Regulation of nonphosphorylated and phosphorylated forms of neurofilament proteins in the prefrontal cortex of human opioid addicts

A pediatric quantitative systems pharmacology model of neurofilament trafficking in spinal muscular atrophy treated with the antisense oligonucleotide nusinersen

Phosphorylated neurofilament heavy subunit (pNfH) has been recently identified as a promising biomarker of disease onset and treatment efficacy in spinal muscular atrophy (SMA). This study introduces a quantitative systems pharmacology model representing the SMA pediatric scenario in the age range of 0-20 years with and without treatment with the antisense oligonucleotide nusinersen. Physiological changes typical of the pediatric age and the contribution of SMA and its treatment to the peripheral pNfH levels were included in the model by extending the equations of a previously developed mathematical model describing the neurofilament trafficking in healthy adults. All model parameters were estimated by fitting data from clinical trials that enrolled SMA patients treated with nusinersen. The data from the control group of the study was employed to build an in silico population of untreated subjects, and the parameters related to the treatment were estimated by fitting individual pNfH time series of SMA patients followed during the treatment. The final model reproduces well the pNfH levels in the presence of SMA in both the treated and untreated conditions. The results were validated by comparing model predictions with the data obtained from an additional cohort of SMA patients. The reported good predictive model performance makes it a valuable tool for investigating pNfH as a biomarker of disease progression and treatment response in SMA and for the in silico evaluation of novel treatment protocols.

An age‐dependent mathematical model of neurofilament trafficking in healthy conditions

Neurofilaments (Nfs) are the major structural component of neurons. Their role as a potential biomarker of several neurodegenerative diseases has been investigated in past years with promising results. However, even under physiological conditions, little is known about the leaking of Nfs from the neuronal system and their detection in the cerebrospinal fluid (CSF) and blood. This study aimed at developing a mathematical model of Nf transport in healthy subjects in the 20–90 age range. The model was implemented as a set of ordinary differential equations describing the trafficking of Nfs from the nervous system to the periphery. Model parameters were calibrated on typical Nf levels obtained from the literature. An age‐dependent function modeled on CSF data was also included and validated on data measured in serum. We computed a global sensitivity analysis of model rates and volumes to identify the most sensitive parameters affecting the model’s steady state. Age, Nf synthesis, and degradation rates proved to be relevant for all model variables. Nf levels in the CSF and in blood were observed to be sensitive to the Nf leakage rates from neurons and to the blood clearance rate, and CSF levels were also sensitive to rates representing CSF turnover. An additional parameter perturbation analysis was also performed to investigate possible transient effects on the model variables not captured by the sensitivity analysis. The model provides useful insights into Nf transport and constitutes the basis for implementing quantitative system pharmacology extensions to investigate Nf trafficking in neurodegenerative diseases.

Specific neuronal subpopulations in the rat basolateral amygdala express high levels of nonphosphorylated neurofilaments

Cortical pyramidal neurons (PNs) containing nonphosphorylated neurofilaments (NNFs) localized with the SMI-32 monoclonal antibody have been shown to be especially vulnerable to degeneration in Alzheimer's disease (AD). The present investigation is the first to study the expression of SMI-32+ NNFs in neurons of the basolateral nuclear complex of the amygdala (BNC), which contains cortex-like PNs and nonpyramidal neurons (NPNs). We observed that PNs in the rat basolateral nucleus (BL), but not in the lateral (LAT) or basomedial (BM) nuclei, have significant levels of SMI-32-ir in their somata with antibody diluents that did not contain Triton X-100, but staining in these cells was greatly attenuated when the antibody diluent contained 0.3% Triton. Using Triton-containing diluents, we found that all SMI-32+ neurons in all three of the BNC nuclei were NPNs. Using a dual-labeling immunoperoxidase technique, we demonstrated that most of these SMI-32+ NPNs were parvalbumin-positive (PV+) or somatostatin-positive NPNs but not vasoactive intestinal peptide-positive or neuropeptide Y-positive NPNs. Using a technique that combines retrograde tracing with SMI-32 immunohistochemistry using intermediate levels of Triton in the diluent, we found that all BNC neurons projecting to the mediodorsal thalamic nucleus (MD) were large NPNs, and most were SMI-32+. In contrast, BNC neurons projecting to the ventral striatum or cerebral cortex were PNs that expressed low levels of SMI-32 immunoreactivity (SMI-32-ir) in the BL, and no SMI-32-ir in the LAT or BM. These data suggest that the main neuronal subpopulations in the BNC that degenerate in AD may be PV+ and MD-projecting NPNs.

Sintocalmy, a Passiflora incarnata Based Herbal, Attenuates Morphine Withdrawal in Mice

Chronic opioid use changes brain chemistry in areas related to reward processes, memory, decision-making, and addiction. Both neurons and astrocytes are affected, ultimately leading to dependence. Passiflora incarnata L. (Passifloraceae) is the basis of frequently used herbals to manage anxiety and insomnia, with proven central nervous system depressant effects. Anti-addiction properties of P. incarnata have been reported. The aim of this study was to investigate the effect of a commercial extract of Passiflora incarnata (Sintocalmy®, Aché Laboratory) in the naloxone-induced jumping mice model of morphine withdrawal. In addition, glial fibrillary acidic protein (GFAP) and S100 calcium-binding protein B (S100B) levels were assessed in the frontal cortex and hippocampus, and DNA damage was verified on blood cells. In order to improve solubilization a Sintocalmy methanol extract (SME) was used. SME is mainly composed by flavonoids isovitexin and vitexin. The effects of SME 50, 100 and 200 mg/kg (i.p.) were evaluated in the naloxone-induced withdrawal syndrome in mice. SME 50 and SME 100 mg/kg decreased naloxone-induced jumping in morphine-dependent mice without reducing locomotor activity. No alterations were found in GFAP levels, however SME 50 mg/kg prevented the S100B increase in the frontal cortex and DNA damage. This study shows anti-addiction effects for a commercial standardized extract of P. incarnata and suggests the relevance of proper clinical assessment.

Does a hypoxic injury from a non-fatal overdose lead to an Alzheimer Disease?

Long term consequence of non-fatal overdose in people who use opioids are not well understood. The intermittent exposure to non-fatal overdose leads to a tauopathy that is often accompanied by abrogated neuroprotective response, abnormal amyloid processing and other pathologies. The scope and limitations of available literature are discussed including neuropathologies associated with opioid and overdose exposures, contributing comorbidities and proteinopathies. Contrasting postmortem data of overdose victims with animal models of opioid neuropathologies and hypoxic injury paints a picture distinct from other proteinopathies as well as effects of moderate opioid exposure. Furthermore the reported biochemical changes and potential targets for therapeutic intervention were mapped pointing to underlying imbalance between tau kinases and phosphatases that is characteristic of Alzheimer Disease.

