The selective 5-HT6 receptor antagonist SLV has putative cognitive- and social interaction enhancing properties in rodent models of cognitive impairment.

In the present study, our aim was to investigate whether the novel highly selective 5-hydroxytryptamine6 (5-HT6) receptor antagonist SLV can ameliorate impairments in cognition and social interaction with potential relevance for both schizophrenia and Alzheimer's disease (AD). SLV sub-chronically - treated Wistar rats reared in isolation showed significantly enhanced prepulse inhibition (PPI) and object recognition performance when compared to vehicle - treated rats. In the isolated rats, also a significant reduction in expression of hippocampal neural cell adhesion molecule polysialylation (NCAM-PSA) was found which was ameliorated following treatment with SLV (30mg/kg). The social engagement deficit in rats exposed in utero (on gestational day 12.5) to valproic acid (VPA) was reversed by treatment with SLV (30mg/kg). SLV (20 and 30mg/kg, p.o.) fully reversed MK-801 - induced deficits in the ORT and also scopolamine - induced deficits in both the Object Recognition Task (ORT) and Object Location Task (OLT) in Wistar rats. In addition, a combination of sub-optimal doses of SLV and donepezil attenuated scopolamine-induced ORT deficits. Furthermore, SLV (10mg/kg, p.o.) reversed spontaneous alternation deficits in the T-maze induced by MK-801 administration in Swiss mice and in aged C57Bl/6J mice. SLV additionally improved T-Maze spatial learning and passive avoidance learning in Sprague-Dawley rats with amyoid-beta (Aß) injections into the hippocampus. In contrast, no benefits were found with SLV or the tested reference compounds (donepezil and RVT-101) on cognitive performance of 12months old Tg2576 mice. Also, in the social recognition task, an absence of cognitive enhancing properties was observed with SLV on "normal forgetting" in Wistar rats. Finally, analysis of spontaneous inhibitory postsynaptic currents (sIPSCs) frequency recorded from pyramidal cells revealed a reduction in the presence of 1µM of SLV. In conclusion, SLV was investigated in several rodent animal models and found to be effective at a least effective dose (LED) of 20mg/kg and 10mg/kg (p.o.) in the rat and the mouse, respectively.

Multiple rodent models and behavioral measures reveal unexpected responses to FTY720 and DMF in experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is a widely-used rodent model for multiple sclerosis (MS), but a single model can hardly capture all features of MS. We investigated whether behavioral parameters in addition to clinical motor function scores could be used to assess treatment efficacy during score-free intervals in the relapsing-remitting EAE model in SJL/J mice. We studied the effects of the clinical reference compounds FTY720 (fingolimod, 0.5mg/kg/day) and dimethyl fumarate (DMF, 20-30 mg/kg/day) on clinical scores in several rodent EAE models in order to generate efficacy profiles. SJL/J mice with relapsing-remitting EAE were studied using behavioral tests, including rotarod, gait analysis, locomotor activity and grip strength. SJL/J mice were also examined according to Crawley's sociability and preference for social novelty test. Prophylactic treatment with FTY720 prevented clinical scores in three of the four EAE rodent models: Dark Agouti (DA) and Lewis rats and C57BL/6J mice. Neither prophylactic nor late-therapeutic treatment with FTY720 reduced clinical scores or reversed deficits in the rotarod test in SJL/J mice, but we observed effects on motor functions and sociability in the absence of clinical scores. Prophylactic treatment with FTY720 improved the gait of SJL/J mice whereas late-therapeutic treatment improved manifestations of reduced social (re)cognition or preference for social novelty. DMF was tested in three EAE models and did not improve clinical scores at the dose used. These data indicate that improvements in behavioral deficits can occur in absence of clinical scores, which indicate subtle drug effects and may have translational value for human MS.

Effects of risperidone, clozapine and the 5-HT6 antagonist GSK-742457 on PCP-induced deficits in reversal learning in the two-lever operant task in male Sprague Dawley rats.

