Short-term memory is modulated by the spontaneous release of endocannabinoids: evidence from hippocampal population codes

The interaction between cannabinoids and long-term synaptic plasticity: A survey on memory formation and underlying mechanisms

Synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), is an essential phenomenon in memory formation as well as maintenance along with many other cognitive functions, such as those needed for coping with external stimuli. Synaptic plasticity consists of gradual changes in the biochemistry and morphology of pre- and postsynaptic neurons, particularly in the hippocampus. Consuming marijuana as a primary source of exocannabinoids immediately impairs attention and working memory-related tasks. Evidence regarding the effects of cannabinoids on LTP and memory is contradictory. While cannabinoids can affect a variety of specific cannabinoid receptors (CBRs) and nonspecific receptors throughout the body and brain, they exert miscellaneous systemic and local cerebral effects. Given the increasing use of cannabis, mainly among the young population, plus its potential adverse long-term effects on learning and memory processes, it could be a future global health challenge. Indeed, the impact of cannabinoids on memory is multifactorial and depends on the dosage, timing, formula, and route of consumption, plus the background complex interaction of the endocannabinoids system with other cerebral networks. Herein, we review how exogenously administrated organic cannabinoids, CBRs agonists or antagonists, and endocannabinoids can affect LTP and synaptic plasticity through various receptors in interaction with other cerebral pathways and primary neurotransmitters.

Activation of cannabinoid type 1 receptors decreases the synchronization of local field potential oscillations in the hippocampus and entorhinal cortex and prolongs the interresponse time during a differential-reinforcement-of-low-rate task

Marijuana intoxication impairs neurocognitive functions. Common side effects of consuming cannabis include time distortion and memory loss. However, the underlying neurophysiological mechanisms involved in these effects remain unclear. We hypothesized that communication between the hippocampal CA1 region and medial entorhinal cortex (MEC) is essential for the transmission of temporal-associated information. We used a differential-reinforcement-of-low-rate (DRL) task, which requires subjects to press a lever at an optimal time point, to correlate the distributions of interresponse time (IRT) with local field potentials (LFPs) recorded in the CA1 and MEC under the effects of a cannabinoid type 1 (CB1) receptor agonist. We used a DRL 10-s schedule and trained the rats to withhold for 10 s before pressing a lever. Our data showed that the percentage of 12.4- to 14-s IRT events rose after activation of CB1 receptors in the MEC. In addition, gamma amplitude synchronization and CA1 theta phase-MEC gamma amplitude coupling decreased during the 6- to 14-s IRT events. These results suggest that activation of CB1 receptors in the MEC disrupt the functional connectivity between the CA1 and the MEC. This inefficient communication may result in increased IRT during a DRL schedule. Overall, we postulate that marijuana intoxication impairs the communication between the CA1 and MEC and influences behavioral performances that require precise timing ability.

Systemic Blockade of the CB1 Receptor Augments Hippocampal Gene Expression Involved in Synaptic Plasticity but Perturbs Hippocampus-Dependent Learning Task

Chronic and acute agonism as well as acute antagonism of CB₁ receptors reveal modulation of learning and memory during stable performance of a delayed-nonmatch-to-sample (DNMS) memory task. However, it remains unclear how chronic blockade of the CB₁ receptor alters acquisition of the behavioral task. We examined the effects of chronic rimonabant exposure during DNMS task acquisition to determine if blockade of the CB₁ receptor with the antagonist rimonabant enhanced acquisition of operant task. Long-Evans rats, trained in the DNMS task before imposition of the trial delay, were surgically implanted with osmotic mini pumps to administer rimonabant (1.0 mg/kg/day) or vehicle (dimethyl sulfoxide/Tween-80/Saline). Following surgical recovery, DNMS training was resumed with the imposition of gradually longer delays (1-30 sec). The number of days required to achieve stable performance with either increasing length of delay or reversal of task contingency was compared between vehicle and rimonabant-treated rats. Following the completion of DNMS training, animals were euthanized, and both hippocampi were harvested for gene expression assay analysis. Rimonabant treatment animals required more time to achieve stable DNMS performance than vehicle-treated controls. Quantitative real-time polymerase chain reaction analysis revealed that the expressions of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit, brain-derived neurotrophic factor, and synapsin 1 (Syn1) were significantly increased. These results are consistent with rimonabant increasing mRNAs for proteins associated with hippocampal synapse remodeling, but that those alterations did not necessarily accelerate the acquisition of an operant behavioral task that required learning new contingencies.

Enhancing effects of acute exposure to cannabis smoke on working memory performance

Numerous preclinical studies show that acute cannabinoid administration impairs cognitive performance. Almost all of this research has employed cannabinoid injections, however, whereas smoking is the preferred route of cannabis administration in humans. The goal of these experiments was to systematically determine how acute exposure to cannabis smoke affects working memory performance in a rat model. Adult male (n = 15) and female (n = 16) Long-Evans rats were trained in a food-motivated delayed response working memory task. Prior to test sessions, rats were exposed to smoke generated by burning different numbers of cannabis or placebo cigarettes, using a within-subjects design. Exposure to cannabis smoke had no effect on male rats' performance, but surprisingly, enhanced working memory accuracy in females, which tended to perform less accurately than males under baseline conditions. In addition, cannabis smoke enhanced working memory accuracy in a subgroup of male rats that performed comparably to the worst-performing females. Exposure to placebo smoke had no effect on performance, suggesting that the cannabinoid content of cannabis smoke was critical for its effects on working memory. Follow-up experiments showed that acute administration of either Δ9-tetrahydrocannabinol (0.0, 0.3, 1.0, 3.0 mg/kg) or the cannabinoid receptor type 1 antagonist rimonabant (0.0, 0.2, 0.6, 2.0 mg/kg) impaired working memory performance. These results indicate that differences in the route, timing, or dose of cannabinoid administration can yield distinct cognitive outcomes, and highlight the need for further investigation of this topic.

