Behavioral Effects Of Cannabinoids Research Articles

Age-related changes in CB1 receptor expression and function and the behavioral effects of cannabinoid receptor ligands

Cannabinoid use has increased among aging individuals. However, little information on age-related differences in the behavioral effects of these agents is available. To explore potential differences in the behavioral effects of cannabinoids, we determined effects of Δ9-tetrahydrocannabinol (THC, 1–10 mg/kg) or rimonabant (0.3–3.2 mg/kg) on operant fixed-ratio responding (FR10) for food in young adult (6 months) and aged (29 months) rats. THC dose-dependently decreased responding for food. Rimonabant alone had little or no effect on responding up to 1.0 mg/kg, but disrupted responding following a 3.2 mg/kg dose. Rimonabant (1.0 mg/kg) partially antagonized response disruption by THC. These effects were similar in young adult and aged rats. However, aging has been reported to change the neurobiology of cannabinoid CB1 receptors. To confirm our rats exhibited such differences, we assessed CB1 receptor binding sites and function in six subcortical (caudate, nucleus accumbens CA1, and CA2/CA3), and three cortical regions (medial prefrontal, temporal, entorhinal) in young adult (6 months) or aged (26 months) male Lewis rats using quantitative autoradiography. CB1 receptor binding sites were reduced in cortical, but not subcortical brain regions of aged rats. CB1 receptor function, at the level of receptor-G protein interaction, was not different in any region studied. Results indicate that down-regulation of CB1 receptor binding sites observed in cortical regions of aged rats was not accompanied by a commensurate decrease in CB1 receptor-stimulated [35S]GTPγS binding, suggesting a compensatory increase in receptor function in cortical areas. Together, our results provide additional evidence of age-related changes in central CB1 receptor populations. However, the functional compensation for decreased CB1 receptor binding may mitigate changes in behavioral effects of cannabinoids. With the rising use of cannabinoid-based therapeutics among aging populations, further evaluation of age-related changes in the cannabinoid system and the impact of these changes on effects of this class of drugs is warranted.

In vivo Bidirectional Modulation of Cannabinoid on the Activity of Globus Pallidus in Rats

Endocannabinoids are bioactive substances which participate in central motor control. The globus pallidus (GP) is a major nucleus in the basal ganglia circuit, which plays an important function in movement regulation. Both cannabinoid receptor type 1 (CB1R) and cannabinoid receptor type 2 (CB2R) are expressed in the GP suggesting GP as a main action area of endocannabinoids. To investigate the direct electrophysiological and behavioral effects of cannabinoids in GP, in vivo single unit extracellular recordings and behavioral tests were performed in rats. Administration of WIN 55,212-2 exerted three neuronal response patterns from all sampled neurons of GP, including (1) increase of the firing rate; (2) decrease of the firing rate; (3) increase and then decrease of the firing rate. Selectively blocking CB1R by AM 251 decreased the firing rate and increased the firing rate. Selectively blocking CB2R by AM 630 did not change the firing rate significantly, which suggested that endocannabinoids modulated the spontaneous firing activity of pallidal neurons mainly via CB1R. Furthermore, co-application of AM 251, but not AM 630, blocked WIN 55,212-2-induced modulation of firing activity of pallidal neurons. Finally, both haloperidol-induced postural behavioral test and elevated body swing test (EBST) showed that unilateral microinjection of WIN 55,212-2 mainly induced contralateral-biased swing and deflection behaviors. Meanwhile, AM 251 produced opposite effect. The present in vivo study revealed that cannabinoids produced complicated electrophysiological and behavioral effects in the GP, which further demonstrated that the GP is a major functional region of endocannabinoid.

Analysis of the Uptake, Metabolism, and Behavioral Effects of Cannabinoids on Zebrafish Larvae.

The Cannabis sativa plant contains numerous phytocannabinoids and terpenes with known or potential biological activity. For decades, plant breeders have been breeding the Cannabis plant to control for a desired ratio of the major cannabinoids. A high-throughput in vivo model to understand the relationship between the chemical composition of different strains and their therapeutic potential then becomes of value. Measuring changes in the behavioral patterns of zebrafish larvae is an established model with which to test the biological activity of neuroactive compounds. However, there is currently little information regarding the uptake kinetics and metabolism of compounds by larvae. In this study, we chose to compare the uptake kinetics and metabolism of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) alone or in combination with their effects on larval behavior. We have shown that both compounds have distinct behavioral patterns and concentration response profiles. Additionally, the uptake kinetics observed for each compound appears to correlate with the change in behavior observed in the behavioral assays. When combinations of THC and CBD were tested there were shifts in both the behavioral activity and the uptake kinetics of each compound compared with when they were tested alone. Finally, the THC/CBD-derived metabolites detected in the larvae are similar to those found in mammalian systems. This study thus provides a model for further testing of additional cannabinoids and potentially plant extracts.

