Effect of repeated administration of delta 9-tetrahydrocannabinol on delayed matching-to-sample performance in rats

Targeting Endocannabinoid System in Epilepsy: For Good or for Bad

Epilepsy is a neurological disorder with a high prevalence worldwide. Several studies carried out during the last decades indicate that the administration of cannabinoids as well as the activation of the endocannabinoid system (ECS) represent a therapeutic strategy to control epilepsy. However, there are controversial studies indicating that activation of ECS results in cell damage, inflammation and neurotoxicity, conditions that facilitate the seizure activity. The present review is focused to present findings supporting this issue. According to the current discrepancies, it is relevant to elucidate the different effects induced by the activation of ECS and determine the conditions under which it facilitates the seizure activity.

Effects of opioid/cannabinoid mixtures on impulsivity and memory in rhesus monkeys

The opioid epidemic underscores the need for safer and more effective treatments for pain. Combining opioid receptor agonists with drugs that relieve pain through nonopioid mechanisms could be a useful strategy for reducing the dose of opioid needed to treat pain, thereby reducing risks associated with opioids alone. Opioid/cannabinoid mixtures might be useful in this context; individually, opioids and cannabinoids have modest effects on cognition, and it is important to determine whether those effects occur with mixtures. Delay discounting and delayed matching-to-sample tasks were used to examine effects of the mu-opioid receptor agonist morphine (0.32-5.6 mg/kg), the cannabinoid CB1/CB2 receptor agonist CP55940 (0.0032-0.1 mg/kg), and morphine/CP55940 mixtures on impulsivity (n = 3) and memory (n = 4) in rhesus monkeys. Alone, each drug decreased rate of responding without modifying choice in the delay-discounting task, and morphine/CP55940 mixtures reduced choice of one pellet in a delay dependent manner, with monkeys instead choosing delayed delivery of the larger number of pellets. With the exception of one dose in one monkey, accuracy in the delayed matching-to-sample task was not altered by either drug alone. Morphine/CP55940 mixtures decreased accuracy in two monkeys, but the doses in the mixture were equal to or greater than doses that decreased accuracy or response rate with either drug alone. Rate-decreasing effects of morphine/CP55940 mixtures were additive. These data support the notion that opioid/cannabinoid mixtures that might be effective for treating pain do not have greater, and might have less, adverse effects compared with larger doses of each drug alone.

The Effects of Cannabinoids on Executive Functions: Evidence from Cannabis and Synthetic Cannabinoids-A Systematic Review

Background—Cannabis is the most popular illicit drug in the Western world. Repeated cannabis use has been associated with short and long-term range of adverse effects. Recently, new types of designer-drugs containing synthetic cannabinoids have been widespread. These synthetic cannabinoid drugs are associated with undesired adverse effects similar to those seen with cannabis use, yet, in more severe and long-lasting forms. Method—A literature search was conducted using electronic bibliographic databases up to 31 December 2017. Specific search strategies were employed using multiple keywords (e.g., “synthetic cannabinoids AND cognition,” “cannabis AND cognition” and “cannabinoids AND cognition”). Results—The search has yielded 160 eligible studies including 37 preclinical studies (5 attention, 25 short-term memory, 7 cognitive flexibility) and 44 human studies (16 attention, 15 working memory, 13 cognitive flexibility). Both pre-clinical and clinical studies demonstrated an association between synthetic cannabinoids and executive-function impairment either after acute or repeated consumptions. These deficits differ in severity depending on several factors including the type of drug, dose of use, quantity, age of onset and duration of use. Conclusions—Understanding the nature of the impaired executive function following consumption of synthetic cannabinoids is crucial in view of the increasing use of these drugs.

