3-(2-hydroxy-4-(1-1-dimethylheptyl)phenyl)-4-(3-hydroxypropyl)cyclohexanol and Schizophrenia

Previous studies have shown that social withdrawal in the phencyclidine (PCP) rat model of schizophrenia results from deficient endocannabinoid-induced activation of CB1 receptors. To understand the underlying cognitive mechanisms of the social deficit in PCP-treated rats, we examined the impact of pharmacological manipulation of the endocannabinoid system on sociability (i.e. social approach) and social novelty preference (which relies on social recognition). Control rats showed a clear preference for a "social" cage (i.e. unfamiliar stimulus rat placed under a wire mesh cage) versus an "empty" cage, and spent more time exploring a "novel" cage (i.e. new stimulus rat) versus a "familiar" cage. In contrast, rats receiving PCP (5 mg/kg, b.i.d. for 7 days, followed by a 7 day-washout period) showed intact sociability, but lacked social novelty preference. This PCP-induced deficit was due to increased activity at CB1 receptors as it was reversed by systemic administration of the CB1 antagonist AM251 (1 mg/kg). In agreement with this hypothesis, the cannabinoid agonist CP55,940 (0.003-0.03 mg/kg) dose-dependently suppressed social novelty preference in control animals without affecting sociability. Taken together, these data suggest that PCP-treated rats have a deficit in social cognition, possibly induced by increased stimulation of CB1 receptors. This deficit, however, is distinct from the social withdrawal previously observed in these animals, as the latter is due to deficient, rather than increased, CB1 stimulation.

Topics: Analysis of Variance; Animals; Cannabinoid Receptor Modulators; Cyclohexanols; Discrimination, Psychological; Disease Models, Animal; Endocannabinoids; Excitatory Amino Acid Antagonists; Exploratory Behavior; Male; Odorants; Phencyclidine; Piperidines; Pyrazoles; Rats; Rats, Wistar; Schizophrenia; Schizophrenic Psychology; Social Behavior Disorders; Social Perception

The neuronal mechanisms underlying social withdrawal, one of the core negative symptoms of schizophrenia, are not well understood. Recent studies suggest an involvement of the endocannabinoid system in the pathophysiology of schizophrenia and, in particular, of negative symptoms. We used biochemical, pharmacological, and behavioral approaches to investigate the role played by the endocannabinoid system in social withdrawal induced by sub-chronic administration of phencyclidine (PCP). Pharmacological enhancement of endocannabinoid levels via systemic administration of URB597, an inhibitor of endocannabinoid degradation, reversed social withdrawal in PCP-treated rats via stimulation of CB1 receptors, but reduced social interaction in control animals through activation of a cannabinoid/vanilloid-sensitive receptor. In addition, the potent CB agonist CP55,940 reversed PCP-induced social withdrawal in a CB₁-dependent manner, whereas pharmacological blockade of CB₁ receptors by either AM251 or SR141716 reduced the time spent in social interaction in control animals. PCP-induced social withdrawal was accompanied by a decrease of anandamide (AEA) levels in the amygdala and prefrontal cortex, and these deficits were reversed by URB597. As CB₁ receptors are predominantly expressed on GABAergic interneurons containing the anxiogenic peptide cholecystokinin (CCK), we also examined whether the PCP-induced social withdrawal resulted from deficient CB₁-mediated modulation of CCK transmission. The selective CCK2 antagonist LY225910 blocked both PCP- and AM251-induced social withdrawal, but not URB597 effect in control rats. Taken together, these findings indicate that AEA-mediated activation of CB₁ receptors is crucial for social interaction, and that PCP-induced social withdrawal results from deficient endocannabinoid transmission.

Topics: Amidohydrolases; Amygdala; Animals; Arachidonic Acids; Benzamides; Cannabinoid Receptor Agonists; Cannabinoid Receptor Antagonists; Carbamates; Cyclohexanols; Dose-Response Relationship, Drug; Endocannabinoids; Male; Phencyclidine; Piperidines; Polyunsaturated Alkamides; Prefrontal Cortex; Pyrazoles; Quinazolinones; Rats; Receptor, Cannabinoid, CB1; Receptor, Cholecystokinin B; Rimonabant; Schizophrenia; Social Behavior