Regulation of cannabinoid CB1 and CB2 receptors, neuroprotective mTOR and pro-apoptotic JNK1/2 kinases in postmortem prefrontal cortex of subjects with major depressive disorder

BACKGROUND

Dysregulations of endocannabinoids and/or cannabinoid (CB) receptors have been implicated in the pathophysiology and treatment of major depressive disorder (MDD).

METHODS

CB₁ and CB₂ receptors, neuroprotective mTOR (mechanistic target of rapamycin) and pro-apoptotic JNK1/2 (c-Jun-N-terminal kinases) were quantified by immunoblotting in postmortem prefrontal cortex of MDD and controls, and further compared in antidepressant (AD)-free and AD-treated subjects. Neuroplastic proteins (PSD-95, Arc, spinophilin) were quantified in MDD brains.

RESULTS

Total cortical CB₁ glycosylated (≈54/64 kDa) receptor was increased in MDD (+20%, n=23, p=0.02) when compared with controls (100%, n=19). This CB₁ receptor upregulation was quantified in AD-treated (+23%, n=14, p=0.02) but not in AD-free (+14%, n=9, p=0.34) MDD subjects. In the same MDD cortical samples, CB₂ glycosylated (≈45 kDa) receptor was unaltered (all MDD: +11%, n=23, p=0.10; AD-free: +12%, n=9, p=0.31; AD-treated: +10%, n=14, p=0.23). In MDD, mTOR activity (p-Ser2448 TOR/t-TOR) was increased (all MDD: +29%, n=18, p=0.002; AD-free: +33%, n=8, p=0.03; AD-treated: +25%, n=10, p=0.04). In contrast, JNK1/2 activity (p-Thr183/Tyr185/t-JNK) was unaltered in MDD subjects. Cortical PSD-95, Arc, and spinophilin contents were unchanged in MDD.

LIMITATIONS

A relative limited sample size. Some MDD subjects had been treated with a variety of ADs. The results must be understood in the context of suicide victims with MDD.

CONCLUSIONS

The upregulation of CB₁ receptor density, but not that of CB₂ receptor, as well as the increased mTOR activity in PFC/BA9 of subjects with MDD (AD-free/treated) support their contributions in the complex pathophysiology of MDD and in the molecular mechanisms of antidepressant drugs.

Ketamine-induced hypnosis and neuroplasticity in mice is associated with disrupted p-MEK/p-ERK sequential activation and sustained upregulation of survival p-FADD in brain cortex: Involvement of GABAA receptor

Ketamine (KET) is an antidepressant and hypnotic drug acting as an antagonist at excitatory NMDA glutamate receptors. The working hypothesis postulated that KET-induced sleep in mice results in dysregulation of mitogen-activated protein kinases (MAPK) MEK-ERK sequential phosphorylation and upregulation of survival p-FADD and other neuroplastic markers in brain. Low (5-15 mg/kg) and high (150 mg/kg) doses of KET on target proteins were assessed by Western immunoblot in mouse brain cortex. During the time course of KET (150 mg/kg)-induced sleep (up to 50 min) p-MEK was increased (up to +79%) and p-ERK decreased (up to -46%) indicating disruption of MEK to ERK signal. Subhypnotic KET (5-15 mg/kg) also revealed uncoupling of p-MEK (+13-81%) to p-ERK (unchanged content). KET did not alter contraregulatory MAPK mechanisms such as inactivated p-MEK1 (ERK dampening) and phosphatases MKP1/2/3 (ERK dephosphorylation). As other relevant findings, KET (5, 15 and 150 mg/kg) upregulated p-FADD in a dose-dependent manner, and for the hypnotic dose the effect paralleled the time course of sleep which resulted in increased p-FADD/FADD ratios. KET (150 mg/kg) also increased NF-κΒ and PSD-95 neuroplastic markers. Flumazenil (a neutral allosteric antagonist at GABA_A receptor) prolonged KET sleep and blocked p-MEK upregulation, indicating the involvement of this receptor as a negative modulator. SL-327 (a MEK inhibitor) augmented KET sleep, further indicating the relevance of reduced p-ERK1/2 in KET-induced hypnosis. These findings suggest that hypnotic and subhypnotic doses of KET inducing uncoupling of p-MEK to p-ERK signal and regulation of p-ERK (downregulation) and p-FADD (upregulation) may participate in the expression of some of its adverse effects (e.g. amnesia, dissociative effects).

Pentobarbital and other anesthetic agents induce opposite regulations of MAP kinases p-MEK and p-ERK, and upregulate p-FADD/FADD neuroplastic index in brain during hypnotic states in mice

Midazolam and ketamine-induced anesthesia were recently shown to induce a disruption of MEK/ERK sequential phosphorylation with parallel upregulation of p-FADD in the mouse brain. The present study was designed to assess whether other structurally diverse anesthetic agents (pentobarbital, ethanol, chloral hydrate, isoflurane) also impair brain p-MEK to p-ERK signal and increase p-FADD during the particular time course of 'sleep' in mice. Pentobarbital (50 mg/kg)-, ethanol (4000 mg/kg)-, chloral hydrate (400 mg/kg)-, and isoflurane (2% in O₂)-induced anesthesia (range: 24-60 min) were associated with unaltered or increased p-MEK1/2 (up to +155%) and decreased p-ERK1/2 (up to -60%) contents, revealing disruption of MEK to ERK activation in mouse brain cortex. These anesthetic agents also upregulated cortical p-FADD (up to +110%), but not total FADD (moderately decreased), which resulted in increased neuroplastic/survival p-FADD/FADD ratios (up to +2.8 fold). The inhibition of pentobarbital metabolism with SKF525-A (a cytochrome P450 inhibitor) augmented barbiturate anesthesia (2.6 times) and induced a greater and sustained upregulation of p-MEK with p-ERK downregulation, as well as prolonged increases of p-FADD content and p-FADD/FADD ratio (effects lasting for more than 240 min). Pentobarbital also upregulated significantly the cortical contents of other markers of neuroplasticity such as the ERK inhibitor p-PEA-15 (up to +46%), the transcription factor NF-κB (up to +27%) and the synaptic density protein PSD-95 (up to +20%) during 'sleep'. The results reveal a paradoxical stimulation of p-MEK without the concomitant (canonical) activation of p-ERK (e.g. with pentobarbital and isoflurane), for which various molecular mechanisms are discussed. The downregulation of brain p-ERK may participate in the manifestations of adverse effects displayed by most hypnotic/anesthetic agents in clinical use (e.g. amnesia).

