Pharmacological and molecular targets in the search for novel antipsychotics

SRI-32743, a novel allosteric modulator, attenuates HIV-1 Tat protein-induced inhibition of the dopamine transporter and alleviates the potentiation of cocaine reward in HIV-1 Tat transgenic mice

Cocaine abuse increases the incidence of HIV-1-associated neurocognitive disorders. We have demonstrated that HIV-1 transactivator of transcription (Tat) allosterically modulates dopamine (DA) reuptake through the human DA transporter (hDAT), potentially contributing to Tat-induced cognitive impairment and potentiation of cocaine conditioned place preference (CPP). This study determined the effects of a novel allosteric modulator of DAT, SRI-32743, on the interactions of HIV-1 Tat, DA, cocaine, and [³H]WIN35,428 with hDAT in vitro. SRI-32743 (50 nM) attenuated Tat-induced inhibition of [³H]DA uptake and decreased the cocaine-mediated dissociation of [³H]WIN35,428 binding in CHO cells expressing hDAT, suggesting a SRI-32743-mediated allosteric modulation of the Tat-DAT interaction. In further in vivo studies utilizing doxycycline-inducible Tat transgenic (iTat-tg) mice, 14 days of Tat expression significantly reduced the recognition index by 31.7% in the final phase of novel object recognition (NOR) and potentiated cocaine-CPP 2.7-fold compared to responses of vehicle-treated control iTat-tg mice. The Tat-induced NOR deficits and potentiation of cocaine-CPP were not observed in saline-treated iTat-tg or doxycycline-treated G-tg (Tat-null) mice. Systemic administration (i.p.) of SRI-32743 prior to behavioral testing ameliorated Tat-induced impairment of NOR (at a dose of 10 mg/kg) and the Tat-induced potentiation of cocaine-CPP (at doses of 1 or 10 mg/kg). These findings demonstrate that Tat and cocaine interactions with DAT may be regulated by compounds interacting at the DAT allosteric modulatory sites, suggesting a potential therapeutic intervention for HIV-infected patients with concurrent cocaine abuse.

Endocannabinoid control of glutamate NMDA receptors: the therapeutic potential and consequences of dysfunction

Glutamate is probably the most important excitatory neurotransmitter in the brain. The glutamate N-methyl-D-aspartate receptor (NMDAR) is a calcium-gated channel that coordinates with G protein-coupled receptors (GPCRs) to establish the efficiency of the synaptic transmission. Cross-regulation between these receptors requires the concerted activity of the histidine triad nucleotide-binding protein 1 (HINT1) and of the sigma receptor type 1 (σ1R). Essential brain functions like learning, memory formation and consolidation, mood and behavioral responses to exogenous stimuli depend on the activity of NMDARs. In this biological context, endocannabinoids are released to retain NMDAR activity within physiological limits. The efficacy of such control depends on HINT1/σ1R assisting in the physical coupling between cannabinoid type 1 receptors (CB1Rs) and NMDARs to dampen their activity. Subsequently, the calcium-regulated HINT1/σ1R protein tandem uncouples CB1Rs to prevent NMDAR hypofunction. Thus, early recruitment or a disproportionate cannabinoid induced response can bring about excess dampening of NMDAR activity, impeding its adequate integration with GPCR signaling. Alternatively, this control circuit can apparently be overridden in situations where bursts of NMDAR overactivity provoke convulsive syndromes. In this review we will discuss the possible relevance of the HINT1/σ1R tandem and its use by endocannabinoids to diminish NMDAR activity and their implications in psychosis/schizophrenia, as well as in NMDAR-mediated convulsive episodes.