We have recently reported that cannabinoid agonists can up-regulate and enhance the activity of serotonin 2A (5-HT2A) receptors in the prefrontal cortex (PFCx). Increased expression and activity of cortical 5-HT2A receptors has been associated with neuropsychiatric disorders, such as anxiety and schizophrenia. Here we report that repeated CP55940 exposure selectively up-regulates GRK5 proteins in rat PFCx and in a neuronal cell culture model. We sought to examine the mechanism underlying the regulation of GRK5 and to identify the role of GRK5 in the cannabinoid agonist-induced up-regulation and enhanced activity of 5-HT2A receptors. Interestingly, we found that cannabinoid agonist-induced up-regulation of GRK5 involves CB2 receptors, β-arrestin 2, and ERK1/2 signaling because treatment with CB2 shRNA lentiviral particles, β-arrestin 2 shRNA lentiviral particles, or ERK1/2 inhibitor prevented the cannabinoid agonist-induced up-regulation of GRK5. Most importantly, we found that GRK5 shRNA lentiviral particle treatment prevented the cannabinoid agonist-induced up-regulation and enhanced 5-HT2A receptor-mediated calcium release. Repeated cannabinoid exposure was also associated with enhanced phosphorylation of CB2 receptors and increased interaction between β-arrestin 2 and ERK1/2. These latter phenomena were also significantly inhibited by GRK5 shRNA lentiviral treatment. Our results suggest that sustained activation of CB2 receptors, which up-regulates 5-HT2A receptor signaling, enhances GRK5 expression; the phosphorylation of CB2 receptors; and the β-arrestin 2/ERK interactions. These data could provide a rationale for some of the adverse effects associated with repeated cannabinoid agonist exposure.

Topics: Analgesics; Animals; Anxiety; Arrestins; beta-Arrestin 2; beta-Arrestins; Calcium; Cell Culture Techniques; Cyclohexanols; G-Protein-Coupled Receptor Kinase 5; Humans; Lentivirus; Male; MAP Kinase Signaling System; Mice; Mitogen-Activated Protein Kinase 3; Models, Biological; Nerve Tissue Proteins; Neurons; Prefrontal Cortex; Rats; Rats, Sprague-Dawley; Receptor, Cannabinoid, CB2; Receptor, Serotonin, 5-HT2A; RNA Interference; Schizophrenia; Up-Regulation

Catechol-O-methyltransferase (COMT) is an important enzyme in the metabolism of dopamine and disturbance in dopamine function is proposed to be central to the pathogenesis of schizophrenia. Clinical epidemiological studies have indicated cannabis use to confer a 2-fold increase in risk for subsequent onset of psychosis, with adolescent-onset use conveying even higher risk. There is evidence that a high activity COMT polymorphism moderates the effects of adolescent exposure to cannabis on risk for adult psychosis. In this paper we compared the effect of chronic adolescent exposure to the cannabinoid WIN 55212 on sensorimotor gating, behaviours related to the negative symptoms of schizophrenia, anxiety- and stress-related behaviours, as well as ex-vivo brain dopamine and serotonin levels, in COMT KO vs. wild-type (WT) mice. Additionally, we examined the effect of pretreatment with the COMT inhibitor tolcapone on acute effects of this cannabinoid on sensorimotor gating in C57BL/6 mice. COMT KO mice were shown to be more vulnerable than WT to the disruptive effects of adolescent cannabinoid treatment on prepulse inhibition (PPI). Acute pharmacological inhibition of COMT in C57BL/6 mice also modified acute cannabinoid effects on startle reactivity, as well as PPI, indicating that chronic and acute loss of COMT can produce dissociable effects on the behavioural effects of cannabinoids. COMT KO mice also demonstrated differential effects of adolescent cannabinoid administration on sociability and anxiety-related behaviour, both confirming and extending earlier reports of COMT×cannabinoid effects on the expression of schizophrenia-related endophenotypes.

Topics: Alleles; Animals; Anxiety; Benzophenones; Benzoxazines; Biogenic Monoamines; Cannabinoid Receptor Agonists; Cannabinoids; Catechol O-Methyltransferase; Catechol O-Methyltransferase Inhibitors; Chromatography, High Pressure Liquid; Cyclohexanols; Enzyme Inhibitors; Mice; Mice, Inbred C57BL; Mice, Knockout; Morpholines; Naphthalenes; Nitrophenols; Pain Measurement; Phenotype; Reflex, Startle; Schizophrenia; Schizophrenic Psychology; Social Behavior; Swimming; Tolcapone

