Paradoxical anxiolytic effect of the 'bath salt' synthetic cathinone MDPV during early abstinence is inhibited by a chemokine CXCR4 or CCR5 receptor antagonist.

Chemokine CXCR4 and CCR5 receptors are best known as HIV co-entry receptors, but evidence that CXCR4 or CCR5 blockade reduces rewarding and locomotor-stimulant effects of psychostimulants in rats suggests a role in psychostimulant use disorders. We investigated the impact of CXCR4 or CCR5 receptor antagonism on anxiety-related effects of the synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV) in the elevated zero-maze (EZM) assay. Rats exposed to a 4-day MDPV binge dosing paradigm and tested 24 or 72 h post-treatment spent more time in the open compartment at the 24-h time point but less time at the 72-h post-binge time point. Daily administration of AMD 3100, a CXCR4 antagonist (10 mg/kg), or maraviroc, a CCR5 antagonist (2.5 mg/kg), during MDPV treatment inhibited the MDPV-induced increase in time spent in the open compartment. Neither antagonist affected the MDPV-induced reduction in time spent in the open compartment at the 72-h post-binge time point. Cocaine, administered in the same paradigm as MDPV, did not increase time spent in the open compartment 24-h post-binge, suggesting specificity to MDPV. The present results identify a surprising anxiolytic-like effect of MDPV 24 h after cessation of repeated exposure that is sensitive to chemokine CXCR4 and CCR5 receptor activity.

Evaluating a school-based science program that teaches the physiological effects of nicotine.

School-based drug prevention programs represent a widely endorsed public health goal, with an important aspect of knowledge-based curricula being education about the physiological effects of drugs. Nicotine is one of the world's most addictive substances and in this program we have used nicotine-induced mammalian-like behaviors in flatworms called planarians to successfully teach students (4th-12th grade; n = 1,616 students) about the physiological and addictive effects of nicotine. An initial study tested the change in knowledge about addictive substances in 6th-12th grade students after they completed a lab examining the effects of two concentrations of nicotine on the number of stereotypies (C-shaped spasms) planarians demonstrate in a 5-minute period of time. Lab discussion focused on developing and testing hypotheses, measurement reliability, and mechanisms of nicotine action. Surveys given pre- and post-lab experience showed that 6th grade students have significantly lower knowledge about nicotine than 7th-12th grade students (6th grade: 40.65 ± 0.78% correct, 7th-12th grade: 59.29 ± 1.71%, p < 0.001) pre-lab, but that students in all grades showed a significant increase in knowledge post-lab (p < 0.001). In 6th grade the lab was effective in improving knowledge about nicotine in urban, suburban and rural schools, p < 0.001, with students in suburban schools showing significantly greater knowledge both pre-test (urban: 37.62 ± 1.45%; suburban: 48.78 ± 1.62%; rural: 37.33 ± 0.99%; p < 0.001) and post-test (urban:60.60 ± 1.85%; suburban: 67.54 ± 1.82%; urban: 61.66 ± 1.18%; p < 0.001). A second study, modifying the lab so that the time spent observing the planarians is reduced to a 1-minute period, showed that students in both 4th and 5th grades had a significant increase in knowledge about the physiological and addictive effects of nicotine post-lab (p < 0.001).

Mitragynine, bioactive alkaloid of kratom, reduces chemotherapy-induced neuropathic pain in rats through α-adrenoceptor mechanism.

BACKGROUND AND PURPOSE: Kratom is a coffee-like plant containing compounds that cause opioid and stimulant effects. The most prevalent bioactive alkaloid of kratom is mitragynine (MG). Opioid effects of MG are apparent (e.g. antinociception and nanomolar affinity for µ, κ and δ opioid receptors), but effects encompassing interactions with additional systems, such as adrenergic and dopaminergic, remain undefined. Given that enhanced adrenergic transmission is a mechanism common to most first-line neuropathic pain medications, we tested the hypothesis that MG reduces chemotherapy-induced neuropathic pain through a mechanism involving α-adrenoceptor activation. METHODS: Rats were injected once with oxaliplatin (6 mg/kg IP) to induce allodynia and then treated with MG (0, 1, 5, 10 mg/kg IP) for 5-7 days. To investigate receptor mechanisms, a fixed dose of MG (5 mg/kg IP) was injected with yohimbine (5 mg/kg IP, α2-adrenoceptor antagonist), prazosin (5 mg/kg IP, α1-adrenoceptor antagonist), or naltrexone (5 mg/kg IP, opioid antagonist). KEY RESULTS: MG (5, 10 mg/kg) dose-dependently reduced mechanical sensitivity in oxaliplatin-injected rats. Anti-allodynic effects of MG were completely inhibited by yohimbine, and significantly reduced by prazosin and naltrexone. MG produced modest hyperlocomotion but only at a dose (30 mg/kg) higher than those required to reduce allodynia. CONCLUSION AND IMPLICATION: The finding that MG reduced neuropathic pain through a mechanism requiring active α-adrenoceptors indicates that the pharmacological profile of MG includes activation of adrenergic, as well as opioid, systems.

