Evidence for separate neuronal mechanisms for the discriminative stimulus and catalepsy induced by delta 9-THC in the rat

The synthetic cannabinoid WIN 55,212-2 attenuates cognitive and motor deficits and reduces amyloid load in 5XFAD Alzheimer mice

BACKGROUND

Alzheimer's disease (AD) is characterized by cognitive decline, with pathological features including amyloid β (Aβ) plaques and inflammation. Despite recent approvals of anti-amyloid antibodies, there remains a need for disease-modifying and easily accessible therapies. The endocannabinoid system presents a promising target for AD treatment, as it regulates various processes implicated in AD pathogenesis.

AIMS

This study assesses the effects of the synthetic cannabinoid WIN 55,212-2 on AD pathology and behavior deficits in aged 5XFAD mice, a well-established AD model.

METHODS

Male 9-month-old 5XFAD mice received either 0.2 mg/kg WIN 55,212-2 or a vehicle solution for 42 days. Memory, anxiety, and motor tests were conducted at 10 months to identify potential changes in behavior and cognition following WIN 55,212-2 treatment. Additionally, the effects of prolonged WIN 55,212-2 treatment on Aβ pathology and neuroinflammation in the brain were quantified immunohistochemically.

RESULTS

Therapeutic WIN 55,212-2 treatment improved the motor performance of 5XFAD mice on the rotarod and rescued memory deficits in the water maze. However, WIN 55,212-2 treatment did not significantly affect anxiety-like behavior in 5XFAD mice. Additionally, prolonged treatment with WIN 55,212-2 reduced Aβ plaque pathology and astrogliosis in the cortex and hippocampus.

CONCLUSIONS

This study highlights the therapeutic potential of WIN 55,212-2 in AD by ameliorating cognitive and motor deficits and reducing neuropathology. These findings support a cannabinoid-based therapy as a promising strategy for AD treatment, with WIN 55,212-2 emerging as a potential candidate.

Chronic exposure to a synthetic cannabinoid improves cognition and increases locomotor activity in Tg4-42 Alzheimer's disease mice

Background

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline and behavior impairments. Despite recent approvals of anti-amyloid antibodies, there remains a need for disease modifying and easily accessible therapies. Emerging evidence suggests that targeting the endocannabinoid system may hold promise for AD therapy as it plays a crucial role in different physiological processes, including learning, memory and anxiety, as well as inflammatory and immune responses.

Objective

In this study, we investigated the therapeutic potential of the synthetic cannabinoid WIN 55,212-2 on memory deficits in Tg4-42 transgenic mice.

Methods

Tg4-42 mice were assigned to two treatment groups to investigate the preventive effects of WIN 55,212-2 after a prolonged washout period, as well as the therapeutic effects of WIN 55,212-2 on behavior. Furthermore, the effects of WIN 55,212-2 treatment on AD pathology, including inflammation, amyloid-β load, neurogenesis, and brain glucose metabolism, were evaluated.

Results

Therapeutic WIN 55,212-2 treatment rescued recognition memory and spatial reference deficits in Tg4-42 mice. Furthermore, therapeutic WIN 55,212-2 administration improved motor performance. In addition, preventative WIN 55,212-2 treatment rescued spatial learning and reference memory deficits. Importantly, WIN 55,212-2 treatment did not affect anxiety-like behavior. However, therapeutic and preventative WIN 55,212-2 treatment resulted in an increase locomotor activity and swimming speed in Tg4-42 mice. WIN-treatment reduced microgliosis in the hippocampus of preventively treated mice and rescued brain glucose metabolism in therapeutically treated Tg4-42 mice.

Conclusions

Our findings emphasize the therapeutic promise of the synthetic cannabinoid WIN 55,212-2 in alleviating behavioral and cognitive deficits linked to AD.

Cannabinoid tetrad effects of oral Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) in male and female rats: sex, dose-effects and time course evaluations

RATIONALE

The legalization of medicinal use of Cannabis sativa in most US states and the removal of hemp from the Drug Enforcement Agency (DEA) controlled substances act has resulted in a proliferation of products containing Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) for oral consumption (e.g., edibles, oils, and tinctures) that are being used for recreational and medicinal purposes.

OBJECTIVE

This study examined the effects of cannabinoids THC and CBD when administered orally on measures of pain sensitivity, body temperature, locomotor activity, and catalepsy (i.e., cannabinoid tetrad) in male and female Sprague Dawley rats.

METHODS

Rats (N = 24, 6 per sex/drug group) were administered THC (1-20 mg/kg), CBD (3-30 mg/kg), or sesame oil via oral gavage. Thermal and mechanical pain sensitivity (tail flick assay, von Frey test), rectal measurements for body temperature, locomotor activity, and the bar-test of catalepsy were completed. A separate group of rats (N = 8/4 per sex) was administered morphine (5-20 mg/kg; intraperitoneal, IP) and evaluated for pain sensitivity as a positive control.

RESULTS

We observed classic tetrad effects of antinociception, hypothermia, hyper- and hypolocomotion, and catalepsy after oral administration of THC that were long lasting (> 7 h). CBD modestly increased mechanical pain sensitivity and produced sex-dependent effects on body temperature and locomotor activity.

CONCLUSIONS

Oral THC and CBD produced long lasting effects that differed in magnitude and time course when compared with other routes of administration. Examination of cannabinoid effects administered via different routes of administration, species, and in both males and females is critical to enhance translation.

