Methamphetamine alters prodynorphin gene expression and dynorphin A levels in rat hypothalamus

Dynorphin/KOP and nociceptin/NOP gene expression and epigenetic changes by cocaine in rat striatum and nucleus accumbens

Cocaine induces neurochemical changes of endogenous prodynorphin-kappa opioid receptor (pDYN-KOP) and pronociceptin/orphaninFQ-nociceptin receptor (pN/OFQ-NOP) systems. Both systems play an important role in rewarding mechanisms and addictive stimulus processing by modulating drug-induced dopaminergic activation in the mesocortico-limbic brain areas. They are also involved in regulating stress mechanisms related to addiction. The aim of this study was to investigate possible changes of gene expression of the dynorphinergic and nociceptinergic system components in the nucleus accumbens (NA) and in medial and lateral caudate putamen (mCPu and lCPu, respectively) of rats, following chronic subcutaneous infusion of cocaine. In addition, the epigenetic histone modifications H3K4me3 and H3K27me3 (an activating and a repressive marker, respectively) at the promoter level of the pDYN, KOP, pN/OFQ and NOP genes were investigated. Results showed that cocaine induced pDYN gene expression up-regulation in the NA and lCPu, and its down-regulation in the mCPu, whereas KOP mRNA levels were unchanged. Moreover, cocaine exposure decreased pN/OFQ gene expression in the NA and lCPu, while NOP mRNA levels appeared significantly increased in the NA and decreased in the lCPu. Specific changes of the H3K4me3 and H3K27me3 levels were found at pDYN, pN/OFQ, and NOP gene promoter, consistent with the observed gene expression alterations. The present findings contribute to better define the role of endogenous pDYN-KOP and pN/OFQ-NOP systems in neuroplasticity mechanisms following chronic cocaine treatment. The epigenetic histone modifications underlying the gene expression changes likely mediate the effects of cocaine on transcriptional regulation of specific gene promoters that result in long-lasting drug-induced plasticity.

Alteration of synaptic activity-regulating genes underlying functional improvement by long-term exposure to an enriched environment in the adult brain

BACKGROUND

Housing animals in an enriched environment (EE) enhances behavioral function. However, the mechanism underlying this EE-mediated functional improvement and the resultant changes in gene expression have yet to be elucidated.

OBJECTIVES

We attempted to investigate the underlying mechanisms associated with long-term exposure to an EE by evaluating gene expression patterns.

METHODS

We housed 6-week-old CD-1 (ICR) mice in standard cages or an EE comprising a running wheel, novel objects, and social interaction for 2 months. Motor and cognitive performances were evaluated using the rotarod test and passive avoidance test, and gene expression profile was investigated in the cerebral hemispheres using microarray and gene set enrichment analysis (GSEA).

RESULTS

In behavioral assessment, an EE significantly enhanced rotarod performance and short-term working memory. Microarray analysis revealed that genes associated with neuronal activity were significantly altered by an EE. GSEA showed that genes involved in synaptic transmission and postsynaptic signal transduction were globally upregulated, whereas those associated with reuptake by presynaptic neurotransmitter transporters were downregulated. In particular, both microarray and GSEA demonstrated that EE exposure increased opioid signaling, acetylcholine release cycle, and postsynaptic neurotransmitter receptors but decreased Na+ / Cl- -dependent neurotransmitter transporters, including dopamine transporter Slc6a3 in the brain. Western blotting confirmed that SLC6A3, DARPP32 (PPP1R1B), and P2RY12 were largely altered in a region-specific manner.

CONCLUSION

An EE enhanced motor and cognitive function through the alteration of synaptic activity-regulating genes, improving the efficient use of neurotransmitters and synaptic plasticity by the upregulation of genes associated with postsynaptic receptor activity and downregulation of presynaptic reuptake by neurotransmitter transporters.

