Enhanced ability of TRPV1 channels in regulating glutamatergic transmission after repeated morphine exposure in the nucleus accumbens of rat

Restoring glutamate homeostasis in the nucleus accumbens via endocannabinoid-mimetic drug prevents relapse to cocaine seeking behavior in rats

Impaired glutamate homeostasis is a key characteristic of the neurobiology of drug addiction in rodent models and contributes to the vulnerability to relapse to drug seeking. Although disrupted astrocytic and presynaptic regulation of glutamate release has been considered to constitute with impaired glutamate homeostasis in rodent model of drug relapse, the involvement of endocannabinoids (eCBs) in this neurobiological process has remained largely unknown. Here, using cocaine self-administration in rats, we investigated the role of endocannabinoids in impaired glutamate homeostasis in the core of nucleus accumbens (NAcore), which was indicated by augmentation of spontaneous synaptic glutamate release, downregulation of metabotropic glutamate receptor 2/3 (mGluR2/3), and mGluR5-mediated astrocytic glutamate release. We found that the endocannabinoid, anandamide (AEA), rather than 2-arachidonoylglycerol elicited glutamate release through presynaptic transient receptor potential vanilloid 1 (TRPV1) and astrocytic cannabinoid type-1 receptors (CB1Rs) in the NAcore of saline-yoked rats. In rats with a history of cocaine self-administration and extinction training, AEA failed to alter synaptic glutamate release in the NAcore, whereas CB1R-mediated astrocytic glutamate release by AEA remained functional. In order to induce increased astrocytic glutamate release via exogenous AEA, (R)-methanandamide (methAEA, a metabolically stable form of AEA) was chronically infused in the NAcore via osmotic pumps during extinction training. Restoration of mGluR2/3 function and mGluR5-mediated astrocytic glutamate release was observed after chronic methAEA infusion. Additionally, priming or cue-induced reinstatement of cocaine seeking was inhibited in methAEA-infused rats. These results demonstrate that enhancing endocannabinoid signaling is a potential pathway to restore glutamate homeostasis and may represent a promising therapeutic strategy for preventing cocaine relapse.

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 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 (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Trans-cinnamaldehyde shows anti-depression effect in the forced swimming test and possible involvement of the endocannabinoid system

Depression is a mental disease that significantly reduces the quality of patients' life. Around 322 million people of all ages carry the heavy burden of depression on a worldwide scale, with a life-time prevalence of 20% according to the WHO. Trans-cinnamaldehyde (TCA) is an excellent COX-2 inhibitor in central nervous system which is a main constituent of GUIZHI as a member of traditional Chinese herb. Furthermore, previous studies demonstrated that TCA suppressed depression-like behavior in chronic unexpected mild stress, plus maze test and open field test. However, the molecular mechanism of TCA anti-depression effect is not clear. We examined the immobility of TCA pretreated male BALB/c mice in the forced swimming test (FST). Results show that TCA (50 mg/kg, po) revealed a significant effect on reduced immobility in the FST, compared with SAL group which indicated that TCA suppressed depression-like behavior. Moreover, TCA elevated the level of 5-HT and decreased the ratio of Glu/GABA in mice hippocampus. Compared with SAL + FST group, TCA + FST group significantly decreased COX-2, TRPV1 and CB1 protein level in mice hippocampus (p < 0.05, p < 0.05, p < 0.01). These findings suggest that TCA treatment exerted anti-depressive effect and was able to regulate neurotransmitters in the FST. This effect may have positive influence on the endocannabinoid (eCB) system.