Pregnenolone blocks cannabinoid-induced acute psychotic-like states in mice

Cannabis-induced acute psychotic-like states (CIAPS) represent a growing health issue, but their underlying neurobiological mechanisms are poorly understood. The use of antipsychotics and benzodiazepines against CIAPS is limited by side effects and/or by their ability to tackle only certain aspects of psychosis. Thus, safer wide-spectrum treatments are currently needed. Although the blockade of cannabinoid type-1 receptor (CB1) had been suggested as a therapeutical means against CIAPS, the use of orthosteric CB1 receptor full antagonists is strongly limited by undesired side effects and low efficacy. The neurosteroid pregnenolone has been recently shown to act as a potent endogenous allosteric signal-specific inhibitor of CB1 receptors. Thus, we tested in mice the potential therapeutic use of pregnenolone against acute psychotic-like effects of Δ⁹-tetrahydrocannabinol (THC), the main psychoactive component of cannabis. We found that pregnenolone blocks a wide spectrum of THC-induced endophenotypes typically associated with psychotic-like states, including impairments in cognitive functions, somatosensory gating and social interaction. In order to capture THC-induced positive psychotic-like symptoms (e.g. perceptual delusions), we adapted a behavioral paradigm based on associations between different sensory modalities and selective devaluation, allowing the measurement of mental sensory representations in mice. Acting at hippocampal CB1 receptors, THC impaired the correct processing of mental sensory representations (reality testing) in an antipsychotic- and pregnenolone-sensitive manner. Overall, this work reveals that signal-specific inhibitors mimicking pregnenolone effects can be considered as promising new therapeutic tools to treat CIAPS.

Long lasting effects of chronic heavy cannabis abuse

BACKGROUND AND OBJECTIVES

The purpose of this study was to evaluate the extent of short-term memory impairment and schizophrenia-like symptoms in heavy and systematic cannabis users and the association between the severity of abuse and the longevity of its persistent symptoms after refraining from such use.

METHODS

A complete psychiatric examination and a psychometric evaluation were performed in 48 solely cannabis users. Additionally, head hair samples were analyzed and the detected cannabinoids levels were correlated with the psychometric findings.

RESULTS

A total of 33.3% (n = 16) of the total examined cannabis users were currently imprisoned. The years of abuse ranged from 1 to 35 years and the median daily dose was 5.84.4 gr and 4.84.0 gr for prisoners (n = 16) and non prisoners (n = 32), respectively. A total of 39.6% of the users experienced hallucinations (mostly auditory), 54.2% experienced delusions (mostly ideas of reference and persecution), 85.4% had organic brain dysfunction in a test addressing visual-motor functioning and visual perception skills, and all users (100%) were found to have organic brain dysfunction in a test of visual memory immediate recall. The cannabinoid metabolite levels in the hair samples were consistent with the reported history of substance abuse and total grams of consumption for the participants below 35 years old (p < .001). Statistically elevated cannabinoids levels were observed in users with auditory hallucinations compared to users without any hallucinations (p = .019).

CONCLUSIONS

The existence of hallucinations, delusions, and organic brain dysfunction in heavy cannabis users seems to be associated with cannabinoid levels in hair. The continuation of persistent symptoms 3 months after the discontinuation of cannabis abuse, was a remarkable finding.

SCIENTIFIC SIGNIFICANCE

We provide evidence that chronic and heavy cannabis abuse results in long-lasting brain dysfunction in all users and in long-lasting schizophrenia-like psychotic symptoms in more than half of all users. These findings suggest a reevaluation of the current classification of cannabis as a "soft narcotic" which erroneously, therefore, is typically considered harmless. (Am J Addict 2017;26:335-342).

5-HT2C receptors in psychiatric disorders: A review

5-HT2Rs have a different genomic organization from other 5-HT2Rs. 5HT2CR undergoes post-transcriptional pre-mRNA editing generating diversity among RNA transcripts. Selective post-transcriptional editing could be involved in the pathophysiology of psychiatric disorders through impairment in G-protein interactions. Moreover, it may influence the therapeutic response to agents such as atypical antipsychotic drugs. Additionally, 5-HT2CR exhibits alternative splicing. Central serotonergic and dopaminergic systems interact to modulate normal and abnormal behaviors. Thus, 5HT2CR plays a crucial role in psychiatric disorders. 5HT2CR could be a relevant pharmacological target in the treatment of neuropsychiatric disorders. The development of drugs that specifically target 5-HT2C receptors will allow for better understanding of their involvement in the pathophysiology of psychiatric disorders including schizophrenia, anxiety, and depression. Among therapeutic means currently available, most drugs used to treat highly morbid psychiatric diseases interact at least partly with 5-HT2CRs. Pharmacologically, 5HT2CRs, have the ability to generate differentially distinct response signal transduction pathways depending on the type of 5HT2CR agonist. Although this receptor property has been clearly demonstrated, in vitro, the eventual beneficial impact of this property opens new perspectives in the development of agonists that could activate signal transduction pathways leading to better therapeutic efficiency with fewer adverse effects.

