Cannabinoid CB1 receptors mediate the effects of corticotropin-releasing factor on the reinstatement of cocaine seeking and expression of cocaine-induced behavioural sensitization

BACKGROUND AND PURPOSE

The endocannabinoid and corticotropin-releasing factor (CRF) systems have been implicated in several long-lasting behavioural effects of prior cocaine experience. The present experiments were designed to probe functional interactions between endocannabinoids and CRF by testing the role of cannabinoid CB₁ receptors in cocaine-related behaviours induced or mediated by CRF.

EXPERIMENTAL APPROACH

In Experiment 1, rats trained to self-administer cocaine were pretreated with the CB₁ receptor antagonist, AM251 (0, 10, 100 or 200 µg, i.c.v.), before tests for reinstatement in response to CRF (0, 0.5 µg, i.c.v.), intermittent footshock stress (0, 0.9 mA) or cocaine (0, 10 mg·kg⁻¹, i.p.). In Experiment 2, rats pre-exposed to cocaine (15–30 mg·kg⁻¹, i.p.) or saline for 7 days were pretreated with AM251 (0, 10 or 100 µg, i.c.v.) before tests for locomotion in response to CRF (0.5 µg, i.c.v.), cocaine (15 mg·kg⁻¹, i.p.) or saline (i.c.v.).

KEY RESULTS

Pretreatment with AM251 selectively interfered with CRF-, but not footshock- or cocaine-induced reinstatement. AM251 blocked the expression of behavioural sensitization induced by challenge injections of both CRF and cocaine.

CONCLUSIONS AND IMPLICATIONS

These findings reveal a mediating role for CB₁ receptor transmission in the effects of CRF on cocaine-related behaviours.     

Chronic Δ⁹-tetrahydrocannabinol treatment in rhesus monkeys: differential tolerance and cross-tolerance among cannabinoids

BACKGROUND AND PURPOSE

The extent to which behavioural effects vary as a function of CB₁ receptor agonist efficacy is not clear. These studies tested the hypothesis that cannabinoid tolerance and cross-tolerance depend upon the CB₁ agonist efficacy of drugs to which tolerance/cross-tolerance develops.

EXPERIMENTAL APPROACH

Sensitivity to cannabinoids, including the cannabinoid antagonist rimonabant, low efficacy agonist Δ⁹-tetrahydrocannabinol (Δ⁹-THC), and high efficacy agonists CP 55940 and WIN 55212-2, was determined before and after chronic Δ⁹-THC treatment in rhesus monkeys. Two measures of behavioural effect were assessed: effects of drugs to decrease fixed ratio responding for food presentation and stimulus-shock termination and discriminative stimulus effects in monkeys discriminating Δ⁹-THC (0.1 mg·kg⁻¹, i.v.).

KEY RESULTS

Δ⁹-THC decreased responding for both food presentation and stimulus-shock termination; these effects were antagonized by the CB₁ antagonist rimonabant. Chronic Δ⁹-THC (1 mg·kg⁻¹ per 12 h, s.c.) resulted in tolerance to the rate-decreasing effects of Δ⁹-THC and cross-tolerance to CP 55940 and WIN 55212-2; however, cross-tolerance was less than tolerance. Chronic Δ⁹-THC increased sensitivity to rimonabant without changing sensitivity to the non-cannabinoids midazolam and ketamine. In monkeys discriminating Δ⁹-THC (0.1 mg·kg⁻¹, i.v.), both CP 55940 and WIN 55212-2 produced high levels of drug-lever responding. Chronic Δ⁹-THC (1 mg·kg⁻¹ per day, s.c.) decreased sensitivity to Δ⁹-THC without producing cross-tolerance to CP 55940 or WIN 55212-2.

CONCLUSIONS AND IMPLICATIONS

In Δ⁹-THC-treated monkeys, the magnitude of tolerance and cross-tolerance to other CB₁ receptor agonists varied inversely with agonist efficacy, suggesting that CB₁ agonist efficacy is an important determinant of behavioural effects.     

Reduced signal transduction by 5-HT4 receptors after long-term venlafaxine treatment in rats

BACKGROUND AND PURPOSE

The 5-HT₄ receptor may be a target for antidepressant drugs. Here we have examined the effects of the dual antidepressant, venlafaxine, on 5-HT₄ receptor-mediated signalling events.

EXPERIMENTAL APPROACH

The effects of 21 days treatment (p.o.) with high (40 mg·kg⁻¹) and low (10 mg·kg⁻¹) doses of venlafaxine, were evaluated at different levels of 5-HT₄ receptor-mediated neurotransmission by using in situ hybridization, receptor autoradiography, adenylate cyclase assays and electrophysiological recordings in rat brain. The selective noradrenaline reuptake inhibitor, reboxetine (10 mg·kg⁻¹, 21 days) was also evaluated on 5-HT₄ receptor density.

