Influence of the cannabinoid agonist HU 210 on cocaine- and CQP 201-403-induced behavioural effects in rat

An emerging trend in Novel Psychoactive Substances (NPSs): designer THC

Since its discovery as one of the main components of cannabis and its affinity towards the cannabinoid receptor CB1, serving as a means to exert its psychoactivity, Δ9-tetrahydrocannabinol (Δ9-THC) has inspired medicinal chemists throughout history to create more potent derivatives. Initially, the goal was to synthesize chemical probes for investigating the molecular mechanisms behind the pharmacology of Δ9-THC and finding potential medical applications. The unintended consequence of this noble intent has been the proliferation of these compounds for recreational use. This review comprehensively covers the most exhaustive number of THC-like cannabinoids circulating on the recreational market. It provides information on the chemistry, synthesis, pharmacology, analytical assessment, and experiences related to the psychoactive effects reported by recreational users on online forums. Some of these compounds can be found in natural cannabis, albeit in trace amounts, while others are entirely artificial. Moreover, to circumvent legal issues, many manufacturers resort to semi-synthetic processes starting from legal products extracted from hemp, such as cannabidiol (CBD). Despite the aim to encompass all known THC-like molecules, new species emerge on the drug users' pipeline each month. Beyond posing a significantly high public health risk due to unpredictable and unknown side effects, scientific research consistently lags behind the rapidly evolving recreational market.

Sex, drugs, and adult neurogenesis: sex-dependent effects of escalating adolescent cannabinoid exposure on adult hippocampal neurogenesis, stress reactivity, and amphetamine sensitization

Cannabinoid exposure during adolescence has adverse effects on neuroplasticity, emotional behavior, cognition, and reward sensitivity in adult rats. We investigated whether escalating doses of the cannabinoid receptor 1 (CB1 R) agonist, HU-210, in adolescence would affect adult hippocampal neurogenesis and behavioral processes putatively modulated by hippocampal neurogenesis, in adult male and female Sprague-Dawley rats. Escalating doses of HU-210 (25, 50, and 100 µg/kg), or vehicle were administered from postnatal day (PND) 35 to 46. Animals were left undisturbed until PND 70, when they were treated with 5-bromo-2-deoxyuridine (BrdU; 200 mg/kg) and perfused 21 days later to examine density of BrdU-ir and BrdU/NeuN cells in the dentate gyrus. In another cohort, hypothalamic-pituitary-adrenal (HPA) axis reactivity to an acute restraint stress (30 min; PND 75) and behavioral sensitization to d-amphetamine sulfate (1-2 mg/kg; PND 105-134) were assessed in adulthood. Adolescent HU-210 administration suppressed the density of BrdU-ir cells in the dentate gyrus in adult male, but not adult female rats. Adolescent HU-210 administration also induced significantly higher peak corticosterone levels and reminiscent of the changes in neurogenesis, this effect was more pronounced in adult males than females. However, adolescent cannabinoid treatment resulted in significantly higher stereotypy scores in adult female, but not male, rats. Thus, adolescent CB1 R activation suppressed hippocampal neurogenesis and increased stress responsivity in adult males, but not females, and enhanced amphetamine sensitization in adult female, but not male, rats. Taken together, increased CB1 R activation during adolescence results in sex-dependent, long-term, changes to hippocampal structure and function, an effect that may shed light on differing vulnerabilities to developing disorders following adolescent cannabinoid exposure, based on sex.

Developmental effects of cannabinoids on zebrafish larvae

Cannabinoids are natural or synthetic compounds related chemically to (-)-(6aR,10aR)-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromen-1-ol (Δ(9)-THC), the principle psychotropic constituent of the hemp plant, Cannabis sativa L. Here we examine the effects of the cannabinoids Δ(9)-THC, (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo [1,2,3-de]-1,4-benzoxazin-6-yl]-1-napthalenylmethanone and 2-[(1R,2R,5R)-5-hydroxy-2-(3-hydroxypropyl) cyclohexyl]-5-(2-methyloctan-2-yl)phenol, and the cannabinoid antagonist (AM 251). Exposures were either acute (1-12-h exposure at 108 hours of postfertilization [hpf]) or chronic (96-h exposure starting at 24 hpf). Geometric range finding was used to determine the experimental concentrations. The concentration of the chemical that kills 50% of the test animals in a given time (LC50) was determined based on cumulative mortality at 5 days of postfertilization. At day 5, behavioral analysis (visual motor response test) was carried out in which movement of individual larvae was analysed using automated video-tracking. With acute exposure, embryos showed a biphasic response to the dark challenge with all three cannabinoids tested. This response consisted of stimulation of the locomotor activity at low concentrations, suppression at high doses. With chronic exposure, embryos habituated to the effects of all three cannabinoids when assayed with the dark challenge phase. Further, the excitation was ameliorated when the antagonist AM 251 was coadministered with the cannabinoid. When AM 251 was administered on its own (chronically or acutely), the locomotor activity was suppressed at high concentrations. We examined the embryos for a range of malformations after chronic exposure to cannabinoid. Only Δ(9)-THC was associated with a significant increase in malformations at 5d (yolk sac and pericardial edema, bent tail/body axis). We conclude that cannabinoids have behavioral effects in zebrafish that are comparable to some of those reported in the literature for mammals. In particular, the acute exposure response resembles behavioral effects reported for adult rodents. Our data are consistent with these behavioral effects being mediated, at least in part, by the CB1 receptor.

