Abstinence from Escalation of Cocaine Intake Changes the microRNA Landscape in the Cortico-Accumbal Pathway.

Cocaine administration alters the microRNA (miRNA) landscape in the cortico-accumbal pathway. These changes in miRNA can play a major role in the posttranscriptional regulation of gene expression during withdrawal. This study aimed to investigate the changes in microRNA expression in the cortico-accumbal pathway during acute withdrawal and protracted abstinence following escalated cocaine intake. Small RNA sequencing (sRNA-seq) was used to profile miRNA transcriptomic changes in the cortico-accumbal pathway [infralimbic- and prelimbic-prefrontal cortex (IL and PL) and nucleus accumbens (NAc)] of rats with extended access to cocaine self-administration followed by an 18-h withdrawal or a 4-week abstinence. An 18-h withdrawal led to differential expression (fold-change > 1.5 and p < 0.05) of 21 miRNAs in the IL, 18 miRNAs in the PL, and two miRNAs in the NAc. The mRNAs potentially targeted by these miRNAs were enriched in the following pathways: gap junctions, neurotrophin signaling, MAPK signaling, and cocaine addiction. Moreover, a 4-week abstinence led to differential expression (fold-change > 1.5 and p < 0.05) of 23 miRNAs in the IL, seven in the PL, and five miRNAs in the NAc. The mRNAs potentially targeted by these miRNAs were enriched in pathways including gap junctions, cocaine addiction, MAPK signaling, glutamatergic synapse, morphine addiction, and amphetamine addiction. Additionally, the expression levels of several miRNAs differentially expressed in either the IL or the NAc were significantly correlated with addiction behaviors. Our findings highlight the impact of acute and protracted abstinence from escalated cocaine intake on miRNA expression in the cortico-accumbal pathway, a key circuit in addiction, and suggest developing novel biomarkers and therapeutic approaches to prevent relapse by targeting abstinence-associated miRNAs and their regulated mRNAs.

Prodromal dysfunction of α5GABA-A receptor modulated hippocampal ripples occurs prior to neurodegeneration in the TgF344-AD rat model of Alzheimer's disease.

Decades of research attempting to slow the onset of Alzheimer's disease (AD) indicates that a better understanding of memory will be key to the discovery of effective therapeutic approaches. Here, we ask whether prodromal neural network dysfunction might occur in the hippocampal trisynaptic circuit by using α5IA (an established memory enhancer and selective negative allosteric modulator of extrasynaptic tonically active α5GABA-A receptors) as a probe drug in TgF344-AD transgenic rats, a model for ß-amyloid induced early onset AD. The results demonstrate that orally bioavailable α5IA increases CA1 pyramidal cell mean firing rates during foraging and peak ripple amplitude during wakeful immobility in wild type F344 rats in a familiar environment. We further demonstrate that CA1 ripples in TgF344-AD rats are nonresponsive to α5IA by 9 months of age, prior to the onset of AD-like pathology and memory dysfunction. TgF344-AD rats express human ß-amyloid precursor protein (with the Swedish mutation) and human presenilin-1 (with a Δ exon 9 mutation) and we found high serum Aß42 and Aß40 levels by 3 months of age. When taken together, this demonstrates, to the best of our knowledge, the first evidence for prodromal α5GABA-A receptor dysfunction in the ripple-generating hippocampal trisynaptic circuit of AD-like transgenic rats. As α5GABA-A receptors are found at extrasynaptic and synaptic contacts, we posit that negative modulation of α5GABA-A receptor mediated tonic as well as phasic inhibition augments CA1 ripples and memory consolidation but that this modulatory mechanism is lost at an early stage of AD onset.

Analysis of telomere length variation and Shelterin complex subunit gene expression changes in ethanol-exposed human embryonic stem cells.

Telomeres protect chromosome ends from degradation. Telomere length (TL) can be altered by aging and environmental stress. Shortened TL has been observed in peripheral blood leukocytes of alcohol dependent subjects and ethanol-exposed somatic cells. To understand the impact of ethanol on telomeres in pluripotent stem cells, we investigated the influence of ethanol on TL and the expression of six Shelterin complex subunit or telomere-regulating genes (POT1, RAP1, TIN2, TPP1, TRF1, and TRF2) in human embryonic stem cells (hESCs), which were exposed to 0, 25, 50, or 100 mM of ethanol for 3, 7, or 14 days. Ethanol-induced TL and Shelterin complex subunit gene expression changes were examined by quantitative polymerase chain reactions. Two-way ANOVA tests indicated that TL variation and expression changes of four associated Shelterin complex subunit genes (POT1, TPP1, TIN2, and TRF2) were mainly dependent on the length of ethanol exposure, while TRF1 and RAP1expression was influenced by ethanol concentration, exposure time, and the interaction of ethanol concentration and exposure time. Tukey's multiple comparison tests showed that TL and the expression of POT1, RAP1, TIN2, TPP1, and TRF1 were decreased after a 7-day (versus a 3-day) ethanol exposure. However, the decreased expression of all six Shelterin complex subunit genes was recovered and TL was not further shortened after a 14-day (versus a 7-day) ethanol exposure, likely due to the adaptation of hESCs to ethanol-induced stress. Our study provided further evidence that TL is regulated and maintained by telomere-regulating genes in stem cells under ethanol stress.

