Effects of acute systemic and intra-cerebral stimulation of cannabinoid receptors on sensorimotor gating, locomotion and spatial memory in rats

Behavioral Effects of Vaporized Delta-8 Tetrahydrocannabinol, Cannabidiol, and Mixtures in Male Rats

Background: The popularity of delta-8 tetrahydrocannabinol (THC) and cannabidiol (CBD) products has seen a sharp increase in use during recent years. Despite the rise in use of these minor cannabinoids, there are little to no pre-clinical behavioral data on their effects, with most pre-clinical cannabis research focusing on the behavioral effects of delta-9 THC. The current experiments aimed to characterize the behavioral effects of delta-8 THC, CBD, and mixtures of these two drugs using a whole-body vapor exposure route of administration in male rats. Methods: Rats were exposed to vapor that contained different concentrations of delta-8 THC, CBD, or CBD/delta-8 THC mixtures during 10 min of exposure. Following 10 min of vapor exposure, locomotor behavior was monitored, or the warm-water tail withdrawal assay was conducted to measure the acute analgesic effects of the vapor exposure. Results: CBD and CBD/delta-8 THC mixtures resulted in a significant increase in locomotion across the entire session. Although delta-8 THC alone had no significant effect on locomotion across the session, the 10 mg concentration of delta-8 THC had a hyperlocomotion effect in the first 30 min of the session followed by a hypolocomotor effect later in the session. In the tail withdrawal assay, a 3/1 mixture of CBD/delta-8 THC resulted in an immediate analgesic effect compared to vehicle vapor. Finally, immediately following vapor exposure, all drugs had a hypothermic effect on body temperature compared to vehicle. Conclusion: This experiment is the first to characterize the behavioral effects of vaporized delta-8 THC, CBD, and CBD/delta-8 THC in male rats. While data were generally congruent with previous research investigating delta-9 THC, future studies should explore abuse liability and validate plasma blood concentrations of these drugs following administration through whole-body vapor exposure.

Effect of Cannabis on Memory Consolidation, Learning and Retrieval and Its Current Legal Status in India: A Review

Cannabis is one of the oldest crops grown, traditionally held religious attachments in various cultures for its medicinal use much before its introduction to Western medicine. Multiple preclinical and clinical investigations have explored the beneficial effects of cannabis in various neurocognitive and neurodegenerative diseases affecting the cognitive domains. Tetrahydrocannabinol (THC), the major psychoactive component, is responsible for cognition-related deficits, while cannabidiol (CBD), a non-psychoactive phytocannabinoid, has been shown to elicit neuroprotective activity. In the present integrative review, the authors focus on the effects of cannabis on the different cognitive domains, including learning, consolidation, and retrieval. The present study is the first attempt in which significant focus has been imparted on all three aspects of cognition, thus linking to its usage. Furthermore, the investigators have also depicted the current legal position of cannabis in India and the requirement for reforms.

HIV Transgenic Rats Demonstrate Impaired Sensorimotor Gating But Are Insensitive to Cannabinoid (Δ9-Tetrahydrocannabinol)-Induced Deficits

BACKGROUND

HIV-associated neurocognitive disorder (HAND) is commonly observed in persons living with HIV (PWH) and is characterized by cognitive deficits implicating disruptions of fronto-striatal neurocircuitry. Such circuitry is also susceptible to alteration by cannabis and other drugs of abuse. PWH use cannabis at much higher rates than the general population, thus prioritizing the characterization of any interactions between HIV and cannabinoids on cognitively relevant systems. Prepulse inhibition (PPI) of the startle response, the process by which the motor response to a startling stimulus is attenuated by perception of a preceding non-startling stimulus, is an operational assay of fronto-striatal circuit integrity that is translatable across species. PPI is reduced in PWH. The HIV transgenic (HIVtg) rat model of HIV infection mimics numerous aspects of HAND, although to date the PPI deficit observed in PWH has yet to be fully recreated in animals.

METHODS

PPI was measured in male and female HIVtg rats and wild-type controls following acute, nonconcurrent treatment with the primary constituents of cannabis: Δ 9-tetrahydrocannabinol (THC; 1 and 3 mg/kg, s.c.) and cannabidiol (1, 10, and 30 mg/kg, i.p.).

RESULTS

HIVtg rats exhibited a significant PPI deficit relative to wild-type controls. THC reduced PPI in controls but not HIVtg rats. Cannabidiol exerted only minor, genotype-independent effects on PPI.

CONCLUSIONS

HIVtg rats exhibit a relative insensitivity to the deleterious effects of THC on the fronto-striatal function reflected by PPI, which may partially explain the higher rates of cannabis use among PWH.

Effects of combined 5-HT2A and cannabinoid receptor modulation on a schizophrenia-related prepulse inhibition deficit in mice

RATIONALE

Prepulse inhibition of the startle reflex (PPI) is disrupted in several psychiatric disorders including schizophrenia. Understanding PPI pharmacology may help elucidate the pathophysiology of these disorders and lead to better treatments. Given the advantages of multi-target approaches for complex mental illnesses treatment, we have investigated the interaction between receptors known to modulate PPI (5-HT_1A and 5-HT_2A) and the neuromodulatory endocannabinoid system.

OBJECTIVES

To investigate serotonin and cannabinoid receptor (CBR) co-modulation in a model of PPI disruption relevant to schizophrenia METHODS: Male Swiss mice were pretreated with WIN 55,212-2 (CBR agonist), rimonabant (CB1R inverse agonist), 8-OH-DPAT (5-HT_1A/7 agonist), and volinanserin (5-HT_2A antagonist) or with a combination of a cannabinoid and a serotonergic drug. PPI disruption was induced by acute administration of MK-801.

RESULTS

WIN 55,212-2 and rimonabant did not change PPI nor block MK-801-induced deficits. 8-OH-DPAT increased PPI in control mice and, in a higher dose, inhibited MK-801-induced impairments. Volinanserin also increased PPI in control and MK-801-treated mice, presenting an inverted U-shaped dose-response curve. Co-administration of either cannabinoid ligand with 8-OH-DPAT did not change PPI; however, the combination of volinanserin with rimonabant increased PPI in both control and MK-801-exposed mice.

CONCLUSIONS

WIN 55,212-2 and rimonabant had similar effects in PPI. Moreover, serotonin and cannabinoid receptors interact to modulate PPI. While co-modulation of CBR and 5-HT_1A receptors did not change PPI, a beneficial effect of 5-HT_2A and CB1R antagonist combination was detected, possibly mediated through potentiation of 5-HT_2A blockade effects by concomitant CB1R blockade.