The role of CA1 CB1 receptors on lithium-induced spatial memory impairment in rats

Lithium, a glycogen synthase kinase-3β (GSK-3β) inhibitor, prevents cannabinoid withdrawal syndrome, but there is limited data exploring the interaction between lithium and cannabinoid system on memory processes. The present study aimed to test the interaction between dorsal hippocampal (CA1 region) cannabinoid system and lithium on spatial memory in rats. Spatial memory was assessed in Morris Water Maze (MWM) apparatus by a single training session of eight trials. The results showed that pre-training intra-CA1 microinjection of ACPA, the cannabinoid type 1 receptor (CB1r) agonist, at doses of 0.001, 0.01 or 1 µg/rat, or AM251, the cannabinoid type 1 receptor (CB1r) antagonist, at doses of 1, 10 or 100 ng/rat, increased escape latency and traveled distance to the platform, suggesting a spatial learning impairment, whereas intraperitoneal administration of lithium (0.5, 1 or 5 mg/kg) had no effect on spatial learning. Also, rats that received lithium plus a lower dose of ACPA (0.001 µg/rat) or AM251 (1 ng/rat) had successful performance in the MWM. In the probe test, the results showed that pre-training administration of lithium (5 mg/kg) and ACPA (0.01 or 1 µg/rat) but not AM251 (at all doses used) impaired spatial memory retrieval. Also, lower dose of ACPA (0.001 µg/rat) or AM251 (1 ng/rat) potentiated the effect of ineffective doses of lithium (0.5 and 1 mg/kg) on spatial memory retrieval, while restored the effect of effective dose of lithium (5 mg/kg). In conclusion, cannabinoids may have a dual effect on lithium-induced spatial memory impairment in rats.

The interactive role of CB1 receptors and L-type calcium channels in hippocampal long-term potentiation in rats

Long-term potentiation (LTP) of synaptic responses is a widely researched model of synaptic plasticity that occurs during learning and memory. The cannabinoid system is an endogenous system that modulate this kind of synaptic plasticity. In addition, voltage dependent calcium channels is essential for induction of LTP at some synapses in the hippocampus. However, there is currently debate over the interaction between L-type calcium channels and cannabinoid system on the synaptic plasticity. In this study, we examined the effects of an acute administration of the cannabinoid antagonist AM251 following a chronic administration of the Ca²⁺ channel blocker verapamil on LTP induction in the hippocampal dentate gyrus(DG) of rats. Male Wistar rats were administered verapamil(10,25,50mg/kg) or saline intraperitoneally(IP) daily for 13days(n=10/group). After this treatment period, animals were anesthetized with an IP injection of urethane; the recording and stimulating electrodes were positioned in the DG and the perforant pathway. After obtaining a steady state baseline response, a single IP injection of saline or AM251(1 or 5mg/kg) was administered. LTP was induced by high-frequency stimulation(HFS). The population spike(PS) amplitude and the slope of excitatory postsynaptic potentials(EPSP) were compared between the experimental groups. The acute administration of the CB1 antagonist AM251 increased LTP induction. The EPSP slopes and PS amplitude in the verapamil and AM251 groups differed after HFS, such that AM251 increased LTP, whereas verapamil decreased LTP induction. These findings suggest that there are functional interactions between the L-type calcium channels and cannabinoid system in this model of synaptic plasticity in the hippocampus.

Synthetic cannabinoid JWH-018 and its halogenated derivatives JWH-018-Cl and JWH-018-Br impair Novel Object Recognition in mice: Behavioral, electrophysiological and neurochemical evidence

It is well known that an impairment of learning and memory function is one of the major physiological effects caused by natural or synthetic cannabinoid consumption in rodents, nonhuman primates and in humans. JWH-018 and its halogenated derivatives (JWH-018-Cl and JWH-018-Br) are synthetic CB1/CB2 cannabinoid agonists, illegally marketed as "Spice" and "herbal blend" for their Cannabis-like psychoactive effects. In the present study the effects of acute exposure to JWH-018, JWH-018-Cl, JWH-018-Br (JWH-018-R compounds) and Δ(9)-THC (for comparison) on Novel Object Recognition test (NOR) has been investigated in mice. Moreover, to better characterize the effects of JWH-018-R compounds on memory function, in vitro electrophysiological and neurochemical studies in hippocampal preparations have been performed. JWH-018, JWH-018-Cl and JWH-018-Br dose-dependently impaired both short- and long-memory retention in mice (respectively 2 and 24 h after training session). Their effects resulted more potent respect to that evoked by Δ(9)-THC. Moreover, in vitro studies showed as JWH-018-R compounds negatively affected electrically evoked synaptic transmission, LTP and aminoacid (glutamate and GABA) release in hippocampal slices. Behavioral, electrophysiological and neurochemical effects were fully prevented by CB1 receptor antagonist AM251 pretreatment, suggesting a CB1 receptor involvement. These data support the hypothesis that synthetic JWH-018-R compounds, as Δ(9)-THC, impair cognitive function in mice by interfering with hippocampal synaptic transmission and memory mechanisms. This data outline the danger that the use and/or abuse of these synthetic cannabinoids may represent for the cognitive process in human consumer.

