Cannabinoid CB1 receptor mediates METH-induced electrophysiological and morphological alterations in cerebellum Purkinje cells.

Our previous studies on cannabinoid type1 receptor (CB1R) activation on Methamphetamine (METH)-induced neurodegeneration and locomotion impairments in male rats suggest an interaction between CB1Rs and METH. However, the role of these receptors in METH-neurotoxicity has not been fully identified. Therefore, the purpose of the present study is to investigate the involvement of CB1Rs in these effects. We conducted an electrophysiological study to evaluate functional interactions between METH and CB1Rs using whole-cell patch current clamp recording. Furthermore, we designed the Nissl staining protocol to assess the effect of METH on the basic cerebellar Purkinje cell structure. Our findings revealed that METH significantly increased the action potential half-width, spontaneous interspike intervals, first spike latency, and decreased the rebound action potential and spontaneous firing frequency. Using CB1R agonist and antagonist, our results showed a significant interaction with some of the electrophysiological alterations induced by METH. Further, Nissl staining revealed that the exposure to the combination of METH and SR141716A resulted in the necrotic cell death. Results of the current study raises the possibility that METH consumption profoundly affect the intrinsic membrane properties of cerebellar Purkinje neurons and cannabinoid system manipulations may counteract some of these effects. In summary, our findings provide further insights into the modulatory role of the endocannabinoid system in METH-induced neurologic changes, which can be used in the development of potential therapeutic interventions for METH dependence.

Effect of intracerebroventricular injection of GABA receptors antagonists on morphine-induced changes in GABA and GLU transmission within the mPFC: an in vivo microdialysis study.

OBJECTIVES: Many studies have focused on ventral tegmental area than of other mesocorticolimbic areas, and implicated a key role for the medial prefrontal cortex (mPFC) in the development of addictive behaviors. So far, the role of gamma-aminobutyric acid (GABA) receptors in the discriminative properties of morphine has received little attention and few studies evaluated the role of these receptors in drug dependence. Hence, we investigated the role of this receptor on morphine- induced GABA/ glutamate (GLU) changes in the mPFC following morphine administration using in vivo microdialysis. MATERIALS AND METHODS: In this study, 60 rats weighing 270-300 g were divided into six groups. First, microdialysis probe was inserted into the mPFC and was perfused with artificial cerebrospinal fluid and collected the baseline samples in all groups. In saline and morphine groups, the saline, in phaclophen and (phaclofen+morphine) groups, phaclofen (100 nmol), and in bicuculline and (bicuculline+morphine) groups, bicuculline (20 nmol) was injected intracerebroventricular. In saline, phaclofen and bicuculline groups 20 min later, animals received saline (0.2 ml, IP) and others groups received morphine (20 mg/kg, IP). RESULTS: Our results showed that morphine increased the average concentration of GABA and decreased the concentration of GLU within mPFC. Pretreatment with phaclofen and bicuculline 20 min before morphine administration had no effect on GABA and GLU release for 100 min. CONCLUSION: The present study indicated that morphine influence the GABA and GLU transmission in mPFC. Therefore evaluation of neurochemistry changes of this neural circuitry may provide further insight into the mechanisms underlying drug dependence.

Effect of Aerobic Exercise on Morphine Self-administration and Pain Modulation in Rats.

BACKGROUND: Exercise reverses retention deficit induced by morphine. The present study investigated the effect of aerobic exercise on tolerance to morphine usage and pain modulation. MATERIALS AND METHODS: Male Wistar rats were divided into four groups as follows: (1) saline group (S), (2) morphine group (M), (3) saline + exercise (S + E), and (4) morphine + exercise group (M + E). The rats were initially trained to receive small pellets of food by pressing an active lever in the self-administration apparatus. The tail-flick and hot-plate tests were used for pain assessment. To perform the experiment, the jugular vein was exposed and cannulated. After recovery, the animals were placed in the self-administration apparatus and allowed to self-administer morphine in 2 h sessions over 11 consecutive days. RESULTS: The morphine group was found to record a higher number of active lever pressings than did the saline one while this parameter decreased in the morphine + exercise group compared with the morphine one. Moreover, the morphine + exercise exhibited lowered pain sensitivity as evidenced to have reduced morphine use in the hot plate test. CONCLUSION: The exercise might be suggested to reduce using of morphine and modulate pain probably through the release of endogenous opioid.

Contribution of CB1Rs in anxiety-related behaviors but not locomotor deficits induced by methamphetamine.

