Effects of BDNF receptor antagonist on the severity of physical and psychological dependence, morphine-induced locomotor sensitization and the ventral tegmental area-nucleus accumbens BDNF levels in morphine- dependent and withdrawn rats

The effect of vitamin D on morphine preference in rats: Possible biochemical and DRD2-GDNF signaling

INTRODUCTION

Despite half a century of research on vitamin D (Vit. D), its link to substance abuse and dependence has only been discussed in recent decades. Evidence also shows the involvement of Vit. D in the evolution of dopaminergic neurons in the nucleus accumbens, an increase in the expression of tyrosine hydroxylase, and the regulation of dopaminergic processes. The novel idea for this work is taken from a hypothesis given about the effectiveness of Vit. D on dopamine signaling pathway. It is therefore presumed that Vit. D can be considered an effective therapeutic approach for narcotic addiction and substance abuse.

METHODS

The animals were assigned into six groups (control, vehicle, Morphine [Mor.], and Vit. D [250, 500, and 1000 IU/kg, i.p.]). Following each conditioning session in a conditioned place preference (CPP) model, the animals received Vit. D. Afterward, the locomotor activity of the animals was assessed using open-field apparatus. Malondialdehyde (MDA), nitric oxide (NO), catalase (CAT), superoxide dismutase (SOD), thiol, and total antioxidant capacity (TAC) were measured in the brain. The relative DRD2 and GDNF expressions (%) were also measured in the hippocampus.

RESULTS

Vit. D administration after Mor. caused a significant increase in the place preference index in the acquisition phase (p < .05). Vit. D altered the oxidation/antioxidation profiles (CAT, SOD, MDA, NO, TAC, and Thiol). Vit. D was more effective than Mor. in the expression of GDNF (p < .0001); however, in the expression of DRD2, this was only the case for 1000 IU Vit. D (p < .0001).

CONCLUSIONS

Considering the increased place preference index induced by Mor., it can be concluded that Vit. D interacts via the oxidative pathway and DRD2-GDNF signaling to potentiate the Mor. effect.

BDNF-AAV has protective effects on morphine-induced conditioned place preference through BDNF, TrkB, and CREB concentration changes in the VTA and NAc

Brain-derived neurotrophic factor (BDNF) is one of the neurotrophic factors that promotes the survival and protection of neurons in many disorders. The potential protective effect of BDNF and its mechanisms on morphine addiction are unclear. In this study, morphine-induced conditioned place preference (CPP) in mice was used to show the effect of BDNF on rewarding behavior. Western blot assays were used to determine the changes caused by BDNF, for example, changes in total BDNF, tropomyosin-related kinase receptor B (TrkB), and cAMP response element binding protein (CREB) in the ventral tegmental area (VTA) and nucleus accumbens (NAc). The results showed that the BDNF-adeno-associated viral vector (BDNF-AAV) injected in the VTA, attenuated morphine-induced CPP with synergistic changes in BDNF/TrkB/CREB concentrations in the VTA and NAc in the CPP acquisition and recurrence phases; however, the attenuation was lower in the extinction phase, with different changes in molecules downstream of the BDNF.

Facilitating mGluR4 activity reverses the long-term deleterious consequences of chronic morphine exposure in male mice

Understanding the neurobiological underpinnings of abstinence from drugs of abuse is critical to allow better recovery and ensure relapse prevention in addicted subjects. By comparing the long-term transcriptional consequences of morphine and cocaine exposure, we identified the metabotropic glutamate receptor subtype 4 (mGluR4) as a promising pharmacological target in morphine abstinence. We evaluated the behavioral and molecular effects of facilitating mGluR4 activity in abstinent mice. Transcriptional regulation of marker genes of medium spiny neurons (MSNs) allowed best discriminating between 4-week morphine and cocaine abstinence in the nucleus accumbens (NAc). Among these markers, Grm4, encoding mGluR4, displayed down-regulated expression in the caudate putamen and NAc of morphine, but not cocaine, abstinent mice. Chronic administration of the mGluR4 positive allosteric modulator (PAM) VU0155041 (2.5 and 5 mg/kg) rescued social behavior, normalized stereotypies and anxiety and blunted locomotor sensitization in morphine abstinent mice. This treatment improved social preference but increased stereotypies in cocaine abstinent mice. Finally, the beneficial behavioral effects of VU0155041 treatment in morphine abstinent mice were correlated with restored expression of key MSN and neural activity marker genes in the NAc. This study reports that chronic administration of the mGluR4 PAM VU0155041 relieves long-term deleterious consequences of morphine exposure. It illustrates the neurobiological differences between opiate and psychostimulant abstinence and points to pharmacological repression of excessive activity of D2-MSNs in the NAc as a promising therapeutic lever in drug addiction.

