Preclinical evidence for combining the 5-HT2C receptor agonist lorcaserin and varenicline as a treatment for nicotine dependence.

Varenicline, a nicotinic acetylcholine receptor partial agonist, is used to treat nicotine dependence. Lorcaserin, a 5-HT2C receptor agonist has been approved in some countries to treat obesity. Based on preclinical and preliminary clinical evidence, lorcaserin may have potential to treat nicotine dependence. These experiments examined in rats the effects of combining varenicline (0.5 or 1 mg/kg) and lorcaserin (0.3, 0.6 and 1 mg/kg) on nicotine self-administration, reinstatement of nicotine seeking, responding for food and impulsive action. Both drugs alone reduced nicotine self-administration. Combining varenicline and 0.6 mg/kg lorcaserin reduced responding to a greater extent than either drug alone. In a relapse model, extinguished nicotine seeking was reinstated by a priming injection of nicotine and nicotine-associated cues. Reinstatement was reduced by varenicline (1 mg/kg) and by lorcaserin (0.3 mg/kg). Combining lorcaserin (0.3 mg/kg) with varenicline (0.5 or 1 mg/kg) reduced reinstatement to a greater degree than either drug alone. Both drugs had minimal effects on responding for food, alone or in combination. In the five-choice serial reaction time test, varenicline (0.5 or 1 mg/kg) increased impulsivity, measured as increased premature responding. This effect was reduced by lorcaserin (0.3 mg/kg). Plasma levels of varenicline or lorcaserin were not altered by co-administration of the other drug. Varenicline and lorcaserin have additive effects on nicotine self-administration, and on nicotine seeking. Lorcaserin prevents impulsivity induced by varenicline. This pattern of effects suggests that co-administration of varenicline and lorcaserin has potential as a treatment for nicotine dependence that may exceed the value of either drug alone.

Novel KV7 ion channel openers for the treatment of epilepsy and implications for detrusor tissue contraction.

Neuronal voltage-gated potassium channels, KV7s, are the molecular mediators of the M current and regulate membrane excitability in the central and peripheral neuronal systems. Herein, we report novel small molecule KV7 openers that demonstrate anti-seizure activities in electroshock and pentylenetetrazol-induced seizure models without influencing Rotarod readouts in mice. The anti-seizure activity was determined to be proportional to the unbound concentration in the brain. KV7 channels are also expressed in the bladder smooth muscle (detrusor) and activation of these channels may cause localized undesired effects. Therefore, the impact of individual KV7 isoforms was investigated in human detrusor tissue using a panel of KV7 openers with distinct activity profiles among KV7 isoforms. KCNQ4 and KCNQ5 mRNA were highly expressed in detrusor tissue, yet a compound that has significantly reduced activity on homomeric KV7.4 did not reduce detrusor contraction. This may suggest that the homomeric KV7.4 channel plays a less significant role in bladder contraction and further investigation is needed.

Examination of the effects of varenicline, bupropion, lorcaserin, or naltrexone on responding for conditioned reinforcement in nicotine-exposed rats.

Smoking tobacco remains one of the leading causes of preventable deaths in North America. Nicotine reinforces smoking behavior, in part, by enhancing the reinforcing properties of reward-related stimuli, or conditioned stimuli (CSs), associated with tobacco intake. To investigate how pharmaceutical interventions may affect this property of nicotine, we examined the effect of four US Food and Drug Administration (FDA) approved drugs on the ability of nicotine to enhance operant responding for a CS as a conditioned reinforcer. Thirsty rats were exposed to 13 Pavlovian sessions where a CS was paired with water delivery. Nicotine (0.4 mg/kg) injections were administered before each Pavlovian session. Then, in separate groups of rats, the effects of varenicline (1 mg/kg), bupropion (10 and 30 mg/kg), lorcaserin (0.6 mg/kg), and naltrexone (2 mg/kg), and their interaction with nicotine on responding for conditioned reinforcement were examined. Varenicline and lorcaserin each reduced nicotine-enhanced responding for conditioned reinforcement, whereas naltrexone had a modest effect of reducing response enhancements by nicotine. In contrast, bupropion enhanced the effect of nicotine on this measure. The results of these studies may inform how pharmaceutical interventions can affect smoking cessation attempts and relapse through diverse mechanisms, either substituting for, or interacting with, the reinforcement-enhancing properties of nicotine.

