Differential effects of Δ9-tetrahydrocannabinol dosing on correlates of schizophrenia in the sub-chronic PCP rat model.

Social withdrawal in the sub-chronic phencyclidine (PCP) rat model, a behavioral correlate of the negative symptoms of schizophrenia, results from deficits in brain endocannabinoid transmission. As cannabis intake has been shown to affect negatively the course and expression of psychosis, we tested whether the beneficial effects of endocannabinoid-mediated CB1 activation on social withdrawal in PCP-treated rats (5 mg/kg, twice daily for 7 days)also occurred after administration of Δ9-tetrahydrocannabinol (THC; 0.1, 0.3, 1.0 mg/kg, i.p.). In addition, we assessed whether THC affected two correlates of positive symptoms: 1) motor activity induced by d-amphetamine (0.5 mg/kg, i.p.), and 2) dopamine neuron population activity in the ventral tegmental area (VTA). After the motor activity test, the brains from d-amphetamine-treated animals were collected and processed for measurements of endocannabinoids and activation of Akt/GSK3ß, two molecular markers involved in the pathophysiology of schizophrenia. In control rats, THC dose-dependently produced social interaction deficits and aberrant VTA dopamine neuron population activity similar to those observed in PCP-treated animals. In PCP-treated rats, only the lowest dose of THC reversed PCP-induced deficits, as well as PCP-induced elevation of the endocannabinoid anandamide (AEA) in the nucleus accumbens. Last, THC activated the Akt/GSK3ß pathway dose-dependently in both control and PCP-treated animals. Taken together, these data suggest that only low doses of THC have beneficial effects on behavioral, neurochemical and electrophysiological correlates of schizophrenia symptoms. This observation may shed some light on the controversial hypothesis of marijuana use as self-medication in schizophrenic patients.

Management of epileptic seizures in school-age children: Educational project dedicated to school staff.

OBJECTIVE: The objective of this study was to educate the school staff for a correct management of epileptic seizures in order to increase the safety of young people at school and promoting the administration of rescue drugs and in order to improve care and reduce improper calls to the health emergency number. METHODS: This project started in January 2016, and it is still ongoing at the Department of Neuroscience of Bambino Gesù Children's Hospital in Rome, Italy. There has been a data cut-off evaluation in November 2018. Two-hour training meetings with the school staff have been organized. The major topics of the training activities were as follows: report what epilepsy is, how to manage students with epileptic seizures, and how to administer rescue medications. During the meetings, the following two questionnaires were administered: one pretest in order to collect personal information and information on awareness of epilepsy, willingness to administer rescue medications, and anxiety in facing a seizure; and one posttest in order to check the knowledge acquired after the training sessions. Statistical analysis was performed using R version 3.2.3 (R Foundation for Statistical Computing, http://www.R-project.org/). Demographics (sex and age) and teaching experience were summarized with descriptive statistics for each variable. Demographics, teaching experience, awareness of disability, and knowledge of epilepsy were correlated to the management of seizures occurring in the classroom before the course; results are reported as odds ratios [OR] and 95% confidence interval (95 CI). RESULTS: Nine hundred school staff members (95% school staff and 5% social workers) entered in the project between January 2016 and November 2018. Seven hundred and forty (82%) returned the questionnaires fulfilled, and not all of them were completely filled. Ninety-eight percent of school staff (676/691) were aware about epilepsy; however, only in 16% (110) the awareness of epilepsy came from medical staff, scientific brochures, or participation in conventions. Thirty-five percent of school staff (248/707) believed that epilepsy reduces learning abilities, and 58% (409/703) believed that children with epilepsy need school support. After the training, 68% of school staff (496/734) correctly filled in the questionnaire related to the management of acute seizures versus 8% of them (57/718) in the prequestionnaire. After the training, 89% of school staff (601/675) were ready to administer rescue medications versus 54% (384/712) before the training. The majority of participants reported that the level of anxiety related to the management of seizures after the training significantly reduced. CONCLUSIONS: Results of this project documented an increase in knowledge of epilepsy, a better knowledge on management of acute seizures in the school settings, a reduction in anxiety, and an increase in willingness to administer rescue medications. Further studies should be planned in order to document the changes in the real-world management of seizures, to evaluate if a reduction in hospital admittances might be reached, and to extend the project by assessing, through a questionnaire, the stigma and prejudices against the children affected by epilepsy by their classmates.