Pharmacoepigenomics of opiates and methadone maintenance treatment: current data and perspectives

Current treatments of opioid addiction include primarily maintenance medications such as methadone. Chronic exposure to opiate and/or long-lasting maintenance treatment induce modulations of gene expression in brain and peripheral tissues. There is increasing evidence that epigenetic modifications underlie these modulations. This review summarizes published results on opioid-induced epigenetic changes in animal models and in patients. The epigenetic modifications observed with other drugs of abuse often used by opiate abusers are also outlined. Specific methadone maintenance treatment induced epigenetic modifications at different treatment stages may be combined with the ones resulting from patients’ substance use history. Therefore, research comparing groups of addicts with similar history and substances use disorders but contrasting for well-characterized treatment phenotypes should be encouraged.

Specialized roles of neurofilament proteins in synapses: Relevance to neuropsychiatric disorders

Neurofilaments are uniquely complex among classes of intermediate filaments in being composed of four subunits (NFL, NFM, NFH and alpha-internexin in the CNS) that differ in structure, regulation, and function. Although neurofilaments have been traditionally viewed as axonal structural components, recent evidence has revealed that distinctive assemblies of neurofilament subunits are integral components of synapses, especially at postsynaptic sites. Within the synaptic compartment, the individual subunits differentially modulate neurotransmission and behavior through interactions with specific neurotransmitter receptors. These newly uncovered functions suggest that alterations of neurofilament proteins not only underlie axonopathy in various neurological disorders but also may play vital roles in cognition and neuropsychiatric diseases. Here, we review evidence that synaptic neurofilament proteins are a sizable population in the CNS and we advance the concept that changes in the levels or post-translational modification of individual NF subunits contribute to synaptic and behavioral dysfunction in certain neuropsychiatric conditions.

Neuropathological alterations in drug abusers : The involvement of neurons, glial, and vascular systems

Because the effects of drug abuse on the cellular elements of the human brain have not been studied systematically, an investigation was performed using histology, immunohistochemistry, and morphometry. The main cortical and subcortical brain areas of 50 polydrug deaths were analyzed as compared with controls.In the brains of drug abusers, a significant neuronal loss was present. Interestingly, the number of glial fibrillary acidic protein (GFAP)-positive astrocytes was reduced. the numerical density of perivascular and parenchymal microglia was increased in the white matter and in most subcortical regions. In the white matter there were widespread β-amyloid precursor protein deposits. Furthermore, there was a prominent vascular hyalinosis, endothelial cell proliferation, and a loss of immunoreactivity for collagen type IV within the vascular basal lamina.The neuronal loss seems to be the result of a direct impairment of nerve cells and, indirectly, to a damage of astrocytes, axons, and the microvasculature. The reduction of GFAP-positive astrocytes is also indicative of a drug-induced damage. The axonal injury suggests a toxic-metabolic drug effect, whereas the concomitant activation of microglia is indicative of a long-standing progressive process. The noninflammatory vasculopathy can be considered as the morphological substrate of a disturbed blood-brain barrier. Our findings demonstrate that drugs of abuse initiate a cascade of interacting toxic, vascular, and hypoxic factors that finally result in widespread disturbances within the complex network of central nervous system cell-cell interactions.

Phosphoproteomics and bioinformatics analyses of spinal cord proteins in rats with morphine tolerance

Introduction

Morphine is the most effective pain-relieving drug, but it can cause unwanted side effects. Direct neuraxial administration of morphine to spinal cord not only can provide effective, reliable pain relief but also can prevent the development of supraspinal side effects. However, repeated neuraxial administration of morphine may still lead to morphine tolerance.

Methods

To better understand the mechanism that causes morphine tolerance, we induced tolerance in rats at the spinal cord level by giving them twice-daily injections of morphine (20 µg/10 µL) for 4 days. We confirmed tolerance by measuring paw withdrawal latencies and maximal possible analgesic effect of morphine on day 5. We then carried out phosphoproteomic analysis to investigate the global phosphorylation of spinal proteins associated with morphine tolerance. Finally, pull-down assays were used to identify phosphorylated types and sites of 14-3-3 proteins, and bioinformatics was applied to predict biological networks impacted by the morphine-regulated proteins.

Results

Our proteomics data showed that repeated morphine treatment altered phosphorylation of 10 proteins in the spinal cord. Pull-down assays identified 2 serine/threonine phosphorylated sites in 14-3-3 proteins. Bioinformatics further revealed that morphine impacted on cytoskeletal reorganization, neuroplasticity, protein folding and modulation, signal transduction and biomolecular metabolism.

Conclusions

Repeated morphine administration may affect multiple biological networks by altering protein phosphorylation. These data may provide insight into the mechanism that underlies the development of morphine tolerance.

Quantitative analysis of astrogliosis in drug-dependent humans

Drug addiction is a chronic, relapsing disease caused by neurochemical and molecular changes in the brain. In this human autopsy study qualitative and quantitative changes of glial fibrillary acidic protein (GFAP)-positive astrocytes in the hippocampus of 26 lethally intoxicated drug addicts and 35 matched controls are described. The morphological characterization of these cells reflected alterations representative for astrogliosis. But, neither quantification of GFAP-positive cells nor the Western blot analysis indicated statistical significant differences between drug fatalities versus controls. However, by semi-quantitative scoring a significant shift towards higher numbers of activated astrocytes in the drug group was detected. To assess morphological changes quantitatively, graph-based representations of astrocyte morphology were obtained from single cell images captured by confocal laser scanning microscopy. Their underlying structures were used to quantify changes in astroglial fibers in an automated fashion. This morphometric analysis yielded significant differences between the investigated groups for four different measures of fiber characteristics (Euclidean distance, graph distance, number of graph elements, fiber skeleton distance), indicating that, e.g., astrocytes in drug addicts on average exhibit significant elongation of fiber structures as well as two-fold increase in GFAP-positive fibers as compared with those in controls. In conclusion, the present data show characteristic differences in morphology of hippocampal astrocytes in drug addicts versus controls and further supports the involvement of astrocytes in human pathophysiology of drug addiction. The automated quantification of astrocyte morphologies provides a novel, testable way to assess the fiber structures in a quantitative manner as opposed to standard, qualitative descriptions.