Targeting the endocannabinoid system: a predictive, preventive, and personalized medicine-directed approach to the management of brain pathologies

Cannabis-inspired medical products are garnering increasing attention from the scientific community, general public, and health policy makers. A plethora of scientific literature demonstrates intricate engagement of the endocannabinoid system with human immunology, psychology, developmental processes, neuronal plasticity, signal transduction, and metabolic regulation. Despite the therapeutic potential, the adverse psychoactive effects and historical stigma, cannabinoids have limited widespread clinical application. Therefore, it is plausible to weigh carefully the beneficial effects of cannabinoids against the potential adverse impacts for every individual. This is where the concept of "personalized medicine" as a promising approach for disease prediction and prevention may take into the account. The goal of this review is to provide an outline of the endocannabinoid system, including endocannabinoid metabolizing pathways, and will progress to a more in-depth discussion of the therapeutic interventions by endocannabinoids in various neurological disorders.

Pharmacological and Behavioral Effects of the Synthetic Cannabinoid AKB48 in Rats

AKB48 is a designer drug belonging to the indazole synthetic cannabinoids class, illegally sold as herbal blend, incense, or research chemicals for their psychoactive cannabis-like effects. In the present study, we investigated the in vivo pharmacological and behavioral effects of AKB48 in male rats and measured the pharmacodynamic effects of AKB48 and simultaneously determined its plasma pharmacokinetic. AKB48 at low doses preferentially stimulated dopamine release in the nucleus accumbens shell (0.25 mg/kg) and impaired visual sensorimotor responses (0.3 mg/kg) without affecting acoustic and tactile reflexes, which are reduced only to the highest dose tested (3 mg/kg). Increasing doses (0.5 mg/kg) of AKB48 impaired place preference and induced hypolocomotion in rats. At the highest dose (3 mg/kg), AKB48 induced hypothermia, analgesia, and catalepsy; inhibited the startle/pre-pulse inhibition test; and caused cardiorespiratory changes characterized by bradycardia and mild bradipnea and SpO2 reduction. All behavioral and neurochemical effects were fully prevented by the selective CB₁ receptor antagonist/inverse agonist AM251. AKB48 plasma concentrations rose linearly with increasing dose and were correlated with changes in the somatosensory, hypothermic, analgesic, and cataleptic responses in rats. For the first time, this study shows the pharmacological and behavioral effects of AKB48 in rats, correlating them to the plasma levels of the synthetic cannabinoid.

Chemical Compound Studied in This Article: AKB48 (PubChem CID: 57404063); AM251 (PubChem CID: 2125).

Oleoylethanolamide Modulates BDNF-ERK Signaling and Neurogenesis in the Hippocampi of Rats Exposed to Δ9-THC and Ethanol Binge Drinking During Adolescence

Oleoylethanolamide is an endogenous NAE that modulates ethanol-seeking behavior and ethanol-induced neuroinflammation. In the present study we further analyze the role of OEA in hippocampal neurogenesis, BDNF-ERK signaling, and spatial memory that are affected by alcohol. Additionally, we addressed the effects of OEA on the association of alcohol and cannabis, a frequent combination in human alcohol addicts, and whose long-term effects are far from being understood. To this end, OEA (10 mg/kg/day, i.p.) was pharmacologically administered for 5 days/week in a preclinical model of adolescent rats with binge-like consumption (1 day/week) of ethanol (3 g/kg, i.g.) combined or not with acute administrations of Δ⁹-THC (5 mg/kg, i.p.) for 5 weeks. OEA restored ethanol/THC-related decreases in both short-term spatial memory (spontaneous alternation by Y-maze) and circulating levels of BDNF, reduced cell proliferation (Mki67 and IdU+ cells) and maturation (Dcx, Calb1), and improved cell survival (Casp3 and BrdU+ cells) in the dorsal hippocampus. Interestingly, OEA alone or combined with THC also decreased the mRNA levels of neurotrophic factors (Bdnf, Ntf3) and the NT3 receptor TrkC, but increased the BDNF receptor TrkB in the hippocampus of ethanol-exposed rats. These effects were likely associated with a OEA-specific phosphorylation of AKT and ERK1, key signaling regulators of cell proliferation and survival. These results suggest a regulatory role of OEA in short-term spatial memory and hippocampal neurogenesis through BDNF/AKT/ERK1 signaling in response to acute THC in an alcoholic context during adolescence.

Sex Differences in the Behavioral and Synaptic Consequences of a Single in vivo Exposure to the Synthetic Cannabimimetic WIN55,212-2 at Puberty and Adulthood

Heavy cannabis consumption among adolescents is associated with significant and lasting neurobiological, psychological and health consequences that depend on the age of first use. Chronic exposure to cannabinoid agonists during the perinatal period or adolescence alters social behavior and prefrontal cortex (PFC) activity in adult rats. However, sex differences on social behavior as well as PFC synaptic plasticity after acute cannabinoid activation remain poorly explored. Here, we determined that the consequences of a single in vivo exposure to the synthetic cannabimimetic WIN55,212-2 differently affected PFC neuronal and synaptic functions after 24 h in male and female rats during the pubertal and adulthood periods. During puberty, single cannabinoid exposure (SCE) reduced play behavior in females but not males. In contrast, the same treatment impaired sociability in both sexes at adulthood. General exploration and memory recognition remained normal at both ages and both sexes. At the synaptic level, SCE ablated endocannabinoid-mediated synaptic plasticity in the PFC of females of both ages and heightened excitability of PFC pyramidal neurons at adulthood, while males were spared. In contrast, cannabinoid exposure was associated with impaired long-term potentiation (LTP) specifically in adult males. Together, these data indicate behavioral and synaptic sex differences in response to a single in vivo exposure to cannabinoid at puberty and adulthood.

Cannabinoids and glial cells: possible mechanism to understand schizophrenia

Clinical and neurobiological findings have reported the involvement of endocannabinoid signaling in the pathophysiology of schizophrenia. This system modulates dopaminergic and glutamatergic neurotransmission that is associated with positive, negative, and cognitive symptoms of schizophrenia. Despite neurotransmitter impairments, increasing evidence points to a role of glial cells in schizophrenia pathobiology. Glial cells encompass three main groups: oligodendrocytes, microglia, and astrocytes. These cells promote several neurobiological functions, such as myelination of axons, metabolic and structural support, and immune response in the central nervous system. Impairments in glial cells lead to disruptions in communication and in the homeostasis of neurons that play role in pathobiology of disorders such as schizophrenia. Therefore, data suggest that glial cells may be a potential pharmacological tool to treat schizophrenia and other brain disorders. In this regard, glial cells express cannabinoid receptors and synthesize endocannabinoids, and cannabinoid drugs affect some functions of these cells that can be implicated in schizophrenia pathobiology. Thus, the aim of this review is to provide data about the glial changes observed in schizophrenia, and how cannabinoids could modulate these alterations.

