Cannabinoids and monoamine neurotransmission with focus on monoamine oxidase

Synergistic interaction between clonidine and ACPA on the modulation of anxiety-like behaviors in non-acute restraint stress and acute restraint stress conditions

The present research examined the possible role of α-2 adrenergic receptor drugs (clonidine, selective α-2 adrenergic receptor agonist, and yohimbine, competitive α-2 adrenoreceptor antagonist,) on the effect of arachidonylcyclopropylamide (ACPA), a cannabinoid CB1 receptor agonist, in non-acute restraint stress (NARS) and acute restraint stress (ARS) mice. The animals were unilaterally implanted with a cannula in the left lateral ventricle. ARS was carried out by movement restraint at a period of 4 h. An elevated plus-maze (EPM) apparatus was used to evaluate anxiety-like behaviors. The results indicated that induction of ARS for 4 h induced anxiogenic-like behavior due to the reduction of %OAT (the percentage of time spent in the open arms) in male mice. Additionally, ARS caused neuronal degeneration in the prefrontal cortex. On the other hand, alone intracerebroventricularly (i.c.v.) infusions of ACPA (0.5 µg/mouse) and clonidine (0.5 µg/mouse) increased %OAT, indicating an anxiolytic-like response in the NARS and ARS mice. In contrast, alone i.c.v. infusions of yohimbine (0.5 µg/mouse) decreased %OAT and %OAE (the percentage of entries to the open arms), proposing an anxiogenic-like effect in the NARS and ARS mice. When the subthreshold dose of ACPA and different doses of clonidine were co-injected, ACPA potentiated the anxiolytic-like behavior produced by clonidine in the ARS mice. On the other hand, when the ineffective dosage of ACPA and different dosages of yohimbine were co-infused, ACPA reversed the anxiogenic-like effect induced by yohimbine in the NARS and ARS mice. Moreover, the results revealed a synergistic effect between ACPA and clonidine upon induction of anxiolytic-like behaviors. It can be concluded that the interaction between clonidine and ACPA modulates the anxiety-like behaviors induced by stress in male mice.

Single or combined exposure to chlorpyrifos and cypermethrin provoke oxidative stress and downregulation in monoamine oxidase and acetylcholinesterase gene expression of the rat's brain

The extensive uses of organophosphates and pyrethroids have made it necessary to investigate the neurotoxicity of their combination as they may implicate in the neurodegenerative syndromes. Monoamine oxidase-A (MAO-A) and acetylcholinesterase (AChE) gene expression in the rat brain were evaluated after independent and combined intoxications with chlorpyrifos and cypermethrin. Twenty-four mature male rats were equally distributed into four groups. The first one was kept as a control group, whereas the second, third and fourth were orally gavage with chlorpyrifos (16.324 mg/kg), cypermethrin (25.089 mg/kg) and their combination (9.254 mg/kg), respectively, for 4 weeks. As compared to the control group, intoxications with chlorpyrifos and/or cypermethrin revealed significant (P < 0.05) declines in the levels of brain neurotransmitters (dopamine and serotonin) plus the enzymatic activities of MAO-A, AChE and sodium-potassium adenosine triphosphatase. The mRNA genes expression of MAO-A and AChE have also confirmed the enzymatic actions. Moreover, the oxidative injury recorded as the levels of malondialdehyde and nitric oxide markedly increased (P < 0.01), while the total thiol content reduced and the histopathological outcomes have confirmed these impacts. In conclusion, chlorpyrifos and cypermethrin revealed antagonistic inhibitions on the brain MAO-A and AChE gene regulation through neurotransmission deteriorations and oxidative damage, which could describe their contributions in the neuropathological progressions.