History of cannabis use is not associated with alterations in striatal dopamine D2/D3 receptor availability

Cannabis use in adolescence is emerging as a risk factor for the development of psychosis. In animal studies, Δ9-tetrahydrocannabinol (THC), the psychoactive component of cannabis, modulates striatal dopaminergic neurotransmission. Alterations in human striatal dopaminergic function have also been reported both in psychosis and in stimulant use. We sought to examine whether striatal dopamine D(2)/D(3) receptor availability was altered in volunteers with a history of cannabis use using a database of previously acquired [(11)C]-raclopride positron emission tomography (PET) scans. Ten [(11)C]-raclopride scans from volunteers with a history of cannabis use were compared to ten control scans using a functional striatal subdivision region of interest (ROI) analysis. No significant differences in either overall striatal BP(ND) values or BP(ND) values in any functional striatal subdivision were found between the two groups. There was also no correlation between lifetime frequency of cannabis use and BP(ND) values. Limbic striatal BP(ND) values were ten percent lower in current nicotine cigarette smokers. These findings suggest that, unlike other drugs of abuse, a history of cannabis use is not associated with alterations in striatal dopamine D(2)/D(3) receptor availability.

Increased brain metabolism after acute administration of the synthetic cannabinoid HU210: a small animal PET imaging study with 18F-FDG

Cannabis use has been shown to alter brain metabolism in both rat models and humans although the observations between both species are conflicting. In the present study, we examined the short term effects of a single-dose injection of the synthetic cannabinoid agonist HU210 on glucose metabolism in the rat brain using small animal (18)F-2-fluoro-deoxyglucose (FDG) Positron Emission Tomography (PET) 15 min (Day 1) and 24h (Day 2) post-injection of the agonist in the same animal. Young adult male Wistar rats received an intra-peritoneal injection of HU210 (100 μg/kg, n=7) or vehicle (n=5) on Day 1. Approximately 1mCi of (18)F-FDG was injected intravenously into each animal at 15 min (Day 1) and 24h (Day 2) post-injection of HU210. A 5-min Computer Tomography (CT) scan followed by a 20-min PET scan was performed 40 min after each (18)F-FDG injection. Standardised Uptake Values (SUVs) were calculated for 10 brain regions of interest (ROIs). Global increased SUVs in the whole brain, hence global brain metabolism, were observed following HU210 treatment on Day 1 compared to the controls (21%, P<0.0001), but not in individual brain regions. On Day 2, however, no statistically significant differences were observed between the treated and control groups. At the 24h time point (Day 2), SUVs in the HU210 treated group returned to control levels (21-30% decrease compared to Day 1), in all ROIs investigated (P<0.0001). In the control group, SUVs did not differ between the two acquisition days in all brain regions. The present results suggest that high-dose HU210 increases brain glucose metabolism in the rat brain shortly after administration, in line with normalised human in vivo studies, an effect that was no longer apparent 24 h later.

Differential treatment regimen-related effects of cannabinoids on D1 and D2 receptors in adolescent and adult rat brain

Animal studies suggest differential effects of cannabinoids on dopamine-related behaviours in adolescence and adulthood however few studies have investigated the underlying neurochemical effects of cannabinoids during adolescence. The aim of the present study was to compare the effects of treatment with the synthetic cannabinoid, HU210, on dopamine receptor density in adolescent and adult rats. Adolescent (postnatal day (PND) 35) and adult (PND 70) rats received a single dose of 100μg/kg HU210 or 25, 50 or 100μg/kg HU210 for 4 or 14 days. Dopamine D1 receptor (D1R) or D2 receptor (D2R) density was measured in the medial and lateral (CPUL) caudate putamen, nucleus accumbens, olfactory tubercle (TU) and substantia nigra (D1R only) using in vitro autoradiography. D1R and D2R densities were 1.6-1.7- and 1.1-1.4-fold higher respectively in adolescent control rats compared to adults. In adult rats, D1R density was increased by 1.2- and 1.3-fold (p<0.05) in CPUL and TU respectively compared to controls, after 14 days of HU210 treatment. A significant overall effect of treatment (p<0.05) on D2R density was also observed in adults after the single dose and 4 and 14 days administration of HU210. In adolescents, an overall effect of treatment on D1R density after a single exposure to HU210 was seen (p=0.0026) but no changes in D1R or D2R densities were observed in other treatment groups. These results suggest that the adolescent rat brain does not display the same compensatory mechanisms activated in the adult brain following cannabinoid treatment.

Methanandamide blocks amphetamine-induced behavioral sensitization in rats

Methanandamide acts at targets which modulate amphetamine-induced behaviors. Therefore, we investigated methanandamide effects on the acute hyperactivity produced by a single injection of amphetamine and behavioral sensitization induced by repeated amphetamine exposure in rats. Methanandamide (5mg/kg, i.p.) did not affect basal locomotor or stereotypical activity. Methanandamide (5mg/kg, i.p.) pretreatment did not alter the acute increase in locomotor or stereotypical activities produced by acute amphetamine (2mg/kg, i.p.). For chronic studies, rats injected with amphetamine (2mg/kg, i.p.) once daily for 3 consecutive days were then challenged with amphetamine (2mg/kg, i.p.) 5 days later. Expression of locomotor sensitization was blocked when methanandamide (5mg/kg, i.p.) was given once, just prior to amphetamine (2mg/kg, i.p.) challenge. In rats co-exposed to methanandamide (5mg/kg, i.p.) and amphetamine (2mg/kg, i.p.) on days 1-3 and then challenged with amphetamine (2mg/kg, i.p.) following 5 days of drug absence, the development of both locomotor and stereotypical sensitization was blocked. The ability of methanandamide to block amphetamine-sensitized behaviors suggests that this pharmacologically diverse lipid regulates signaling events impacted by repeated psychostimulant exposure.

