Suppressing effect of CMPPE, a new positive allosteric modulator of the GABAB receptor, on alcohol self-administration and reinstatement of alcohol seeking in rats

Positive allosteric modulators (PAMs) of the GABAB receptor constitute a class of pharmacological agents gaining increasing attention in the alcohol research field because of their ability to suppress several alcohol-related behaviors in rodents. CMPPE is a novel GABAB PAM, still limitedly characterized in vivo. It was therefore of interest to test its ability to affect operant, oral self-administration of alcohol and cueinduced reinstatement of alcohol seeking in alcohol-preferring rats. To this end, female Sardinian alcohol-preferring (sP) rats were trained to lever-respond for alcohol (15% v/v) under the fixed ratio (FR) 5 (FR5) schedule of reinforcement. Once lever-responding had stabilized, rats were exposed to test sessions (under the FR5 [Experiment 1] and progressive ratio [PR; Experiment 2] schedules of reinforcement) preceded by treatment with CMPPE (0, 2.5, 5, and 10 mg/kg; intraperitoneally [i.p.]). In Experiment 3, once lever-responding had stabilized, rats underwent an extinction responding phase and then a single reinstatement session during which lever-responding was resumed by the non-contingent presentation of a complex of alcohol-associated cues; CMPPE (0, 2.5, 5, and 10 mg/kg; i.p.) was administered before the reinstatement session. Selectivity of CMPPE actionwas assessed by evaluating the effect of CMPPE (0, 2.5, 5, and 10 mg/kg; i.p.) on self-administration of a chocolate solution in male Wistar rats (Experiment 4). In Experiments 1 and 2, treatment with 5 and 10 mg/kg CMPPE reduced lever-responding and breakpoint for alcohol. In Experiment 3, treatment with 5 and 10 mg/kg CMPPE suppressed reinstatement of alcohol seeking. In Experiment 4, no dose of CMPPE affected lever-responding for the chocolate solution. These results extend to CMPPE the ability of all previously tested GABAB PAMs to affect alcohol-motivated behaviors in rodents and confirm that these effects are a shared feature of the entire class of GABAB PAMs. This conclusion is of relevance in view of the forthcoming transition of GABAB PAMs to clinical testing

Operant, oral alcohol self-administration: Sex differences in Sardinian alcohol-preferring rats

Sardinian alcohol-preferring (sP) rats have been selectively bred, over almost forty years and for more than 100 generations, for high alcohol preference and consumption. Rats of the sP line have served as animal model of excessive alcohol consumption for more than 120 published studies. With very few exceptions however, these studies have always employed male sP rats, and little is known on alcohol-related behaviors in female sP rats. The present study was designed to fill, at least in part, this gap. To this end, operant self-administration of alcohol under the fixed ratio 4 schedule of reinforcement was compared between male, intact female, and ovariectomized female sP rats. Additional aims were (i) investigation of whether, and to which extent, estrous cycle influenced alcohol self-administration in sP rats and (ii) investigation of whether alcohol selfadministration in male, intact female, and ovariectomized female sP rats differed in sensitivity to pharmacological manipulation. Lever-responding for alcohol resulted to be steadily higher in male than intact and ovariectomized female sP rats; conversely, because of large sex differences in rat body weight, estimated amount of self-administered alcohol (expressed in g/kg) did not differ among the 3 sP rat groups or occasionally resulted to be higher in intact female than male and ovariectomized female sP rats. Blood alcohol levels deriving from self-administered alcohol (i) did not differ among the 3 sP rat groups, (ii) achieved values known to result in measurable psychopharmacological effects, and (iii) positively correlated with both number of lever-responses for alcohol and estimated amount of self-administered alcohol. Treatment with both the opioid receptor antagonist, naloxone (0, 0.3, 1, and 3 mg/kg, i.p.), and the positive allosteric modulator of the GABAB receptor, GS39783 (0, 25, 50, and 100 mg/kg, i.g.), reduced alcohol self-administration with comparable potency and efficacy in the 3 sP rat groups. Impact of estrous cycle on alcohol self-administration was relatively modest, limited to a tendency toward a reduction in number of lever-responses for alcohol and estimated amount of self-administered alcohol in estrus and metestrus. Together, the results of the present study provide the first characterization of alcoholseeking and -taking behavior in female sP rats

Reducing effect of saikosaponin A, an active ingredient of Bupleurum falcatum, on alcohol self-administration in rats: Possible involvement of the GABAB receptor