KEY RESULTS

Treatment with a high dose (40 mg·kg⁻¹) of venlafaxine did not alter 5-HT₄ mRNA expression, but decreased the density of 5-HT₄ receptors in caudate-putamen (% reduction = 26 ± 6), hippocampus (% reduction = 39 ± 7 and 39 ± 8 for CA1 and CA3 respectively) and substantia nigra (% reduction = 49 ± 5). Zacopride-stimulated adenylate cyclase activation was unaltered following low-dose treatment (10 mg·kg⁻¹) while it was attenuated in rats treated with 40 mg·kg⁻¹ of venlafaxine (% reduction = 51 ± 2). Furthermore, the amplitude of population spike in pyramidal cells of CA1 of hippocampus induced by zacopride was significantly attenuated in rats receiving either dose of venlafaxine. Chronic reboxetine did not modify 5-HT₄ receptor density.

CONCLUSIONS AND IMPLICATIONS

Our data indicate a functional desensitization of 5-HT₄ receptors after chronic venlafaxine, similar to that observed after treatment with the classical selective inhibitors of 5-HT reuptake.     

Evodiamine improves congnitive abilities in SAMP8 and APP(swe)/PS1(ΔE9) transgenic mouse models of Alzheimer's disease

Aim:

To investigate the effect of evodiamine (a quinolone alkaloid from the fruit of Evodia rutaecarpa) on the progression of Alzheimer''s disease in SAMP8 and APP^swe/PS1^ΔE9 transgenic mouse models.

Methods:

The mice at age of 5 months were randomized into the model group, two evodiamine (50 mg·kg⁻¹·d⁻¹ and 100 mg·kg⁻¹·d⁻¹) groups and an Aricept (2 mg·kg⁻¹·d⁻¹) group. The littermates of no-transgenic mice and senescence accelerated mouse/resistance 1 mice (SAMR1) were used as controls. After 4 weeks of treatment, learning abilities and memory were assessed using Morris water-maze test, and glucose uptake by the brain was detected using positron emission tomography/computed tomography (PET/CT). Expression levels of IL-1β, IL-6, and TNF-α in brain tissues were detected using ELISA. Expression of COX-2 protein was determined using Western blot.

Results:

In Morris water-maze test, evodiamine (100 mg·kg⁻¹·d⁻¹) significantly alleviated the impairments of learning ability and memory. Evodiamine (100 mg·kg⁻¹·d⁻¹) also reversed the inhibition of glucose uptake due to development of Alzheimer''s disease traits in mice. Furthermore, the dose of evodiamine significantly decreased the expression of IL-1β, IL-6, TNF-α, and COX-2 that were involved in the inflammation due to Alzheimer''s disease.

Conclusion:

The results indicate that evodiamine (100 mg·kg⁻¹·d⁻¹) improves cognitive abilities in the transgenic models of Alzheimer''s disease.     

5-HT(6) receptor agonists and antagonists enhance learning and memory in a conditioned emotion response paradigm by modulation of cholinergic and glutamatergic mechanisms

BACKGROUND AND PURPOSE

5-HT₆ receptors are abundant in the hippocampus, nucleus accumbens and striatum, supporting their role in learning and memory. Selective 5-HT₆ receptor antagonists produce pro-cognitive effects in several learning and memory paradigms while 5-HT₆ receptor agonists have been found to enhance and impair memory.

EXPERIMENTAL APPROACH

The conditioned emotion response (CER) paradigm was validated in rats. Then we examined the effect of the 5-HT₆ receptor antagonist, EMD 386088 (10 mg·kg⁻¹, i.p.), and agonists, E-6801 (2.5 mg·kg⁻¹, i.p.) and EMD 386088 (5 mg·kg⁻¹, i.p.) on CER-induced behaviour either alone or after induction of memory impairment by the muscarinic receptor antagonist, scopolamine (0.3 mg·kg⁻¹, i.p) or the NMDA receptor antagonist, MK-801 (0.1 mg·kg⁻¹, i.p).

KEY RESULTS

Pairing unavoidable foot shocks with a light and tone cue during CER training induced a robust freezing response, providing a quantitative index of contextual memory when the rat was returned to the shock chamber 24 h later. Pretreatment (−20 min pre-training) with scopolamine or MK-801 reduced contextual freezing 24 h after CER training, showing production of memory impairment. Immediate post-training administration of 5-HT₆ receptor antagonist, SB-270146, and agonists, EMD 386088 and E-6801, had little effect on CER freezing when given alone, but all significantly reversed scopolamine- and MK-801-induced reduction in freezing.

CONCLUSION AND IMPLICATIONS

Both the 5-HT₆ receptor agonists and antagonist reversed cholinergic- and glutamatergic-induced deficits in associative learning. These findings support the therapeutic potential of 5-HT₆ receptor compounds in the treatment of cognitive dysfunction, such as seen in Alzheimer''s disease and schizophrenia.     