Effect of a single psilocybin treatment on Fos protein expression in male rat brain.

Psilocybin has received attention as a treatment for depression, stress disorders and drug and alcohol addiction. To help determine the mechanisms underlying its therapeutic effects, here we examined acute effects of a range of behaviourally relevant psilocybin doses (0.1-3 mg/kg SC) on regional expression of Fos, the protein product of the immediate early gene, c-fos in brain areas involved in stress, reward and motivation in male rats. We also determined the cellular phenotypes activated by psilocybin, in a co-labeling analysis with NeuN, a marker of mature neurons, or Olig1, a marker of oligodendrocytes. In adult male Sprague-Dawley rats, psilocybin increased Fos expression dose dependently in several brain regions, including the frontal cortex, nucleus accumbens, central and basolateral amygdala and locus coeruleus. These effects were most marked in the central amygdala. Double labeling experiments showed that Fos was expressed in both neurons and oligodendrocytes. These results extend previous research by determining Fos expression in multiple brain areas at a wider psilocybin dose range, and the cellular phenotypes expressing Fos. The data also highlight the amygdala, especially the central nucleus, a key brain region involved in emotional processing and learning and interconnected with other brain areas involved in stress, reward and addiction, as a potentially important locus for the therapeutic effects of psilocybin. Overall, the present findings suggest that the central amygdala may be an important site through which the initial brain activation induced by psilocybin is translated into neuroplastic changes, locally and in other regions that underlie its extended therapeutic effects.

Effects of 5-HT2C receptor stimulation in male mice on behaviour and Fos expression: Feeding, reward and impulsivity.

Serotonin modulates many motivated behaviours via multiple receptor subtypes. Agonists at 5-HT2C receptors have potential for treating behavioural problems associated with obesity and drug use. In this work we examined the impact of the 5-HT2C receptor agonist lorcaserin on several motivated behaviours related to feeding, reward and waiting impulsivity, and on neuronal activation in key brain areas mediating those behaviours. In male C57BL/6J mice effects of lorcaserin (0.2, 1 and 5 mg/kg) were examined on feeding, and on operant responding for a palatable reward. Feeding was reduced only at 5 mg/kg, whereas operant responding was reduced at 1 mg/kg. At a much lower dose range lorcaserin 0.05-0.2 mg/kg also reduced impulsive behaviour measured as premature responding in the 5-choice serial reaction time (5-CSRT) test, without affecting attention or ability to perform the task. Lorcaserin induced Fos expression in brain regions related to feeding (paraventricular nucleus and arcuate nucleus), reward (ventral tegmental area), and impulsivity (medial prefrontal cortex, VTA) although these effects did not show the same differential sensitivity to lorcaserin as the behavioural measures. These results indicate a broad profile of action of 5-HT2C receptor stimulation on brain circuitry and on motivated behaviours, but with clear evidence of differential sensitivity across behavioural domains. This is exemplified by the fact that impulsive behaviour was reduced at a much lower dose range than was feeding behaviour. Along with previous work, and some clinical observations, this work supports the idea that 5-HT2C agonists may be useful for behavioural problems associated with impulsivity.

The Effects of Drug Treatments for ADHD in Measures of Cognitive Performance.

Based on core symptoms of inattention and deficient impulse control, and the identification of effective pharmacotherapies such as amphetamine (AMP; Adderall®), methylphenidate (MPH; Ritalin®), and atomoxetine (ATX; Strattera®), ADHD is a clinical condition which provides opportunity for translational research. Neuropsychological tests such as the 5-Choice and Continuous Performance Tasks, which measure aspects of attention and impulse control in animals and humans, provide scope for both forward (animal to human) and reverse (human to animal) translation. Rodent studies support pro-attentive effects of AMP and MPH and effectiveness in controlling some forms of impulsive behavior. In contrast, any pro-attentive effects of ATX appear to be less consistent, the most reliable effects of ATX are recorded in tests of impulsivity. These differences may account for AMP and MPH being recognized as first-line treatments for ADHD with a higher efficacy relative to ATX. DSM-5 classifies three "presentations" of ADHD: predominantly inattentive type (ADHD-I), predominantly hyperactive/impulsive type (ADHD-HI), or combined (ADHD-C). Presently, it is unclear whether AMP, MPH, or ATX has differential levels of efficacy across these presentation types. Nonetheless, these studies encourage confidence for the forward translation of NCEs in efforts to identify newer pharmacotherapies for ADHD.