Attenuation of basal and cocaine-enhanced locomotion and nucleus accumbens dopamine in cannabinoid CB1-receptor-knockout mice

RATIONALE

Effect of cannabinoid CB1 receptor deletion on cocaine's actions is controversial. This is partly based on findings in CB1-receptor-knockout (CB1(-/-)) mice with CD1 genetic background.

OBJECTIVES

In the present study, we used CB1(-/-) mice with a C57BL/6J genetic background to further investigate the role of CB1 receptors in cocaine's action.

MATERIALS AND METHODS

Locomotor activity was assessed using AccuScan locomotor chambers. Brain extracellular dopamine (DA) levels were measured by in vivo microdialysis and by fast-scan cyclic voltammetry in the nucleus accumbens (NAc).

RESULTS

CB1(-/-) mice displayed a significant reduction in basal levels of locomotion and extracellular DA, as well as in cocaine-enhanced locomotion and extracellular DA, as compared to their wild-type (CB1(+/+)) littermates. The reduction in basal and cocaine-enhanced DA appears to be related to a reduction in basal DA release, not to an increase in DA clearance, as indicated by fast-scan cyclic voltammetry in brain slices. Pharmacological blockade of CB1 receptors by SR141716 inhibited locomotion and NAc DA release in CB1(+/+) mice.

CONCLUSIONS

The present findings suggest an important role for CB1 receptors in mediating cocaine's behavioral and neurochemical effects.

HU210-induced downregulation in cannabinoid CB1 receptor binding strongly correlates with body weight loss in the adult rat

In vitro autoradiography was used to examine changes in cannabinoid CB1 receptors (targeted with [(3)H] CP55,940) in rats treated with the potent cannabinoid agonist HU210. Animals were administered with HU210 (25, 50, 100 microg/kg) for 4 or 14 days or received a single 100 microg/kg injection of HU210 and sacrificed 24 h later. The acute dose resulted in a decrease in binding in the caudate putamen and hippocampus. A dose dependent, region-specific reduction (P < 0.0001) in [(3)H] CP55,940 binding was seen in all brain regions examined after 4 and 14 days treatment. A decrease in body weight was recorded during the first 4 days of treatment but after this animals began to gain weight. Correlations (0.865 < r < 0.659, P < 0.0001) between body weight on day four and CB1 receptor binding were found in all brain regions examined suggesting that downregulation of CB1 receptors may contribute to the induction of tolerance to body weight loss induced by HU210.

Enhancement of endocannabinoid neurotransmission through CB1 cannabinoid receptors counteracts the reinforcing and psychostimulant effects of cocaine

Cannabinoids, in contrast to typical drugs of abuse, have been shown to exert complex effects on behavioural reinforcement and psychomotor function. We have shown that cannabinoid agonists lack reinforcing/rewarding properties in the intracranial self-stimulation (ICSS) paradigm and that the CB1 receptor (CB1R) agonist WIN55,212-2 attenuates the reward-facilitating actions of cocaine. We sought to determine the effects of the endocannabinoid neurotransmission enhancer AM-404 (1, 3, 10, 30 mg/kg) on the changes in ICSS threshold and locomotion elicited by cocaine and extend the study of the effects of WIN55,212-2 (0.3, 1, 3 mg/kg) on cocaine-induced hyperlocomotion. AM-404 did not exhibit reward-facilitating properties, and actually increased self-stimulation threshold at the highest dose. Cocaine significantly reduced self-stimulation threshold, without altering maximal rates of responding. AM-404 (10 mg/kg) attenuated this action of cocaine, an effect which was reversed by pretreatment with the selective CB1R antagonist SR141716A. WIN55,212-2 decreased locomotion at the two highest doses, an effect that was blocked by SR141716A; AM-404 had no effect on locomotion. Cocaine caused a significant, dose-dependent increase in locomotion, which was reduced by WIN55,212-2 and AM-404. SR141716A blocked the effects of WIN55,212-2 and AM-404 on cocaine-induced hyperlocomotion. SR141716A alone had no effect on ICSS threshold or locomotion. These results indicate that cannabinoids may interfere with brain reward systems responsible for the expression of acute reinforcing/rewarding properties of cocaine, and provide further evidence that the cannabinoid system could be explored as a potential drug discovery target for the treatment of psychostimulant addiction and pathological states associated with psychomotor overexcitability.

The role of CB1 receptors in psychostimulant addiction

Recent studies have implicated the endocannabinoid (eCB) system in the neuronal mechanisms underlying substance dependence. Here, we review results of studies using cannabinoid receptor subtype 1 (CB1) knockout mice as well as CB1 antagonists to elucidate the role of this neurotransmitter system in psychostimulant addiction. The overall picture is that CB1 receptors appear not to be involved in psychostimulant reward, nor in the development of dependence to such substances. In contrast, the eCB system appears to play a role in the persistence of psychostimulant addiction. In particular, CB1 receptors have been found to play a cardinal role in mediating reinstatement of previously extinguished drug-seeking behavior upon re-exposure to the drug or drug-associated cues. The anatomical loci as well as the neuronal mechanisms of the relapse-preventing effects of CB1 antagonists are still poorly understood, although interactions of the eCB system with afferent glutamatergic and possibly dopaminergic projections to the nucleus accumbens are most likely involved. In addition, CB1 receptors seem to modulate drug-related memories, in line with the hypothesized role of the eCB system in memory-related plasticity. Together, these findings suggest that modulators of the eCB system represent a promising novel type of therapy to treat drug addiction.