Drug- and cue-induced reinstatement of cannabinoid-seeking behaviour in male and female rats: influence of ovarian hormones

Background and purpose:

Animal and human studies have shown that sex and hormones are key factors in modulating addiction. Previously, we have demonstrated that self-administration of the cannabinoid CB₁ receptor agonist WIN55,212-2 (WIN; 12.5 µg·kg⁻¹ per infusion) is dependent on sex, intact female rats being more sensitive than males to the reinforcing properties of cannabinoids, and on the oestrous cycle, ovariectomized (OVX) females being less responsive than intact females.

Experimental approach:

This follow-up study investigated whether sex and ovarian function also affect reinstatement of cannabinoid-seeking in rats after exposure to drug or cue priming.

Key results:

After priming with 0.15 or 0.3 mg·kg⁻¹ WIN, intact female rats exhibited stronger reinstatement than males and OVX females. Responses of intact female rats were higher than those of male and OVX rats even after priming with a drug-associated visual (Light) or auditory (Tone) cue, or a WIN + Light combination. However, latency to the first response did not differ between intact and OVX female rats, and males showed the longest latency to initiate lever-pressing activity.

Conclusions and implications:

Our study provides compelling evidence for a pivotal role of sex and the oestrous cycle in modulating cannabinoid-seeking, with ovariectomy diminishing drug and cue-induced reinstatement. However, it is possible that sex differences during self-administration training are responsible for sex differences in reinstatement. Finding that not only drug primings but also acute exposure to drug-associated cues can reinstate responding in rats could have significant implications for the development of pharmacological and behavioural treatments of abstinent female and male marijuana smokers.This article is part of a themed issue on Cannabinoids. To view the editorial for this themed issue visit http://dx.doi.org/10.1111/j.1476-5381.2010.00831.x     

Mechanisms mediating the ability of caffeine to influence MDMA (��Ecstasy��)-induced hyperthermia in rats

Background and purpose:

Caffeine exacerbates the hyperthermia associated with an acute exposure to 3,4 methylenedioxymethamphetamine (MDMA, ‘Ecstasy’) in rats. The present study investigated the mechanisms mediating this interaction.

Experimental approach:

Adult male Sprague-Dawley rats were treated with caffeine (10 mg·kg⁻¹; i.p.) and MDMA (15 mg·kg⁻¹; i.p.) alone and in combination. Core body temperatures were monitored before and after drug administration.

Key results:

Central catecholamine depletion blocked MDMA-induced hyperthermia and its exacerbation by caffeine. Caffeine provoked a hyperthermic response when the catecholamine releaser d-amphetamine (1 mg·kg⁻¹) was combined with the 5-HT releaser d-fenfluramine (5 mg·kg⁻¹) or the non-selective dopamine receptor agonist apomorphine (1 mg·kg⁻¹) was combined with the 5-HT₂ receptor agonist DOI (2 mg·kg⁻¹) but not following either agents alone. Pretreatment with the dopamine D₁ receptor antagonist Schering (SCH) 23390 (1 mg·kg⁻¹), the 5-HT₂ receptor antagonist ketanserin (5 mg·kg⁻¹) or α₁-adreno- receptor antagonist prazosin (0.2 mg·kg⁻¹) blocked MDMA-induced hyperthermia and its exacerbation by caffeine. Co-administration of a combination of MDMA with the PDE-4 inhibitor rolipram (0.025 mg·kg⁻¹) and the adenosine A_1/2 receptor antagonist 9-chloro-2-(2-furanyl)-[1,2,4]triazolo[1,5-C]quinazolin-5-amine 15943 (10 mg·kg⁻¹) or the A_2A receptor antagonist SCH 58261 (2 mg·kg⁻¹) but not the A₁ receptor antagonist DPCPX (10 mg·kg⁻¹) exacerbated MDMA-induced hyperthermia.

Conclusions and implications:

A mechanism comprising 5-HT and catecholamines is proposed to mediate MDMA-induced hyperthermia. A combination of adenosine A_2A receptor antagonism and PDE inhibition can account for the exacerbation of MDMA-induced hyperthermia by caffeine.     

Preclinical characterization of WAY-211612: a dual 5-HT uptake inhibitor and 5-HT1A receptor antagonist and potential novel antidepressant

Background and purpose

As a combination of 5-HT selective reuptake inhibitor (SSRI) with 5-HT_1A receptor antagonism may yield a rapidly acting antidepressant, WAY-211612, a compound with both SSRI and 5-HT_1A receptor antagonist activities, was evaluated in preclinical models.

Experimental approach

Occupancy studies confirmed the mechanism of action of WAY-211612, while its in vivo profile was characterized in microdialysis and behavioural models.