Several lines of evidence have indicated that Methamphetamine (METH) exposure leads to neurodegenerative changes in the dopaminergic neurons and subsequently may predispose users to motor deficit. On the other hand, there is a reciprocal regulation between the endocannabinoid and the dopaminergic systems. Previous studies also showed that the endocannabinoids are involved in the signaling mechanisms of various brain regions related to motor and cognitive functions. The cerebellum seems as a rational target to investigate the action of cannabinoids on motor coordination because of the high concentration of the cannabinoid receptor in the molecular layer of it and other regions involved in motor activity. The behavioral effects of systemic CBR agonist (3mg/kg/day WIN55,212-2) and antagonist (10mg/kg SR141716A) treatment on METH-induced motor deficits in rats were assessed using open field, rota-rod, and grip tests. Our results show that motor coordination and muscle strength significantly decreased in the animals received METH (5mg/kg, daily×3days) as compared to the saline groups. Pretreatment with neither WIN55,212-2 nor SR141716A had no effects on impairments induced by METH. Meanwhile, motor activity and anxiety-related behaviors significantly increased in the animals that received METH and pretreatment with SR141716A significantly attenuated anxiety-related behaviors induced by METH. In sum, our findings show that anxiety-related behaviors induced by METH can be affected by CB1R manipulation and provide evidence that antagonism of CB1R at high dose cannot reverse the deteriorative METH-induced locomotion changes.

Attenuation Effect of Cannabinoid Type 1 Receptor Activation on Methamphetamine-Induced Neurodegeneration and Locomotion Impairments among Male Rats.

BACKGROUND: A number of neuroimaging studies on human addicts have revealed that abuse of Methamphetamine (METH) can induce neurodegenerative changes in various brain regions like the cerebral cortex and cerebellum. Although the underlying mechanisms of METH-induced neurotoxicity have been studied, the cellular and molecular mechanisms of METH-induced neurotoxicity remain to be clarified. Previous studies implicated that cannabinoid type 1 receptors (CB1Rs) exert neuroprotective effects on several models of cerebral toxicity, but their role in METH-induced neurotoxicity has been rarely investigated. Moreover, the cerebellum was considered as a potential target to evaluate the effects of cannabinoids on locomotion activity as the CB1Rs are most widely distributed in the molecular layer of cerebellum. Therefore, the present study was carried out to evaluate whether neurodegeneration induced in the cerebellum tissue implicated in locomotion deficit induced by METH. METHODS: In the current study, open field test was used to examine locomotor activity. Using hematoxylin and eosin (H&E) staining, morphology of the cerebellar vermis was investigated after repeated exposure to METH. Then, the effects of CB1Rs antagonist [SR17141A, 10 mg/kg, intraperitoneally (IP)] and CB1Rs agonist [WIN55, 212-2 (WIN), 3 mg/kg] against METH-induced neurodegeneration and locomotor deficit were assessed. FINDINGS: The results of the present study demonstrated that repeated exposure to METH increased cerebellar degeneration level as compared to the saline and dimethyl sulfoxide (DMSO) groups. In addition, METH-treated rats showed hyperactivity as compared to the saline and DMSO groups. Pretreatment with WIN significantly attenuated neurodegeneration and hyperactivity induced by METH. CONCLUSION: The findings of this study provided evidence that CB1Rs may serve as a therapeutic strategy for attenuation of METH-induced locomotor deficits.

The effect of vitamin C on morphine self-administration in rats.

BACKGROUND: Recent studies have shown that addiction may be caused by abnormality of neurotransmission in the brain. Two neurotransmitters that involve into morphine addiction are dopamine and glutamate. The glutamatergic and dopaminergic systems are also involved in morphine tolerance and morphine withdrawal syndrome signs. Ascorbic acid (AA), as the antioxidant releases from the glutamatergic neurons, modulates the action of the dopamine and glutamate systems. In this study, the effect of AA on morphine self-administration and morphine withdrawal symptoms has been investigated. MATERIALS AND METHODS: Male Wistar rats (250 - 300g) were anesthetized with ketamine (11%) and xailazine (15%). The cannula was inserted into the right jugular vein, and it was fixed subcutaneously on the skull. After surgery the animals were placed in individual home cages, and they were allowed to recover from the operation for five days, before the test. The animals were subjected to self-administration morphine for12 consecutive days, two-hour/sessions. The number of infusions and number of active and passive lever pressings were recorded. RESULTS: An intra peritoneal injection of Ascorbic acid (AA) (400 mg/kg, i.p.), 30 minutes before morphine self-administration, produced a significant decrease in 12 days self-administration of morphine and withdrawal syndrome signs (P < 0.05). The morphine withdrawal signs (MWS) were recorded after naloxone precipitation, which decreased significantly with the injection of AA (400,700mg/kg), (<0.05). The number of self-infusions and the number of active lever pressings had significantly decreased after AA injection (P < 0.05). CONCLUSION: The chronic administration of AA may prevent the development of tolerance and physical dependence on morphine self-administration via the glutamatergic system.

Effect of electrical stimulation of nucleus accumbens with low, median and high currents intensities on conditioned place preference induced by morphine in rats.

