Selective CB1 Receptor Research Articles

Role of orexin-2 and CB1 receptors within the periaqueductal gray matter in lateral hypothalamic-induced antinociception in rats.

Orexin plays an important role in pain modulation. Orexin-1 and orexin-2 receptors (Ox1r and Ox2r) are found at high density in the ventrolateral periaqueductal gray matter (vlPAG). Our previous study showed that chemical stimulation of the lateral hypothalamus with carbachol induces antinociception in the tail-flick test, a model of acute pain, and Ox1r-mediated antinociception in the vlPAG is modulated by the activity of vlPAG CB1 receptors. In the current study, TCS OX2 29, an Ox2r antagonist (5, 15, 50, 150, and 500 nmol/l), was microinjected into the vlPAG 5 min before the administration of carbachol (125 nmol/l). TCS OX2 29 dose dependently reduced carbachol-induced antinociception. In a second set of experiments, animals were treated with carbachol 5 min after intra-vlPAG administration of 15 nmol/l TCS OX2 29 and 1 nmol/l AM251 (a selective CB1 receptor antagonist), or 150 nmol/l TCS OX2 29 and 10 nmol/l AM251. The findings showed that the antinociceptive effect of orexin is partially mediated by activation of vlPAG Ox2 receptors. Furthermore, the administration of ineffective doses of Ox2 and CB1 receptor antagonists reduced the lateral hypothalamus-induced antinociception. It seems that Ox2 and CB1 receptors act through different pathways and Ox2r-mediated antinociception is not dependent on CB1 receptor activity.

Long-lasting alterations of hippocampal GABAergic neurotransmission in adult rats following perinatal Δ9-THC exposure

The long-lasting effects of gestational cannabinoids exposure on the adult brain of the offspring are still controversial. It has already been shown that pre- or perinatal cannabinoids exposure induces learning and memory disruption in rat adult offspring, associated with permanent alterations of cortical glutamatergic neurotransmission and cognitive deficits.In the present study, the risk of long-term consequences induced by perinatal exposure to cannabinoids on rat hippocampal GABAergic system of the offspring, has been explored. To this purpose, pregnant rats were treated daily with Delta9–tetrahydrocannabinol (Δ9-THC; 5mg/kg) or its vehicle.Perinatal exposure to Δ9-THC induced a significant reduction (p<0.05) in basal and K+-evoked [3H]-GABA outflow of 90-day-old rat hippocampal slices. These effects were associated with a reduction of hippocampal [3H]-GABA uptake compared to vehicle exposed group. Perinatal exposure to Δ9-THC induced a significant reduction of CB1 receptor binding (Bmax) in the hippocampus of 90-day-old rats. However, a pharmacological challenge with either Δ9-THC (0.1μM) or WIN55,212-2 (2μM), similarly reduced K+-evoked [3H]-GABA outflow in both experimental groups. These reductions were significantly blocked by adding the selective CB1 receptor antagonist SR141716A.These findings suggest that maternal exposure to cannabinoids induces long-term alterations of hippocampal GABAergic system. Interestingly, previous behavioral studies demonstrated that, under the same experimental conditions as in the present study, perinatal cannabinoids exposure induced cognitive impairments in adult rats, thus resembling some effects observed in humans. Although it is difficult and sometimes misleading to extrapolate findings obtained from animal models to humans, the possibility that an alteration of hippocampus aminoacidergic transmission might underlie, at least in part, some of the cognitive deficits affecting the offspring of marijuana users, is supported.

Involvement of endocannabinoid neurotransmission in the bed nucleus of stria terminalis in cardiovascular responses to acute restraint stress in rats.

