Cholinergic M4 receptors are involved in morphine-induced expression of behavioral sensitization by regulating dopamine function in the nucleus accumbens of rats

Relationship between the role of muscarinic M3 receptors in morphine-induced conditioned place preference and the mesolimbic dopamine system

Opioid use disorder mainly results from functional defects in the brain reward loop, which includs the ventral tegmental area (VTA) and nucleus accumbens (NAc; consisting of shell and core, NAcS and NAcC). Reward effects contribute to opioid use disorder. RMTg M₃ receptors play a role in opioid reward by regulating the γ-aminobutyric acid (GABA) neuron activity. Dopamine D₁ receptors expressed on GABA neurons regulate opioid reward by mediating the dopamine neuron activity in the VTA. Therefore, we investigated the effect of activating M₃ receptors by microinjecting pilocarpine into the RMTg along with activating D₁ receptors by microinjecting SKF38393 into the VTA on morphine-induced reward effect, using the conditioned place preference (CPP) paradigm (locomotion was also recorded). We also investigated whether the activation of M₃ receptors in the RMTg influenced dopamine release in the NAcS. The results showed that the inhibitory role of RMTg pilocarpine (60 μg/rat) infusions in morphine-induced CPP was reversed by VTA SKF38393 (4 μg/rat) infusions. Moreover, morphine (5 mg/kg, i.p.) increased dopamine release in the NAcS, which was blunted by microinjecting pilocarpine (60 μg/rat) into the RMTg. These results indicate that RMTg M₃ receptors mediate morphine-induced reward effect, which is probably related to the dopamine activity within the VTA and NAcS. The relationship between RMTg M₃ receptors and the mesolimbic dopamine system could be a potential direction for the treatment of opioid use disorder, but further verification through more comprehensive techniques is needed.

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

Effects of biperiden (cholinergic muscarinic m1/m4 receptor antagonist) on ethanol conditioned place preference in mice

BACKGROUND

Previous studies suggest that muscarinic cholinergic receptors might act upon the dopamine release in the mesolimbic system and alter drug-reinforcing values related to drug craving.

AIMS

We examined the effects of systemic biperiden administration, a muscarinic cholinergic (M1/M4) receptor antagonist, on ethanol (dose of 2 g/Kg) conditioned place preference (CPP), neuronal activation, dopamine and its metabolites levels in the nucleus accumbens.

METHODS

Thirty minutes before the ethanol-induced CPP test, mice received saline or biperiden at doses of 1.0, 5.0, or 10.0 mg/kg. The time spent in each compartment was recorded for 15 min. After the CPP protocol, animals were euthanized, and we investigated the activation of the nucleus accumbens by immunohistochemistry for Fos. We also quantified dopamine, homovanillic acid (HVA), and dihydroxyphenylacetic acid (DOPAC) levels in the nucleus accumbens by high-performance liquid chromatography (HPLC). Additionally, the rotarod was employed to evaluate the effects of biperiden on motor coordination.

RESULTS

Biperiden at different doses (1.0, 5.0, and 10.0 mg/kg) blocked the expression of ethanol-induced CPP. These biperiden doses increased the number of Fos-positive cells and the dopamine turnover in the nucleus accumbens. None of the doses affected the motor coordination evaluated by the rotarod.

CONCLUSIONS

Our results show that biperiden can modulate the effect of alcohol reward, and its mechanism of action may involve a change in dopamine and cholinergic mesolimbic neurotransmission.

M3 but not M4 muscarinic receptors in the rostromedial tegmental nucleus are involved in the acquisition of morphine-induced conditioned place preference

Opioids strongly inhibit GABAergic neurons in the rostromedial tegmental nucleus (RMTg) that expresses μ-opioid receptors to induce rewarding and psychomotor effects. M₃ and M₄ muscarinic receptors are co-localized with μ-opioid receptors at these GABAergic neurons. This study explored whether RMTg M₃ and M₄ muscarinic receptors are involved in regulating opioid-induced reward and locomotion via a conditioned place preference (CPP) paradigm. Selective muscarinic receptor agonists and antagonists were both singly and combinatorically injected into the RMTg to examine their effects on the acquisition of systemic morphine-induced CPP and locomotor activity. The M₃ muscarinic receptor agonist, pilocarpine, inhibited the acquisition of morphine-induced CPP, whereas its antagonist, 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP, 1 μg/side), reversed the inhibitory effect of pilocarpine (30 μg/side). Additionally, 4-DAMP increased locomotor activity while pilocarpine (30 μg/side) partially decreased locomotor activity when combined with morphine. In contrast, the M₄ muscarinic receptor agonist, LY2033298 (0.1 and 0.2 μg/side), and antagonist, tropicamide (20 and 40 μM/side), did not affect the acquisition of morphine-induced CPP or locomotor activity. Taken together, our findings suggest that RMTg M₃ muscarinic receptors are involved in opioid-induced rewarding and psychomotor effects. Therefore, RMTg M₃ muscarinic receptors may represent a promising target for the treatment of opioid addiction.