Exploring the neuroimmunopharmacology of opioids: an integrative review of mechanisms of central immune signaling and their implications for opioid analgesia

Vastly stimulated by the discovery of opioid receptors in the early 1970s, preclinical and clinical research was directed at the study of stereoselective neuronal actions of opioids, especially those played in their crucial analgesic role. However, during the past decade, a new appreciation of the non-neuronal actions of opioids has emerged from preclinical research, with specific appreciation for the nonclassic and nonstereoselective sites of action. Opioid activity at Toll-like receptors, newly recognized innate immune pattern recognition receptors, adds substantially to this unfolding story. It is now apparent from molecular and rodent data that these newly identified signaling events significantly modify the pharmacodynamics of opioids by eliciting proinflammatory reactivity from glia, the immunocompetent cells of the central nervous system. These central immune signaling events, including the release of cytokines and chemokines and the associated disruption of glutamate homeostasis, cause elevated neuronal excitability, which subsequently decreases opioid analgesic efficacy and leads to heightened pain states. This review will examine the current preclinical literature of opioid-induced central immune signaling mediated by classic and nonclassic opioid receptors. A unification of the preclinical pharmacology, neuroscience, and immunology of opioids now provides new insights into common mechanisms of chronic pain, naive tolerance, analgesic tolerance, opioid-induced hyperalgesia, and allodynia. Novel pharmacological targets for future drug development are discussed in the hope that disease-modifying chronic pain treatments arising from the appreciation of opioid-induced central immune signaling may become practical.

Mass spectrometry screening reveals peptides modulated differentially in the medial prefrontal cortex of rats with disparate initial sensitivity to cocaine

To better understand why certain individuals are more vulnerable to cocaine abuse and addiction, we identify peptide markers associated with individual variation in sensitivity to the behavioral effects of cocaine. Previous studies in rats show that low, compared to high, cocaine responders are more sensitive to cocaine-induced behavioral plasticity (sensitization), exhibit enhanced conditioning to cocaine's rewarding effects, and are more motivated to self administer cocaine. In the current study, we combine matrix-assisted laser desorption/ionization mass spectrometry with multivariate statistical methods to analyze tissue extracts from rat dorsal striatum, nucleus accumbens, and medial prefrontal cortex (mPFC) to examine trends in peptide changes that coincide with behavioral phenotype. Peptide profiles of these three regions from individual animals were characterized via mass spectrometry. Resulting mass peaks that were statistically different between these groups were identified using principal component analysis. The mass peaks were then identified in pooled samples via multistage liquid chromatography mass spectrometry. A total of 74 peptides from 28 proteins were sequenced from defined brain regions. Statistically significant changes in peak intensities for seven peptides were found in the mPFC of rats given a single injection of 10 mg/kg cocaine, with low cocaine responders showing approximately 2-fold increase in peak intensities for the acetylated N terminus peptides of stathmin and Hint 1, as well as truncated ATP synthase. These results suggest that distinct peptide profiles in the mPFC are associated with individuals that exhibit reduced sensitivity to the behavioral effects of cocaine.

Differential damage in the frontal cortex with aging, sporadic and familial Alzheimer's disease

In order to understand relationships between executive and structural deficits in the frontal cortex of patients within normal aging or Alzheimer's disease, we studied frontal pathological changes in young and old controls compared to cases with sporadic (AD) or familial Alzheimer's disease (FAD). We performed a semi-automatic computer assisted analysis of the distribution of beta-amyloid (Abeta) deposits revealed by Abeta immunostaining as well as of neurofibrillary tangles (NFT) revealed by Gallyas silver staining in Brodman areas 10 (frontal polar), 12 (ventro-infero-median) and 24 (anterior cingular), using tissue samples from 5 FAD, 6 sporadic AD and 10 control brains. We also performed densitometric measurements of glial fibrillary acidic protein, principal compound of intermediate filaments of astrocytes, and of phosphorylated neurofilament H and M epitopes in areas 10 and 24. All regions studied seem almost completely spared in normal old controls, with only the oldest ones exhibiting a weak percentage of beta-amyloid deposit and hardly any NFT. On the contrary, all AD and FAD cases were severely damaged as shown by statistically significant increased percentages of beta-amyloid deposit, as well as by a high number of NFT. FAD cases (all from the same family) had statistically more beta-amyloid and GFAP than sporadic AD cases in both areas 10 and 24 and statistically more NFT only in area 24. The correlation between the percentage of beta-amyloid and the number of NFT was significant only for area 24. Altogether, these data suggest that the frontal cortex can be spared by AD type lesions in normal aging, but is severely damaged in sporadic and still more in familial Alzheimer's disease. The frontal regions appear to be differentially vulnerable, with area 12 having the less amyloid burden, area 24 the less NFT and area 10 having both more amyloid and more NFT. This pattern of damage in frontal regions may represent a strong neuroanatomical support for the deterioration of attention and cognitive capacities as well as for the presence of emotional and behavioral troubles in AD patients.

Expression of transcripts for myelin related genes in postmortem brain from cocaine abusers

Chronic abuse of cocaine is known to cause neuroadaptive changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). In addition, altered expression of the myelin-related genes MBP, MOBP, PLP1 as well as of MAL2 in NAc was recently reported by gene array analysis in brains from cocaine abusers. In the present study we used in situ hybridization to quantify transcript expression of these four genes, as well as for the myelin-related transcripts encoding quaking, EDG2, claudin-11, transferrin, CNP, and MAG in caudate, putamen, internal capsule, and NAc in postmortem brain from cocaine abusers and matched comparison subjects. Most transcripts were not different between these groups in these striatal regions, and contrary to previous reports, we did not detect any changes in the NAc. However, expression of the transcript encoding PLP1 was significantly decreased in ventral and dorsal regions of the caudate, putamen, and in the internal capsule. Additionally, expression of claudin-11 and transferrin was decreased in the caudate and internal capsule, respectively. PLP1 is expressed at very high levels in oligodendrocytes and is essential in maintaining stability of myelin sheets. Based on these findings, altered expression of PLP1 in most areas of the striatum suggests that widespread changes to the myelin structure could be associated with the adaptive changes following chronic cocaine abuse.