Effects of pimavanserin and lorcaserin on alcohol self-administration and reinstatement in male and female rats.

The neurotransmitter serotonin (5-hydroxytryptamine; 5-HT) modulates fundamental motivational processes, and the neurochemical and behavioural effects of drugs of abuse. Recently, attention has focused on the role of 5-HT acting via 5-HT2A and 5-HT2C receptor sub-types in this regard. We examined the impact of manipulating 5-HT2A and 5-HT2C receptor mediated function on several aspects of alcohol self-administration and alcohol-seeking behaviour in male and female rats. Specifically, experiments investigated the effect of the 5-HT2A inverse agonist/antagonist pimavanserin, and the 5-HT2C receptor agonist lorcaserin on these behaviours. In male and female rats trained to respond for alcohol reinforcement on fixed ratio (FR) and progressive ratio (PR) schedules of reinforcement pimavanserin (0.3, 1 and 3 mg/kg) had no consistent effect on responding. Lorcaserin (0.25, 0.5 and 1 mg/kg) reduced these behaviours in both sexes. Following extinction of responding for alcohol, alcohol-seeking was reinstated by cues previously paired with alcohol. Pimavanserin (1 mg/kg) and lorcaserin (0.5 mg/kg) significantly reduced this reinstatement. In a two-bottle 24 h intermittent access procedure pimavanserin had no significant effects, but lorcaserin reduced alcohol consumption in both sexes at 1, 4 and 24 h after access to alcohol was allowed. Finally, as determined using in vivo microdialysis, alcohol increased, and lorcaserin (0.5 mg/kg) reduced, extracellular levels of DA in the NAc in male rats. In rats treated with lorcaserin prior to alcohol injection the net effect was that DA levels were not changed compared to those measured in control rats. These results suggest that blocking 5-HT2A receptor activity has a very limited action to reduce alcohol-seeking. Activating 5-HT2C receptors had a broader behavioural profile to reduce alcohol self-administration, alcohol drinking and alcohol seeking. These effects may partly result from a blunting of the effect of alcohol on mesolimbic DA release.

5-HT2A and 5-HT2C receptors as potential targets for the treatment of nicotine use and dependence.

Nicotine use and dependence, typically achieved through cigarette smoking, but increasingly through vape products, is the leading cause of preventable death today. Despite a recognition that many current smokers would like to quit, the success rate at doing so is low and indicative of the persistent nature of nicotine dependence and the high urge to relapse. There are currently three main forms of pharmacotherapy approved as aids to treat nicotine dependence: a variety of nicotine replacement products (NRT's), the mixed NA/DA reuptake inhibitor bupropion (Zyban®), and the preferential nicotinic α4ß2 receptor agonist drug, varenicline (Chantix®); the latter being generally recognized to be the most effective. However, each of these approaches afford only limited efficacy, and various other pharmacological approaches are being explored. This chapter focusses on approaches targeted to the serotonin (5-HT) system, namely, selective serotonin reuptake inhibitors (SSRI's) which served a pioneer role in the investigation of serotoninergic modulators in human smoking cessation trials; and secondly drugs selectively interacting with the 5-HT2A and 5-HT2C receptor systems. From an efficacy perspective, measured as smoking abstinence, the 5-HT2A agonist psychedelics, namely psilocybin, seem to show the most promise; although as the article highlights, these findings are both preliminary and there are significant challenges to the route to approval, and therapeutic use of this class should they reach approval status. Additional avenues include 5-HT2C receptor agonists, which until recently was pioneered by lorcaserin, and 5-HT2A receptor antagonists represented by pimavanserin. Each of these approaches has distinct profiles across preclinical tests of nicotine dependence, and may have therapeutic potential. It is anticipated as diagnostic and predictive biomarkers emerge, they may provide opportunities for subject stratification and opportunities for personalizing smoking cessation treatment. The clinical assessment of SSRI, 5-HT2A and/or 5-HT2C receptor-based treatments may be best served by this process.

Contrasting effects of d-amphetamine and atomoxetine on measures of impulsive action and choice.