Chemokine CCR5 and cocaine interactions in the brain: Cocaine enhances mesolimbic CCR5 mRNA levels and produces place preference and locomotor activation that are reduced by a CCR5 antagonist.

C-C chemokine receptor type 5, also known as CCR5 or CD195, is best known as a viral co-receptor that facilitates entry of HIV into cells. Evidence that CCR5 knockout mice display fewer dopamine neurons, lower striatal dopamine levels, and reduced locomotor activation compared to wild types also suggest a link between CCR5 receptors and cocaine dependence. Here, we tested the hypothesis using male Sprague-Dawley rats that cocaine-induced locomotor activation and conditioned place preference (CPP) are inhibited by a FDA-approved CCR5 antagonist (maraviroc), and that CCR5 gene expression in mesolimbic substrates is enhanced by repeated cocaine exposure. Pretreatment with maraviroc (1, 2.5, 5 mg/kg, IP) reduced hyperlocomotion induced by acute cocaine (10 mg/kg) without affecting spontaneous locomotor activity. For CPP experiments, rats conditioned with cocaine (10 mg/kg × 4 days, IP) were injected with maraviroc (1, 2.5, 5 mg/kg, IP) before each injection of cocaine. Maraviroc dose-dependently inhibited development of cocaine CPP, with a dose of 5 mg/kg producing a significant reduction. In rats treated repeatedly with cocaine (10 mg/kg × 4 days, IP), CCR5 gene expression was upregulated in the nucleus accumbens and ventral tegmental area but mRNA levels of CCR5 ligands (i.e., CCL3, CCL4 and CCL5) were not affected. Our results suggest that mesolimbic CCR5 receptors are dysregulated by cocaine exposure and, similar to CXCR4 and CCR2 receptors, influence behavioral effects related to the abuse liability of cocaine.

Predator odor produces anxiety-like behavioral phenotype in planarians that is counteracted by fluoxetine.

Avoidant behavior is a characteristic feature post-traumatic stress disorder (PTSD) and is modeled in mammals with predator odor. Light avoidance is a hallmark behavioral reaction in planarians. We hypothesized that planarians exposed to frog extract would display enhanced light avoidance that is prevented by fluoxetine. Enhanced light avoidance (i.e., less time spent in light compartment of a dish split into light and dark sides) after a 30-min frog extract exposure (0.0001-0.01%) manifested 15 min post-exposure, persisted for at least 24 h, and was counteracted by fluoxetine (10 µM). These results suggest conservation of an anxiety-like behavioral phenotype.

Mu Opioid Receptor Agonist DAMGO Produces Place Conditioning, Abstinence-induced Withdrawal, and Naltrexone-Dependent Locomotor Activation in Planarians.