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.

Modulation of the endocannabinoid system: therapeutic potential against cocaine dependence

Dependence on cocaine is still a main unresolved medical and social concern, and in spite of research efforts, no pharmacological therapy against cocaine dependence is yet available. Recent studies have shown that the endocannabinoid system participates in specific stages and aspects of drug dependence in general, and some of this evidence suggests an involvement of the cannabinoid system in cocaine effects. For example, cocaine administration has been shown to alter brain endocannabinoid levels, and the endocannabinoid system has been involved in long-term modifications of brain processes that might play a role in neuro/behavioral effects of psychostimulant drugs like cocaine. Human studies show that marijuana dependence is frequently associated with cocaine dependence, and that the cannabinoid receptor CNR1 gene polymorphism might be related to cocaine addiction. This article will review the main papers in the field showing how a modulation of different components of the cannabinoid system might interact with some of the neurobiological/behavioral effects of cocaine related to its reinforcing effects, evaluated in preclinical models or in clinical settings. The goal of this review will be to provide insights into the complex picture of cocaine abuse and addiction, and to extrapolate from such endocannabinoid-cocaine interactions useful information to test the therapeutic potential of cannabinoid ligands and endocannabinoid-level enhancers against cocaine dependence for future preclinical/clinical trials.

Increased sensitivity of adolescent spontaneously hypertensive rats, an animal model of attention deficit hyperactivity disorder, to the locomotor stimulation induced by the cannabinoid receptor agonist WIN 55,212-2

Converging evidence points to adolescence as a critical period for the onset of a wide range of neuropsychiatric disorders, including attention deficit hyperactivity disorder (ADHD) and drug abuse. Spontaneously hypertensive rats (SHR) are generally considered to be a suitable genetic model for the study of ADHD, since they display hyperactivity, impulsivity, poorly sustained attention, cognitive deficits and increased novelty seeking. Despite the high prevalence of ADHD among adolescents, studies using SHR have mainly been performed on adult animals. The aim of the present study was to evaluate the effect of acute intraperitoneal (i.p.) administration of the cannabinoid receptor agonist WIN 55,212-2 (0.25-2.5 mg/kg) on locomotor activity and anxiety-like behavior in male adolescent and adult SHR and Wistar rats using the open field and elevated plus-maze tests. WIN 55,212-2 at doses of 0.25 and 1.25 mg/kg (i.p.) selectively promoted locomotor stimulation in adolescent SHR in the open field, but not in adult SHR or Wistar rats (regardless of age). The effect of WIN 55,212-2 (0.25 mg/kg, i.p.) on locomotion of adolescent SHR was reversed by pretreatment with the selective cannabinoid CB1 receptor antagonist AM 251 (0.25 mg/kg, i.p.). Moreover, although the present doses of WIN 55,212-2 had no effect on anxiety-related behaviors in any of the animal groups evaluated in the open field (central locomotion) or elevated plus-maze (time and entries in open arms), the highest dose of WIN 55,212-2 tested (2.5 mg/kg, i.p.) significantly decreased the number of closed-arm entries (an index of locomotor activity) of adolescent rats of both the Wistar and SHR strains in the elevated plus-maze. The present results indicate strain- and age-related effects of cannabinoids on locomotor activity in rats, extending the notion that adolescence and ADHD represent risk factors for the increased sensitivity to the effects of drugs.

Chronic treatment with Delta-9-tetrahydrocannabinol alters the structure of neurons in the nucleus accumbens shell and medial prefrontal cortex of rats

The potential of repeated exposure to Delta(9)-tetrahydrocannabinol (Delta(9)-THC) to produce long-lasting changes in synaptic connections in a manner similar to other drugs of abuse was evaluated in Sprague-Dawley rats. For 12 days, rats received two i.p. injections per day (8 h apart) of vehicle, a low dose of Delta(9)-THC (0.5 mg/kg), or escalating doses of Delta(9)-THC (0.5-4.0 mg/kg). Thirty days later, they were evaluated for sensitized locomotor activity (during the night cycle) for 60 min on each of three trials. Using a within-groups design, rats were tested following an injection of vehicle, 0.5 mg/kg Delta(9)-THC or 2.0 mg/kg Delta(9)-THC. The rats showed no evidence of sensitized locomotor activity in any group. Twenty-four hours after the final sensitization test, their brains were removed and then processed for Golgi-Cox staining. Prior exposure to Delta(9)-THC (both the low dose and the escalating doses) increased the length of the dendrites as well as the number of dendritic branches in the shell of the nucleus accumbens and in the medial prefrontal cortex, but not in the hippocampus, striatum, orbital frontal cortex, parietal cortex, or occipital cortex. These results are similar to those evident in brains of rats sensitized to amphetamine, and support previous findings that cannabinoids promote DA activity in the mesolimbic DA system.