The orexin-1 receptor antagonist SB-334867 decreases sympathetic responses to a moderate dose of methamphetamine and stress

We recently discovered that inhibiting neurons in the dorsomedial hypothalamus (DMH) attenuated hyperthermia, tachycardia, hypertension, and hyperactivity evoked by the substituted amphetamine 3, 4-methylenedioxymethamphetamine (MDMA). Neurons that synthesize orexin are also found in the region of the DMH. As orexin and its receptors are involved in the regulation of heart rate and temperature, they would seem to be logical candidates as mediators of the effects evoked by amphetamines. The goal of this study was to determine if blockade of orexin-1 receptors in conscious rats would suppress cardiovascular and thermogenic responses evoked by a range of methamphetamine (METH) doses. Male Sprague-Dawley rats (n=6 per group) were implanted with telemetric transmitters measuring body temperature, heart rate, and mean arterial pressure. Animals were randomized to receive pretreatment with either the orexin-1 receptor antagonist SB-334867 (10mg/kg) or an equal volume of vehicle. Thirty minutes later animals were given intraperitoneal (i.p.) injections of either saline, a low (1mg/kg), moderate (5mg/kg) or high (10mg/kg) dose of METH. Pretreatment with SB-334867 significantly attenuated increases in body temperature and mean arterial pressure evoked by the moderate but not the low or high dose of METH. Furthermore, animals treated with SB-334867, compared to vehicle, had lower temperature and heart rate increases after the stress of an i.p. injection. In conclusion, temperature and cardiovascular responses to a moderate dose of METH and to stress appear to involve orexin-1 receptors. The failure to affect a low and a high dose of METH suggests a complex pharmacology dependent on dose. A better understanding of this may lead to the knowledge of how monoamines influence the orexin system and vice versa.

Regulation of opioid gene expression in the rat brainstem by 3,4-methylenedioxymethamphetamine (MDMA): role of serotonin and involvement of CREB and ERK cascade

The amphetamine analogue 3,4-methylendioxymetamphetamine (MDMA, Ecstasy) causes complex adaptations at the molecular and cellular levels altering the activity of different brain neurotransmitters. The present study aims to verify the effects of single and repeated injections of MDMA on dynorphin and nociceptin systems gene regulation in the brainstem, an area rich in neurons containing serotonin. Both acute and chronic (twice a day for 7 days) MDMA (8 mg/kg) induced a marked increase in prodynorphin mRNA levels as well as in cAMP response element-binding protein (CREB) and extracellular signal-regulated kinase-1/2 (ERK1/2) phosphorylation, without causing any effect on kappa opioid receptor or nociceptin system (both pronociceptin and its receptor) genes expression, in this brain region. The blockade of 5HT1/5HT2 receptors by methysergide abolished the acute MDMA-induced increase in prodynorphin. Moreover, the concomitant chronic administration of both methysergide and MDMA (7 days) induced a significant increase in all the dynorphin or nociceptin system genes expression and in CREB and ERK phosphorylation. Our data suggest the involvement of dynorphin in the effects evoked by MDMA in the brainstem, possibly via CREB and ERK1/2 cascade activation, since the ERK inhibitor PD98059 prevented the MDMA-induced prodynorphin gene expression, and, acutely, also through the involvement of serotoninergic mechanisms. Chronically, it is also possible to hypothesize a general inhibitor role of serotonin in the effects evoked by MDMA. Moreover, these findings strengthen the hypothesis, already proposed, of a neuroprotective role for both CREB and dynorphin.

Reward processing by the opioid system in the brain

The opioid system consists of three receptors, mu, delta, and kappa, which are activated by endogenous opioid peptides processed from three protein precursors, proopiomelanocortin, proenkephalin, and prodynorphin. Opioid receptors are recruited in response to natural rewarding stimuli and drugs of abuse, and both endogenous opioids and their receptors are modified as addiction develops. Mechanisms whereby aberrant activation and modifications of the opioid system contribute to drug craving and relapse remain to be clarified. This review summarizes our present knowledge on brain sites where the endogenous opioid system controls hedonic responses and is modified in response to drugs of abuse in the rodent brain. We review 1) the latest data on the anatomy of the opioid system, 2) the consequences of local intracerebral pharmacological manipulation of the opioid system on reinforced behaviors, 3) the consequences of gene knockout on reinforced behaviors and drug dependence, and 4) the consequences of chronic exposure to drugs of abuse on expression levels of opioid system genes. Future studies will establish key molecular actors of the system and neural sites where opioid peptides and receptors contribute to the onset of addictive disorders. Combined with data from human and nonhuman primate (not reviewed here), research in this extremely active field has implications both for our understanding of the biology of addiction and for therapeutic interventions to treat the disorder.

