M. Julia García-Fuster

Chronic morphine induces up-regulation of the pro-apoptotic Fas receptor and down-regulation of the anti-apoptotic Bcl-2 oncoprotein in rat brain.

This study was designed to assess the influence of activation and blockade of the endogenous opioid system in the brain on two key proteins involved in the regulation of programmed cell death: the pro‐apoptotic Fas receptor and the anti‐apoptotic Bcl‐2 oncoprotein. The acute treatment of rats with the μ‐opioid receptor agonist morphine (3 – 30 mg kg−1, i.p., 2 h) did not modify the immunodensity of Fas or Bcl‐2 proteins in the cerebral cortex. Similarly, the acute treatment with low and high doses of the antagonist naloxone (1 and 100 mg kg−1, i.p., 2 h) did not alter Fas or Bcl‐2 protein expression in brain cortex. These results discounted a tonic regulation through opioid receptors on Fas and Bcl‐2 proteins in rat brain. Chronic morphine (10 – 100 mg kg−1, 5 days, and 10 mg kg−1, 13 days) induced marked increases (47 – 123%) in the immunodensity of Fas receptor in the cerebral cortex. In contrast, chronic morphine (5 and 13 days) decreased the immunodensity of Bcl‐2 protein (15 – 30%) in brain cortex. Chronic naloxone (10 mg kg−1, 13 days) did not alter the immunodensities of Fas and Bcl‐2 proteins in the cerebral cortex. The concurrent chronic treatment (13 days) of naloxone (10 mg kg−1) and morphine (10 mg kg−1) completely prevented the morphine‐induced increase in Fas receptor and decrease in Bcl‐2 protein immunoreactivities in the cerebral cortex. The results indicate that morphine, through the sustained activation of opioid receptors, can promote abnormal programmed cell death by enhancing the expression of pro‐apoptotic Fas receptor protein and damping the expression of anti‐apoptotic Bcl‐2 oncoprotein.

Persistent Alterations in Cognitive Function and Prefrontal Dopamine D2 Receptors Following Extended, but Not Limited, Access to Self-Administered Cocaine

Drug addicts have deficits in frontocortical function and cognition even long after the discontinuation of drug use. It is not clear, however, whether the cognitive deficits are a consequence of drug use, or are present prior to drug use, and thus are a potential predisposing factor for addiction. To determine if self-administration of cocaine is capable of producing long-lasting alterations in cognition, rats were allowed access to cocaine for either 1 h/day (short access, ShA) or 6 h/day (long access, LgA) for 3 weeks. Between 1 and 30 days after the last self-administration session, we examined performance on a cognitively demanding test of sustained attention that requires an intact medial prefrontal cortex. The expression levels of dopamine D1 and D2 receptor mRNA and D2 protein in the prefrontal cortex were also examined. Early after discontinuation of drug use, LgA (but not ShA) animals were markedly impaired on the sustained attention task. Although the LgA animals improved over time, they continued to show a persistent pattern of performance deficits indicative of a disruption of cognitive flexibility up to 30 days after the discontinuation of drug use. This was accompanied by a significant decrease in DA D2 (but not D1) mRNA in the medial and orbital prefrontal cortex, and D2 receptor protein in the medial prefrontal cortex of LgA (but not ShA) animals. These findings establish that repeated cocaine use is capable of producing persistent alterations in the prefrontal cortex and in cognitive function, and illustrate the usefulness of extended access self-administration procedures for studying the neurobiology of addiction.

Immunodensity and mRNA expression of A2A adenosine, D2 dopamine, and CB1 cannabinoid receptors in postmortem frontal cortex of subjects with schizophrenia: effect of antipsychotic treatment

RationaleDopamine D2 receptors are the main target of antipsychotic drugs. In the brain, D2 receptors coexpress with adenosine A2A and CB1 cannabinoid receptors, leading to functional interactions.ObjectivesThe protein and messenger RNA (mRNA) contents of A2A, D2, and CB1 receptors were quantified in postmortem prefrontal cortex of subjects with schizophrenia.Materials and methodsThe study was performed in subjects suffering schizophrenia (n = 31) who mainly died by suicide, matched with non-schizophrenia suicide victims (n = 13) and non-suicide controls (n = 33). The density of receptor proteins was evaluated by immunodetection techniques, and their relative mRNA expression was quantified by quantitative real-time polymerase chain reaction.ResultsIn schizophrenia, the densities of A2A (90 ± 6%, n = 24) and D2-like receptors (95 ± 5%, n = 22) did not differ from those in controls (100%). Antipsychotic treatment did not induce changes in the protein expression. In contrast, the immunodensity of CB1 receptors was significantly decreased (71 ± 7%, n = 11; p < 0.05) in antipsychotic-treated subjects with schizophrenia but not in drug-free subjects (104 ± 13%, n = 11). The relative mRNA amounts encoding for A2A, D2, and CB1 receptors were similar in brains of drug-free, antipsychotic-treated subjects with schizophrenia and controls.ConclusionsThe findings suggest that antipsychotics induce down-regulation of CB1 receptors in brain. Since A2A, D2, and CB1 receptors coexpress on brain GABAergic neurons and reductions in markers of GABA neurotransmission have been identified in schizophrenia, a lower density of CB1 receptor induced by antipsychotics could represent an adaptative mechanism that reduces the endocannabinoid-mediated suppression of GABA release, contributing to the normalization of cognitive functions in the disorder.