Cannabinoids disrupt memory encoding by functionally isolating hippocampal CA1 from CA3.

Much of the research on cannabinoids (CBs) has focused on their effects at the molecular and synaptic level. However, the effects of CBs on the dynamics of neural circuits remains poorly understood. This study aims to disentangle the effects of CBs on the functional dynamics of the hippocampal Schaffer collateral synapse by using data-driven nonparametric modeling. Multi-unit activity was recorded from rats doing an working memory task in control sessions and under the influence of exogenously administered tetrahydrocannabinol (THC), the primary CB found in marijuana. It was found that THC left firing rate unaltered and only slightly reduced theta oscillations. Multivariate autoregressive models, estimated from spontaneous spiking activity, were then used to describe the dynamical transformation from CA3 to CA1. They revealed that THC served to functionally isolate CA1 from CA3 by reducing feedforward excitation and theta information flow. The functional isolation was compensated by increased feedback excitation within CA1, thus leading to unaltered firing rates. Finally, both of these effects were shown to be correlated with memory impairments in the working memory task. By elucidating the circuit mechanisms of CBs, these results help close the gap in knowledge between the cellular and behavioral effects of CBs.

P.6.c.003 Environmental, genetic and epigenetic components in drug abuse and relapse to drug seeking

The past decade has witnessed a number of societal and political changes that have raised critical questions about the long-term impact of marijuana (Cannabis sativa) that are especially important given the prevalence of its abuse and that potential long-term effects still largely lack scientific data. Disturbances of the epigenome have generally been hypothesized as the molecular machinery underlying the persistent, often tissue-specific transcriptional and behavioral effects of cannabinoids that have been observed within one’s lifetime and even into the subsequent generation. Here, we provide an overview of the current published scientific literature that has examined epigenetic effects of cannabinoids. Though mechanistic insights about the epigenome remain sparse, accumulating data in humans and animal models have begun to reveal aberrant epigenetic modifications in brain and the periphery linked to cannabis exposure. Expansion of such knowledge and causal molecular relationships could help provide novel targets for future therapeutic interventions.

Behavioral effects of cannabinoids on zebrafish larvae

Behavioral effects of cannabinoids on zebrafish larvae

Genetic vs. pharmacological inactivation of COMT influences cannabinoid-induced expression of schizophrenia-related phenotypes

Catechol-O-methyltransferase (COMT) is an important enzyme in the metabolism of dopamine and disturbance in dopamine function is proposed to be central to the pathogenesis of schizophrenia. Clinical epidemiological studies have indicated cannabis use to confer a 2-fold increase in risk for subsequent onset of psychosis, with adolescent-onset use conveying even higher risk. There is evidence that a high activity COMT polymorphism moderates the effects of adolescent exposure to cannabis on risk for adult psychosis. In this paper we compared the effect of chronic adolescent exposure to the cannabinoid WIN 55212 on sensorimotor gating, behaviours related to the negative symptoms of schizophrenia, anxiety- and stress-related behaviours, as well as ex-vivo brain dopamine and serotonin levels, in COMT KO vs. wild-type (WT) mice. Additionally, we examined the effect of pretreatment with the COMT inhibitor tolcapone on acute effects of this cannabinoid on sensorimotor gating in C57BL/6 mice. COMT KO mice were shown to be more vulnerable than WT to the disruptive effects of adolescent cannabinoid treatment on prepulse inhibition (PPI). Acute pharmacological inhibition of COMT in C57BL/6 mice also modified acute cannabinoid effects on startle reactivity, as well as PPI, indicating that chronic and acute loss of COMT can produce dissociable effects on the behavioural effects of cannabinoids. COMT KO mice also demonstrated differential effects of adolescent cannabinoid administration on sociability and anxiety-related behaviour, both confirming and extending earlier reports of COMT×cannabinoid effects on the expression of schizophrenia-related endophenotypes.