Effects of fatty acid amide hydrolase (FAAH) inhibitors on working memory in rats

RATIONALE

Manipulations of the endocannabinoid system could potentially produce therapeutic effects with minimal risk of adverse cannabis-like side effects. Inhibitors of fatty acid amide hydrolase (FAAH) increase endogenous levels of the cannabinoid-receptor agonist, anandamide, and show promise for treating a wide range of disorders. However, their effects on learning and memory have not been fully characterized.

OBJECTIVES

We determined the effects of five structurally different FAAH inhibitors in an animal model of working memory known to be sensitive to impairment by delta-9 tetrahydrocannabinol (THC).

METHODS

A delayed nonmatching-to-position procedure was used in rats. Illuminated nosepoke holes were used to provide sample cues (left versus right) and record responses (correct versus incorrect) after delays ranging from 0 to 28 s. Various test drugs were given acutely up to two times per week before daily sessions.

RESULTS

One FAAH inhibitor, AM3506 (3 mg/kg), decreased accuracy in the memory task. Four other FAAH inhibitors (URB597, URB694, PF-04457845, and ARN14633) and a monoacylglycerol lipase inhibitor (JZL184, which blocks the degradation of the endocannabinoid 2-arachidonoylglycerol) had no effect. Testing of AM3506 in combination with antagonists for receptors known to be affected by anandamide and other fatty acid amides indicated that the impairment induced by AM3506 was mediated by cannabinoid CB1 receptors, and not by alpha-type peroxisome proliferator-activated receptors (PPAR-alpha) or vanilloid transient receptor potential cation channels (TRPV1).

CONCLUSIONS

FAAH inhibitors differ with respect to their potential for memory impairment, abuse liability, and probably other cannabis-like effects, and they should be evaluated individually for specific therapeutic and adverse effects.

Because difficulty is not the same for everyone: the impact of complexity in working memory is associated with cannabinoid 1 receptor genetic variation in young adults

Individual differences in working memory ability are mainly revealed when a demanding challenge is imposed. Here, we have associated cannabinoid 1 (CB1) receptor genetic variation rs2180619 (AA, AG, GG), which is located in a potential CNR1 regulatory sequence, with performance in working memory. Two-hundred and nine Mexican-mestizo healthy young participants (89 women, 120 men, mean age: 23.26 years, SD = 2.85) were challenged to solve a medium (2-back) vs. a high (3-back) difficulty N-back tasks. All subjects responded as expected, performance was better with the medium than the high demand task version, but no differences were found among genotypes while performing each working memory (WM) task. However, the cost of the level of complexity in N-back paradigm was double for GG subjects than for AA subjects. It is noteworthy that an additive-dosage allele relation was found for G allele in terms of cost of level of complexity. These genetic variation results support that the endocannabinoid system, evaluated by rs2180619 polymorphism, is involved in WM ability in humans.

Multifractal analysis of information processing in hippocampal neural ensembles during working memory under Δ⁹-tetrahydrocannabinol administration

BACKGROUND

Multifractal analysis quantifies the time-scale-invariant properties in data by describing the structure of variability over time. By applying this analysis to hippocampal interspike interval sequences recorded during performance of a working memory task, a measure of long-range temporal correlations and multifractal dynamics can reveal single neuron correlates of information processing.

NEW METHOD

Wavelet leaders-based multifractal analysis (WLMA) was applied to hippocampal interspike intervals recorded during a working memory task. WLMA can be used to identify neurons likely to exhibit information processing relevant to operation of brain-computer interfaces and nonlinear neuronal models.

RESULTS

Neurons involved in memory processing ("Functional Cell Types" or FCTs) showed a greater degree of multifractal firing properties than neurons without task-relevant firing characteristics. In addition, previously unidentified FCTs were revealed because multifractal analysis suggested further functional classification. The cannabinoid type-1 receptor (CB1R) partial agonist, tetrahydrocannabinol (THC), selectively reduced multifractal dynamics in FCT neurons compared to non-FCT neurons.

COMPARISON WITH EXISTING METHODS

WLMA is an objective tool for quantifying the memory-correlated complexity represented by FCTs that reveals additional information compared to classification of FCTs using traditional z-scores to identify neuronal correlates of behavioral events.

CONCLUSION

z-Score-based FCT classification provides limited information about the dynamical range of neuronal activity characterized by WLMA. Increased complexity, as measured with multifractal analysis, may be a marker of functional involvement in memory processing. The level of multifractal attributes can be used to differentially emphasize neural signals to improve computational models and algorithms underlying brain-computer interfaces.

Donor/recipient enhancement of memory in rat hippocampus

The critical role of the mammalian hippocampus in the formation, translation and retrieval of memory has been documented over many decades. There are many theories of how the hippocampus operates to encode events and a precise mechanism was recently identified in rats performing a short-term memory task which demonstrated that successful information encoding was promoted via specific patterns of activity generated within ensembles of hippocampal neurons. In the study presented here, these “representations” were extracted via a customized non-linear multi-input multi-output (MIMO) mathematical model which allowed prediction of successful performance on specific trials within the testing session. A unique feature of this characterization was demonstrated when successful information encoding patterns were derived online from well-trained “donor” animals during difficult long-delay trials and delivered via online electrical stimulation to synchronously tested naïve “recipient” animals never before exposed to the delay feature of the task. By transferring such model-derived trained (donor) animal hippocampal firing patterns via stimulation to coupled naïve recipient animals, their task performance was facilitated in a direct “donor-recipient” manner. This provides the basis for utilizing extracted appropriate neural information from one brain to induce, recover, or enhance memory related processing in the brain of another subject.

