline or high doses of binge or chronic METH and sacrificed at three different time points thereafter. DNA methylation analysis, immunohistochemistry and next-generation sequencing (NGS) were performed on the dorsal dentate gyrus samples. Binge METH triggered hypomethylation, while chronic METH triggered hypermethylation of the CpG-2 site. Both METH regimens were associated with increased intensities in poly(A)-binding protein 1 (PABP1, a SINE regulatory protein)-like immunohistochemical staining in the dentate gyrus. The amplification of several ID element sequences was significantly higher in the chronic METH group than in the control group a week after METH, and they mapped to genes coding for proteins regulating cell growth and proliferation, transcription, protein function as well as for a variety of transporters. The results suggest that chronic METH induces ID element retrotransposition in the dorsal dentate gyrus and may affect hippocampal neurogenesis.

Ethanol Stimulates Endoplasmic Reticulum Inositol Triphosphate and Sigma Receptors to Promote Withdrawal-Associated Loss of Neuron-Specific Nuclear Protein/Fox-3

BACKGROUND

Prior studies demonstrate that ethanol (EtOH) exposure induces the release of intracellular calcium (CA(2+) ) in modulation of γ-aminobutyric acid-ergic tone and produces concomitant alterations in sigma (σ)-1 protein expression that may contribute to the development EtOH dependence. However, the influence of CA(2+) released from endoplasmic reticulum (ER)-bound inositol triphosphate (IP3) and σ-1 receptors in regulating hippocampal function has yet to be delineated.

METHODS

Rat hippocampal explants were subjected to chronic intermittent EtOH (CIE) exposure with or without the addition of IP3 inhibitor xestospongin C (0 to 0.5 μM) or σ-1 receptor antagonist BD-1047 (0 to 80 μM). Hippocampal viability was assessed via immunohistochemical labeling of neuron-specific nuclear protein (NeuN)/Fox-3 in CA1, CA3, and dentate gyrus (DG) subregions.

RESULTS

Exposure to CIE produced consistent and significant decreases of NeuN/Fox-3 in each primary cell layer of the hippocampal formation. Co-exposure to xestospongin reversed these effects in the CA1 subregion and significantly attenuated these effects in the CA3 and DG regions. Xestospongin application also significantly increased NeuN/Fox-3 immunofluorescence in EtOH-naïve hippocampi. Co-exposure to 20 μM BD-1047 also reversed the loss of NeuN/Fox-3 during CIE exposure in each hippocampal cell layer, whereas exposure to 80 μM BD-1047 did not alter NeuN/Fox-3 in EtOH-treated hippocampi. By contrast, 80 μM BD-1047 application significantly increased NeuN/Fox-3 immunofluorescence in EtOH-naïve hippocampi in each subregion.

CONCLUSIONS

These data suggest that EtOH stimulates ER IP3 and σ-1 receptors to promote hippocampal loss of NeuN/Fox-3 during CIE.

Drug-induced neurotoxicity in addiction medicine: From prevention to harm reduction

Neurotoxicity is considered as a major cause of neurodegenerative disorders. Most drugs of abuse have nonnegligible neurotoxic effects many of which are primarily mediated by several dopaminergic and glutamatergic neurotransmitter systems. Although many researchers have investigated the medical and cognitive consequences of drug abuse, the neurotoxicity induced by these drugs still requires comprehensive attention. The science of neurotoxicity promises to improve preventive and therapeutic strategies for brain disorders such as Alzheimer disease and Parkinson's disease. However, its clinical applications for addiction medicine remain to be defined adequately. This chapter reviews the most commonly discussed mechanisms underlying neurotoxicity induced by common drugs of abuse including amphetamines, cocaine, opiates, and alcohol. In addition, the known factors that trigger and/or predispose to drug-induced neurotoxicity are discussed. These factors include drug-related, individual-related, and environmental insults. Moreover, we introduce some of the potential pharmacological antineurotoxic interventions deduced from experimental animal studies. These interventions involve various targets such as dopaminergic system, mitochondria, cell death signaling, and NMDA receptors, among others. We conclude the chapter with a discussion of addicted patients who might benefit from such interventions.

Inhibition of sigma-1 receptor reduces N-methyl-D-aspartate induced neuronal injury in methamphetamine-exposed and -naive hippocampi

Acute and prolonged methamphetamine (METH) exposure has been reported to moderate the function of N-methyl-d-aspartate type glutamate receptors (NMDAr) in the hippocampus. These effects have been found to be associated with enhanced NMDAr-dependent release of Ca(2+) from IP(3)-sensitive intracellular stores. The present studies were designed to extend these findings and examine the role of the endoplasmic membrane (ER) bound orphan receptor, the sigma-1 receptor, in NMDA-induced neuronal injury and METH withdrawal-potentiated NMDA-induced neuronal injury. Organotypic hippocampal slice cultures were exposed to METH (0 or 100microM) for 6 days and withdrawn for 7 days, then exposed to NMDA (0 or 5microM) for 24h. Additional cultures were also exposed to this regimen and were co-incubated with BD1047 (100microM), a specific inhibitor of ER-bound sigma-1 receptors, for the 24h NMDA exposure. Cytotoxicity was assessed by analysis of propidium iodide uptake. These studies demonstrated that protracted METH exposure and withdrawal significantly potentiated the neuronal injury produced by NMDA exposure. Further, co-exposure to BD1047 with NMDA markedly attenuated neuronal injury in METH-naïve and METH-withdrawn organotypic cultures. As a whole, these data demonstrate that prolonged METH exposure, even at non-toxic concentrations, significantly alters glutamate receptor signaling. Inhibition of sigma-1 receptor-dependent Ca(2+) release from the ER entirely prevented NMDA-induced toxicity in METH-naïve cultures and markedly reduced METH-potentiated toxicity. These findings demonstrate the importance of Ca(2+)-induced intracellular Ca(2+) release in excitotoxic insult and suggest that blockade of glutamatergic overactivity may represent a therapeutic target in the treatment of METH withdrawal.

Neurotoxic effects of methamphetamine on rat hippocampus pyramidal neurons

Methamphetamine (MAP) is known to alter behavior and cause deficits in learning and memory. While the major site of action of MAP is on mesolimbic dopaminergic pathways, the effects on learning and memory raise the possibility of important actions in the hippocampus. We have studied electrophysiologic and morphologic effects of MAP in the CA1 region of hippocampus from young male rats chronically exposed to MAP, male rats exposed during gestation only and the effects of bath perfusion of MAP onto brain slices from control rats. Pyramidal neurons in brain slices from chronically exposed rats had reduced membrane potential and membrane resistance. Long-term potentiation (LTP) was reduced as compared to control, but when MAP was acutely perfused over control slices the amplitude of LTP was increased. LTP in young adult animals that had been gestationally exposed to MAP showed reduced LTP as compared to controls. Morphologically CA1 pyramidal neurons in chronically exposed animals showed a high prevalence of extensive blebbing of dendrites. We conclude that the NMDA receptor and the process of LTP are also targets of MAP dysfunction, at least in the hippocampus.