Behavioural effects of quinpirole following withdrawal of chronic treatment with the CB1 agonist, HU-210, in rats

The present study investigated spontaneous and quinpirole-induced motor responses of in rats, following withdrawal from chronic treatment with the potent cannabinoid agonist HU-210. Withdrawal from chronic HU-210 (20 microg/kg daily, 14 days) produced a decrease in spontaneous activity at 1 and 2 days and enhanced the hyperactivity induced by acute administration of the dopamine D2 agonist quinpirole (0.5 mg/kg) at 4 days after the end of HU-210 treatment. Administration of quinpirole on day 4 of withdrawal from chronic HU-210 enhanced stereotyped responses and induced jumping behaviour. These results suggest that withdrawal from chronic exposure to cannabinoid agonists could induce a time-dependent alteration in dopamine D2 psychomotor function, leading to a behavioural disorganization, comparable to acute psychotic episodes after continuous cannabinoids.

WIN 55,212-2-induced reduction of cocaine hyperlocomotion: Possible inhibition of 5-HT3 receptor function

We examined the effect of WIN 55,212-2 (an agonist of cannabinoid receptors) and its enantiomer WIN 55,212-3, as well as of ondansetron (an antagonist of serotonin (5-HT)(3) receptors) on the cocaine-induced locomotor hyperactivity in rats. WIN 55,212-2, but not WIN 55,212-3, in doses of 3 and 6 mg/kg which did not affect the basal locomotor activity, dose-dependently reduced the hyperactivation evoked by cocaine. The inhibitory effect of WIN 55,212-2 was not affected by rimonabant (an antagonist of cannabinoid receptors). Like in the case of WIN 55,212-2, the cocaine-induced hyperlocomotion was reduced in a dose-dependent manner by ondansetron (0.03-0.3 mg/kg). The obtained results indicate that the inhibitory effect of WIN 55,212-2 on cocaine hyperactivation is stereoselective and is not mediated by cannabinoid receptors. Moreover, together with the literature data they may suggest that this effect of WIN 55,212-2 involves inhibition of the 5-HT(3) receptor function.

Windows of vulnerability to psychopathology and therapeutic strategy in the adolescent rodent model

Adolescence comes in association with puberty, when maturation and rearrangement of major neurotransmitter pathways and functions are still taking place. The neurobiological processes occurring in the brain during this developmental period have been so far poorly investigated. Yet, it is during adolescence that some major neuropsychiatric disorders may become evident, including ADHD, schizophrenia, and drug abuse. Moreover, the age-related neurobehavioural plasticity renders adolescents particularly vulnerable to the consequences of psychoactive drug exposure. In this view, there is an increased likelihood that addiction will develop when psychoactive drug use starts early during adolescence. From all these observations adolescence emerges as a critical phase in development. In the present review, we focus on recent neurobiological characterization of adolescent rats and mice. As for vulnerability to addictive behaviour, nicotine exposure during adolescence dose-dependently down-regulated levels of AMPA GluR2/3 subunits in the striatum, suggesting a reduced neurobehavioural plasticity in adult subjects. Comparable exposure during adulthood had opposite effects. It was found consistently that exposure to nicotine during adolescence, but not similar exposure in the post-adolescent period, increased the expression of specific subunits of the acetylcholine receptor in adult rats, thus enhancing the reinforcing efficacy of nicotine in a self-administration paradigm. The present data identified a specific age-window, characterized by long-term effects on behavioural and neurochemical indexes, of vulnerability. With respect to potential therapeutic approaches in ADHD, we studied the adolescent spontaneously-hypertensive-rat (SHR) in an intolerance-to-delay operant-behaviour paradigm. The model was further validated by the finding that impulsivity was reduced by chronic methylphenidate administration. Impulsive SHR animals were characterized by reduced cannabinoid CB1 receptor density in the prefrontal cortex. Interestingly, an acute cannabinoid agonist increased levels of self-control behaviour in these animals. The present data suggest that pharmacological modulation of the cannabinoid system might improve some behavioural anomalies seen in ADHD. In conclusion, modelling the adolescent phase in rats and mice appears to be useful for the investigation of determinants of vulnerability to addiction and to other early-onset neuropsychiatric disorders.

Similar effects of cocaine and immobilization stress on the levels of heat-shock proteins and stress-activated protein kinases in the rat hippocampus, and on swimming behaviors: the contribution of dopamine and benzodiazepine receptors

Cocaine (COC) has been reported to cause effects similar to physiological stressors in the brain neuroendocrinal system, including heat-shock protein (HSP) expression, although these effects have not been elucidated in detail. In the present study, we examined the effects of repeated (4 days) treatments with cocaine hydrochloride (35 mg/kg, i.p.) and 10 min immobilization stress (IM) on the distribution of HSP (HSP27, HSP60, HSP70, HSC70) and stress-activated protein kinase (SAPK) (SAPKalpha, SAPKbeta, SAPKgamma) immunoreactive nerve cells (positive cells) in the rat hippocampus. The swimming behaviors of the rats in the forced swimming test were also examined. In both COC and IM groups, an early enhancement (5 h time point) of hippocampal HSP (HSP27, HSP60, HSP70, HSC70) and SAPK (SAPKbeta, SAPKgamma) positive cells was observed, whereas a recovery (SAPKs) or attenuation (HSP60 and HSC70) was observed at the 24 h time point. In both groups, a depression of the swimming behaviors (attenuation in the activity counts and time until immobility) below the control level was observed at the 5 h point, but a recovery was observed at the 24 h time point. At the 48 h time point, all parameters returned to the control level. These alterations in the levels of HSPs and SAPKs, and the swimming behaviors were similar to those observed in the stress (IM) group, and were characteristic in that all of these alterations were attenuated by the benzodiazepine inverse agonist, Ro 15-4513 (5 mg/kg, i.p.), and the dopamine D1 receptor antagonist, SCH23390 (0.5 mg/kg, i.p.), which was not observed in the groups treated with another stressor-like drug (bicuculline).

