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Reinforcing effects of compounds lacking intrinsic efficacy at α1 subunit-containing GABAA receptor subtypes in midazolam- but not cocaine-experienced rhesus monkeys.

ABSTRACT: Benzodiazepines are prescribed widely but their utility is limited by unwanted side effects, including abuse potential. The mechanisms underlying the abuse-related effects of benzodiazepines are not well understood, although α1 subunit-containing GABAA receptors have been proposed to have a critical role. Here, we examine the reinforcing effects of several compounds that vary with respect to intrinsic efficacy at α2, α3, and α5 subunit-containing GABAA receptors but lack efficacy at α1 subunit-containing GABAA receptors ('α1-sparing compounds'): MRK-623 (functional selectivity for α2/α3 subunit-containing receptors), TPA023B (functional selectivity for α2/α3/α5 subunit-containing receptors), and TP003 (functional selectivity for α3 subunit-containing receptors). The reinforcing effects of the α1-sparing compounds were compared with those of the non-selective benzodiazepine receptor partial agonist MRK-696, and non-selective benzodiazepine receptor full agonists, midazolam and lorazepam, in rhesus monkeys trained to self-administer midazolam or cocaine, under a progressive-ratio schedule of intravenous (i.v.) drug injection. The α1-sparing compounds were self-administered significantly above vehicle levels in monkeys maintained under a midazolam baseline, but not under a cocaine baseline over the dose ranges tested. Importantly, TP003 had significant reinforcing effects, albeit at lower levels of self-administration than non-selective benzodiazepine receptor agonists. Together, these results suggest that α1 subunit-containing GABAA receptors may have a role in the reinforcing effects of benzodiazepine-type compounds in monkeys with a history of stimulant self-administration, whereas α3 subunit-containing GABAA receptors may be important mediators of the reinforcing effects of benzodiazepine-type compounds in animals with a history of sedative-anxiolytic/benzodiazepine self-administration.

SUBMITTER: Shinday NM

PROVIDER: S-EPMC3629390 | biostudies-other | 2013 May

REPOSITORIES: biostudies-other

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Project description:BackgroundAlcohol's ability to potentiate the activity of γ-aminobutyric acid (GABA) at GABAA receptors has been implicated as a key mechanism underlying the behavioral effects of alcohol. The complex molecular biology of these receptors raises the possibility that particular receptor subtypes may play unique roles in alcohol's abuse-related effects and that subtype-selective ligands with therapeutic specificity against alcohol might be developed. This study evaluated the capacity of α5GABAA receptor ligands to alter selectively the reinforcing effects of alcohol.MethodsTwo groups of rhesus monkeys were trained to orally self-administer alcohol or sucrose under fixed-ratio schedules and limited daily access conditions. In addition, following daily self-administration sessions, the behavior of each monkey was scored for both species-typical and drug-induced behaviors.ResultsConcentrations of 1 to 6% alcohol maintained self-administration above water levels, engendered pharmacologically relevant blood alcohol levels ranging from 90 to 160 mg/dl, and produced changes in behavior typical of alcohol intoxication. Concentrations of 0.3 to 3% sucrose also reliably maintained self-administration. The α5GABAA receptor agonist QH-ii-066 enhanced and the α5GABAA receptor inverse agonist L-655,708 inhibited alcohol, but not sucrose drinking. The changes in alcohol drinking could be reversed with the α5GABAA receptor antagonist XLi-093. However, L-655,708 increased yawning in both alcohol and sucrose drinkers, possibly indicative of an anxiogenic effect.ConclusionsThese findings suggest a prominent and specific role for α5GABAA receptor mechanisms in the reinforcing effects of alcohol. Moreover, these results suggest that α5GABAA receptors may represent a novel pharmacological target for the development of medications to reduce drinking. Of ligands modulating this receptor, α5GABAA receptor inverse agonists may hold the most promise as alcohol pharmacotherapies.

Project description:Introduction Benzodiazepines (BZs) are prescribed as anxiolytics, but their use is limited by side effects including abuse liability and daytime drowsiness. Neuroactive steroids are compounds that, like BZs, modulate the effects of GABA at the GABAA receptor. In a previous study, combinations of the BZ triazolam and neuroactive steroid pregnanolone produced supra-additive (i.e., greater than expected effects based on the drugs alone) anxiolytic effects but infra-additive (i.e., lower than expected effects based on the drugs alone) reinforcing effects in male rhesus monkeys, suggestive of an improved therapeutic window. Methods Female rhesus monkeys (n=4) self-administered triazolam, pregnanolone, and triazolam-pregnanolone combinations intravenously under a progressive-ratio schedule. In order to assess characteristic sedative-motor effects of BZ-neuroactive steroid combinations, female rhesus monkeys (n=4) were administered triazolam, pregnanolone, and triazolam-pregnanolone combinations. Trained observers, blinded to condition, scored the occurrence of species-typical and drug-induced behaviors. Results In contrast to our previous study with males, triazolam-pregnanolone combinations had primarily supra-additive reinforcing effects in three monkeys but infra-additive reinforcing effects in one monkey. Scores for deep sedation (i.e., defined as atypical loose-limbed posture, eyes closed, does not respond to external stimuli) and observable ataxia (any slip, trip, fall, or loss of balance) were significantly increased by both triazolam and pregnanolone. When combined, triazolam-pregnanolone combinations had supra-additive effects for inducing deep sedation, whereas observable ataxia was attenuated, likely due to the occurrence of robust sedative effects. Discussion These results suggest that significant sex differences exist in self-administration of BZ-neuroactive steroid combinations, with females likely to show enhanced sensitivity to reinforcing effects compared with males. Moreover, supra-additive sedative effects occurred for females, demonstrating a higher likelihood of this adverse effect when these drug classes are combined.

