Elevation of endogenous anandamide impairs LTP,learning, and memory through CB1 receptor signaling in mice

In rodents, many exogenous and endogenous cannabinoids, such as anandamide (AEA) and 2‐arachidonyl glycerol (2‐AG), have been shown to play an important role in certain hippocampal memory processes. However, the mechanisms by which endogenous AEA regulate this processes are not well understood. Here the effects of AEA on long‐term potentiation (LTP), hippocampal‐dependent learning and memory tasks, pERK1/2, pCaMKIV, and pCREB signaling events in both cannabinoid receptor type 1 (CB1R) wild‐type (WT) and knockout (KO) mice were assessed following administration of URB597, an inhibitor of the fatty acid amide hydrolase (FAAH). Acute administration of URB597 enhanced AEA levels without affecting the levels of 2‐AG or CB1R in the hippocampus and neocortex as compared to vehicle. In hippocampal slices, URB597 impaired LTP in CB1R WT but not in KO littermates. URB597 impaired object recognition, spontaneous alternation and spatial memory in the Y‐maze test in CB1R WT mice but not in KO mice. Furthermore, URB597 enhanced ERK phosphorylation in WT without affecting total ERK levels in WT or KO mice. URB597 impaired CaMKIV and CREB phosphorylation in WT but not in KO mice. CB1R KO mice have a lower pCaMKIV/CaMKIV ratio and higher pCREB/CREB ratio as compared to WT littermates. Our results indicate that pharmacologically elevated AEA impair LTP, learning and memory and inhibit CaMKIV and CREB phosphorylation, via the activation of CB1Rs. Collectively, these findings also suggest that pharmacological elevation of AEA beyond normal concentrations is also detrimental for the underlying physiological responses. © 2014 Wiley Periodicals, Inc.     

Conditioned place preference to morphine in cannabinoid CB1 receptor knockout mice

Recent reports have suggested an involvement of the brain cannabinoid system in the morphine-reward pathway. To address this question we evaluated whether CB1 receptor knockout mice would show a conditioned place preference to morphine. CB1 receptor knockout mice developed a strong place preference to 4 and 8 mg/kg morphine, similar to that in wild-type Swiss-Webster mice. This data thus does not support a contribution of the brain cannabinoid system to morphine reward.     

Kappa- and delta-opioid receptor functional activities are increased in the caudate putamen of cannabinoid CB1 receptor knockout mice

The purpose of this study was to examine the functional interaction between endogenous opioid and cannabinoid receptor systems in the caudate putamen and nucleus accumbens. We therefore examined by autoradiography the functional activity and density of micro-, kappa- and delta-opioid receptors in both brain regions of cannabinoid CB1 receptor knockout mice. Functional activity was estimated by measuring agonist-stimulated [35S]GTPgammaS binding. Results showed that deletion of the CB1 cannabinoid receptor markedly increased kappa-opioid (50%) and delta-opioid (42%) receptor activities whereas no differences were found in micro-opioid receptor in the caudate putamen. In contrast, binding autoradiography showed a similar density of micro-, kappa- and delta-opioid receptors between mutant and wild-type mice. No differences were found in densities or activities of micro-, kappa- and delta-opioid receptors between mutant and wild-type mice in the nucleus accumbens. Taken together, our results revealed that deletion of CB1 cannabinoid receptors produced a pronounced increase in the activity of kappa- and delta-opioid receptors in the caudate putamen. This endogenous interaction between opioid and cannabinoid receptors may be relevant to further understand a variety of neuroadaptative processes involving the participation of opioid receptors, such as motor behaviour, emotional responses and drug dependence.     

Prolonged glucocorticoid treatment decreases cannabinoid CB1 receptor density in the hippocampus

Experimental studies indicate a bidirectional, functional relationship between glucocorticoids and the endocannabinoid system; however, the effects of repeated glucocorticoid treatment on the endocannabinoid system have not been examined. In this study, we treated male rats with either a single dose or a 21-day course of treatment with corticosterone (20 mg/kg) and measured hippocampal cannabinoid CB(1) receptor expression and endocannabinoid content. The 21-day, but not the single, administration of corticosterone significantly reduced both the binding site density and amount of protein of the hippocampal cannabinoid CB(1) receptor without affecting affinity for the CB(1) receptor agonist, [(3)H]CP55940. With regard to hippocampal endocannabinoid content, acute corticosterone treatment resulted in a significant reduction in anandamide but did not affect 2-arachidonylglycerol, while repeated corticosterone treatment did not alter content of either anandamide or 2-arachidonylglycerol. These data support the hypothesis that the cannabinoid CB(1) receptor is under negative regulation by glucocorticoids in the hippocampus, and suggest that hippocampal cannabinoid CB(1) receptor signaling could be reduced under conditions associated with hypersecretion of glucocorticoids, such as chronic stress.     

Association of anandamide with altered binocular depth inversion illusion in schizophrenia

Objectives: Binocular depth inversion illusion (BDII) represents an illusion of visual perception that involves higher-order visual and cognitive processes. Its impairment has been linked to psychotic conditions and identified as a marker for at-risk mental states. The endogenous cannabinoid system (ECS) is involved in various neurophysiological processes. One of its key components, anandamide, is involved in the pathophysiology of schizophrenia. Little is known about its impact on BDII alterations. Therefore, we explored associations between BDII and anandamide levels.

Methods: BDII was conducted and blood and CSF were taken in 28 first-episode antipsychotic-naïve schizophrenia (SZ) patients and 81 healthy controls (HC). Serum and CSF anandamide levels were determined by high-performance liquid chromatography/mass spectrometry.

