WIN-55,212-2 chronically implanted into the CA3 region of the dorsal hippocampus impairs learning: a novel method for studying chronic, brain-area-specific effects of cannabinoids

Astroglial cannabinoid signaling and behavior

In neuroscience, the explosion of innovative and advanced technical accomplishments is fundamental to understanding brain functioning. For example, the possibility to distinguish glial and neuronal activities at the synaptic level and/or the appearance of new genetic tools to specifically monitor and manipulate astroglial functions revealed that astrocytes are involved in several facets of behavioral control. In this sense, the discovery of functional presence of type-1 cannabinoid receptors in astrocytes has led to identify important behavioral responses mediated by this specific pool of cannabinoid receptors. Thus, astroglial type-1 cannabinoid receptors are in the perfect place to play a role in a complex scenario in which astrocytes sense neuronal activity, release gliotransmitters and modulate the activity of other neurons, ultimately controlling behavioral responses. In this review, we will describe the known behavioral implications of astroglial cannabinoid signaling and highlight exciting unexplored research avenues on how astroglial cannabinoid signaling could affect behavior.

Chronic low dose of AM404 ameliorates the cognitive impairment and pathological features in hyperglycemic 3xTg-AD mice

RATIONALE

Hyperglycemia accelerates the progression of Alzheimer's disease (AD), and GSK3β plays a potential link between AD and hyperglycemia. Therefore, a direct or indirect GSK3β inhibition may have potential to delay the progression of AD. Our previous biochemical assay identified AM404 as a GSK3β inhibitor at high dose (IC50 = 5.353 μM); however, other study suggests that AM404 impaired synaptic plasticity of hippocampus at high dose (10 mg/kg; i.p.). Therefore, the dose and duration of treatment are crucial for the effects of AM404.

OBJECTIVE

The effects and molecular mechanisms of AM404 at low dose were evaluated from in vitro to in vivo models.

METHODS

AM404 (0.1-0.5 μM) was tested on tau hyperphosphorylated mouse hippocampal primary cultures treated with Wortmannin (WT) and GF109203X (GFX). Hyperglycemic triple transgenic AD (3×Tg-AD) mice at 6 months old were intraperitoneally injected with AM404 (0.25 mg/kg) for 4 weeks. The spatial learning and memory of mice were measured using the Morris water maze. Mouse brain and serum samples were collected for pathological analyses.

RESULTS

AM404 (0.5 μM) exhibited significantly augmented neuroprotection toward tau hyperphosphorylation in primary cultures. The chronic systemic administration of AM404 (0.25 mg/kg) attenuated cognitive deficits in hyperglycemic 3×Tg-AD mice. Moreover, chronic low dose of AM404 significantly attenuated Aβ production, tau protein phosphorylation, and inflammation associated with an increase of pS473Akt and pS9-GSK3β. Therefore, AM404 at low dose, not only increased neuroprotection, but also ameliorated cognitive deficit, could be partly by regulating the Akt/GSK3β signaling, which may contribute to downregulation of Aβ, tau hyperphosphorylation, and inflammation in hyperglycemic 3×Tg-AD mice.

CONCLUSIONS

These results highlight that chronic administration of AM404 at low dose may be through the Akt/GSK3β pathway to ameliorate the impairment in hyperglycemic 3×Tg-AD mice.

Hippocampal Protein Kinase C Signaling Mediates the Short-Term Memory Impairment Induced by Delta9-Tetrahydrocannabinol

Cannabis affects cognitive performance through the activation of the endocannabinoid system, and the molecular mechanisms involved in this process are poorly understood. Using the novel object-recognition memory test in mice, we found that the main psychoactive component of cannabis, delta9-tetrahydrocannabinol (THC), alters short-term object-recognition memory specifically involving protein kinase C (PKC)-dependent signaling. Indeed, the systemic or intra-hippocampal pre-treatment with the PKC inhibitors prevented the short-term, but not the long-term, memory impairment induced by THC. In contrast, systemic pre-treatment with mammalian target of rapamycin complex 1 inhibitors, known to block the amnesic-like effects of THC on long-term memory, did not modify such a short-term cognitive deficit. Immunoblot analysis revealed a transient increase in PKC signaling activity in the hippocampus after THC treatment. Thus, THC administration induced the phosphorylation of a specific Ser residue in the hydrophobic-motif at the C-terminal tail of several PKC isoforms. This significant immunoreactive band that paralleled cognitive performance did not match in size with the major PKC isoforms expressed in the hippocampus except for PKCθ. Moreover, THC transiently enhanced the phosphorylation of the postsynaptic calmodulin-binding protein neurogranin in a PKC dependent manner. These data demonstrate that THC alters short-term object-recognition memory through hippocampal PKC/neurogranin signaling.

The effects anandamide signaling in the prelimbic cortex and basolateral amygdala on coping with environmental stimuli in rats

RATIONALE

Several lines of recent evidence suggest that endocannabinoids affect behavior by influencing the general patterns of challenge responding.