Unlike the behavioral effects planarians display when exposed to cocaine, amphetamines, cathinones, ethanol and sucrose, effects of opioid receptor agonists, especially mu opioid receptor agonists, are poorly defined in these flatworms. Here, we tested the hypothesis that planarians exposed to a selective mu opioid receptor agonist, DAMGO (0.1, 1, 10 µM), would display a triad of opioid-like effects (place conditioning, abstinence-induced withdrawal, and motility changes). DAMGO was selected versus morphine because of its greater mu opioid receptor selectivity. In place conditioning and abstinence experiments, the planarian light/dark test (PLDT) was utilized (i.e., planarians are placed into a petri dish containing water that is split into light and dark compartments and time spent in the compartments is determined). Planarians conditioned with DAMGO (1 µM) spent more time on the drug-paired side compared to water controls. In abstinence experiments, planarians exposed to DAMGO for 30 min were removed and then placed into water, where light avoidance (e.g. defensive responding) and depressant-like effects (i.e., decreased motility) were quantified. Compared to water controls, DAMGO-withdrawn planarians spent less time in the light (10 µM) and displayed decreased motility (1, 10 µM). Acute DAMGO exposure (1 µM) produced hypermotility that was antagonized by naltrexone (1, 10, 100 µM). In contrast, acute exposure to the kappa opioid receptor agonist U50,488H (0.1, 1, 10 µM) resulted in decreased motility. Our results show that a mu opioid agonist produces mammalian-like behavioral responses in planarians that may be related to addiction and suggest opioid-like behavioral effects are conserved in invertebrates.

Chemokines and 'bath salts': CXCR4 receptor antagonist reduces rewarding and locomotor-stimulant effects of the designer cathinone MDPV in rats.

BACKGROUND AND PURPOSE: Little is known about how chemokine systems influence the behavioral effects of designer cathinones and psychostimulants. The chemokine CXCL12 and its principal receptor target, CXCR4, are of particular interest because CXCR4 activation enhances mesolimbic dopamine output that facilitates psychostimulant reward, reinforcement, and locomotor activation. Repeated cocaine enhances CXCL12 gene expression in the midbrain and produces conditioned place preference (CPP) that is inhibited by a CXCR4 antagonist. Yet, interactions between chemokines and synthetic cathinones remain elusive. METHODS: We tested the hypothesis that an FDA-approved CXCR4 antagonist (AMD3100) inhibits MDPV-induced reward, locomotor activation and positive affective state in rats using a triad of behavioral assays (CPP, open field, and 50-kHz ultrasonic vocalizations [USVs]). KEY RESULTS: AMD3100 (1, 2.5, 5, 10 mg/kg, ip) significantly reduced MDPV (2 mg/kg, ip)-evoked hyper-locomotion in a dose-related manner. AMD3100 (1, 5, 10 mg/kg) administered during CPP conditioning caused a significant, dose-dependent reduction of MDPV (2 mg/kg x 4 days) place preference. MDPV injection elicited significantly greater 50 kHz USVs in vehicle-pretreated rats but not in AMD3100-pretreated rats. CONCLUSION AND IMPLICATION: A CXCR4 antagonist reduced the rewarding and locomotor-activating effects of MDPV. Our results identify the existence of chemokine/cathinone interactions and suggest the rewarding and stimulant effects of MDPV, similar to cocaine, require an active CXCL12/CXCR4 system.

Dopamine D1-Like Receptor Agonist and D2-Like Receptor Antagonist (-)-Stepholidine Reduces Reinstatement of Drug-Seeking Behavior for 3,4-Methylenedioxypyrovalerone (MDPV) in Rats.

Psychostimulant reinforcement is mediated by stimulation of both dopamine (DA) D1-like and D2-like receptors, suggesting that pharmacotherapy agents with a dual DA receptor mechanism may be useful for managing psychostimulant abuse. (-)-Stepholidine (L-SPD) is a Chinese herbal extract that functions as a D1-like receptor agonist and D2-like receptor antagonist. L-SPD has been shown to attenuate the reinforcing effects of heroin; however, its effects on the synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV) have not been examined. The current study determined the effects of L-SPD on reinstatement of MDPV-seeking behavior in the drug intravenous self-administration (IVSA) and conditioned place preference (CPP) paradigms. To determine whether the effects of L-SPD were specific to psychostimulant reinforcement, we also examined its effects on sucrose-seeking behavior. Using a locomotor activity assay, we tested the locomotor effects of L-SPD, as well as its effects on MDPV-induced hyperactivity. The results of a battery of in vitro binding and functional assays confirmed that L-SPD functioned as a D1-like receptor agonist and D2-like receptor antagonist. In behavioral experiments, L-SPD dose-dependently attenuated cue plus MDPV-primed reinstatement of MDPV-seeking behavior in the IVSA model. The highest dose of L-SPD also attenuated MDPV-primed reinstatement of MDPV CPP, as well as cue-induced reinstatement of sucrose-seeking. L-SPD had no significant locomotor effects, and did not modulate the robust hyperactivity induced by MDPV. The current findings show for the first time a robust reinstatement effect with MDPV, which can be reduced by L-SPD. These results establish a role for DA receptors in drug-seeking behavior for MDPV.

