Methamphetamine differentially regulates hippocampal glucocorticoid and mineralocorticoid receptor mRNAs in Fischer and Lewis rats

Role of aldosterone and mineralocorticoid receptor (MR) in addiction: A scoping review

Preclinical and human studies suggest a role of aldosterone and mineralocorticoid receptor (MR) in addiction. This scoping review aimed to summarize (1) the relationship between alcohol and other substance use disorders (ASUDs) and dysfunctions of the aldosterone and MR, and (2) how pharmacological manipulations of MR may affect ASUD-related outcomes. Our search in four databases (MEDLINE, Embase, Web of Science, and Cochrane Library) indicated that most studies focused on the relationship between aldosterone, MR, and alcohol (n = 30), with the rest focused on opioids (n = 5), nicotine (n = 9), and other addictive substances (n = 9). Despite some inconsistencies, the overall results suggest peripheral and central dysregulations of aldosterone and MR in several species and that these dysregulations depended on the pattern of drug exposure and genetic factors. We conclude that MR antagonism may be a promising target in ASUD, yet future studies are warranted.

Striatal miR-183-5p inhibits methamphetamine-induced locomotion by regulating glucocorticoid receptor signaling

MicroRNA (miRNA)-mediated striatal gene regulation may play an important role in methamphetamine (METH) addiction. This study aimed to identify changes in novel miRNAs and their target genes during METH self-administration and investigate their roles in METH-induced locomotion. RNA sequencing analysis revealed that mir-183-5p was upregulated in the striatum of METH self-administered rats, and target gene prediction revealed that the glucocorticoid receptor (GR) gene, Nr3c1, was a potential target gene for mir-183-5p. We confirmed that single and repeated METH administrations increased METH-induced locomotion and plasma corticosterone levels in rats. Additionally, increased miR-185-5p expression and decreased GR gene expression were observed only in the repeated-METH-injection group but not in the single-injection group. We then investigated the effects of miR-183-5p on METH-induced locomotion using a miR-183-5p mimic and inhibitor. Injection of a mir-183-5p mimic in the striatum of rats attenuated METH-induced locomotion, whereas injection of a miR-183-5p inhibitor enhanced the locomotor activity in METH-administered rats. Furthermore, the miR-183-5p mimic reduced the phosphorylation of tyrosine hydroxylase (TH) whereas the inhibitor increased it. Taken together, these results indicate that repeated METH injections increase striatal miR-183-5p expression and regulate METH-induced locomotion by regulating GR expression in rats, thereby suggesting a potential role of miR-183-5p as a novel regulator of METH-induced locomotion.

Prevention of relapse to methamphetamine self-administration by environmental enrichment: involvement of glucocorticoid receptors

RATIONALE

In rodents, environmental enrichment (EE) produces both preventive and curative effects on drug addiction, and this effect is believed to depend at least in part on EE's actions on the stress system.

OBJECTIVES

This study investigated whether exposure to EE during abstinence reduces methamphetamine seeking after extended self-administration. In addition, we investigated whether these effects are associated with alterations in the levels of glucocorticoid receptors (GR) in the brain and whether administration of GR antagonists blocks methamphetamine relapse.

METHODS

We allowed rats to self-administer methamphetamine for twenty 14-h sessions. After 3 weeks of abstinence either in standard (SE) or EE conditions, we measured methamphetamine seeking in a single 3-h session. Then, we used western blot techniques to measure GR levels in several brain areas. Finally, in an independent group of rats, after methamphetamine self-administration and abstinence in SE, we administered the GR antagonist mifepristone, and we investigated methamphetamine seeking.

RESULTS

Exposure to EE reduced methamphetamine seeking and reversed methamphetamine-induced increases in GR levels in the ventral and dorsal hippocampus. In addition, EE decreased GR levels in the amygdala in drug-naive animals, but this effect was prevented by previous exposure to methamphetamine. Administration of mifepristone significantly decreased methamphetamine seeking.

CONCLUSIONS

The anti-craving effects of EE are paralleled by restoration of methamphetamine-induced dysregulation of GR in the hippocampus. These results provide support for the hypothesis that the effect of EE on methamphetamine relapse is at least in part mediated by EE's action on the brain stress system.

