Transient inactivation of the nucleus accumbens reduces both the expression and acquisition of morphine-induced conditioned place preference in rats

Anterior cingulate cortex and its projections to the ventral tegmental area regulate opioid withdrawal, the formation of opioid context associations and context-induced drug seeking

Clinical evidence suggests that there are correlations between activity within the anterior cingulate cortex (ACC) following re-exposure to drug-associated contexts and drug craving. However, there are limited data contributing to our understanding of ACC function at the cellular level during re-exposure to drug-context associations as well as whether the ACC is directly related to context-induced drug seeking. Here, we addressed this issue by employing our novel behavioral procedure capable of measuring the formation of drug-context associations as well as context-induced drug-seeking behavior in male mice (8–12 weeks of age) that orally self-administered oxycodone. We found that mice escalated oxycodone intake during the long-access training sessions and that conditioning with oxycodone was sufficient to evoke conditioned place preference (CPP) and drug-seeking behaviors. Additionally, we found that thick-tufted, but not thin-tufted pyramidal neurons (PyNs) in the ACC as well as ventral tegmental area (VTA)-projecting ACC neurons had increased intrinsic membrane excitability in mice that self-administered oxycodone compared to controls. Moreover, we found that global inhibition of the ACC or inhibition of VTA-projecting ACC neurons was sufficient to significantly reduce oxycodone-induced CPP, drug seeking, and spontaneous opioid withdrawal. These results demonstrate a direct role of ACC activity in mediating context-induced opioid seeking among other behaviors, including withdrawal, that are associated with the DSM-V criteria of opioid use disorder.

The controlling role of nitric oxide within the shell of nucleus accumbens in the stress-induced metabolic disturbance

CONTEXT AND OBJECTIVES

The involvement of the nitricergic system within the shell part of the nucleus accumbens (NAc) was evaluated in the metabolic disturbances due to stress.

MATERIALS AND METHODS

Male Wistar rats were cannulated in the shell of the left NAc. They received either saline or different doses of L-arginine and/or L-NAME five minutes before each stress session, for four days. Plasma cortisol concentration, food and water intake, time elapsing for eating, animal weight changes and adrenal gland weight were recorded.

RESULTS

The L-arginine 1 μg/rat decreased the level of cortisol, water and food intake and time of feeding and increased the adrenal weight. But L-NAME at 1 μg/rat had opposite effects on these factors. However, the drugs showed similar effects at 10 μg/rat.

CONCLUSION

Injection of nitric oxide modifiers into the left side of NAc shell part may have an interactive role with sub-chronic stress in metabolic behaviour.

Drug-Induced Conditioned Place Preference and Its Practical Use in Substance Use Disorder Research

The conditioned place preference (CPP) paradigm is a well-established model utilized to study the role of context associations in reward-related behaviors, including both natural rewards and drugs of abuse. In this review article, we discuss the basic history, various uses, and considerations that are tied to this technique. There are many potential takeaway implications of this model, including negative affective states, conditioned drug effects, memory, and motivation, which are all considered here. We also discuss the neurobiology of CPP including relevant brain regions, molecular signaling cascades, and neuromodulatory systems. We further examine some of our prior findings and how they integrate CPP with self-administration paradigms. Overall, by describing the fundamentals of CPP, findings from the past few decades, and implications of using CPP as a research paradigm, we have endeavored to support the case that the CPP method is specifically advantageous for studying the role of a form of Pavlovian learning that associates drug use with the surrounding environment.

The role of nucleus accumbens shell on acquisition and retrieval stages of morphine state dependent learning

AIM

In the present study, the effect of transient inactivation of the shell subregion of the nucleus accumbens (NAC shell) by lidocaine on the acquisition and retrieval stages of passive avoidance learning (PAL) and memory and morphine state-dependent learning (SDL) in male wistar rats was investigated.

METHODOLOGY

Adult male wistar rats weighing (220-250 g) were used. Lidocaine hydrochloride was bilaterally injected into the shell area of the nucleus accumbens 5 min before of subcutaneous morphine administration.

