Morphine-withdrawal aversive memories and their extinction modulate H4K5 acetylation and Brd4 activation in the rat hippocampus and basolateral amygdala

Chromatin modification is a crucial mechanism in several important phenomena in the brain, including drug addiction. Persistence of drug craving and risk of relapse could be attributed to drug-induced epigenetic mechanisms that seem to be candidates explaining long-lasting drug-induced behaviour and molecular alterations. Histone acetylation has been proposed to regulate drug-seeking behaviours and the extinction of rewarding memory of drug taking. In this work, we studied the epigenetic regulation during conditioned place aversion and after extinction of aversive memory of opiate withdrawal. Through immunofluorescence assays, we assessed some epigenetic marks (H4K5ac and p-Brd4) in crucial areas related to memory retrieval -basolateral amygdala (BLA) and hippocampus-. Additionally, to test the degree of transcriptional activation, we evaluated the immediate early genes (IEGs) response (Arc, Bdnf, Creb, Egr-1, Fos and Nfkb) and Smarcc1 (chromatin remodeler) through RT-qPCR in these nuclei. Our results showed increased p-Brd4 and H4K5ac levels during aversive memory retrieval, suggesting a more open chromatin state. However, transcriptional activation of these IEGs was not found, therefore suggesting that other secondary response may already be happening. Additionally, Smarcc1 levels were reduced due to morphine chronic administration in BLA and dentate gyrus. The activation markers returned to control levels after the retrieval of aversive memories, revealing a more repressed chromatin state. Taken together, our results show a major role of the tandem H4K5ac/p-Brd4 during the retrieval of aversive memories. These results might be useful to elucidate new molecular targets to improve and develop pharmacological treatments to address addiction and to avoid drug relapse.

Molecular Mechanisms Underlying the Retrieval and Extinction of Morphine Withdrawal-Associated Memories in the Basolateral Amygdala and Dentate Gyrus

Despite their indisputable efficacy for pain management, opiate prescriptions remain highly controversial partially due to their elevated addictive potential. Relapse in drug use is one of the principal problems for addiction treatment, with drug-associated memories being among its main triggers. Consequently, the extinction of these memories has been proposed as a useful therapeutic tool. Hence, by using the conditioned place aversion (CPA) paradigm in rats, we investigated some of the molecular mechanisms that occurr during the retrieval and extinction of morphine withdrawal memories in the basolateral amygdala (BLA) and the hippocampal dentate gyrus (DG), which control emotional and episodic memories, respectively. The retrieval of aversive memories associated with the abstinence syndrome paralleled with decreased mTOR activity and increased Arc and GluN1 expressions in the DG. Additionally, Arc mRNA levels in this nucleus very strongly correlated with the CPA score exhibited by the opiate-treated rats. On the other hand, despite the unaltered mTOR phosphorylation, Arc levels augmented in the BLA. After the extinction test, Arc and GluN1 expressions were raised in both the DG and BLA of the control and morphine-treated animals. Remarkably, Homer1 expression in both areas correlated almost perfectly with the extinction showed by morphine-dependent animals. Moreover, Arc expression in the DG correlated strongly with the extinction of the CPA manifested by the group treated with the opiate. Finally, our results support the coordinated activity of some of these neuroplastic proteins for the extinction of morphine withdrawal memories in a regional-dependent manner. Present data provide evidence of differential expression and activity of synaptic molecules during the retrieval and extinction of aversive memories of opiate withdrawal in the amygdalar and hippocampal regions that will likely permit the development of therapeutic strategies able to minimize relapses induced by morphine withdrawal-associated aversive memories.

Distinct Regulation of Dopamine D3 Receptor in the Basolateral Amygdala and Dentate Gyrus during the Reinstatement of Cocaine CPP Induced by Drug Priming and Social Stress

Relapse in the seeking and intake of cocaine is one of the main challenges when treating its addiction. Among the triggering factors for the recurrence of cocaine use are the re-exposure to the drug and stressful events. Cocaine relapse engages the activity of memory-related nuclei, such as the basolateral amygdala (BLA) and the hippocampal dentate gyrus (DG), which are responsible for emotional and episodic memories. Moreover, D3 receptor (D3R) antagonists have recently arisen as a potential treatment for preventing drug relapse. Thus, we have assessed the impact of D3R blockade in the expression of some dopaminergic markers and the activity of the mTOR pathway, which is modulated by D3R, in the BLA and DG during the reinstatement of cocaine-induced conditioned place preference (CPP) evoked by drug priming and social stress. Reinstatement of cocaine CPP paralleled an increasing trend in D3R and dopamine transporter (DAT) levels in the BLA. Social stress, but not drug-induced reactivation of cocaine memories, was prevented by systemic administration of SB-277011-A (a selective D3R antagonist), which was able, however, to impede D3R and DAT up-regulation in the BLA during CPP reinstatement evoked by both stress and cocaine. Concomitant with cocaine CPP reactivation, a diminution in mTOR phosphorylation (activation) in the BLA and DG occurred, which was inhibited by D3R blockade in both nuclei before the social stress episode and only in the BLA when CPP reinstatement was provoked by a cocaine prime. Our data, while supporting a main role for D3R signalling in the BLA in the reactivation of cocaine memories evoked by social stress, indicate that different neural circuits and signalling mechanisms might mediate in the reinstatement of cocaine-seeking behaviours depending upon the triggering stimuli.