Synthetic cannabinoid JWH-018 and its halogenated derivatives JWH-018-Cl and JWH-018-Br impair Novel Object Recognition in mice: Behavioral, electrophysiological and neurochemical evidence

It is well known that an impairment of learning and memory function is one of the major physiological effects caused by natural or synthetic cannabinoid consumption in rodents, nonhuman primates and in humans. JWH-018 and its halogenated derivatives (JWH-018-Cl and JWH-018-Br) are synthetic CB1/CB2 cannabinoid agonists, illegally marketed as "Spice" and "herbal blend" for their Cannabis-like psychoactive effects. In the present study the effects of acute exposure to JWH-018, JWH-018-Cl, JWH-018-Br (JWH-018-R compounds) and Δ(9)-THC (for comparison) on Novel Object Recognition test (NOR) has been investigated in mice. Moreover, to better characterize the effects of JWH-018-R compounds on memory function, in vitro electrophysiological and neurochemical studies in hippocampal preparations have been performed. JWH-018, JWH-018-Cl and JWH-018-Br dose-dependently impaired both short- and long-memory retention in mice (respectively 2 and 24 h after training session). Their effects resulted more potent respect to that evoked by Δ(9)-THC. Moreover, in vitro studies showed as JWH-018-R compounds negatively affected electrically evoked synaptic transmission, LTP and aminoacid (glutamate and GABA) release in hippocampal slices. Behavioral, electrophysiological and neurochemical effects were fully prevented by CB1 receptor antagonist AM251 pretreatment, suggesting a CB1 receptor involvement. These data support the hypothesis that synthetic JWH-018-R compounds, as Δ(9)-THC, impair cognitive function in mice by interfering with hippocampal synaptic transmission and memory mechanisms. This data outline the danger that the use and/or abuse of these synthetic cannabinoids may represent for the cognitive process in human consumer.

Cannabis and adolescent brain development

Heavy cannabis use has been frequently associated with increased rates of mental illness and cognitive impairment, particularly amongst adolescent users. However, the neurobiological processes that underlie these associations are still not well understood. In this review, we discuss the findings of studies examining the acute and chronic effects of cannabis use on the brain, with a particular focus on the impact of commencing use during adolescence. Accumulating evidence from both animal and human studies suggests that regular heavy use during this period is associated with more severe and persistent negative outcomes than use during adulthood, suggesting that the adolescent brain may be particularly vulnerable to the effects of cannabis exposure. As the endocannabinoid system plays an important role in brain development, it is plausible that prolonged use during adolescence results in a disruption in the normative neuromaturational processes that occur during this period. We identify synaptic pruning and white matter development as two processes that may be adversely impacted by cannabis exposure during adolescence. Potentially, alterations in these processes may underlie the cognitive and emotional deficits that have been associated with regular use commencing during adolescence.

A cannabinoid CB(1) receptor antagonist ameliorates impairment of recognition memory on withdrawal from MDMA (Ecstasy)

(+/-)-3,4-Methylenedioxymethamphetamine (MDMA, 'Ecstasy') abusers have persistent neuropsychiatric deficits including memory impairments after the cessation of abuse. On the other hand, cannabinoid CB(1) receptors have been implicated in learning/memory, and are highly expressed in the hippocampus, a region of the brain believed to have an important function in certain forms of learning and memory. In this study, we clarified the mechanism underlying the cognitive impairment that develops during MDMA withdrawal from the standpoint of the cannabinoid CB(1) receptors. Mice were administered MDMA (10 mg/kg, i.p.) once a day for 7 days. On the 7th day of withdrawal, a novel object recognition task was performed and the amount of cannabinoid CB(1) receptor protein was measured with western blotting. Recognition performance was impaired on the 7th day of withdrawal. This impairment was blocked by AM251, a cannabinoid CB(1) receptor antagonist, administered 30 min before the training trial or co-administered with MDMA. At this time, the level of cannabinoid CB(1) receptor protein increased significantly in the hippocampus but not the prefrontal cortex or striatum. This increase of CB(1) receptor protein in the hippocampus was also blocked by the co-administration of AM251. Furthermore, CB(1) receptor knockout mice showed no impairment of recognition performance on the withdrawal from MDMA. The impairment of recognition memory during withdrawal from MDMA may result from the activation of cannabinoid CB(1) receptors in the hippocampus.