RESULTS

pre-training and pre-test infusion of lidocaine into the NAC shell significantly impaired PAL and memory. Furthermore, Pre-training administration of morphine (5 mg/kg, s.c.) in a step-through passive avoidance task induced state-dependent learning with impaired memory retrieval on the test day. The impairment of memory was restored after pre-test administration of the same dose of morphine. This phenomenon has been named as morphine state dependent learning (SDL). Moreover, Pre-training and pre-test inactivation of the NAC shell impaired morphine SDL.

CONCLUSIONS

The results suggest the role of NAC shell as a common structure in the PAL and morphine SDL. It is suggested that NAC shell as a common area plays a critical role in the acquisition and retrieval stages of PAL and also morphine SDL.

Transient Inactivation of Shell Part of Nucleus Accumbens Inhibits and Exacerbates Stress-Induced Metabolic Alterations in Wistar Rats

Introduction:

The role of different parts of the extended amygdala in metabolic signs of stress is not well understood. In the present study, we decided to evaluate the impact of the shell part of nucleus accumbens (NAc) on metabolic disturbance induced by electro foot shock stress using transient inactivation method in the rat.

Methods:

Male Wistar rats (W: 230–250 g) were canuulated unilaterally in the shell part of nucleus accumbens and left one week for recovery. Five minutes before each stress session, the animals either received sterile saline (0.25 μl/side) (control) or lidocaine 2% (0.25 μl/side) (experiment). Blood samples were taken from rats’ retro-orbital sinus for plasma corticosterone measurements. In addition, animals’ weight gain, food and water intake, locomotor activity, and rearing were recorded.

Results:

Stress reduced weight gain and food intake, increased water intake and plasma corticosterone level, and reduces locomotor activity and rearing. Transient inactivation of the right side of the NAc inhibits the stress effect on weight gain, water intake and plasma corticosterone level, but not food intake. However, when the left side of the NAc was inactivated, only weight gain was affected and other parameters were not differing from stress group. Even thought, the plasma corticosterone level was elevated.

Conclusion:

In conclusion, our data indicated that right side of shell part of NAc transient inactivation leads to reduction in metabolic signs of stress but left side of shell part of the NAc inactivation even exacerbates stress signs.

Dopamine D1 receptor agonist treatment attenuates extinction of morphine conditioned place preference while increasing dendritic complexity in the nucleus accumbens core

The dopamine D1 receptor (D1R) has a role in opioid reward and conditioned place preference (CPP), but its role in CPP extinction is undetermined. We examined the effect of D1R agonist SKF81297 on the extinction of opioid CPP and associated dendritic morphology in the nucleus accumbens (NAc), a region involved with reward integration and its extinction. During the acquisition of morphine CPP, mice received morphine and saline on alternate days; injections were given immediately before each of eight daily conditioning sessions. Mice subsequently underwent six days of extinction training designed to diminish the previously learned association. Mice were treated with either 0.5mg/kg SKF81297, 0.8mg/kg SKF81297, or saline immediately after each extinction session. There was a dose-dependent effect, with the highest dose of SKF81297 attenuating extinction, as mice treated with this dose had significantly higher CPP scores than controls. Analysis of medium spiny neuron morphology revealed that in the NAc core, but not in the shell, dendritic arbors were significantly more complex in the morphine conditioned, SKF81297-treated mice compared to controls. In separate experiments using mice conditioned with only saline, SKF81297 administration after extinction sessions had no effect on CPP and produced differing effects on dendritic morphology. At the doses used in our experiments, SKF81297 appears to maintain previously learned opioid conditioned behavior, even in the face of new information. The D1R agonist's differential, rather than unidirectional, effects on dendritic morphology in the NAc core suggests that it may be involved in encoding reward information depending on previously learned behavior.