Amphetamine (AMP) and atomoxetine (ATX) represent two of the most widely studied drug treatments used in the investigation of impulsive behaviour. While both drugs have relatively well defined effects in tests designed to investigate impulsive action (e.g. 5-choice task; 5-CSRTT), the effects of both drugs in tests of impulsive choice (e.g. delay discounting) are less consistent. In the present study both AMP and ATX were tested in a rodent gambling task (rGT) and delay discounting in rats separately trained to either an ascending or descending delay schedule. Effects of both drugs were compared to measures of impulsive action (premature (PREM) responses) and perseverative (PSV) responses measured in the 5-choice and rGT tasks. Consistent with previous studies, AMP (0.1-1 mg/kg) increased both PREM and PSV responses, and ATX (0.5-2 mg/kg) reduced both measures in the 5-choice and rGT tasks. At equivalent doses ATX had no reliable effect on choice behaviour in either the rGT or delay discounting suggesting a null effect of this drug on impulsive choice and risky decision making. The effects of AMP were more complex, with a subtle shift in preference to a low risk (P1) choice in the rGT, and an effect on discounting that was unrelated to reinforcer value, but instead dependent on delay sequence and baseline choice preference. One aspect to these outcomes is to highlight the importance of multiple methodological factors when assessing drug effects on complex behaviours such as impulsive choice, and question what are the most appropriate test conditions under which to examine these drugs on discounting.

Low Doses of Psilocybin and Ketamine Enhance Motivation and Attention in Poor Performing Rats: Evidence for an Antidepressant Property.

Long term benefits following short-term administration of high psychedelic doses of serotonergic and dissociative hallucinogens, typified by psilocybin and ketamine respectively, support their potential as treatments for psychiatric conditions such as major depressive disorder. The high psychedelic doses induce perceptual experiences which are associated with therapeutic benefit. There have also been anecdotal reports of these drugs being used at what are colloquially referred to as "micro" doses to improve mood and cognitive function, although currently there are recognized limitations to their clinical and preclinical investigation. In the present studies we have defined a low dose and plasma exposure range in rats for both ketamine (0.3-3 mg/kg [10-73 ng/ml]) and psilocybin/psilocin (0.05-0.1 mg/kg [7-12 ng/ml]), based on studies which identified these as sub-threshold for the induction of behavioral stereotypies. Tests of efficacy were focused on depression-related endophenotypes of anhedonia, amotivation and cognitive dysfunction using low performing male Long Evans rats trained in two food motivated tasks: a progressive ratio (PR) and serial 5-choice (5-CSRT) task. Both acute doses of ketamine (1-3 mg/kg IP) and psilocybin (0.05-0.1 mg/kg SC) pretreatment increased break point for food (PR task), and improved attentional accuracy and a measure of impulsive action (5-CSRT task). In each case, effect size was modest and largely restricted to test subjects characterized as "low performing". Furthermore, both drugs showed a similar pattern of effect across both tests. The present studies provide a framework for the future study of ketamine and psilocybin at low doses and plasma exposures, and help to establish the use of these lower concentrations of serotonergic and dissociative hallucinogens both as a valid scientific construct, and as having a therapeutic utility.

Lorcaserin: A review of its preclinical and clinical pharmacology and therapeutic potential.

The selective 5-HT2C receptor agonist lorcaserin, in conjunction with lifestyle modification, was approved by the FDA in 2012 for weight management. It has been marketed in the US as Belviq® since 2013. This article provides a review of the preclinical and clinical pharmacology of lorcaserin, including its pharmacokinetic and safety profiles. Preclinical studies with lorcaserin initially focused on simple measures of food intake and body weight gain, but have now expanded to include studies on its effects on appetitive aspects of feeding behaviour and models of binge-eating. A significant number of studies have also shown that lorcaserin alters behaviours related to drug use and addiction, in rodents and non-human primates. Potential clinically-relevant effects of lorcaserin have also been reported in models of pain and seizure-like activity. Not surprisingly, the majority of clinical work with lorcaserin has focused on its effects on weight gain, and on physiological processes related to energy intake. However, results of clinical trials and experimental laboratory studies involving lorcaserin are now appearing which describe effects on a range of other behaviours and physiological functions. These include smoking cessation, cocaine self-administration, and behavioural and brain responses to food cues. All of this work suggests that lorcaserin may have therapeutic potential for a variety of disorders and conditions beyond obesity. Based on clinical experience, including the outcomes from several, large, well-powered clinical obesity trials at the approved 10mg BID dose both pre and post approval, a priori concerns about cardiac valvulopathy have largely been allayed. However, as with any recently approved first-in-class pharmacotherapy, there may be yet-unknown risks, as well as benefits, associated with use of lorcaserin. Nonetheless, the current safety profile and an expanding post approval safety data base should encourage further experimental laboratory-based and clinical trial-based research with lorcaserin in targeted populations to investigate its full therapeutic potential.

