Activation of cannabinoid CB1 receptors in the central amygdala impairs inhibitory avoidance memory consolidation via NMDA receptors

Targeting mediodorsal thalamic CB1 receptors to inhibit dextromethorphan-induced anxiety/exploratory-related behaviors in rats: The post-weaning effect of exercise and enriched environment on adulthood anxiety

Dextromethorphan (DXM) is an effective over-the-counter antitussive with an alarming increase as an abused drug for recreational purposes. Although reports of the association between DXM administration and anxiety, there are few investigations into the underlying DMX mechanisms of anxiogenic action. Thus, the present study aimed to investigate the role of the mediodorsal thalamus (MD) cannabinoid CB1 receptors (CB1Rs) in DXM-induced anxiety/exploratory-related behaviors in adult male Wistar rats. Animals were bilaterally cannulated in the MD regions. After one week, anxiety and exploratory behaviors were measured using an elevated plus-maze task (EPM) and a hole-board apparatus. Results showed that DXM (3-7 mg/kg, i. p.) dose-dependently increased anxiety-like behaviors. Intra-MD administration of ACPA (2.5-10 ng/rat), a selective CB1 receptor agonist, decreased anxiety-like effects of DXM. The blockade of MD CB1 receptors by AM-251 (40-120 ng/rat) did not affect the EPM task. However, it potentiated the anxiogenic response of an ineffective dose of DXM (3 mg/kg) in the animals. Moreover, the effect of post-weaning treadmill exercise (TEX) and enriched environment (EE) were examined in adulthood anxiety under the drug treatments. Juvenile rats were divided into TEX/EE and control groups. The TEX/EE-juvenile rats were placed on a treadmill and then exposed to EE for five weeks. Interestingly, compared to untreated animals, post-weaning TEX/EE inhibited the anxiety induced by DXM or AM-251/DXM. It can be concluded that the MD endocannabinoid system plays an essential role in the anxiogenic effect of dextromethorphan. Moreover, post-weaning exercise alongside an enriched environment may have an inhibitory effect on adulthood anxiety-like behaviors.

Extended amygdala, conditioned withdrawal and memory consolidation

Opioid withdrawal can be associated to environmental cues through classical conditioning. Exposure to these cues can precipitate a state of conditioned withdrawal in abstinent subjects, and there are suggestions that conditioned withdrawal can perpetuate the addiction cycle in part by promoting the storage of memories. This review discusses evidence supporting the hypothesis that conditioned withdrawal facilitates memory consolidation by activating a neurocircuitry that involves the extended amygdala. Specifically, the central amygdala, the bed nucleus of the stria terminalis, and the nucleus accumbens shell interact functionally during withdrawal, mediate expression of conditioned responses, and are implicated in memory consolidation. From this perspective, the extended amygdala could be a neural pathway by which drug-seeking behaviour performed during a state of conditioned withdrawal is more likely to become habitual and persistent.

How do stupendous cannabinoids modulate memory processing via affecting neurotransmitter systems?

In the present study, we wanted to review the role of cannabinoids in learning and memory in animal models, with respect to their interaction effects with six principal neurotransmitters involved in learning and memory including dopamine, glutamate, GABA (γ-aminobutyric acid), serotonin, acetylcholine, and noradrenaline. Cannabinoids induce a wide-range of unpredictable effects on cognitive functions, while their mechanisms are not fully understood. Cannabinoids in different brain regions and in interaction with different neurotransmitters, show diverse responses. Previous findings have shown that cannabinoids agonists and antagonists induce various unpredictable effects such as similar effect, paradoxical effect, or dualistic effect. It should not be forgotten that brain neurotransmitter systems can also play unpredictable roles in mediating cognitive functions. Thus, we aimed to review and discuss the effect of cannabinoids in interaction with neurotransmitters on learning and memory. In addition, we mentioned to the type of interactions between cannabinoids and neurotransmitter systems. We suggested that investigating the type of interactions is a critical neuropharmacological issue that should be considered in future studies.

State-dependent memory and its modulation by different brain areas and neurotransmitters

The state-dependent memory defines as a state that the retrieval of recently obtained information may be potential if the subject exists in a similar physiological situation as for the period of the encoding stage. Studies revealed that exogenous and endogenous compounds could induce state-dependent memory. The state-dependent memory made it probable to differentiate the effects of drugs per se on learning from the effects due to alterations in drug state during the task. Studies proposed the role of regions beyond the limbic formation and illustrated that state-dependent memory produced by various neurotransmitter systems and pharmacological compounds. Our review of the literature revealed that: (a) re-administration of drugs on the same state induce state-dependent memory; (b) many neurotransmitters induce endogenous state-dependent memory; (c) there are cross state-dependent learning and memory between some drugs; (d) some sites of the brain including the CA1 areas of the hippocampus, central nucleus of the amygdala (CeA), septum, ventral tegmental area (VTA), and nucleus accumbens (NAC) are involved in state-dependent memory. See also Figure 1(Fig. 1).