Novelty-induced emotional arousal modulates cannabinoid effects on recognition memory and adrenocortical activity

Although it is well established that cannabinoid drugs can influence cognitive performance, the findings-describing both enhancing and impairing effects-have been ambiguous. Here, we investigated the effects of posttraining systemic administration of the synthetic cannabinoid agonist WIN55,212-2 (0.1, 0.3, or 1.0 mg/kg) on short- and long-term retention of object recognition memory under two conditions that differed in their training-associated arousal level. In male Sprague-Dawley rats that were not previously habituated to the experimental context, WIN55,212-2 administered immediately after a 3-min training trial, biphasically impaired retention performance at a 1-h interval. In contrast, WIN55,212-2 enhanced 1-h retention of rats that had received extensive prior habituation to the experimental context. Interestingly, immediate posttraining administration of WIN55,212-2 to non-habituated rats, in doses that impaired 1-h retention, enhanced object recognition performance at a 24-h interval. Posttraining WIN55,212-2 administration to habituated rats did not significantly affect 24-h retention. In light of intimate interactions between cannabinoids and the hypothalamic-pituitary-adrenal axis, we further investigated whether cannabinoid administration might differently influence training-induced glucocorticoid activity in rats in these two habituation conditions. WIN55,212-2 administered after object recognition training elevated plasma corticosterone levels in non-habituated rats whereas it decreased corticosterone levels in habituated rats. Most importantly, following pretreatment with the corticosterone-synthesis inhibitor metyrapone, WIN55,212-2 effects on 1- and 24-h retention of non-habituated rats became similar to those seen in the low-aroused habituated animals, indicating that cannabinoid-induced regulation of adrenocortical activity contributes to the environmentally sensitive effects of systemically administered cannabinoids on short- and long-term retention of object recognition memory.

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.

Design of optimal stimulation patterns for neuronal ensembles based on Volterra-type hierarchical modeling

This paper presents a general methodology for the optimal design of stimulation patterns applied to neuronal ensembles in order to elicit a desired effect. The methodology follows a variant of the hierarchical Volterra modeling approach that utilizes input-output data to construct predictive models that describe the effects of interactions among multiple input events in an ascending order of interaction complexity. The illustrative example presented in this paper concerns the multi-unit activity of CA1 neurons in the hippocampus of a rodent performing a learned delayed-nonmatch-to-sample (DNMS) task. The multi-unit activity of the hippocampal CA1 neurons is recorded via chronically implanted multi-electrode arrays during this task. The obtained model quantifies the likelihood of having correct performance of the specific task for a given multi-unit (spatiotemporal) activity pattern of a CA1 neuronal ensemble during the 'sample presentation' phase of the DNMS task. The model can be used to determine computationally (off-line) the 'optimal' multi-unit stimulation pattern that maximizes the likelihood of inducing the correct performance of the DNMS task. Our working hypothesis is that application of this optimal stimulation pattern will enhance performance of the DNMS task due to enhancement of memory formation and storage during the 'sample presentation' phase of the task.

Working memory performance in young adults is associated to the AATn polymorphism of the CNR1 gene

Working memory (WM) depends on several neural networks and neurochemical systems. One of them is the endocannabinoid (eCB) system, which CB1 receptor (CB1R) is widely distributed all over the brain. The stimulation of CB1R by agonists reduces WM efficiency. The CNR1 human gene (6q14-15) encodes the CB1R. AATn polymorphism of the CNR1 gene has been related to psychiatric disorders, and to procedural learning and attention in healthy subjects. The aim of this exploratory research was to test whether AATn polymorphism of the CNR1 is related to the WM performance, by measuring n-back task. Mexican healthy young adults (n = 94) performed the WM n-back task. One of the most frequent AATn allele in our sample was the AAT12. We formed three groups, as a function of the AATn genotype: AAT ≤ 12/AAT≤12, AAT ≤ 12/AAT > 12 and AAT > 12/AAT > 12, and their accuracy on the n-back task was compared. WM accuracy differed among genotypes (P=0.03): AAT ≤ 12/AAT≤12 group had a higher performance than the AAT > 12/AAT > 12 group (statistical power: 0.65, f(2) = 0.20, P<0.05). These results suggest that the fewer AATn repeats of the CNR1 gene, the better WM performance, and sustain the idea that eCB system participates in the modulation of the human brain network involved in WM.

Closing the loop for memory prosthesis: detecting the role of hippocampal neural ensembles using nonlinear models

A major factor involved in providing closed loop feedback for control of neural function is to understand how neural ensembles encode online information critical to the final behavioral endpoint. This issue was directly assessed in rats performing a short-term delay memory task in which successful encoding of task information is dependent upon specific spatio-temporal firing patterns recorded from ensembles of CA3 and CA1 hippocampal neurons. Such patterns, extracted by a specially designed nonlinear multi-input multi-output (MIMO) nonlinear mathematical model, were used to predict successful performance online via a closed loop paradigm which regulated trial difficulty (time of retention) as a function of the "strength" of stimulus encoding. The significance of the MIMO model as a neural prosthesis has been demonstrated by substituting trains of electrical stimulation pulses to mimic these same ensemble firing patterns. This feature was used repeatedly to vary "normal" encoding as a means of understanding how neural ensembles can be "tuned" to mimic the inherent process of selecting codes of different strength and functional specificity. The capacity to enhance and tune hippocampal encoding via MIMO model detection and insertion of critical ensemble firing patterns shown here provides the basis for possible extension to other disrupted brain circuitry.