Vaporized Cannabis differentially modulates sexual behavior of female rats according to the dose

Studies exploring the effect of compounds that modulate the endocannabinoid system on sexual behavior have yielded contradictory results. However, the effect of smoked Cannabis in women has been consistently associated with an increase in sexual drive. Therefore, it can be speculated that vaporized Cannabis will augment sexually motivated components of the sexual behavior of female rats. To test this hypothesis, we compared the sexual behavior of late-proestrous female rats in a bilevel chamber after vaporizing 0, 200 or 400 mg of Cannabis flowers (containing 18% of delta-9-THC and undetectable levels of cannabidiol) during 10 min. We found that both doses of Cannabis increased the duration of the lordosis response, whereas the highest dose also reduced the lordosis quotient of females. The lowest dose of Cannabis augmented the display of hops and darts without altering the expression of sexual solicitations of females, while the highest one did not affect the expression of hops and darts but reduced sexual solicitations. These effects were not accompanied by alterations of females' ambulatory behavior. The increment of the duration of lordosis response produced by both doses of Cannabis could be associated to a general effect of this drug in sensory processing, as can be an enhancement of females' sensory reactivity to male's stimulation. However, the reduction in the display of solicitations and lordosis in response to mounting observed in females exposed to the highest dose when compared to control and 200 mg of Cannabis groups indicates a reduction of sexual receptivity and motivation. This differential effect of vaporized Cannabis according to the dose employed, suggests that it modulates sexual behavior in a complex way, impacting neural circuits that control different aspects of this social behavior.

Cannabinoids differentially modulate cortical information transmission through the sensorimotor or medial prefrontal basal ganglia circuits

BACKGROUND AND PURPOSE

In the sensorimotor (SM) and medial prefrontal (mPF) basal ganglia (BG) circuits, the cortical information is transferred to the substantia nigra pars reticulata (SNr) through the hyperdirect trans-subthalamic pathway and through the direct and indirect trans-striatal pathways. The cannabinoid CB₁ receptor, which is highly expressed in both BG circuits, may participate in the regulation of motor and motivational behaviours. Here, we investigated the modulation of cortico-nigral information transmission through the BG circuits by cannabinoids.

EXPERIMENTAL APPROACH

We used single-unit recordings of SNr neurons along with simultaneous electrical stimulation of motor or mPF cortex in anaesthetized rats.

KEY RESULTS

Cortical stimulation elicited a triphasic response in the SNr neurons from both SM and mPF-BG circuits, which consisted of an early excitation (hyperdirect transmission pathway), an inhibition (direct transmission pathway), and a late excitation (indirect transmission pathway). In the SM circuit, after Δ⁹ -tetrahydrocannabinol or WIN 55,212-2 administration, the inhibition and the late excitation were decreased or completely lost, whereas the early excitation response remained unaltered. However, cannabinoid administration dramatically decreased all the responses in the mPF circuit. The CB₁ receptor antagonist AM251 (2 mg·kg^-1 , i.v.) did not modify the triphasic response, but blocked the effects induced by cannabinoid agonists.

CONCLUSIONS AND IMPLICATIONS

CB₁ receptor activation modulates the SM information transmission through the trans-striatal pathways and profoundly decreases the cortico-BG transmission through the mPF circuit. These results may be relevant for elucidating the involvement of the cannabinoid system in motor performance and in decision making or goal-directed behaviour.

Effect of cannabidiolic acid and ∆9-tetrahydrocannabinol on carrageenan-induced hyperalgesia and edema in a rodent model of inflammatory pain

RATIONALE

Cannabidiol (CBD), a non-intoxicating component of cannabis, or the psychoactive Δ⁹-tetrahydrocannabiol (THC), shows anti-hyperalgesia and anti-inflammatory properties.

OBJECTIVES

The present study evaluates the anti-inflammatory and anti-hyperalgesia effects of CBD's potent acidic precursor, cannabidiolic acid (CBDA), in a rodent model of carrageenan-induced acute inflammation in the rat hind paw, when administered systemically (intraperitoneal, i.p.) or orally before and/or after carrageenan. In addition, we assess the effects of oral administration of THC or CBDA, their mechanism of action, and the efficacy of combined ineffective doses of THC and CBDA in this model. Finally, we compare the efficacy of CBD and CBDA.

RESULTS

CBDA given i.p. 60 min prior to carrageenan (but not 60 min after carrageenan) produced dose-dependent anti-hyperalgesia and anti-inflammatory effects. In addition, THC or CBDA given by oral gavage 60 min prior to carrageenan produced anti-hyperalgesia effects, and THC reduced inflammation. The anti-hyperalgesia effects of THC were blocked by SR141716 (a cannabinoid 1 receptor antagonist), while CBDA's effects were blocked by AMG9810 (a transient receptor potential cation channel subfamily V member 1 antagonist). In comparison to CBDA, an equivalent low dose of CBD did not reduce hyperalgesia, suggesting that CBDA is more potent than CBD for this indication. Interestingly, when ineffective doses of CBDA or THC alone were combined, this combination produced an anti-hyperalgesia effect and reduced inflammation.

CONCLUSION

CBDA or THC alone, as well as very low doses of combined CBDA and THC, has anti-inflammatory and anti-hyperalgesia effects in this animal model of acute inflammation.