Characterization of Amphetamine, Methylphenidate, Nicotine, and Atomoxetine on Measures of Attention, Impulsive Action, and Motivation in the Rat: Implications for Translational Research.

Amphetamine (AMP), methylphenidate (MPH), and atomoxetine (ATX) are approved treatments for ADHD, and together with nicotine (NIC), represent pharmacological agents widely studied on cognitive domains including attention and impulsive action in humans. These agents thus represent opportunities for clinical observation to be reinvestigated in the preclinical setting, i.e., reverse translation. The present study investigated each drug in male, Long Evans rats trained to perform either (1) the five-choice serial reaction time task (5-CSRTT), (2) Go/NoGo task, or (3) a progressive ratio (PR) task, for the purpose of studying each drug on attention, impulsive action and motivation. Specific challenges were adopted in the 5-CSRTT designed to tax attention and impulsivity, i.e., high frequency of stimulus presentation (sITI), variable reduction in stimulus duration (sSD), and extended delay to stimulus presentation (10-s ITI). Initially, performance of a large (> 80) cohort of rats in each task variant was conducted to examine performance stability over repeated challenge sessions, and to identify subgroups of "high" and "low" attentive rats (sITI and sSD schedules), and "high" and "low" impulsives (10-s ITI). Using an adaptive sequential study design, the effects of AMP, MPH, ATX, and NIC were examined and contrasting profiles noted across the tests. Both AMP (0.03-0.3 mg/kg) and MPH (1-6 mg/kg) improved attentional performance in the sITI but not sSD or 10-s ITI condition, NIC (0.05-0.2 mg/kg) improved accuracy across all conditions. ATX (0.1-1 mg/kg) detrimentally affected performance in the sITI and sSD condition, notably in "high" performers. In tests of impulsive action, ATX reduced premature responses notably in the 10-s ITI condition, and also reduced false alarms in Go/NoGo. Both AMP and NIC increased premature responses in all task variants, although AMP reduced false alarms highlighting differences between these two measures of impulsive action. The effect of MPH was mixed and appeared baseline dependent. ATX reduced break point for food reinforcement suggesting a detrimental effect on motivation for primary reward. Taken together these studies highlight differences between AMP, MPH, and ATX which may translate to their clinical profiles. NIC had the most reliable effect on attentional accuracy, whereas ATX was reliably effective against all tests of impulsive action.

Effects of 5-HT2C receptor modulation and the NA reuptake inhibitor atomoxetine in tests of compulsive and impulsive behaviour.

Drug repositioning has gained strategic value as a reaction to high attrition rates of new drugs as they pass through the clinical development process. The 5-HT2C receptor agonist lorcaserin (Belviq®), and the selective NA reuptake inhibitor atomoxetine (Strattera®) represent two drugs FDA approved for obesity and ADHD respectively. Although both drugs are of differing pharmacological class, each share a property of regulating impulsive behaviours in preclinical studies, and thus represent candidates for consideration in clinical conditions labelled as 'impulsive-compulsive disorders'. The present studies investigated both drugs, as well as the highly selective 5-HT2C agonist CP-809101 in two tests of compulsive action: schedule-induced polydipsia (SIP) and increased perseverative [PSV] (and premature [PREM]) responses emitted during an extended ITI 5-choice task. While lorcaserin (0.06-0.6 mg/kg), CP-809101 (0.1-1 mg/kg) and atomoxetine (0.1-1 mg/kg) each reduced both PREM and PSV measures in the 5-choice task, at equivalent doses only lorcaserin and CP-809101 affected excessive water intake in the SIP task, atomoxetine (0.1-2 mg/kg) was essentially ineffective. Further evidence supporting a role of the 5-HT2C receptor as an important regulator of impulsive-compulsive behaviours, the selective antagonist SB-242084 produced the opposing effects to lorcaserin, i.e promoting both impulsive and compulsive behaviours. The profile of atomoxetine may suggest differences in the nature of compulsive action measured either as non-regulatory drinking in the SIP task, and PSV responses made in a 5-choice task. These studies support the consideration of 5-HT2C receptor agonists, typified by lorcaserin, and atomoxetine as potential treatments for clinical conditions categorised as 'impulsive-compulsive disorders'. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Characterization of the potent and highly selective A2A receptor antagonists preladenant and SCH 412348 [7-[2-[4-2,4-difluorophenyl]-1-piperazinyl]ethyl]-2-(2-furanyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine] in rodent models of movement disorders and depression.