Endocannabinoid signalling has been reported as an important neurochemical mechanism involved in responses to stress. Previous studies provided evidence of endocannabinoid release in the bed nucleus of the stria terminalis (BNST) during aversive stimuli. Nevertheless, a possible involvement of this neurochemical mechanism in stress responses has never been evaluated. Therefore, in the present study we investigated the involvement of BNST endocannabinoid neurotransmission, acting via local CB1 receptors, in the cardiovascular responses to acute restraint stress in rats. The selective CB1 receptor antagonist AM251 (1, 30 and 100 pmol 100 nL(-1) ) and/or the fatty acid amide hydrolase (FAAH) enzyme inhibitor URB597 (30 pmol 100 nL(-1) ) or the monoacylglycerol lipase (MAGL) enzyme inhibitor JZL184 (30 pmol 100 nL(-1) ) was microinjected into the BNST before the acute restraint stress. Microinjection of AM251 into the BNST enhanced the tachycardia caused by restraint stress, without affecting the increase in arterial pressure and the sympathetic-mediated cutaneous vasoconstrictor response. Conversely, the increased endogenous levels of AEA in the BNST evoked by local treatment with the FAAH enzyme inhibitor URB597 decreased restraint-evoked tachycardia. Inhibition of the hydrolysis of 2-arachidonoylglycerol (2-AG) in the BNST by local microinjection of the MAGL enzyme inhibitor JZL184 also decreased the HR response. These effects of URB597 and JZL184 were abolished by BNST pretreatment with AM251. These findings indicate an involvement of BNST endocannabinoid neurotransmission, acting via CB1 receptors, in cardiovascular adjustments during emotional stress, which may be mediated by the local release of either AEA or 2-AG.

Effect of the novel synthetic cannabinoids AKB48 and 5F-AKB48 on "tetrad", sensorimotor, neurological and neurochemical responses in mice. In vitro and in vivo pharmacological studies.

AKB48 and its fluorinate derivate 5F-AKB48 are two novel synthetic cannabinoids belonging to a structural class with an indazole core structure. They are marketed as incense, herbal preparations or chemical supply for their psychoactive Cannabis-like effects. The present study was aimed at investigating the in vitro and in vivo pharmacological activity of AKB48 and 5F-AKB48 in male CD-1 mice and comparing their in vivo effects with those caused by the administration of Δ9-THC and JWH-018. In vitro competition binding experiments performed on mouse and human CB1 and CB2 receptors revealed a nanomolar affinity and potency of the AKB48 and 5F-AKB48. In vivo studies showed that AKB48 and 5F-AKB48, induced hypothermia, increased pain threshold to both noxious mechanical and thermal stimuli, caused catalepsy, reduced motor activity, impaired sensorimotor responses (visual, acoustic and tactile), caused seizures, myoclonia, hyperreflexia and promoted aggressiveness in mice. Moreover, microdialysis study in freely moving mice showed that systemic administration of AKB48 and 5F-AKB48 stimulated dopamine release in the nucleus accumbens. Behavioural, neurological and neurochemical effects were fully prevented by the selective CB1 receptor antagonist/inverse agonist AM 251. For the first time, the present study demonstrates the overall pharmacological effects induced by the administration of AKB48 and 5F-AKB48 in mice and suggests that the fluorination can increase the power and/or effectiveness of SCBs. Furthermore, this study outlines the potential detrimental effects of SCBs on human health.

Anti-nociceptive and desensitizing effects of olvanil on capsaicin-induced thermal hyperalgesia in the rat.

BackgroundOlvanil (NE 19550) is a non-pungent synthetic analogue of capsaicin, the natural pungent ingredient of capsicum which activates the transient receptor potential vanilloid type-1 (TRPV1) channel and was developed as a potential analgesic compound. Olvanil has potent anti-hyperalgesic effects in several experimental models of chronic pain. Here we report the inhibitory effects of olvanil on nociceptive processing using cultured dorsal root ganglion (DRG) neurons and compare the effects of capsaicin and olvanil on thermal nociceptive processing in vivo; potential contributions of the cannabinoid CB1 receptor to olvanil’s anti-hyperalgesic effects were also investigated.MethodsA hot plate analgesia meter was used to evaluate the anti-nociceptive effects of olvanil on capsaicin-induced thermal hyperalgesia and the role played by CB1 receptors in mediating these effects. Single cell calcium imaging studies of DRG neurons were employed to determine the desensitizing effects of olvanil on capsaicin-evoked calcium responses. Statistical analysis used Student’s t test or one way ANOVA followed by Dunnett’s post-hoc test as appropriate.ResultsBoth olvanil (100 nM) and capsaicin (100 nM) produced significant increases in intracellular calcium concentrations [Ca2+]i in cultured DRG neurons. Olvanil was able to desensitise TRPV1 responses to further capsaicin exposure more effectively than capsaicin. Intraplantar injection of capsaicin (0.1, 0.3 and 1 μg) produced a robust TRPV1-dependant thermal hyperalgesia in rats, whilst olvanil (0.1, 0.3 and 1 μg) produced no hyperalgesia, emphasizing its lack of pungency. The highest dose of olvanil significantly reduced the hyperalgesic effects of capsaicin in vivo. Intraplantar injection of the selective cannabinoid CB1 receptor antagonist rimonabant (1 μg) altered neither capsaicin-induced thermal hyperalgesia nor the desensitizing properties of olvanil, indicating a lack of involvement of CB1 receptors.ConclusionsOlvanil is effective in reducing capsaicin-induced thermal hyperalgesia, probably via directly desensitizing TRPV1 channels in a CB1 receptor-independent fashion. The results presented clearly support the potential for olvanil in the development of new topical analgesic preparations for treating chronic pain conditions while avoiding the unwanted side effects of capsaicin treatments.