Chronic treatment and withdrawal of the cannabinoid agonist WIN 55,212-2 modulate the sensitivity of presynaptic receptors involved in the regulation of monoamine syntheses in rat brain

Brain monoamines are involved in many neurochemical and behavioral effects of cannabinoids, but little is known on the regulation of noradrenaline, dopamine, and serotonin (5-HT) synthesis in cannabinoid addiction. This study investigated in rat brain the chronic effects of the potent cannabinoid agonist WIN 55,212-2 and of rimonabant-precipitated withdrawal, as well as the sensitivity of synthesis-modulating inhibitory receptors, on the accumulation of L-3,4-dihydroxyphenylalanine (DOPA) and 5-HTP after decarboxylase inhibition. Acute WIN (8 mg/kg; 1 h) increased DOPA synthesis in cortex (52%), hippocampus (51%), and cerebellum (56%) and decreased DOPA accumulation in striatum (31%). Acute WIN also decreased the synthesis of 5-HTP in all brain regions (40-53%). Chronic WIN (2-8 mg/kg; 5 days) and/or antagonist-precipitated withdrawal induced tolerance to the acute effects of WIN on the accumulation of DOPA (cortex and striatum) and 5-HTP (all brain regions). The inhibitory effect of clonidine (alpha2-agonist; 1 mg/kg) on the accumulation of DOPA (15-41%) and 5-HTP (22-41%) was markedly decreased or abolished after chronic WIN and precipitated withdrawal, mainly in noradrenergic and serotonergic brain regions, which indicated desensitization of alpha2-autoreceptors and alpha2-heteroreceptors regulating the synthesis of noradrenaline and 5-HT. In WIN-dependent rats (chronic and withdrawal states), the effect of a low dose of (+/-)-8-hydroxy-2-(di-n-propylamino)-tetralin (5-HT1A agonist; 0.1 mg/kg) on the accumulation of precursor amino acids was markedly potentiated in cerebellum and striatum, indicating the induction of supersensitivity of 5-HT1A-autoreceptors and 5-HT1A-heteroreceptors that regulate the synthesis of 5-HT, noradrenaline, and dopamine in these brain regions. These chronic adaptations in presynaptic receptor function could play a relevant role in cannabinoid addiction.

Gonadal hormone modulation of the behavioral effects of Δ 9-tetrahydrocannabinol in male and female rats

Female rats are more sensitive than males to many behavioral effects of cannabinoids. The purpose of the present study was to determine if sex differences in the antinociceptive and motoric effects of Δ 9-tetrahydrocannabinol (THC) are due to activational effects of gonadal steroid hormones. THC-induced antinociception (tail withdrawal, paw pressure tests) and motoric effects (horizontal locomotion, catalepsy) were compared in male and female gonadectomized rats that were chronically treated with hormone (testosterone in males, estradiol in females) vs. those that were gonadectomized and had no hormone replacement. THC's effects were also compared between gonadally intact females tested during vaginal estrus vs. diestrus. THC (5 and 10 mg/kg i.p.) produced very similar antinociceptive effects in no-hormone vs. testosterone-treated males, but significantly less locomotor suppression in testosterone-treated males than those with no hormone replacement. In gonadectomized females, estradiol enhanced THC's antinociceptive but not motoric effects. In gonadally intact, cycling females, 5 mg/kg THC produced slightly to significantly greater behavioral effects in estrous than in diestrous females. These results suggest that sex differences in THC-induced behavioral effects in the adult rat can be attributed to activational effects of testosterone in males and/or estradiol in females.

CB1 receptor stimulation in specific brain areas differently modulate anxiety-related behaviour

There is a general consensus that the effects of cannabinoid agonists on anxiety seem to be biphasic, with low doses being anxiolytic and high doses ineffective or possibly anxiogenic. Besides the behavioural effects of cannabinoids on anxiety, very few papers have dealt with the neuroanatomical sites of these effects. We investigated the effect on rat anxiety behavior of local administration of THC in the prefrontal cortex, basolateral amygdala and ventral hippocampus, brain regions belonging to the emotional circuit and containing high levels of CB1 receptors. THC microinjected at low doses in the prefrontal cortex (10μg) and ventral hippocampus (5μg) induced in rats an anxiolytic-like response tested in the elevated plus-maze, whilst higher doses lost the anxiolytic effect and even seemed to switch into an anxiogenic profile. Low THC doses (1μg) in the basolateral amygdala produced an anxiogenic-like response whereas higher doses were ineffective. All these effects were CB1-dependent and closely linked to modulation of CREB activation. Specifically, THC anxiolytic activity in the prefrontal cortex and ventral hippocampus was paralleled by an increase in CREB activation, whilst THC anxiogenic response in the basolateral amygdala was paralleled by a decrease in CREB activation. Our results suggest that while a mild activation of CB1 receptors in the prefrontal cortex and ventral hippocampus attenuates anxiety, a slight CB1 receptor stimulation in the amygdala results in an anxiogenic-like response. The molecular underpinnings of these effects involve a direct stimulation of CB1 receptors ending in pCREB modulation and/or a possible alteration in the fine tuning of local neuromodulator release.