Psychosis and synthetic cannabinoids

Synthetic cannabinoid (SC) products have gained popularity as abused drugs over the past decade in many countries. The SCs broadly impact psychological state (e.g., mood, suicidal thoughts and psychosis) and physiological functions (e.g., cardiovascular, gastrointestinal and urinary). This review is about the effects of SCs on psychotic symptoms in clinical settings and the potentially relevant chemistry and mechanisms of action for SCs. Induction of psychotic symptoms after consuming SC products were reported, including new-onset psychosis and psychotic relapses. The role of SCs in psychosis is more complex than any single chemical component might explain, and these effects may not be a simple extension of the typical effects of cannabis or natural cannabinoids.

The long-term cognitive consequences of adolescent exposure to recreational drugs of abuse

During adolescence, the brain continues to undergo vital developmental processes. In turn, complex behavioral and cognitive skills emerge. Unfortunately, neurobiological development during adolescence can be influenced by environmental factors such as drug exposure. Engaging in drug use during adolescence has been a long-standing health concern, especially how it predicts or relates to drug using behavior later in life. However, recent findings suggest that other behavioral domains, such as learning and memory, are also vulnerable to adolescent drug use. Moreover, it is becoming increasingly apparent that deficits in learning and memory following adolescent drug use endure into adulthood, well after drug exposure has subsided. Although persistent effects suggest an interaction between drug exposure and ongoing development during adolescence, the exact acute and long-term consequences of adolescent drug exposure on substrates of learning and memory are not fully understood. Thus, this review will summarize human and animal findings on the enduring cognitive deficits due to adolescent drug exposure. Moreover, due to the fact that adolescents are more likely to consume drugs of abuse legally available to adults, this review will focus on alcohol, nicotine, and marijuana. Further, given the critical role of the frontal cortex and hippocampus in various learning and memory domains, the impact adolescent use of the previous listed drugs on the neurobiology within these regions will also be discussed.

The synthetic cannabinoid 5F-AMB changes the balance between excitation and inhibition of layer V pyramidal neurons in the mouse medial prefrontal cortex

RATIONALE

5F-AMB is one of the synthetic cannabinoids (SCs) designed to potentiate the ability to activate cannabinoid 1 (CB1) receptors and is abused worldwide. Although inhalation of 5F-AMB elicits serious adverse effects including impaired memory and consciousness, it is not known whether and how 5F-AMB affects the activity of pyramidal neurons in the medial prefrontal cortex (mPFC), a brain region associated with higher functions such as memory and cognition.

OBJECTIVES

In the present study, we examined the effects of 5F-AMB on mPFC layer V (L5) pyramidal neurons using in vitro whole-cell patch-clamp recordings.

RESULTS

Bath application of 5F-AMB attenuated the frequency but not the amplitude of spontaneous excitatory and inhibitory postsynaptic currents (sEPSCs and sIPSCs). The attenuating effects of 5F-AMB were abolished by the CB1 receptor antagonist AM251. 5F-AMB also attenuated the frequency of miniature EPSCs and IPSCs recorded in the presence of tetrodotoxin. Moreover, the extent of attenuating effects of 5F-AMB on stimulus-evoked EPSCs was significantly larger than that on evoked IPSCs.

CONCLUSIONS

These findings suggest that 5F-AMB attenuates both excitatory and inhibitory transmission in mPFC L5 pyramidal neurons via the activation of CB1 receptors located in presynaptic terminals. Further, the net impact of 5F-AMB on L5 pyramidal neurons is inhibition due to the change in balance between excitation and inhibition. This inhibitory effect might at least partly contribute to the expression of the adverse effects induced by 5F-AMB inhalation.

Pharmaco-toxicological effects of the novel third-generation fluorinate synthetic cannabinoids, 5F-ADBINACA, AB-FUBINACA, and STS-135 in mice. In vitro and in vivo studies

INTRODUCTION

5F-ADBINACA, AB-FUBINACA, and STS-135 are 3 novel third-generation fluorinate synthetic cannabinoids that are illegally marketed as incense, herbal preparations, or research chemicals for their psychoactive cannabis-like effects.

METHODS

The present study aims at investigating the in vitro and in vivo pharmacological activity of 5F-ADBINACA, AB-FUBINACA, and STS-135 in male CD-1 mice, comparing their in vivo effects with those caused by the administration of Δ⁹ -THC and JWH-018. In vitro competition binding experiments revealed a nanomolar affinity and potency of the 5F-ADBINACA, AB-FUBINACA, and STS-135 on mouse and human CB₁ and CB₂ receptors. Moreover, these synthetic cannabinoids induced neurotoxicity in murine neuro-2a cells.

RESULTS

In vivo studies showed that 5F-ADBINACA, AB-FUBINACA, and STS-135 induced hypothermia; increased pain threshold to both noxious mechanical and thermal stimuli; caused catalepsy; reduced motor activity; impaired sensorimotor responses (visual, acoustic, and tactile); caused seizures, myoclonia, and hyperreflexia; and promoted aggressiveness in mice. Behavioral and neurological effects were fully prevented by the selective CB₁ receptor antagonist/inverse agonist AM 251. Differently, the visual sensory response induced by STS-135 was only partly prevented by the AM 251, suggesting a CB₁ -independent mechanism.

CONCLUSIONS

For the first time, the present study demonstrates the pharmaco-toxicological effects induced by the administration of 5F-ADBINACA, AB-FUBINACA, and STS-135 in mice and suggests their possible detrimental effects on human health.

Effect of the novel synthetic cannabinoids AKB48 and 5F-AKB48 on "tetrad", sensorimotor, neurological and neurochemical responses in mice. In vitro and in vivo pharmacological studies

RATIONALE

AKB48 and its fluorinate derivate 5F-AKB48 are two novel synthetic cannabinoids belonging to a structural class with an indazole core structure. They are marketed as incense, herbal preparations or chemical supply for their psychoactive Cannabis-like effects.

OBJECTIVES

The present study was aimed at investigating the in vitro and in vivo pharmacological activity of AKB48 and 5F-AKB48 in male CD-1 mice and comparing their in vivo effects with those caused by the administration of Δ⁹-THC and JWH-018.

RESULTS

In vitro competition binding experiments performed on mouse and human CB₁ and CB₂ receptors revealed a nanomolar affinity and potency of the AKB48 and 5F-AKB48. In vivo studies showed that AKB48 and 5F-AKB48, induced hypothermia, increased pain threshold to both noxious mechanical and thermal stimuli, caused catalepsy, reduced motor activity, impaired sensorimotor responses (visual, acoustic and tactile), caused seizures, myoclonia, hyperreflexia and promoted aggressiveness in mice. Moreover, microdialysis study in freely moving mice showed that systemic administration of AKB48 and 5F-AKB48 stimulated dopamine release in the nucleus accumbens. Behavioural, neurological and neurochemical effects were fully prevented by the selective CB₁ receptor antagonist/inverse agonist AM 251.

CONCLUSIONS

For the first time, the present study demonstrates the overall pharmacological effects induced by the administration of AKB48 and 5F-AKB48 in mice and suggests that the fluorination can increase the power and/or effectiveness of SCBs. Furthermore, this study outlines the potential detrimental effects of SCBs on human health.