Improvement of Petroselinum crispum on Morphine Toxicity in Prefrontal Cortex in Rats

Background:

Petroselinum crispum (P. Crispum) is an associate of the umbelliferae family with several therapeutic attributes. Morphine is known as a major risk factor in the development of functional disorder of several organs.

Objective:

This study was designed to evaluate the effects of P. Crispum extract against morphine-induced damage to the brain prefrontal cortex (PC) of rats.

Materials and Methods:

In this experimental study, 64 Wistar male rats were randomly assigned to 8 groups: Sham group, Morphine group, P. Crispum groups (50, 100, and 150 mg/kg), and Morphine + P. Crispum groups. Daily intraperitoneal treatment applied for 20 days. Ferric reducing/antioxidant power method was hired to determine the total antioxidant capacity (TAC). The number of dendritic spines was investigated by Golgi staining technique. Cresyl violet staining method was used to determine the number of neurons in the PC region. Furthermore, Griess technique was used to determine the level of serum nitrite oxide.

Results:

Morphine administration increased nitrite oxide levels and decreased TAC, density of neuronal dendritic spines and neurons compared to the sham group significantly (P < 0.05). In whole doses of the P. Crispum and Morphine + P. Crispum groups, the number of neurons and neuronal dendritic spines increased significantly while nitrite oxide level and TAC decreased compared to the morphine group (P < 0.05).

Conclusion:

It seems that the administration of P. Crispum extract protects the animals against oxidative stress and nitrite oxide, also improves some PC parameters including the number of neurons, and dendritic spines because of the morphine application.

The Effects of Hydroalcoholic Extract of Satureja khuzestanica on Naloxone-Induced Morphine Withdrawal Symptoms in Wistar Rats

Introduction: The inflammatory system, oxidative stress, and cholinergic pathways are some important factors in long-term opioid dependence withdrawal. The adverse effects of some adjunctive medications on withdrawal symptoms treatment limit their clinical efficiency and finding compounds with inhibitory effects on opioid dependence can be helpful. The antioxidant, antinociceptive, and anti-inflammatory properties of Satureja khuzestanica extract (SKE) have been noted. Additionally, it could reduce morphine analgesic tolerance. Given that no study has assessed the effect of SKE on morphine-induced withdrawal symptoms, we have tried to investigate it in this study. Methods: Male Wistar rats were used in this study. The rats were treated with morphine for 7 days. The control group received saline, and intervention groups received SKE intragastrically by gavage (100 mg/kg, 50 mg/kg, and 25 mg/kg) 15 minutes before morphine injections. Five hours after the last injection, naloxone was used and withdrawal symptoms were assessed for one hour. SPSS software version 16.0 was used for statistical analysis, and P≤0.05 was considered statistically significant. Results: SKE diminished weight loss and jumping (P≤0.001). It decreased grooming behaviors and cramps (P≤0.01). SKE was found to decrease morphine withdrawal symptoms and 100 mg/kg was the most effective dose. Additionally, different doses of SKE were able to eliminate ptosis, diarrhea, and teeth chattering in animals; however, different doses had different effects on withdrawal symptoms. Conclusion: Naloxone significantly increased the frequency of jumping, cramps, weight loss, grooming, and induced ptosis, diarrhea, and teeth chattering. Treatment with SKE can significantly reduce morphine withdrawal symptoms. This can be done through its ability to decrease inflammation.

The orphan receptor GPR88 blunts the signaling of opioid receptors and multiple striatal GPCRs

GPR88 is an orphan G protein-coupled receptor (GPCR) considered as a promising therapeutic target for neuropsychiatric disorders; its pharmacology, however, remains scarcely understood. Based on our previous report of increased delta opioid receptor activity in Gpr88 null mice, we investigated the impact of GPR88 co-expression on the signaling of opioid receptors in vitro and revealed that GPR88 inhibits the activation of both their G protein- and β-arrestin-dependent signaling pathways. In Gpr88 knockout mice, morphine-induced locomotor sensitization, withdrawal and supra-spinal analgesia were facilitated, consistent with a tonic inhibitory action of GPR88 on µOR signaling. We then explored GPR88 interactions with more striatal versus non-neuronal GPCRs, and revealed that GPR88 can decrease the G protein-dependent signaling of most receptors in close proximity, but impedes β-arrestin recruitment by all receptors tested. Our study unravels an unsuspected buffering role of GPR88 expression on GPCR signaling, with intriguing consequences for opioid and striatal functions.