Neurotransmission systems in Parkinson’s disease

Parkinson’s disease (PD) is histologically characterized by the accumulation of α-synuclein particles, known as Lewy bodies. The second most common neurodegenerative disorder, PD is widely known because of the typical motor manifestations of active tremor, rigidity, and postural instability, while several prodromal non-motor symptoms including REM sleep behavior disorders, depression, autonomic disturbances, and cognitive decline are being more extensively recognized. Motor symptoms most commonly arise from synucleinopathy of nigrostriatal pathway. Glutamatergic, γ-aminobutyric acid (GABA)ergic, cholinergic, serotoninergic, and endocannabinoid neurotransmission systems are not spared from the global cerebral neurodegenerative assault. Wide intrabasal and extrabasal of the basal ganglia provide enough justification to evaluate network circuits disturbance of these neurotransmission systems in PD. In this comprehensive review, English literature in PubMed, Science direct, EMBASE, and Web of Science databases were perused. Characteristics of dopaminergic and non-dopaminergic systems, disturbance of these neurotransmitter systems in the pathophysiology of PD, and their treatment applications are discussed.

Assessing Allosteric Modulation of CB1 at the Receptor and Cellular Levels

The cannabinoid CB1 receptor is abundant in the central nervous system and regulates neuronal transmission and other key physiological processes including those leading to pain, inflammation, memory, and feeding behavior. CB1 is activated by the endogenous ligands, arachidonoyl ethanolamine and 2-arachidonoyl glycerol, by various synthetic ligands (e.g., CP55940), and by Δ9-tetrahydrocannabinol, the psychoactive component of Cannabis sativa. These CB1 ligands are orthosteric and transduce downstream signals by binding CB1 and primarily inducing Gi coupling, but Gs and β-arrestin coupling are also possible. Recently, allosteric modulators for CB1 were discovered that bind to topographically distinct sites and can noncompetitively impact the potency and efficacy of orthosteric compounds. These offer the exciting potential for mechanistic analyses and for developing therapeutics. Yet, it is critical to elucidate whether a compound is a positive allosteric modulator or a negative allosteric modulator of orthosteric ligand-induced CB1 profiles to understand pathway specificity and ameliorate diseases. In this chapter, we present equilibrium and kinetic binding analysis to reveal the impact of allosteric modulators on CB1. Also described are activities consistent with CB1 activation (or inactivation) and include cellular internalization of CB1 and downstream signaling patterns. Since many CB1 allosteric modulators do not enhance G protein coupling, it is critical to distinguish CB1 activation and biased signaling patterns via β-arrestin from CB1 inactivation. These strategies can illuminate pathway specificity and are valuable for the fine-tuning of CB1 function.

Marijuana Compounds: A Nonconventional Approach to Parkinson's Disease Therapy

Parkinson's disease (PD), a neurodegenerative disorder, is the second most common neurological illness in United States. Neurologically, it is characterized by the selective degeneration of a unique population of cells, the nigrostriatal dopamine neurons. The current treatment is symptomatic and mainly involves replacement of dopamine deficiency. This therapy improves only motor symptoms of Parkinson's disease and is associated with a number of adverse effects including dyskinesia. Therefore, there is unmet need for more comprehensive approach in the management of PD. Cannabis and related compounds have created significant research interest as a promising therapy in neurodegenerative and movement disorders. In this review we examine the potential benefits of medical marijuana and related compounds in the treatment of both motor and nonmotor symptoms as well as in slowing the progression of the disease. The potential for cannabis to enhance the quality of life of Parkinson's patients is explored.

Are Alcohol Anti-relapsing and Alcohol Withdrawal Drugs Useful in Cannabinoid Users?

Cannabinoids are still classified as illegal psychoactive drugs despite their broad and increasingly acknowledged therapeutic potential. These substances are most famous for their wide recreational use, particularly among young adults to either alter the state of consciousness, intensify pleasure induced by other psychoactive substances or as an alternative to the previously abused drugs. It is important to emphasize that cannabinoids are often taken together with a variety of medications intended for the treatment of alcohol use disorder (AUD) or alcohol withdrawal syndrome (AWS). These medications include disulfiram, acamprosate, and naltrexone. In this paper, we summarize recent advances in the knowledge of possible beneficial effects and interactions between cannabinoids and drugs commonly used for treatment of AUD and AWS either comorbid or existing as a separate disorder.

Promising cannabinoid-based therapies for Parkinson's disease: motor symptoms to neuroprotection

Parkinson’s disease (PD) is a slow insidious neurological disorder characterized by a loss of dopaminergic neurons in the midbrain. Although several recent preclinical advances have proposed to treat PD, there is hardly any clinically proved new therapeutic for its cure. Increasing evidence suggests a prominent modulatory function of the cannabinoid signaling system in the basal ganglia. Hence, use of cannabinoids as a new therapeutic target has been recommended as a promising therapy for PD. The elements of the endocannabinoid system are highly expressed in the neural circuit of basal ganglia wherein they bidirectionally interact with dopaminergic, glutamatergic, and GABAergic signaling systems. As the cannabinoid signaling system undergoes a biphasic pattern of change during progression of PD, it explains the motor inhibition typically observed in patients with PD. Cannabinoid agonists such as WIN-55,212-2 have been demonstrated experimentally as neuroprotective agents in PD, with respect to their ability to suppress excitotoxicity, glial activation, and oxidative injury that causes degeneration of dopaminergic neurons. Additional benefits provided by cannabinoid related compounds including CE-178253, oleoylethanolamide, nabilone and HU-210 have been reported to possess efficacy against bradykinesia and levodopa-induced dyskinesia in PD. Despite promising preclinical studies for PD, use of cannabinoids has not been studied extensively at the clinical level. In this review, we reassess the existing evidence suggesting involvement of the endocannabinoid system in the cause, symptomatology, and treatment of PD. We will try to identify future threads of research that will help in the understanding of the potential therapeutic benefits of the cannabinoid system for treating PD.