Key results

WAY-211612 inhibited 5-HT reuptake (K_i = 1.5 nmol·L⁻¹; K_B = 17.7 nmol·L⁻¹) and exhibited full 5-HT_1A receptor antagonist activity (K_i = 1.2 nmol·L⁻¹; K_B = 6.3 nmol·L⁻¹; I_max 100% in adenyl cyclase assays; K_B = 19.8 nmol·L⁻¹; I_max 100% in GTPγS). WAY-211612 (3 and 30 mg·kg⁻¹, po) occupied 5-HT reuptake sites in rat prefrontal cortex (56.6% and 73.6% respectively) and hippocampus (52.2% and 78.5%), and 5-HT_1A receptors in the prefrontal cortex (6.7% and 44.7%), hippocampus (8.3% and 48.6%) and dorsal raphe (15% and 83%). Acute or chronic treatment with WAY-211612 (3–30 mg·kg⁻¹, po) raised levels of cortical 5-HT approximately twofold, as also observed with a combination of an SSRI (fluoxetine; 30 mg·kg⁻¹, s.c.) and a 5-HT_1A antagonist (WAY-100635; 0.3 mg·kg⁻¹, s.c). WAY-211612 (3.3–30 mg·kg⁻¹, s.c.) decreased aggressive behaviour in the resident-intruder model, while increasing the number of punished crossings (3–30 mg·kg⁻¹, i.p. and 10–56 mg·kg⁻¹, po) in the mouse four-plate model and decreased adjunctive drinking behaviour (56 mg·kg⁻¹, i.p.) in the rat scheduled-induced polydipsia model.

Conclusions and implications

These findings suggest that WAY-211612 may represent a novel antidepressant.     

Synthetic and plant-derived cannabinoid receptor antagonists show hypophagic properties in fasted and non-fasted mice

Background and purpose:

Obesity is a severe health problem in the modernized world and understanding the central nervous mechanisms underlying food-seeking behaviour and reward are at the forefront of medical research. Cannabinoid receptors have proven an efficient target to suppress hunger and weight gain by their pharmacological inactivation.

Experimental approach:

A standard fasted protocol and a novel long-term home-cage observation system with free-feeding animals were used to assess the feeding behaviour of mice treated with the CB₁ antagonist AM251. Similarly, the effects of the phytocannabinoid Δ⁹-tetrahydrocannabivarin (Δ⁹-THCV), which behaves like a CB₁ antagonist, were also determined in free-feeding animals.

Key results:

AM251 suppressed food intake and weight gain in fasted and non-fasted animals. The suppression of food intake by AM251 (10 mg·kg⁻¹) endured for a period of 6–8 h when administered acutely, and was continuous when injected for four consecutive days. Pure Δ⁹-THCV also induced hypophagia and weight reduction at doses as low as 3 mg·kg⁻¹. No rebound was observed on the following day with all drug groups returning to normal activity and feeding regimes. However, a Δ⁹-THCV-rich cannabis-extract failed to suppress food intake and weight gain, possibly due to residual Δ⁹-tetrahydrocannabinol (Δ⁹-THC) in the extract. This Δ⁹-THC effect was overcome by the co-administration of cannabidiol.

Conclusions and implications:

The data strongly suggest (i) the long-term home-cage observation system is a sensitive and obesity-relevant tool, and (ii) the phytocannabinoid Δ⁹-THCV is a novel compound with hypophagic properties and a potential treatment for obesity.     

Combined effects of THC and caffeine on working memory in rats

BACKGROUND AND PURPOSE

Cannabis and caffeine are two of the most widely used psychoactive substances. Δ⁹-Tetrahydrocannabinol (THC), the main psychoactive constituent of cannabis, induces deficits in short-term memory. Caffeine, a non-selective adenosine receptor antagonist, attenuates some memory deficits, but there have been few studies addressing the effects of caffeine and THC in combination. Here, we evaluate the effects of these drugs using a rodent model of working memory.

EXPERIMENTAL APPROACH

Rats were given THC (0, 1 and 3 mg·kg⁻¹, i.p.) along with caffeine (0, 1, 3 and 10 mg·kg⁻¹, i.p.), the selective adenosine A₁-receptor antagonist CPT (0, 3 and 10 mg·kg⁻¹) or the selective adenosine A_2A-receptor antagonist {"type":"entrez-protein","attrs":{"text":"SCH58261","term_id":"1052882304","term_text":"SCH58261"}}SCH58261 (0 and 5 mg·kg⁻¹) and were tested with a delayed non-matching-to-position procedure in which behaviour during the delay was automatically recorded as a model of memory rehearsal.

KEY RESULTS

THC alone produced memory deficits at 3 mg·kg⁻¹. The initial exposure to caffeine (10 mg·kg⁻¹) disrupted the established pattern of rehearsal-like behaviour, but tolerance developed rapidly to this effect. CPT and {"type":"entrez-protein","attrs":{"text":"SCH58261","term_id":"1052882304","term_text":"SCH58261"}}SCH58261 alone had no significant effects on rehearsal or memory. When a subthreshold dose of THC (1 mg·kg⁻¹) was combined with caffeine (10 mg·kg⁻¹) or CPT (10 mg·kg⁻¹), memory performance was significantly impaired, even though performance of the rehearsal-like pattern was not significantly altered.