Recent studies demonstrated that treatment with saikosaponin A (SSA) - an active ingredient of the medicinal herb, Bupleurum falcatum L. - selectively suppressed, likely via a GABAB receptor-mediated mechanism, intravenous self-administration of morphine and cocaine in rats [Yoon et al., 2012; 2013]. The present study was designed to investigate whether the capacity of SSA to suppress morphine and cocaine self-administration extends to oral alcohol self-administration. To this end, selectively bred Sardinian alcohol-preferring (sP) rats were trained to lever-respond on a Fixed Ratio (FR) 4 (FR4) schedule of reinforcement for alcohol (15%, v/v) in daily 30-min sessions. Once responding had stabilized, rats were tested under the FR4 (measure of alcohol reinforcing properties) and Progressive Ratio (PR; measure of alcohol motivational properties) schedules of reinforcement. The possible involvement of the GABAB receptor system was investigated testing the effect of (a) pretreatment with the GABAB receptor antagonist, SCH50911, and (b) combined treatment with the positive allosteric modulator of the GABAB receptor, GS39783. Treatment with SSA (0, 0.25, 0.5, and 1 mg/kg, i.p.) markedly reduced lever-responding for alcohol, amount of self-administered alcohol, and breakpoint for alcohol (defined as the lowest response requirement not achieved in the PR experiment). Pretreatment with 2 mg/kg SCH50911 (i.p.) resulted in a partial blockade of the reducing effect of 0.5 mg/kg SSA on lever-responding for alcohol and amount of self-administered alcohol. Combination of per se ineffective doses of GS39783 (5 mg/kg, i.g.) and SSA (0.1 mg/kg, i.p.) reduced lever-responding for alcohol and amount of self-administered alcohol. These results (a) extend to alcohol self-administration the capacity of SSA to suppress morphine and cocaine self-administration in rats and (b) suggest that the GABAB receptor system is likely part of the neural substrate underlying the reducing effect of SSA on alcohol self-administration

Suppressing effect of COR659 on alcohol, sucrose, and chocolate self-administration in rats: Involvement of the GABAB and cannabinoid CB1 receptors

Rationale and objectives COR659 [methyl2-(4-chlorophenylcarboxamido)-4-ethyl-5-methylthiophene-3-carboxylate] is a new, positive allosteric modulator (PAM) of the GABAB receptor. This study evaluated whether COR659 shared with previously tested GABAB PAMs the capacity to reduce alcohol self-administration in rats. Results Treatment with non-sedative doses of COR659 (2.5, 5, and 10 mg/kg; i.p.) suppressed lever-responding for alcohol (15% v/v) in Sardinian alcohol-preferring (sP) rats under the fixed ratio (FR) 4 (FR4) and progressive ratio (PR) schedules of reinforcement; COR659 was more potent and effective than the reference GABAB PAM, GS39783. Treatment with COR659, but not GS39783, suppressed (a) lever-responding for a sucrose solution (1–3% w/v) in sP rats under the FR4 and PR schedules, (b) lever-responding for a chocolate solution [5% (w/v) Nesquik®] in Wistar rats under the FR10 and PR schedules, and (c) cue-induced reinstatement of chocolate seeking in Wistar rats. Treatment with COR659 was completely ineffective on lever-responding (FR10) for regular food pellets in food-deprived Wistar rats. Pretreatment with the GABAB receptor antagonist, SCH50911, partially blocked COR659-induced reduction of alcohol self-administration, being ineffective on reduction of chocolate self-administration. Pretreatment with the cannabinoid CB1 receptor antagonist, AM4113, fully blocked COR659-induced reduction of chocolate self-administration, being ineffective on reduction of alcohol self-administration. Conclusions COR659 might exert its behavioral effects via a composite mechanism: (i) positive allosteric modulation of the GABAB receptor, responsible for a large proportion of reduction of alcohol self-administration; (ii) an action at other receptor system(s), including the cannabinoid CB1 receptor, through which COR659 affects seeking and consumption of highly palatable foods

Anti-addictive properties of COR659 – Additional pharmacological evidence and comparison with a series of novel analogues