Naltrexone does not attenuate the effects of intravenous Δ9-tetrahydrocannabinol in healthy humans

Although a wealth of preclinical evidence indicates an interplay between the μ-opioid (MOR) and cannabinoid 1 receptor (CB1R) systems, the precise nature of the cross modulation in humans is unclear. The objective of this study was to evaluate the effects of pretreatment with the MOR antagonist, naltrexone, on the subjective, behavioural and cognitive effects of the CB1R agonist, Δ9-tetrahydrocannabinol (THC), in healthy human subjects. Healthy human subjects, screened carefully for any medical or psychiatric illness, were administered either placebo or active naltrexone (25 mg) orally on each test day, followed 45 min later by placebo and 165 min later by active i.v. THC (0.025 mg/kg) in a randomized, fixed-order, double-blind manner. Subjective, behavioural and cognitive effects were assessed before and at several points after each drug administration. THC produced expected effects, including euphoria, anxiety, transient perceptual alterations, transient psychotomimetic effects and cognitive impairments. However, naltrexone did not produce any effects alone, nor did it attenuate any of THC's effects. Thus, in healthy human subjects who use cannabis intermittently, MOR antagonism does not modulate the common acute subjective, behavioural and cognitive effects of THC.

Endocannabinoid modulation of dopaminergic motor circuits

There is substantial evidence supporting a role for the endocannabinoid system as a modulator of the dopaminergic activity in the basal ganglia, a forebrain system that integrates cortical information to coordinate motor activity regulating signals. In fact, the administration of plant-derived, synthetic or endogenous cannabinoids produces several effects on motor function. These effects are mediated primarily through the CB(1) receptors that are densely located in the dopamine-enriched basal ganglia networks, suggesting that the motor effects of endocannabinoids are due, at least in part, to modulation of dopaminergic transmission. On the other hand, there are profound changes in CB(1) receptor cannabinoid signaling in the basal ganglia circuits after dopamine depletion (as happens in Parkinson's disease) and following l-DOPA replacement therapy. Therefore, it has been suggested that endocannabinoid system modulation may constitute an important component in new therapeutic approaches to the treatment of motor disturbances. In this article we will review studies supporting the endocannabinoid modulation of dopaminergic motor circuits.

Enhancement of the behavioral effects of endogenous and exogenous cannabinoid agonists by phenylmethyl sulfonyl fluoride

Marijuana's effects in humans are most often reported as intoxicating or therapeutic; yet, some humans report dysphoria or other negative affect. To evaluate whether differences in endocannabinoid levels might account for this variability, the present study examined whether sensitivity to cannabinoids changed when anandamide (AEA) metabolism was inhibited through administration of phenylmethyl sulfonyl fluoride (PMSF) a non-specific irreversible amidase inhibitor. Male Long Evans rats were trained to discriminate 3 mg/kg Δ(9)-tetrahydrocannabinol (THC) versus vehicle in 2-lever drug discrimination procedure. ED(50)s for THC and CP 55,940 were lower when administered with PMSF than alone. PMSF administration also potentiated characteristic cannabimimetic effects of THC in ICR mice. Potentiation of AEA's in vivo effects by PMSF were also observed, primarily as a consequence of PMSF inhibition of the enzyme fatty acid amide hydrolase. Enhancement of the effects of THC and CP 55,940 through this mechanism is unlikely, as these cannabinoids are predominantly metabolized through the P450 system. Mass spectrometry revealed that, in the presence of THC, endogenous AEA levels in the brain decreased and that this decrease was prevented by PMSF, suggesting that increased AEA levels may have acted additively with exogenously administered cannabinoids to increase cannabimimetic effects. These findings may account for the varying affect in response to marijuana in humans or cannabinoids in animals while also suggesting that metabolic inhibitors of AEA may potentiate marijuana's intoxicating effects in humans. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Modulation by female sex hormones of the cannabinoid-induced catalepsy and analgesia in ovariectomized mice

Cannabinoids are psychoactive compounds with many pharmacological properties such as analgesia, sedation and catalepsy most of which are mediated by cannabinoid CB1 receptors. In the present study, we evaluated whether the ovarian sex hormones are involved in the cannabinoid-induced catalepsy and analgesia in ovariectomized female mice. Female NMRI mice (weighing 25-30 g) were divided into 3 main groups: unoperated, sham-operated and ovariectomized. Both the catalepsy and analgesia induced by different doses of the synthetic cannabinoid WIN 55,212-2 (2 and 4 mg/kg, i.p.) were examined in the groups in the presence or absence of the cannabinoid CB1 antagonist AM251 (0.5 mg/kg). We also evaluated effects of estradiol valerate (10 mg/kg) and progesterone (25 mg/kg) on catalepsy and analgesia induced by WIN 55,212-2 in ovariectomized mice. The antinociceptive effect of WIN 55,212-2 was significantly (P<0.01) enhanced in ovariectomized mice, which was prevented by pretreatment with estradiol but not by progesterone. There was no significant difference in the cannabinoid-induced catalepsy between control and ovariectomized mice. However, pretreatment with progesterone but not estradiol potentiated the cataleptic effect of low dose of WIN 55,212-2 (2 mg/kg) in ovariectomized mice (P<0.01). The present data demonstrated for the first time that ovarian sex steroids could modulate both cannabinoid-induced catalepsy and analgesia in female ovariectomized mice.