Ventral hippocampal overexpression of Cannabinoid Receptor Interacting Protein 1 (CNRIP1) produces a schizophrenia-like phenotype in the rat.

Adolescent cannabis use has been implicated as a risk factor for schizophrenia; however, it is neither necessary nor sufficient. Previous studies examining this association have focused primarily on the role of the cannabinoid receptor 1 (CB1R) with relatively little known about a key regulatory protein, the cannabinoid receptor interacting protein 1 (CNRIP1). CNRIP1 is an intracellular protein that interacts with the C-terminal tail of CB1R and regulates its intrinsic activity. Previous studies have demonstrated aberrant CNRIP1 DNA promoter methylation in post-mortem in human patients with schizophrenia, and we have recently reported decreased methylation of the CNRIP1 DNA promoter in the ventral hippocampus (vHipp) of a rodent model of schizophrenia susceptibility. To examine whether augmented CNRIP1 expression could contribute to the pathology of schizophrenia, we performed viral-mediated overexpression of CNRIP1 in the vHipp of Sprague Dawley rats. We then tested these rats for behavioral correlates of schizophrenia symptoms, followed by electrophysiology to determine the effects on the dopamine system, known to underlie psychosis. Here, we report that overexpression of vHipp CNRIP1 induces impairments in latent inhibition and social interaction, similar to those observed in individuals with schizophrenia and in rodent models of the disease. Furthermore, rats overexpressing vHipp CNRIP1 displayed a significant increase in ventral tegmental area (VTA) dopamine neuron population activity, a putative correlate of psychosis. These data provide evidence that alterations in CNRIP1 may contribute to the pathophysiology of schizophrenia, as overexpression is sufficient to produce neurophysiological and behavioral correlates consistently observed in rodent models of the disease.

Adolescent Synthetic Cannabinoid Exposure Produces Enduring Changes in Dopamine Neuron Activity in a Rodent Model of Schizophrenia Susceptibility.

Background: Epidemiological studies recognize cannabis intake as a risk factor for schizophrenia, yet the majority of adolescents who use marijuana do not develop psychosis. Similarly, the abuse of synthetic cannabinoids poses a risk for psychosis. For these reasons, it is imperative to understand the effects of adolescent cannabinoid exposure in susceptible individuals. Methods: We recently developed a novel rodent model of schizophrenia susceptibility, the F2 methylazoxymethanol acetate rat, where only a proportion (~40%) of rats display a schizophrenia-like phenotype. Using this model, we examined the effects of adolescent synthetic cannabinoid exposure (0.2 mg/kg WIN55, 212-2, i.p.) or adolescent endocannabinoid upregulation (0.3 mg/kg URB597, i.p.) on dopamine neuron activity and amphetamine sensitivity in adulthood. Results: Adolescent synthetic cannabinoid exposure significantly increased the proportion of susceptible rats displaying a schizophrenia-like hyperdopaminergic phenotype after puberty without producing any observable alterations in control rats. Furthermore, this acquired phenotype appears to correspond with alterations in parvalbumin interneuron function within the hippocampus. Endocannabinoid upregulation during adolescence also increased the proportion of susceptible rats developing an increase in dopamine neuron activity; however, it did not alter the behavioral response to amphetamine, further emphasizing differences between exogenous and endogenous cannabinoids. Conclusions: Taken together, these studies provide experimental evidence that adolescent synthetic cannabinoid exposure may contribute to psychosis in susceptible individuals.

The cannabinoid transporter inhibitor OMDM-2 reduces social interaction: Further evidence for transporter-mediated endocannabinoid release.