Unraveling the molecular mechanisms involved in alcohol intake and withdrawal in adolescent mice exposed to alcohol during early life stages

Alcohol interferes with foetal development and prenatal alcohol exposure can lead to adverse effects known as foetal alcohol spectrum disorders. We aimed to assess the underlying neurobiological mechanisms involved in alcohol intake and withdrawal in adolescent mice exposed to alcohol during early life stages, in discrete brain areas. Pregnant C57BL/6 female mice were exposed to binge alcohol drinking from gestation to weaning. Subsequently, alcohol seeking and taking behaviour were evaluated in male adolescent offspring, as assessed in the two-bottle choice and oral self-administration paradigms. Brain area samples were analysed to quantify AMPAR subunits GluR1/2 and pCREB/CREB expression following alcohol self-administration. We measured the expression of mu and kappa opioid receptors both during acute alcohol withdrawal (assessing anxiety alterations by the EPM test) and following reinstatement in the two-bottle choice paradigm. In addition, alcohol metabolism was analysed by measuring blood alcohol concentrations under an acute dose of 3 g/kg alcohol. Our findings demonstrate that developmental alcohol exposure enhances alcohol intake during adolescence, which is associated with a decrease in the pCREB/CREB ratio in the hippocampus, prefrontal cortex and striatum, while the GluR1/GluR2 ratio showed a decrease in the hippocampus. Moreover, PLAE mice showed behavioural alterations, such as increased anxiety-like responses during acute alcohol withdrawal, and higher BAC levels. No significant changes were identified for mu and kappa opioid receptors mRNA expression. The current study highlights that early alcohol exposed mice increased alcohol consumption during late adolescence. Furthermore, a diminished CREB signalling and glutamatergic neuroplasticity are proposed as underpinning neurobiological mechanisms involved in the sensitivity to alcohol reinforcing properties.

[Pharmacology of neuroprotection in acute ischemic stroke]

INTRODUCTION

Stroke leads the list of causes of disability in adults and represents the second leading cause of death worldwide. Knowledge about the pathophysiology of ischemic stroke has improved substantially over the past 25 years, and, as a result of this, new therapeutic strategies have been developed with two main aims: restoration of cerebral flow and the minimization of the deleterious effects of ischemia on neurons. Although so far there are no drugs approved for the neuroprotection therapy in stroke, there are some compounds with promising results.

DEVELOPMENT

This paper makes a critical review of several studies on the preclinical stroke neuroprotection with drugs aimed to protect the brain tissue adjacent to the damaged central area or ischemic penumbra zone until either the physiological mechanisms or the treatment stop the ischemic insult. We expose the potential neuroprotective properties of these treatments mainly based on inhibiting excitotoxicity processes mediated by gamma-aminobutyric acid receptors, glutamate release and interacting with ion channels such as calcium and sodium. We focus on drugs which have shown to be capable of modulating intracellular degenerative pathways in mitochondria mediated apoptosis or the expression of apoptotic proteins in experimental models.

CONCLUSION

It is very likely that the neuroprotective effects require a poly-drug therapy that combines different mechanisms of action.

[Is good old minocycline a new neuroprotective drug?]

INTRODUCTION

During the last decade, the neuroprotective effects of minocycline have been a matter of an intense debate. A broad amount of contradictory studies can be found in the scientific literature, going from neuroprotection to the exacerbation of toxicity in diverse experimental models. Such differences could be the result of minocycline acting on multiple pharmacological targets.

DEVELOPMENT

In the present review we will go over these pharmacological targets and the effects derived from their modulation by minocycline. Among others, its antioxidant activity derived from its chemical structure or its modulator effect on several enzymes such as nitric oxide synthase will be reviewed. Furthermore, the effects of minocycline on the intracellular pathways implicated in neurodegenerative processes including apoptosis stages, activation decision and execution will be addressed.

CONCLUSIONS

All the mechanisms described herein have not escaped to a scientific community needed of new therapeutic drugs for the treatment of neurodegenerative conditions. However, the sparse clinical trials carried out so far are mainly aimed at assessing its tolerability and safety or are still in progress. We believe that more studies, both clinical and pre-clinical, should be carried out in order to ascertain the therapeutic window and the neurodegenerative disorders in which minocycline could be useful.

[The role of protein p53 in neurodegenerative processes throughout the 25 years of its history]

INTRODUCTION

In this review we will study the role of protein p53 in neurodegenerative processes and conduct a detailed analysis of the mechanisms responsible for regulating its levels and biological activity. We analyse the neuropathologies in which this protein is involved, such as Alzheimer's and Parkinson's diseases and amyotrophic lateral sclerosis, and we will also examine its regulation by second messengers such as the reactive species of oxygen and calcium, showing the signalling paths involved in the apoptotic processes.

DEVELOPMENT

The year 2004 sees the 25th anniversary of the discovery of protein p53. At first p53 was wrongly attributed with an oncogenic function due to its capacity to bind to the T antigen of the virus SV40 in transformed cells. Nevertheless, it was not until 1989 that it was attributed with its true physiological function as a tumour-suppressing protein. This milestone constitutes a turning point in the short life of this protein. Protein p53 plays a fundamental role in the mechanisms the cell uses to respond to damage or mutation in the genome. There is, therefore, a correlation between deletions or mutations in the p53 gene and the development of some kinds of cancer; additionally, increases in the protein levels of its native form have been reported in pathologies where apoptotic processes are high.

CONCLUSIONS

Protein p53 plays an essential role in the mechanisms by which the cell responds to damage or mutation in the genome. It can activate two signalling mechanisms that lead either to stopping the cell cycle or to the death of the cell due to apoptosis if the cell cannot repair the damage to the genome. There is a correlation between its deletions and mutations and the development of cancer, and increases in its native form have been described in pathologies where apoptotic processes are high, as is the case of some neurodegenerative diseases.