Opioid receptor agonists enhance the phosphorylation state of Fas-associated death domain (FADD) protein in the rat brain: Functional interactions with casein kinase Iα, Gαi proteins, and ERK1/2 signaling

Opioid drugs have been proposed to promote anti-apoptotic signals in brain through inhibition of FADD protein [García-Fuster et al., 2007. Effects of opiate drugs on Fas-associated protein with death domain (FADD) and effector caspases in the rat brain: Regulation by the ERK1/2 MAP kinase pathway. Neuropsychopharmacology 32, 399-411]. FADD phosphorylation by casein kinase Ialpha (CKIalpha) appears to regulate its non-apoptotic activity. This study investigated the effects of opioids on p-FADD in rat brain, as well as various mechanisms that could link opioid receptors with p-FADD, including the modulation of CKIalpha, Galpha(i) proteins and ERK1/2 signaling. In rat, mouse and human brains, various anti-p-FADD antibodies immunodetected the monomeric and oligomeric forms of this protein, irrespective of the antibody origin and specific Ser191 or Ser194 phosphorylation site. Acute mu- and delta-agonists increased, through specific opioid receptor mechanisms, the content of oligomeric and monomeric p-FADD forms in rat cortical homogenates (25-61%) and subcellular compartments, with most relevant effects for sufentanil in membrane (239%) and nucleus (136%). p-FADD induction vanished with repeated (5days) morphine but not SNC-80, and opioid withdrawal induced a new (morphine) or sustained (SNC-80) stimulatory effect (32-33%). The kappa-agonist (-)-U-50488H failed to stimulate p-FADD. Sufentanil reduced CKI protein and kinase activity in the cytosol (30-37%). Morphine, but not SNC-80, augmented CKIalpha in cytosol, membrane and nucleus (36-104%). In contrast to FADD, the ability of SNC-80 to stimulate p-FADD was not sensitive to ERK1/2 blockade. Pertussis toxin did not prevent the opposite effects of SNC-80 on p-FADD and FADD because the toxin by itself markedly altered their basal contents, indicating that FADD could be a novel toxin target. The upregulation of p-FADD induced by mu/delta-agonists could play a relevant role in the anti-apoptotic and/or neuroplastic effects of opioids.

Decreased Proliferation of Adult Hippocampal Stem Cells During Cocaine Withdrawal: Possible Role of the Cell Fate Regulator FADD

The current study uses an extended access rat model of cocaine self-administration (5-h session per day, 14 days), which elicits several features manifested during the transition to human addiction, to study the neural adaptations associated with cocaine withdrawal. Given that the hippocampus is thought to have an important role in maintaining addictive behavior and appears to be especially relevant to mechanisms associated with withdrawal, this study attempted to understand how extended access to cocaine impacts the hippocampus at the cellular and molecular levels, and how these alterations change over the course of withdrawal (1, 14, and 28 days). Therefore, at the cellular level, we examined the effects of cocaine withdrawal on cell proliferation (Ki-67+ and NeuroD+ cells) in the DG. At the molecular level, we employed a ‘discovery’ approach with gene expression profiling in the DG to uncover novel molecules possibly implicated in the neural adaptations that take place during cocaine withdrawal. Our results suggest that decreased hippocampal cell proliferation might participate in the adaptations associated with drug removal and identifies 14 days as a critical time-point of cocaine withdrawal. At the 14-day time-point, gene expression profiling of the DG revealed the dysregulation of several genes associated with cell fate regulation, highlighting two new neurobiological correlates (Ascl-1 and Dnmt3b) that accompany cessation of drug exposure. Moreover, the results point to Fas-Associated protein with Death Domain (FADD), a molecular marker previously associated with the propensity to substance abuse and cocaine sensitization, as a key cell fate regulator during cocaine withdrawal. Identifying molecules that may have a role in the restructuring of the hippocampus following substance abuse provides a better understanding of the adaptations associated with cocaine withdrawal and identifies novel targets for therapeutic intervention.

