Involvement of D1- and D2-like dopamine receptors in the dentate gyrus in the acquisition, expression, and extinction of the morphine-induced conditioned place preference in rats

The dopamine D1 receptor antagonist SCH-23390 blocks the acquisition, but not expression of mitragynine-induced conditioned place preference in rats

Mitragynine (MG) is the primary active constituent of Mitragyna speciosa Korth (kratom), a psychoactive Southeast Asian plant with potential therapeutic use. Numerous studies support roles of dopaminergic system in drug reward. However, the involvement of the dopaminergic system in mediating MG reward and drug-seeking is poorly understood. Using conditioned place preference (CPP) paradigm, the present study aims to evaluate the roles of the dopamine (DA) D1 receptor in the acquisition and expression of MG-induced CPP in rats. The effects of SCH-23390, a selective DA D1 receptor antagonist, on the acquisition of MG-induced CPP were first investigated. Rats were pre-treated systemically with SCH-23390 (0, 0.1 and 0.3 mg/kg, i.p.) prior to MG (10 mg/kg) conditioning sessions. Next, we tested the effects of the DA D1 receptor antagonist on the expression of MG-induced CPP. Furthermore, the effects of a MG-priming dose (5 mg/kg) on the reinstatement of extinguished CPP were tested. The results showed that SCH-23390 dose-dependently suppressed the acquisition of a MG-induced CPP. In contrast, SCH-23390 had no effect on the expression of a MG-induced CPP. The findings of this study suggested a crucial role of the DA D1 receptor in the acquisition, but not the expression of the rewarding effects of MG in a CPP test. Furthermore, blockade of the D1-like receptor during conditioning did not prevent MG priming effects on CPP reinstatement test, suggesting no role for the DA D1 receptor in reinstatement sensitivity.

The inhibitory effect of cannabidiol on the rewarding properties of methamphetamine in part mediates by interacting with the hippocampal D1-like dopamine receptors

Cannabidiol (CBD) is a potential treatment to decrease the rewarding properties of psychostimulants. However, the exact mechanism and distinct neuroanatomical areas responsible for the CBD's effects remain unclear. Indicatively, the D1-like dopamine receptors (D1R) in the hippocampus (HIP) are essential for expressing and acquiring drug-associated conditioned place preference (CPP). Therefore, given that involving D1Rs in reward-related behaviors and the encouraging results of CBD in attenuating the psychostimulant's rewarding effects, the present study sought to investigate the role of D1Rs of the hippocampal dentate gyrus (DG) in the inhibitory effects of CBD on the acquisition and expression of METH-induced CPP. To this end, over a 5-day conditioning period by METH (1 mg/kg; sc), different groups of rats were given intra-DG SCH23390 (0.25, 1, or 4 μg/0.5 μl, saline) as a D1Rs antagonist before ICV administration of CBD (10 μg/5 μl, DMSO12%). In addition, a different set of animals, after the conditioning period, received a single dose of SCH23390 (0.25, 1, or 4 μg/0.5 μl) before CBD (50 μg/5 μl) administration on the expression day. The results showed that SCH23390 (1 and 4 μg) significantly reduced the suppressive effects of CBD on the acquisition of METH place preference (P < 0.05 and P < 0.001, respectively). Furthermore, the highest dose of SCH23390 (4 μg) in the expression phase remarkably abolished the preventive effects of CBD on the expression of METH-seeking behavior (P < 0.001). In conclusion, the current study revealed that CBD's inhibitory effect on rewarding properties of METH partially acts through D1Rs in the DG area of the HIP.

PPARγ/Adiponectin axis attenuates methamphetamine-induced conditional place preference via the hippocampal AdipoR1 signaling pathway