Chronic Delta9-tetrahydrocannabinol during adolescence increases sensitivity to subsequent cannabinoid effects in delayed nonmatch-to-position in rats

Early-onset marijuana use has been associated with short- and long-term deficits in cognitive processing. In human users, self-selection bias prevents determination of the extent to which these effects result only from drug use. This study examined the long-term effects of Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the major psychoactive constituent of marijuana, in a delayed nonmatch-to-position task (DNMP). Male Long-Evans rats were injected daily with 10 mg/kg Delta(9)-THC during or after adolescence [postnatal days (PN) 21-50 or PN50-79, respectively] or with vehicle. On PN91, training in DNMP was initiated. Successful acquisition and pharmacological challenge began on approximately PN300. Decreases in accuracy were observed at lower doses of Delta(9)-THC in Delta(9)-THC-treated rats (versus vehicle-treated rats). Administration of chronic Delta(9)-THC at a younger age tended to enhance this effect. While anandamide did not decrease accuracy in any group, rats treated with Delta(9)-THC during adolescence initiated fewer trials at the 30 mg/kg dose of anandamide than did rats in the other two groups. To the extent tested, these differences were pharmacologically selective for cannabinoids, as scopolamine (positive control) decreased accuracy at the same dose in all groups and amphetamine (negative control) did not affect accuracy in any of the groups at doses that did not impair overall responding. These results suggest that repeated administration of a modest dose of Delta(9)-THC during adolescence (PN21-50) or shortly thereafter (PN50-79) produces a long-term increase in latent sensitivity to cannabinoid-induced impairment of performance in a complex operant task.

Cannabinoids and prefrontal cortical function: Insights from preclinical studies

Marijuana use has been associated with disordered cognition across several domains influenced by the prefrontal cortex (PFC). Here, we review the contribution of preclinical research to understanding the effects of cannabinoids on cognitive ability, and the mechanisms by which cannabinoids may affect the neurochemical processes in the PFC that are associated with these impairments. In rodents, acute administration of cannabinoid agonists produces deficits in working memory, attentional function and reversal learning. These effects appear to be largely dependent on CB1 cannabinoid receptor activation. Preclinical studies also indicate that the endogenous cannabinoid system may tonically regulate some mnemonic processes. Effects of cannabinoids on cognition may be mediated via interaction with neurochemical processes in the PFC and hippocampus. In the PFC, cannabinoids may alter dopaminergic, cholinergic and serotonergic transmission. These mechanisms may underlie cognitive impairments observed following marijuana intake in humans, and may also be relevant to other disorders of cognition. Preclinical research will further enhance our understanding of the interactions between the cannabinoid system and cognitive functioning.

Cannabinoid function in learning, memory and plasticity

Marijuana and its psychoactive constituents induce a multitude of effects on brain function. These include deficits in memory formation, but care needs to be exercised since many human studies are flawed by multiple drug abuse, small sample sizes, sample selection and sensitivity of psychological tests for subtle differences. The most robust finding with respect to memory is a deficit in working and short-term memory. This requires intact hippocampus and prefrontal cortex, two brain regions richly expressing CB1 receptors. Animal studies, which enable a more controlled drug regime and more constant behavioural testing, have confirmed human results and suggest, with respect to hippocampus, that exogenous cannabinoid treatment selectively affects encoding processes. This may be different in other brain areas, for instance the amygdala, where a predominant involvement in memory consolidation and forgetting has been firmly established. While cannabinoid receptor agonists impair memory formation, antagonists reverse these deficits or act as memory enhancers. These results are in good agreement with data obtained from electrophysiological recordings, which reveal reduction in neural plasticity following cannabinoid treatment, and increased plasticity following antagonist exposure. The mixed receptor properties of the pharmacological tool, however, make it difficult to define the exact role of any CB1 receptor population in memory processes with any certainty. This makes it all the more important that behavioural studies use selective administration of drugs to specific brain areas, rather than global administration to whole animals. The emerging role of the endogenous cannabinoid system in the hippocampus may be to facilitate the induction of long-term potentiation/the encoding of information. Administration of exogenous selective CB1 agonists may therefore disrupt hippocampus-dependent learning and memory by 'increasing the noise', rather than 'decreasing the signal' at potentiated inputs.