Reasoning and problem solving deficits have been reported in schizophrenic patients. In the present study, we have tested rats in a two-lever reversal learning task in a Skinner box to model these deficits. In other studies using the Skinner box, atypical antipsychotics fully reversed phencyclidine (PCP)-induced impairments in reversal learning which is in contrast to clinical observations where antipsychotics lack the ability to fully reverse cognitive deficits in schizophrenia. Therefore, it can be argued that the outcome of these tests may lack predictive value. In the present study, after training on a spatial discrimination between two levers, rats were exposed to a reversal of the previously learned stimulus-response contingency during 5 days. We first investigated the effects of sub-chronic treatment with the non-competitive N-methyl-d-aspartate (NMDA) antagonists dizocilpine (MK-801) and PCP on reversal learning and extinction in male Sprague Dawley rats. Subsequently, we studied the effects of different PCP treatment regimes. Then, we investigated whether the atypical antipsychotics risperidone and clozapine and the 5-hydroxytryptamine6 (5-HT6) antagonist GSK-742457 could reverse the PCP-induced deficits. All drugs were administered subcutaneously (s.c.). MK-801 did not impair reversal learning, while PCP (1.0 and 2.0 mg/kg) induced a clear deficit in reversal learning. Both compounds, however, disrupted extinction at all tested doses. Risperidone and clozapine were both ineffective in significantly ameliorating the PCP-induced deficit in reversal learning which fits well with the clinical observations. The lowest dose of clozapine (1.25 mg/kg) had an intermediate effect in ameliorating the deficit in reversal learning induced by PCP (not different from control or PCP-treated rats). The lowest dose of GSK-742457 (0.63 mg/kg) fully reversed the PCP-induced deficits while the higher dose (5.0 mg/kg) had an intermediate effect.

A novel highly selective 5-HT6 receptor antagonist attenuates ethanol and nicotine seeking but does not affect inhibitory response control in Wistar rats.

Recent studies suggest a potential role for 5-hydroxytryptamine(6) (5-HT(6)) receptors in the regulation of addictive behavior. In the present study, our aim was to investigate whether the novel highly selective 5-HT(6) receptor antagonist compound (CMP) 42 affected nicotine and ethanol seeking behavior in Wistar rats. We have also studied whether CMP 42 had beneficial effects in a model of impulse control, as measured in the 5-choice serial reaction time task (5-CSRTT). Rats were trained to nose poke to receive intravenous infusions of nicotine or an ethanol drop. CMP 42 (3-30 mg/kg intraperitoneally, i.p.) was administered to investigate the effects on nicotine self-administration. Rats were also tested for cue-induced reinstatement of nicotine and ethanol seeking. In addition, the effects of CMP 42 were studied on the number of anticipatory responses in the 5-CSRTT. CMP 42 was effective in reducing nicotine self-administration and reinstatement of nicotine seeking at a dose of 30 mg/kg (i.p.). CMP 42 was also effective in reducing reinstatement of ethanol seeking (30 mg/kg i.p.). In contrast, CMP 42 did not affect anticipatory responding at doses tested, indicating no effects on impulse control. These results add to a body of evidence implicating the 5-HT(6) receptor as a viable target for the control of drug abuse. Specifically, we demonstrated for the first time effects on nicotine self-administration and on nicotine and ethanol reinstatement. Further, these effects are probably not mediated by effects on impulse control.

Two novel 5-HT6 receptor antagonists ameliorate scopolamine-induced memory deficits in the object recognition and object location tasks in Wistar rats.

The 5-hydroxytryptamine(6) (5-HT(6)) receptor has been suggested to play an important role in the regulation of memory and cognition. In the present study, our aim was to investigate whether the novel, selective 5-HT(6) antagonists compound (CMP) X and CMP Y and the reference 5-HT(6) antagonist GSK-742457 could ameliorate impairments in episodic memory in 3-months-old male Wistar rats. The acetylcholinesterase inhibitor (AChEI) donepezil (Aricept®, approved for symptomatic treatment of Alzheimer's disease, AD) was used as a positive reference compound. First, effects of the 5-HT(6) antagonists CMP X, CMP Y and GSK-742457 were investigated on object recognition task (ORT) performance in rats treated with the muscarinic antagonist scopolamine (0.1mg/kg, administered intraperitoneally, i.p., 30 min before trial 1). Second, effects of the combination of suboptimal doses of 5-HT(6) antagonists CMP X and CMP Y with the AChEI donepezil were studied, to determine whether the 5-HT(6) antagonists show additive synergism with donepezil in the ORT. Finally, effects of CMP Y, GSK-742457 and donepezil were investigated on object location task (OLT) performance in rats treated with scopolamine. Donepezil (1mg/kg, oral administration, p.o.), GSK-742457 (3mg/kg, i.p.), CMP X (3mg/kg, i.p.) and CMP Y (30 mg/kg, p.o.), all ameliorated the scopolamine-induced deficits in object recognition. In the ORT, we have found that combined administration of subthreshold doses of CMP X (1mg/kg, i.p.) and CMP Y (10mg/kg, p.o.) with the AChEI donepezil (0.1mg/kg, p.o.), enhanced memory performance in Wistar rats with deficits induced by scopolamine. Donepezil (0.1mg/kg, p.o.) alone had no discernable effects on performance. This suggests additive synergistic effects of the 5-HT(6) antagonists (CMP X and CMP Y) with donepezil on cognitive impairment. Finally, donepezil (1mg/kg, p.o.), GSK-742457 (10mg/kg, p.o.) and CMP Y (30 mg/kg, p.o.) also reduced scopolamine-induced deficits in the OLT. In conclusion, the 5-HT(6) antagonists were found to clearly improve episodic memory deficits induced by scopolamine. In addition, co-administration of the 5-HT(6) receptor antagonists CMP X and CMP Y with the AChEI donepezil to cognitively impaired rats also resulted in potentially additive enhancing effects on cognition. This suggests that these compounds could have potential as monotherapy, but also as adjunctive therapy in patients with AD treated with common treatments such as donepezil.