Involvement of medial prefrontal cortex alpha-2 adrenoceptors on memory acquisition deficit induced by arachidonylcyclopropylamide, a cannabinoid CB1 receptor agonist, in rats; possible involvement of Ca2+ channels

Functional interactions between cannabinoid and alpha-2 adrenergic systems in cognitive control in the medial prefrontal cortex (mPFC) seem possible. The present study evaluated the possible role of alpha-2 adrenoceptors of the prefrontal cortex on effect of arachidonylcyclopropylamide (ACPA), a cannabinoid CB1 receptor (CB1R) agonist, in adult male Wistar rats. The animals were bilaterally implanted with chronic cannulae in the mPFC, trained in a step-through task, and tested 24 h after training to measure step-through latency. Results indicate that pre-training microinjection of ACPA (0.05 and 0.5 μg/rat) and clonidine (alpha-2 adrenoceptor agonist; 1 and 2 μg/rat) reduce memory acquisition. Pre-training subthreshold dose of clonidine (0.5 µg/rat) restored memory-impairing effect of ACPA (0.05 and 0.5 µg/rat). On the other hand, pre-training administration of the alpha-2 adrenoceptor antagonist yohimbine in all doses used (0.5, 1, and 2 μg/rat) did not affect memory acquisition by itself, while a subthreshold dose of yohimbine (2 µg/rat) potentiated memory impairment induced by ACPA (0.005 µg/rat). Finally, a subthreshold dose of SKF96365 (a Ca(2+) channel blocker) blocked clonidine and yohimbine effect of memory responses induced by ACPA. In conclusion, these data indicate that mPFC alpha-2 adrenoceptors play an important role in ACPA-induced amnesia and Ca(2+) channels have a critical role this phenomenon.

Drugs related to monoamine oxidase activity

Progress in understanding the role of monoamine neurotransmission in pathophysiology of neuropsychiatric disorders was made after the discovery of the mechanisms of action of psychoactive drugs, including monoamine oxidase (MAO) inhibitors. The increase in monoamine neurotransmitter availability, decrease in hydrogen peroxide production, and neuroprotective effects evoked by MAO inhibitors represent an important approach in the development of new drugs for the treatment of mental disorders and neurodegenerative diseases. New drugs are synthesized by acting as multitarget-directed ligands, with MAO, acetylcholinesterase, and iron chelation as targets. Basic information is summarized in this paper about the drug-induced regulation of monoaminergic systems in the brain, with a focus on MAO inhibition. Desirable effects of MAO inhibition include increased availability of monoamine neurotransmitters, decreased oxidative stress, decreased formation of neurotoxins, induction of pro-survival genes and antiapoptotic factors, and improved mitochondrial functions.

Novel psychoactive substances: the pharmacology of stimulants and hallucinogens

There are increasing levels of concern relating to the rapidly evolving novel psychoactive substances/NPS and web markets' scenarios. The paper aims at providing an overview of the clinical pharmacological issues related to some of the most popular NPS categories, e.g. stimulants and hallucinogens. NPS intake is typically associated with the imbalance of a complex range of neurotransmitter pathways/receptors, namely: dopamine; cannabinoid/CB1; and 5-HT2A. The intake is almost invariably undetectable with standard screening tests. Hence, it may frequently occur that the acute management of NPS misusers will need to focus on decreasing levels of both self/outward-directed aggression and agitation. Benzodiazepines may be considered as first line treatment. Alternatively, propofol and/or antipsychotics can be administered. Focus will be as well on treatment of possible rhabdomyolysis and hyperthermia. Indeed, future studies should inform better tailored management/treatment strategies.

Molecular Mechanisms of Cannabis Signaling in the Brain

Cannabis has been cultivated and used by humans for thousands of years. Research for decades was focused on understanding the mechanisms of an illegal/addictive drug. This led to the discovery of the vast endocannabinoid system. Research has now shifted to understanding fundamental biological questions related to one of the most widespread signaling systems in both the brain and the body. Our understanding of cannabinoid signaling has advanced significantly in the last two decades. In this review, we discuss the state of knowledge on mechanisms of Cannabis signaling in the brain and the modulation of key brain neurotransmitter systems involved in both brain reward/addiction and psychiatric disorders. It is highly probable that various cannabinoids will be found to be efficacious in the treatment of a number of psychiatric disorders. However, while there is clearly much potential, marijuana has not been properly vetted by the medical-scientific evaluation process and there are clearly a range of potentially adverse side-effects-including addiction. We are at crossroads for research on endocannabinoid function and therapeutics (including the use of exogenous treatments such as Cannabis). With over 100 cannabinoid constituents, the majority of which have not been studied, there is much Cannabis research yet to be done. With more states legalizing both the medicinal and recreational use of marijuana the rigorous scientific investigation into cannabinoid signaling is imperative.