Amphetamine effects on dopamine levels and behavior following cannabinoid exposure during adolescence

The cannabis gateway hypothesis purports that early exposure to cannabis is a risk factor for subsequent use of other addictive drugs, e.g., psychostimulants. Neurobiological sensitization, consistent with a gateway hypothesis, was currently studied in regard to amphetamine response. Rats were exposed to 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] 1.25 mg/kg, intraperitoneally; i.p. for 5 days during early adolescence. Amphetamine (0.5 mg/kg, i.p.) or WIN 55,212-2 (1.25 mg/kg, i.p.) was administered in late adolescence and in vivo dopamine levels were simultaneously measured in the nucleus accumbens. Locomotor and stereotyped behaviors were also monitored in rats pretreated with WIN 55,212-2 (0.625, 1.25 or 2.5 mg/kg) or Delta-9-tetrahydrocannabinol (0.75, 1.5 or 3.0 mg/kg, i.p.) for 5 days during early adolescence and challenged with amphetamine (0.5 or 2.0 mg/kg) in late adolescence or as adults. Pretreatment with WIN 55,212-2 or Delta-9-tetrahydrocannabinol during early adolescence did not alter the dopaminergic or behavioral responses to amphetamine in adolescence or adulthood. In conclusion, these findings do not support the cannabis gateway hypothesis in regard to subsequent amphetamine exposure.

The spontaneously hypertensive-rat as an animal model of ADHD: evidence for impulsive and non-impulsive subpopulations

Attention-deficit hyperactivity disorder (ADHD) is a neuropsychiatric syndrome, affecting human infants and adolescents. Two main behavioural features are reported: (1). impaired attention and (2). an impulsive-hyperactive behavioural trait. The latter has been studied in a series of experiments, using the spontaneously hypertensive-rat (SHR) strain (which is regarded as a validated animal model for ADHD) in operant tasks. Food-restricted SHRs and their Wistar-Kyoto (WKY) controls were tested during adolescence (i.e. post-natal days 30-45), in operant chambers provided with two nose-poking holes. Nose-poking in one hole (H1) resulted in the immediate delivery of a small amount of food, whereas nose-poking in the other hole (H5) delivered a larger amount of food after a delay, which was increased progressively each day (0-100 s). As expected, all animals showed a shift in preference from the large (H5) to the immediate (H1) reinforcer as the delay length increased. Impulsivity can be measured by the steepness of this preference-delay curve. The two strains differed in home-cage circadian activity, SHRs being more active than WKYs at several time-points. During the test for impulsivity, inter-individual differences were completely absent in the WKY strain, whereas a huge inter-individual variability was evident for SHRs. On the basis of the median value of average hole-preference, we found an 'impulsive' SHR subgroup, with a very quick shift towards the H1 hole, and a flat-slope ('non-impulsive') SHR subgroup, with little or no shift. The impulsive subpopulation also presented reduced noradrenaline levels in both cingulated and medial-frontal cortex, as well as reduced serotonin turnover in the latter. Also, cannabinoid CB1 receptor density resulted significantly lower in the prefrontal cortex of impulsive SHRs, when compared to both the non-impulsive subgroup and control WKYs. Interestingly, acute administration of a cannabinoid agonist (WIN 55,212, 2 mg/kg s.c.) normalized the impulsive behavioural profile, without any effect on WKY rats. Thus, two distinct subpopulations, differing for impulsive behaviour and specific neurochemical parameters, were evidenced within adolescent SHRs. These results support the notion that a reduced cortical density of cannabinoid CB1 receptors is associated with enhanced impulsivity. This behavioural trait can be positively modulated by administration of a cannabinoid agonist. Present results confirm and extend previous literature, indicating that adolescent SHRs represent a suitable animal model for the preclinical investigation of the early-onset ADHD syndrome.

WIN 55,212-2 decreases the reinforcing actions of cocaine through CB1 cannabinoid receptor stimulation

CB(1) cannabinoid receptor agonists show a different profile compared to other drugs of abuse on the basis of experimental data that reveal their reinforcing properties. Thus, there are controversial data in the literature concerning the ability of CB(1) receptor agonists to reinforce behavioral responses in experimental animals, i.e. to lower self-stimulation thresholds, and to support self-administration or conditioned place preference. The aim of the present study was to examine the effects of WIN 55,212-2, a potent CB(1) receptor agonist (graded doses 0.1, 0.3, 1 mg/kg, i.p.), on the rewarding efficacy of lateral hypothalamic self-stimulation and on the systemic cocaine-induced potentiation of brain-stimulation reward. WIN 55,212-2 did not affect lateral hypothalamic self-stimulation thresholds both in drug nai;ve rats and in rats pretreated with the drug, whereas it produced a significant, dose-dependent decrease in the maximal rate of responding, i.e. in the performance of the animals. Cocaine (5.0 mg/kg, i.p.) produced a significant reduction in self-stimulation threshold, without altering maximal rates of responding. Importantly, WIN 55,212-2 attenuated the effect of cocaine at the two higher doses tested. The effects of the CB(1) receptor agonist were reversed by pretreatment with the selective CB(1) receptor antagonist SR 141716A (0.02 mg/kg, i.p.) that did not by itself affect cocaine's action. These results indicate that acute stimulation of CB(1) receptors per se does not affect baseline self-stimulation, but reduces the reinforcing effects induced by cocaine. Taken together these findings suggest that cannabinoids may interfere with brain-reward systems responsible for the expression of acute reinforcing properties of drugs of abuse, such as cocaine, and provide evidence that the cannabinoid system could be an interesting drug discovery and development target for the treatment of drug addiction.