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.

A nonlinear model for hippocampal cognitive prosthesis: memory facilitation by hippocampal ensemble stimulation

Collaborative investigations have characterized how multineuron hippocampal ensembles encode memory necessary for subsequent successful performance by rodents in a delayed nonmatch to sample (DNMS) task and utilized that information to provide the basis for a memory prosthesis to enhance performance. By employing a unique nonlinear dynamic multi-input/multi-output (MIMO) model, developed and adapted to hippocampal neural ensemble firing patterns derived from simultaneous recorded CA1 and CA3 activity, it was possible to extract information encoded in the sample phase necessary for successful performance in the nonmatch phase of the task. The extension of this MIMO model to online delivery of electrical stimulation delivered to the same recording loci that mimicked successful CA1 firing patterns, provided the means to increase levels of performance on a trial-by-trial basis. Inclusion of several control procedures provides evidence for the specificity of effective MIMO model generated patterns of electrical stimulation. Increased utility of the MIMO model as a prosthesis device was exhibited by the demonstration of cumulative increases in DNMS task performance with repeated MIMO stimulation over many sessions on both stimulation and nonstimulation trials, suggesting overall system modification with continued exposure. Results reported here are compatible with and extend prior demonstrations and further support the candidacy of the MIMO model as an effective cortical prosthesis.

A hippocampal cognitive prosthesis: multi-input, multi-output nonlinear modeling and VLSI implementation

This paper describes the development of a cognitive prosthesis designed to restore the ability to form new long-term memories typically lost after damage to the hippocampus. The animal model used is delayed nonmatch-to-sample (DNMS) behavior in the rat, and the "core" of the prosthesis is a biomimetic multi-input/multi-output (MIMO) nonlinear model that provides the capability for predicting spatio-temporal spike train output of hippocampus (CA1) based on spatio-temporal spike train inputs recorded presynaptically to CA1 (e.g., CA3). We demonstrate the capability of the MIMO model for highly accurate predictions of CA1 coded memories that can be made on a single-trial basis and in real-time. When hippocampal CA1 function is blocked and long-term memory formation is lost, successful DNMS behavior also is abolished. However, when MIMO model predictions are used to reinstate CA1 memory-related activity by driving spatio-temporal electrical stimulation of hippocampal output to mimic the patterns of activity observed in control conditions, successful DNMS behavior is restored. We also outline the design in very-large-scale integration for a hardware implementation of a 16-input, 16-output MIMO model, along with spike sorting, amplification, and other functions necessary for a total system, when coupled together with electrode arrays to record extracellularly from populations of hippocampal neurons, that can serve as a cognitive prosthesis in behaving animals.

Endocannabinoid tone versus constitutive activity of cannabinoid receptors

This review evaluates the cellular mechanisms of constitutive activity of the cannabinoid (CB) receptors, its reversal by inverse agonists, and discusses the pitfalls and problems in the interpretation of the research data. The notion is presented that endogenously produced anandamide (AEA) and 2-arachidonoylglycerol (2-AG) serve as autocrine or paracrine stimulators of the CB receptors, giving the appearance of constitutive activity. It is proposed that one cannot interpret inverse agonist studies without inference to the receptors' environment vis-à-vis the endocannabinoid agonists which themselves are highly lipophilic compounds with a preference for membranes. The endocannabinoid tone is governed by a combination of synthetic pathways and inactivation involving transport and degradation. The synthesis and degradation of 2-AG is well characterized, and 2-AG has been strongly implicated in retrograde signalling in neurons. Data implicating endocannabinoids in paracrine regulation have been described. Endocannabinoid ligands can traverse the cell's interior and potentially be stored on fatty acid-binding proteins (FABPs). Molecular modelling predicts that the endocannabinoids derived from membrane phospholipids can laterally diffuse to enter the CB receptor from the lipid bilayer. Considering that endocannabinoid signalling to CB receptors is a much more likely scenario than is receptor activation in the absence of agonist ligands, researchers are advised to refrain from assuming constitutive activity except for experimental models known to be devoid of endocannabinoid ligands.

Memory encoding in hippocampal ensembles is negatively influenced by cannabinoid CB1 receptors

It has previously been demonstrated that the detrimental effect on the performance of a delayed nonmatch to sample (DNMS) memory task by exogenously administered cannabinoid (CB1) receptor agonist, WIN 55212-2 (WIN), is reversed by the receptor antagonist rimonabant. In addition, rimonabant administered alone elevates DNMS performance, presumably through the suppression of negative modulation by released endocannabinoids during normal task performance. Other investigations have shown that rimonabant enhances encoding of DNMS task-relevant information on a trial-by-trial, delay-dependent basis. In this study, these reciprocal pharmacological actions were completely characterized by long-term, chronic intrahippocampal infusion of both agents (WIN and rimonabant) in successive 2-week intervals. Such long-term exposure allowed extraction and confirmation of task-related firing patterns, in which rimonabant reversed the effects of CB1 agonists. This information was then utilized to artificially impose the facilitatory effects of rimonabant and to reverse the effects of WIN on DNMS performance, by delivering multichannel electrical stimulation in the same firing patterns to the same hippocampal regions. Direct comparison of normal and WIN-injected subjects, in which rimonabant injections and ensemble firing facilitated performance, verified reversal of the modulation of hippocampal memory processes by CB1 receptor agonists, including released endocannabinoids.

