Methamphetamine abstinence induces changes in μ-opioid receptor, oxytocin and CRF systems: Association with an anxiogenic phenotype

Highlights

• METH withdrawal induces anxiety-related symptoms in mice.

• METH administration and withdrawal causes neuroadaptations in the OT system.

• Persistent increase in striatal MOPr following METH treatment.

• Amygdalar c-Fos⁺/CRF⁺ neurons are increased in METH-treated/withdrawn mice.

Abstract

The major challenge in treating methamphetamine addicts is the maintenance of a drug free-state since they experience negative emotional symptoms during abstinence, which may trigger relapse. The neuronal mechanisms underlying long-term withdrawal and relapse are currently not well-understood. There is evidence suggesting a role of the oxytocin (OTR), μ-opioid receptor (MOPr), dopamine D₂ receptor (D₂R), corticotropin-releasing factor (CRF) systems and the hypothalamic-pituitary-adrenal (HPA)-axis in the different stages of methamphetamine addiction. In this study, we aimed to characterize the behavioral effects of methamphetamine withdrawal in mice and to assess the modulation of the OTR, MOPr, D₂R, CRF and HPA-axis following chronic methamphetamine administration and withdrawal. Ten-day methamphetamine administration (2 mg/kg) increased OTR binding in the amygdala, whilst 7 days of withdrawal induced an upregulation of this receptor in the lateral septum. Chronic methamphetamine treatment increased plasma OT levels that returned to control levels following withdrawal. In addition, methamphetamine administration and withdrawal increased striatal MOPr binding, as well as c-Fos⁺/CRF⁺ neuronal expression in the amygdala, whereas an increase in plasma corticosterone levels was observed following METH administration, but not withdrawal. No differences were observed in the D₂R binding following METH administration and withdrawal. The alterations in the OTR, MOPr and CRF systems occurred concomitantly with the emergence of anxiety-related symptoms and the development of psychomotor sensitization during withdrawal. Collectively, our findings indicate that chronic methamphetamine use and abstinence can induce brain-region specific neuroadaptations of the OTR, MOPr and CRF systems, which may, at least, partly explain the withdrawal-related anxiogenic effects.

Introduction

Methamphetamine (METH) is a potent psychostimulant drug with a high prevalence of worldwide abuse (Eslami-Shahrbabaki et al., 2015). Chronic METH use has been shown to induce emotional impairment including anxiety and depression, as well as psychotic behaviors in humans (see Panenka et al., 2013). Even after long-term abstinence from METH use, former addicts suffer from cognitive and emotional symptoms, which may act as a motivational trigger to re-administer the drug and relapse (Zorick et al., 2010). Currently, there is no effective pharmacotherapy for the treatment of METH addiction.

Although several mechanisms have been suggested, the mechanisms underpinning METH addiction/withdrawal and its behavioral and emotional consequences remain unclear. Recent evidence has implicated the oxytocin (OT) system in the modulation of several METH addiction processes (see McGregor and Bowen, 2012). In particular, pre-clinical studies in rodents showed that intracerebroventricular (i.c.v.) OT administration reduces METH-induced hyper-locomotion (Qi et al., 2008) and intra-nucleus accumbens core (AcbC) oxytocin administration attenuates METH-induced conditioned place preference (CPP) (Baracz et al., 2012). Moreover, i.c.v. administration of oxytocin facilitated the extinction of METH-induced CPP and i.c.v (Qi et al., 2009). as well as intra-hippocampal and intra-medial prefrontal cortex (Han et al., 2014) administration of OT prevented stress-induced reinstatement of METH-seeking. Similarly, intra-AcbC (Baracz et al., 2014), as well as peripheral (Carson et al., 2010, Cox et al., 2013) administration of OT attenuated METH-primed reinstatement in rodents. In addition, Hicks et al. (2014) showed that a 10-day oxytocin administration during adolescence was able to decrease the motivation to self-administer METH and to attenuate priming-induced reinstatement of METH-seeking during adulthood in rats. The involvement of the oxytocinergic system in METH addiction is also supported by biochemical findings showing that systemic administration of OT decreases METH-induced enhancement in Fos expression in the subthalamic nucleus and AcbC in rats (see McGregor and Bowen, 2012) and that OTR binding is increased in the amygdala following a 10-day METH administration regimen in mice (Zanos et al., 2014b). Together, these findings provide evidence for a key role of OT in METH addiction and highlight OT's “antireward/anticraving” and relapse prevention potential in METH addiction.