Activation of cannabinoid CB1 receptors suppresses the ROS-induced hypersensitivity of rat vagal lung C-fiber afferents

BackgroundReactive oxygen species (ROS), including H2O2, have been shown to induce hypersensitivity of vagal lung C-fibers (VLCFs) mainly through receptor potential ankyrin 1 (TRPA1) and P2X receptors. Cannabinoids (CBs) exert antinociceptive effects by binding to specific CB receptors, designated CB1 and CB2 (type 2) for type 1 and type 2, respectively. We investigated whether activation of CB receptors can suppress ROS-mediated VLCF hypersensitivity and, if so, what type(s) of CB receptors are involved. MethodsAerosolized H2O2 (0.05%) was inhaled by anesthetized spontaneously breathing rats (n = 304) to sensitize VLCFs. Airway reflex reactivity to intravenous capsaicin, a VLCF stimulant, was measured. Perivagal pretreatments with various types of agonists and antagonists, a technique that can modulate VLCF sensitivity, were made to delineate the roles of the CB receptors. ResultsAerosolized H2O2 induced an augmented apneic response to capsaicin, which was blocked by bilateral vagotomy or by perivagal capsaicin treatment, suggesting that the response is mediated through VLCFs. Perivagal treatment with HU210 (a nonselective CB agonist) or ACPA (a selective CB1 receptor agonist), but not JWH133 (a CB2 receptor agonist), attenuated this H2O2-induced VLCF hypersensitivity. The suppressive effects of HU210 and ACPA were prevented by an additional treatment with AM251 (a selective CB1 antagonist), but not with AM630 (a selective CB2 antagonist). Perivagal treatment with a combination of ACPA, HC030031 (a TRPA1 receptor antagonist), and iso-PPADS (a P2X receptor antagonist) further attenuated the H2O2-induced VLCF hypersensitivity, as compared with treatment with a combination of HC030031 and iso-PPADS. ConclusionsOur results suggest that activation of CB1 receptors may suppress the ROS-mediated VLCF hypersensitivity through a mechanism that is at least partly distinct from the function of TRPA1 and P2X receptors.

Basolateral amygdala CB1 cannabinoid receptors are involved in cross state-dependent memory retrieval between morphine and ethanol

Ethanol and morphine are largely co-abused and affect memory formation. The present study intended to investigate the involvement of cannabinoid CB1 receptors of the basolateral amygdala (BLA) in cross state-dependent memory retrieval between morphine and ethanol. Adult male Wistar rats received bilateral cannulation of the BLA, and memory retrieval was measured in step-through type passive avoidance apparatus. Our results showed that post-training intraperitoneal (i.p.) administration of morphine (6mg/kg) induced amnesia. Pre-test administration of ethanol (0.5g/kg, i.p.) significantly improved morphine-induced memory impairment, suggesting that there is cross state-dependent memory retrieval between morphine and ethanol. It should be considered that pre-test administration of ethanol (0.1 and 0.5g/kg, i.p.) by itself had no effect on memory retrieval in the passive avoidance task. Interestingly, pre-test intra-BLA microinjection of different doses of WIN55,212-2 (0.1, 0.2 and 0.3μg/rat), a non-selective CB1/CB2 receptor agonist, plus an ineffective dose of ethanol (0.1g/kg, i.p.) improved morphine-induced memory impairment. Intra-BLA microinjection of AM251 (0.4–0.6ng/rat), a selective CB1 receptor antagonist, inhibited the improved effect of ethanol (0.5g/kg, i.p.) on morphine response. Pre-test intra-BLA microinjection of WIN55,212-2 or AM251 had no effect on memory retrieval or morphine-induced amnesia. Taken together, it can be concluded that morphine and ethanol can induce state-dependent memory retrieval. In addition, the BLA endocannabinoid system mediates via CB1 receptors the functional interaction of morphine and ethanol state-dependent memory retrieval which may depend on the rewarding effects of the drugs.