Cocaine Withdrawal Causes Delayed Dysregulation of Stress Genes in the Hippocampus

Relapse, even following an extended period of withdrawal, is a major challenge in substance abuse management. Delayed neurobiological effects of the drug during prolonged withdrawal likely contribute to sustained vulnerability to relapse. Stress is a major trigger of relapse, and the hippocampus regulates the magnitude and duration of stress responses. Recent work has implicated hippocampal plasticity in various aspects of substance abuse. We asked whether changes in stress regulatory mechanisms in the hippocampus may participate in the neuroadaptations that occur during prolonged withdrawal. We therefore examined changes in the rat stress system during the course of withdrawal from extended daily access (5-hours) of cocaine self-administration, an animal model of addiction. Tissue was collected at 1, 14 and 28 days of withdrawal. Plasma corticosterone levels were determined and corticosteroid receptors (GR, MR, MR/GR mRNA ratios) and expression of other stress-related molecules (HSP90AA1 and HSP90AB1 mRNA) were measured in hippocampal subfields using in situ hybridization. Results showed a delayed emergence of dysregulation of stress genes in the posterior hippocampus following 28 days of cocaine withdrawal. This included increased GR mRNA in DG and CA3, increased MR and HSP90AA1 mRNA in DG, and decreased MR/GR mRNA ratio in DG and CA1. Corticosterone levels progressively decreased during the course of withdrawal, were normalized following 28 days of withdrawal, and were correlated negatively with GR and positively with MR/GR mRNA ratio in DG. These results suggest a role for the posterior hippocampus in the neuroadaptations that occur during prolonged withdrawal, and point to a signaling partner of GR, HSP90AA1, as a novel dysregulated target during cocaine withdrawal. These delayed neurobiological effects of extended cocaine exposure likely contribute to sustained vulnerability to relapse.

Effects of constitutive deletion of opioid receptors on the basal densities of Fas and Fas-associated protein with death domain (FADD) in the mouse brain: A δ-opioid tone inhibits FADD

The acute effects of opiate drugs and opiate addiction have been associated with modulation of Fas/FADD (Fas-Associated protein with Death Domain) signaling complex in the rat brain. This study investigated the possible existence of endogenous opioid tones regulating the basal activities of Fas receptor forms and FADD in the brain, using gene-targeted mice lacking mu-, delta- or kappa-opioid peptide receptors (KO mice). In mu-KO mice, but not in delta- or kappa-KO mice, the basal immunodensity of native Fas (35 kDa monomeric form) was decreased in the cerebral cortex (33%) when compared with WT littermates. In delta-KO mice, but not in mu- or kappa-KO mice, the basal content of 120 kDa Fas aggregates (complexes of monomers relevant in Fas signaling) was markedly increased in the cortex (93%). In contrast, no differences between genotypes were observed in the basal expression of glycosylated Fas (51/48/45 kDa forms). Notably, the basal content of FADD (the adaptor protein that couples Fas to caspases and transmits the death signal) was increased in the cerebral cortex of delta-KO mice (48%), but not in mu- or kappa-KO mice. In addition, the basal content of phosphorylated FADD at Ser191 (the relevant species of FADD implicated in nonapoptotic signals) was also upregulated in the cortices of delta-opioid receptor KO mice (6.5-11.0-fold). The results suggest that mu-receptors tonically stimulate (through endogenous opioid peptides) the activation of native Fas, whereas delta-receptors tonically inhibit the expression of Fas aggregates and that of FADD and phosphorylated FADD (Ser191) in the mouse brain. These data are in line with the acute opposite modulation of Fas and FADD induced by mu- and delta-opiate agonists, and strongly support the notion of an anti-apoptotic delta-opioid tone that restrains Fas signaling.