Identification of a high-affinity binding site involved in the transport of endocannabinoids

Phytocannabinoids, such as the principal bioactive component of marijuana, delta9-tetrahydrocannabinol, have been used for thousands of years for medical and recreational purposes. delta9-Tetrahydrocannabinol and endogenous cannabinoids (e.g., anandamide) initiate their agonist properties by stimulating the cannabinoid family of G protein-coupled receptors (CB1 and CB2). The biosynthesis and physiology of anandamide is well understood, but its mechanism of uptake (resulting in signal termination by fatty acid amide hydrolase) has been elusive. Mounting evidence points to the existence of a specific anandamide transport protein; however, no direct evidence for this protein has been provided. Here, we use a potent, competitive small molecule inhibitor of anandamide uptake (LY2318912, IC50 7.27 +/- 0.510 nM) to identify a high-affinity, saturable anandamide transporter binding site (LY2318912; K(d) = 7.62 +/- 1.18 nM, B(max) = 31.6 +/- 1.80 fmol/mg protein) that is distinct from fatty acid amide hydrolase. Systemic administration of the inhibitor into rodents elevates anandamide levels 5-fold in the brain and demonstrates efficacy in the formalin paw-licking model of persistent pain with no obvious adverse effects on motor function. Identification of the anandamide transporter binding site resolves a missing mechanistic link in endocannabinoid signaling, and in vivo results suggest that endocannabinoid transporter antagonists may provide a strategy for positive modulation of cannabinoid receptors.

Involvement of mu-, delta- and kappa-opioid receptor subtypes in the discriminative-stimulus effects of delta-9-tetrahydrocannabinol (THC) in rats

RATIONALE

Many behavioral effects of delta-9-tetrahydrocannabinol (THC), including its discriminative-stimulus effects, are modulated by endogenous opioid systems.

OBJECTIVE

To investigate opioid receptor subtypes involved in the discriminative effects of THC.

METHODS

Rats trained to discriminate 3 mg/kg i.p. of THC from vehicle using a two-lever operant drug-discrimination procedure, were tested with compounds that bind preferentially or selectively to either mu-, delta- or kappa-opioid receptors.

RESULTS

The preferential mu-opioid receptor agonist heroin (0.3-1.0 mg/kg, i.p.), the selective delta-opioid receptor agonist SNC-80 (1-10 mg/kg, i.p.) and the selective kappa-opioid receptor agonist U50488 (1-10 mg/kg, i.p.) did not produce generalization to the discriminative effects of THC when given alone. However, heroin, but not SNC-80 or U50488, significantly shifted the dose-response curve for THC discrimination to the left. Also, the preferential mu-opioid receptor antagonist naltrexone (0.1-1 mg/kg, i.p.), the selective delta-opioid receptor antagonist, naltrindole (1-10 mg/kg, i.p.) and the kappa-opioid receptor antagonist nor-binaltorphimine (n-BNI, 5 mg/kg, s.c.), did not significantly reduce the discriminative effects of the training dose of THC. However, naltrexone, but not naltrindole or n-BNI, significantly shifted the dose-response curve for THC discrimination to the right. Finally, naltrexone, but not naltrindole or n-BNI, blocked the leftward shift in the dose-response curve for THC discrimination produced by heroin.

CONCLUSIONS

mu- but not delta- or kappa-opioid receptors are involved in the discriminative effects of THC. Given the role that mu-opioid receptors play in THC's rewarding effects, the present findings suggest that discriminative-stimulus effects and rewarding effects of THC involve similar neural mechanisms.

Behavioral effects of inhibition of cannabinoid metabolism: The amidase inhibitor AM374 enhances the suppression of lever pressing produced by exogenously administered anandamide

Biochemical investigations have identified putative enzymatic pathways for the synthesis and metabolism of endogenous cannabinoids. Anandamide amidase is an enzyme that metabolizes anandamide into arachadonic acid and ethanolamine. Using in vitro methods, various inhibitors of amidase have been identified. The present studies were undertaken to determine if the amidase inhibitor AM 374 could enhance the effects of intraperitoneal (IP) injections of anandamide. Three studies were conducted to investigate the effects of various drug treatments on fixed ratio 5 operant lever pressing for food reinforcement. In the first study, the effects of different doses of anandamide were assessed, and it was demonstrated that 5.0 and 10.0 mg/kg anandamide IP significantly suppressed lever pressing, while 2.5 mg/kg produced very little effect. The second study tested the effects of intraventricular (ICV) injections of AM 374, and it was observed that doses up to 10.0, 20.0 and 40 microg AM 374 had no significant effect upon lever pressing. The third study investigated the combined effect of AM374 with a low dose of anandamide. Rats received two drug injections: one ICV and one IP. Four different drug treatments were assessed: 1) ICV vehicle + IP vehicle, 2) ICV vehicle + 2.5 mg/kg anandamide IP, 3) ICV 20.0 microg AM 374 + IP vehicle, and 4) ICV 20 microg AM 374 + 2.5 mg/kg anandamide IP. Combined administration of AM 374 plus anandamide led to a significant decrease in lever pressing compared to either AM374 or anandamide administered alone. Observations of the animals treated with the combination of AM374 plus anandamide indicated that the drug combination resulted in motor slowing, which is consistent with the notion that stimulation of cannabinoid receptors produced a motor deficit that interfered with lever pressing. Although AM374 produced no effect on its own, this amidase inhibitor did enhance the behavioral effect of a low dose of anandamide. These results are consistent with the notion that AM 374 inhibited the enzymatic breakdown of exogenously injected anandamide. This type of procedure can be used to assess a variety of different compounds for their ability to inhibit cannabinoid metabolism.