The 5-HT6 serotonin receptor antagonist SB-271046 attenuates the development and expression of nicotine-induced locomotor sensitisation in Wistar rats.

5-HT(6) receptors are almost exclusively expressed in the central nervous system, particularly in areas relevant for addictive behaviour. Based on this, together with other data, this receptor may be a viable target for the control of drug abuse. The present study tested the ability of the 5-HT(6) receptor antagonist SB-271046 to attenuate the development and expression of nicotine-induced behavioural sensitisation. Rats were habituated to the test apparatus prior to experimentation (day 0) and locomotor activity recorded. On days 1 and 5, animals were placed in locomotor test apparatus and after 30 min injected with SB-271046 (1, 3, and 6 mg/kg, intraperitoneally IP) or vehicle. Thirty minutes later, nicotine (0.4 mg/kg, subcutaneously SC) or saline were administered and activity recorded for 60 min. On days 2, 3 and 4 treatments were performed in the home cage. After 17 days of withdrawal (day 23), a challenge test was performed with nicotine (0.4 mg/kg SC) or saline. In a separate experiment of similar design the effects of SB-271046 (1, 3, and 6 mg/kg IP) was tested for its ability to reduce the expression of behavioural sensitisation (day 23). SB-271046 dose dependently reduced the development and expression of nicotine sensitisation vs respective controls. In conclusion, the 5-HT(6) receptor antagonist SB-271046 reduced both the development and expression of nicotine sensitisation, suggesting that the 5-HT(6) receptor may be a viable target for the control of nicotine abuse. Further studies are warranted to substantiate this conclusion and further understand the role of 5-HT(6) receptors in addiction.

SLV330, a cannabinoid CB(1) receptor antagonist, attenuates ethanol and nicotine seeking and improves inhibitory response control in rats.

Cannabinoid CB(1) receptor (CB(1)R) signaling has been shown to play a role in the regulation of addictive behavior. In the present study, our aim was to investigate whether the CB(1)R antagonist SLV330 could reduce ethanol and nicotine self-administration and cue-induced reinstatement of ethanol and nicotine seeking behavior in Wistar rats. In operant chambers, rats were learned to emit a specific response (nose poke) in order to receive an ethanol solution or intravenous injections of nicotine. Discrete light and tone cues were presented during ethanol and nicotine delivery. These cues are particularly important for drug self-administration behavior and, through Pavlovian conditioning, acquire conditioned reinforcing and motivational properties and are therefore able to generate and maintain drug-seeking behavior. Subsequently, the CB(1)R antagonist SLV330 (doses ranging from 1 to 10mg/kg, given orally, p.o.) was administered to investigate the effects on drug self-administration. In addition, responding for ethanol and nicotine was extinguished. Then, the animals were tested for cue-induced reinstatement of ethanol and nicotine seeking and treated with vehicle or SLV330. Finally, the effects of SLV330 were studied on the number of anticipatory responses in the 5-choice serial reaction time task (5-CSRTT) in order to determine whether this compound could also increase impulse control in Wistar rats. The CB(1) antagonist SLV330 was effective in reducing ethanol self-administration at a lowest effective dose (LED) of 10mg/kg (p.o.) and reinstatement of ethanol seeking at a LED of 3mg/kg (p.o.). SLV330 was also effective in reducing nicotine self-administration and reinstatement of nicotine seeking, although at a LED of 10mg/kg (p.o.). Finally, SLV330 decreased time delay-dependent anticipatory responding (LED of 3.0mg/kg, p.o.), indicating an increased inhibitory control. These findings are in agreement with results reported with other CB(1) antagonists. The combined action of reducing the reinforcing and motivational properties of nicotine and alcohol and the improvement of impulse control supports the idea that the cannabinoid system is a promising target for anti-relapse medication.

SLV330, a cannabinoid CB1 receptor antagonist, ameliorates deficits in the T-maze, object recognition and Social Recognition Tasks in rodents.