Experimental evidence suggests that the transport of endocannabinoids might work bi-directionally. Accordingly, it is possible that pharmacological blockade of the latter affects not only the re-uptake, but also the release of endocannabinoids, thus preventing them from stimulating CB1 receptors. We used biochemical, pharmacological, and behavioral approaches to investigate the effects of the transporter inhibitor OMDM-2 on social interaction, a behavioral assay that requires activation of CB1 receptors. The underlying mechanisms of OMDM-2 were compared with those of the Fatty Acid Amide Hydrolase (FAAH) inhibitor URB597. Systemic administration of OMDM-2 reduced social interaction, but in contrast to URB597-induced social deficit, this effect was not reversed by the TRPV1 antagonist capsazepine. The CB1 antagonist AM251, which did not affect URB597-induced social withdrawal, exacerbated OMDM-2 effect. In addition, the potent CB1 agonist CP55,940 reversed OMDM-2-, but not URB597-, induced social withdrawal. Blockade of CB1 receptor by AM251 reduced social interaction and the cholecystokinin CCK2 antagonist LY225910 reversed this effect. Similarly, OMDM-2-induced social withdrawal was reversed by LY225910, whereas URB597 effect was not. Elevation of endocannabinoid levels by URB597 or JZL184, an inhibitor of 2-AG degradation, failed to reverse OMDM-2-induced social withdrawal, and did not show additive effects on cannabinoid measurements when co-administered with OMDM-2. Taken together, these findings indicate that OMDM-2 impaired social interaction in a manner that is consistent with reduced activation of presynaptic CB1 receptors. As cannabinoid reuptake inhibitors may impair endocannabinoid release, caution should be taken when using these drugs to enhance endocannabinoid tone in vivo.

Anxiety does not contribute to social withdrawal in the subchronic phencyclidine rat model of schizophrenia.

Social withdrawal should not be considered a direct measure of the negative symptoms of schizophrenia as it may result not only from asociality (primary negative symptom) but also from other altered processes such as anxiety. To understand the contribution of these two factors to social deficit, we investigated whether the social withdrawal observed in the subchronic phencyclidine (PCP) rat model of schizophrenia could be attributed to increased anxiety. Compared to saline controls, PCP-treated rats (5 mg/kg, twice daily for 7 days, followed by a washout period) spent significantly less time in social interaction, but did not show anxiety-like behaviors in different relevant behavioral paradigms. In addition, their social deficit was not affected by a behavioral procedure known to reduce anxiety-like behavior (repeated exposure to the same partner) nor by systemic administration of the classical anxiolytic diazepam. In contrast, PCP-induced social withdrawal was reversed by the cannabinoid agonist CP55,940, a drug with known anxiogenic properties. Furthermore, when using the social approach task, PCP-treated animals performed similarly to control animals treated with diazepam, but not to those treated with the anxiogenic compound pentylenetetrazole. Taken together, our results indicate that PCP-induced social withdrawal cannot be attributed to increased anxiety. These data are discussed in the context of primary versus secondary negative symptoms and the deficit syndrome of schizophrenia.

Differential induction of dyskinesia and neuroinflammation by pulsatile versus continuous l-DOPA delivery in the 6-OHDA model of Parkinson's disease.

Neuroinflammation is associated with l-DOPA treatment in Parkinson's disease (PD), suggesting a role in l-DOPA-induced dyskinesia (LID), however it is unclear whether increased inflammation is specifically related to the dyskinetic outcome of l-DOPA treatment. Diversely from oral l-DOPA, continuous intrajejunal l-DOPA infusion is associated with very low dyskinetic outcome in PD patients. We reproduced these regimens of administration in 6-OHDA-lesioned hemiparkinsonian rats, where dyskinetic responses and striatal neuroinflammation induced by chronic pulsatile (DOPAp) or continuous (DOPAc) l-DOPA were compared. Moreover, we investigated the contribution of a peripheral inflammatory challenge with lipopolysaccharide (LPS), to DOPAp-induced dyskinetic and neuroinflammatory responses. Rats 6-OHDA-infused in the medial forebrain bundle received two weeks treatment with DOPAp, DOPAc via subcutaneous osmotic minipumps, or DOPAp followed by DOPAc. l-DOPA plasma levels were measured in all experimental groups. An independent group of rats received one peripheral dose of LPS 24h before DOPAp treatment. Abnormal involuntary movements (AIMs) were evaluated as a rat model of LID. Immunoreactivity (IR) for OX-42, microglial and neuronal TNF-α, iNOS and GFAP was quantified in denervated and contralateral striatum. In addition, serum TNF-α was measured. The 6-OHDA denervation induced a mild microgliosis in the striatum two weeks after neurotoxin infusion, and increased TNF-α IR in microglia. Rats receiving the DOPAp treatment developed AIMs and displayed increased striatal OX-42, microglial TNF-α, iNOS and GFAP. Moreover, TNF-α IR was also increased in a subpopulation of striatal neurons. Conversely, DOPAc did not induce AIMs or inflammatory responses in either drug-naïve animals or rats that were previously dyskinetic when exposed to DOPAp. Serum TNF-α was not altered by any l-DOPA treatment. LPS pre-treatment increased the degree of DOPAp-induced AIMs and striatal IR for OX-42, TNF-α, iNOS and GFAP. Altogether the present findings indicate that in the 6-OHDA model, chronic l-DOPA induces striatal inflammatory responses, which however depend upon the administration regimen and the dyskinetic outcome of drug treatment. The potentiation of dyskinetic responses by LPS suggests a reciprocal causal link between neuroinflammation and LID.