Functional interaction between orexin-1 and CB1 receptors in the periaqueductal gray matter during antinociception induced by chemical stimulation of the lateral hypothalamus in rats.

Chemical stimulation of the lateral hypothalamus (LH) with carbachol induces antinociception which is antagonized by blockade of orexin receptors in some pain modulatory sites in the tail-flick test. In this study, we evaluated the role of orexin-1 and CB1 receptors in the periaqueductal gray matter (PAG), a critical pain modulatory site, in mediation of antinociceptive responses induced by LH stimulation in rats. One hundred thirty-two adult male albino Wistar rats weighing 180-250g were unilaterally implanted with two separate cannulae into the LH and ventrolateral PAG (vlPAG). Intra-vlPAG administration of SB334867, as a selective orexin-1 receptor antagonist (0.5, 1.5, 5, 15 and 50nM), or AM251, as a selective CB1 receptor antagonist (1, 3, 10, 30 and 100nM), was performed just 5min before carbachol (125nM) microinjection into the LH. Our findings showed that SB334867 or AM251 administration dose dependently prevented the development of LH-induced antinociception in rats. Treatment with two antagonists at the same time could not intensify their effects in comparison with separate administration of antagonists. It seems that antinociceptive effect of intra-LH administration of carbachol is mediated, at least partially, through the activation of orexin-1 and CB1 receptors in the vlPAG. This work demonstrates a pain modulatory role of the orexinergic system via the PAG in hypothalamic-mediated analgesia suggesting that orexins can be advantageously targeted to achieve analgesia. WHAT DOES THIS STUDY ADD?: OX1 receptor antagonist (SB334867) administration into the ventrolateral periaqueductal gray matter (vlPAG) dose dependently blocked the carbachol-induced antinociception. CB1 receptor antagonist (AM251) microinjection in the vlPAG prevented carbachol-induced antinociception in a dose-dependent manner. Concurrent administration of SB334867 and AM251 into the vlPAG did not reinforce the antinociceptive responses.

Activation of cannabinoid CB1 receptors in the ventral hippocampus improved stress-induced amnesia in rat

The ventral hippocampus (VH) has a high distribution of cannabinoid CB1 receptors which are important in modulating stress responses. Stress exposure activates the hypothalamic-pituitary-adrenal axis (HPA) which can impact hippocampal formation to change hippocampus-based memories. The purpose of the present study was to determine the possible role of the VH cannabinoid CB1 receptors in stress-induced amnesia using a step-through passive avoidance procedure in male Wistar rats. In order to induce acute stress, the animals were placed on an elevated platform for different time periods (10, 20 and 30min). Our results indicated that post-training 20 and 30min exposure to stress, but not 10min, induced amnesia. Post-training microinjection of a cannabinoid CB1 receptor agonist, arachydonilcyclopropylamide (ACPA; 2.5-7.5ng/rat) into the VH (intra-VH) induced amnesia. Interestingly, post-training intra-VH microinjection of the same doses of ACPA improved stress-induced amnesia. On the other hand, post-training intra-VH microinjection of a selective CB1 receptor antagonist, AM-251 (20–50ng/rat) with exposure to an ineffective stress (10min) potentiated the effect of stress on memory consolidation and induced amnesia. It should be noted that post-training intra-VH microinjection of the same doses of AM-251 alone had no effect on memory consolidation. Our results revealed that post-training intra-VH microinjection of AM-251, prior to ACPA microinjection, inhibited the reversal effect of ACPA on acute elevated platform stress. Taken together, it can be concluded that exposure to post-training inescapable stress impaired memory consolidation. The impairing effects of stress on memory retrieval may be mediated by the VH cannabinoid CB1 receptors.