The psychotomimetic effects of intravenous delta-9-tetrahydrocannabinol in healthy individuals: implications for psychosis

Recent advances in the understanding of brain cannabinoid receptor function have renewed interest in the association between cannabinoid compounds and psychosis. In a 3-day, double-blind, randomized, and counterbalanced study, the behavioral, cognitive, and endocrine effects of 0, 2.5, and 5 mg intravenous delta-9-tetrahydrocannabinol (Delta-9-THC) were characterized in 22 healthy individuals, who had been exposed to cannabis but had never been diagnosed with a cannabis abuse disorder. Prospective safety data at 1, 3, and 6 months poststudy was also collected. Delta-9-THC (1) produced schizophrenia-like positive and negative symptoms; (2) altered perception; (3) increased anxiety; (4) produced euphoria; (5) disrupted immediate and delayed word recall, sparing recognition recall; (6) impaired performance on tests of distractibility, verbal fluency, and working memory (7) did not impair orientation; (8) increased plasma cortisol. These data indicate that Delta-9-THC produces a broad range of transient symptoms, behaviors, and cognitive deficits in healthy individuals that resemble some aspects of endogenous psychoses. These data warrant further study of whether brain cannabinoid receptor function contributes to the pathophysiology of psychotic disorders.

Activation of brain prostanoid EP3 receptors via arachidonic acid cascade during behavioral suppression induced by Delta8-tetrahydrocannabinol

We have previously shown that behavioral changes induced by cannabinoid were due to an elevation of prostaglandin E2 (PGE2) via the arachidonic acid cascade in the brain. In the present study, we investigated the participation of the prostanoid EP3 receptor, the target of PGE2 in the brain, in behavioral suppression induced by Delta8-tetrahydrocannabinol (Delta8-THC), an isomer of the naturally occurring Delta9-THC, using a one-lever operant task in rats. Intraperitoneal administration of Delta8-THC inhibited the lever-pressing behavior, which was significantly antagonized by both the selective cannabinoid CB1 receptor antagonist SR141716A and the cyclooxygenase inhibitor diclofenac. Furthermore, intracerebroventricular (i.c.v.) administration of PGE2 significantly inhibited the lever-pressing performance similar to Delta8-THC. Prostanoid EP3 receptor antisense-oligodeoxynucleotide (AS-ODN; twice a day for 3 days, i.c.v.) significantly decreased prostanoid EP3 receptor mRNA levels as determined by the RT-PCR analysis in the cerebral cortex, hippocampus and midbrain. AS-ODN also antagonized the PGE2-induced suppression of the lever pressing. In the same way, the suppression of lever-pressing behavior by Delta8-THC was significantly improved by AS-ODN. It is concluded that the suppression of lever-pressing behavior by cannabinoid is due to activation of the prostanoid EP3 receptor through an elevation of PGE2 in the brain.

The cannabinoid agonist WIN 55,212-2 reduces sensorimotor gating and recognition memory in rats

Cannabinoids can disrupt short-term memory in humans and animals and induce learning deficits and other cognitive impairments. In the present study we examined the role of a full cannabinoid agonist in short-term memory, sensorimotor gating, and the acquisition and expression of an operant learning paradigm in rats. We tested the effects of the synthetic cannabinoid WIN 55,212-2 (0.6 and 1.2 mg/kg) on short-term memory in social and object recognition tests, on prepulse inhibition (PPI) of startle, as well as on lever pressing for palatable food. Injections of 0.6 and 1.2 mg/kg WIN 55,212-2 impaired recognition memory and PPI in a dose-dependent manner, but had no effect on lever-pressing acquisition or expression, or on food preference. The PPI deficit was reversed by the administration of 0.1 mg/kg haloperidol. These data suggest that the synthetic cannabinoid WIN 55,212-2 does not lead to a general impairment of learning in an appetitive instrumental task, but significantly affects short-term memory and sensorimotor integration. The impairment in recognition and PPI might be due to deficits in attention-based short-term information processing.