Distinct neuronal activation patterns are associated with PCP-induced social withdrawal and its reversal by the endocannabinoid-enhancing drug URB597.

The fatty acid amide hydrolase inhibitor, URB597, an endocannabinoid enhancing drug, reverses social withdrawal in the sub-chronic PCP rat model of schizophrenia, but reduces social interaction (SI) in controls. To identify the anatomical substrates associated with PCP-induced social withdrawal and the contrasting effects of URB597 on SI in PCP- versus saline-treated rats, we analyzed SI-induced c-Fos expression in 28 brain areas relevant to schizophrenia and/or social behavior following vehicle or URB597 administration. In saline-treated rats, SI was accompanied by changes in c-Fos expression in the infralimbic and orbitofrontal cortices, dorsomedial caudate putamen, ventrolateral nucleus of the septum, dorsolateral periaqueductal gray (dlPAG) and central amygdala. Except for the dlPAG, these changes were not observed in PCP-treated rats or in saline-treated rats receiving URB597. In the dorsomedial part of the bed nucleus of the stria terminalis (dmBNST), SI-induced c-Fos expression was observed only in PCP-treated rats. Interestingly, URB597 in PCP-treated rats restored a similar c-Fos expression pattern as observed in saline-treated rats: activation of the orbitofrontal cortex, inhibition of the central amygdala and suppression of activation of the dmBNST. These data suggest that orbitofrontal cortex, central amygdala and dmBNST play a critical role in the reversal of PCP-induced social withdrawal by URB597.

THC and endocannabinoids differentially regulate neuronal activity in the prefrontal cortex and hippocampus in the subchronic PCP model of schizophrenia.

Cannabis use has been associated with an increased risk to develop schizophrenia as well as symptom exacerbation in patients. In contrast, clinical studies have revealed an inverse relationship between the cerebrospinal fluid levels of the endocannabinoid anandamide and symptom severity, suggesting a therapeutic potential for endocannabinoid-enhancing drugs. Indeed, preclinical studies have shown that these drugs can reverse distinct behavioral deficits in a rodent model of schizophrenia. The mechanisms underlying the differences between exogenous and endogenous cannabinoid administration are currently unknown. Using the phencyclidine (PCP) rat model of schizophrenia, we compared the effects on neuronal activity of systematic administration of delta-9-tetrahydrocannabinol (THC) with the fatty acid amide hydrolase inhibitor URB597. Specifically, we found that the inhibitory response in the prefrontal cortex to THC administration was absent in PCP-treated rats. In contrast, an augmented response to endocannabinoid upregulation was observed in the prefrontal cortex of PCP-treated rats. Interestingly, differential effects were also observed at the neuronal population level, as endocannabinoid upregulation induced opposite effects on coordinated activity when compared with THC. Such information is important for understanding why marijuana and synthetic cannabinoid use may be contraindicated in schizophrenia patients while endocannabinoid enhancement may provide a novel therapeutic approach.

Disruption of social cognition in the sub-chronic PCP rat model of schizophrenia: Possible involvement of the endocannabinoid system.

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.

Schizophrenia-Like Phenotype Inherited by the F2 Generation of a Gestational Disruption Model of Schizophrenia.