A recent study found that COR659 (methyl 2-[(4-chlorophenyl)carboxamido]-4-ethyl-5-methylthiophene-3-carboxylate) reduced operant alcohol and chocolate self-administration in rats; COR659 also suppressed cue-induced reinstatement of chocolate seeking in rats. COR659 apparently exerts its effects via a composite mechanism, including positive allosteric modulation of the GABAB receptor and an action at the cannabinoid CB1 receptor. The present study investigated whether the reducing effect of COR659 on alcohol and chocolate self-administration was maintained after repeated treatment and if COR659 affected cue-induced reinstatement of alcohol seeking; additionally, it evaluated the ability of 9 structural analogues of COR659 – designed modifying the substituents on the phenylcarboxamido moiety and replacing the thiophene with the pyridine ring – to affect alcohol and chocolate self-administration. Alcohol self-administration experiments employed Sardinian alcohol-preferring (sP) rats trained to lever-respond for alcohol (15% v/v). Chocolate self-administration experiments employed Wistar rats trained to lever-respond for a chocolate solution (5% w/v Nesquik®). In the reinstatement experiment, previously extinguished lever-responding for alcohol in sP rats was reinstated by the non-contingent presentation of an alcohol-associated complex of cues. All drugs were tested at the doses of 0, 2.5, 5, and 10 mg/kg (i.p.). 10-Day treatment with COR659 produced a dose-related reduction of both alcohol and chocolate self-administration, with limited loss of efficacy on continuing treatment. Acute COR659 suppressed reinstatement of alcohol seeking. Among the 9 tested analogues, only COR657 (methyl 2-(benzoylamino)-4-ethyl-5-methylthiophene-3-carboxylate) decreased alcohol self-administration similarly to COR659; all other compounds produced modest, or even no, effect on alcohol self-administration. COR659 excluded, no compound altered chocolate self-administration. These results confirm and extend the ability of COR659 to reduce several behaviors motivated by alcohol and palatable food in rats. Comparison of COR659 to its analogues provided disparate results that do not currently allow any conclusive structure-activity relationship to be hypothesized, as their diverse pharmacological profile apparently does not depend on physicochemical properties

Suppressing effect of saikosaponin A, an active ingredient of Bupleurum falcatum, on chocolate self-administration and reinstatement of chocolate seeking in rats

Recent lines of experimental evidence have indicated that saikosaponin A (SSA) - a bioactive ingredient of the medicinal plant, Bupleurum falcatum L. - suppressed alcohol, morphine, and cocaine self-administration in rats. The present paper was designed to assess whether the protective properties of SSA on addiction-related behaviors generalize to a hyperpalatable food such as a chocolate-flavored beverage (CFB). To this end, rats were initially trained to lever-respond for CFB [5% (w/v) Nesquik(®) powder in water] under fixed ratio (FR) 10 (FR10) schedule of reinforcement. Once lever-responding reached stable levels, rats were treated acutely with two different dose ranges of SSA (0, 0.25, 0.5, and 1mg/kg; 0, 1, 2.5, and 5mg/kg; i.p.) and exposed to the FR10 and progressive ratio (PR) schedules of reinforcement in four independent experiments. The effect of acutely administered SSA (0, 0.25, 0.5, and 1mg/kg; i.p.) on cue-induced reinstatement of seeking behavior for CFB was also assessed. Under the FR and PR schedules of reinforcement, treatment with SSA diminished lever-responding for CFB, amount of self-administered CFB, and breakpoint for CFB. All variables were virtually completely suppressed after treatment with 5mg/kg SSA. Treatment with SSA also suppressed reinstatement of CFB-seeking behavior. No dose of SSA altered rat motor-performance, evaluated exposing all rats to an inverted screen test immediately after the self-administration session. These results demonstrate that acute treatment with SSA potently suppressed several addictive-like behaviors motivated by highly hedonic nourishment. These data extend to a highly rewarding natural stimulus the anti-addictive properties of SSA recently disclosed in rats self-administering alcohol, morphine, and cocain

Anxiety-like behaviors at the end of the nocturnal period in sP rats with a “history” of unpredictable, limited access to alcohol.