Involvement of Spinal CB1 Cannabinoid Receptors on the Antinociceptive Effect of Celecoxib in Rat Formalin Test

Background: The pivotal role of cyclooxygenase-2 (COX-2) inhibitors in inflammatory pain is well documented, but its mechanism is not entirely clear. Nonsteroidal anti-inflammatory drugs (NSAIDs) as inhibitors of COX could inhibit fatty acid amide hydrolase, the enzyme responsible for the metabolism of endocannabinoids. Therefore, it is expected that celecoxib administration (selective COX-2 inhibitor) preserve the increased level of endocannabinoids after noxious stimuli, which leads to more pain suppression. Objectives: This study was designed to evaluate the interaction between the intrathecally administered celecoxib in combination with rimonabant, a selective cannabinoid CB1 receptor antagonist/reverse agonist on the pain behavior induced by formalin test in rat. Materials and Methods: Male Wistar rats with inserted lumbar intrathecal catheters were randomly grouped and tested in blinded manner by the same experimenter. Antinociceptive effects of different intrathecally doses of celecoxib (0.5, 5 and 10 µg/rat) in absence and with pretreatment of rimonabant at doses of 100 and 200 µg/rat were examined on the formalin test. Results: Celecoxib reduced the pain behavior in both phases of the formalin test, but this antinociceptive effect was a dose-dependent manner in the late phase. Rimonabant alone induced hyperalgesia as compared with the control group and pretreatment of rats with rimonabant reversed the analgesic activity of celecoxib. Conclusions: Antinociceptive effect of celecoxib may be mediated partly through the cannabinoid system. These effects are possibly attributed to inhibition of endocannabinoid degradation and consequently enhancement of endocannabinoids concentration at the spinal cord level. However, the hyperalgesic effects of rimonabant are not fully responsible for the reversal of celecoxib analgesia. Accordingly, NSAIDs intensify their effects through maintenance of the endocannabinoid tone. Therefore, combination of NSAIDs and cannabinoid agents could be used for synergistic effects.

Involvement of Endocannabinoids in Alcohol "Binge" Drinking: Studies of Mice with Human Fatty Acid Amide Hydrolase Genetic Variation and After CB1 Receptor Antagonists.

The endocannabinoid system has been found to play an important role in modulating alcohol intake. Inhibition or genetic deletion of fatty acid amide hydrolase (FAAH; a key catabolic enzyme for endocannabinoids) leads to increased alcohol consumption and preference in rodent models. A common human single-nucleotide polymorphism (SNP; C385A, rs324420) in the FAAH gene is associated with decreased enzymatic activity of FAAH, resulting in increased anandamide levels in both humans and FAAH C385A knock-in mice. As this FAAH SNP has been reported to be associated with altered alcohol abuse, the present study used these genetic knock-in mice containing the human SNP C385A to determine the impact of variant FAAH gene on alcohol "binge" drinking in the drinking-in-the-dark (DID) model. We found that the FAAH(A/A) mice had greater alcohol intake and preference than the wild-type FAAH(C/C) mice, suggesting that increased endocannabinoid signaling in FAAH(A/A) mice led to increased alcohol "binge" consumption. The specificity on alcohol vulnerability was suggested by the lack of any FAAH genotype difference on sucrose or saccharin intake. Using the "binge" DID model, we confirmed that selective CB1 receptor antagonist AM251 reduced alcohol intake in the wild-type mice. These data suggest that there is direct and selective involvement of the human FAAH C385A SNP and CB1 receptors in alcohol "binge" drinking.

Effect of nucleus accumbens shell 5-HT4 receptors on the impairment of ACPA-induced emotional memory consolidation in male Wistar rats.

The present study investigates the effects of 5-HT4 receptors of the nucleus accumbens (NAc) shell on the impairment of emotional memory consolidation induced by cannabinoid CB1 receptor stimulation. The elevated plus maze test-retest paradigm was used to assess memory in adult male Wistar rats. Intra-NAc shell administration of ACPA (selective cannabinoid CB1 receptor agonist 0.006 µg/rat) and RS23597 (5-HT4 receptor antagonist 0.01 µg/rat), immediately after training, decreased emotional memory consolidation, suggesting a drug-induced amnesia, whereas post-training intra-NAc shell microinjections of RS67333 (5-HT4 receptor agonist 0.016 µg/rat) increased emotional memory consolidation. Interestingly, RS67333 exerted a dual effect on ACPA-induced behaviors, potentiating and restoring amnesia caused by the subthreshold and effective doses of ACPA, respectively. However, neither RS23597 nor AM251 (CB1 receptor antagonist 30, 60 and 120 ng/rat) affected emotional memory consolidation. Nonetheless, a subthreshold dose of AM251 (120 ng/rat) reversed the amnesia induced by ACPA (0.006 µg/rat) and RS23597 (0.01 µg/rat). None of the above doses altered the locomotor activity. In conclusion, our results suggest that the NAc-shell 5-HT4 receptors are involved in the modulation of ACPA-induced amnesia.