CONCLUSION AND IMPLICATIONS

Caffeine did not counteract memory deficits induced by THC but actually exacerbated them. These results are consistent with recent findings that adenosine A₁ receptors modulate cannabinoid signalling in the hippocampus.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7     

Inverse agonism of cannabinoid CB1 receptors potentiates LiCl-induced nausea in the conditioned gaping model in rats

BACKGROUND AND PURPOSE

Cannabinoid CB₁ receptor antagonists/inverse agonists, potentiate toxin-induced nausea and vomiting in animal models. Here, we sought to determine if this potentiated nausea was mediated by inverse agonism or neutral antagonism of the CB₁ receptor, and if the potentiated nausea would be produced by intracerebroventricular (icv) administration of an inverse agonist.

EXPERIMENTAL APPROACH

The conditioned gaping model of nausea in rats was used to compare the CB₁ receptor antagonist/inverse agonist, AM251, and the CB₁ receptor neutral antagonists, AM6527 (centrally and peripherally active) and AM6545 (peripherally active), in potentiating conditioned gaping produced by lithium chloride (LiCl) solution. The effect of icv (lateral ventricle and 4th ventricle) administration of AM251 on LiCl-induced gaping in this model was also evaluated.

KEY RESULTS

At a dose that did not produce conditioned gaping on its own, systemically administered AM251 (1.25 mg·kg⁻¹) potentiated LiCl-induced conditioned gaping and reduced sucrose palatability; however, even doses as high as 8 mg·kg⁻¹ of AM6545 and AM6527 neither potentiated LiCl-induced conditioned gaping nor reduced sucrose palatability. Infusions of AM251 into the lateral ventricles (1.25, 12.5 and 125 µg) or the 4th ventricle (2.5, 12.5 and 125 µg) did not potentiate LiCl-induced conditioned gaping reactions, but all doses attenuated saccharin palatability during the subsequent test.

CONCLUSIONS AND IMPLICATIONS

Inverse agonism, but not neutral antagonism, of CB₁ receptors potentiated toxin-induced nausea. This effect may be peripherally mediated or may be mediated centrally by action on CB₁ receptors, located distal to the cerebral ventricles.     

Testosterone ameliorates streptozotocin-induced memory impairment in male rats

Aim： To study the effects of testosterone on streptozotocin （STZ）-induced memory impairment in male rats.
Methods： Adult male Wistar rats were intracerebroventricularly （icv） infused with STZ （750 μg） on d 1 and d 3, and a passive avoidance task was assessed 2 weeks after the first injection of STZ. Castration surgery was performed in another group of rats, and the passive avoidance task was assessed 4 weeks after the operation. Testosterone （1 mg·kg^-1·d^-1, sc）, the androgen receptor antagonist flutamide （10 mg·kg^-1·d^-1, ip）, the estrogen receptor antagonist tamoxifen （1 mg·kg^-1·d^-1, ip） or the aromatase inhibitor letrozole （4 mg·kg^-1·d^-1, ip） were administered for 6 d after the first injection of STZ.
Results： STZ administration and castration markedly decreased both STL1 （the short memory） and STL2 （the long memory） in passive avoidance tests. Testosterone replacement almost restored the STL1 and STL2 in castrated rats, and significantly prolonged the STL1 and STL2 in STZ-treated rats. Administration of flutamide, letrozole or tamoxifen significantly impaired the memory in intact rats, and significantly attenuated the testosterone replacement in improving STZ- and castration-induced memory impairment.
Conclusion： Testosterone administration ameliorates STZ- and castration-induced memory impairment in male Wistar rats.     

Double blockade of angiotensin II (AT(1) )-receptors and ACE does not improve weight gain and glucose homeostasis better than single-drug treatments in obese rats

BACKGROUND AND PURPOSE

Combination therapies are becoming increasingly important for the treatment of high blood pressure. Little is known about whether double blockade of angiotensin II (AT₁) receptors and angiotensin-converting enzyme (ACE) exert synergistic metabolic effects.

EXPERIMENTAL APPROACH

Spontaneously hypertensive rats were allowed to choose between palatable chocolate bars and standard chow and were simultaneously treated with the AT₁ blocker telmisartan (8 mg·kg_bw⁻¹·day⁻¹), the ACE inhibitor ramipril (4 mg·kg_bw⁻¹·day⁻¹) or a combination of the two (8 + 4 mg·kg_bw⁻¹·day⁻¹) for 12 weeks.