Both environmental and genetic factors contribute to schizophrenia; however, the exact etiology of this disorder is not known. Animal models are utilized to better understand the mechanisms associated with neuropsychiatric diseases, including schizophrenia. One of these involves gestational administration of methylazoxymethanol acetate (MAM) to induce a developmental disruption, which in turn produces a schizophrenia-like phenotype in post-pubertal rats. The mechanisms by which MAM produces this phenotype are not clear; however, we now demonstrate that MAM induces differential DNA methylation, which may be heritable. Here we demonstrate that a subset of both second (F2) and third (F3) filial generations of MAM-treated rats displays a schizophrenia-like phenotype and hypermethylation of the transcription factor, Sp5. Specifically, ventral tegmental area of dopamine neuron activity was examined using electrophysiology as a correlate for the dopamine hyperfunction thought to underlie psychosis in patients. Interestingly, only a subset of F2 and F3 MAM rats exhibited increases in dopamine neuron population activity, indicating that this may be a unique model with a susceptibility to develop a schizophrenia-like phenotype. An increase in dopamine system function in rodent models has been previously associated with decreases in hippocampal GABAergic transmission. In line with these observations, we found a significant correlation between hippocampal parvalbumin expression and dopamine neuron activity in F2 rats. These data therefore provide evidence that offspring born from MAM-treated rats possess a susceptibility to develop aspects of a schizophrenia-like phenotype and may provide a useful tool to investigate gene-environment interactions.

Role of the satiety factor oleoylethanolamide in alcoholism.

Oleoylethanolamide (OEA) is a satiety factor that controls motivational responses to dietary fat. Here we show that alcohol administration causes the release of OEA in rodents, which in turn reduces alcohol consumption by engaging peroxisome proliferator-activated receptor-alpha (PPAR-α). This effect appears to rely on peripheral signaling mechanisms as alcohol self-administration is unaltered by intracerebral PPAR-α agonist administration, and the lesion of sensory afferent fibers (by capsaicin) abrogates the effect of systemically administered OEA on alcohol intake. Additionally, OEA is shown to block cue-induced reinstatement of alcohol-seeking behavior (an animal model of relapse) and reduce the severity of somatic withdrawal symptoms in alcohol-dependent animals. Collectively, these findings demonstrate a homeostatic role for OEA signaling in the behavioral effects of alcohol exposure and highlight OEA as a novel therapeutic target for alcohol use disorders and alcoholism.

Simultaneous inhibition of fatty acid amide hydrolase and monoacylglycerol lipase shares discriminative stimulus effects with Δ9-tetrahydrocannabinol in mice.

Monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH) inhibitors exert preclinical effects indicative of therapeutic potential (i.e., analgesia). However, the extent to which MAGL and FAAH inhibitors produce unwanted effects remains unclear. Here, FAAH and MAGL inhibition was examined separately and together in a Δ(9)-tetrahydrocannabinol (Δ(9)-THC; 5.6 mg/kg i.p.) discrimination assay predictive of subjective effects associated with cannabis use, and the relative contribution of N-arachidonoyl ethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) in the prefrontal cortex, hippocampus, and caudate putamen to those effects was examined. Δ(9)-THC dose-dependently increased Δ(9)-THC appropriate responses (ED50 value = 2.8 mg/kg), whereas the FAAH inhibitors PF-3845 [N-3-pyridinyl-4-[[3-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenyl]methyl]-1-piperidinecarboxamide] and URB597 [(3'-​(aminocarbonyl)[1,​1'-​biphenyl]-​3-​yl)-​cyclohexylcarbamate] or a MAGL inhibitor JZL184 [4-​nitrophenyl-​4-​(dibenzo[d][1,​3]dioxol-​5-​yl(hydroxy)methyl)piperidine-​1-​carboxylate] alone did not substitute for the Δ(9)-THC discriminative stimulus. The nonselective FAAH/MAGL inhibitors SA-57 [4-[2-(4-chlorophenyl)ethyl]-1-piperidinecarboxylic acid 2-(methylamino)-2-oxoethyl ester] and JZL195 [4-​nitrophenyl 4-​(3-​phenoxybenzyl)piperazine-​1-​carboxylate] fully substituted for Δ(9)-THC with ED50 values equal to 2.4 and 17 mg/kg, respectively. Full substitution for Δ(9)-THC was also produced by a combination of JZL184 and PF-3845, but not by a combination of JZL184 and URB597 (i.e., 52% maximum). Cannabinoid receptor type 1 antagonist rimonabant attenuated the discriminative stimulus effects of Δ(9)-THC, SA-57, JZL195, and the combined effects of JZL184 and PF-3845. Full substitution for the Δ(9)-THC discriminative stimulus occurred only when both 2-AG and AEA were significantly elevated, and the patterns of increased endocannabinoid content were similar among brain regions. Overall, these results suggest that increasing both endogenous 2-AG and AEA produces qualitatively unique effects (i.e., the subjective effects of cannabis) that are not obtained from increasing either 2-AG or AEA separately.