Precondition of right frontal region with anodal tDCS can restore the fear memory impairment induced by ACPA in male mice

Fear memory and learning cause behavioural patterns such as fight or flight responses, which increase survival probability, but unfit processing of fear memory and learning can lead to maladaptive behaviours and maladies such as phobias, Post-Traumatic Stress Disorder (PTSD) and anxiety disorders. The growing prevalence of these maladies shows the need to quest novel methods for their treatment. We used anodal transcranial direct current stimulation (tDCS) on the right frontal region as a precondition neuromodulator and arachidonylcyclopropylamide (ACPA), a selective CB1 cannabinoid receptor agonist, as a fear memory impairing agent to assess their effects on contextual and auditory fear conditioning (reliable model for fear studies). Right frontal anodal tDCS (0.2 mA for. 20 minutes) 24 hours before the train did not alter contextual and auditory learning and memory in short-term (24 hrs after the training phase). Moreover, intraperitoneal pre-train injection of ACPA (0.1 mg/kg) alone, decreased both contextual and auditory learning and memory in short- but not long-term. Right frontal anodal tDCS improved short-term contextual fear memory in subthreshold doses of ACPA. On the other hand, right frontal anodal tDCS in long-term improved (lower doses of ACPA) and restored (higher doses of ACPA) both fear memories. These findings showed that, aforementioned approach could cause durable learning and memory improvements. Also this combined modality could be useful for fear extinction training and maladies which inflict amnesia.

Dorsal hippocampal NMDA receptors mediate the interactive effects of arachidonylcyclopropylamide and MDMA/ecstasy on memory retrieval in rats

A combination of cannabis and ecstasy may change the cognitive functions more than either drug alone. The present study was designed to investigate the possible involvement of dorsal hippocampal NMDA receptors in the interactive effects of arachidonylcyclopropylamide (ACPA) and ecstasy/MDMA on memory retrieval. Adult male Wistar rats were cannulated into the CA1 regions of the dorsal hippocampus (intra-CA1) and memory retrieval was examined using the step-through type of passive avoidance task. Intra-CA1 microinjection of a selective CB1 receptor agonist, ACPA (0.5-4ng/rat) immediately before the testing phase (pre-test), but not after the training phase (post-training), impaired memory retrieval. In addition, pre-test intra-CA1 microinjection of MDMA (0.5-1μg/rat) dose-dependently decreased step-through latency, indicating an amnesic effect of the drug by itself. Interestingly, pre-test microinjection of a higher dose of MDMA into the CA1 regions significantly improved ACPA-induced memory impairment. Moreover, pre-test intra-CA1 microinjection of a selective NMDA receptor antagonist, D-AP5 (1 and 2μg/rat) inhibited the reversal effect of MDMA on the impairment of memory retrieval induced by ACPA. Pre-test intra-CA1 microinjection of the same doses of D-AP5 had no effect on memory retrieval alone. These findings suggest that ACPA or MDMA consumption can induce memory retrieval impairment, while their co-administration improves this amnesic effect through interacting with hippocampal glutamatergic-NMDA receptor mechanism. Thus, it seems that the tendency to abuse cannabis with ecstasy may be for avoiding cognitive dysfunction.

α-Linolenic Acid, A Nutraceutical with Pleiotropic Properties That Targets Endogenous Neuroprotective Pathways to Protect against Organophosphate Nerve Agent-Induced Neuropathology

α-Linolenic acid (ALA) is a nutraceutical found in vegetable products such as flax and walnuts. The pleiotropic properties of ALA target endogenous neuroprotective and neurorestorative pathways in brain and involve the transcription factor nuclear factor kappa B (NF-κB), brain-derived neurotrophic factor (BDNF), a major neuroprotective protein in brain, and downstream signaling pathways likely mediated via activation of TrkB, the cognate receptor of BDNF. In this review, we discuss possible mechanisms of ALA efficacy against the highly toxic OP nerve agent soman. Organophosphate (OP) nerve agents are highly toxic chemical warfare agents and a threat to military and civilian populations. Once considered only for battlefield use, these agents are now used by terrorists to inflict mass casualties. OP nerve agents inhibit the critical enzyme acetylcholinesterase (AChE) that rapidly leads to a cholinergic crisis involving multiple organs. Status epilepticus results from the excessive accumulation of synaptic acetylcholine which in turn leads to the overactivation of muscarinic receptors; prolonged seizures cause the neuropathology and long-term consequences in survivors. Current countermeasures mitigate symptoms and signs as well as reduce brain damage, but must be given within minutes after exposure to OP nerve agents supporting interest in newer and more effective therapies. The pleiotropic properties of ALA result in a coordinated molecular and cellular program to restore neuronal networks and improve cognitive function in soman-exposed animals. Collectively, ALA should be brought to the clinic to treat the long-term consequences of nerve agents in survivors. ALA may be an effective therapy for other acute and chronic neurodegenerative disorders.