10nononeRecent research found that exposure of selectively bred, Sardinian alcohol-preferring (sP) rats to multiple alcohol concentrations (10%, 20%, and 30%, v/v), under the 4-bottle "alcohol vs. water" choice regimen, in daily 1-h drinking sessions with an unpredictable time schedule, promoted high intakes of alcohol (≥2 g/kg) when the drinking session occurred over the final hours of the dark phase of the light/dark cycle. The present study investigated whether these high intakes of alcohol (a) were associated with alterations in rats' emotional state (Experiment 1) and (b) were pharmacologically manipulable (Experiment 2). In both experiments, over a period of 12 days, sP rats were initially exposed daily to a 1-h drinking session during the dark phase; time of alcohol exposure was changed each day and was unpredictable to rats. The day after this 12-day drinking phase, rats were (a) exposed to the Social Interaction (SI) test at the 1st or 12th hour of the dark phase with no alcohol available (Experiment 1) or (b) treated with the positive allosteric modulator of the GABAB receptor, GS39783 (0, 25, 50, and 100 mg/kg, intragastrically [i.g.]), and exposed to a drinking session at the 12th hour of the dark phase (Experiment 2). In Experiment 1, rats exposed to the SI test during the 12th hour spent approximately 35% less time in "social" behaviors than rats exposed to the SI test during the 1st hour. No difference in "social" behaviors was observed between alcohol-naive sP rats exposed to the SI test at the 1st and 12th hour. In Experiment 2, all doses of GS39783 selectively reduced alcohol intake. These results suggest that (a) expectation of alcohol availability likely exacerbated the anxiety-like state of sP rats and (b) the GABAB receptor is part of the neural substrate underlying these exceptionally high intakes of alcohol in sP rats.openColombo, G.; Lobina, C.; Maccioni, P.; Carai, M. A. M.; Lorrai, I.; Zaru, A.; Contini, A.; Mugnaini, Claudia; Corelli, Federico; Gessa, G.Colombo, G.; Lobina, C.; Maccioni, P.; Carai, M. A. M.; Lorrai, I.; Zaru, A.; Contini, A.; Mugnaini, Claudia; Corelli, Federico; Gessa, G

Suppressing effect of the novel positive allosteric modulator of the GABAB receptor, COR659, on locomotor hyperactivity induced by different drugs of abuse

COR659 is a recently synthesized positive allosteric modulator (PAM) of the GABAB receptor. Similarly to all GABAB PAMs tested to date, COR659 has been reported to suppress different alcohol-related behaviors in rodents. The present study was designed to assess whether the anti-addictive properties of COR659 extend to drugs of abuse other than alcohol. Specifically, it investigated the effect of COR659 on cocaine-, amphetamine-, nicotine-, and morphine-induced locomotor hyperactivity in mice. To this aim, independent groups of CD1 mice were acutely pretreated with COR659 (0, 10, and 20 mg/kg; i.p.), then acutely treated with cocaine (0 and 10 mg/kg, s.c.), amphetamine (0 and 5 mg/kg; s.c.), nicotine (0 and 0.05 mg/kg; s.c.), or morphine (0 and 20 mg/kg; s.c.), and finally exposed for 60 min to a photocell-equipped motility cage. When given alone, both doses of COR659 were ineffective on spontaneous locomotor activity. Pretreatment with COR659 reduced, or even suppressed, the increase in motility counts induced by cocaine, amphetamine, nicotine, and morphine. Since locomotor hyperactivity is an attribute common to drugs of abuse, the results of the present study constitute the first line of evidence on the extension of the preclinical, anti-addictive profile of COR659 to cocaine, amphetamine, nicotine, and morphine

Increases in compulsivity, inflammation, and neural injury in HIV transgenic rats with escalated methamphetamine self-administration under extended-access conditions

The abuse of stimulants, such as methamphetamine (METH), is associated with treatment non-compliance, a greater risk of viral transmission, and the more rapid clinical progression of immunological and central nervous system human immunodeficiency virus (HIV) disease. The behavioral effects of METH in the setting of HIV remain largely uncharacterized. We used a state-of-the-art paradigm of the escalation of voluntary intravenous drug self-administration in HIV transgenic (Tg) and wildtype rats. The rats were first allowed to self-administer METH under short-access (ShA) conditions, which is characterized by a nondependent and more "recreational" pattern of METH use, and then allowed to self-administer METH under long-access (LgA) conditions, which leads to compulsive (dependent) METH intake. HIV Tg and wildtype rats self-administered equal amounts of METH under ShA conditions. HIV Tg rats self-administered METH under LgA conditions following a 4-week enforced abstinence period to model the intermittent pattern of stimulant abuse in humans. These HIV Tg rats developed greater motivation to self-administer METH and self-administered larger amounts of METH. Impairments in function of the medial prefrontal cortex (mPFC) contribute to compulsive drug and alcohol intake. Gene expression profiling of the mPFC in HIV Tg rats with a history of escalated METH self-administration under LgA conditions showed transcriptional evidence of increased inflammation, greater neural injury, and impaired aerobic glucose metabolism than wildtype rats that self-administered METH under LgA conditions. The detrimental effects of the interaction between neuroHIV and escalated METH intake on the mPFC are likely key factors in the greater vulnerability to excessive drug intake in the setting of HIV