Methamphetamine (METH) is a highly addictive psychostimulant. The adipocyte-derived hormone adiponectin has a broad spectrum of functions in the brain. However, limited research has been conducted on the effect of adiponectin signaling on METH-induced conditioned place preference (CPP) and knowledge of the underlying neural mechanisms is scarce. The METH induced adult male C57/BL6J mice model were used for testing the therapeutic activities of intraperitoneal injection of AdipoRon or Rosiglitazone, and AdipoR1 overexpression in hippocampal dentate gyrus (DG), and chemogenetic inhibiting the neural activity of DG, and the changes of neurotrophic factors, synaptic molecules, and glutamate receptors, and inflammatory cytokines were also measured. We found that adiponectin expression was significantly reduced in METH addicted patients and mice. Our findings also showed that injection of AdipoRon or Rosiglitazone alleviated the METH-induced CPP behavior. Moreover, the expression of AdipoR1 in the hippocampus was also reduced, and AdipoR1 overexpression blocked the development of METH-induced CPP behavior through regulatory effects on neurotrophic factors, synaptic molecules, and glutamate receptors. The observed inhibitory neural activity of the hippocampal dentate gyrus (DG) induced via a chemogenetic approach produced a therapeutic effect on the METH-induced CPP behavior. Finally, we identified an abnormal expression of some key inflammatory cytokines through the PPARγ/Adiponectin/AdipoR1 axis. This study demonstrates that adiponectin signaling is a promising diagnostic and therapeutic target for METH addiction.

The role of hippocampus in memory reactivation: an implication for a therapeutic target against opioid use disorder

Purpose of the review

The abuse of opioids induces many terrible problems in human health and social stability. For opioid-dependent individuals, withdrawal memory can be reactivated by context, which is then associated with extremely unpleasant physical and emotional feelings during opioid withdrawal. The reactivation of withdrawal memory is considered one of the most important reasons for opioid relapse, and it also allows for memory modulation based on the reconsolidation phenomenon. However, studies exploring withdrawal memory modulation during the reconsolidation window are lacking. By summarizing the previous findings about the reactivation of negative emotional memories, we are going to suggest potential neural regions and systems for modulating opioid withdrawal memory.

Recent findings

Here, we first present the role of memory reactivation in its modification, discuss how the hippocampus participates in memory reactivation, and discuss the importance of noradrenergic signaling in the hippocampus for memory reactivation. Then, we review the engagement of other limbic regions receiving noradrenergic signaling in memory reactivation. We suggest that noradrenergic signaling targeting hippocampus neurons might play a potential role in strengthening the disruptive effect of withdrawal memory extinction by facilitating the degree of memory reactivation.

Summary

This review will contribute to a better understanding of the mechanisms underlying reactivation-dependent memory malleability and will provide new therapeutic avenues for treating opioid use disorders.

Systemic administration of N-acetylcysteine during the extinction period and on the reinstatement day decreased the maintenance of morphine rewarding properties in the rats

Many animal studies and early clinical trials suggested that N-acetylcysteine (NAC) may benefit addiction treatment. The present study tried to evaluate whether chronic administration of systemic NAC during the extinction period and acute administration of systemic NAC on the reinstatement day could reduce the maintenance of the morphine rewarding properties in the conditioned place preference (CPP) paradigm in the rats. Ninety-six adult male Wistar rats (190-220 g) were examined with morphine (7 mg/kg; sc) and saline (1 mL/kg; sc) during the 3-day conditioning phase in the CPP paradigm. After the acquisition of morphine CPP, different doses of NAC were daily administered during the extinction period (5, 10, 25, and 50 mg/kg; ip), or 30 min before the CPP test on the reinstatement day (2, 5, 10, 25, and 50 mg/kg; ip). Conditioning score and locomotor activity were recorded by the video tracking system and Ethovision software after acquisition on the post-conditioning day, the extinction period, and reinstatement day. Daily NAC administration in high doses (25 and 50 mg/kg; ip) reduced extinction-responding compared with the vehicle-control group during the extinction period. Although a single injection of NAC in doses 10, 25, 50 mg/kg decreased the reinstatement of morphine-induced CPP, two lower doses (2 and 5 mg/kg) could not significantly reduce the CPP scores. These are the first data suggesting that NAC's application during the extinction period could attenuate the morphine reward-associated behaviors in the rats. Moreover, NAC could inhibit the reinstatement of morphine CPP, which adds to the growing appreciation that the NAC may have potential therapeutic use in combating morphine dependence. It can be consistent with the hypothesis of the involvement of the glutamatergic system in the pathophysiology of addiction.