Loss of Sfrp2 contributes to the neurological disorders related with morphine withdrawal via Wnt/β-catenin signaling

Morphine administration is a medical problem characterized by compulsive opioid use that causes terrible negative consequences. The exact mechanisms of morphine-induced dependence and morphine withdrawal symptoms remain unclear. Recent studies have revealed that the upregulation of Wnt/β-catenin signaling plays important roles in morphine exposure and morphine withdrawal. Secreted frizzled-related protein 2 (Sfrp2) can prevent the activation of Wnt/β-catenin signaling by competing with the Frizzled receptor for Wnt ligands. We conducted this study aimed to evaluate the effect of iatrogenic trauma induced by stereotactic surgery and the protective effect of stereotaxic Sfrp2 injection on morphine withdrawal symptoms in Male Sprague Dawley (SD) rats. Many techniques including western blot analysis and immunoprecipitation were used. Anxiety-related behaviors, morphine withdrawal syndrome, and dendritic spines were also examined in male SD rats after morphine treatment and stereotaxic injection of Sfrp2. Western blot results suggested that Wnt signaling was activated in the nucleus accumbens of SD rats suffering from morphine withdrawal and that Sfrp2 attenuated the overexpression of Wnt signaling. Similarly, the withdrawal-like symptoms of morphine dependent rats were abrogated by intracerebral Sfrp2 injection. The iatrogenic trauma induced by stereotactic surgery showed no influence on the Wnt signaling and withdrawal-like symptoms. Moreover, the results of Golgi-cox staining and DiI staining indicated that the damage on proximal spine density caused by morphine treatment was restored by intracerebral Sfrp2 injection. Together, the data presented here indicated that Sfrp2 abrogated the neurological disorders and loss of proximal spine related with morphine withdrawal via Wnt/β-catenin signaling.

Altered Activity of SK Channel Underpins Morphine Withdrawal Relevant Psychiatric Deficiency in Infralimbic to Accumbens Shell Pathway

Drug addiction can be viewed as a chronic psychiatric disorder that is related to dysfunction of neural circuits, including reward deficits, stress surfeits, craving changes, and compromised executive function. The nucleus accumbens (NAc) plays a crucial role in regulating craving and relapse, while the medial prefrontal cortex (mPFC) represents a higher cortex projecting into the NAc that is active in the management of executive function. In this study, we investigated the role of the small conductance calcium-activated potassium channels (SK channels) in NAc and mPFC after morphine withdrawal. Action potential (AP) firing of neurons in the NAc shell was enhanced via the downregulations of the SK channels after morphine withdrawal. Furthermore, the expression of SK2 and SK3 subunits in the NAc was significantly reduced after 3 weeks of morphine withdrawal, but was not altered in the dorsal striatum. In mPFC, the SK channel subunits were differentially expressed. To be specific, the expression of SK3 was upregulated, while the expression of SK2 was unchanged. Furthermore, the AP firing in layer 5 pyramidal neurons of the infralimbic (IL) cortex was decreased via the upregulations of the SK channel-related tail current after 3 weeks of morphine withdrawal. These results suggest that the SK channel plays a specific role in reward circuits following morphine exposure and a period of drug withdrawal, making it a potential target for the prevention of relapse.

Blockade of TRPV1 Inhibits Methamphetamine-induced Rewarding Effects

Methamphetamine (MAP) is the most widely used psychostimulant in the world, but the exact mechanisms underlying MAP addiction are not yet fully understood. Recent studies have identified the distribution of TRPV1 in several brain regions that are related to drug addiction, including nucleus accumbens (NAc) and dorsal striatum (DSt). In the present study, we performed conditioned place preference (CPP) and self-administration tests to examine the effects of capsazepine (CPZ) and SB366791 (SB) on MAP reward. We found that both CPZ and SB significantly inhibited MAP-induced CPP and self-administration; in contrast, TRPV1 knock-out (KO) mice did not develop MAP-induced CPP. Real-time RT-PCR, Western blot and quantitative autoradiographic tests showed up-regulation of TRPV1 mRNA and protein expression in the NAc and/or DSt regions of mice exhibiting MAP-induced CPP. In addition, an in vivo microdialysis experiment showed that CPZ dramatically reduced dopamine (DA) levels in the NAc region of MAP-treated mice. Furthermore, attenuated dopamine transporter (DAT) binding levels in the NAc and DSt regions of MAP-induced CPP mice were reversed by CPZ. Together, these data suggest that TRPV1 plays an important role in MAP reward via the modulation of DA release and DAT density, thereby providing a novel therapeutic target for MAP addiction.