OBJECTIVES

Here, we investigated the brain mechanisms underlying this phenomenon in rats.

METHODS

The anandamide hydrolysis inhibitor URB597 was condensed into the tip of stainless steel cannulae, which were chronically implanted slightly above the prelimbic cortex (PRL) or the basolateral amygdala (BLA), two important regions of coping and endocannabinoid action. Thereafter, we investigated behavioral responsiveness to ambient light level in the elevated plus-maze and conditioned fear tests.

RESULTS

URB597 concentration was ~30 μg/mg protein in target areas; local brain anandamide levels increased threefold, without significant changes in 2-arachidonoylglycerol. High levels of illumination halved the time spent by controls in the open arms of the plus-maze. No similar decrease was observed in rats with URB597 implants in the PRL. High light decreased conditioned fear by 30 % in controls, but not in rats with prelimbic URB597 implants. Unresponsiveness to environmental challenges was not attributable to the anxiolytic effects of anandamide enhancement, as implants induced paradoxical anxiogenic-like effects under low light, which could be explained by effects on stimulus responsiveness rather than by effects on anxiety. URB597 implants targeting the BLA did not affect stimulus responsiveness.

CONCLUSIONS

Our findings show that elevated prelimbic anandamide signaling leads to less environment-dependent (more autonomous) behavioral responses to challenges, which is an attribute of active coping styles. These findings are discussed in light of two emerging concepts of endocannabinoid roles, particularly "emotional homeostasis" and "active coping."

Endocannabinoid system: potential novel targets for treatment of schizophrenia

Accumulating epidemiological evidences suggest that cannabis use during adolescence is a potential environmental risk for the development of psychosis, including schizophrenia. Consistently, clinical and preclinical studies, using pharmacological approaches and genetically engineered animals to target endocannabinoid signaling, reveal the multiple varieties of endocannabinoid system-mediated human and animal behaviors, including cognition and emotion. Recently, there has been substantial progress in understanding the molecular mechanisms of the endocannabinoid system for synaptic communications in the central nervous system. Furthermore, the impact of endocannabinoid signaling on diverse cellular processes during brain development has emerged. Thus, although schizophrenia has etiological complexities, including genetic heterogeneities and multiple environmental factors, it now becomes crucial to explore molecular pathways of convergence of genetic risk factors and endocannabinoid signaling, which may provide us with clues to find novel targets for therapeutic intervention. In this review, epidemiological, clinical, and pathological evidences on the role of the endocannabinoid system in the pathophysiologies of schizophrenia will be presented. We will also make a brief overview of the recent progress in understanding molecular mechanisms of the endocannabinoid system for brain development and function, with particular focus on cannabinoid receptor type 1 (CB1R)-mediated cascade, the most well-characterized cannabinoid receptor. Lastly, we will discuss the potential of the endocannabinoid system in finding novel therapeutic targets for prevention and treatment of schizophrenia.

Spontaneous object recognition and its relevance to schizophrenia: a review of findings from pharmacological, genetic, lesion and developmental rodent models

RATIONALE

Spontaneous (novel) object recognition (SOR) is one of the most widely used rodent behavioural tests. The opportunity for rapid data collection has made SOR a popular choice in studies that explore cognitive impairment in rodent models of schizophrenia, and that test the efficacy of drugs intended to reverse these deficits.

OBJECTIVES

We provide an overview of the many recent studies that have used SOR to explore the mnemonic effects of manipulation of the key transmitter systems relevant to schizophrenia-the dopamine, glutamate, GABA, acetylcholine, serotonin and cannabinoid systems-alone or in combination. We also review the use of SOR in studying memory in genetically modified mouse models of schizophrenia, as well as in neurodevelopmental and lesion models. We end by discussing the construct and predictive validity, and translational relevance, of SOR with respect to cognitive impairment in schizophrenia.

RESULTS

Perturbation of the dopamine or glutamate systems can generate robust and reliable impairment in SOR. Impaired performance is also seen following antagonism of the muscarinic acetylcholine system, or exposure to cannabinoid agonists. Cognitive enhancement has been reported using alpha7-nicotinic acetylcholine receptor agonists and 5-HT(6) antagonists. Among non-pharmacological models, neonatal ventral hippocampal lesions and maternal immune activation can impair SOR, while mixed results have been obtained with mice carrying mutations in schizophrenia risk-associated genes, including neuregulin and COMT.

CONCLUSIONS

While SOR is not without its limitations, the task represents a useful method for studying manipulations with relevance to cognitive impairment in schizophrenia, as well as the interactions between them.