Therapeutic Potential of Cannabinoids in Psychosis

Over recent years, the interest in the endocannabinoid system (ECS) as a new target for the treatment of schizophrenia has evolved. The ECS represents one of the most relevant neurotransmitter systems in the brain and mainly fulfills a homeostatic role in terms of neurotransmission but also with respect to inflammatory processes. Two main approaches to the modulation of endocannabinoid functioning have been chosen so far. First, the selective blockade or inverse agonism of the type 1 cannabinoid receptor has been tested for the improvement of acute psychotic symptoms, as well as for the improvement of cognitive functions in schizophrenia. This was not effective in either case. Second, the modulation of endocannabinoid levels by use of the phytocannabinoid cannabidiol and selective fatty acid amide hydrolase inhibitors has been proposed, and the antipsychotic properties of cannabidiol are currently being investigated in humans. Unfortunately, for most of these trials that have focused on psychopathological and cognitive effects of cannabidiol, no published data are available. However, there is first evidence that cannabidiol may ameliorate psychotic symptoms with a superior side-effect profile compared with established antipsychotics. In conclusion, several clinical trials targeting the ECS in acute schizophrenia have either been completed or are underway. Although publicly available results are currently limited, preliminary data indicate that selected compounds modulating the ECS may be effective in acute schizophrenia. Nevertheless, so far, sample sizes of patients investigated are not sufficient to come to a final judgment, and no maintenance studies are available to ensure long-term efficacy and safety.

Cannabidiol enhances anandamide signaling and alleviates psychotic symptoms of schizophrenia

Cannabidiol is a component of marijuana that does not activate cannabinoid receptors, but moderately inhibits the degradation of the endocannabinoid anandamide. We previously reported that an elevation of anandamide levels in cerebrospinal fluid inversely correlated to psychotic symptoms. Furthermore, enhanced anandamide signaling let to a lower transition rate from initial prodromal states into frank psychosis as well as postponed transition. In our translational approach, we performed a double-blind, randomized clinical trial of cannabidiol vs amisulpride, a potent antipsychotic, in acute schizophrenia to evaluate the clinical relevance of our initial findings. Either treatment was safe and led to significant clinical improvement, but cannabidiol displayed a markedly superior side-effect profile. Moreover, cannabidiol treatment was accompanied by a significant increase in serum anandamide levels, which was significantly associated with clinical improvement. The results suggest that inhibition of anandamide deactivation may contribute to the antipsychotic effects of cannabidiol potentially representing a completely new mechanism in the treatment of schizophrenia.

Potential antipsychotic properties of central cannabinoid (CB1) receptor antagonists

Delta(9)-Tetrahydrocannabinol (Delta(9)-THC), the principal psychoactive constituent of the Cannabis sativa plant, and other agonists at the central cannabinoid (CB(1)) receptor may induce characteristic psychomotor effects, psychotic reactions and cognitive impairment resembling schizophrenia. These effects of Delta(9)-THC can be reduced in animal and human models of psychopathology by two exogenous cannabinoids, cannabidiol (CBD) and SR141716. CBD is the second most abundant constituent of Cannabis sativa that has weak partial antagonistic properties at the CB(1) receptor. CBD inhibits the reuptake and hydrolysis of anandamide, the most important endogenous CB(1) receptor agonist, and exhibits neuroprotective antioxidant activity. SR141716 is a potent and selective CB(1) receptor antagonist. Since both CBD and SR141716 can reverse many of the biochemical, physiological and behavioural effects of CB(1) receptor agonists, it has been proposed that both CBD and SR141716 have antipsychotic properties. Various experimental studies in animals, healthy human volunteers, and schizophrenic patients support this notion. Moreover, recent studies suggest that cannabinoids such as CBD and SR141716 have a pharmacological profile similar to that of atypical antipsychotic drugs. In this review, both preclinical and clinical studies investigating the potential antipsychotic effects of both CBD and SR141716 are presented together with the possible underlying mechanisms of action.