The dual FAAH/MAGL inhibitor JZL195 has enhanced effects on endocannabinoid transmission and motor behavior in rats as compared to those of the MAGL inhibitor JZL184.

The biological actions of the endocannabinoids anandamide and 2-arachidonoyl glycerol (2-AG) are terminated by enzymatic hydrolysis of these lipids via fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively. While several selective FAAH inhibitors have been developed and characterized in vitro and in vivo, none of the initial MAGL blockers have shown adequate potency and specificity for in vivo applications. More recently, a selective MAGL inhibitor, JZL184, has been shown to produce a long-lasting elevation of brain 2-AG, as well as cannabinoid-like behavioral responses in mice. However, its effectiveness in rats remains controversial. Indeed, although JZL184 can elicit behavioral responses that are mediated, at least in part, via activation of cannabinoid CB1 receptors, several reports indicate that this compound does not alter 2-AG levels in this species. In this study we compared the behavioral and neurochemical effects of JZL 184 with those of the dual FAAH/MAGL inhibitor JZL195, and showed that systemic administration of the former can selectively elevate brain 2-AG in rats and produce motor suppression through a CB1-independent mechanism. These findings indicate that, despite its lower potency against rat MAGL, JZL184 can be used to enhance 2-AG transmission and elicit behavioral responses in rodents.

Phencyclidine-induced social withdrawal results from deficient stimulation of cannabinoid CB1 receptors: implications for schizophrenia.

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.

Exercise-induced endocannabinoid signaling is modulated by intensity.

Endocannabinoids (eCB) are endogenous ligands for cannabinoid receptors that are densely expressed in brain networks responsible for reward. Recent work shows that exercise activates the eCB system in humans and other mammals, suggesting eCBs are partly responsible for the reported improvements in mood and affect following aerobic exercise in humans. However, exercise-induced psychological changes reported by runners are known to be dependent on exercise intensity, suggesting that any underlying molecular mechanism should also change with varying levels of exercise intensity. Here, we examine circulating levels of eCBs following aerobic exercise (treadmill running) in recreationally fit human runners at four different intensities. We show that eCB signaling is indeed intensity dependent, with significant changes in circulating eCBs observed following moderate intensities only (very high and very low intensity exercises do not significantly alter circulating eCB levels). Our results are consistent with intensity-dependent psychological state changes with exercise and therefore support the hypothesis that eCB activity is related to neurobiological effects of exercise. Thus, future studies examining the role of exercise-induced eCB signaling on neurobiology or physiology must take exercise intensity into account.

Novel codrugs with GABAergic activity for dopamine delivery in the brain.

This study investigates the use of codrugs of the GABAergic agent 2-phenyl-imidazo[1,2-a]pyridinacetamide and dopamine (DA) or ethyl ester L-Dopa (LD) as a strategy to deliver DA and simultaneously activate GABA-receptors in the brain. For this purpose, both DA and LD ethyl ester were linked by carbamate bond to imidazo[1,2-a]pyridine acetamide moieties to yield two DA- and two LD-imidazopyridine derivatives. These compounds were evaluated in vitro to assess their stability, binding affinities and cell membrane transport, and in vivo to assess their bio-availability via microdialysis studies. The two DA derivatives were adequately stable in buffered solution, but underwent cleavage in diluted human serum. By contrast, the LD derivatives were unstable in buffered solution. Receptor binding studies showed that the DA-imidazopyridine carbamates had binding affinity for benzodiazepine receptors in the nanomolar range. Brain microdialysis experiments indicated that intraperitoneal administration of the DA derivatives sustained DA levels in rat striatum over a 4-h period. These results suggest that DA-imidazopyridine carbamates are new DA codrugs with potential application for DA replacement therapy.

Anti-dyskinetic mechanisms of amantadine and dextromethorphan in the 6-OHDA rat model of Parkinson's disease: role of NMDA vs. 5-HT1A receptors.