Neurosteroid Actions in Memory and Neurologic/Neuropsychiatric Disorders.

Memory dysfunction is a symptomatic feature of many neurologic and neuropsychiatric disorders; however, the basic underlying mechanisms of memory and altered states of circuitry function associated with disorders of memory remain a vast unexplored territory. The initial discovery of endogenous neurosteroids triggered a quest to elucidate their role as neuromodulators in normal and diseased brain function. In this review, based on the perspective of our own research, the advances leading to the discovery of positive and negative neurosteroid allosteric modulators of GABA type-A (GABAA), NMDA, and non-NMDA type glutamate receptors are brought together in a historical and conceptual framework. We extend the analysis toward a state-of-the art view of how neurosteroid modulation of neural circuitry function may affect memory and memory deficits. By aggregating the results from multiple laboratories using both animal models for disease and human clinical research on neuropsychiatric and age-related neurodegenerative disorders, elements of a circuitry level view begins to emerge. Lastly, the effects of both endogenously active and exogenously administered neurosteroids on neural networks across the life span of women and men point to a possible underlying pharmacological connectome by which these neuromodulators might act to modulate memory across diverse altered states of mind.

Cocaine-induced chromatin remodeling increases brain-derived neurotrophic factor transcription in the rat medial prefrontal cortex, which alters the reinforcing efficacy of cocaine.

Cocaine self-administration alters patterns of gene expression in the brain that may underlie cocaine-induced neuronal plasticity. In the present study, male Sprague Dawley rats were allowed to self-administer cocaine (0.25 mg/infusion) 2 h/d for 14 d, followed by 7 d of forced abstinence. Compared with yoked saline control rats, cocaine self-administration resulted in increased brain-derived neurotrophic factor (BDNF) protein levels in the rat medial prefrontal cortex (mPFC). To examine the functional relevance of this finding, cocaine self-administration maintained under a progressive ratio schedule of reinforcement was assessed after short hairpin RNA-induced suppression of BDNF expression in the mPFC. Decreased BDNF expression in the mPFC increased the cocaine self-administration breakpoint. Next, the effect of cocaine self-administration on specific BDNF exons was assessed; results revealed selectively increased BDNF exon IV-containing transcripts in the mPFC. Moreover, there were significant cocaine-induced increases in acetylated histone H3 (AcH3) and phospho-cAMP response element binding protein (pCREB) association with BDNF promoter IV. In contrast, there was decreased methyl-CpG-binding protein 2 (MeCP2) association with BDNF promoter IV in the mPFC of rats that previously self-administered cocaine. Together, these results indicate that cocaine-induced increases in BDNF promoter IV transcript in the mPFC are driven by increased binding of AcH3 and pCREB as well as decreased MeCP2 binding at this BDNF promoter. Collectively, these results indicate that cocaine self-administration remodels chromatin in the mPFC, resulting in increased expression of BDNF, which appears to represent a compensatory neuroadaptation that reduces the reinforcing efficacy of cocaine.

Metabotropic glutamate receptor 5 (mGluR5) antagonists attenuate cocaine priming- and cue-induced reinstatement of cocaine seeking.

Accumulating evidence suggests that metabotropic glutamate receptors (mGluRs) are involved in both cocaine reinforcement and the reinstatement of cocaine-seeking behavior. In the present experiments, rats were trained to self-administer cocaine under fixed ratio (for cocaine priming-induced reinstatement) or second-order (for cocaine cue-induced reinstatement) schedules of reinforcement. Lever pressing was then extinguished followed by a reinstatement phase where operant responding was promoted by either cocaine itself or cocaine-associated light cues. Results indicated that systemic administration of the mGluR5 antagonists 2-methyl-6-(phenylethynyl)pyridine (MPEP: 1 and 3mg/kg i.p.) or 3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP: 0.1 and 1mg/kg i.p.) dose-dependently attenuated reinstatement of drug seeking induced by a systemic priming injection of 10mg/kg cocaine. Systemic administration of MTEP (0.1 and 1mg/kg i.p.) also dose-dependently attenuated cocaine cue-induced reinstatement of drug seeking. Systemic administration of neither MPEP nor MTEP influenced the reinstatement of sucrose seeking, which indicates that the effects of these compounds on cocaine seeking were reinforcer specific. Additionally, administration of MPEP (1microg/0.5microl) into the nucleus accumbens shell, a brain region that plays a critical role in cocaine seeking, attenuated cocaine priming-induced reinstatement of drug seeking. These results add to a growing literature indicating that mGluR antagonists attenuate the reinstatement of cocaine seeking. Importantly, the current findings also suggest that activation of mGluR5s specifically in the nucleus accumbens shell may promote the reinstatement of cocaine seeking.

Phosphorylation-dependent trafficking of GluR2-containing AMPA receptors in the nucleus accumbens plays a critical role in the reinstatement of cocaine seeking.