Cannabis increases the risk of schizophrenia in genetically vulnerable individuals. In this study we aim to show that the schizophrenia susceptibility gene neuregulin 1 (Nrg1) modulates the development of tolerance to cannabinoids in mice. Nrg1 heterozygous (HET) and wild-type (WT) mice were treated daily for 15 d with the synthetic analogue of Δ9-tetrahydrocannabinol, CP55,940 (0.4 mg/kg). We measured the impact of this exposure on locomotor activity, anxiety, prepulse inhibition (PPI), body temperature and FosB/ΔFosB immunohistochemistry. Tolerance to CP55,940-induced hypothermia and locomotor suppression developed more rapidly in Nrg1 HET mice than WT mice. Conversely in the light-dark test, while tolerance to the anxiogenic effect of CP55,940 developed in WT mice over days of testing, Nrg1 hypomorphs maintained marked anxiety even after 15 d of treatment. Repeated cannabinoid exposure selectively increased FosB/ΔFosB expression in the lateral septum, ventral part (LSV) of Nrg1 HET but not WT mice. On day 1 of exposure opposite effects of CP55,940 treatment were observed on PPI, i.e. it was facilitated in Nrg1 hypomorphs and impaired in WT mice, despite the drug significantly impairing the acoustic startle reflex equally in both genotypes. These effects of CP55,940 on PPI were not maintained as both genotypes became tolerant to cannabinoid action with repeated exposure. Our results highlight that Nrg1 modulates the development of cannabinoid tolerance dependent on the parameter being measured. Furthermore, these data reinforce the notion that the VLS is an important brain region involved in Nrg1-cannabinoid interactions.

Topics: Animals; Anxiety; Behavior, Animal; Brain; Cannabinoids; Cyclohexanols; Disease Models, Animal; Dronabinol; Drug Tolerance; Exploratory Behavior; Genotype; Heterozygote; Male; Mice; Mice, Mutant Strains; Motor Activity; Neuregulin-1; Proto-Oncogene Proteins c-fos; Psychotropic Drugs; Reflex, Startle; Schizophrenia

The posterior cingulate cortex (PCC) has recently been implicated in the pathophysiology of schizophrenia, through both animal and human studies. We have recently shown abnormal glutamate, GABA, and muscarinic receptor binding in the PCC in schizophrenia. In addition, there is evidence for an abnormal endogenous cannabinoid system in schizophrenia. The endogenous cannabinoid system, including CB1 receptors, is proposed to play a role in modulating neurotransmission via affecting the release of a variety of neurotransmitters, (e.g. GABA). In the present study, we used quantitative autoradiography to investigate the binding of [(3)H]CP-55940 to CB1 receptors in the PCC in schizophrenia subjects compared to controls. A significant 25% increase in CB1 binding was found in the superficial layers (layer I, II) of the PCC of schizophrenia subjects compared to controls, none of whom had recently used cannabis. There was no statistical difference in CB1 binding in the deeper layers (layers III-VI) between the two groups. There were no significant correlations between CB1 binding density and age, PMI, pH, brain weight, freezer storage time, or final recorded antipsychotic drug dose. These results show an increase in CB1 receptor density in the PCC in schizophrenia, and therefore provide support for a role of the endogenous cannabinoid system in schizophrenia.

Topics: Adult; Aged; Autoradiography; Case-Control Studies; Cyclohexanols; Gyrus Cinguli; Humans; Male; Middle Aged; Postmortem Changes; Receptors, Cannabinoid; Schizophrenia; Statistics, Nonparametric; Tritium

A number of studies suggested that cannabis use can cause or exacerbate psychoses and may increase the risk of developing schizophrenia. These findings suggest that changes in the cannabinoid system of the brain may be involved in the pathology of schizophrenia. To determine whether changes in the cannabinoid system were present in the brains of subjects with schizophrenia, we used in situ radioligand binding and autoradiography to measure the binding of [3H]CP-55940 to the cannabinoid-1 receptor in the dorsolateral prefrontal cortex (Brodmann's area 9), caudate-putamen and areas of the temporal lobe from schizophrenic and control subjects, some of whom had ingested cannabis close to death. There was an increase in the density of [3H]CP-55940 binding to cannabinoid-1 receptors in the dorsolateral prefrontal cortex from subjects with schizophrenia (mean+/-S.E.M.: 142+/-9.9 vs 119+/-6.6fmol/mg estimated tissue equivalents; P<0.05) that was independent of recent cannabis ingestion. There was an increase in the density of cannabinoid-1 receptors in the caudate-putamen from subjects who had recently ingested cannabis (151+/-9.0 vs 123+/-7.2fmol/mg estimated tissue equivalents; P<0.05) that was independent of diagnoses. These data indicate that there are changes in cannabinoid-1 receptors in the dorsolateral prefrontal cortex that may prove to be associated with the pathology of schizophrenia. By contrast, changes in the density of cannabinoid-1 receptors may occur in the caudate-putamen in response to cannabis ingestion.

Topics: Brain; Cannabinoids; Cannabis; Cyclohexanols; Dronabinol; Humans; In Vitro Techniques; Radioligand Assay; Receptors, Cannabinoid; Receptors, Drug; Schizophrenia; Substance-Related Disorders