Amantadine and dextromethorphan suppress levodopa (L-DOPA)-induced dyskinesia (LID) in patients with Parkinson's disease (PD) and abnormal involuntary movements (AIMs) in the unilateral 6-hydroxydopamine (6-OHDA) rat model. These effects have been attributed to N-methyl-d-aspartate (NMDA) antagonism. However, amantadine and dextromethorphan are also thought to block serotonin (5-HT) uptake and cause 5-HT overflow, leading to stimulation of 5-HT(1A) receptors, which has been shown to reduce LID. We undertook a study in 6-OHDA rats to determine whether the anti-dyskinetic effects of these two compounds are mediated by NMDA antagonism and/or 5-HT(1A) agonism. In addition, we assessed the sensorimotor effects of these drugs using the Vibrissae-Stimulated Forelimb Placement and Cylinder tests. Our data show that the AIM-suppressing effect of amantadine was not affected by the 5-HT(1A) antagonist WAY-100635, but was partially reversed by the NMDA agonist d-cycloserine. Conversely, the AIM-suppressing effect of dextromethorphan was prevented by WAY-100635 but not by d-cycloserine. Neither amantadine nor dextromethorphan affected the therapeutic effects of L-DOPA in sensorimotor tests. We conclude that the anti-dyskinetic effect of amantadine is partially dependent on NMDA antagonism, while dextromethorphan suppresses AIMs via indirect 5-HT(1A) agonism. Combined with previous work from our group, our results support the investigation of 5-HT(1A) agonists as pharmacotherapies for LID in PD patients.

Acetaminophen differentially enhances social behavior and cortical cannabinoid levels in inbred mice.

Supratherapeutic doses of the analgesic acetaminophen (paracetomol) are reported to promote social behavior in Swiss mice. However, we hypothesized that it might not promote sociability in other strains due to cannabinoid CB(1) receptor-mediated inhibition of serotonin (5-HT) transmission in the frontal cortex. We examined the effects of acetaminophen on social and repetitive behaviors in comparison to a cannabinoid agonist, WIN 55,212-2, in two strains of socially-deficient mice, BTBR and 129S1/SvImJ (129S). Acetaminophen (100mg/kg) enhanced social interactions in BTBR, and social novelty preference and marble burying in 129S at serum levels of ≥70 ng/ml. Following acetaminophen injection or sociability testing, anandamide (AEA) increased in BTBR frontal cortex, while behavior testing increased 2-arachidonyl glycerol (2-AG) levels in 129S frontal cortex. In contrast, WIN 55,212-2 (0.1mg/kg) did not enhance sociability. Further, we expected CB(1)-deficient (+/-) mice to be less social than wild-type, but instead found similar sociability. Given strain differences in endocannabinoid response to acetaminophen, we compared cortical CB(1) and 5-HT(1A) receptor density and function relative to sociable C57BL/6 mice. CB(1) receptor saturation binding (Bmax=958±117 fmol/mg protein), and affinity for [(3)H] CP55,940 (K(D)=3±0.8 nM) was similar in frontal cortex among strains. CP55,940-stimulated [(35)S] GTPγS binding in cingulate cortex was 136±12, 156±22, and 75±9% above basal in BTBR, 129S and C57BL/6 mice. The acetaminophen metabolite para-aminophenol (1 µM) failed to stimulate [(35)S] GTPγS binding. Hence, it appears that other indirect actions of acetaminophen, including 5-HT receptor agonism, may underlie its sociability promoting properties outweighing any CB(1) mediated suppression by locally-elevated endocannabinoids in these mice.

New insights on endocannabinoid transmission in psychomotor disorders.

The endocannabinoids are lipid signaling molecules that bind to cannabinoid CB(1) and CB(2) receptors and other metabotropic and ionotropic receptors. Anandamide and 2-arachidonoyl glycerol, the two best-characterized examples, are released on demand in a stimulus-dependent manner by cleavage of membrane phospholipid precursors. Together with their receptors and metabolic enzymes, the endocannabinoids play a key role in modulating neurotransmission and synaptic plasticity in the basal ganglia and other brain areas involved in the control of motor functions and motivational aspects of behavior. This mini-review provides an update on the contribution of the endocannabinoid system to the regulation of psychomotor behaviors and its possible involvement in the pathophysiology of Parkinson's disease and schizophrenia.