Cannabidiol, among Other Cannabinoid Drugs, Modulates Prepulse Inhibition of Startle in the SHR Animal Model: Implications for Schizophrenia Pharmacotherapy

Schizophrenia is a severe psychiatric disorder that involves positive, negative and cognitive symptoms. Prepulse inhibition of startle reflex (PPI) is a paradigm that assesses the sensorimotor gating functioning and is impaired in schizophrenia patients as well as in animal models of this disorder. Recent data point to the participation of the endocannabinoid system in the pathophysiology and pharmacotherapy of schizophrenia. Here, we focus on the effects of cannabinoid drugs on the PPI deficit of animal models of schizophrenia, with greater focus on the SHR (Spontaneously Hypertensive Rats) strain, and on the future prospects resulting from these findings.

Effect of JWH-250, JWH-073 and their interaction on "tetrad", sensorimotor, neurological and neurochemical responses in mice

JWH-250 and JWH-073 are two synthetic cannabinoid agonists with nanomolar affinity at CB1 and CB2 receptors. They are illegally marketed within "herbal blend" for theirs psychoactive effects greater than those produced by Cannabis. Recently, we analyzed an "herbal" preparation containing a mixture of both JWH-250 and JWH-073. The present study was aimed at investigating the in vitro and in vivo pharmacological activity of JWH-250 and JWH-073 in male CD-1 mice. In vitro competition binding experiments performed on mouse and human CB1 and CB2 receptors revealed a nanomolar affinity and potency of the JWH-250 and JWH-073. In vivo studies showed that JWH-250 and JWH-073, administered separately, induced a marked hypothermia, increased pain threshold to both noxious mechanical and thermal stimuli, caused catalepsy, reduced motor activity, impaired sensorimotor responses (visual, acoustic and tactile), caused seizures, myoclonia, hyperreflexia and promote aggressiveness in mice. Moreover, microdialysis study in freely moving mice showed that systemic administration of JWH-250 and JWH-073 stimulated dopamine release in the nucleus accumbens in a dose-dependent manner. Behavioral, neurological and neurochemical effects were fully prevented by the selective CB1 receptor antagonist/inverse agonist AM 251. Co-administration of ineffective doses of JWH-250 and JWH-073 impaired visual sensorimotor responses, improved mechanical pain threshold and stimulated mesolimbic DA transmission in mice, living unchanged all other behavioral and physiological parameters. For the first time the present study demonstrates the overall pharmacological effects induced by the administration of JWH-250 and JWH-073 in mice and it reveals their potentially synergistic action suggesting that co-administration of different synthetic cannabinoids may potentiate the detrimental effects of individual compounds increasing their dangerousness and abuse potential.

JWH-018 impairs sensorimotor functions in mice

Naphthalen-1-yl-(1-pentylindol-3-yl)methanone (JWH-018) is a synthetic cannabinoid agonist illegally marketed in "Spice" and "herbal blend" for its psychoactive effect greater than those produced by cannabis. In rodents JWH-018 reproduces typical effects of (-)-Δ(9)-THC or Dronabinol® (Δ(9)-THC) such as hypothermia, analgesia, hypolocomotion and akinesia, while its effects on sensorimotor functions are still unknown. Therefore, the aim of the present study is to investigate the effect of acute administration of JWH-018 (0.01-6mg/kg i.p.) on sensorimotor functions in male CD-1 mice and to compare its effects with those caused by the administration of Δ(9)-THC (0.01-6mg/kg i.p.). A specific battery of behavioral tests were adopted to investigate effects of cannabinoid agonists on sensorimotor functions (visual, auditory, tactile) and neurological changes (convulsion, myoclonia, hyperreflexia) while video-tracking analysis was used to study spontaneous locomotion. JWH-018 administration inhibited sensorimotor responses at lower doses (0.01-0.1mg/kg), reduced spontaneous locomotion at intermediate/high doses (1-6mg/kg) and induced convulsions, myoclonia and hyperreflexia at high doses (6mg/kg). Similarly, administration of Δ(9)-THC reduced sensorimotor responses in mice but it did not inhibit spontaneous locomotion and it did not induce neurological alterations. All behavioral effects and neurological alterations were prevented by the administration of the selective CB1 receptor antagonist/inverse agonist 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide (AM 251). For the first time these data demonstrate that JWH-018 impairs sensorimotor responses in mice. This aspect should be carefully evaluated to better understand the potential danger that JWH-018 may pose to public health, with particular reference to decreased performance in driving and hazardous works.

Partial genetic deletion of neuregulin 1 modulates the effects of stress on sensorimotor gating, dendritic morphology, and HPA axis activity in adolescent mice

Stress has been linked to the pathogenesis of schizophrenia. Genetic variation in neuregulin 1 (NRG1) increases the risk of developing schizophrenia and may help predict which high-risk individuals will transition to psychosis. NRG1 also modulates sensorimotor gating, a schizophrenia endophenotype. We used an animal model to demonstrate that partial genetic deletion of Nrg1 interacts with stress to promote neurobehavioral deficits of relevance to schizophrenia. Nrg1 heterozygous (HET) mice displayed greater acute stress-induced anxiety-related behavior than wild-type (WT) mice. Repeated stress in adolescence disrupted the normal development of higher prepulse inhibition of startle selectively in Nrg1 HET mice but not in WT mice. Further, repeated stress increased dendritic spine density in pyramidal neurons of the medial prefrontal cortex (mPFC) selectively in Nrg1 HET mice. Partial genetic deletion of Nrg1 also modulated the adaptive response of the hypothalamic-pituitary-adrenal axis to repeated stress, with Nrg1 HET displaying a reduced repeated stress-induced level of plasma corticosterone than WT mice. Our results demonstrate that Nrg1 confers vulnerability to repeated stress-induced sensorimotor gating deficits, dendritic spine growth in the mPFC, and an abberant endocrine response in adolescence.

Peripheral and intra-dorsolateral striatum injections of the cannabinoid receptor agonist WIN 55,212-2 impair consolidation of stimulus-response memory

The endocannabinoid system plays a major role in modulating memory. In the present study, we examined whether cannabinoid agonists influence the consolidation of stimulus-response/habit memory, a form of memory dependent upon the dorsolateral striatum (DLS). In Experiment 1, rats were trained in a cued platform water maze task in which animals were released from different start points and in order to escape had to find a cued platform which was moved to various spatial locations across trials. Immediately following training, rats received an i.p. injection of the cannabinoid receptor agonist WIN 55,212-2 (1 or 3mg/kg) or a vehicle solution. In Experiment 2, rats were trained in a forced-response version of the water plus-maze task in which a consistent body-turn response was reinforced across trials. Immediately following training, rats received an i.p. injection of WIN 55,212-2 (3 mg/kg) or vehicle. In Experiment 3, rats were trained in the cued platform task and after training received bilateral intra-DLS WIN 55,212-2 (100 ng/.5 μL or 200 ng/.5 μL) or vehicle. In Experiments 1-3, the higher doses of WIN 55,212-2 were associated with significant memory impairments, relative to vehicle-treated controls. The results indicate that peripheral or intra-DLS administration of a cannabinoid receptor agonist impairs consolidation of DLS-dependent memory. The findings are discussed within the context of previous research encompassing cannabinoids and DLS-dependent learning and memory processes, and the possibility that cannabinoids may be used to treat some habit-like human psychopathologies (e.g. posttraumatic stress disorder) is considered.