Characterizing intercellular signaling peptides in drug addiction

Intercellular signaling peptides (SPs) coordinate the activity of cells and influence organism behavior. SPs, a chemically and structurally diverse group of compounds responsible for transferring information between neurons, are broadly involved in neural plasticity, learning and memory, as well as in drug addiction phenomena. Historically, SP discovery and characterization has tracked advances in measurement capabilities. Today, a suite of analytical technologies is available to investigate individual SPs, as well as entire intercellular signaling complements, in samples ranging from individual cells to entire organisms. Immunochemistry and in situ hybridization are commonly used for following preselected SPs. Discovery-type investigations targeting the transcriptome and proteome are accomplished using high-throughput characterization technologies such as microarrays and mass spectrometry. By integrating directed approaches with discovery approaches, multiplatform studies fill critical gaps in our knowledge of drug-induced alterations in intercellular signaling. Throughout the past 35 years, the National Institute on Drug Abuse has made significant resources available to scientists that study the mechanisms of drug addiction. The roles of SPs in the addiction process are highlighted, as are the analytical approaches used to detect and characterize them.

Chronic morphine exposure alters the dendritic morphology of pyramidal neurons in visual cortex of rats

Repeated treatment of psychotropic drugs produces changes in brain and behavior that far outlast their initial neuropharmacological effects. The nature of persistent drug-induced neural plasticity is of interest because it is thought to contribute to the development of drug dependency and addiction. To determine if chronic morphine treatment alters the morphology of visual cortical neurons, we statistically examined the dendrites of layer III pyramidal neurons in the primary visual cortex of both morphine-treated and saline-control rats. Compared with control rats, the pyramidal cells of morphine-treated animals showed a significant decrease in the total dendritic length (24%) and a significant reduction (27%) in the dendritic spine density of dendritic arborization at the level of the second branch order. Our results suggest that some of the persistent neurobehavioral consequences and cognitive impairment resulting from repeated exposure to morphine may involve a reorganization of synaptic connectivity in visual cortical neurons.

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

This study was designed to assess the effects of opiate treatment on the expression of Fas-associated protein with death domain (FADD) in the rat brain. FADD is involved in the transmission of Fas-death signals that have been suggested to contribute to the development of opiate tolerance and addiction. Acute treatments with high doses of sufentanil and morphine (mu-agonists), SNC-80 (delta-agonist), and U50488H (kappa-agonist) induced significant decreases (30-60%) in FADD immunodensity in the cerebral cortex, through specific opioid receptor mechanisms (effects antagonized by naloxone, naltrindole, or nor-binaltorphimine). The cannabinoid CB1 receptor agonist WIN 55,212-2 did not alter FADD content in the brain. Chronic (5 days) morphine (10-100 mg/kg), SNC-80 (10 mg/kg), or U50488H (10 mg/kg) was associated with the induction of tachyphylaxis to the acute effects. In morphine- and SNC-80-tolerant rats, antagonist-precipitated (2 h) or spontaneous withdrawal (24-48 h) induced a new and sustained inhibition of FADD (13-50%). None of these treatments altered the densities of caspases 8/3 (including the active cleaved forms) in the brain. Pretreatment of rats with SL 327 (a selective MEK1/2 inhibitor that blocks ERK activation) fully prevented the reduction of FADD content induced by SNC-80 in the cerebral cortex (43%) and corpus striatum (29%), demonstrating the direct involvement of ERK1/2 signaling in the regulation of FADD by the opiate agonist. The results indicate that mu- and delta-opioid receptors have a prominent role in the modulation of FADD (opposite to that of Fas) shortly after initiating treatment. Opiate drugs (and specifically the delta-agonists) could promote survival signals in the brain through inhibition of FADD, which in turn is dependent on the activation of the antiapoptotic ERK1/2 signaling pathway.

Rnd family genes are differentially regulated by 3,4-methylenedioxymethamphetamine and cocaine acute treatment in mice brain

Drugs of abuse induce alterations in cytoskeletal and cytoskeleton associated genes in several brain areas. We have previously shown that acute MDMA regulates the mRNA level of Rnd3, a Rho GTPase involved in actin cytoskeleton regulation, in mice striatum. In this study we investigated the effects of single administration of cocaine, another psychostimulant with a slightly different mechanism of action, on the mRNA levels of the three members of the Rnd genes family (Rnd1, Rnd2 and Rnd3). Mice were treated with either MDMA (9 mg/kg) or cocaine (20 mg/jg) and brain samples (i.e. hippocampus, striatum and prefrontal cortex) were processed for quantitative real-time PCR assay 1, 2, 4 and 6 h after the injections. The expression level of Rnd2 was differentially affected depending on the drug, brain area and time point after injection. Interestingly the two drugs up-regulate Rnd3 gene expression in the three structures tested with some differences in the timing. The effects of MDMA on Rnd3 appear earlier in the hippocampus as compared to cocaine, while it is the opposite in the prefrontal cortex. However, in the dorsal striatum, the two drugs induce an early and significant up-regulation of Rnd3 expression that is longer-lasting in the case of MDMA. In the case of cocaine contrarily to what was observed with MDMA, this modulation could not be blocked with the ERK activation inhibitor SL327 suggesting that the two drugs lead to the same effect on Rnd3 by two distinct pathways.

Intermittent administration of morphine alters protein expression in rat nucleus accumbens

Repeated exposure to drugs of abuse causes time-dependent neuroadaptive changes in the mesocorticolimbic system of the brain that are considered to underlie the expression of major behavioral characteristics of drug addiction. We used a 2-D gel-based proteomics approach to examine morphine-induced temporal changes in protein expression and/or PTM in the nucleus accumbens (NAc) of morphine-sensitized rats. Rats were pretreated with saline [1 mL/kg subcutaneously (s.c.)] or morphine (10 mg/kg, s.c.) once daily for 14 days and the animals were decapitated 1 day later. The NAc was extracted and proteins resolved by 2-DE. Several protein functional groups were found to be regulated in the morphine-treated group, representing cytoskeletal proteins, proteins involved in neurotransmission, enzymes involved in energy metabolism and protein degradation, and a protein that regulates translation.

Neurofilament phosphoforms: surrogate markers for axonal injury, degeneration and loss

This review on the role of neurofilaments as surrogate markers for axonal degeneration in neurological diseases provides a brief background to protein synthesis, assembly, function and degeneration. Methodological techniques for quantification are described and a protein nomenclature is proposed. The relevance for recognising anti-neurofilament autoantibodies is noted. Pathological implications are discussed in view of immunocytochemical, cell-culture and genetic findings. With reference to the present symposium on multiple sclerosis, the current literature on body fluid levels of neurofilaments in demyelinating disease is summarised.