Repeated systemic administration of the nutraceutical alpha-linolenic acid exerts neuroprotective efficacy, an antidepressant effect and improves cognitive performance when given after soman exposure

Exposure to nerve agents results in severe seizures or status epilepticus caused by the inhibition of acetylcholinesterase, a critical enzyme that breaks down acetylcholine to terminate neurotransmission. Prolonged seizures cause brain damage and can lead to long-term consequences. Current countermeasures are only modestly effective against the brain damage supporting interest in the evaluation of new and efficacious therapies. The nutraceutical alpha-linolenic acid (LIN) is an essential omega-3 polyunsaturated fatty acid that has a wide safety margin. Previous work showed that a single intravenous injection of alpha-linolenic acid (500 nmol/kg) administered before or after soman significantly protected against soman-induced brain damage when analyzed 24h after exposure. Here, we show that administration of three intravenous injections of alpha-linolenic acid over a 7 day period after soman significantly improved motor performance on the rotarod, enhanced memory retention, exerted an anti-depressant-like activity and increased animal survival. This dosing schedule significantly reduced soman-induced neuronal degeneration in four major vulnerable brain regions up to 21 days. Taken together, alpha-linolenic acid reduces the profound behavioral deficits induced by soman possibly by decreasing neuronal cell death, and increases animal survival.

Tenuifolin, a secondary saponin from hydrolysates of polygalasaponins, counteracts the neurotoxicity induced by Aβ25-35 peptides in vitro and in vivo

Alzheimer's disease (AD) is associated with damage to hippocampal neurons and declines in cognitive functions. The accumulation of amyloid peptides is regarded as a crucial event in the initiation of AD. The neurotoxicity induced by Aβ25-35 peptides was used to screen for cytoprotective factors in vitro, and the cognitive deficits induced by the injection of Aβ25-35 into the hippocampus were used to evaluate effect on learning and memory. Our previous study revealed that hydrolysate of polygalasaponins (HPS) clearly improve the cognitive deficits induced by the injection of Aβ25-35 in mice, but the potential active constituent of HPS remains unclear. The purposes of this study were to separate and purify the secondary saponins of HPS, screen for neuroprotective effects of the constituents in vitro, and to evaluate the effect of cognition in vivo. Various chromatographic methods were used to separate and purify the HPS. The neuroprotective effects were examined in Aβ25-35-damage-induced PC12 cells. The protective effect of tenuifolin on the cognitive impairments induced by Aβ25-35 injection was assessed using the Morris water maze and step-through passive avoidance tests. Tenuifolin and fallaxsaponin A were isolated from the HPS. Tenuifolin possessed neuroprotective effects against Aβ25-35-induced apoptosis in PC12 cells and significantly improved the cognitive deficits induced by the intrahippocampal injection of Aβ25-35 in mice. Thus, tenuifolin is one of the active constituents of HPS against the neurotoxicity induced by Aβ25-35 peptides in vitro and in vivo.

Pre-encoding administration of amphetamine or THC preferentially modulates emotional memory in humans

RATIONALE

Many addictive drugs are known to have effects on learning and memory, and these effects could motivate future drug use. Specifically, addictive drugs may affect memory of emotional events and experiences in ways that are attractive to some users. However, few studies have investigated the effects of addictive drugs on emotional memory in humans.

OBJECTIVES

This study examined the effects of the memory-enhancing drug dextroamphetamine (AMP) and the memory-impairing drug Δ(9)-tetrahydrocannabinol (THC) on emotional memory in healthy volunteers.

METHODS

Participants completed three experimental sessions across which they received capsules containing placebo and two doses of either AMP (10 and 20 mg; N = 25) or THC (7.5 and 15 mg; N = 25) before viewing pictures of positive (pleasant), neutral, and negative (unpleasant) scenes. Memory for the pictures was assessed 2 days later, under drug-free conditions.

RESULTS

Relative to placebo, memory for emotional pictures was improved by AMP and impaired by THC, but neither drug significantly affected memory for unemotional pictures. Positive memory biases were not observed with either drug, and there was no indication that the drugs' memory effects were directly related to their subjective or physiological effects alone.

CONCLUSIONS

This study provides the first clear evidence that stimulant drugs can preferentially strengthen, and cannabinoids can preferentially impair, memory for emotional events in humans. Although addictive drugs do not appear to positively bias memory, the possibility remains that these drugs' effects on emotional memory could influence drug use among certain individuals.