Effects of cannabinoid and vanilloid drugs on positive and negative-like symptoms on an animal model of schizophrenia: the SHR strain

Studies have suggested that the endocannabinoid system is implicated in the pathophysiology of schizophrenia. We have recently reported that Spontaneously Hypertensive Rats (SHRs) present a deficit in social interaction that is ameliorated by atypical antipsychotics. In addition, SHRs display hyperlocomotion - reverted by atypical and typical antipsychotics. These results suggest that this strain could be useful to study negative symptoms (modeled by a decrease in social interaction) and positive symptoms (modeled by hyperlocomotion) of schizophrenia and the effects of potential drugs with an antipsychotic profile. The aim of this study was to investigate the effects of WIN55-212,2 (CB1/CB2 agonist), ACEA (CB1 agonist), rimonabant (CB1 inverse agonist), AM404 (anandamide uptake/metabolism inhibitor), capsaicin (agonist TRPV1) and capsazepine (antagonist TRPV1) on the social interaction and locomotion of control animals (Wistar rats) and SHRs. The treatment with rimonabant was not able to alter either the social interaction or the locomotion presented by Wistar rats (WR) and SHR at any dose tested. The treatment with WIN55-212,2 decreased locomotion (1mg/kg) and social interaction (0.1 and 0.3mg/kg) of WR, while the dose of 1mg/kg increased social interaction of SHR. The treatment with ACEA increased (0.3mg/kg) and decreased (1mg/kg) locomotion of both strain. The administration of AM404 increased social interaction and decreased locomotion of SHR (5mg/kg), and decreased social interaction and increased locomotion in WR (1mg/kg). The treatment with capsaicin (2.5mg/kg) increased social interaction of both strain and decreased locomotion of SHR (2.5mg/kg) and WR (0.5mg/kg and 2.5mg/kg). In addition, capsazepine (5mg/kg) decreased locomotion of both strains and increased (5mg/kg) and decreased (10mg/kg) social interaction of WR. Our results indicate that the schizophrenia-like behaviors displayed by SHR are differently altered by cannabinoid and vanilloid drugs when compared to control animals and suggest the endocannabinoid and the vanilloid systems as a potential target for the treatment of schizophrenia.

Effects of cannabinoid drugs on the deficit of prepulse inhibition of startle in an animal model of schizophrenia: the SHR strain

Clinical and neurobiological findings suggest that the cannabinoids and the endocannabinoid system may be implicated in the pathophysiology and treatment of schizophrenia. We described that the spontaneously hypertensive rats (SHR) strain presents a schizophrenia behavioral phenotype that is specifically attenuated by antipsychotic drugs, and potentiated by proschizophrenia manipulations. Based on these findings, we have suggested this strain as an animal model of schizophrenia. The aim of this study was to evaluate the effects of cannabinoid drugs on the deficit of prepulse inhibition (PPI) of startle, the main paradigm used to study sensorimotor gating impairment related to schizophrenia, presented by the SHR strain. The following drugs were used: (1) WIN55212,2 (cannabinoid agonist), (2) rimonabant (CB1 antagonist), (3) AM404 (anandamide uptake inhibitor), and (4) cannabidiol (CBD; indirect CB1/CB2 receptor antagonist, among other effects). Wistar rats (WRs) and SHRs were treated with vehicle (VEH) or different doses of WIN55212 (0.3, 1, or 3 mg/kg), rimonabant (0.75, 1.5, or 3 mg/kg), AM404 (1, 5, or 10 mg/kg), or CBD (15, 30, or 60 mg/kg). VEH-treated SHRs showed a decreased PPI when compared to WRs. This PPI deficit was reversed by 1 mg/kg WIN and 30 mg/kg CBD. Conversely, 0.75 mg/kg rimonabant decreased PPI in SHR strain, whereas AM404 did not modify it. Our results reinforce the role of the endocannabinoid system in the sensorimotor gating impairment related to schizophrenia, and point to cannabinoid drugs as potential therapeutic strategies.

The endocannabinoid system: an emotional buffer in the modulation of memory function

Extensive evidence indicates that endocannabinoids modulate cognitive processes in animal models and human subjects. However, the results of endocannabinoid system manipulations on cognition have been contradictory. As for anxiety behavior, a duality has indeed emerged with regard to cannabinoid effects on memory for emotional experiences. Here we summarize findings describing cannabinoid effects on memory acquisition, consolidation, retrieval and extinction. Additionally, we review findings showing how the endocannabinoid system modulates memory function differentially, depending on the level of stress and arousal associated with the experimental context. Based on the evidence reviewed here, we propose that the endocannabinoid system is an emotional buffer that moderates the effects of environmental context and stress on cognitive processes.

Involvement of cannabinoid receptors in the amygdala and prefrontal cortex of rats in fear learning, consolidation, retrieval and extinction

Cannabinoid receptors 1 (CB1R) have been shown to be a crucial part of the neuromodulatory endocannabinoid system which is involved in emotional learning and memory. We here investigated in rats the role of CB1R in the basolateral amygdala (BLA) and medial prefrontal cortex (mPFC) in different phases of fear learning, memory and extinction. We used the fear potentiated startle paradigm to measure the effects of local microinfusion of the CB1R agonist WIN 55,212-2 (WIN) or the CB1R antagonist AM251 on acquisition, consolidation, retrieval and extinction of fear. No effects on fear acquisition of WIN or AM251 were found in the BLA or mPFC. WIN impaired fear retrieval in the BLA and in mPFC. Also, WIN reduced fear consolidation in the BLA but not in the mPFC. AM251 decreased fear consolidation after mPFC infusion. Likewise, fear extinction was impaired by AM251 infused into the mPFC. Our data indicate that fear memory consolidation and retrieval, as well as extinction are regulated differentially by amygdaloid and cortical CB1R.

Pharmacological effects of cannabinoids on the reference and working memory functions in mice

RATIONALE

Evidence indicates cannabinoid receptor agonists impair performance in procedures to assess memory that may also be confounded by motivational or motor effects, both of which occur with cannabinoids. Thus, convergence of evidence from a variety of procedures that differ in motivation, attention, arousal and response requirements, but share a common reliance on memory, is required. There are no current reports on cannabinoid effects on mice tested in the radial arm maze.