Upcoming agents for the treatment of schizophrenia: mechanism of action, efficacy and tolerability

Since the introduction of a group of atypical antipsychotics in the 1990s, there has been a decline in the rate of new antipsychotics being introduced into clinical practice. However, with increasing safety and efficacy concerns over currently available drugs and a dearth of options available for atypical depot formulations, there is a considerable need for the development of new formulations and agents. This review examines the profile of seven antipsychotic drugs currently in the premarketing stage of development and summarizes their mechanism of action, clinical potential and safety.Asenapine is an antipsychotic with activity for multiple receptors and has potential to improve negative and cognitive symptoms of schizophrenia. Bifeprunox is a partial dopamine D2 and serotonin 5-HT(1A) receptor agonist showing a less than convincing efficacy profile, but which may offer safety advantages over available agents by means of a reduced risk of metabolic complications. Iloperidone is a D2 and 5-HT(2A) receptor antagonist requiring further studies to establish its effectiveness. It has a high affinity for alpha(1)-adrenoceptors, which can lead to associated haemodynamic adverse effects. Nemonapride is essentially a typical antipsychotic drug, similar in structure to sulpiride, which has been available for some time in Japan. It has efficacy against positive symptoms and has shown some antidepressant and anxiolytic properties, although efficacy data for it are somewhat limited. Norclozapine (N-desmethylclozapine) is a major metabolite of clozapine formed by its demethylation. Its partial agonist activity at D2 receptors has raised interest in it as an antipsychotic in its own right. In addition, it appears to have muscarinic agonist activity, which is believed to be responsible for the observed positive effects it has on cognition. It was envisaged to be effective as an adjunct to other agents or at high doses in the treatment of refractory schizophrenia, although a recent randomized, controlled study showed that it was no more effective than placebo in patients with schizophrenia experiencing an acute psychotic episode. Olanzapine pamoate depot injection has shown comparable efficacy to oral olanzapine in several studies. However, it has provoked considerable safety concerns by its association with inadvertent intravascular injection events in numerous patients. This accidental intravascular administration of olanzapine pamoate leads to excessive sedation, confusion, dizziness and altered speech. Post-injection observation periods and postmarketing surveillance are planned following the introduction of the depot. Paliperidone palmitate is the palmitate ester of paliperidone, the major metabolite of risperidone, and is formulated as a long-acting injection for intramuscular use. Its pharmacology is comparable to risperidone, having D2 and 5-HT(2A) receptor antagonist activity. Efficacy studies have shown positive results, and because paliperidone has no antagonistic activity at cholinergic receptors, it has low potential for anticholinergic adverse effects, including cognitive dysfunction. However, with higher doses, the frequency of extrapyramidal side effects and orthostatic hypotension have been shown to be greater than with placebo.

Cognitive dysfunction in neuropsychiatric disorders: selected serotonin receptor subtypes as therapeutic targets

The indolamine, serotonin (5-hydroxytryptamine-5-HT) was identified and initially characterized around the middle of the twentieth century and it is now known to participate in multiple physiologic processes in mammalians. As a neurotransmitter, 5-HT is well documented to play a significant role in the pathophysiology and treatment of a variety of psychiatric disorders including anxiety, depression, and schizophrenia. In addition, there is also some evidence to suggest that 5-HT function in the brain may be important (particularly in the behavioral disturbances) in various forms of dementia including Alzheimer's disease. While 5-HT is undoubtedly involved in cognitive function, its role in specific domains of cognition (attention, learning, and memory, etc.) is poorly understood. This understanding has been impeded to some extent by the many complex interactions between 5-HT neurons and other neuronal phenotypes, 5-HT receptor heterogeneity, and the conflicting results of some behavioral experiments in animals conducted to date. Through the combined use of modern molecular biology, transgenic animal models, and other more traditional research methods such as medicinal chemistry and classical pharmacology, a clearer picture of the role of serotonin and its receptor subtypes in mnemonic processes is beginning to emerge, however. Considerable data now support the argument that selective ligands at specific 5-HT receptor subtypes can serve as therapeutic agents designed to enhance cognitive function in psychiatric disorders such as schizophrenia as well as age-related neurodegenerative illnesses such as Alzheimer's disease. The purpose of this review is to provide a brief overview of these therapeutic targets within the 5-HT system and the pharmacologic approaches (including the most recently developed compounds) designed to enhance memory function.