Dose-dependent effects of Delta9-tetrahydrocannabinol on rates of local cerebral glucose utilization in rat

Recent reports have demonstrated that Delta(9)-tetrahydrocannabinol (Delta(9)-THC) stimulates locomotor activity at low doses (<2.5 mg/kg), while higher doses (>2.5 mg/kg) produce decreases in spontaneous activity. Using quantitative 2-[(14)C]deoxyglucose (2-DG) autoradiography, we systematically studied the effects of acute Delta(9)-THC on rates of local cerebral glucose utilization. The first series of experiments was designed to determine if Delta(9)-THC-mediated changes in cerebral metabolism followed a clear dose-response relationship. Adult male Sprague-Dawley rats were treated with either vehicle or Delta(9)-THC (0.25-2.5 mg/kg) and the 2-DG procedure was initiated 15 min following exposure. Administration of 2.5 mg/kg Delta(9)-THC produced significant decreases in cerebral metabolism in most brain regions studied. In contrast, administration of 0.25 mg/kg Delta(9)-THC produced no significant alterations in any brain region studied, while 1.0 mg/kg of Delta(9)-THC produced a restricted pattern of metabolic decreases. Significant decreases in metabolism following 1.0 mg/kg were concentrated in structures subserving limbic and sensory functions. In a second series of experiments, the effects of pretreatment with the cannabinoid receptor antagonist SR141716A (1.0 mg/kg) on Delta(9)-THC-induced changes in functional activity were measured. Pretreatment with SR141716A attenuated the majority of functional changes produced by Delta(9)-THC, suggesting that these effects are primarily mediated by central cannabinoid receptors. Moreover, these findings indicate that the effects of Delta(9)-THC on cerebral metabolism are dose-dependent and that there are regional differences in the metabolic response to acute cannabinoid exposure.

Sex differences in antinociceptive and motoric effects of cannabinoids

Cannabinoids are currently used for the treatment of excessive weight loss and nausea; however, there are very few studies that have examined cannabinoid effects in females of any species. A previous study has shown that there are sex differences in cannabinoid pharmacokinetics in rats, suggesting that there could be sex differences in cannabinoid-induced behaviors. To address this issue, Delta9-tetrahydrocannabinol, 11-hydroxy-Delta9-tetrahydrocannabinol (natural cannabinoids) or (-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)-phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol) (CP55940, a synthetic cannabinoid) was administered i.p. to male and female Sprague-Dawley rats, who were tested on the 50 degrees C warm water tail withdrawal, paw pressure, catalepsy bar and spontaneous locomotor activity tests at various times post-injection. At the doses tested, all three cannabinoid agonists produced greater effects in females than males in two or more behavioral tests. This study demonstrates that there are sex differences in the behavioral effects of cannabinoids in the rat.

Effects of cannabinoids on prefrontal neuronal responses to ventral tegmental area stimulation

Cannabinoids activate the firing of mesoprefrontocortical dopamine neurons and release dopamine in the prefrontal cortex. This study was undertaken with the aim of clarifying the interaction between cannabinoids and mesocortical system in the prefrontal cortex. The effect of Delta9-tetrahydrocannabinol (Delta9-THC) and the synthetic CB1 agonist WIN55,212-2 (WIN) was studied by extracellular single unit recordings, in chloral hydrate anaesthetised rats, on the spontaneous activity of pyramidal neurons and on the inhibition produced on these neurons by the electrical stimulation of the ventral tegmental area (VTA). Intravenously administered Delta9-THC and WIN (1.0 and 0.5 mg/kg, respectively), increased the firing rate of pyramidal neurons projecting to the VTA. VTA stimulation produced a phasic inhibition (167 +/- 6 ms) in 79% of prefrontal cortex pyramidal neurons. Delta9-THC and WIN reverted this inhibition in 73% and 100% of the neurons tested, respectively. The subsequent administration of the selective CB1 antagonist SR141716A (1 mg/kg) readily suppressed the effects of both cannabinoids and restored the inhibitory response to VTA stimulation. Moreover, when administered alone, SR141716A prolonged the inhibition in 55.6% of the neurons tested. The results indicate that stimulation of CB1 receptors by cannabinoids results in an enhanced excitability of prefrontal cortex pyramidal neurons as indexed by the suppression of the inhibitory effect of VTA stimulation and by the increase in firing rate of antidromically identified neurons projecting to the VTA. Furthermore, our results support the view that endogenous cannabinoids exert a negative control on dopamine activity in the prefrontal cortex. This study may be relevant in helping to understand the influence of cannabinoids on cognitive processes mediated by the prefrontal cortex.