Hippocampal D1-but not D2-like dopamine receptors modulate the phosphorylation of ERK in food deprivation-induced reinstatement of morphine in extinguished rats

Reinstatement to drug abuse is the most challenging issue in the treatment of addiction. Thus, knowledge of the involved neurobiological mechanisms of reinstatement is a fundamental necessity. There is substantial and crucial evidence that dopamine is implicated in motivational processes such as relapse. Our behavioral results reported that the administration of dopamine receptor antagonists inhibited reinstatement of morphine in food-deprived rats. Previous studies have indicated that the ERK pathway plays a critical role in the cellular responses to stress and reward. Therefore, the purpose of the current study was to evaluate the effect of intra-dentate gyrus administration of dopamine receptor antagonists on the phosphorylation of hippocampal ERK in the reinstatement phase of morphine reward in food-deprived rats. All groups of animals passed conditioned place preference and were bilaterally given different doses of D1- or D2-like dopamine compounds (0.25, 1 and 4 μg/0.5 μl) into the dentate gyrus. Immediately after the reinstatement phase, each animal was euthanized, and the hippocampi were immediately dissected. Then, the p-ERK/ERK ratio was evaluated using Western blot analysis. The principal findings in this study demonstrated that intra-dentate gyrus administration of the highest dose of the D1-like receptor antagonist could enhance the hippocampal p-ERK/ERK ratio in food-deprived rats while the D2-Like receptor antagonist failed to change this ratio.

Endogenous Opiates and Behavior: 2018

This paper is the forty-first consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2018 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (2), the roles of these opioid peptides and receptors in pain and analgesia in animals (3) and humans (4), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (5), opioid peptide and receptor involvement in tolerance and dependence (6), stress and social status (7), learning and memory (8), eating and drinking (9), drug abuse and alcohol (10), sexual activity and hormones, pregnancy, development and endocrinology (11), mental illness and mood (12), seizures and neurologic disorders (13), electrical-related activity and neurophysiology (14), general activity and locomotion (15), gastrointestinal, renal and hepatic functions (16), cardiovascular responses (17), respiration and thermoregulation (18), and immunological responses (19).

Effects of dopamine D1- and D2-like receptors in the CA1 region of the hippocampus on expression and extinction of morphine-induced conditioned place preference in rats

Considering the extent of drug use and its relapse rate worldwide, in the present study, we explored the role of intra-CA1 administration of D1-like and D2-like receptor antagonists on the expression and extinction of morphine-induced CPP. To induce morphine CPP, adult male Wistar rats received a daily subcutaneous injection of morphine (5 mg/kg) during a 3-day conditioning phase. Different doses of SCH23390 (0.25, 1 or 4 μg/0.5 μl saline), as a selective D1-like receptor antagonist, and sulpiride (0.25, 1, or 4 μg/0.5 μl DMSO), as a selective D2-like receptor antagonist, were bilaterally microinjected into the CA1 region in the expression and extinction phases 1 h before CPP evaluation. Conditioning scores and locomotor activities were recorded during the tests. Results indicated that the injection of the antagonists into the CA1 region dose-dependently attenuated the expression of the morphine-induced CPP and sulpiride revealed prominent behavioral results compared to SCH23390 in the expression phases. Furthermore, microinjections of SCH23390 and sulpiride shortened the extinction phase of the morphine-induced CPP without changing the locomotor activity. The results indicated the involvement of D1- and D2-like receptors within the CA1 region in the expression and extinction of rewarding properties of morphine.

Contribution of D1R-expressing neurons of the dorsal dentate gyrus and Cav1.2 channels in extinction of cocaine conditioned place preference