BDNF receptor antagonism during the induction of morphine dependence exacerbates the severity of physical dependence and ameliorates psychological dependence in rats

This study examined the effects of systemic administration of the TrkB receptor antagonist (ANA-12) during induction of morphine dependence on the severity of physical and psychological dependence and the cerebrospinal fluid (CSF) BDNF levels in morphine-dependent and withdrawn rats. Rats became morphine-dependent by increasing daily doses of morphine for 7 days, along with ANA-12 injection. Then, rats were tested for the severity of physical dependence on morphine (spontaneous withdrawal signs), anxiety-like (the elevated plus maze), depressive-like (sucrose preference test) behaviors after spontaneous morphine withdrawal. Also, the CSF BDNF levels were assessed 2 h after the last dose of morphine and day 13 after morphine withdrawal in morphine-dependent and withdrawn rats. We found that the morphine withdrawal signs were significantly higher in morphine dependent rats receiving ANA-12 on days of 5-7 after morphine withdrawal, also ANA-12 exacerbated overall dependence severity. While, the percentage of time spent in the open arms and sucrose preference were higher in morphine-dependent rats receiving ANA-12 than morphine-dependent rats receiving saline. Also, the ANA-12 injection decreased the CSF BDNF levels following morphine dependence, while increased it after morphine withdrawal. We conclude that the ANA-12 exacerbated the severity of physical morphine dependence but attenuated the anxiety/depressive-like behaviors in morphine-dependent and withdrawn rats. Also, ANA-12 injection was able to reverse the changes in the CSF BDNF levels. Therefore, ANA-12 is not more likely to complete treatment for opiate addiction.

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).

Chronic morphine intoxication reduces binding of HuD to BDNF long 3'-UTR, while morphine withdrawal stimulates BDNF expression in the frontal cortex of male Wistar rats

BACKGROUND

Brain-derived neurotrophic factor (BDNF) mediates opiate dependence phenomenon. In the brain of morphine dependent animals BDNF level is controlled transcriptionally, however, post-transcriptional mechanisms of BDNF regulation in this context remain unknown. Regulation of mRNA by binding of specific proteins to the 3'-untranslated region (3'-UTR) is one of such mechanisms. Among RNA-binding proteins neuronal Hu antigen D (HuD) is the best characterized positive regulator of BDNF, however its involvement in opiate dependence remains obscure. We suggested that HuD binding to the BDNF 3'-UTR may be linked to changes in BDNF expression induced by morphine. The aim of this study was to investigate potential association of HuD with BDNF 3'-UTR in relation to BDNF expression (Exon- and 3'-UTR-specific mRNA variants and protein level) in the frontal cortex and midbrain of male Wistar rats after chronic morphine intoxication and spontaneous withdrawal in dependent animals.

RESULTS

After chronic morphine intoxication but not during morphine withdrawal HuD binding to the long BDNF 3'-UTR in the frontal cortex decreased as compared with the corresponding control group, however after intoxication BDNF expression did not change. The level of BDNF Exon I as well as mature BDNF polypeptide increased in the frontal cortex upon morphine withdrawal, while no changes in HuD binding could be detected.

CONCLUSION

Thus, contrary to the assumption, HuD-BDNF 3'-UTR interaction and BDNF expression in the frontal cortex differentially change in a manner dependent on the context of morphine action.

Decreased Neuronal Excitability in Medial Prefrontal Cortex during Morphine Withdrawal is associated with enhanced SK channel activity and upregulation of small GTPase Rac1

Rationale: Neuroadaptations in the medial prefrontal cortex (mPFC) and Nucleus Accumbens (NAc) play a role in the disruption of control-reward circuits in opioid addiction. Small Conductance Calcium-Activated Potassium (SK) channels in the mPFC have been implicated in neuronal excitability changes during morphine withdrawal. However, the mechanism that modulates SK channels during withdrawal is still unknown.