Methamphetamine administration increases hepatic CYP1A2 but not CYP3A activity in female guinea pigs

Methamphetamine use has increased over the past decade and the first use of methamphetamine is most often when women are of reproductive age. Methamphetamine accumulates in the liver; however, little is known about the effect of methamphetamine use on hepatic drug metabolism. Methamphetamine was administered on 3 occassions to female Dunkin Hartley guinea pigs of reproductive age, mimicking recreational drug use. Low doses of test drugs caffeine and midazolam were administered after the third dose of methamphetamine to assess the functional activity of cytochrome P450 1A2 and 3A, respectively. Real-time quantitative polymerase chain reaction was used to quantify the mRNA expression of factors involved in glucocorticoid signalling, inflammation, oxidative stress and drug transporters. This study showed that methamphetamine administration decreased hepatic CYP1A2 mRNA expression, but increased CYP1A2 enzyme activity. Methamphetamine had no effect on CYP3A enzyme activity. In addition, we found that methamphetamine may also result in changes in glucocorticoid bioavailability, as we found a decrease in 11β-hydroxysteroid dehydrogenase 1 mRNA expression, which converts inactive cortisone into active cortisol. This study has shown that methamphetamine administration has the potential to alter drug metabolism via the CYP1A2 metabolic pathway in female guinea pigs. This may have clinical implications for drug dosing in female methamphetamine users of reproductive age.

Hypothalamic-pituitary-adrenal axis responsiveness to methamphetamine is modulated by gonadectomy in males

Sex differences in patterns of methamphetamine (MA) abuse have been reported with females (humans and rodents) showing an elevated addiction phenotype. Previous findings indicate MA-induced hypothalamic-pituitary-adrenal (HPA) axis activation is also sexually dimorphic with females exhibiting an elevated glucocorticoid release and differential neural activation patterns within HPA axis-associated brain regions. These effects may contribute to sex differences in abuse. To determine the role of gonadal hormones in mediating sex differences in MA-induced glucocorticoids, male and female C57BL/6J mice were gonadectomized or sham-operated, and following recovery, injected with MA (5mg/kg) and sacrificed 60min or 120min later. Blood was collected for corticosterone radioimmunoassay, and brains were used to assess c-Fos, and c-Fos co-localization with glucocorticoid receptor (GR). At 120min after MA injection, corticosterone levels were elevated in females compared to males and gonadectomy in males increased corticosterone to female levels. C-Fos was greater in females than males in the medial preoptic area, bed nucleus of the stria terminalis, basolateral amygdala, and central amygdala. Female gonadectomy had little effect on either corticosterone or c-Fos, while male gonadectomy elevated c-Fos in the central amygdala. Relative to sham males, gonadectomized males also showed decreased c-Fos/GR cell number in the CA3 hippocampal area compared to sham males, indicating a central site for attenuated negative feedback. Together, these findings indicate that androgens regulate MA-induced activation of the HPA axis, potentially by enhancing negative feedback. These sex and gonadal hormone effects on the HPA axis may contribute to sex differences in MA abuse patterns.

Immediate and lasting effects of chronic daily methamphetamine exposure on activation of cells in hypothalamic-pituitary-adrenal axis-associated brain regions

RATIONALE

Chronic methamphetamine (MA) abuse leads to dependence and symptoms of withdrawal after use has ceased. Negative mood states associated with withdrawal, as well as drug reinstatement, have been linked to drug-induced disruption of the hypothalamic-pituitary-adrenal (HPA) axis. However, effects of chronic MA exposure or acute MA exposure following withdrawal on neural activation patterns within brain regions that regulate the HPA axis are unknown.

OBJECTIVES

In this study, neural activation patterns were assessed by quantification of c-Fos protein in mice exposed to different regimens of MA administration.

METHODS

(Experiment 1) Adult male mice were treated with MA (5 mg/kg) or saline once or once daily for 10 days. (Experiment 2) Mice were treated with MA or saline once daily for 10 days and following a 10-day withdrawal period were re-administered a final dose of MA or saline. c-Fos was quantified in brains after the final injection.

RESULTS

(Experiment 1) Compared to exposure to a single dose of MA (5 mg/kg), chronic MA exposure decreased the number of c-Fos expressing cells in the paraventricular hypothalamus, dorsomedial hypothalamus, central amygdala, basolateral amygdala, bed nucleus of the stria terminalis (BNST), and CA3 hippocampal region. (Experiment 2) Compared to mice receiving their first dose of MA, mice chronically treated with MA, withdrawn, and re-administered MA, showed decreased c-Fos expressing cells within the central and basolateral amygdala, BNST, and CA3.

CONCLUSIONS

HPA axis-associated amygdala, extended amygdala, and hippocampal regions endure lasting effects following chronic MA exposure and therefore may be linked to stress-related withdrawal symptoms.

Methamphetamine and the hypothalamic-pituitary-adrenal axis

Psychostimulants such as methamphetamine (MA) induce significant alterations in the function of the hypothalamic-pituitary-adrenal (HPA) axis. These changes in HPA axis function are associated with altered stress-related behaviors and might contribute to addictive processes such as relapse. In this mini-review we discuss acute and chronic effects of MA (adult and developmental exposure) on the HPA axis, including effects on HPA axis associated genes/proteins, brain regions, and behaviors such as anxiety and depression. A better understanding of the mechanisms through which MA affects the HPA axis may lead to more effective treatment strategies for MA addiction.