Results: BDII scores were significantly elevated in SZ versus HC, indicating a disruption of illusionary revision of percepts in SZ. Anandamide levels were significantly higher in CSF of SZ compared to HC, while serum anandamide was not. However, we found specific association differences of anandamide levels and BDII scores between schizophrenia patients and controls in serum.

Conclusions: These findings support the hypothesis of an involvement of anandamide in cognitive processes impaired in schizophrenia and are consistent with a protective effect of elevated anandamide levels herein.     

Worsening of Huntington disease phenotype in CB1 receptor knockout mice

Huntington's disease (HD) is a progressive neurodegenerative genetic disorder which leads to motor, cognitive and psychiatric disturbances. The primary neuropathological hallmark is atrophy of the striatum. Cannabinoid CB1 receptors (CB1Rs) are particularly enriched in the striatum and previous works indicate their early loss of expression in HD, even before symptom occurrence. However, pathophysiological significance of this loss of expression remains unclear. In addition, whether specific modulation of CB1R is able to mitigate striatal neuron fate in HD remains currently controversial. In order to gain further insights on the potential role of CB1R in HD physiopathology, we evaluated the pathophysiological consequences of a genetic deletion of CB1R in the N171-82Q transgenic model and following 3-nitropropionic (3NP) intoxication. Taken together our data demonstrate that CB1R knockout (1) worsens motor performances in N171-82Q mice and (2) increases mouse susceptibility to 3NP. These results suggest that functional changes in CB1R may contribute to the physiopathological development of HD.     

Impaired hippocampal glucoregulation in the cannabinoid CB1 receptor knockout mice as revealed by an optimized in vitro experimental approach

Several techniques exist to study the rate of glucose uptake and metabolism in the brain but most of them are not sufficiently robust to permit extensive pharmacological analysis. Here we optimized an in vitro measurement of the simultaneous accumulation of the metabolizable and non-metabolizable ³H and ¹⁴C d-glucose analogues; permitting convenient large-scale studies on glucose uptake and metabolism in brain slices. Next, we performed an extensive pharmacological characterization on the putative glucoregulator role of the endocannabinoid system in the hippocampal slices of the rat, and the wild-type and the CB₁ cannabinoid receptor (CB₁R) knockout mice.We observed that ³H-3-O-methylglucose is a poor substrate to measure glucose uptake in the hippocampus. ³H-2-deoxyglucose is a better substrate but its uptake is still lower than that of ¹⁴C-U-d-glucose, from which the slices constantly metabolize and dissipate ¹⁴C atoms. Thus, uptake and the metabolism values are not to be used as standalones but as differences between a control and a treatment.The CB₁R knockout mice exhibited ∼10% less glucose uptake and glucose carbon atom dissipation in comparison with the wild-type mice. This may represent congenital defects as acute treatments of the rat and mouse slices with cannabinoid agonists, antagonists and inhibitors of endocannabinoid uptake/metabolism failed to induce robust changes in either the uptake or the metabolism of glucose.In summary, we report here an optimized technique ideal to complement other metabolic approaches of high spatiotemporal resolution. This technique allowed us concluding that CB₁Rs are at least indirectly involved in hippocampal glucoregulation.     

Müller cells express the cannabinoid CB2 receptor in the vervet monkey retina

The presence of the cannabinoid receptor type 1 (CB1R) has been largely documented in the rodent and primate retinae in recent years. There is, however, some controversy concerning the presence of the CB2 receptor (CB2R) within the central nervous system. Only recently, CB2R has been found in the rodent retina, but its presence in the primate retina has not yet been demonstrated. The aim of this study was twofold: 1) to characterize the distribution patterns of CB2R in the monkey retina and compare this distribution with that previously reported for CB1R and 2) to resolve the controversy on the presence of CB2R in the neural component of the retina. We therefore thoroughly examined the cellular localization of CB2R in the vervet monkey (Chlorocebus sabeus) retina, using confocal microscopy. Our results demonstrate that CB2R, like CB1R, is present throughout the retinal layers, but with striking dissimilarities. Double labeling of CB2R and glutamine synthetase shows that CB2R is restricted to Müller cell processes, extending from the internal limiting membrane, with very low staining, to the external limiting membrane, with heavy labeling. We conclude that CB2R is indeed present in the retina but exclusively in the retinal glia, whereas CB1R is expressed only in the neuroretina. These results extend our knowledge on the expression and distribution of cannabinoid receptors in the monkey retina, although further experiments are still needed to clarify their role in retinal functions. J. Comp. Neurol. J. Comp. Neurol. 521:2399–2415, 2013. © 2013 Wiley Periodicals, Inc.     

Increase of morphine withdrawal in mice lacking A2a receptors and no changes in CB1/A2a double knockout mice

CB1 cannabinoid and A2a adenosine receptors are highly expressed in the central nervous system where they modulate numerous physiological processes including emotional behaviour and the responses of several drugs of abuse. To investigate the contribution of these receptors in emotional-like responses and opioid dependence we have generated CB1/A2a double deficient mice (CB1-/-/A2a-/-). The spontaneous locomotor activity was reduced in double knockout as compared to wild-type animals. Emotional-like responses of CB1-/-/A2a-/- mice were investigated using the elevated plus-maze and the lit-dark box. Mutant mice exhibited an increased level of anxiety in both behavioural models. The specific involvement of CB1 and A2a receptors in morphine dependence was evaluated by using A2a knockout mice and CB1/A2a double mutant mice. The severity of naloxone-precipitated morphine withdrawal syndrome was significantly increased in the absence of A2a adenosine receptors whereas no modifications were observed in the double knockout mice. These results suggest that both receptors participate in the control of emotional behaviour and seem to play an opposite role in the expression of opioid physical dependence.