OBJECTIVES

The objective was to determine the effects of the cannabinoid agonist CP 55940 and the dependence of any such effects on the CB1 receptor using the CB1 receptor antagonist SR 141716A on two strains of mice in the eight-arm radial maze procedure.

METHODS

Male C57BL/6J (N = 36) and C3H/HEJ (N = 12) mice were trained to a criterion and then were treated (IP) with vehicle + vehicle, SR 141716A + vehicle, vehicle + CP 55940 and SR 141716A + CP 55940 in a fully balanced mixed design prior to further tests in the maze. Reference (long-term) and working (short-term) memory were assessed.

RESULTS

CP 55940 impaired performance of the reference memory task in the C57BL/6J strain but not the C3H/HEJ strain; SR 141716A reversed the effect of CP 55940 on these measures. CP 55940 also increased working memory errors in the C57BL/6J mice only, which was not affected by SR 141716A.

CONCLUSION

The present study provides evidence for a strain-specific effect of a dose of CP 55940 on reference memory. While the cannabinoid agonist also impaired working memory in one strain, this effect was apparently not mediated by CB1 receptors.

The endocannabinoid system and the brain

The psychoactive constituent in cannabis, Δ(9)-tetrahydrocannabinol (THC), was isolated in the mid-1960s, but the cannabinoid receptors, CB1 and CB2, and the major endogenous cannabinoids (anandamide and 2-arachidonoyl glycerol) were identified only 20 to 25 years later. The cannabinoid system affects both central nervous system (CNS) and peripheral processes. In this review, we have tried to summarize research--with an emphasis on recent publications--on the actions of the endocannabinoid system on anxiety, depression, neurogenesis, reward, cognition, learning, and memory. The effects are at times biphasic--lower doses causing effects opposite to those seen at high doses. Recently, numerous endocannabinoid-like compounds have been identified in the brain. Only a few have been investigated for their CNS activity, and future investigations on their action may throw light on a wide spectrum of brain functions.

Cannabinoid CB₂ receptor-mediated regulation of impulsive-like behaviour in DBA/2 mice

BACKGROUND AND PURPOSE

This study evaluated gene expression differences between two mouse strains, characterized by opposite impulsivity-like traits and the involvement of the cannabinoid CB(2) receptor in the modulation of impulsivity.

EXPERIMENTAL APPROACH

Behavioural tests were conducted to compare motor activity, exploration and novelty seeking, attention and cognitive and motor impulsivity (delayed reinforcement task: session duration 30 min; timeout 30 s) between A/J and DBA/2 mice. Expression of genes for dopamine D(2) receptors, CB(1) and CB(2) receptors were measured in the cingulate cortex (CgCtx), caudate-putamen (CPu), accumbens (Acc), amygdala (Amy) and hippocampus (Hipp). Involvement of CB(2) receptors in impulsivity was evaluated in DBA/2 mice with a CB(2) receptor agonist (JWH133) and an antagonist (AM630).

KEY RESULTS

DBA/2 mice presented higher motor and exploratory activity, pre-pulse inhibition impairment and higher cognitive and motor impulsivity level than A/J mice. In addition, DBA/2 mice showed lower (CgCtx, Acc, CPu) D(2) receptor, lower (Amy) and higher (CgCtx, Acc, CPu, Hipp) CB(1) receptor and higher (CgCtx, Acc, Amy) and similar (CPu, Hipp) CB(2) receptor gene expressions. Treatment with JWH133 (0.5, 1, 3 mg·kg(-1), i.p.) reduced cognitive and motor impulsivity level, accompanied by CB(2) receptor down-regulation (CgCtx, Acc, Amy) but did not modify other behaviours. In contrast, AM630 (1, 2, 3 mg·kg(-1), i.p.) improved pre-pulse inhibition and reduced novelty seeking behaviour in DBA/2 mice.

CONCLUSIONS AND IMPLICATIONS

CB(2) receptors might play an important role in regulating impulsive behaviours and should be considered a promising therapeutic target in the treatment of impulsivity-related disorders.

Effects of Δ9-Tetrahydrocannabinol Administration on Human Encoding and Recall Memory Function: A Pharmacological fMRI Study

Deficits in memory function are an incapacitating aspect of various psychiatric and neurological disorders. Animal studies have recently provided strong evidence for involvement of the endocannabinoid (eCB) system in memory function. Neuropsychological studies in humans have shown less convincing evidence but suggest that administration of cannabinoid substances affects encoding rather than recall of information. In this study, we examined the effects of perturbation of the eCB system on memory function during both encoding and recall. We performed a pharmacological MRI study with a placebo-controlled, crossover design, investigating the effects of Δ9-tetrahydrocannabinol (THC) inhalation on associative memory-related brain function in 13 healthy volunteers. Performance and brain activation during associative memory were assessed using a pictorial memory task, consisting of separate encoding and recall conditions. Administration of THC caused reductions in activity during encoding in the right insula, the right inferior frontal gyrus, and the left middle occipital gyrus and a network-wide increase in activity during recall, which was most prominent in bilateral cuneus and precuneus. THC administration did not affect task performance, but while during placebo recall activity significantly explained variance in performance, this effect disappeared after THC. These findings suggest eCB involvement in encoding of pictorial information. Increased precuneus activity could reflect impaired recall function, but the absence of THC effects on task performance suggests a compensatory mechanism. These results further emphasize the eCB system as a potential novel target for treatment of memory disorders and a promising target for development of new therapies to reduce memory deficits in humans.

Glucocorticoids interact with the hippocampal endocannabinoid system in impairing retrieval of contextual fear memory

There is extensive evidence that glucocorticoid hormones impair the retrieval of memory of emotionally arousing experiences. Although it is known that glucocorticoid effects on memory retrieval impairment depend on rapid interactions with arousal-induced noradrenergic activity, the exact mechanism underlying this presumably nongenomically mediated glucocorticoid action remains to be elucidated. Here, we show that the hippocampal endocannabinoid system, a rapidly activated retrograde messenger system, is involved in mediating glucocorticoid effects on retrieval of contextual fear memory. Systemic administration of corticosterone (0.3-3 mg/kg) to male Sprague-Dawley rats 1 h before retention testing impaired the retrieval of contextual fear memory without impairing the retrieval of auditory fear memory or directly affecting the expression of freezing behavior. Importantly, a blockade of hippocampal CB1 receptors with AM251 prevented the impairing effect of corticosterone on retrieval of contextual fear memory, whereas the same impairing dose of corticosterone increased hippocampal levels of the endocannabinoid 2-arachidonoylglycerol. We also found that antagonism of hippocampal β-adrenoceptor activity with local infusions of propranolol blocked the memory retrieval impairment induced by the CB receptor agonist WIN55,212-2. Thus, these findings strongly suggest that the endocannabinoid system plays an intermediary role in regulating rapid glucocorticoid effects on noradrenergic activity in impairing memory retrieval of emotionally arousing experiences.