The adenosine A(2A) receptor has been implicated in the underlying biology of various neurological and psychiatric disorders, including Parkinson's disease (PD) and depression. Preladenant and SCH 412348 [7-[2-[4-2,4-difluorophenyl]-1-piperazinyl]ethyl]-2-(2-furanyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine] are potent competitive antagonists of the human A(2A) receptor (K(i) = 1.1 and 0.6 nM, respectively) and have >1000-fold selectivity over all other adenosine receptors, making these compounds the most selective A(2A) receptor antagonists reported to date. Both compounds attenuate hypolocomotion induced by the A(2A) receptor agonist CGS-21680 [2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosine], suggesting that they inhibit A(2A) receptor activity in vivo. Their high degree of selectivity and robust in vivo activity make preladenant and SCH 412348 useful tools to investigate the role of the A(2A) receptor system in animal models of PD and depression. Oral administration of preladenant and SCH 412348 (0.1-1 mg/kg) to rats potentiated 3,4-dihydroxy-L-phenylalanine (L-Dopa)-induced contralateral rotations after 6-hydroxydopamine lesions in the medial forebrain bundle and potently attenuated the cataleptic effects of haloperidol. Preladenant (1 mg/kg) inhibited L-Dopa-induced behavioral sensitization after repeated daily administration, which suggests a reduced risk of the development of dyskinesias. Finally, preladenant and SCH 412348 exhibited antidepressant-like profiles in models of behavioral despair, namely the mouse tail suspension test and the mouse and rat forced swim test. These studies demonstrate that preladenant and SCH 412348 are potent and selective A(2A) receptor antagonists and provide further evidence of the potential therapeutic benefits of A(2A) receptor inhibition in PD (with reduced risk of dyskinesias) and depression (one of the primary nonmotor symptoms of PD).

Evaluation of Selective 5-HT2C Agonists in Acute Seizure Models.

The 5-HT releaser/reuptake inhibitor fenfluramine has been recently reported to provide benefit as an adjunctive treatment for Dravet and Lennox-Gastaut syndromes, two types of severe childhood epilepsy. Despite its enhancement of 5-HT function, many effects of fenfluramine have been demonstrated to be dependent on 5-HT2C receptor activation, suggesting that 5-HT2C receptor activation may have an anticonvulsant property. The present study was designed to evaluate fenfluramine and 5-HT agonists of varying 5-HT2C agonist selectivity, the relatively nonselective mCPP and Ro 60-0175, and the selective 5-HT2C agonists lorcaserin and CP-809101 across a variety of acute seizure tests conducted in adult rats and mice, which have been instrumental in identifying the majority of clinically efficacious antiepileptic drugs. Tests included the maximal electroshock seizure (MES), MES threshold, and 6 Hz electrical convulsive seizure models and the chemoconvulsant pentylenetetrazole test. The effect of mCPP, lorcaserin, and CP-809101 against electrically evoked seizures in amygdala kindled rats was also investigated. Overall, at doses known to interact with 5-HT2CR, there was no clear class-related effect of these agonists in any test. The only notable antiseizure effect of fenfluramine was inhibition of MES-induced tonic seizures in the rat. The current preclinical studies using the classical acute seizure tests and an amygdala kindling model do not identify a reliable antiseizure effect of fenfluramine, an agent now used in the treatment of human epilepsies, including Dravet syndrome and Lennox-Gastaut syndrome. Given the nature of these epilepsies, early life and/or genetic models may have better construct validity and be more appropriate for further study.