Transient inactivation of the nucleus accumbens (NAc) shell prominently ameliorates responses to acute stress in female rats

It is clear that the stress response differs between females and males. Moreover, the nucleus accumbens shell is considered a critical area in the brain's response to stress. In the present study we investigate the effect of the transient inactivation of the NAc shell on the metabolic and hormonal disturbance induced by acute stress in female rats. Female Wistar rats were canulated uni- or bilaterally in the NAc shell before stress induction. Electric foot shock was applied to the animals and lidocaine hydrochloride was administered intra-acumbally 5min before each stress session. Food and water intake, delay to eating time, plasma corticosterone, estradiol and progesterone were measured after stress administration. Our results indicate that food intake increased whereas water intake decreased in stress group, furthermore, delay in the onset of eating also was observed. In addition, plasma corticosterone and progesterone concentrations were increased whereas estradiol was decreased. Transient inactivation of right side of NAc shell inhibited the stress effect on food intake; however, the effect of stress was exacerbated when the left part of the NAc shell was inhibited. Transient inactivation of both NAc shell sides augmented the stress effect on water intake. The same results also obtained for the effect of stress on delay to eating time. Lidocaine administration inhibited the effects of stress on all of the hormones we tested. It can be concluded that the NAc shell plays an important role in the mediation of stress responses in female rats and this influence shows asymmetrical manner.

Effect of Transient Inactivation of Ventral Tegmental Area on the Expression and Acquisition of Nicotine-Induced Conditioned Place Preference in Rats

Background:

Nicotine can activate dopaminergic neurons within the ventral tegmental area (VTA). However, there is no evidence about complete inhibition of VTA on nicotine reinforcement.

Methods:

in the present study, we used conditioned-place preference (CPP) method to study the effect of transient inhibition of left and/or right side of the VTA by lidocaine on nicotine reward properties. Male Wistar rats seven days after recovery from surgery and cannulation were conditioned to nicotine (1.5 mg/kg) in an unbiased designed CPP apparatus. Five min before each nicotine injection in conditioning phase, lidocaine (2%) was administered either uni- or bi-laterally into the VTA (0.5µl/rat).

Results:

results revealed that lidocaine administration into the left but not right side of the VTA reduced nicotine CPP significantly. The reduction was potentiated when lidocaine injected in to both sides of the VTA. In addition, the number of compartment crossing was reduced when lidocaine injected in both side of VTA as well as left side. On the other hand, rearing was reduced when lidocaine injected to the right but not left side of VTA. At last, sniffing was reduced only in the group in which received lidocaine in both side of VTA. Sniffing and rearing increased in the group in which received lidocaine in right side.

Conclusion:

It is concluded that the right and left side of VTA play different role in nicotine-induced activity and reward.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Blocking TRPV1 in nucleus accumbens inhibits persistent morphine conditioned place preference expression in rats

The function of TRPV1 (transient receptor potential vanilloid subfamily, member 1) in the central nervous system is gradually elucidated. It has been recently proved to be expressed in nucleus accumbens (NAc), a region playing an essential role in mediating opioid craving and taking behaviors. Based on the general role of TRPV1 antagonist in blocking neural over-excitability by both pre- and post-synaptic mechanisms, TRPV1 antagonist capsazepine (CPZ) was tested for its ability to prohibit persistent opioid craving in rats. In the present study, we assessed the expression of TRPV1 in nucleus accumbens and investigated the effect of CPZ in bilateral nucleus accumbens on persistent morphine conditioned place preference (mCPP) in rats. We also evaluated the side-effect of CPZ on activity by comparing cross-beam times between groups. We found that morphine conditioned place preference increased the TRPV1 expression and CPZ attenuated morphine conditioned place preference in a dose-dependent and target-specific manner after both short- and long-term spontaneous withdrawal, reflected by the reduction of the increased time in morphine-paired side. CPZ (10 nM) could induce prolonged and stable inhibition of morphine conditioned place preference expression. More importantly, CPZ did not cause dysfunction of activity in the subjects tested, which indicates the inhibitory effect was not obtained at the sacrifice of regular movement. Collectively, these results indicated that injection of TRPV1 antagonist in nucleus accumbens is capable of attenuating persistent morphine conditioned place preference without affecting normal activity. Thus, TRPV1 antagonist is one of the promising therapeutic drugs for the treatment of opioid addiction.