A possible mechanism underlying the effects of OT on METH addiction might involve its direct effects on the dopaminergic system in the brain. Indeed, it has been shown that systemic OT administration directly facilitates dopamine turnover in the striatum of treatment-naïve and cocaine-treated rats (see Sarnyai and Kovacs, 1994). Furthermore, Qi et al. (2008) demonstrated that i.c.v OT administration reduces METH-induced increase in dopamine turnover in the striatum of mice. Since METH use has been associated with lower levels of dopamine D₂ receptor (D₂R) availability in striatum (Wang et al., 2012), and OTR are co-localized and functionally interact with D₂R in striatum (Romero-Fernandez et al., 2013), it can be postulated that these two receptor systems might functionally interact to also regulate several METH addiction processes.

Numerous studies have also implicated the CRF system in METH addiction. CRF mRNA levels are increased in Acb following a single METH injection (Martin et al., 2012). Likewise, increased CRF levels were observed in the amygdala and plasma of rats undergoing withdrawal from METH self-administration (Nawata et al., 2012). Furthermore, administration of a non-selective CRF receptor antagonist attenuated stress-induced reinstatement of METH-seeking (Nawata et al., 2012) and administration of CRF-R₁ antagonists decreased both cue-and priming-induced reinstatement of METH-seeking (Moffett and Goeders, 2007). Interestingly, alterations in the CRF system have been shown to be associated with increased anxiety-like behavior and stress-induced reinstatement of METH-seeking in rodents (Nawata et al., 2012), indicating that the CRF system might be involved in the behavioral consequences of METH addiction, including anxiety and stress. CRF is considered as an important integrator of the hypothalamic-pituitary-adrenal (HPA) axis in the modulation of stress responses (Bale et al., 2002). METH administration has been also shown to induce a dysregulation of the HPA axis. Specifically, adolescent METH users have higher cortisol levels following exposure to stress (King et al., 2010) and METH administration increases plasma corticosterone levels in rodents (Grace et al., 2010).

The MOPr system has been also shown to be involved in METH addiction processes. In particular, MOPr knockout mice exhibit decreased METH-induced hyper-locomotion and stereotypy and do not manifest behavioral sensitization to METH (Shen et al., 2010). Chiu et al. (2006) demonstrated a down-regulation of MOPr binding in brain membranes following an 8-day withdrawal period from chronic METH administration, which was followed by a rebound increase after 21 days of withdrawal in mice suggesting involvement of the MOPr system during METH abstinence. Conversely, MOPr gene expression and protein levels were reduced in the frontal cortex of mice following long-term withdrawal from repeated METH administration (Yamamoto et al., 2011).

Therefore, in the present study we aimed to characterize the behavioral consequences of METH abstinence in a mouse model of chronic METH use and withdrawal. Specifically, we hypothesized that withdrawal from chronic METH administration induces emotional impairment (i.e., anxiety and/or depression). We then investigated whether a 10-day METH administration and 7 days of withdrawal induce alterations on the central OT, D₂R, and MOPr systems, as well as on the HPA axis and the amygdalar CRF. This study assesses a whole range of different CNS systems in a mouse model of METH abstinence. Our findings shed light into brain region-specific neuroadaptations, which might be involved in driving specific METH abstinence-induced behaviors.