Subchronic Cannabinoid Agonist (WIN 55,212-2) Treatment during Cocaine Abstinence Alters Subsequent Cocaine Seeking Behavior

The co-abuse of marijuana with cocaine is widespread, but it has not been until recently that the relationship between the behavioral effects of cannabinoids and cocaine has begun to be unveiled in animal models. Male Wistar rats were trained to intravenously self-administer cocaine until a stable baseline was reached. Rats then were subjected to a 5-day cocaine deprivation period during which they were treated daily with the cannabinoid receptor agonist WIN 55,212-2 (R-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate) (0, 0.3, 1, and 3 mg/kg; i.p.). Following this subchronic treatment, rats were tested, in counterbalanced order, in a test of anxiety (elevated plus-maze), as well as extinction and cue-induced reinstatement tests, the latter conducted according to a between-within procedure. Subchronic administration of WIN 55,212-2 was found to produce dose-dependent alterations of performance in the extinction, reinstatement, and anxiety tests with the lowest dose of WIN 55,212-2 producing the highest resistance to extinction and reinstatement, and the highest dose of WIN 55,212-2 producing the highest anxiolytic activity. Subchronic treatment with WIN 55,212-2 in rats without a history of cocaine self-administration did not affect anxiety levels. The results suggest an important role of the cannabinoid system in neuronal processes underlying cocaine seeking behavior. However, further studies will be necessary to understand possible implications of these findings for a role of the cannabinoid system as a treatment target for human cocaine abuse.

ROLE OF DORSAL HIPPOCAMPAL CANNABINOID RECEPTORS AND NITRIC OXIDE IN ANXIETY LIKE BEHAVIOURS IN RATS USING THE ELEVATED PLUS‐MAZE TEST

1. The important role of the cannabinoid system in the modulation of anxiety like behaviours in clinical and experimental studies has been proposed. However, investigations into this effect of cannabinoids has produced contradictory results. It has been reported that different neurotransmitters, such as nitric oxide (NO), are involved in the behavioural effects of cannabinoids. The hippocampus is also an important brain region in the modulation of anxiety in which CB1 receptors are densely expressed. The present study was designed to evaluate the interactions between cannabinoid and NO systems in the CA1 brain region of the rats using the plus-maze test. 2. Rats were anaesthetized with ketamine and xylazine and special cannulas were inserted stereotaxically into the CA1 region of the dorsal hippocampus. After 1 week recovery, the effects of intra-CA1 administration of WIN55212-2 (1, 2.5 and 5 microg/rat), AM251 (2, 10 and 50 ng/rat), L-arginine (0.01, 0.1 and 1 microg/rat) and N(G)-nitro-L-arginine methyl ester (L-NAME; 1, 10 and 100 ng/rat) on percentage open arm time (%OAT) and percentage open arm entries (%OAE) were determined. Moreover, the effects of pretreatment with AM251 (2 ng/rat), L-arginine (0.01 microg/rat) and L-NAME (1 ng/rat) on the response induced by intra-CA1 administration of WIN55212-2 were also assessed. 3. The administration of either L-arginine or L-NAME into the CA1 region produced significant anxiogenic-like responses, whereas administration of AM251 induced anxiolytic effects. Intra-CA1 injection of WIN55212-2 produced a significant anxiogenic-like effect that was reversed by AM251 and was also altered by L-NAME, but not by L-arginine. 4. These data imply that cannabinoids may have anxiogenic-like effects in the CA1 region of the hippocampus in which CB1 receptors and NO may be involved.

Sex differences in behavioral effects of cannabinoids

This review summarizes the existing literature on sex differences in the effects of cannabinoid drugs on behavior, primarily in the adult rodent. These preclinical studies, taken together with preliminary reports of sex differences in cannabinoid effects in humans, suggest that sex of subject may be an important modulating factor in a variety of cannabinoid effects. When sex differences are found, females are usually more sensitive than males to cannabinoids. Both pharmacokinetic and pharmacodynamic variables may contribute to sex differences in behavioral effects of cannabinoids. Given the significant therapeutic potential of cannabinoid agonists and antagonists — as well as their widespread recreational use — it will be important to determine the reliability and functional significance of, as well as mechanisms underlying sex differences in cannabinoid effects.

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, Δ 9-tetrahydrocannabinol, 11-hydroxy-Δ 9-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 °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.

Localisation of cannabinoid receptors in the rat brain using antibodies to the intracellular C-terminal tail of CB.