The 5-HT2C receptor agonist Ro60-0175 reduces cocaine self-administration and reinstatement induced by the stressor yohimbine, and contextual cues.

Previously, we showed that the 5-HT2C receptor agonist Ro60-0175 reduces cocaine self-administration, and the ability of cocaine to reinstate responding after extinction of drug-seeking behavior. The present experiments extended these findings further by determining whether the effects of Ro60-0175 on self-administration were sustained with repeated treatment, and whether Ro60-0175 altered reinstatement induced by the pharmacological stressor yohimbine, or by the context in which self-administration occurred. In Experiment 1, Ro60-0175 (1 mg/kg, s.c.) reduced cocaine (0.25 mg/infusion) self-administration maintained by a progressive ratio schedule. This reduction was sustained over eight daily injections. In Experiment 2, rats self-administered cocaine in daily 2 h sessions for 15 days on a FR1 schedule. Following extinction, yohimbine (1 mg/kg, i.p.) reinstated responding, and this effect was reduced dose dependently by Ro60-0175 (0.3-3 mg/kg, s.c.). In Experiment 3, rats were trained to respond for cocaine on a FR1 schedule in a distinct environmental context (A); responding was then extinguished in a different context (B). Reinstatement tests occurred in either context A or B. Responding was reinstated only when rats were tested in the original self-administration context (A). This reinstatement was reduced dose dependently by Ro60-0175. All effects of Ro60-0175 were blocked by the 5-HT2C receptor antagonist SB242084. Thus, Ro60-0175, acting via 5-HT2C receptors, reduces cocaine self-administration and cocaine-seeking triggered by a stressor and by drug-associated cues. The effects of Ro60-0175 do not exhibit tolerance within the 8-day test period. These results indicate that selective 5-HT2C receptor agonists may be a useful pharmacological strategy for treatment of drug abuse.

Design, synthesis, and evaluation of fused heterocyclic analogs of SCH 58261 as adenosine A2A receptor antagonists.

SCH 58261 is a reported adenosine A(2A) receptor antagonist which is active in rat in vivo models of Parkinson's Disease upon ip administration. However, it has poor selectivity versus the A(1) receptor and does not demonstrate oral activity. Quinoline analogs have improved upon the selectivity and pharmacokinetics of SCH 58261, but were difficult to handle due to poor aqueous solubility. We report the design and synthesis of fused heterocyclic analogs of SCH 58261 with aqueous solubility as well as improved A(2A) receptor binding selectivity and pharmacokinetic properties. In particular, the tetrahydronaphthyridine 4s has excellent A(2A) receptor in vitro binding affinity and selectivity, is active orally in a rat in vivo model of Parkinson's Disease, and has aqueous solubility of 100 microM at physiological pH.

Effects of the NMDA receptor antagonists dizocilpine and Ro 63-1908 on delay-discounting and risky decision-making in a gambling task.

Previous studies demonstrated that NMDA receptor antagonists such as dizocilpine (MK801) and the GluN2B NMDA antagonist Ro 63-1908 promote impulsive action (motor impulsivity). The effects of these treatments on impulsive choice and decision-making is less well characterized. Two experiments were undertaken. In the first experiment, given evidence for delay order as a factor in choice selection, the effect of dizocilpine was examined in a delay discounting task with separate groups of male Long-Evans rats trained to a schedule of either ascending (i.e. 0-40 s), or descending delays (i.e. 40-0 s). Under the ascending-delay schedule, dizocilpine (0.03-0.06 mg/kg SC) reduced discounting, yet on the descending-delay schedule discounting was increased. Subgrouping rats according to discounting rate under vehicle pretreatment were consistent with a treatment-induced choice perseveration. In a second experiment, male Long-Evans rats were trained to a gambling task (rGT). Neither dizocilpine (0.01-0.06 mg/kg SC) nor Ro 63-1908 (0.1-1 mg/kg SC) shifted choice from the advantageous to the disadvantageous options. However dizocilpine, and marginally Ro 63-1908, increased choice of the least risky, but suboptimal option. This effect was most evident in rats that initially preferred the disadvantageous options. Consistent with previous studies, both treatments increased measures of motor impulsivity. These results demonstrate that dizocilpine has effects on discounting dependent on delay order and likely reflective of perseveration. On the rGT task, neither dizocilpine nor Ro 63-1908 promoted risky choice, yet both NMDA receptor antagonists increased impulsive action.