Effect of JWH-250, JWH-073 and their interaction on “tetrad”, sensorimotor, neurological and neurochemical responses in mice

JWH-250 and JWH-073 are two synthetic cannabinoid agonists with nanomolar affinity at CB1 and CB2 receptors. They are illegally marketed within “herbal blend” for theirs psychoactive effects greater than those produced by Cannabis. Recently, we analyzed an “herbal” preparation containing a mixture of both JWH-250 and JWH-073. The present study was aimed at investigating the in vitro and in vivo pharmacological activity of JWH-250 and JWH-073 in male CD-1 mice. In vitro competition binding experiments performed on mouse and human CB1 and CB2 receptors revealed a nanomolar affinity and potency of the JWH-250 and JWH-073. In vivo studies showed that JWH-250 and JWH-073, administered separately, induced a marked hypothermia, increased pain threshold to both noxious mechanical and thermal stimuli, caused catalepsy, reduced motor activity, impaired sensorimotor responses (visual, acoustic and tactile), caused seizures, myoclonia, hyperreflexia and promote aggressiveness in mice. Moreover, microdialysis study in freely moving mice showed that systemic administration of JWH-250 and JWH-073 stimulated dopamine release in the nucleus accumbens in a dose-dependent manner. Behavioral, neurological and neurochemical effects were fully prevented by the selective CB1 receptor antagonist/inverse agonist AM 251. Co-administration of ineffective doses of JWH-250 and JWH-073 impaired visual sensorimotor responses, improved mechanical pain threshold and stimulated mesolimbic DA transmission in mice, living unchanged all other behavioral and physiological parameters. For the first time the present study demonstrates the overall pharmacological effects induced by the administration of JWH-250 and JWH-073 in mice and it reveals their potentially synergistic action suggesting that co-administration of different synthetic cannabinoids may potentiate the detrimental effects of individual compounds increasing their dangerousness and abuse potential.

Behavioural and pharmacological characterization of a novel cannabinomimetic adamantane-derived indole, APICA, and considerations on the possible misuse as a psychotropic spice abuse, in C57bl/6J mice

The novel adamantane derivative APICA (N-(adamantan-1-yl)-1-pentyl-1H-indole-3-carboxamide) was recently identified as a cannabinomimetic indole of abuse. Despite its novel structure, APICA recalls cannabinomimetic indoles, such as representative member JWH-018.In present study, the effects of APICA (1–3mg/kg, i.p.) were tested in C57BL/6J mice, in the Tetrad task which includes the assessment of: body temperature; locomotor activity and behavioural reactivity; nociception; motor coordination; declarative memory. Furthermore, pre-treatment with the CB1 antagonist AM251 (3mg/kg, i.p.) or the CB2 antagonist AM630 (3mg/kg, i.p.) was carried out to characterize APICA activity.Our results show that APICA was able to dose-dependently decrease locomotor activity and behavioural reactivity in the open field, whereas only the highest dose was able to induce hypothermia, analgesia, motor incoordination and recognition memory impairment, with respect to vehicle (p<0.01; p<0.001).The pretreatment with the CB1 antagonist AM251 elicited an increase in body temperature, total distance travelled in the open field, latency to fall down in the Rotarod, and a decrease in tail flick latency (p<0.05; p<0.01). On the other hand, pretreatment with AM630 did not induced significant differences on APICA effects.This study supports preliminary reports on APICA cannabinomimetic properties, extending its detrimental effects on cognitive function. Moreover, these properties can be attributed to the CB1 receptor activity, indicating APICA as a selective CB1 receptor agonist.

Correlations between the Memory-Related Behavior and the Level of Oxidative Stress Biomarkers in the Mice Brain, Provoked by an Acute Administration of CB Receptor Ligands.