Project description:The reinforcing effects and long-term consequences of cocaine self-administration have been associated with brain regions of the mesolimbic dopamine pathway, namely the nucleus accumbens (NAc). Studies of cocaine-induced biochemical adaptations in rodent models have advanced our knowledge; however, unbiased detailed assessments of intracellular alterations in the primate brain are scarce, yet essential, to develop a comprehensive understanding of cocaine addiction. To this end, two-dimensional difference in gel electrophoresis (2D-DIGE) was used to compare changes in cytosolic protein abundance in the NAc between rhesus monkeys self-administering cocaine and controls. Following image normalization, spots with significantly differential image intensities (P<0.05) were identified, excised, trypsin digested and analyzed by matrix-assisted laser-desorption ionization time-of-flight time-of-flight (MALDI-TOF-TOF). In total, 1098 spots were subjected to statistical analysis with 22 spots found to be differentially abundant of which 18 proteins were positively identified by mass spectrometry. In addition, approximately 1000 protein spots were constitutively expressed of which 21 proteins were positively identified by mass spectrometry. Increased levels of proteins in the cocaine-exposed monkeys include glial fibrillary acidic protein, syntaxin-binding protein 3, protein kinase C isoform, adenylate kinase isoenzyme 5 and mitochondrial-related proteins, whereas decreased levels of proteins included beta-soluble N-ethylmaleimide-sensitive factor attachment protein and neural and non-neural enolase. Using a complimentary proteomics approach, the differential expression of phosphorylated proteins in the cytosolic fraction of these subjects was examined. Two-dimensional gel electrophoresis (2DGE) was followed by gel staining with Pro-Q Diamond phosphoprotein gel stain, enabling differentiation of approximately 150 phosphoprotein spots between the groups. Following excision and trypsin digestions, MALDI-TOF-TOF was used to confirm the identity of 15 cocaine-altered phosphoproteins. Significant increased levels were detected for gamma-aminobutyric acid type A receptor-associated protein 1, 14-3-3 gamma-protein, glutathione S-transferase and brain-type aldolase, whereas significant decreases were observed for beta-actin, Rab GDP-dissociation inhibitor, guanine deaminase, peroxiredoxin 2 isoform b and several mitochondrial proteins. Results from these studies indicate coordinated dysregulation of proteins related to cell structure, signaling, metabolism and mitochondrial function. These data extend and compliment previous studies of cocaine-induced biochemical alterations in human postmortem brain tissue, using an animal model that closely recapitulates the human condition and provide new insight into the molecular basis of the disease and potential targets for pharmacotherapeutic intervention.

Project description:Chronic cocaine use is associated with neurobiological and cognitive deficits that persist into abstinence, hindering success of behavioral treatment strategies and perhaps increasing likelihood of relapse. The effects of current cocaine use and abstinence on neurobiology and cognition are not well characterized.Adult male rhesus monkeys with an extensive cocaine self-administration history (? 5 years) and age-matched control animals (n = 4/group) performed cognitive tasks in morning sessions and self-administered cocaine or food in afternoon sessions. Positron emission tomography and [(18)F]-fluorodeoxyglucose were employed to assess cerebral metabolic rates of glucose utilization during cognitive testing.Cocaine-experienced monkeys required significantly more trials and committed more errors on reversal learning and multidimensional discriminations, compared with control animals. Cocaine-naive, but not cocaine-experienced, monkeys showed greater metabolic rates of glucose utilization during a multidimensional discrimination task in the caudate nucleus, hippocampus, anterior and posterior cingulate, and regions associated with attention, error detection, memory, and reward. Using a delayed match-to-sample task, there were no differences in baseline working memory performance between groups. High-dose cocaine self-administration disrupted delayed match-to-sample performance but tolerance developed. Acute abstinence from cocaine did not affect performance, but by day 30 of abstinence, accuracy increased significantly, while performance of cocaine-naive monkeys was unchanged.These data document direct effects of cocaine self-administration on cognition and neurobiological sequelae underlying cognitive deficits. Improvements in working memory can occur in abstinence, albeit across an extended period critical for treatment seekers, suggesting pharmacotherapies designed to enhance cognition may improve success of current behavioral modification strategies.

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Reinforcing effects of compounds lacking intrinsic efficacy at α1 subunit-containing GABAA receptor subtypes in midazolam- but not cocaine-experienced rhesus monkeys.

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