Opposing effects of 5-HT(2A) and 5-HT(2C) receptor antagonists in the rat and mouse on premature responding in the five-choice serial reaction time test.

RATIONALE: Serotonin (5-HT) has been linked to impulsivity with recent data suggesting that different receptor sub-types exert opposing influences on this behaviour. OBJECTIVES: This work characterised the effects of 5-HT(2A) (ketanserin, (+/-)2,3-dimethoxyphenyl-1-[2-4-(piperidine)-methanol] [M100907]), 5-HT(2B) (6-chloro-5-methyl-1-(5-quinolylcarbamoyl) indoline [SB215505]) and 5-HT(2C) (6-chloro-5-methyl-1-[2-(2-methylpyridyl-3-oxy)-pyrid-5-yl carbomyl] indoline [SB242084]) receptor antagonists on impulsive behaviour, measured in the five-choice serial reaction time test (5CSRTT), in rats and mice. The effects of (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) and (S)-2-(chloro-5-fluoro-indol-1-yl)-1-methylethylamine 1:1 C4H4O4 (Ro60-0175), two compounds that have been used extensively as agonists for the 5-HT(2A) and 5-HT(2C) receptor, were also measured. MATERIALS AND METHODS: Rats and mice were trained on the 5CSRTT in which reinforcement is earned for detecting and correctly responding to brief presentations of a stimulus light. Impulsivity in this task is measured as premature responding, before stimulus presentation. Several variants of the task were used in which the inter-trial interval (ITI) length was manipulated to alter basal levels of premature responding. RESULTS: In the rat, ketanserin and M100907 reduced and SB242084 enhanced premature responding. SB215505 had no effect. DOI generally disrupted responding, while Ro60-0175 reduced premature responding when a long ITI was used. In mice, M100907 reduced and SB242084 increased premature responding when the ITI was lengthened. The effects of these drugs on other aspects of performance were less robust. M100907 and ketanserin did not affect response accuracy but tended to slow speed of responding; SB242084 occasionally increased speed of responding and slightly reduced accuracy. CONCLUSIONS: Serotonin exerts both excitatory and inhibitory influences on motor impulsivity via 5-HT(2A) and 5-HT(2C) receptors in both rats and mice.

The effect of caffeine to increase reaction time in the rat during a test of attention is mediated through antagonism of adenosine A2A receptors.

Caffeine produces effects on cognitive function particularly relating to aspects of attention such as reaction time. Considering the plasma exposure levels following regular caffeine intake, and the affinity of caffeine for known protein targets, these effects are likely mediated by either the adenosine A(1) or A(2A) receptor. In the present studies, two rat strains [Long-Evans (LE) and CD] were trained to asymptote performance in a test of selective attention, the 5-choice serial reaction time task (5-CSRTT). Next, the effects of caffeine were compared to the selective A(2A) antagonists, SCH 412348 and KW-6002 (Istradefylline), and the A(1) antagonist, DPCPX. Further studies compared the psychostimulant effects of each drug. Finally, we tested the A(2A) agonist, CGS-21680, on 5-CSRTT performance and given the antipsychotic potential of this drug class, studied the interaction between CGS-21680 and amphetamine in this task. Caffeine (3-10mg/kg IP) increased reaction time in both LE and CD rats, with no effect on accuracy, an effect replicated by SCH 412348 (0.1-1mg/kg PO) and KW-6002 (1-3mg/kg PO), but not DPCPX (3-30 mg/kg PO). At least with SCH 412348, these effects were at doses that were not overtly psychostimulant. In contrast, CGS-21680 (0.03-0. 3mg/kg IP) slowed reaction speed and increased omissions. Interestingly, at a comparatively low dose of 0.03 mg/kg, CGS-21680 attenuated the increased premature responding produced by amphetamine (1mg/kg IP). The present results suggest that the attention-enhancing effects of caffeine are mediated through A(2A) receptor blockade, and selective A(2A) receptor antagonists may have potential as therapies for attention-related disorders. Furthermore, the improvement in response control in amphetamine-treated rats following CGS-21680 pretreatment supports the view that A(2A) agonists have potential as novel antipsychotics.