Acute or chronic effects of cannabinoids on spontaneous or pharmacologically induced yawning in rats

Yawning is a reflex or event that is not fully understood. It is controlled by many neurotransmitters and neuropeptides and can be induced pharmacologically by cholinergic or dopaminergic agonists. Amongst their many actions, cannabinoids acting on cannabinoid (CB(1) or CB(2)) receptors can alter cholinergic and/or dopaminergic activity. This study examined the effects of Delta(8)-tetrahydrocannabinol (Delta(8)-THC) administered acutely (2.5 mg/kg intraperitoneally [ip], 15 min before test) or chronically (5 mg/kg for 30 days followed by 24 h or 7 days of discontinuation) on yawning induced by pilocarpine, a cholinergic agonist (0, 1, 2, 4 or 8 mg/kg ip), or apomorphine, a dopaminergic agonist (0, 20, 40 or 80 microg/kg subcutaneously [sc]). Acute effects of different doses of Delta(9)-tetrahydrocannabinol (Delta(9)-THC: 0, 0.5, 1.25 or 2.5 mg/kg ip) on yawning induced by pilocarpine (2 mg/kg ip) or apomorphine (40 microg/kg sc) were also investigated. Both pilocarpine and apomorphine produced yawning in a dose-related manner. Acute administration of Delta(8)-THC and Delta(9)-THC significantly reduced yawning induced by both pilocarpine and apomorphine. Chronic administration of Delta(8)-THC did not change yawning induced by either agonist 24 h or 7 days after discontinuation of Delta(8)-THC. However, a high frequency of spontaneous yawning was observed 7 days after Delta(8)-THC discontinuation. These results suggest that cannabinoid agonists inhibited yawning induced by cholinergic or dopaminergic agonists. In addition, the increased frequency of spontaneous yawning following cessation of chronic administration of a cannabinoid agonist may be of importance as a withdrawal sign for these drugs.

Behavioral sensitization to amphetamine follows chronic administration of the CB1 agonist WIN 55,212-2 in Lewis rats

The extent to which acute and repeated administration of the CB(1) agonist WIN 55,212-2 would affect the stimulatory properties of amphetamine was assessed in Lewis rats. In the first experiment, Lewis rats were treated with either 1 mg/kg of WIN 55,212-2 or vehicle and subsequently treated with 2 mg/kg amphetamine. Acute treatment with WIN 55,212-2 initially increased locomotor activity and then attenuated the stimulating effect of amphetamine on locomotion and exploration (as measured by rears). In a separate experiment, Lewis rats were given daily injections of either WIN 55,212-2 (1 mg/kg) or vehicle for 10 days and the effects of amphetamine were assessed at 1 and 3 days following the last chronic cannabinoid treatment. Those rats, which had been treated with WIN 55,212-2, had an enhanced response to amphetamine with rearing but not with ambulatory movements, suggesting the occurrence of behavioral cross-sensitization to the ability of amphetamine to increase rearing. These data add to the growing evidence that there is at least some overlap between those neural systems acted upon by cannabinoids and those that are believed to be involved in incentive properties associated with other drugs of abuse.

Neuroleptic-like profile of the cannabinoid agonist, HU 210, on rodent behavioural models

(1) The present study was performed to assess the effects exerted by the cannabinoid (CB) agonist, (-)11-hydroxy-delta8-tetrahydrocannabinol-dymethylheptyl (HU 210; 12.5-50 microg/kg ip), on rodent behavioural tests involving dopamine (DA) transmission; in comparison, the DA D2 antagonist, S(-)-3-chloro-5-ethyl-N-[(1-ethyl-2-pyrrolidinyl)methyl]-6-hydroxy-2-methoxy-benzamide hydrochloride ((-)eticlopride; 50 microg/kg sc), was used. (2) In rats, HU 210, at all doses, potently antagonized penile erection (PE) and stretching-yawning (SY) typically elicited by the DA D2/D3 agonists, 6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]-azepine (B-HT 920) and +/-7-hydroxy-N,N-di-n-propylaminotetralin hydrobromide (7-OH-DPAT) both at 100 pg/kg ip. (3) In nonreserpinized mice, HU 210 impaired motor ability assessed by means of a motor test battery, and B-HT 920 (1 mg/kg ip) worsened the phenomenon. (4) In reserpinized mice, HU 210 at 50 microg/kg counteracted the amelioration exerted by B-HT 920 (1 mg/kg ip) on reserpine-induced akinesia. (5) As all these effects were similarly displayed by (-)eticlopride (50 microg/kg sc), our data suggest a neuroleptic-like profile of acute HU 210 in animal behavioural tests.