Glutamate carboxypeptidase II (GCPII) inhibitor 2-PMPA reduces rewarding effects of the synthetic cathinone MDPV in rats: a role for N-acetylaspartylglutamate (NAAG).

RATIONALE: Metabotropic glutamate 2 and 3 (mGluR2/3) receptors are implicated in drug addiction as they limit excessive glutamate release during relapse. N-acetylaspartylglutamate (NAAG) is an endogenous mGluR2/3 agonist that is inactivated by the glutamate carboxypeptidase II (GCPII) enzyme. GCPII inhibitors, and NAAG itself, attenuate cocaine-seeking behaviors. However, their effects on the synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV) have not been examined. OBJECTIVES: We determined whether withdrawal following repeated MDPV administration alters GCPII expression in corticolimbic regions. We also examined whether a GCPII inhibitor (2-(phosphonomethyl)-pentanedioic acid (2-PMPA)), and NAAG, reduce the rewarding and locomotor-stimulant effects of MDPV in rats. METHODS: GCPII was assessed following repeated MDPV exposure (7 days). The effects of 2-PMPA and NAAG on acute MDPV-induced hyperactivity were determined using a locomotor test. We also examined the inhibitory effects of 2-PMPA and NAAG on MDPV-induced place preference, and whether the mGluR2/3 antagonist LY341495 could prevent these effects. RESULTS: MDPV withdrawal reduced GCPII expression in the prefrontal cortex. Systemic injection of 2-PMPA (100 mg/kg) did not affect the hyperactivity produced by MDPV (0.5-3 mg/kg). However, nasal administration of NAAG did reduce MDPV-induced ambulation, but only at the highest dose (500 µg/10 µl). We also showed that 2-PMPA (10-30 mg/kg) and NAAG (10-500 µg/10 µl) dose-dependently attenuated MDPV place preference, and that the effect of NAAG was blocked by LY341495 (3 mg/kg). CONCLUSIONS: These findings demonstrate that MDPV withdrawal produces dysregulation in the endogenous NAAG-GCPII signaling pathway in corticolimbic circuitry. Systemic administration of the GCPII inhibitor 2-PMPA, or NAAG, attenuates MDPV reward.

Synthetic cathinone MDPV downregulates glutamate transporter subtype I (GLT-1) and produces rewarding and locomotor-activating effects that are reduced by a GLT-1 activator.

Synthetic cathinones produce dysregulation of monoamine systems, but their effects on the glutamate system and the influence of glutamate on behavioral effects related to cathinone abuse are unknown. A principal regulator of glutamate homeostasis is glutamate transporter subtype 1 (GLT-1), an astrocytic protein that clears glutamate from the extracellular space and influences behavioral effects of established psychostimulants. We hypothesized that repeated administration of the synthetic cathinone, MDPV (3,4-methylenedioxypyrovalerone), would affect GLT-1 expression in the corticolimbic circuit, and that a GLT-1 activator (ceftriaxone, CTX) would reduce rewarding and locomotor-stimulant effects of MDPV in rats. GLT-1 protein expression in the nucleus accumbens (NAcc), but not prefrontal cortex (PFC), was decreased following withdrawal (2, 5 and 10 days) from repeated MDPV treatment, but not immediately after the last MDPV injection. CTX (200 mg/kg) pretreatment did not affect acute locomotor activation produced by MDPV (0.5, 1, 3 mg/kg). However, CTX (200 mg/kg) administered during a 7-day MDPV treatment paradigm attenuated the development of MDPV-induced sensitization of repetitive movements in rats challenged with MDPV following 11 days of drug abstinence. Pretreatment with CTX (200 mg/kg) during a 4-day MDPV (2 mg/kg) conditioned place preference (CPP) paradigm reduced the development of place preference produced by MDPV. The present data demonstrate dysregulation of corticolimbic glutamate transport systems during withdrawal from chronic MDPV exposure, and show that a GLT-1 transporter activator disrupts behavioral effects of MDPV that are related to synthetic cathinone abuse.