Glial fibrillary acidic protein mRNA levels in the cingulate cortex of individuals with depression, bipolar disorder and schizophrenia

Recent studies have shown a decrease in glial number and glial fibrillary acidic protein (GFAP) levels in the frontal and cingulate cortices of individuals with mood disorders and schizophrenia. In an attempt to verify and expand these findings we examined GFAP messenger ribonucleic acid (mRNA) levels in postmortem sections of the anterior cingulate cortex (ACC) from the Stanley Neuropathology Consortium (SNC). The consortium consists of 15 cases in each of four groups (schizophrenia, bipolar disorder, non-psychotic depression and unaffected controls). By in situ hybridization, we found higher levels of GFAP mRNA in white matter and at the pial surface as compared with gray matter levels in all cases. In the white matter of ACC we detected a significant effect of diagnosis (P<0.04) with GFAP mRNA levels decreased in individuals with schizophrenia and bipolar disorder as compared with normal controls. In the gray matter there was a significant effect of layer (P<0.01) with the highest levels of GFAP mRNA in layer VI in all groups. As in the white matter, the mean GFAP mRNA levels were decreased in individuals with schizophrenia and bipolar disorder as compared with the unaffected controls, however the difference failed to reach statistical significance. Thus, astrocytes positive for GFAP may contribute to the decrease in glial density previously described in subjects with major mental illness, however the relative contribution of astrocytes may vary with diagnosis.

Proteomic analysis of phosphotyrosyl proteins in morphine-dependent rat brains

Morphine has been used as a potent analgesic, having a high propensity to induce tolerance and physical dependence following their repeated administration. Although the mechanisms that underlie the development of dependence on morphine remain unclear, previous studies suggested that phosphorylations of diverse types of cellular proteins are crucial determinants of the neuroadaptive mechanisms associated with morphine dependence. Thus, understanding global phosphorylation events induced by chronic morphine administration is essential for understanding the complex signaling mechanisms of morphine dependence. This study characterized the alteration of tyrosine phosphorylation of frontal cortical proteins in morphine-dependent rat brains using a proteomic approach. Dependence was produced by continuous intracerebroventricular (i.c.v.) infusion of morphine (26 nmol/microl/h) for 72 h via osmotic minipumps in rats. Phosphotyrosyl (p-Tyr) protein spots in brain frontal cortical regions were detected by two-dimensional electrophoresis (2-DE) and immunoblotting with anti-p-Tyr-specific antibodies. The protein spots showing significant changes in tyrosine phosphorylation were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). Similar patterns of protein expression were detected by 2-DE gels in morphine-dependent and saline-treated control rat brains. However, phosphotyrosine 2-DE images of the frontal cortical proteins from saline-treated control and morphine-dependent rat brains were apparently different. The densities of most matched p-Tyr protein spots were increased in morphine-dependent rat brains compared with that of control samples. Additional p-Tyr protein spots were detected in 2-DE image of morphine-dependent rat brains. Fifty of p-Tyr protein spots, corresponding to 40 different proteins, were identified from 2-DE gels of morphine-dependent rat brains. The identified proteins include enzymes, cytoskeletal proteins, cell signaling molecules, and other proteins. In conclusion, the first available phosphotyrosine proteomic resources of morphine dependence were established using an animal model. The findings illustrate the potential of proteomics as an effective technique for studying phosphorylation events of morphine dependence in brains.

Cytoskeletal genes regulation by chronic morphine treatment in rat striatum

It has been previously suggested that morphine can regulate the expression and function of some proteins of the cytoskeleton. In the present study, we used real-time quantitative polymerase chain reaction to examine the effects of chronic morphine administration, in rat striatum, on 14 proteins involved in microtubule polymerization and stabilization, intracellular trafficking, and serving as markers of neuronal growth and degeneration. Chronic morphine treatment led to modulation of the mRNA level of seven of the 14 genes tested. Glial fibrillary acidic protein (Gfap) and activity-regulated cytoskeleton-associated protein (Arc) mRNA were upregulated, while growth associated protein (Gap43), clathrin heavy chain (Cltc), alpha-tubulin, Tau, and stathmin were downregulated. In order to determine if the regulation of an mRNA correlates with a modulation of the expression of the corresponding protein, immunoblot analyses were performed. With the exception of Gap43, the levels of Cltc, Gfap, Tau, stathmin, and alpha-tubulin proteins were found to be in good agreement with those from mRNA quantification. These results demonstrate that neuroadaptation to chronic morphine administration in rat striatum implies modifications of the expression pattern of several genes and proteins of the cytoskeleton and cytoskeleton-associated components.

Decreased expression of NEFH and PCP4/PEP19 in the prefrontal cortex of alcoholics

Patients with alcoholism exhibit behavioral adaptations to ethanol such as tolerance, dependence, and addiction. Molecular mechanisms that underlie these altered behavioral responses to ethanol are largely unclear. We have performed oligonucleotide microarray analysis in postmortem prefrontal cortices of alcoholics. Among about 12,000 genes represented on microarray, a total of 79 genes showed differential expression changes in alcoholics compared with control subjects, consisting of 54 up- and 25 down-regulated genes. Altered expressions in alcoholics were observed in genes having a wide range of biological functions. The remarkable findings were up-regulation of myelin-related genes and molecular chaperones in alcoholics. Among the genes identified, decreased expressions of NEFH and PCP4/PEP19 were further examined. NEFH encodes a component of neurofilament protein in neurons. PCP4/PEP19 encodes protein involved in calcium signaling and neuronal apoptosis. Observation of their down-regulations in alcoholics in microarray analysis was confirmed by real-time quantitative RT-PCR, and was also confirmed in the independent set of postmortem brains of alcoholics. The present results may provide some insights into understanding the mechanism of ethanol-induced altered behavioral responses at the molecular level.

Long-term regulation of signalling components of adenylyl cyclase and mitogen-activated protein kinase in the pre-frontal cortex of human opiate addicts

Opiate addiction involves the development of chronic adaptive changes in micro -opioid receptors and associated pathways (e.g. cAMP signalling) which lead to neuronal plasticity in the brain. This study assessed the status of cAMP and mitogen-activated protein kinase (MAPK) pathways in brains (pre-frontal cortex) of chronic opiate addicts. In these subjects (n = 24), the immunodensities of adenylyl cyclase-I, PKA Calpha, total and phosphorylated CREB were not different from those in sex-, age- and PMD-matched controls. Moreover, the ratio pCREB/tCREB was similar in opiate addicts (0.74) and controls (0.76), further indicating that opiate addiction in humans is not associated with an upregulation of several key components of cAMP signalling in the pre-frontal cortex. In contrast, the components of MAPK cascade (Ras/c-Raf-1/MEK/ERK) were decreased in the same brains. Notably, pronounced downregulations of phosphorylated MEK (85%) and ERK1/2 (pERK1: 81%; pERK2: 80%) were quantitated in brains of opiate addicts. Chronic morphine treatment in rats (10-100 mg/kg for 5 days) was also associated with decreases of pERK1/2 (59-68%) in the cortex. In SH-SY5Y cells, morphine also stimulated the activity of pERK1/2 (2.5-fold) and the MEK inhibitor PD98059 blocked this effect (90%). The abnormalities of MAPK signalling might have important consequences in the long term development of various forms of neural plasticity associated with opiate addiction in humans.