BACKGROUND: Some investigators indicated the effect of electrical or chemical stimulation on different parts of the brain and its effect on animal's behaviors. Furthermore, drug addiction is known to be associated with dysfunction of memory and motivational systems. In this study, we aimed to evaluate the effect of electrical stimulation of nucleus accumbens (NAc) with different currents intensities on conditioned place preference (CPP) induced by morphine. MATERIALS AND METHODS: Male Wistar rats were randomly divided for experimental groups (n = 8). We investigated the influence of electrical stimulation with different current intensities (low: 15 µA, median: 50 µA and high: 100 µA) on NAc with ineffective and effective dose of morphine (0.5 and 5 mg/kg, respectively) on acquisition and expression of morphine-induced place conditioning in male rats. RESULTS: The doses of subcutaneous administration morphine (2.5 and 5 mg/kg, P < 0.05 and P < 0.001; respectively) induced CPP compared with saline group. Furthermore, our findings are showed that electrical stimulation (100 µA) of NAc suppressed morphine-induced CPP. It revealed impairment of learning and memory formation in conditioning process due to morphine administration. CONCLUSION: It is possible that high current intensity (100 µA) had an accompanied effect by a reversal of the increased tissue contents of dopamine and its metabolites in the NAc of morphine-induced CPP rats. Furthermore, high current intensity in combination with ineffective dose of morphine (0.5 mg/kg) increased morphine-induced CPP probability via the prove reward system.

The Role of GABAB Receptors in Morphine Self-Administration.

BACKGROUND: There is only little information about the effects of GABA receptors agonist and antagonist on morphine self-administration. Present study was designed to assess role of GABAB receptors in the regulation of morphine-reinforced self-administration. METHODS: THIS STUDY WAS PERFORMED IN FOUR GROUPS OF RATS: (1) Saline group, which received saline in the self-administration session. (2) Morphine group, which received morphine in saline solution in the self-administration session. (3) Baclofen + Morphine group, which received both baclofen 20 min before self- administration test and morphine in the self-administration session. (4) Phaclofen + Morphine group, which received both phaclofen 20 min before self- administration test and morphine in the self-administration session. The number of lever pressing and self-infusion were recorded. RESULTS: Morphine significantly increased the number of active lever pressing dose dependently in self-administration session in comparative with saline group. Administration of baclofen, 20 min before morphine self-administration produced significant decrease in the initiation of morphine self-administration during all session. Conversely, pre-treatment of phaclofen increased the number of active lever pressing and self-infusion in this test. CONCLUSION: Our results indicated a short-term treatment by baclofen, reduced morphine-maintenance response in a dose-dependent manner, suggesting that GABAB receptor agonists could be useful for reversing the neuroadaptations related to opiates.

Lesion of medial prefrontal cortex reduces morphine-induced extracellular dopamine level in the ventral tegmental area: a microdialysis study in rats.

Drug addiction is a chronic disorder characterized by compulsive drug-seeking behavior despite severe negative consequences. Most abused drugs increase dopamine release in the ventral tegmental area (VTA) and in the nucleus accumbens (NA). The medial prefrontal cortex (mPFC), a part of the mesocorticolimbic dopaminergic system, receives dopaminergic projections from VTA; and in turn, sends glutamatergic projections to both VTA and NA. The present study was designed to further investigate the involvement of the mPFC in the release of dopamine in the VTA by using in vivo microdialysis and high performance liquid chromatography with electrochemical detection (HPLC­ECD). Electrical lesion of the mPFC decreased the level of dopamine in the VTA to approximately 26.8% of basal level. Acute morphine (40 mg/kg i.p.) treatment increased the level of dopamine in the VTA, while the lesion of mPFC immediately before morphine administration attenuated the effects of acute morphine on the level of dopamine. These results suggest that the mPFC modulates dopamine release into the VTA.

Different current intensities electrical stimulation of prelimbic cortex of mPFC produces different effects on morphine-induced conditioned place preference in rats.

The medial prefrontal cortex (mPFC) is a part of brain reward system involved in higher cognitive functions such as learning and memory. The mPFC receives strong dopaminergic innervations from ventral tegmental area (VTA) that comprises a portion of the mesolimbic dopaminergic system (MLDS), and in turn sends glutamate projection to both the VTA and nucleus accumbens (NAc). In the present study, we investigated the influence of electrical stimulation with different current intensities on prelimbic cortex (PL, subdivision of mPFC) (25, 50, 100, and 150 µA) with and without an effective dose of morphine (0.5 and 5 mg/kg) on CPP during conditioning and post-conditioning phases. Subcutaneous administration of morphine 5mg/kg produced significant CPP in comparison with saline group. Our findings also showed that electrical stimulation of PL (100 µA) suppressed morphine-induced CPP that reveals impaired learning and memory formation in the process of conditioning through the blocking connection from the hippocampus to the prelimbic cortex of mPFC. A lowest current intensity (25 µA) in combination with ineffective dose of morphine (0.5 mg/kg) increased morphine-induced CPP probability via the prove reward system.