The endocannabinoid system, through cannabinoid (CB) receptors, is involved in memory-related responses, as well as in processes that may affect cognition, like oxidative stress processes. The purpose of the experiments was to investigate the impact of CB1 and CB2 receptor ligands on the long-term memory stages in male Swiss mice, using the passive avoidance (PA) test, as well as the influence of these compounds on the level of oxidative stress biomarkers in the mice brain. A single injection of a selective CB1 receptor antagonist, AM 251, improved long-term memory acquisition and consolidation in the PA test in mice, while a mixed CB1/CB2 receptor agonist WIN 55,212-2 impaired both stages of cognition. Additionally, JWH 133, a selective CB2 receptor agonist, and AM 630, a competitive CB2 receptor antagonist, significantly improved memory. Additionally, an acute administration of the highest used doses of JWH 133, WIN 55,212-2, and AM 630, but not AM 251, increased total antioxidant capacity (TAC) in the brain. In turn, the processes of lipids peroxidation, expressed as the concentration of malondialdehyde (MDA), were more advanced in case of AM 251. Thus, some changes in the PA performance may be connected with the level of oxidative stress in the brain.

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.

Cannabinoid receptor agonists modulate calcium channels in rat retinal müller cells

While activation of cannabinoid CB1 receptor (CB1R) regulates a variety of retinal neuronal functions by modulating ion channels in these cells, effect of activated cannabinoid receptors on Ca2+ channels in retinal Müller cells is still largely unknown. In the present work we show that three subunits of T-type Ca2+ channels, CaV3.1, CaV3.2 and CaV3.3, as well as one subunit of L-type Ca2+ channels, CaV1.2, were expressed in rat Müller cells by immunofluorescent staining. Consistently, nimodipine- and mibefradil-sensitive Na+ currents through L- and T-type Ca2+ channels could be recorded electrophysiologically. The cannabinoid receptor agonist WIN55212-2 significantly suppressed Ca2+ channel currents, mainly the T-type one, in acutely isolated rat Müller cells in a dose-dependent manner, with an IC50 of 3.98μM. The WIN55212-2 effect was not blocked by AM251/SR141716, specific CB1R antagonists. Similar suppression of the currents was observed when anandamide (AEA) and 2-arachidonoyl glycerol (2-AG), endogenous ligands of cannabinoid receptors, were applied. Moreover, even though CB2 receptors (CB2Rs) were expressed in rat Müller cells, the effects of WIN55212-2 and 2-AG on Ca2+ channel currents were not blocked by AM630, a selective CB2R antagonist. However, the effect of AEA could be partially rescued by AM630. These results suggest that WIN55212-2 and 2-AG receptor-independently suppressed the Ca2+ channel currents in Müller cells, while AEA suppressed the currents partially through CB2Rs. The existence of receptor-dependent and -independent mechanisms suggests that cannabinoids may modulate Müller cell functions through multiple pathways.

Involvement of CB1 and TRPV1 receptors of the ventrolateral periaqueductal gray in physical stress-evoked cardiovascular responses during in rats

The periaqueductal gray (PAG) is a mesencephalic structure that surrounds the cerebral aqueduct. The PAG was functionally divided into four longitudinal columns: the dorsomedial, dorsolateral, lateral and the ventrolateral (vlPAG). Microinjection of endocannabinoid or endovanilloid antagonists into the vlPAG blocked the cardiovascular responses to a physical stress: hemorrhage. Microinjection of excitatory amino acids into the vlPAG caused decreases in blood pressure, heart rate, sympathetic activity, as well as antinociception, quiescence and hyporeactivity. This syndrome is often associated with pathophysiological conditions such as the loss of large volumes of blood. Experimental studies have established that in mammals hemodynamic responses to blood loss consist of three phases: Phase I compensatory normotensive; Phase II decompensatory, hypotensive and phase III recompensatory post-hemorrhage, when the pressure returns to normal levels. Recent reports have shown that the endocannabinoid system is associated with the pathophysiology of hypotension in various forms of shock, including the hemorrhagic. Interestingly, it has been shown that the hypotension caused by blood loss was prevented by a systemic pretreatment with the CB1 antagonist SR141716; the CB1 receptors are densely expressed along the PAG. In the present study, we evaluated the participation of vlPAG CB1 receptors in the cardiovascular responses evoked by hemorrhage. Local microinjection of AM251 (0.25 nmol), a selective CB1 receptor antagonist, into the vlPAG caused a delayed onset of the hypotension, when compared to the control and the tachycardia evoked by hemorrhage was abolished. The pretreatment of the vlPAG with a lower dose of AM251 (0.025 nmol), abolished both the hypotension and the tachycardia caused by hemorrhage. Importantly, the pretreatment of the vlPAG with both doses of AM251, did not significantly alter the recompensatory phase of hemorrhage. We consider that the delayed hypotensive response observed after the pretreatment of vlPAG with the highest dose of AM251 (0.25 nmol), could be due to nonspecific effects of AM251. Much has been investigated on the interaction between the endocannabinoid system and the vanilloid system. Furthermore, recent findings indicate that TRPV1 receptors are also expressed in the PAG. Then, we pretreated the vlPAG with two doses of the transient receptor potential vanilloid type 1 (TRPV1) antagonist capsazepine (2.5 and 15 nmol). Pretreatment of the vlPAG with 15 nmol of capsazepine significantly reduced the hypotension and tachycardia evoked by hemorrhage. However, when we microinjected capsazepine at a dose of 2.5 nmol, we observed total blockade of the hypotension and a reduction in the tachycardiac response evoked by hemorrhage. These data suggest that TRPV1 and CB1 receptors present in the vlPAG participate in cardiovascular modulation during hemorrhage.