KEY RESULTS

Although food-dependent energy intake was increased by telmisartan and telmisartan + ramipril compared with ramipril or controls, body weight gain, abundance of fat and plasma leptin levels were decreased. Increased insulin levels in response to an oral glucose tolerance test were comparably attenuated by telmisartan and telmisartan + ramipril, but not by ramipril. During an insulin tolerance test, glucose utilization was equally as effectively improved by telmisartan and telmisartan + ramipril. In response to a stress test, ACTH, corticosterone and glucose increased in controls. These stress reactions were attenuated by telmisartan and telmisartan + ramipril.

CONCLUSIONS AND IMPLICATIONS

The combination of telmisartan + ramipril was no more efficacious in regulating body weight and glucose homeostasis than telmisartan alone. However, telmisartan was more effective than ramipril in improving metabolic parameters and in reducing body weight. The association between the decrease in stress responses and the diminished glucose levels after stress supports our hypothesis that the ability of telmisartan, as an AT₁ receptor blocker, to alleviate stress reactions may contribute to its hypoglycaemic actions.     

Teneurin C-terminal associated peptide-1 blocks the effects of corticotropin-releasing factor on reinstatement of cocaine seeking and on cocaine-induced behavioural sensitization

BACKGROUND AND PURPOSE

The stress-related neuropeptide, corticotropin-releasing factor (CRF), has become an important focus of studies of cocaine addiction, and in particular, the effects of stress on cocaine-related behaviours. A recently discovered peptide system, the teneurin C-terminal associated peptides (TCAP), has been implicated in the regulation of the stress response, via a CRF-related mechanism. Here we have determined whether treatment with TCAP-1, a synthetic analogue of TCAP, modulated two cocaine-related behaviours induced by CRF: reinstatement of cocaine seeking, and expression of cocaine-induced behavioural sensitization.

EXPERIMENTAL APPROACH

In Experiment 1, rats trained to self-administer cocaine were given acute or repeated (once daily for 5 days) i.c.v. injections of TCAP-1 before tests for reinstatement in response to CRF (105 pmol, i.c.v.), intermittent footshock stress (0.9 mA), or cocaine (15 mg·kg⁻¹, i.p.). In Experiment 2, rats pre-exposed to cocaine (15–30 mg·kg⁻¹, i.p.) or saline for 7 days were treated with TCAP-1 (once daily for 5 days; i.c.v.) and subsequently tested for locomotor responses to CRF (105 pmol, i.c.v.) or cocaine (15 mg·kg⁻¹, i.p.).

KEY RESULTS

Five day pre-exposure with TCAP-1 blocked CRF-, but not footshock- or cocaine-induced reinstatement of cocaine seeking; acute pretreatment with TCAP-1 was without effect in all test conditions. Similarly, repeated TCAP-1 pre-exposure blocked the cocaine-sensitized locomotor response to CRF, but not to cocaine.

CONCLUSIONS AND IMPLICATIONS

Repeated TCAP-1 exposure induced robust and selective inhibition of cocaine-related behavioural responses to CRF, suggesting that TCAP-1 may normalize signalling within CRF systems dysregulated by cocaine exposure.     

Virodhamine relaxes the human pulmonary artery through the endothelial cannabinoid receptor and indirectly through a COX product

Background and purpose:

The endocannabinoid virodhamine is a partial agonist at the cannabinoid CB₁ receptor and a full agonist at the CB₂ receptor, and relaxes rat mesenteric arteries through endothelial cannabinoid receptors. Its concentration in the periphery exceeds that of the endocannabinoid anandamide. Here, we examined the influence of virodhamine on the human pulmonary artery.

Experimental approach:

Isolated human pulmonary arteries were obtained during resections for lung carcinoma. Vasorelaxant effects of virodhamine were examined on endothelium-intact vessels precontracted with 5-HT or KCl.

Key results:

Virodhamine, unlike WIN 55,212-2, relaxed 5-HT-precontracted vessels concentration dependently. The effect of virodhamine was reduced by endothelium denudation, two antagonists of the endothelial cannabinoid receptor, cannabidiol and O-1918, and a high concentration of the CB₁ receptor antagonist rimonabant (5 μM), but only slightly attenuated by the NOS inhibitor L-NAME and not affected by a lower concentration of rimonabant (100 nM) or by the CB₂ and vanilloid receptor antagonists SR 144528 and capsazepine, respectively. The COX inhibitor indomethacin and the fatty acid amide hydrolase inhibitor URB597 and combined administration of selective blockers of small (apamin) and intermediate and large (charybdotoxin) conductance Ca²⁺-activated K⁺ channels attenuated virodhamine-induced relaxation. The vasorelaxant potency of virodhamine was lower in KCl- than in 5-HT-precontracted preparations.

Conclusions and implications:

Virodhamine relaxes the human pulmonary artery through the putative endothelial cannabinoid receptor and indirectly through a COX-derived vasorelaxant prostanoid formed from the virodhamine metabolite, arachidonic acid. One or both of these mechanisms may stimulate vasorelaxant Ca²⁺-activated K⁺ channels.     