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.

Pharmacological elevation of anandamide impairs short-term memory by altering the neurophysiology in the hippocampus

In rodents, many exogenous cannabinoid agonists including Δ(9)-THC and WIN55,212-2 (WIN-2) have been shown to impair short-term memory (STM) by inhibition of hippocampal neuronal assemblies. However, the mechanisms by which endocannabinoids such as anandamide and 2-arachidonyl glycerol (2-AG) modulate STM processes are not well understood. Here the effects of anandamide on performance of a Delayed-Non-Match-to-Sample (DNMS) task (i.e. STM task) and concomitant hippocampal ensemble activity were assessed following administration of either URB597 (0.3, 3.0 mg/kg), an inhibitor of the Fatty Acid Amide Hydrolase (FAAH), AM404 (1.5, 10.0 mg/kg), a putative anandamide uptake/FAAH inhibitor, or R-methanandamide (3.0, 10.0 mg/kg), a stable analog of anandamide. Principal cells from hippocampal CA3/CA1 were recorded extracellularly by multi-electrode arrays in Long-Evans rats during DNMS task (1-30 s delays) performance and tracked throughout drug administration and recovery. Both R-methanandamide and URB597 caused dose- and delay-dependent deficits in DNMS performance with suppression of hippocampal ensemble activity during the encoding (sample) phase. R-methanandamide-induced effects were not reversed by capsaicin excluding a contribution of TRPV-1 receptors. AM404 produced subtle deficits at longer delay intervals but did not alter hippocampal neuronal activity during task-specific events. Collectively, these data indicate that endocannabinoid levels affect performance in a STM task and their pharmacological elevation beyond normal concentrations is detrimental also for the underlying physiological responses. They also highlight a specific window of memory processing, i.e. encoding, which is sensitive to cannabinoid modulation.

A cortical neural prosthesis for restoring and enhancing memory

A primary objective in developing a neural prosthesis is to replace neural circuitry in the brain that no longer functions appropriately. Such a goal requires artificial reconstruction of neuron-to-neuron connections in a way that can be recognized by the remaining normal circuitry, and that promotes appropriate interaction. In this study, the application of a specially designed neural prosthesis using a multi-input/multi-output (MIMO) nonlinear model is demonstrated by using trains of electrical stimulation pulses to substitute for MIMO model derived ensemble firing patterns. Ensembles of CA3 and CA1 hippocampal neurons, recorded from rats performing a delayed-nonmatch-to-sample (DNMS) memory task, exhibited successful encoding of trial-specific sample lever information in the form of different spatiotemporal firing patterns. MIMO patterns, identified online and in real-time, were employed within a closed-loop behavioral paradigm. Results showed that the model was able to predict successful performance on the same trial. Also, MIMO model-derived patterns, delivered as electrical stimulation to the same electrodes, improved performance under normal testing conditions and, more importantly, were capable of recovering performance when delivered to animals with ensemble hippocampal activity compromised by pharmacologic blockade of synaptic transmission. These integrated experimental-modeling studies show for the first time that, with sufficient information about the neural coding of memories, a neural prosthesis capable of real-time diagnosis and manipulation of the encoding process can restore and even enhance cognitive, mnemonic processes.

Cannabinoid receptor activation modifies NMDA receptor mediated release of intracellular calcium: implications for endocannabinoid control of hippocampal neural plasticity

Chronic activation or inhibition of cannabinoid receptors (CB1) leads to continuous suppression of neuronal plasticity in hippocampus and other brain regions, suggesting that endocannabinoids may have a functional role in synaptic processes that produce state-dependent transient modulation of hippocampal cell activity. In support of this, it has previously been shown in vitro that cannabinoid CB1 receptors modulate second messenger systems in hippocampal neurons that can regulate operation of intracellular processes including receptors which release calcium from intracellular stores. Here we demonstrate in hippocampal slices a similar endocannabinoid action on excitatory glutamatergic synapses via modulation of NMDA-receptor mediated intracellular calcium levels in confocal imaged neurons. Calcium entry through glutamatergic NMDA-mediated ion channels increases intracellular calcium concentrations by modifying release from ryanodine-sensitive channels in endoplasmic reticulum. The studies reported here show that NMDA-elicited increases in Calcium Green fluorescence are enhanced by CB1 receptor antagonists (i.e., Rimonabant), and inhibited by CB1 agonists (i.e., WIN 55,212-2). Suppression of endocannabinoid breakdown by either reuptake inhibition (AM404) or fatty-acid amide hydrolase inhibition (URB597) produced suppression of NMDA-elicited calcium increases comparable to WIN 55,212-2, while enhancement of calcium release provoked by endocannabinoid receptor antagonists (Rimonabant) was shown to depend on the blockade of CB1receptor mediated de-phosphorylation of Ryanodine receptors. Such CB1 receptor modulation of NMDA elicited increases in intracellular calcium may account for the respective disruption and enhancement by CB1 agents of trial-specific hippocampal neuron ensemble firing patterns during performance of a short-term memory task, reported previously from this laboratory.