Cannabinoid CB(1) receptor (CB(1)R) signaling has been suggested to play an important role in the regulation of memory and cognition. In the present study, our aim was to investigate whether the CB(1)R antagonist SLV330 (doses ranging from 0.3 to 10mg/kg, given orally, p.o.) could ameliorate impairments in distinct aspects of cognition using different disruption models in both mice and rats. Effects of SLV330 were tested on working memory deficits in the T-maze Continuous Alternation Task (T-CAT) in mice; episodic memory deficits in the Object Recognition Task (ORT) and Social Recognition Task (SRT) in rats. The acetylcholinesterase inhibitor (AChEI) donepezil (Aricept, approved for symptomatic treatment of Alzheimer's disease) and nicotine were used as reference compounds. SLV330 markedly improved aging and scopolamine-induced memory deficits in the T-CAT in mice with a lowest effective dose (LED) of 1mg/kg p.o., while reversing the cognitive dysfunction induced by the N-methyl-D-aspartate (NMDA) antagonist dizocilpine (MK-801) only at the middle dose of 3mg/kg. In the ORT, we have found that combined administration of subthreshold doses of SLV330 (1mg/kg, p.o.) and the AChEI donepezil (0.1mg/kg, p.o.), that had no discernable effects on performance when given alone, enhanced memory performance in Wistar rats with deficits induced by the muscarinic antagonist scopolamine, suggestive of additive synergistic effects of SLV330 and donepezil on cognitive impairment. Finally, SLV330 was found to have cognition enhancing properties in a time delay paradigm in the SRT at a LED dose of 3mg/kg (p.o.). In conclusion, the CB(1)R antagonist SLV330 was found to clearly improve memory in several preclinical models for cognitive impairment.

Attentional performance of (C57BL/6Jx129Sv)F2 mice in the five-choice serial reaction time task.

Impaired attention is evident in several neurological and psychiatric disorders. In the present study, attentional capabilities were measured in the operant five-choice serial reaction time task (5-CSRTT) in male (C57BL/6Jx129Sv)F2 hybrid (B6129F2) mice. Main aims were to validate and standardize the test in these mice: to setup procedures, measure potential beneficial effects of sub-chronic nicotine in degraded versions of the 5-CSRTT (by decreasing stimulus duration, inducing white noise and making the stimuli unpredictable) and study disruptive effects of additional administration of the muscarinic antagonist scopolamine. During the baseline pre-nicotine sessions, the B6129F2 mice attained a very good performance in the test (95% accuracy). As stimulus duration was reduced from 2 s to 1 s, response accuracy of the mice decreased. Mice treated with nicotine (0.16 mg/kg) attained significantly higher response accuracy and had a lower percentage of incorrect responses in comparison with the solvent-treated animals. No further beneficial effects of nicotine were found. Reduced response accuracy was also obtained when stimulus duration was reduced from 1 s to 0.5 s and when a variable intertrial interval was introduced. Noise interpolation between trials did not impair performance. Finally, scopolamine (0.16 mg/kg) disrupted attentional functioning. Although most studies have been performed in rats, these results add to the existing evidence that the 5-CSRTT can also be used to assess attentional performance in mice. This offers the opportunity to test transgenic and knockout mice with similar background as the B6129F2 as animal models of psychiatric and neurological diseases.

Combined uridine and choline administration improves cognitive deficits in spontaneously hypertensive rats.

Rationale. Hypertension is considered a risk factor for the development of cognitive disorders, because of its negative effects on cerebral vasculature and blood flow. Genetically induced hypertension in rats has been associated with a range of cognitive impairments. Therefore, spontaneously hypertensive rats (SHR) can potentially be used as a model for cognitive deficits in human subjects. Consecutively, it can be determined whether certain food components can improve cognition in these rats. Objective. The present study aimed to determine whether SHR display specific deficits in attention, learning, and memory function. Additionally, effects of chronic uridine and choline administration were studied. Methods. 5-7 months old SHR were compared with normotensive Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats. (a) The operant delayed non-matching-to-position (DNMTP) test was used to study short-term memory function. (b) The five-choice serial reaction time (5-CSRT) task was used to assess selective visual attention processes. (c) Finally, the Morris water maze (MWM) acquisition was used as a measure for spatial learning and mnemonic capabilities. Results. (1) SHR exhibited significantly impaired performance in the 5-CSRT test in comparison with the two other rat strains. Both the SHR and WKY showed deficits in spatial learning when compared with the SD rats. (2) Uridine and choline supplementation normalized performance of SHR in the 5-CSRT test. (3) In addition, uridine and choline treatment improved MWM acquisition in both WKY and SHR rats. Conclusion. The present results show that the SHR have a deficiency in visual selective attention and spatial learning. Therefore, the SHR may provide an interesting model in the screening of substances with therapeutic potential for treatment of cognitive disorders. A combination of uridine and choline administration improved selective attention and spatial learning in SHR.