Methods: Rats were exposed for one week to daily morphine injections (10 mg·kg^-1 s.c.) followed by conditional place preference (CPP) assessment. One week after withdrawal, electrophysiological, morphological and molecular biological methods were applied to investigate the effects of morphine on SK channels in mPFC, including infralimbic (IL), prelimbic (PrL) cortices and NAc (core and shell). We verified the hypothesis that Rac1, a member of Rho family of small GTPases, implicated in SK channel regulation, modulate SK channel neuroadaptations during opiate withdrawal.

Results: One week after morphine withdrawal, the neuronal excitability of layer 5 pyramidal neurons in IL was decreased, but not in PrL. Whereas, the excitability was increased in NAc-shell, but not in NAc-core. In mPFC, the expression of the SK3 subunit was enhanced after one-week of withdrawal compared to controls. In the IL, Rac1 signaling was increased during withdrawal, and the Rac1 inhibitor NSC23766 disrupted SK current, which increased neuronal firing. Suppression of Rac1 inhibited morphine-induced CPP and expression of SK channels in IL.

Conclusions: These findings highlight the potential value of SK channels and the upstream molecule Rac1, which may throw light on the therapeutic mechanism of neuromodulation treatment for opioid dependence.

Effect of crocin on morphine tolerance and serum BDNF levels in a rat model of neuropathic pain

BACKGROUND

Chronic use of morphine treatment for neuropathic pain leads to morphine-induced analgesic tolerance. Crocin contained in Crocus sativus L., exerts anti-inflammatory and analgesic effects. This study examined the effects of crocin on morphine tolerance and serum BDNF levels on neuropathic pain induced by chronic constriction injury (CCI) in rats.

METHODS

CCI model of neuropathic pain was done in male Wistar rats (200-250 g). Rats were treated with crocin (15 or 30 mg/kg, intraperitoneally) alone or simultaneously with morphine (10 mg/kg, subcutaneously) during or after induction of CCI. Pain behavioral responses including mechanical allodynia and thermal hyperalgesia were measured from days of 15-27 after CCI. Then, rats were evaluated for serum BDNF levels on days 14 and/or 27.

RESULTS

We found that morphine tolerance developed after the induction of neuropathic pain. The injection of crocin (15 and 30 mg/kg) was able to enhance analgesic effect of morphine by reduction of mechanical allodynia on days 15-27 post-surgery in CCI rats. While preemptive administration of crocin at a lower dose (15 mg/kg) maintained the analgesic effect of morphine. Morphine injection and/or co-administration with crocin (15, 30 mg/kg) decreased serum BDNF levels in CCI rats.

CONCLUSION

These findings indicate that crocin may have a therapeutic effect to maintain morphine analgesic efficacy and also to prevent the development of morphine tolerance in neuropathic pain, but probably not through BDNF.

Pharmacological modulation of the behavioral effects of social defeat in memory and learning in male mice

RATIONALE

Previous studies have demonstrated that repeated social defeat (RSD) stress only induces cognitive deficits when experienced during adulthood. However, RSD increases cocaine-rewarding effects in adult and adolescent mice, inducing different expressions of proBDNF in the ventral tegmental area.

OBJECTIVE

The aim of the present study was to evaluate the effect of cocaine administration in socially defeated adult or adolescent mice on learning, memory, and anxiety. Additionally, the role of BDNF was also studied.

METHODS

Adolescent and young adult mice were exposed to four episodes of social defeat or exploration (control), being treated with a daily injection of four doses of saline or 1 mg/kg of cocaine 3 weeks after the last social defeat. Other groups were treated with the TrkB receptor antagonist ANA-12 during this 21-day period. After this treatment, their cognitive and anxiogenic profiles were evaluated, along with the expression of BDNF, pCREB, and pERK1/2 in the dentate gyrus (DG) and basolateral amygdala (BLA).

RESULTS

Cocaine induced an increased expression of pCREB and BDNF in the DG and BLA only in defeated animals. Although RSD did not affect memory, the administration of cocaine induced memory impairments only in defeated animals. Defeated adult mice needed more time to complete the mazes, and this effect was counteracted by cocaine administration. RSD induced anxiogenic effects only when experienced during adulthood and cocaine induced a general anxiolytic effect. Blockade of Trkb decreased memory retention without affecting spatial learning and modified anxiety on non-stressed mice depending on their age.

CONCLUSION

Our results demonstrate that the long-lasting effects of social defeat on anxiety and cognition are modulated by cocaine administration. Our results highlight that the BDNF signaling pathway could be a target to counteract the effects of cocaine on socially stressed subjects.