Hippocampal dynorphin immunoreactivity increases in response to gonadal steroids and is positioned for direct modulation by ovarian steroid receptors

The hippocampal formation (HF) is involved in modulating learning related to drug abuse. While HF-dependent learning is regulated by both endogenous opioids and estrogen, the interaction between these two systems is not well understood. The mossy fiber (MF) pathway formed by dentate gyrus (DG) granule cell axons is involved in some aspects of learning and contains abundant amounts of the endogenous opioid peptide dynorphin (DYN). To examine the influence of ovarian steroids on DYN expression, we used quantitative light microscopic immunocytochemistry to measure DYN levels in normal cycling rats as well as in two established models of hormone-treated ovariectomized (OVX) rats. Rats in estrus had increased levels of DYN-immunoreactivity (ir) in the DG and certain CA3 lamina compared with rats in proestrus or diestrus. OVX rats exposed to estradiol for 24 h showed increased DYN-ir in the DG and CA3, while those with 72 h estradiol exposure showed increases only in the DG. Six hours of estradiol exposure produced no change in DYN-ir. OVX rats chronically implanted with medroxyprogesterone also showed increased DYN-ir in the DG and CA3. Next, dual-labeling electron microscopy (EM) was used to evaluate the subcellular relationships of estrogen receptor (ER) alpha-, ERbeta and progestin receptor (PR) with DYN-labeled MFs. ERbeta-ir was in some DYN-labeled MF terminals and smaller terminals, and had a subcellular association with the plasmalemma and small synaptic vesicles. In contrast, ERalpha-ir was not in DYN-labeled terminals, although some DYN-labeled small terminals synapsed on ERalpha-labeled dendritic spines. PR labeling was mostly in CA3 axons, some of which were continuous with DYN-labeled terminals. These studies indicate that ovarian hormones can modulate DYN in the MF pathway in a time-dependent manner, and suggest that hormonal effects on the DYN-containing MF pathway may be directly mediated by ERbeta and/or PR activation.

Chronic and acute effects of 3,4-methylenedioxy-N-methylamphetamine ('Ecstasy') administration on the dynorphinergic system in the rat brain

The prodynorphin system is implicated in the neurochemical mechanism of psychostimulants. Exposure to different drugs of abuse can induce neuroadaptations in the brain and affect opioid gene expression. The present study aims to examine the possibility of a common neurobiological substrate in drug addiction processes. We studied the effects of single and repeated 3,4-methylenedioxy-N-methylamphetamine ('Ecstasy') on the gene expression of the opioid precursor prodynorphin, and on the levels of peptide dynorphin A in the rat brain. Acute (8 mg/kg, intraperitoneally) 3,4-methylenedioxy-N-methylamphetamine markedly raised, two hours later, prodynorphin mRNA levels in the prefrontal cortex, and in the caudate putamen, whereas it decreased gene expression in the ventral tegmental area. Chronic (8 mg/kg, intraperitoneally, twice a day for 7 days) 3,4-methylenedioxy-N-methylamphetamine increased prodynorphin mRNA in the nucleus accumbens, hypothalamus and caudate putamen and decreased it in the ventral tegmental area. Dynorphin A levels increased after chronic treatment in the ventral tegmental area and decreased after acute treatment in the nucleus accumbens, prefrontal cortex and hypothalamus. These findings confirm the role of the dynorphinergic system in mediating the effects of drugs of abuse, such as 3,4-methylenedioxy-N-methylamphetamine, in various regions of the rat brain, which may be important sites for the opioidergic mechanisms activated by addictive drugs.

Concomitant loss of dynorphin, NARP, and orexin in narcolepsy

BACKGROUND

Narcolepsy with cataplexy is associated with a loss of orexin/hypocretin. It is speculated that an autoimmune process kills the orexin-producing neurons, but these cells may survive yet fail to produce orexin.

OBJECTIVE

To examine whether other markers of the orexin neurons are lost in narcolepsy with cataplexy.

METHODS

We used immunohistochemistry and in situ hybridization to examine the expression of orexin, neuronal activity-regulated pentraxin (NARP), and prodynorphin in hypothalami from five control and two narcoleptic individuals.

RESULTS

In the control hypothalami, at least 80% of the orexin-producing neurons also contained prodynorphin mRNA and NARP. In the patients with narcolepsy, the number of cells producing these markers was reduced to about 5 to 10% of normal.

CONCLUSIONS

Narcolepsy with cataplexy is likely caused by a loss of the orexin-producing neurons. In addition, loss of dynorphin and neuronal activity-regulated pentraxin may contribute to the symptoms of narcolepsy.

Endogenous opiates: 1999

This paper is the twenty-second installment of the annual review of research concerning the opiate system. It summarizes papers published during 1999 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunologic responses.