Developmental methamphetamine exposure results in short- and long-term alterations in hypothalamic-pituitary-adrenal-axis-associated proteins

Developmental exposure to methamphetamine (MA) causes long-term behavioral and cognitive deficits. One pathway through which MA might induce these deficits is by elevating glucocorticoid levels. Glucocorticoid overexposure during brain development can lead to long-term disruptions in the hypothalamic-pituitary-adrenal (HPA) axis. These disruptions affect the regulation of stress responses and may contribute to behavioral and cognitive deficits reported following developmental MA exposure. Furthermore, alterations in proteins associated with the HPA axis, including vasopressin, oxytocin, and glucocorticoid receptors (GR), are correlated with disruptions in mood and cognition. We therefore hypothesized that early MA exposure will result in short- and long-term alterations in the expression of HPA axis-associated proteins. Male mice were treated with MA (5 mg/kg daily) or saline from postnatal day (P) 11 to P20. At P20 and P90, mice were perfused and their brains processed for vasopressin, oxytocin, and GR immunoreactivity within HPA axis-associated regions. At P20, there was a significant decrease in the number of vasopressin-immunoreactive cells and the area occupied by vasopressin immunoreactivity in the paraventricular nucleus (PVN) of MA-treated mice, but no difference in oxytocin immunoreactivity in the PVN, or GR immunoreactivity in the hippocampus or PVN. In the central nucleus of the amygdala, the area occupied by GR immunoreactivity was decreased by MA. At P90, the number of vasopressin-immunoreactive cells was still decreased, but the area occupied by vasopressin immunoreactivity no longer differed from saline controls. No effects of MA were found on oxytocin or GR immunoreactivity at P90. Thus developmental MA exposure has short- and long-term effects on vasopressin immunoreactivity and short-term effects on GR immunoreactivity.

Methamphetamine regulation of sulfotransferase 1A1 and 2A1 expression in rat brain sections

Sulfotransferase catalyzed sulfation regulates the biological activities of various neurotransmitters/hormones and detoxifies xenobiotics. Rat sulfotransferase rSULT1A1 catalyzes the sulfation of neurotransmitters and xenobiotic phenolic compounds. rSULT2A1 catalyzes the sulfation of hydroxysteroids and xenobiotic alcoholic compounds. In this work, Western blot and real-time RT-PCR were used to investigate the effect of methamphetamine on rSULT1A1 and rSULT2A1 protein and mRNA expression in rat cerebellum, frontal cortex, hippocampus, and striatum. After 1-day treatment, significant induction of rSULT1A1 was observed only in the cerebellum; rSULT2A1 was induced significantly in the cerebellum, frontal cortex, and hippocampus. After 7 days of exposure, rSULT1A1 was induced in the cerebellum, frontal cortex, and hippocampus, while rSULT2A1 was induced significantly in all four regions. Western blot results agreed with the real-time RT-PCR results, suggesting that the induction occurred at the gene transcriptional level. Results indicate that rSULT1A1 and rSULT2A1 are expressed in rat frontal cortex, cerebellum, striatum, and hippocampus. rSULT1A1 and rSULT2A1are inducible by methamphetamine in rat brain sections in a time dependable manner. rSULT2A1 is more inducible than rSULT1A1 by methamphetamine in rat brain sections. Induction activity of methamphetamine is in the order of cerebellum>frontal cortex, hippocampus>striatum. These results suggest that the physiological functions of rSULT1A1 and rSULT2A1 in different brain regions can be affected by methamphetamine.

Strain dependent effects of prenatal stress on gene expression in the rat hippocampus

Multiple animal models have been developed to recapitulate phenotypes of the human disease, schizophrenia. A model that simulates many of the cognitive and sensory deficits of the disorder is the use of random variable prenatal stress (PS) in the rat. These deficits suggest a molecular origin in the hippocampus, a brain region that plays a role in the regulation of stress. To study both hippocampal gene expression changes in offspring of prenatally stressed dams and to address genetic variability, we used a random array of prenatal stressors in three different rat strains with diverse responses to stress: Fischer, Sprague-Dawley, and Lewis rats. Candidate genes involved in stress, schizophrenia, cognition, neurotrophic effects, and immunity were selected for assessment by real-time quantitative PCR under resting conditions and following a brief exposure to restraint stress. PS resulted in significant differences in gene expression in the offspring that were strain dependent. mRNA expression for the N-methyl-D-aspartate receptor subtype 2B (Grin2b) was increased, and tumor necrosis factor-alpha (Tnfα) transcript was decreased in PS Sprague-Dawley and Lewis rats, but not in the Fischer rats. Expression of brain-derived neurotrophic factor (Bdnf) mRNA in the hippocampus was increased after an acute stress in all controls of each strain, yet a decrease was seen after acute stress in the PS Sprague-Dawley and Lewis rats. Expression of the glucocorticoid receptor (Nr3c1) was decreased in the Fischer strain when compared to Lewis or Sprague-Dawley rats, though the Fischer rats had markedly higher α7 nicotinic receptor (Chrna7) expression. The expression differences seen in these animals may be important elements of the phenotypic differences seen due to PS and genetic background.