Cannabinoid receptor activation disrupts the internal structure of hippocampal sharp wave-ripple complexes

Cannabinoid agonists impair hippocampus-dependent learning and memory. Using mouse hippocampal slice preparations, we examined the effect of anandamide, an endogenous cannabinoid, on sharp wave-ripple (SW-R) complexes, which are believed to mediate memory consolidation during slow-wave sleep or behavioral immobility. Anandamide reduced the frequency of SW-Rs recorded from the CA3 region, and this effect was abolished by AM251, a cannabinoid CB1-receptor antagonist. We further addressed the action of anandamide using a functional multineuron calcium imaging technique. Anandamide reduced the firing rate of hippocampal neurons as well as disrupted the temporal coordination of their firings during SW-R.

Failure to sustain prepulse inhibition in adolescent marijuana users

BACKGROUND

Marijuana use is typically initiated during adolescence, which is a critical period for neural development. Studies have reported reductions in prepulse inhibition (PPI) among adults who use marijuana chronically, although no human studies have been conducted during the critical adolescent period.

METHODS

This study tested PPI of acoustic startle among adolescents who were either frequent marijuana users or naïve to the drug (Controls). Adolescents were tested using two intensities of prepulses (70 and 85 dB) combined with a 105 dB startle stimulus, delivered across two testing blocks.

RESULTS

There was a significant interaction of group by block for PPI; marijuana users experienced a greater decline in the PPI across the testing session than Controls. The change in PPI of response magnitude for users was predicted by change in urine THC/creatinine after at least 18 h of abstinence, the number of joints used during the previous week before testing, as well as self-reported DSM-IV symptoms of marijuana tolerance, and time spent using marijuana rather than participating in other activities.

CONCLUSIONS

These outcomes suggest that adolescents who are frequent marijuana users have problems maintaining prepulse inhibition, possibly due to lower quality of information processing or sustained attention, both of may contribute to continued marijuana use as well as attrition from marijuana treatment.

The role of cannabinoids in modulating emotional and non-emotional memory processes in the hippocampus

Cannabinoid agonists generally have a disruptive effect on memory, learning, and operant behavior that is considered to be hippocampus-dependent. Nevertheless, under certain conditions, cannabinoid receptor activation may facilitate neuronal learning processes. For example, CB₁ receptors are essential for the extinction of conditioned fear associations, indicating an important role for this receptor in neuronal emotional learning and memory. This review examines the diverse effects of cannabinoids on hippocampal memory and plasticity. It shows how the effects of cannabinoid receptor activation may vary depending on the route of administration, the nature of the task (aversive or not), and whether it involves emotional memory formation (e.g., conditioned fear and extinction learning) or non-emotional memory formation (e.g., spatial learning). It also examines the memory stage under investigation (acquisition, consolidation, retrieval, extinction), and the brain areas involved. Differences between the effects of exogenous and endogenous agonists are also discussed. The apparently biphasic effects of cannabinoids on anxiety is noted as this implies that the effects of cannabinoid receptor agonists on hippocampal learning and memory may be attributable to a general modulation of anxiety or stress levels and not to memory per se. The review concludes that cannabinoids have diverse effects on hippocampal memory and plasticity that cannot be categorized simply into an impairing or an enhancing effect. A better understanding of the involvement of cannabinoids in memory processes will help determine whether the benefits of the clinical use of cannabinoids outweigh the risks of possible memory impairments.

The synthetic cannabinoid WIN 55212-2 differentially modulates thigmotaxis but not spatial learning in adolescent and adult animals

Unlike Δ(9)-THC, the synthetic compound WIN 55212-2 (WIN) is a full agonist of endogenous cannabinoid receptors. Previous work has shown Δ(9)-THC to affect adolescent and adult animals differently on numerous behavioral measures of spatial memory, anxiety, and locomotor activity. However, far less is known about the developmental and neurobehavioral effects of WIN. To address this, we assessed the effect of WIN (1mg/kg) on spatial learning in adolescent and adult rats using the Morris water maze. While all animals demonstrated decreased swim distance across days, WIN affected adolescents and adults differently. It improved performance in adolescents and resulted in a nearly significant performance decrement in adults. However, these effects were significantly related to thigmotaxis, which declined across days in the water maze testing protocol. WIN reduced thigmotaxis on days 1 and 2 (but not days 3-5) only in adolescents. The effect of age, treatment, and the age×treatment interaction was eliminated after controlling for thigmotaxis. These results indicate that WIN affects thigmotaxis rather than spatial reference memory. More importantly, these findings indicate a dissociation between the developmental effects of THC and the synthetic CB1 receptor agonist, WIN 55212-2. We suggest that the role of thigmotaxis be carefully evaluated in future neurodevelopmental studies of spatial learning, especially those investigating the endocannabinoid system.

The endocannabinoid system and psychiatric disorders

The present review summarizes the latest information on the role and the pharmacological modulation of the endocannabinoid system in mood disorders and its potential implication in psychotic disorders such as schizophrenia. Reduced functionality might be considered a predisposing factor for major depression, so boosting endocannabinoid tone might be a useful alternative therapeutic approach for depressive disorders. The picture regarding endocannabinoids and anxiety is more complicated since either too much or too little anandamide can lead to anxiety states. However, a small rise in its level in specific brain areas might be beneficial for the response to a stressful situation and therefore to tone down anxiety. This effect might be achieved with low doses of cannabinoid indirect agonists, such as blockers of the degradative pathway (i.e. FAAH) or re-uptake inhibitors. Moreover several lines of experimental and clinical evidence point to a dysregulation of the endocannabinoid system in schizophrenia. The high anandamide levels found in schizophrenic patients, negatively correlated with psychotic symptoms, point to a protective role, whereas the role of 2-arachidonoyl glycerol is still unclear. There is a potential for pharmacological manipulation of the endocannabinoid system as a novel approach for treating schizophrenia, although experimental findings are still controversial, often with different effects depending on the drug, the dose, the species and the model used for simulating positive or negative symptoms. Besides all these limitations, SR141716A and cannabidiol show the most constant antipsychotic properties in dopamine- and glutamate-based models of schizophrenia, with profiles similar to an atypical antipsychotic drug.

Alterations to pre-pulse inhibition (PPI) in chronic cannabis users are secondary to sustained attention deficits

RATIONALE

Given the hypothesised association between cannabis use and schizophrenia, and the well documented alterations in pre-pulse inhibition (PPI) that are observed in schizophrenia, it is of interest to examine the effects of cannabis use on PPI.

OBJECTIVE

The objective of the study was to use novel methodology for the measurement and characterisation of attentional modulation of PPI, in order to examine the nature of PPI in chronic cannabis users.