The involvement of medial septum 5-HT1 and 5-HT2 receptors on ACPA-induced memory consolidation deficit: possible role of TRPC3, TRPC6 and TRPV2.

The present study evaluates the roles of serotonergic receptors of the medial septum on amnesia induced by arachidonylcyclopropylamide (ACPA; as selective cannabinoid CB1 receptor agonist) in adult male Wistar rats. Cannulae were implanted in the medial septum of the brain of the rats. The animals were trained in a passive avoidance learning apparatus, and were tested 24 hours after training for step-through latency. Results indicated that post-training medial septum administration of CP94253 (5-HT1B/1D receptor agonist) and cinancerine (as 5-HT2 receptor antagonist) reduced the step-through latency showing an amnesic response, while GR127935 (5-HT1B/1D receptor antagonist) and αm5htm (as 5-HT2A/2B/2D receptor agonist) did not alter memory consolidation by themselves. On continuing the test, the results showed that CP94253 increased and GR127935 did not alter ACPA (0.02 µg/rat)-induced memory impairment, respectively. Other data indicated that αm5htm induced a modulatory effect, while cinancerine restored ACPA-induced amnesia. Using SKF-96365 (inhibitor of transient receptor potential TRPC3/6 and TRPV2 channels) demonstrated that TRPC3, TRPC3 and TRPV2 channels have a significant role, according to our results.

Pharmacological activation of CB2 receptors counteracts the deleterious effect of ethanol on cell proliferation in the main neurogenic zones of the adult rat brain.

Chronic alcohol exposure reduces endocannabinoid activity and disrupts adult neurogenesis in rodents, which results in structural and functional alterations. Cannabinoid receptor agonists promote adult neural progenitor cell (NPC) proliferation. We evaluated the protective effects of the selective CB1 receptor agonist ACEA, the selective CB2 receptor agonist JWH133 and the fatty-acid amide-hydrolase (FAAH) inhibitor URB597, which enhances endocannabinoid receptor activity, on NPC proliferation in rats with forced consumption of ethanol (10%) or sucrose liquid diets for 2 weeks. We performed immunohistochemical and stereological analyses of cells expressing the mitotic phosphorylation of histone-3 (phospho-H3+) and the replicating cell DNA marker 5-bromo-2'-deoxyuridine (BrdU+) in the main neurogenic zones of adult brain: subgranular zone of dentate gyrus (SGZ), subventricular zone of lateral ventricles (SVZ) and hypothalamus. Animals were allowed ad libitum ethanol intake (7.3 ± 1.1 g/kg/day) after a controlled isocaloric pair-feeding period of sucrose and alcoholic diets. Alcohol intake reduced the number of BrdU+ cells in SGZ, SVZ, and hypothalamus. The treatments (URB597, ACEA, JWH133) exerted a differential increase in alcohol consumption over time, but JWH133 specifically counteracted the deleterious effect of ethanol on NPC proliferation in the SVZ and SGZ, and ACEA reversed this effect in the SGZ only. JWH133 also induced an increased number of BrdU+ cells expressing neuron-specific β3-tubulin in the SVZ and SGZ. These results indicated that the specific activation of CB2 receptors rescued alcohol-induced impaired NPC proliferation, which is a potential clinical interest for the risk of neural damage in alcohol dependence.