Feasibility of central cannabinoid CB1 receptor imaging with [124I]AM281 PET demonstrated in a schizophrenic patient

We studied central cannabinoid CB1 receptors in a schizophrenic patient using the pyrazole derivative AM281 labelled with the positron-emitting nuclide iodine-124. A dynamic positron emission tomography (PET) acquisition with simultaneous blood sampling was performed up to 1.5 h post-injection. The classical Logan plot analysis was applied to generate a three-dimensional map of distribution volume (DV). The map was spatially normalised into the Montreal Neurological Institute stereotactic space. Using a volume of interest (VOI) template, mean values of DV were extracted from multiple grey matter regions and white matter (as a reference). As a measure of regional receptor availability, ratios of DV in grey matter to DV in white matter minus one (DVR-1) were calculated. The highest receptor binding was observed in the striatum and the pallidum (DVR-1: 0.35-0.37). Binding in basal ganglia regions was lower on the left than the right side. Moderately high binding was seen in the frontal cortex (0.22), the temporal cortex (0.18) and the cerebellum (0.15). In conclusion, 124I-AM281 PET can be used to reveal areas with prominent CB1 receptor binding. Nevertheless, limited image contrast and relatively high radiation exposure (physical half-life of 124I: 4 days) have to be taken into account. Asymmetric receptor binding may possibly reflect pathologic changes in schizophrenia.

A Sleep-Promoting Role for the Drosophila Serotonin Receptor 1A

BACKGROUND

Although sleep is an important process essential for life, its regulation is poorly understood. The recently developed Drosophila model for sleep provides a powerful system to genetically and pharmacologically identify molecules that regulate sleep. Serotonin is an important neurotransmitter known to affect many behaviors, but its role in sleep remains controversial.

RESULTS

We generated or obtained flies with genetically altered expression of each of three Drosophila serotonin receptor subtypes (d5-HT1A, d5-HT1B, and d5-HT2) and assayed them for baseline sleep phenotypes. The data indicated a sleep-regulating role for the d5-HT1A receptor. d5-HT1A mutant flies had short and fragmented sleep, which was rescued by expressing the receptor in adult mushroom bodies, a structure associated with learning and memory in Drosophila. Neither the d5-HT2 receptor nor the d5-HT1B receptor, which was previously implicated in circadian regulation, had any effect on baseline sleep, indicating that serotonin affects sleep and circadian rhythms through distinct receptors. Elevating serotonin levels, either pharmacologically or genetically, enhanced sleep in wild-type flies. In addition, serotonin promoted sleep in some short-sleep mutants, suggesting that it can compensate for some sleep deficits.

CONCLUSIONS

These data show that serotonin promotes baseline sleep in Drosophila. They also link the regulation of sleep behavior by serotonin to a specific receptor in a distinct region of the fly brain.

Mental retardation genes in drosophila: New approaches to understanding and treating developmental brain disorders

Drosophila melanogaster is emerging as a valuable genetic model system for the study of mental retardation (MR). MR genes are remarkably similar between humans and fruit flies. Cognitive behavioral assays can detect reductions in learning and memory in flies with mutations in MR genes. Neuroanatomical methods, including some at single-neuron resolution, are helping to reveal the cellular bases of faulty brain development caused by MR gene mutations. Drosophila fragile X mental retardation 1 (dfmr1) is the fly counterpart of the human gene whose malfunction causes fragile X syndrome. Research on the fly gene is leading the field in molecular mechanisms of the gene product's biological function and in pharmacological rescue of brain and behavioral phenotypes. Future work holds the promise of using genetic pathway analysis and primary neuronal culture methods in Drosophila as tools for drug discovery for a wide range of MR and related disorders.

Dopaminergic contribution to the regulation of emotional perception

Dopamine (DA) acts as a key neurotransmitter in the brain. Numerous studies have shown its regulatory role in motor and cognitive function. However, the impairment of emotional processes in neurologic and psychiatric pathologies involving the dopaminergic system (Parkinson disease, schizophrenia, autism, Attention Deficit Hyperactivity Disorder, Huntington disease, frontal lobe lesions), as well as the influence that administration of dopaminergic agonists/antagonists exert on the processing of emotion, suggest a role for DA in emotional processes. Moreover, emotional processes are dependent upon a variety of structures, the majority of which form part of the limbic system and are subject to DA innervation. In reviewing the literature, the amygdala emerges as a brain structure critical for emotional processing. It may also be implicated in deficits in emotional recognition found in two major disorders where DA's implication is clear: Parkinson disease and schizophrenia. In addition, the amygdala's response to emotional tasks is likely to be altered by the administration of both agonist and antagonist dopaminergic drugs. Experimental studies reinforce the idea of a dopaminergic contribution to emotional response, as suggested by biochemical, pharmacologic, and lesion experiments. Although the implication of the dopaminergic system in emotional processing appears to be clearly documented, the contribution of specific DA receptor subtypes, or of the DA cotransmitters cholecystokinin and neurotensin, or even glutamate, is, however, still unclear. Altogether, these observations suggest that DA has, undoubtedly, a direct and/or indirect role in the full emotional process.