Chronic MDMA induces neurochemical changes in the hippocampus of adolescent and young adult rats: Down-regulation of apoptotic markers

While hippocampus is a brain region particularly susceptible to the effects of MDMA, the cellular and molecular changes induced by MDMA are still to be fully elucidated, being the dosage regimen, the species and the developmental stage under study great variables. This study compared the effects of one and four days of MDMA administration following a binge paradigm (3×5 mg/kg, i.p., every 2 h) on inducing hippocampal neurochemical changes in adolescent (PND 37) and young adult (PND 58) rats. The results showed that chronic MDMA caused hippocampal protein deficits in adolescent and young adult rats at different levels: (1) impaired serotonergic (5-HT2A and 5-HT2C post-synaptic receptors) and GABAergic (GAD2 enzyme) signaling, and (2) decreased structural cytoskeletal neurofilament proteins (NF-H, NF-M and NF-L). Interestingly, these effects were not accompanied by an increase in apoptotic markers. In fact, chronic MDMA inhibited proteins of the apoptotic pathway (i.e., pro-apoptotic FADD, Bax and cytochrome c) leading to an inhibition of cell death markers (i.e., p-JNK1/2, cleavage of PARP-1) and suggesting regulatory mechanisms in response to the neurochemical changes caused by the drug. The data, together with the observed lack of GFAP activation, support the view that chronic MDMA effects, regardless of the rat developmental age, extends beyond neurotransmitter systems to impair other hippocampal structural cell markers. Interestingly, inhibitory changes in proteins from the apoptotic pathway might be taking place to overcome the protein deficits caused by MDMA.

Monoamine receptor agonists, acting preferentially at presynaptic autoreceptors and heteroreceptors, downregulate the cell fate adaptor FADD in rat brain cortex

FADD is a crucial adaptor of death receptors that can engage apoptosis or survival actions (e.g. neuroplasticity) through its phosphorylated form (p-FADD). Although FADD was shown to participate in receptor mechanisms related to drugs of abuse, little is known on its role in the signaling of classic neurotransmitters (dopamine, noradrenaline, and serotonin) in brain. This study assessed the modulation of FADD (and p-FADD/FADD ratio, as an index of neuroplasticity) and FLIP-L (a neuroprotective FADD interacting partner), as well as the role of MEK-ERK signaling, after activation of monoamine auto/heteroreceptors by selective agonists in rat cortex. Acute depletion of monoamines with reserpine, but not with AMPT or PCPA, reduced FADD (28%) and increased p-FADD/FADD ratio (1.34-fold). Activation of presynaptic α2A-adrenoceptors (UK-14304 and clonidine), 5-HT1A receptors (8-OH-DPAT), and D2 dopamine receptor (bromocriptine) dose-dependently decreased FADD (up to 54%) and increased p-FADD (up to 29%) and p-FADD/FADD ratios (up to 2.93-fold), through specific receptor mechanisms. Activation of rat 5-HT1B autoreceptor in axon terminals by CP-94253 did not modulate FADD forms. Activation of postsynaptic D1 dopamine receptor by SKF-81297 also reduced FADD (25%) and increased p-FADD (32%). Disruption of MEK-ERK activation with SL327 did not modify clonidine (α2A-adrenoceptor)-induced FADD inhibition, indicating that agonist effect was not dependent on ERK signaling. The various monoamine receptor agonists and antagonists did not alter FLIP-L content, or the activation of executioner caspase-3 and PARP-1 cleavage, indicating that the agonists attenuated apoptotic signals and promoted neuroplasticity through FADD regulation. These novel results indicate that inhibition of pro-apoptotic FADD adaptor could function as a common signaling step in the initial activation of monoamine receptors in the brain.

Comparative effects of amphetamine-like psychostimulants on rat hippocampal cell genesis at different developmental ages.

The aim of this study was to compare the effects of amphetamine-like psychostimulant drugs (i.e., MDMA, methamphetamine, D-amphetamine) on rat hippocampal cell genesis at different developmental ages (i.e., early adolescence vs. young adulthood) to determine if there were periods of vulnerability to drug-induced brain changes. Although adolescence is a period of great vulnerability to the neurochemical effects of specific drugs of abuse, several reports suggest that adult rats are more susceptible than adolescents to the negative effects of these drugs. The main results suggest that the effects of these amphetamine drugs on cell genesis depend on the rats developmental age, with the young adult period being more sensitive than the early adolescent one. In particular, MDMA and methamphetamine, but not D-amphetamine impaired hippocampal cell genesis (i.e., cell proliferation and cell survival) in young adult rats. These effects were dependent on the accumulative dose administered, as they were only observed with the highest dose tested (12 pulses of 5mg/kg over 4days: 60mg/kg total). The present results extend previous reports on adolescent insensitivity (i.e., better adaptation) to amphetamine-drugs and suggest for young adult rats certain degree of hippocampal damage that may mediate some of the addiction-like behaviors that depend on this brain region. Moreover, the present results, in line with previous data, suggest a possible role for the neuroplasticity marker BDNF and serotonin in regulating cell survival, as mBDNF protein regulation paralleled hippocampal cell survival and 5-HT2C-receptor content in young adult rats treated with these psychostimulant drugs.