Mitochondria: key players in the neurotoxic effects of amphetamines

Amphetamines are a class of psychotropic drugs with high abuse potential, as a result of their stimulant, euphoric, emphathogenic, entactogenic, and hallucinogenic properties. Although most amphetamines are synthetic drugs, of which methamphetamine, amphetamine, and 3,4-methylenedioxymethamphetamine ("ecstasy") represent well-recognized examples, the use of natural related compounds, namely cathinone and ephedrine, has been part of the history of humankind for thousands of years. Resulting from their amphiphilic nature, these drugs can easily cross the blood-brain barrier and elicit their well-known psychotropic effects. In the field of amphetamines' research, there is a general consensus that mitochondrial-dependent pathways can provide a major understanding concerning pathological processes underlying the neurotoxicity of these drugs. These events include alterations on tricarboxylic acid cycle's enzymes functioning, inhibition of mitochondrial electron transport chain's complexes, perturbations of mitochondrial clearance mechanisms, interference with mitochondrial dynamics, as well as oxidative modifications in mitochondrial macromolecules. Additionally, other studies indicate that amphetamines-induced neuronal toxicity is closely regulated by B cell lymphoma 2 superfamily of proteins with consequent activation of caspase-mediated downstream cell death pathway. Understanding the molecular mechanisms at mitochondrial level involved in amphetamines' neurotoxicity can help in defining target pathways or molecules mediating these effects, as well as in developing putative therapeutic approaches to prevent or treat the acute- or long-lasting neuropsychiatric complications seen in human abusers.

Drug discovery strategies that focus on the endocannabinoid signaling system in psychiatric disease

INTRODUCTION

The endocannabinoid (eCB) system plays an important role in the control of mood, and its dysregulation has been implicated in several psychiatric disorders. Targeting the eCB system appears to represent an attractive and novel approach to the treatment of depression and other mood disorders. However, several failed clinical trials have diminished enthusiasm for the continued development of eCB-targeted therapeutics for psychiatric disorders, despite the encouraging preclinical data and promising preliminary results obtained with the synthetic cannabinoid nabilone for treating post-traumatic stress disorder.

AREAS COVERED

This review describes the eCB system's role in modulating cell signaling within the brain. There is a specific focus on eCB's regulation of monoamine neurotransmission and the stress axis, as well as how dysfunction of this interaction can contribute to the development of psychiatric disorders. Additionally, the review provides discussion on compounds and drugs that target this system and might prove to be successful for the treatment of mood-related psychiatric disorders.

EXPERT OPINION

The discovery of increasingly selective modulators of CB receptors should enable the identification of optimal therapeutic strategies. It should also maximize the likelihood of developing safe and effective treatments for debilitating psychiatric disorders.

Cannabinoid-induced changes in respiration of brain mitochondria

Cannabinoids exert various biological effects that are either receptor-mediated or independent of receptor signaling. Mitochondrial effects of cannabinoids were interpreted either as non-receptor-mediated alteration of mitochondrial membranes, or as indirect consequences of activation of plasma membrane type 1 cannabinoid receptors (CB1). Recently, CB1 receptors were confirmed to be localized to the membranes of neuronal mitochondria, where their activation directly regulates respiration and energy production. Here, we performed in-depth analysis of cannabinoid-induced changes of mitochondrial respiration using both an antagonist/inverse agonist of CB1 receptors, AM251 and the cannabinoid receptor agonists, Δ(9)-tetrahydrocannabinol (THC), cannabidiol, anandamide, and WIN 55,212-2. Relationships were determined between cannabinoid concentration and respiratory rate driven by substrates of complex I, II or IV in pig brain mitochondria. Either full or partial inhibition of respiratory rate was found for the tested drugs, with an IC50 in the micromolar range, which verified the significant role of non-receptor-mediated mechanism in inhibiting mitochondrial respiration. Effect of stepwise application of THC and AM251 evidenced protective role of AM251 and corroborated the participation of CB1 receptor activation in the inhibition of mitochondrial respiration. We proposed a model, which includes both receptor- and non-receptor-mediated mechanisms of cannabinoid action on mitochondrial respiration. This model explains both the inhibitory effect of cannabinoids and the protective effect of the CB1 receptor inverse agonist.