Role of α1- and α2-GABA(A) receptors in mediating the respiratory changes associated with benzodiazepine sedation

BACKGROUND AND PURPOSE

The molecular substrates underlying the respiratory changes associated with benzodiazepine sedation are unknown. We examined the effects of different doses of diazepam and alprazolam on resting breathing in wild-type (WT) mice and clarified the contribution of α1- and α2-GABA_A receptors, which mediate the sedative and muscle relaxant action of diazepam, respectively, to these drug effects using point-mutated mice possessing either α1H101R- or α2H101R-GABA_A receptors insensitive to benzodiazepine.

EXPERIMENTAL APPROACH

Room air breathing was monitored using whole-body plethysmography. Different groups of WT mice were injected i.p. with diazepam (1–100 mg·kg⁻¹), alprazolam (0.3, 1 or 3 mg·kg⁻¹) or vehicle. α1H101R and α2H101R mice received 1 or 10 mg·kg⁻¹ diazepam or 0.3 or 3 mg·kg⁻¹ alprazolam. Respiratory frequency, tidal volume, time of expiration and time of inspiration before and 20 min after drug injection were analysed.

KEY RESULTS

Diazepam (10 mg·kg⁻¹) decreased the time of expiration, thereby increasing the resting respiratory frequency, in WT and α2H101R mice, but not in α1H101R mice. The time of inspiration was shortened in WT and α1H101R mice, but not in α2H101R mice. Alprazolam (1–3 mg·kg⁻¹) stimulated the respiratory frequency by shortening expiration and inspiration duration in WT mice. This tachypnoeic effect was partially conserved in α1H101R mice while absent in α2H101R mice.

CONCLUSIONS AND IMPLICATIONS

These results identify a specific role for α1-GABA_A receptors and α2-GABA_A receptors in mediating the shortening by benzodiazepines of the expiratory and inspiratory phase of resting breathing respectively.     

A cannabinoid receptor, sensitive to O-1918, is involved in the delayed hypotension induced by anandamide in anaesthetized rats

Background and purpose:

Intravenous injection of the endocannabinoid anandamide induces complex cardiovascular changes via cannabinoid CB₁, CB₂ and vanilloid TRPV1 receptors. Recently, evidence has been accumulating that in vitro, but not in vivo, anandamide relaxes blood vessels, via an as yet unidentified, non-CB₁ vascular cannabinoid receptor, sensitive to O-1918 (1,3-dimethoxy-5-2-[(1R,6R)-3-methyl-6-(1-methylethenyl)-2-cyclohexen-1-yl]-benzene). We here examined whether the anandamide-induced hypotension in urethane-anaesthetized rats was also mediated via a non-CB₁ vascular cannabinoid receptor.

Experimental approach:

Effects of two antagonists (O-1918 and cannabidiol) of the non-CB₁ vascular cannabinoid receptor on anandamide-induced changes in mean, systolic and diastolic blood pressure (MBP, SBP, DBP), mesenteric (MBF) and renal (RBF) blood flow and heart rate (HR) in urethane-anaesthetized rats was examined.

Key results:

In anaesthetized rats, anandamide (1.5–3 µmol·kg⁻¹) and its stable analogue methanandamide (0.5 µmol·kg⁻¹) caused a delayed and prolonged decrease in MBP, SBP, DBP, MBF and RBF by about 10–30% of the respective basal values without changing HR. In pithed rats, anandamide (3 µmol·kg⁻¹) decreased blood pressure by about 15–20% of the basal value without affecting HR, MBF and RBF. All vascular changes were reduced by about 30–70% by cannabidiol and O-1918 (3 µmol·kg⁻¹, each).

Conclusions and implications:

Non-CB₁ cannabinoid vascular receptors, sensitive to O-1918, contribute to the hypotensive effect of anandamide in anaesthetized rats. Activation of these receptors may be therapeutically important as the endocannabinoid system could be activated as a compensatory mechanism in various forms of hypertension.     

Low dose of propranolol down-modulates bone resorption by inhibiting inflammation and osteoclast differentiation

BACKGROUND AND PURPOSE

Bones are widely innervated, suggesting an important role for the sympathetic regulation of bone metabolism, although there are controversial studies. We investigated the effects of propranolol in a model of experimental periodontal disease.

EXPERIMENTAL APPROACH

Rats were assigned as follows: animals without ligature; ligated animals receiving vehicle and ligated animals receiving 0.1, 5 or 20 mg·kg⁻¹ propranolol. After 30 days, haemodynamic parameters were measured by cardiac catheterization. Gingival tissues were removed and assessed for IL-1β, TNF-α and cross-linked carboxyterminal telopeptides of type I collagen (CTX) by elisa, or intercellular adhesion molecule 1 (ICAM-1), receptor activator of NF-κ B ligand (RANKL) and osteoprotegerin (OPG) by Western blot analysis. Sections from the mandibles were evaluated for bone resorption. Also, we analysed the ability of propranolol to inhibit osteoclastogenesis in vitro.