A growing body of evidence indicates that enhanced AMPA-mediated glutamate transmission in the core of the nucleus accumbens is critically involved in cocaine priming-induced reinstatement of drug seeking, an animal model of relapse. However, the extent to which increased glutamate transmission in the other major subregion of the nucleus accumbens, the shell, contributes to the reinstatement of cocaine seeking remains unclear. In the present experiments, administration of the AMPA/kainate receptor antagonist CNQX (0, 0.03, or 0.3 mug) into either the core or the shell of the nucleus accumbens before a systemic cocaine priming injection (10 mg/kg, i.p.) dose-dependently attenuated the reinstatement of drug seeking. Cocaine priming-induced reinstatement of cocaine seeking also was associated with increases in GluR2-pSer880 in the nucleus accumbens shell. The phosphorylation of GluR2 by PKC at Ser880 plays an important role in the trafficking of GluR2-containing AMPA receptors from the plasma membrane. The current results showed that administration of a cell-permeable peptide that disrupts GluR2 trafficking (Pep2-EVKI) into either the accumbens core or shell attenuated cocaine-induced reinstatement of drug seeking. Together, these findings indicate that changes in AMPA receptor-mediated glutamate transmission in both the nucleus accumbens core and shell are necessary for the reinstatement of drug seeking induced by a priming injection of cocaine. The present results also demonstrate that the reinstatement of cocaine seeking is associated with increases in the phosphorylation-dependent trafficking of GluR2-containing AMPA receptors in the nucleus accumbens.

CaMKII: a biochemical bridge linking accumbens dopamine and glutamate systems in cocaine seeking.

Increases in dopamine and glutamate transmission in the nucleus accumbens independently promote the reinstatement of cocaine seeking, an animal model of relapse. Here we have tested whether cocaine reinstatement in rats depends on interactions between accumbal dopamine and glutamate systems that are mediated by Ca(2+)/calmodulin-mediated kinase II (CaMKII). We show that stimulation of D1-like dopamine receptors in the nucleus accumbens shell reinstates cocaine seeking by activating L-type Ca(2+) channels and CaMKII. Cocaine reinstatement is associated with D1-like dopamine receptor-dependent increases in accumbens shell CaMKII phosphorylated on Thr286 and glutamate receptor 1 (GluR1) phosphorylated on Ser831 (a known CaMKII phosphorylation site), in addition to increases in cell-surface expression of GluR1-containing AMPA receptors in the shell. Consistent with these findings, cocaine reinstatement is attenuated by intra-shell administration of AAV10-GluR1-C99, a vector that impairs the transport of GluR1-containing AMPA receptors. Thus, CaMKII may be an essential link between accumbens shell dopamine and glutamate systems involved in the neuronal plasticity underlying cocaine craving and relapse.

The mesolimbic dopamine system: the final common pathway for the reinforcing effect of drugs of abuse?

In this review we will critically assess the hypothesis that the reinforcing effect of virtually all drugs of abuse is primarily dependent on activation of the mesolimbic dopamine system. The focus is on five classes of abused drugs: psychostimulants, opiates, ethanol, cannabinoids and nicotine. For each of these drug classes, the pharmacological and physiological mechanisms underlying the direct or indirect influence on mesolimbic dopamine transmission will be reviewed. Next, we evaluate behavioral pharmacological experiments that specifically assess the influence of activation of the mesolimbic dopamine system on drug reinforcement, with particular emphasis on animal experiments using drug self-administration paradigms. There is overwhelming evidence that all five classes of abused drugs increase dopamine transmission in limbic regions of the brain through interactions with a variety of transporters, ionotropic receptors and metabotropic receptors. Behavioral pharmacological experiments indicate that increased dopamine transmission is clearly both necessary and sufficient to promote psychostimulant reinforcement. For the other four classes of abused substances, self-administration experiments suggest that although increasing mesolimbic dopamine transmission plays an important role in the reinforcing effects of opiates, ethanol, cannabinoids and nicotine, there are also dopamine-independent processes that contribute significantly to the reinforcing effects of these compounds.

Anatomy and pharmacology of cocaine priming-induced reinstatement of drug seeking.

Cocaine addiction in human addicts is characterized by a high rate of relapse following successful detoxification. Relapse to drug taking/seeking can be precipitated by several stimuli including, but not limited to, re-exposure to cocaine itself. In order to understand the mechanisms underlying cocaine craving, a substantial effort has been devoted to elucidating the anatomical and neurochemical bases underlying cocaine priming-induced reinstatement, an animal model of relapse. Here, we review evidence that changes in dopaminergic and glutamatergic transmission in limbic/basal ganglia circuits of interconnected nuclei including the medial prefrontal cortex, nucleus accumbens, ventral pallidum, amygdala, hippocampus, orbitofrontal cortex, neostriatum and thalamus underlie cocaine priming-induced reinstatement of cocaine seeking. Maladaptive changes in the processing of motivationally relevant stimuli by these circuits following cocaine self-administration result in drug craving and compulsive drug seeking upon re-exposure to cocaine.