Cocaine-associated contextual cues can trigger relapse behavior by recruiting the hippocampus. Extinction of cocaine-associated contextual memories can reduce cocaine-seeking behavior, however the molecular mechanisms within the hippocampus that underlie contextual extinction behavior and subsequent reinstatement remain poorly understood. Here, we extend our previous findings for a role of Ca_v1.2 L-type Ca²⁺ channels in dopamine 1 receptor (D1R)-expressing cells in extinction of cocaine conditioned place preference (CPP) in adult male mice. We report that attenuated cocaine CPP extinction in mice lacking Ca_v1.2 channels in D1R-expressing cells (D1^cre, Ca_v1.2^fl/fl) can be rescued through chemogenetic activation of D1R-expressing cells within the dorsal dentate gyrus (dDG), but not the dorsal CA1 (dCA1). This is supported by the finding that Ca_v1.2 channels are required in excitatory cells of the dDG, but not in the dCA1, for cocaine CPP extinction. Examination of the role of S1928 phosphorylation of Ca_v1.2, a protein kinase A (PKA) site using S1928A Ca_v1.2 phosphomutant mice revealed no extinction deficit, likely due to homeostatic scaling up of extinction-dependent S845 GluA1 phosphorylation in the dDG. However, phosphomutant mice failed to show cocaine-primed reinstatement which can be reversed by chemogenetic manipulation of excitatory cells in the dDG during extinction training. These findings outline an essential role for the interaction between D1R, Ca_v1.2, and GluA1 signaling in the dDG for extinction of cocaine-associated contextual memories.

Image-guided cranial irradiation-induced ablation of dentate gyrus neurogenesis impairs extinction of recent morphine reward memories

Dentate gyrus adult neurogenesis is implicated in the formation of hippocampal-dependent contextual associations. However, the role of adult neurogenesis during reward-based context-dependent paradigms-such as conditioned place preference (CPP)-is understudied. Therefore, we used image-guided, hippocampal-targeted X-ray irradiation (IG-IR) and morphine CPP to explore whether dentate gyrus adult neurogenesis plays a role in reward memories created in adult C57BL/6J male mice. In addition, as adult neurogenesis appears to participate to a greater extent in retrieval and extinction of recent (<48 hr posttraining) versus remote (>1 week posttraining) memories, we specifically examined the role of adult neurogenesis in reward-associated contextual memories probed at recent and remote timepoints. Six weeks post-IG-IR or Sham treatment, mice underwent morphine CPP. Using separate groups, retrieval of recent and remote reward memories was found to be similar between IG-IR and Sham treatments. Interestingly, IG-IR mice showed impaired extinction-or increased persistence-of the morphine-associated reward memory when it was probed 24-hr (recent) but not 3-weeks (remote) postconditioning relative to Sham mice. Taken together, these data show that hippocampal-directed irradiation and the associated decrease in dentate gyrus adult neurogenesis affect the persistence of recently-but not remotely-probed reward memory. These data indicate a novel role for adult neurogenesis in reward-based memories and particularly the extinction rate of these memories. Consideration of this work may lead to better understanding of extinction-based behavioral interventions for psychiatric conditions characterized by dysregulated reward processing.

Effect of acute and chronic restraint stress on electrical activity of prefrontal cortex neurons in the reinstatement of extinguished methamphetamine-induced conditioned place preference: An electrophysiological study

Increased vulnerability to drug abuse has been observed after exposure to stress and the prefrontal cortex (PFC) plays a major role in the control of the stress response and reward pathway. The current study was conducted to clarify the effects of acute and chronic restraint stress on PFC neural activity during the reinstatement of methamphetamine (METH)-induced conditioned place preference (CPP) in rats. Following the establishment of CPP (METH 0.5 mg/kg; s.c. for 3 days) and the extinction phase, male Wistar rats were divided into threshold (0.25 mg/kg; s.c.) and sub-threshold (0.125 mg/kg; s.c.) METH-treated super groups to induce reinstatement. Each super group contained control (non-stressed), acute restraint stress (ARS) and chronic restraint stress (CRS) groups. in vivo single unit recordings were performed on the urethane-anesthetized rats in these groups. After baseline recordings (10-min period) of the neurons in the PFC, their firing activity was recorded for 50 min during the reinstatement phase after injection of METH. The results showed that the threshold dose, but not the sub-threshold dose, of METH significantly increased PFC neural activity in the non-stressed animals. The sub-threshold dose of METH notably changed this activity in both the ARS and CRS groups. These changes in the excited neurons after the sub-threshold dose in the ARS and CRS groups were significantly higher than those in the non-stressed group. It appears that the PFC is implicated in the associated reward pathway and stress functions. METH affected the firing rate of PFC neurons and stress amplified the effect of METH on changes in the neuronal firing rate in the PFC.