Methamphetamine alters expression of DNA methyltransferase 1 mRNA in rat brain

Methamphetamine, a potent and indirect dopaminergic agonist, also increases glucocorticoid hormone secretion. Glucocorticoid hormones facilitate behavioral effects of methamphetamine in rodents. Several reports suggest that glucocorticoid hormones modulate expression of DNA (cytosine-5-)-methyltransferase 1 (Dnmt1). Dnmt1 was originally recognized as being involved in DNA replication, but a recent study found high levels of Dnmt1 in rodent brains, suggesting a neuron-specific unknown function of Dnmt1. In the present study, we found subchronic methamphetamine treatment (4 mg/kg, i.p., once daily for 21 days) to induce different patterns of Dnmt1 mRNA expression in the nucleus caudatus and nucleus accumbens of two inbred rat strains, Fischer 344/N (increased Dnmt1) and Lewis/N (decreased Dnmt1). These patterns paralleled methamphetamine-induced striatal glucocorticoid receptor mRNA in these two rat strains in our previous study. Because Fischer rats have a hyperresponsive negative feedback in their hypothalamic-pituitary-adrenocortical (HPA) axis and thus a shorter duration corticosterone response to subchronic methamphetamine treatment, they were resistant to sensitizing effects of methamphetamine and their glucocorticoid receptor mRNA levels were upregulated. Lewis rats which have a hyporesponsive feedback in their HPA axis and a longer duration of corticosterone secretion with subchronic methamphetamine were prone to methamphetamine sensitization and their striatal glucocorticoid receptor mRNA levels were downregulated. Our present data suggest that methamphetamine results in differential DNA methylation as well as gene expression in the nucleus caudatus and nucleus accumbens of F344 and Lewis rats. Methamphetamine-induced differences in gene expression might be related to the contrasting susceptibilities of these rats to behavioral and neurochemical effects of methamphetamine.

Genetic susceptibility to substance dependence

Despite what is often believed, the majority of those who experiment with substances with a dependence potential do not develop dependence. However, there is a subpopulation of users that easily becomes dependent on substances, and these individuals exhibit pre-existing comorbid traits, including novelty seeking and antisocial behavior. There appears to be a genetic basis for the susceptibility to dependence and these comorbid traits. Animal studies have identified specific genes that can alter susceptibility to dependence and response to novelty. The mechanisms underlying the genetic susceptibility to dependence and response to novelty are complex, but genetic susceptibility plays a significant role in the transition from substance use to dependence and from chronic use to addiction. We discuss two models to explain how genetic variations alter dependence susceptibility. Identification of the specific genes involved in these processes would help to identify individuals that are vulnerable to dependence/addiction and to devise novel treatment strategies.

Acute and chronic continuous methamphetamine have different long-term behavioral and neurochemical consequences

We compared two different methamphetamine dosing regimens and found distinct long-term behavioral and neurochemical changes. Adult rats were treated with 1-day methamphetamine injection (3x5 mg/kg s.c., 3 h apart) or 7-day methamphetamine minipump (20 mg/kg/day s.c.). The minipump regimen models the sustained methamphetamine plasma levels in some human bingers whereas the 1-day regimen models a naive user overdose. On withdrawal days 7 and 28, rats were acutely challenged with cocaine to test for behavioral sensitization and subsequently sacrificed for caudate and accumbens dopamine tissue content. Other rats were analyzed on withdrawal days 3, 7 or 28 using voltammetry in caudate slices. On withdrawal days 7 and 28, the methamphetamine injection but not the minipump rats showed behavioral cross-sensitization to cocaine. There was no change in baseline dopamine release, reuptake or sensitivity to quinpirole in any treatment group on either withdrawal day. However, consistent with the behavioral sensitization, cocaine had a greater effect in potentiating dopamine release and in blocking dopamine reuptake in methamphetamine injection versus saline irrespective of withdrawal day. The minipump group showed tolerance to the dopamine releasing effect of cocaine on withdrawal day 28 and had lower dopamine tissue content in the caudate versus the methamphetamine injection group. Dopamine turnover as measured by the DOPAC/dopamine ratio tended to be higher in the minipump-treated rats. These data suggest that the behavioral cross-sensitization seen in the methamphetamine injection rats could be in part due to the increased potency of cocaine in blocking dopamine reuptake and in increasing dopamine release. The decreased potency of cocaine in the caudate slices from the minipump-treated group may be related to decreased dopamine tissue content.