METHODS

PPI was measured in 34 chronic cannabis users (who were otherwise healthy) and 32 healthy controls, across a range of startling stimulus intensities, during two attention set conditions, one in which they were instructed to attend to the auditory stimuli and one in which they were instructed to ignore the auditory stimuli and focus on a visual task. Curves of best fit were fitted to the startle magnitudes, across the stimulus intensities. A number of reflex parameters were extracted from these logistic functions, each of which reflects a different characteristic of the startle response.

RESULTS

Cannabis users failed to show attentional modulation of any of the reflex parameters and showed altered PPI, relative to controls, but only when they were instructed to sustain attention to the auditory stimuli.

CONCLUSION

Cannabis users showed an attention-dependant alteration in PPI, which appeared to reflect a deficit in sustain attention, and which was different to that which has been observed in schizophrenia using the same methodology.

The CB1 receptor agonist, WIN 55,212-2, dose-dependently disrupts object recognition memory in adult rats

Drugs that act as agonists at the cannabinoid CB(1) receptor have been reported to interfere with a diverse range of cognitive functions, including object recognition memory. However, to date, most of the studies conducted on this aspect of memory have suggested that these effects occur mainly in pubertal or pre-pubertal, rather than adult, rats. In this study we revisited this issue and evaluated the effects of a single s.c. injection of the CB(1) receptor agonist, WIN 55,212-2 ('WIN'), at 1, 3 or 5mg/kg, on object recognition memory. We found that WIN significantly reduced the total exploration time for objects at the 5mg/kg dose only (P<0.05). This was presumably due to its sedative effects at this dose. However, the discrimination index, which controlled for the general effects of WIN on object exploration, was significantly reduced only for the 1mg/kg WIN group (P<0.05), suggesting that only at this low dose did WIN specifically interfere with object discrimination. These results suggest that WIN can interfere with object recognition memory even in adult rats following a single injection of a low dose.

Hippocampal CB(1) receptors mediate the memory impairing effects of Delta(9)-tetrahydrocannabinol

It is firmly established that the hippocampus, a brain region implicated in spatial learning, episodic memory, and consolidation, contains a high concentration of CB(1) receptors. Moreover, systemic and intrahippocampal administration of cannabinoid agonists have been shown to impair hippocampal-dependent memory tasks. However, the degree to which CB(1) receptors in the hippocampus play a specific functional role in the memory disruptive effects of marijuana or its primary psychoactive constituent Delta(9)-tetrahydrocannabinol (Delta(9)-THC) is unknown. This study was designed to determine whether hippocampal CB(1) receptors play a functional role in the memory disruptive effects of systemically administered cannabinoids, using the radial arm maze, a well characterized rodent model of working memory. Male Sprague-Dawley rats were implanted with bilateral cannulae aimed at the CA1 region of the dorsal hippocampus. The CB(1) receptor antagonist, rimonabant, was delivered into the hippocampus before to a systemic injection of either Delta(9)-THC or the potent cannabinoid analog, CP-55,940. Strikingly, intrahippocampal administration of rimonabant completely attenuated the memory disruptive effects of both cannabinoids in the radial arm maze task, but did not affect other pharmacological properties of cannabinoids, as assessed in the tetrad assay (that is, hypomotility, analgesia, catalepsy, and hypothermia). Infusions of rimonabant just dorsal or ventral to the hippocampus did not prevent Delta(9)-THC-induced memory impairment, indicating that its effects on mnemonic function were regionally selective. These findings provide compelling evidence in support of the view that hippocampal CB(1) receptors play a necessary role in the memory disruptive effects of marijuana.

Peripheral and central sites of action for the non-selective cannabinoid agonist WIN 55,212-2 in a rat model of post-operative pain

BACKGROUND AND PURPOSE

Activation of cannabinoid (CB) receptors decreases nociceptive transmission in inflammatory or neuropathic pain states. However, the effects of CB receptor agonists in post-operative pain remain to be investigated. Here, we characterized the anti-allodynic effects of WIN 55,212-2 (WIN) in a rat model of post-operative pain.

EXPERIMENTAL APPROACH

WIN 55,212-2 was characterized in radioligand binding and in vitro functional assays at rat and human CB(1) and CB(2) receptors. Analgesic activity and site(s) of action of WIN were assessed in the skin incision-induced post-operative pain model in rats; receptor specificity was investigated using selective CB(1) and CB(2) receptor antagonists.

KEY RESULTS

WIN 55,212-2 exhibited non-selective affinity and agonist efficacy at human and rat CB(1) versus CB(2) receptors. Systemic administration of WIN decreased injury-induced mechanical allodynia and these effects were reversed by pretreatment with a CB(1) receptor antagonist, but not with a CB(2) receptor antagonist, given by systemic, intrathecal and supraspinal routes. In addition, peripheral administration of both CB(1) and CB(2) antagonists blocked systemic WIN-induced analgesic activity.

CONCLUSIONS AND IMPLICATIONS

Both CB(1) and CB(2) receptors were involved in the peripheral anti-allodynic effect of systemic WIN in a pre-clinical model of post-operative pain. In contrast, the centrally mediated anti-allodynic activity of systemic WIN is mostly due to the activation of CB(1) but not CB(2) receptors at both the spinal cord and brain levels. However, the increased potency of WIN following i.c.v. administration suggests that its main site of action is at CB(1) receptors in the brain.

Behavioural disturbances and altered Fos protein expression in adult rats after chronic pubertal cannabinoid treatment

Cannabis is one of the world's most popular recreational drugs. However, little is known about long-lasting cellular and neurobehavioural effects of chronic cannabinoid intake, especially during puberty where cannabis use among humans is commonly initiated. This study in rats investigates the long-term effect of pubertal cannabinoid treatment on prepulse inhibition (PPI), locomotor activity and on anxiety in the elevated-plus maze during adulthood. Furthermore, changes in adult basic neuronal activity, assessed by c-Fos immunoreactivity (Fos IR), and a potentially altered Fos expression after acute treatment with dopaminergic drugs was evaluated. Chronic treatment with the synthetic cannabinoid full agonist WIN 55,212-2 (WIN; 1.2 mg/kg) was carried out over 25 days of the rats' puberty and subsequent behavioural testing was conducted in adult animals. Finally, Fos IR was evaluated in several brain regions under basal conditions and after acute administration of haloperidol (0.1 mg/kg) and apomorphine (2 mg/kg). Chronic WIN treated animals exhibited a lasting disruption of PPI. These rats were also more active in the open field and less anxious in the elevated-plus maze than their vehicle treated controls. Additionally, when comparing Fos IR in selected brain regions, these animals displayed altered basal neuronal activity and responded differently to acute application of haloperidol or apomorphine. Taken together, these results indicate that chronic stimulation of the cannabinoid receptor CB(1) during the rats' puberty not only leads to persistent behavioural changes but also to cellular long-term adaptations within brain regions critical for drug of abuse or neuropsychiatric diseases.