Permissive role of dopamine D(2) receptors in the hypothermia induced by delta(9)-tetrahydrocannabinol in rats

Cannabinoids produce analgesia, hypomotility, catalepsy, cognitive deficits and positive reinforcement. Moreover, Delta(9)-tetrahydrocannabinol (9-THC) and synthetic cannabinoids stimulate dopaminergic neurons and increase dopamine release in different brain areas. In order to clarify the role of endogenously released dopamine in the hypothermic response to cannabinoids, the effect of D(1) and D(2) dopamine receptor agonists and antagonists on Delta(9)-THC-induced hypothermia was studied in rats. Delta(9)-THC (2.5 and 5 mg/kg intraperitoneally [IP]) decreased body temperature in a dose-related manner. This effect was antagonized not only as expected by the CB(1) cannabinoid receptor antagonist SR 141716A (0.5 mg/kg, IP) but also, unexpectedly, by the dopaminergic D(2) receptor antagonists S(-)-sulpiride (5 and 10 mg/kg, IP) and S(-)-raclopride (1 and 3 mg/kg, IP). Conversely, the hypothermic effect of Delta(9)-tetrahydrocannabinol was potentiated by the D(2) dopamine receptor agonists (-)-quinpirole (0.025 and 0.500 mg/kg, SC) and (+)-bromocriptine (0.5 and 1 mg/kg, IP). In contrast, the Delta(9)-THC-induced hypothermic effect was not modified by either by the D(1) dopamine agonist SKF 38393 (10 mg/kg SC) or by the D(1) dopamine antagonist SCH 23390 (0.5 mg/kg SC). These results suggest that the D(2) dopamine receptors have a permissive role in the hypothermic action of cannabinoids.

Role of the endogenous cannabinoid system in the regulation of motor activity

One of the prominent pharmacological features of drugs acting at the brain cannabinoid receptor (CB1) is the induction of alterations in motor behavior. Catalepsy, immobility, ataxia, or the impairment of complex behavioral acts are observed after acute administration of either natural and synthetic cannabinoid receptor agonists or the endogenous CB1 ligand anandamide. The dense presence of CB1 receptors in the cerebellum and in the basal ganglia, especially at the outflow nuclei (substantia nigra and the internal segment of the globus pallidus), supports the existence of an endogenous cannabinoid system regulating motor activity. In the basal ganglia, the functionality of the anandamide-CB1 system is poorly understood. Dual effects are often observed after the administration of CB1 ligands in animal models of pharmacological manipulation of basal ganglia transmitter systems, indicating that the activity of the anandamide-CB1 system depends on the ongoing activation of the different elements of the basal ganglia. This finding is in agreement with the proposed activity-dependent release of anandamide from a plasmalemma precursor. Additionally, a potential state-dependent bidirectional coupling of the CB1 receptor to the adenylate cyclase transduction system has also been described. From this perspective, the endogenous cannabinoid system can be proposed as a local regulator of neurotransmission processes within the basal ganglia. This system may serve as a counterregulatory homeostatic mechanism preserving the functional role of basal ganglia circuits in coding the serial order of events that constitute movement.

Cannabinoids excite dopamine neurons in the ventral tegmentum and substantia nigra

Extracellular recordings were used to determine the effects of cannabinoids on the activity of dopamine neurons within the ventral tegmental area (VTA) and substantia nigra pars compacta (SNC). Systemic administration of the natural psychoactive cannabinoid delta 9-tetrahydrocannabinol (delta 9-THC) and the synthetic cannabimimetic aminoalkylindole WIN 55,212-2 produced dose-dependent increases in firing rate and burst firing in both neuronal populations. These effects appear to be specific as the non-psychoactive cannabidiol and the inactive enantiomer WIN 55,212-3 failed to alter either parameter of neuronal excitability. Furthermore, dopamine neurons in the VTA were more sensitive than those in the SNC to the stimulatory actions of delta 9-THC. These results may provide a mechanism by which psychoactive cannabinoids increase extracellular dopamine levels in mesolimbic and striatal tissues, and thereby contribute to the reinforcing effects of marijuana.

Delta 9-tetrahydrocannabinol impairs spatial memory through a cannabinoid receptor mechanism

The purpose of the present study was to investigate whether the cannabinoid and cholinergic systems impair working memory through a common mechanism. This hypothesis was tested by examining whether the cannabinoid antagonist SR141716A would ameliorate radial-arm performance deficits caused by either the naturally occurring cannabinoid, delta 9-THC, or scopolamine, a muscarinic antagonist. In addition, we evaluated whether the cholinesterase inhibitor, physostigmine, would prevent delta 9-THC-induced impairment of spatial memory. Finally, because the locomotor suppressive effects of cannabinoids may decrease radial arm choice accuracy independent of a direct effect on memory, we examined the impact of increasing the intertrial error on radial arm choice accuracy. As previously reported, delta 9-THC impaired maze performance (ED50 = 3.0 mg/kg). Increasing the intertrial interval from 5 s to 30 s resulted in a three-fold increase in the amount of time required to complete the maze without affecting choice accuracy. Importantly, SR141716A prevented delta 9-THC-induced deficits in radial-arm choice accuracy in a dose-dependent manner (AD50 = 2.4 mg/kg); however, the cannabinoid antagonist failed to improve the disruptive effects of scopolamine. Conversely, physostigmine failed to improve performance deficits produced by delta 9-THC. These data provide strong evidence that delta 9-THC impairs working memory through direct action at cannabinoid receptors. Moreover, these results suggest that scopolamine and delta 9-THC do not impair spatial memory in a common serial pathway, though they may converge on a third neurochemical system.