Endogenous cannabinoid, 2-arachidonoylglycerol, attenuates naloxone-precipitated withdrawal signs in morphine-dependent mice

In the present study, we examined the effects of endogenous ligand 2-arachidonoylglycerol (2-AG) on naloxone-precipitated withdrawal in morphine-dependent mice, in comparison with that of two cannabinoid agonists, an ingredient of Cannabis sativa Delta(8)-tetrahydrocannabinol (Delta(8)-THC) and the synthetic cannabinoid CB1 receptor agonist HU-210. 2-AG at a dose of 10 microg per mouse (i.c.v.) significantly inhibited both jumping and forepaw tremor as signs of withdrawal following naloxone challenge in morphine-dependent mice. Furthermore, both Delta(8)-THC and HU-210 significantly attenuated these symptoms of withdrawal in morphine-dependent mice. Therefore, it is suggested that inactivation of the endogenous cannabinoid system is related to the induction of withdrawal syndrome in morphine-dependent mice. Moreover, hyperlocomotor activity in morphine-dependent mice was markedly increased by Delta(8)-THC 10 mg/kg, which had no effect in naive mice. This finding suggested that in morphine dependence, upregulation of cannabinoid CB1 receptors occurred. Non-psychoactive CB1 receptor agonists or accelerators of endocannabinoid synthesis may be potential as therapeutic drugs for opiate withdrawal symptoms.

Behavioral suppression induced by cannabinoids is due to activation of the arachidonic acid cascade in rats

Tetrahydrocannabinol (THC) is the principle psychoactive ingredient of marijuana and produces various psychoactive effects through the brain cannabinoid (CB1) receptor. The CB1 receptor belongs to the seven-transmembrane domain family of G-protein-coupled receptors and is involved in the arachidonic acid cascade in the brain. Few reports have attempted to clarify the functional role of endogenous cannabinoid and the arachidonic acid cascade through the CB1 receptor using a behavioral paradigm. Therefore, in this study, we clarified the mechanism of cannabinoid-induced suppression of lever pressing in rats, focusing on the arachidonic acid cascade as a novel second messenger of CB1 receptor. Delta(8)-THC and the potent synthetic CB1 receptor agonist HU-210 dose-dependently inhibited lever-pressing performance. The Delta(8)-THC-induced suppression was significantly antagonized by the cyclooxygenase (COX) inhibitors diclofenac (32 mg/kg, i.p.), aspirin (10 mg/kg, i.p.) and indomethacin (10 mg/kg, i.p.). The suppressive effect of HU-210 was also significantly antagonized by 32 mg/kg diclofenac. Prostaglandin E(2) (3.2 microg/rat, i.c.v.), the final product of the arachidonic acid cascade, significantly inhibited lever pressing similar to Delta(8)-THC and HU-210. In conclusion, we found that suppression of lever-pressing behavior induced by cannabinoids was mediated through activation of the arachidonic acid cascade via the CB1 receptor. Therefore, it is possible that the psychoactive effects of cannabinoid are due to an increase in the formation of PGE(2) in the brain.

Recognition memory in rats--I. Concepts and classification

Recognition is the process by which a subject is aware that a stimulus has been previously experienced. It requires that the characteristics of events are perceived, discriminated, identified and then compared (matched) against a memory of the characteristics of previously experienced events. Understanding recognition memory, its underlying neuronal mechanisms, its dysfunction and alleviation of the latter by putative cognition enhancing drugs is a major research target and has triggered a wealth of animal studies. One of the most widely used animals for this purpose is the rat, and it is the rat's recognition memory which is the focus of this review. In this first part, concepts of recognition memory, stages of mnemonic processing and paradigms for the measurement of the rat's recognition memory will be discussed. In two subsequent articles (parts II and III) we will focus on the neuronal mechanisms underlying recognition memory in rats. Three major points arise from the comparison of paradigms that have in the past been used to assess recognition memory in rats. First, it should be realized that some tasks which, at face value, can all be considered to measure recognition memory in rats, may not assess recognition memory at all but may, for example, be based on recall rather than recognition. Second, it is evident that different types of recognition memory can be distinguished and that tasks differ in the type of recognition memory taxed. Some paradigms, for example, measure familiarity, whereas others assess recency. Furthermore, paradigms differ as to whether spatial stimuli or items are employed. Third, different processes, ranging from stimulus-response learning to the formation of concepts, may be involved to varying extent in different tasks. These are important considerations and question the predictive validity of the results obtained from studies examining, for example, the effects of putative cognition enhancing drugs.