Effects of SR141716A on Cognitive and Depression-Related Behavior in an Animal Model of Premotor Parkinson's Disease

A previous study from our laboratory revealed that moderate nigral dopaminergic degeneration caused emotional and cognitive deficits in rats, paralleling early signs of Parkinson's disease. Recent evidence suggests that the blockade of cannabinoid CB₁ receptors might be beneficial to alleviate motor inhibition typical of Parkinson's disease. Here, we investigated whether antagonism of CB₁ receptors would improve emotional and cognitive deficits in a rat model of premotor Parkinson's disease. Depression-like behavior and cognition were assessed with the forced swim test and the social recognition test, respectively. Confirming our previous study, rats injected with 6-hydroxydopamine in striatum presented emotional and cognitive alterations which were improved by acute injection of SR141716A. HPLC analysis of monoamine levels demonstrated alterations in the striatum and prefrontal cortex after SR141716A injection. These findings suggest a role for CB₁ receptors in the early symptoms caused by degeneration of dopaminergic neurons in the striatum, as observed in Parkinson's disease.

Neuropsychological consequences of alcohol and drug abuse on different components of executive functions

Several studies have shown alterations in different components of executive functioning in users of different drugs, including cannabis, cocaine and heroin. However, it is difficult to establish a specific association between the use of each of these drugs and executive alterations, since most drug abusers are polysubstance abusers, and alcohol is a ubiquitous confounding factor. Moreover, in order to study the association between consumption of different drugs and executive functioning, the patterns of quantity and duration of drugs used must be considered, given the association between these parameters and the executive functioning alteration degree. Based on the multicomponent approach to executive functions, the aims of the present study were: (i) to analyse the differential contribution of alcohol versus cocaine, heroin and cannabis use on executive functions performance; and (ii) to analyse the contribution made by the severity of the different drugs used (quantity and duration patterns) on these functions in a sample of polysubstance abusers that requested treatment for cannabis-, cocaine- or heroin-related problems. We administered measures of fluency, working memory, analogical reasoning, interference, cognitive flexibility, decision-making and self-regulation to two groups: 60 substance-dependent individuals (SDIs) and 30 healthy control individuals (HCIs). SDIs had significantly poorer performance than HCIs across all of the executive domains assessed. Results from hierarchical regression models showed the existence of common correlates of the use of alcohol, cannabis and cocaine on verbal fluency and decision-making; common correlates of quantity of cannabis and cocaine use on verbal working memory and analogical reasoning; common correlates of duration of cocaine and heroin use on shifting; and specific effects of duration of cocaine use on inhibition measures. These findings indicate that alcohol abuse is negatively associated with fluency and decision-making deficits, whereas the different drugs motivating treatment have both generalized and specific deleterious effects on different executive components.

Recruitment of hippocampal neurons to encode behavioral events in the rat: alterations in cognitive demand and cannabinoid exposure

Successful performance by rats of a delayed-nonmatch-to-sample (DNMS) task is hippocampal dependent. We have shown that neurons in hippocampus differentially encode task-relevant events. These responses are critical for correct DNMS performance and are diminished by exogenous cannabinoids. We therefore reasoned that hippocampal neural correlates of behavior are likely shaped during learning; however, to date, no work has examined these correlates during DNMS acquisition training. Consequently, the present study assessed the emergence of hippocampal neural encoding when (i) cognitive task demands were increased through prolongation of delay intervals between sample and nonmatch phase and (ii) when animals are under cannabinoid treatment and performance is compromised. Adult, male Long-Evans rats were trained to perform the DNMS task without delay and then implanted with multielectrode recording arrays directed to CA3 and CA1 subfields of the hippocampus. Following recovery, single units were isolated and animals divided into two treatment groups: vehicle or WIN 55,212-2 (WIN-2, 0.35 mg/kg). Ensemble firing was monitored during retraining in DNMS task at 0 s, and subsequently delay intervals were progressively increased to 1-10 s, 11-20 s, and 21-30 s when animals met criterion (80% correct) at each respective interval. Hippocampal CA3 and CA1 principal cells were isolated and recorded throughout treatment. Extension of the delay led to an increase in the number of task-correlated neurons in controls. This recruitment of novel cells was reduced/prevented in the presence of WIN-2 and was paralleled by impairment in acquisition learning at longer delay intervals. Moreover, WIN-2 suppressed hippocampal ensemble firing during the sample (encoding) but not nonmatch phase of the DNMS task across all delays. These cannabinoid-induced alterations in hippocampal neuronal activity may explain the observed deficits in DNMS performance.

Anormalidades cognitivas no uso da cannabis

OBJETIVO: Evidências de que o uso de cannabis prejudica funções cognitivas em humanos têm-se acumulado nas décadas recentes. O propósito desta revisão é o de atualizar o conhecimento nesta área com novos achados a partir da literatura mais recente. MÉTODO: As buscas na literatura foram realizadas utilizando-se o banco de dados Web of Science até fevereiro de 2010. Foram buscados os termos "cannabi*" ou "marijuana" e "cogniti*" ou "memory" ou "attention" ou "executive function", e os estudos em humanos foram revisados preferencialmente em relação aos estudos em animais. DISCUSSÃO: O uso de cannabis prejudica a memória, a atenção, o controle inibitório, as funções executivas e a tomada de decisões, tanto durante como após o período de intoxicação aguda, persistindo por horas, dias, semanas ou mais após o último uso. Os estudos de desafio farmacológico em humanos estão elucidando a natureza e os substratos neurais das alterações cognitivas associadas a vários canabinoides. O uso pesado ou de longo prazo de cannabis parece resultar em anormalidades cognitivas mais duradouras e possivelmente em alterações cerebrais estruturais. Efeitos cognitivos adversos maiores estão associados ao uso de cannabis quando este começa no início da adolescência. CONCLUSÃO: O sistema canabinoide endógeno está envolvido nos mecanismos de regulação neural que modulam os processos subjacentes a uma gama de funções cognitivas que estão prejudicadas pela cannabis. Os déficits em usuários humanos muito provavelmente refletem, portanto, neuroadaptações e o funcionamento alterado do sistema canabinoide endógeno.