The CB(1)-type cannabinoid receptor mediates physiologic effects of Delta(9)-tetrahydrocannabinol, the psychoactive ingredient of the drug marijuana. In this report, the authors analyse the expression of CB(1) in the rat brain by using antibodies to the C-terminal 13 amino acids of the receptor. Western blot analysis of rat brain membranes revealed a prominent immunoreactive band with a molecular mass ( approximately 53 kDa) consistent with that predicted for CB(1) from the rat cDNA sequence. In addition, however, less intense immunoreactive bands corresponding to glycosylated ( approximately 62 kDa) and putative N-terminally shorter ( approximately 45 kDa) isoforms of CB(1) were detected. The distribution of CB(1)-immunoreactivity in rat brain was similar to the distribution of binding sites for radiolabelled cannabinoids, with high levels of expression in the olfactory system, the hippocampal formation, the basal ganglia, the cerebellum, and the neocortex. This provides important evidence that CB(1) is likely to be largely responsible for mediating effects of cannabinoids in the brain. CB(1) immunoreactivity was associated with nerve fibre systems and axon terminals but was not detected in neuronal somata. This is consistent with the presynaptic inhibitory effects of cannabinoids on neurotransmitter release in the brain. Detailed immunocytochemical analysis of anatomically or functionally related regions of the brain revealed the location of CB(1) receptors within identified neural circuits. Determination of the cellular and subcellular location of CB(1) within known neuronal circuits of the brain provides an anatomic framework for interpretation of the neurophysiologic and behavioural effects of cannabinoids.

Behavioral effects of cannabinoid agents in animals.

Two subtypes of cannabinoid receptors have been identified to date, the CB1 receptor, essentially located in the CNS, but also in peripheral tissues, and the CB2 receptor, found only at the periphery. The identification of delta9-tetrahydrocannabinol (delta9-THC) as the major active component of marijuana (Cannabis sativa), the recent emergence of potent synthetic ligands and the identification of anandamide and sn-2 arachidonylglycerol as putative endogenous ligands for cannabinoid receptors in the brain, have contributed to advancing cannabinoid pharmacology and approaching the neurobiological mechanisms involved in physiological and behavioral effects of cannabinoids. Most of the agonists exhibit nonselective affinity for CB1/CB2 receptors, and delta9-THC and anandamide probably act as partial agonists. Some recently synthesized molecules are highly selective for CB2 receptors, whereas selective agonists for the CB1 receptors are not yet available. A small number of antagonists exist that display a high selectivity for either CB1 or CB2 receptors. Cannabinomimetics produce complex pharmacological and behavioral effects that probably involve numerous neuronal substrates. Interactions with dopamine, acetylcholine, opiate, and GABAergic systems have been demonstrated in several brain structures. In animals, cannabinoid agonists such as delta9-THC, WIN 55,212-2, and CP 55,940 produce a characteristic combination of four symptoms, hypothermia, analgesia, hypoactivity, and catalepsy. They are reversed by the selective CB1 receptor antagonist, SR 141716, providing good evidence for the involvement of CB1-related mechanisms. Anandamide exhibits several differences, compared with other agonists. In particular, hypothermia, analgesia, and catalepsy induced by this endogenous ligand are not reversed by SR 141716. Cannabinoid-related processes seem also involved in cognition, memory, anxiety, control of appetite, emesis, inflammatory, and immune responses. Agonists may induce biphasic effects, for example, hyperactivity at low doses and severe motor deficits at larger doses. Intriguingly, although cannabis is widely used as recreational drug in humans, only a few studies revealed an appetitive potential of cannabimimetics in animals, and evidence for aversive effects of delta9-THC, WIN 55,212-2, and CP 55,940 is more readily obtained in a variety of tests. The selective blockade of CB1 receptors by SR 141716 impaired the perception of the appetitive value of positive reinforcers (food, cocaine, morphine) and reduced the motivation for sucrose, beer and alcohol consumption, indicating that positive incentive and/or motivational processes could be under a permissive control of CB1-related mechanisms. There is little evidence that cannabinoid systems are activated under basal conditions. However, by using SR 141716 as a tool, a tonic involvement of a CB1-mediated cannabinoid link has been demonstrated, notably in animals suffering from chronic pain, faced with anxiogenic stimuli or highly motivational reinforcers. Some effects of SR 141716 also suggest that CB1-related mechanisms exert a tonic control on cognitive processes. Extensive basic research is still needed to elucidate the roles of cannabinoid systems, both in the brain and at the periphery, in normal physiology and in diseases. Additional compounds, such as selective CB1 receptor agonists, ligands that do not cross the blood brain barrier, drugs interfering with synthesis, degradation or uptake of endogenous ligand(s) of CB receptors, are especially needed to understand when and how cannabinoid systems are activated. In turn, new therapeutic strategies would likely to emerge.