RESULTS

Propranolol at 0.1 and 5 mg·kg⁻¹ reduced the bone resorption as well as ICAM-1 and RANKL expression. However, only 0.1 mg·kg⁻¹ reduced IL-1β, TNF-α and CTX levels as well as increased the expression of OPG, but did not alter any of the haemodynamic parameters. Propranolol also suppressed in vitro osteoclast differentiation and resorptive activity by inhibiting the nuclear factor of activated T cells (NFATc)1 pathway and the expression of tartrate-resistant acid phosphatase (TRAP), cathepsin K and MMP-9.

CONCLUSIONS AND IMPLICATIONS

Low doses of propranolol suppress bone resorption by inhibiting RANKL-mediated osteoclastogenesis as well as inflammatory markers without affecting haemodynamic parameters.     

AVE8134, a novel potent PPARα agonist, improves lipid profile and glucose metabolism in dyslipidemic mice and type 2 diabetic rats

Aim:

AVE8134 is a structurally novel potent PPARα agonist. The aim of this study is to investigate the efficacy of AVE8134 on lipid profile and glucose metabolism in dyslipidemic mice and type 2 diabetic rats.

Methods:

A cell based PPAR Gal4 transactivation assay was constructed for testing the activities of AVE8134 at 3 different PPAR isoforms in vitro. Transgenic human Apo A1 (hApo A1) mice and insulin-resistant ZDF rats were used to evaluate the effects of AVE8134 in vivo.

Results:

AVE8134 was a full PPARα dominated PPAR agonist (the values of EC₅₀ for human and rodent PPARα receptor were 0.01 and 0.3 μmol/L, respectively). AVE8134 was not active at PPARδ receptor. In female hApo A1 mice, AVE8134 (1–30 mg·kg⁻¹·d⁻¹, po for 12 d) dose-dependently lowered the plasma triglycerides, and increased the serum HDL-cholesterol, hApo A1 and mouse Apo E levels. In female ZDF rats, AVE8134 (3–30 mg·kg⁻¹·d⁻¹ for 2 weeks) improved insulin-sensitivity index. In pre-diabetic male ZDF rats (at the age of 7 weeks), AVE8134 (10 mg·kg⁻¹·d⁻¹ for 8 weeks) produced an anti-diabetic action comparable to rosiglitazone, without the PPARγ mediated adverse effects on body weight and heart weight. In male ZDF rats (at the age of 6 weeks), AVE8134 (20 mg·kg⁻¹·d⁻¹ for 12 weeks) increased mRNA levels of the target genes LPL and PDK4 about 20 fold in the liver, and there was no relevant effect with rosiglitazone.

Conclusion:

AVE8134 improves lipid profile and glucose metabolism in dyslipidemic mice and type 2 diabetic rats.     

The α7 nicotinic ACh receptor agonist compound B and positive allosteric modulator PNU-120596 both alleviate inflammatory hyperalgesia and cytokine release in the rat

BACKGROUND AND PURPOSE

Agonists selective for the α7 nicotinic acetylcholine (nACh) receptor produce anti-hyperalgesic effects in rodent models of inflammatory pain, via direct actions on spinal pain circuits and possibly via attenuated release of peripheral pro-inflammatory mediators. Increasingly, allosteric modulation of ligand-gated receptors is recognized as a potential strategy to obtain desired efficacy in the absence of the putative adverse effects associated with agonist activation.

EXPERIMENTAL APPROACH

We compared the anti-hyperalgesic and anti-inflammatory effects of the α7 nACh receptor agonist compound B with the positive allosteric modulator (PAM) PNU-120596 and the standard non-steroidal anti-inflammatory drug (NSAID), diclofenac, in rats with hind paw inflammation induced by either formalin, carrageenan or complete Freund''s adjuvant (CFA).

KEY RESULTS

When administered before carrageenan, both diclofenac (30 mg·kg⁻¹) and PNU-120596 (30 mg·kg⁻¹) significantly reduced mechanical hyperalgesia and weight-bearing deficits for up to 4 h. Compound B (30 mg·kg⁻¹) also attenuated both measures of pain-like behaviour, albeit less robustly. Whereas compound B and PNU-120596 attenuated the carrageenan-induced increase in levels of TNF-α and IL-6 within the hind paw oedema, diclofenac only attenuated IL-6 levels. Established mechanical hyperalgesia induced by carrageenan or CFA was also partially reversed by compound B and PNU-120596. However, diclofenac was considerably more efficacious. Formalin-induced nocifensive behaviours were only reversed by compound B, albeit at doses which disrupted motor performance.

CONCLUSIONS AND IMPLICATIONS

α7 nACh receptor PAMs could prove to be useful in the treatment of inflammatory pain conditions, which respond poorly to NSAIDs or in situations where NSAIDs are contra-indicated.