Protective effects of cannabinoid receptor agonists against cocaine and other convulsant-induced toxic behavioural symptoms

Based on the previously reported co-localization and relationship between cannabinoid and dopamine receptors, the effects of cannabinoid receptor agonists against cocaine-induced toxic behavioural symptoms, including convulsive seizures, were examined in mice. The anticonvulsant effect of several cannabimimetics against seizures induced by other convulsants was also compared. The cannabinoid receptor agonists CP 55940 ((-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)-cyclohexanol) and WIN 55212-2 ((R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone), and the endogenous cannabinoid anandamide were co-administered intraperitoneally with cocaine (75 mg kg(-1)) or other convulsants such as bicuculline, methyl 6,7-dimethoxy-4-ethyl-beta-carboline-carboxylate (DMCM), L-glutamic acid and N-methyl-D-aspartate (NMDA). CP 55940 (2.5 mg kg(-1)) and anandamide (15 mg kg(-1)) significantly antagonized cocaine-induced lethality, and CP 55940 and WIN 55212-2 (2.5 mg kg(-1)) significantly attenuated the severity of cocaine-induced convulsive seizures. Furthermore, ataxic hyperactivity, which was observed only in the cocaine-treated group of mice and could be evaluated by their activity counts, was also depressed in the groups of mice co-treated with each of the three cannabinoid agonists. However, none of these agonists protected against bicuculline- or DMCM-induced lethality or convulsive seizures. In contrast, all of the cannabinoid agonists, most notably anandamide, antagonized both L-glutamic acid (2 g kg(-1))- and NMDA (200 mg kg(-1))-induced convulsive seizures. These data support the previously reported close correlation between dopamine and cannabinoid receptors, and between cannabinoid agonists, especially anandamide, and glutamate (NMDA) receptors. Furthermore, these results suggest a potential therapeutic role for cannabinoid agonists against cocaine- and other-convulsant-induced toxicities.

Chronic treatment with Delta(9)-tetrahydrocannabinol enhances the locomotor response to amphetamine and heroin. Implications for vulnerability to drug addiction

Cannabis sativa preparations are some of the most widely used illicit recreational drugs. In addition to their direct addictive potential, cannabinoids may influence the sensitivity to other drugs. The aim of the present study was to determine if a cross-sensitization between Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and other drugs (amphetamine and heroin) could be demonstrated. We examined the effects of a chronic treatment with Delta(9)-THC (0.6, 3 and 15mg/kg, ip) on the locomotor response to amphetamine (1mg/kg, ip) and heroin (1mg/kg, ip). Chronic treatment with Delta(9)-THC resulted in tolerance to the initial hypothermic and anorexic effects. Pre-treatment with Delta(9)-THC increased the locomotor responses to amphetamine and heroin. This cross-sensitization was time-dependent as it was observed three days after the last injection of Delta(9)-THC for amphetamine, and a relatively long time after the end of chronic treatment (41 days) for heroin. Moreover, the enhanced response to amphetamine or heroin was noted in some individuals only: the high-responder rats (HR). These animals have previously been shown to be vulnerable to drug taking behaviors. It is hypothesised that repeated use of Cannabis derivates may facilitate progression to the consumption of other illicit drugs in vulnerable individuals.

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.

Hu 210: a potent tool for investigations of the cannabinoid system

The synthetic compound HU 210 displays a multiplicity of biochemical, pharmacological, and behavioral effects, most of which have been demonstrated to be dependent on a selective agonistic activity at CB(1) and CB(2) cannabinoid receptors and to involve the main neurotransmitter systems. Results obtained in various studies suggest a potential clinical application of this highly potent drug (e.g., as antipyretic, antiinflammatory, analgesic, antiemetic, and antipsychotic agent) as well as its usefulness in research aimed to develop a better understanding of the involvement of the endogenous cannabinoid system in a number of physiopathological functions.

Inhibitory effects of the cannabinoid agonist HU 210 on rat sexual behaviour

The present study investigates the effects induced by the cannabinoid agonist HU 210 (25-100 microg/kg, administered intraperitoneally [i.p.]) on the following parameters: (a) sexual behaviour of male rats, categorised on the basis of seven consecutive mating pretests as sexually active (SA) and sexually inactive (SI) and (b) sexual receptivity of ovariectomised female rats displaying hormonally induced heat. The data obtained show that HU 210, administered in acute or subchronic mode (once daily for 7 and 14 days), impaired the copulatory pattern of SA rats in a dose- and mode-dependent manner, decreasing their sexual drive, mainly as represented by an increase in mount and intromission latencies, and affecting ejaculation mechanisms (represented as a decrease in intromission frequency and increase in ejaculation latency). After subchronic treatment with the highest dose had been suspended for 2 weeks, SA males' performance was still impaired. In SI rats, acute injections of the drug (25 and 50 microg/kg, i.p.) at the higher dose increased contact latency and decreased genital exploration time towards the female. Acute HU 210 (25-100 microg/kg, i.p.) also inhibited female sexual behaviour, potently reducing lordosis quotient and lordosis intensity.

Effects of the cannabinoid receptor agonist, HU 210, on ingestive behaviour and body weight of rats

The effect of the synthetic cannabinoid receptor agonist, (-)11-hydroxy-Delta(8)-tetrahydrocannabinol-dymethylheptyl (HU 210), on rat body weight and eating and drinking behaviour was examined. In Experiment 1, the drug (25, 50 or 100 microg/kg), sub-chronically administered for 4 days, produced a dose- and time-dependent loss of body weight that, at the highest dose, was not regained by 7 days after the drug was stopped, and remained markedly below that of vehicle-treated animals. In Experiment 2, food and water intakes, which were evaluated in fasted rats, tested as in Experiment 1, were significantly inhibited only by the dose of 100 microgram/kg, and this effect was still present 7 days after the last injection of the drug. The possibility that the effects observed are not directly dependent on the control of appetite and might be ascribable to stress-related phenomena is discussed.