The endocannabinoid transport inhibitor AM404 differentially modulates recognition memory in rats depending on environmental aversiveness

Cannabinoid compounds may influence both emotional and cognitive processes depending on the level of environmental aversiveness at the time of drug administration. However, the mechanisms responsible for these responses remain to be elucidated. The present experiments investigated the effects induced by the endocannabinoid transport inhibitor AM404 (0.5-5 mg/kg, i.p.) on both emotional and cognitive performances of rats tested in a Spatial Open Field task and subjected to different experimental settings, named High Arousal (HA) and Low Arousal (LA) conditions. The two different experimental conditions influenced emotional reactivity independently of drug administration. Indeed, vehicle-treated rats exposed to the LA condition spent more time in the center of the arena than vehicle-treated rats exposed to the HA context. Conversely, the different arousal conditions did not affect the cognitive performances of vehicle-treated animals such as the capability to discriminate a spatial displacement of the objects or an object substitution. AM404 administration did not alter locomotor activity or emotional behavior of animals exposed to both environmental conditions. Interestingly, AM404 administration influenced the cognitive parameters depending on the level of emotional arousal: it impaired the capability of rats exposed to the HA condition to recognize a novel object while it did not induce any impairing effect in rats exposed to the LA condition. These findings suggest that drugs enhancing endocannabinoid signaling induce different effects on recognition memory performance depending on the level of emotional arousal induced by the environmental conditions.

Effects of endocannabinoid system modulation on cognitive and emotional behavior

Cannabis has long been known to produce cognitive and emotional effects. Research has shown that cannabinoid drugs produce these effects by driving the brain’s endogenous cannabinoid system and that this system plays a modulatory role in many cognitive and emotional processes. This review focuses on the effects of endocannabinoid system modulation in animal models of cognition (learning and memory) and emotion (anxiety and depression). We review studies in which natural or synthetic cannabinoid agonists were administered to directly stimulate cannabinoid receptors or, conversely, where cannabinoid antagonists were administered to inhibit the activity of cannabinoid receptors. In addition, studies are reviewed that involved genetic disruption of cannabinoid receptors or genetic or pharmacological manipulation of the endocannabinoid-degrading enzyme, fatty acid amide hydrolase (FAAH). Endocannabinoids affect the function of many neurotransmitter systems, some of which play opposing roles. The diversity of cannabinoid roles and the complexity of task-dependent activation of neuronal circuits may lead to the effects of endocannabinoid system modulation being strongly dependent on environmental conditions. Recent findings are reviewed that raise the possibility that endocannabinoid signaling may change the impact of environmental influences on emotional and cognitive behavior rather than selectively affecting any specific behavior.

Cannabinoids alter spontaneous firing, bursting, and cell synchrony of hippocampal principal cells

Both natural and synthetic cannabinoid receptor (e.g., CB1) agonists such as Δ(9)-THC, WIN 55,212-2 (WIN-2), and HU-210 disrupt spatial cognition presumably through the inhibition of synchrony of hippocampal ensemble firing to task-related events. Although the CB1 receptor agonist CP 55,940 also disrupts the synchronous firing of hippocampal neurons, it does not seem to affect the average firing rate. This difference is not readily explained by the chemical structure and pharmacology of the different compounds thus warranting a more detailed examination into (i) how other cannabinoids affect the spontaneous firing, bursting, and cell synchrony of hippocampal principal cells located in CA3 and CA1 subfields, and (ii) whether these effects are indeed mediated through CB1 receptors, which will be explored by the selective antagonist AM-251. Male Long-Evans rats surgically implanted with multielectrode arrays to hippocampal CA3 and CA1 were anesthetized and principal cells discharging at 0.25-6.0 Hz were isolated and "tracked" following the systemic administration of Tween-80, Δ(9)-THC (1 or 3 mg/kg) or WIN-2 (1 mg/kg) or HU-210 (100 μg/kg), and 1.5 mg/kg AM-281. All cannabinoids except for 1 mg/kg Δ(9) -THC reliably reduced average firing rates and altered "burst" characteristics, which were reversible with AM-281 for Δ(9)-THC and WIN-2 but not for HU-210. In addition, all cannabinoids disrupted intrasubfield and intersubfield ensemble synchrony of pyramidal cells, which is an effect insensitive to AM-281 and thus unlikely to be CB1 mediated. We consider these cannabinoid effects on spike timing and firing/bursting of principal hippocampal neurons carried by CB1 and non-CB1 receptors to be physiological underpinnings of the cognitive impairments inherent to cannabinoid exposure.

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.

Cannabinoid modulation of executive functions

Executive functions are higher-order cognitive processes such as attention, behavioural flexibility, decision-making, inhibitory control, planning, time estimation and working memory that exert top-down control over behaviour. In addition to the role of cannabinoid signaling in other cognitive functions such as mnemonic processes, interest in its involvement in executive functions has arisen more recently. Here, we will briefly review some of the recent findings indicating a modulatory role of cannabinoid action on executive functioning. In addition, a growing body of evidence suggests that in particular adolescents are more vulnerable for the deleterious effects of drugs of abuse such as cannabis on cognitive functioning. Therefore, in this paper we will also briefly discuss some recent developments in this research field.