Are CB(1) Receptor Antagonists Nootropic or Cognitive Impairing Agents?

For more than a decade, a considerable amount of research has examined the effects of rimonabant (SR 141716) and other CB(1) receptor antagonists in both in vivo and in vitro models of learning and memory. In addition to its utility in determining whether the effects of drugs are mediated though a CB(1) receptor mechanism of action, these antagonists are useful in providing insight into the physiological function of the endogenous cannabinoid system. Several groups have reported that CB(1) receptor antagonists enhance memory duration in a variety of spatial and operant paradigms, but not in all paradigms. Conversely, disruption of CB(1) receptor signaling also impairs extinction learning in which the animal actively suppresses a learned response when reinforcement has been withheld. These extinction deficits occur in aversively motivated tasks, such as in fear conditioning or escape behavior in the Morris water maze task, but not in appetitively motivated tasks. Similarly, in electrophysiological models, CB(1) receptor antagonists elicit a variety of effects, including enhancement of long-term potentiation (LTP), while disrupting long-term depression (LTD) and interfering with transient forms of plasticity, including depolarization-induced suppression of inhibition (DSI) and depolarization-induced suppression of excitation (DSE). The collective results of the in vivo and in vitro studies employing CB(1) receptor antagonists, demonstrate that these receptors play integral roles in different components of cognitive processing. Functionally, pharmacological blockade of CB(1) receptors may strengthen memory duration, but interferes with extinction of learned behaviors that are associated with traumatic or aversive memories.

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.

Roles of the endocannabinoid system in learning and memory

The endocannabinoid system (ECS) plays a central role in the regulation of learning and memory processes. The fine-tuned regulation of neural transmission by the system is likely to be the mechanism underlying this important function. In this chapter, we review the data in the literature showing the direct involvement of the physiological activation of cannabinoid receptors in the modulation of different forms of learning and memory. When possible, we also address the likely mechanisms of this involvement. Finally, given the apparent special role of the ECS in the extinction of fear, we propose a reasonable model to assess how neuronal networks could be influenced by the endocannabinoids in these processes. Overall, the data reviewed indicate that, despite the enormous progress of recent years, much is still to be done to fully elucidate the mechanisms of the ECS influence on learning and memory processes.

Differential endocannabinoid regulation of extinction in appetitive and aversive Barnes maze tasks

CB 1 receptor-compromised animals show profound deficits in extinguishing learned behavior from aversive conditioning tasks, but display normal extinction learning in appetitive operant tasks. However, it is difficult to discern whether the differential involvement of the endogenous cannabinoid system on extinction results from the hedonics or the required responses associated with the disparate tasks. Here, we report that the CB 1 receptor antagonist rimonabant disrupts extinction learning in an aversive, but not in an appetitive, Barnes maze conditioning task. Accordingly, these results provide compelling support for the hypothesis that the endogenous cannabinoid system plays a necessary role in the extinction of aversively motivated behaviors but is expendable for appetitively motivated behaviors.

Endocannabinoids modulate encoding of sequential memory in the rat hippocampus

RATIONALE

This report investigated the role of endocannabinoids in the encoding of task-relevant information by ensembles of hippocampal neurons under conditions in which the CB1 receptor antagonist, rimonabant, was administered during performance of a short-term memory delayed non-match to sample (DNMS) task in rats.

OBJECTIVE

The influence of endocannabinoids on the encoding of task relevant information was determined via examination of the firing patterns of ensembles of CA1/CA3 hippocampal neurons during individual trials while rats performed a DNMS task.

MATERIALS AND METHODS

Multivariate discriminant analysis of the firing patterns of ensembles of hippocampal neurons was used to extract trial-specific codes for task-relevant information under different types of trial sequences.

RESULTS

It was discovered that rimonabant blocked an inherent hippocampal memory encoding bias used by all animals. This bias was characterized as the preferential encoding of sample information on individual trials based on the similarity (i.e., same or different) and duration of the delay in the preceding trial.

CONCLUSIONS

The results indicate that endocannabinoids are a major influence on the strategic encoding biases of hippocampal ensembles and that pharmacological blockade of CB1 receptors facilitated performance by eliminating such influences.

The cannabinoid CB(1) receptor antagonist CE prolongs spatial memory duration in a rat delayed radial arm maze memory task

The cannabinoid receptor system plays an integral role in learning and memory. Moreover, the cannabinoid CB(1) receptor antagonist rimonabant has been found to improve performance in a variety of animal memory models. The present study tested whether a novel and potent cannabinoid CB(1) receptor antagonist, CE, would prolong the duration of spatial memory. Rats were trained in a two-phase radial arm maze procedure, consisting of acquisition and retrieval tests, which were separated by an 18 h delay. CE was administered 30 min before the acquisition phase, immediately after the acquisition phase, or 30 min before the retrieval test to assess its effects on acquisition and retrieval processes. CE administered before and immediately after the acquisition phase significantly decreased the number of errors committed during the retrieval test. On the other hand, CE administered 30 min before the retrieval test had no effect on the number of errors committed. These findings demonstrate that CE improves memory by acting on consolidation, rather than retrieval, processes and further suggest that the endocannabinoid system has an important role in modulating memory duration.

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.