Selective MAO-B inhibitors: a lesson from natural products

Monoamine oxidases (MAOs) are mitochondrial bound enzymes, which catalyze the oxidative deamination of monoamine neurotransmitters. Inside the brain, MAOs are present in two isoforms: MAO-A and MAO-B. The activity of MAO-B is generally higher in patients affected by neurodegenerative diseases like Alzheimer's and Parkinson's. Therefore, the search for potent and selective MAO-B inhibitors is still a challenge for medicinal chemists. Nature has always been a source of inspiration for the discovery of new lead compounds. Moreover, natural medicine is a major component in all traditional medicine systems. In this review, we present the latest discoveries in the search for selective MAO-B inhibitors from natural sources. For clarity, compounds have been classified on the basis of structural analogy or source: flavonoids, xanthones, tannins, proanthocyanidins, iridoid glucosides, curcumin, alkaloids, cannabinoids, and natural sources extracts. MAO inhibition values reported in the text are not always consistent due to the high variability of MAO sources (bovine, pig, rat brain or liver, and human) and to the heterogeneity of the experimental protocols used.

Spice drugs are more than harmless herbal blends: a review of the pharmacology and toxicology of synthetic cannabinoids

"K2" and "Spice" drugs (collectively hereafter referred to as Spice) represent a relatively new class of designer drugs that have recently emerged as popular alternatives to marijuana, otherwise characterized as "legal highs". These drugs are readily available on the Internet and sold in many head shops and convenience stores under the disguise of innocuous products like herbal blends, incense, or air fresheners. Although package labels indicate "not for human consumption", the number of intoxicated people presenting to emergency departments is dramatically increasing. The lack of validated and standardized human testing procedures and an endless supply of potential drugs of abuse are primary reasons why researchers find it difficult to fully characterize clinical consequences associated with Spice. While the exact chemical composition and toxicology of Spice remains to be determined, there is mounting evidence identifying several synthetic cannabinoids as causative agents responsible for psychoactive and adverse physical effects. This review provides updates of the legal status of common synthetic cannabinoids detected in Spice and analytical procedures used to test Spice products and human specimens collected under a variety of clinical circumstances. The pharmacological and toxicological consequences of synthetic cannabinoid abuse are also reviewed to provide a future perspective on potential short- and long-term implications.

Stress-induced sensitization of cortical adrenergic receptors following a history of cannabinoid exposure

The cannabinoid receptor agonist, WIN 55,212-2, increases extracellular norepinephrine levels in the rat frontal cortex under basal conditions, likely via desensitization of inhibitory α2-adrenergic receptors located on norepinephrine terminals. Here, the effect of WIN 55,212-2 on stress-induced norepinephrine release was assessed in the medial prefrontal cortex (mPFC), in adult male Sprague-Dawley rats using in vivo microdialysis. Systemic administration of WIN 55,212-2 30 min prior to stressor exposure prevented stress-induced cortical norepinephrine release induced by a single exposure to swim when compared to vehicle. To further probe cortical cannabinoid-adrenergic interactions, postsynaptic α2-adrenergic receptor (AR)-mediated responses were assessed in mPFC pyramidal neurons using electrophysiological analysis in an in vitro cortical slice preparation. We confirm prior studies showing that clonidine increases cortical pyramidal cell excitability and that this was unaffected by exposure to acute stress. WIN 55,212-2, via bath application, blocked postsynaptic α2-AR mediated responses in cortical neurons irrespective of exposure to stress. Interestingly, stress exposure prevented the desensitization of α2-AR mediated responses produced by a history of cannabinoid exposure. Together, these data indicate the stress-dependent nature of cannabinoid interactions via both pre- and postsynaptic ARs. In summary, microdialysis data indicate that cannabinoids restrain stress-induced cortical NE efflux. Electrophysiology data indicate that cannabinoids also restrain cortical cell excitability under basal conditions; however, stress interferes with these CB1-α2 AR interactions, potentially contributing to over-activation of pyramidal neurons in mPFC. Overall, cannabinoids are protective of the NE system and cortical excitability but stress can derail this protective effect, potentially contributing to stress-related psychopathology. These data add to the growing evidence of complex, stress-dependent modulation of monoaminergic systems by cannabinoids and support the potential use of cannabinoids in the treatment of stress-induced noradrenergic dysfunction.