Neurofilament proteins and cAMP pathway in brains of mu-, delta- or kappa-opioid receptor gene knock-out mice: effects of chronic morphine administration

Opiate addiction is associated with abnormalities of neurofilament (NF) proteins and upregulation of cAMP signaling in the brain, which may modulate neuronal plasticity. This study investigated, using gene-targeted mice lacking mu-, delta- or kappa-opioid receptors, the role of these receptors in modulating the basal activity and the chronic effects of morphine on both intracellular targets. In WT mice, chronic treatment (5 days) with morphine (20-100 mg/kg) resulted in decreases in the immunodensity of neurofilament (NF)-L in the cerebral cortex (14-23%). In contrast, chronic morphine did not decrease NF-L in cortices of mu-, delta-, and kappa-KO mice, suggesting the involvement of the three types of opioid receptors in this effect of morphine. Also, the marked increase in phosphorylated NF-H induced by chronic morphine in WT mice (two-fold) was abolished in mu -KO mice. In cortex and/or striatum of mu-, delta- and kappa-KO mice, the basal immunodensities of Galphai1/2 proteins, the catalytic isoform (Calpha) of protein kinase A (PKA) and the total content of cAMP response element-binding protein (CREB, the nuclear target of PKA) were not different from those of WT mice. In contrast, phosphorylated CREB (the active form of this transcription factor) was reduced in cortex and/or striatum (23-26%) of mu- and delta-KO mice, but not in kappa-KO animals. These results suggest that the endogenous opioid tone acting on mu-/delta-receptors tonically stimulate CREB activation in the brain. In cortex and/or striatum of WT mice, chronic morphine did not induce upregulation of the main components of the cAMP signaling pathway. In contrast, chronic morphine treatment in mu-KO mice, but not in delta- or kappa-KO, resulted in a paradoxical upregulation of Galphai1/2 (12-19%), PKA (19-21%,) and phosphorylated CREB (21-73%), but not total CREB, in cortex and/or striatum. The induction of heterologous receptor adaptations in mu-KO mice may explain this paradoxical effect of morphine.

Decreased immunodensities of micro-opioid receptors, receptor kinases GRK 2/6 and beta-arrestin-2 in postmortem brains of opiate addicts

The homologous regulation of opioid receptors, through G protein-coupled receptor kinases (GRKs) and beta-arrestins, is an initial step in the complex molecular mechanisms leading to opiate tolerance and dependence. This study was designed to evaluate in parallel the contents of immunolabeled micro-opioid receptors (glycosylated proteins), two representative GRKs (GRK 2 and GRK 6) and beta-arrestin-2 in brains of opiate addicts who had died of an opiate overdose (heroin or methadone). The immunodensities of micro-opioid receptors were decreased (66 kDa protein: 24%, n=24, P<0.0001; 85 kDa protein: 16%, n=24, P<0.05) in the prefrontal cortex of opiate addicts compared with sex-, age-, and PMD-matched controls. This down-regulation of brain micro-opioid receptors was more pronounced in opiate addicts dying of a heroin overdose (27-30%, n=13) than in those who died of a methadone overdose (5-16%, n=11). In the same brains, significant decreases in the immunodensities of GRK 2 (19%, n=24, P<0.05), GRK 6 (25%, n=24, P<0.002) and beta-arrestin-2 (22%, n=24, P< 0.0005) were also quantitated. In contrast, the content of alpha-internexin (a neuronal marker used as a negative control) was not changed in brains of opiate addicts. In these subjects, there was a significant correlation between the densities of GRK 6 and beta-arrestin-2 (r=0.63, n=24, P=0.001), suggesting that both proteins are regulated in a coordinated manner by opiate drugs in the brain. The results indicate that opiate addiction in humans (tolerant state) is associated with down-regulation of brain micro-opioid receptors and regulatory GRK 2/6 and beta-arrestin-2 proteins. These molecular adaptations may be relevant mechanisms for the induction of opiate tolerance in brains of opiate addicts.

Downregulation of neuronal cdk5/p35 in opioid addicts and opiate-treated rats: relation to neurofilament phosphorylation

Neuronal cyclin-dependent kinase-5 (Cdk5) and its neuron-specific activator p35 play a major role in regulating the cytoskeleton dynamics. Since opioid addiction was associated with hyperphosphorylation of neurofilament (NF) in postmortem human brains, this study was undertaken to assess the status of the cdk5/p35 complex and its relation with NF-H phosphorylation in brains of chronic opioid abusers. Decreased immunodensities of cdk5 (18%) and p35 (26-44%) were found in the prefrontal cortex of opioid addicts compared with matched controls. In the same brains, the densities of p25 (a truncated neurotoxic form of p35), phosphatase PP2Ac and mu-calpain were found unaltered. Acute treatment of rats with morphine (30 mg/kg, 2 h) increased the density of cdk5 (35%), but not that of p35, in the cerebral cortex. In contrast, chronic morphine (10-100 mg/kg for 5 days) induced marked decreases in cdk5 (40%) and p35 (47%) in rat brain. In brains of opioid addicts, the density of phosphorylated NF-H was increased (43%) as well as the ratio of phosphorylated to nonphosphorylated NF-H forms (two-fold). In these brains, phosphorylated NF-H significantly correlated with p35 (r=0.58) but not with cdk5 (r=0.03). The results suggest that opiate addiction is associated with downregulation of cdk5/p35 levels in the brain. This downregulation and the aberrant hyperphosphorylation of NF-H proteins might have important consequences in the development of neural plasticity associated with opiate addiction in humans.

Transcriptional profiling in the human prefrontal cortex: evidence for two activational states associated with cocaine abuse

CNS-focused cDNA microarrays were used to examine gene expression profiles in dorsolateral prefrontal cortex (dlPFC, Area 46) from seven individual sets of age- and post-mortem interval-matched male cocaine abusers and controls. The presence of cocaine and related metabolites was confirmed by gas chromatography-mass spectrometry. Sixty-five transcripts were differentially expressed, indicating alterations in energy metabolism, mitochondria and oligodendrocyte function, cytoskeleton and related signaling, and neuronal plasticity. There was evidence for two distinct states of transcriptional regulation, with increases in gene expression predominating in subjects testing positive for a metabolite indicative of recent 'crack' cocaine abuse and decreased expression profiles in the remaining cocaine subjects. This pattern was confirmed by quantitative polymerase chain reaction for select transcripts. These data suggest that cocaine abuse targets a distinct subset of genes in the dlPFC, resulting in either a state of acute activation in which increased gene expression predominates, or a relatively destimulated, refractory phase.