Pharmacological specificity of the discriminative stimulus effects of delta 9-tetrahydrocannabinol in rhesus monkeys

delta 9-Tetrahydrocannabinol (delta 9-THC) discrimination has been used as an animal model of cannabis intoxication in humans. While numerous studies have examined the discriminative stimulus effects of cannabinoids in rats and pigeons, studies with monkeys have been rare. In the present study, rhesus monkeys, trained to discriminate delta 9-THC from vehicle in a two-lever drug discrimination procedure, were tested with a variety of psychoactive drugs, including cannabinoids as well as drugs from other classes. Results showed that delta 9-THC discrimination showed pharmacological specificity, in that none of the non-cannabinoid drugs fully substituted for delta 9-THC. In contrast, the classical cannabinoids, delta 9-THC and delta 8-THC, and the novel cannabinoids, WIN 55212-2 and 1-butyl-2-methyl-3-(1-naphthoyl)indole, produced full dose-dependent substitution for delta 9-THC in all monkeys. A heptyl indole derivative failed to substitute for delta 9-THC, but it also did not displace [3H] CP 55940 from its binding site. These findings are consistent with those of previous cannabinoid discrimination studies with rats and suggest that results of delta 9-THC discrimination studies in rhesus monkeys may be predictive of the subjective effects of cannabinoid drugs in humans.

Discriminative stimulus effects of anandamide in rats

Anandamide (arachidonylethanolamide), a putative endogenous ligand for the cannabinoid receptor, produces a tetrad of behavioral effects in mice characteristic of psychoactive cannabinoids including catalepsy, antinociception, hypothermia, and hypomobility. The present study examined the discriminative stimulus effects of anandamide in rats trained to discriminate delta 9-tetrahydrocannabinol or the potent cannabinoid receptor ligand CP 55,940 [(-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)-phenyl]-trans-4-(3- hydroxypropyl)cyclohexanol)] from vehicle. Intraperitoneal injections of anandamide substituted for delta 9-tetrahydrocannabinol and for CP 55,940; however, unlike substitution dose-effect curves with the training drugs, anandamide substitution occurred at a single dose (30 or 45 mg/kg) and was accompanied by severe decreases in response rates. The results of the present study suggest that, although systemic anandamide administration may have cannabimimetic effects similar to those of delta 9-tetrahydrocannabinol and CP 55,940, some differences in the behavioral effects of anandamide and other psychoactive cannabinoids also are apparent.

Discriminative stimulus effects of delta 9-tetrahydrocannabinol and delta 9-11-tetrahydrocannabinol in rats and rhesus monkeys

Previous reports have suggested that delta 9-11-tetrahydrocannabinol (delta 9-11-THC), an exocyclic analog of delta 9-tetrahydrocannabinol (delta 9-THC), may have weak agonist effects as well as antagonistic properties. The purpose of the present study was to examine the effects of delta 9-11-THC in substitution and antagonism tests in rats and in rhesus monkeys trained to discriminate delta 9-THC from vehicle in two-lever drug-discrimination procedures. The substitution studies showed that delta 9-11-THC generalizes from the training dose of delta 9-THC in rats and in monkeys, although it was less potent in both species. The magnitude of the potency difference was greater in monkeys than in rats. When administered immediately following injection with the training dose of delta 9-THC, delta 9-11-THC failed to block the delta 9-THC cue in rats and showed a lack of dose-responsive inhibition in monkeys. These results suggest that delta 9-11-THC is devoid of antagonistic properties in the drug discrimination paradigm.

Quantitation of rodent catalepsy by a computer-imaging technique

Catalepsy is usually defined as a behavioral state in which an animal maintains an unnatural posture for an extended period of time. While numerous laboratory models have been developed for assessing catalepsy, a common problem encountered with most procedures is the difficulty in quantitating immobility. Measurement of catalepsy is still frequently subjective in nature. To eliminate this subjectivity, a computer-based technique was developed for quantitating catalepsy in mice and rats as measured on the elevated ring. The system consisted of a video camera that was focused on either three mice or two rats. Their behavior was recorded during a 5-min session on videotape that was subsequently transmitted to a Macintosh II microcomputer via a Scion Image-Capture 2 board. A modification of the NIH Image 1.17 public domain program allowed the image of the rat to be transformed to a purely black or white image by assigning pixel values of either 0 or 256. The subsequent captured image was preprocessed in an identical manner and each pixel was subtracted from its corresponding pixel in the previous frame. Thus, changes in animal posture between the two frames can be quantitated. One subtraction cycle (acquisition, bilevel processing, and subtraction) was repeated at an average rate of approximately one per second. To quantitate immobility by image analysis, each frame was subtracted from the previous frame during a 5-min session. The resulting data were sorted according to the magnitude of movement (number of changed pixels) and plotted vs. time.(ABSTRACT TRUNCATED AT 250 WORDS)