Widespread but regionally specific effects of experimenter- versus self-administered morphine on dendritic spines in the nucleus accumbens, hippocampus, and neocortex of adult rats

We studied the effects of self-administered (SA) vs. experimenter-administered (EA) morphine on dendritic spines in the hippocampal formation (CA1 and dentate), nucleus accumbens shell (NAcc-s), sensory cortex (Par1 and Oc1), medial frontal cortex (Cg3), and orbital frontal cortex (AID) of rats. Animals in the SA group self-administered morphine in 2-h sessions (0.5 mg/kg/infusion, i.v.) for an average of 22 sessions and animals in the EA group were given daily i.v. injections of doses that approximated the total session dose for matched rats in Group SA (average cumulative dose/session of 7.7 mg/kg). Control rats were given daily i.v. infusions of saline. One month after the last treatment the brains were processed for Golgi-Cox staining. In most brain regions (Cg3, Oc1, NAcc-s) morphine decreased the density of dendritic spines, regardless of mode of administration (although to a significantly greater extent in Group SA). However, only SA morphine decreased spine density in the hippocampal formation and only EA morphine decreased spine density in Par1. Interestingly, in the orbital frontal cortex morphine significantly increased spine density in both Groups SA and EA, although to a much greater extent in Group SA. We conclude: 1) Morphine has persistent (at least 1 month) effects on the density of dendritic spines in many brain regions, and on many different types of cells (medium spiny neurons, pyramidal cells, and granule cells); 2) The effect of morphine on spine density (and presumably synaptic organization) varies as a function of both brain region and mode of drug administration; and 3) The ability of morphine to remodel synaptic inputs in a regionally specific manner may account for the many different long-term sequelae associated with opioid use.

G protein-coupled receptor kinases, beta-arrestin-2 and associated regulatory proteins in the human brain: postmortem changes, effect of age and subcellular distribution

G protein-coupled receptor kinases (GRKs) and beta-arrestin-2 play a crucial role in the regulation of neurotransmitter receptors in brain. In this study, GRK2, GRK6, beta-arrestin-2 and associated regulatory proteins (Gbeta proteins and protein phosphatase (PP)-2A) were quantitated in human brains (immunodensity with specific antibodies) to assess for postmortem changes (pattern of protein degradation) and to investigate the effect of aging on these regulatory proteins as well as their subcellular distribution (cytosol and membrane fractions). In brain (prefrontal cortex, total homogenate) of healthy subjects (n=14) the immunodensities of GRK2 (r=-0.76), GRK6 (r=-0.64), beta-arrestin-2 (r=-0.57), Gbeta proteins (r=-0.59) and neurofilament (NF)-L (r=-0.64), but not PP-2A, declined markedly with the length of postmortem delay (PMD, 3-81 h). With these linear decay models, the average decreases per 12 h of PMD (from 12 to 72 h) were 7-11% for the various proteins. The immunodensities of GRK2 (r=-0.71), GRK6 (r=-0.61), and beta-arrestin-2 (r=-0.54) in human brain (n=12) also declined with aging (16 to 87 years) and the average decreases per decade (from 20 to 80 years) were 3-5%. In contrast, the immunodensities of PP-2A, Gbeta and NF-L in brain did not correlate significantly with the age of the subject at death (16-87 years). The immunodensities of GRK2/6 and beta-arrestin-2 showed marked individual variations and were strongly reduced after several freeze/thaw cycles. In the prefrontal cortex the subcellular distribution (cytosol/membrane) of the two GRKs differed markedly (GRK2: 60%/40%; GRK6: 5%/95%), and that of beta-arrestin-2 was as expected for a soluble protein (60%/40%). In brains of healthy subjects, the immunodensities of cytosolic GRK2 and beta-arrestin-2 correlated, respectively, with those of membrane-associated GRK2 (r=0.67, P=0.049, n=9) and membrane-associated beta-arrestin-2 (r=0.77, P=0.01, n=9). The results of this study emphasize the importance of examining relevant variables (PMD, age) and potential artifacts (individual variation, freeze-thawing effect) when designing signal transduction studies in neuropsychiatric disorders using the postmortem human brain.

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

1. 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. 2. The acute treatment of rats with the mu-opioid receptor agonist morphine (3-30 mg x 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 x 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. 3. Chronic morphine (10-100 mg x kg(-1), 5 days, and 10 mg x 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 x kg(-1), 13 days) did not alter the immunodensities of Fas and Bcl-2 proteins in the cerebral cortex. 4. The concurrent chronic treatment (13 days) of naloxone (10 mg x kg(-1)) and morphine (10 mg x kg(-1)) completely prevented the morphine-induced increase in Fas receptor and decrease in Bcl-2 protein immunoreactivities in the cerebral cortex. 5. 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.

Acute and chronic effects of morphine and naloxone on the phosphorylation of neurofilament-H proteins in the rat brain

Increased amounts of phosphorylated neurofilaments (pNF-H and pNF-M) are found in postmortem brains of opioid addicts. Because of the potential relevance of aberrant pNF in opioid addiction (alterations of neuronal cytoskeleton and associated functions), the effects of opiate drugs on pNF-H were investigated in rat brain. Acute morphine (30 mg/kg, 2 h) induced a marked increase in the immunodensity of pNF-H in the cerebral cortex (93%). Chronic morphine (10-100 mg/kg for 5 days) followed by opiate withdrawal resulted in a time-dependent decline in pNF-H (induction of tolerance). Thus, 2 h after the last dose of morphine, the abundance of pNF-H was still increased (27%), which was followed (6-24 h) by down-regulation of pNF-H (5% increase at 6 h; 5% decrease at 12 h, and 29% decrease at 24 h). The acute (10 mg/kg for 2 h) and chronic (2 x 10 mg/kg for 14 days) treatments with naloxone, an opioid receptor antagonist, did not alter pNF-H in the cerebral cortex, suggesting that the opioid receptors (probably the mu-type) modulating the phosphorylation state of NF-H are not tonically activated by endogenous opioids. The results indicate that morphine addiction is associated with an aberrant hyperphophorylation of NF-H in the rat brain.