Differential effects of clozapine and haloperidol on interval timing in the supraseconds range

The effects of clozapine (0.6, 1.2, and 2.4 mg/kg) and haloperidol (0.03, 0.06, and 0.12 mg/kg) on the timing of 10, 30, and 90-s intervals were characterized in rats. Each drug's effect on timing behavior was assessed following intraperitoneal injections using a variant of the peak-interval procedure. Although haloperidol proportionately shifted peak times rightward in a manner consistent with a decrease in clock speed, clozapine exerted the opposite effect and proportionately shifted peak times leftward in a manner consistent with an increase in clock speed. These results support the proposal that typical antipsychotic drugs such as haloperidol and atypical antipsychotic drugs such as clozapine exert differential effects on dopaminergic, serotonergic, and glutamatergic systems within the cortex and striatum, two brain regions shown to be crucial for interval timing.

The search for novel antipsychotics: pharmacological and molecular targets

There can be little doubt that the newer, atypical, antipsychotic drugs provide improved treatment for many patients suffering from schizophrenia. However, the significant gains in tolerability produced by these drugs have not generally been accompanied by major advances in clinical efficacy. In particular, negative and cognitive symptoms, which may represent the core deficit of the disease, remain inadequately treated. There is, therefore, a pressing need for more effective drugs. A number of drug discovery and development programmes are currently underway in parallel with significant research into the basic neurobiology of the disease. All antipsychotic drugs currently used in the clinic are antagonists at dopamine D2 receptors, and dopamine neurotransmission seems likely to remain a major biological target for research. However, novel approaches to modulate dopaminergic neurotransmission selectively in relevant brain regions may be required. In addition, a range of non-dopaminergic targets including glutamate, serotonin, neurokinins and acetylcholine are also of major interest. It is likely, however, that the importance of many of these targets may lie in their relationships to and interactions with dopaminergic mechanisms. Finally, advances in genetics and molecular biology are identifying genes associated with a susceptibility to develop schizophrenia. It remains to be seen whether or not these genes and their associated proteins will provide molecular targets for successful drug discovery.

A role for cannabinoid CB1 receptors in mood and anxiety disorders

Mood and anxiety disorders, the most prevalent of the psychiatric disorders, cause immeasurable suffering worldwide. Despite impressive advances in pharmacological therapies, improvements in efficacy and side-effect profiles are needed. The present literature review examines the role that the endocannabinoid system may play in these disorders and the potential value of targeting this system in the search for novel and improved medications. Cannabis and its major psychoactive component (-)-trans-delta9-tetrahydrocannabinol, have profound effects on mood and can modulate anxiety and mood states. Cannabinoid receptors and other protein targets in the central nervous system (CNS) that modulate endocannabinoid function have been described. The discovery of selective modulators of some of these sites that increase or decrease endocannabinoid neurotransmission, primarily through the most prominent of the cannabinoid receptors in the CNS, the CB1 receptors, combined with transgenic mouse technology, has enabled detailed investigations into the role of these CNS sites in the regulation of mood and anxiety states. Although data point to the involvement of the endocannabinoid system in anxiety states, the pharmacological evidence seems contradictory: both anxiolytic- and anxiogenic-like effects have been reported with both endocannabinoid neurotransmission enhancers and blockers. Due to advances in the development of selective compounds directed at the CB1 receptors, significant progress has been made on this target. Recent biochemical and behavioural findings have demonstrated that blockade of CB1 receptors engenders antidepressant-like neurochemical changes (increases in extracellular levels of monoamines in cortical but not subcortical brain regions) and behavioural effects consistent with antidepressant/antistress activity in rodents.

Selective serotonin 5-HT2A receptor antagonist EMD 281014 improves delayed matching performance in young and aged rhesus monkeys

RATIONALE

The superior cognitive effects of atypical neuroleptics over typical agents reported in the schizophrenia literature are often attributed to the more prominent antagonist activity of the atypical drugs at serotonin 5HT(2A) receptors. However, atypical neuroleptics also have activity at many additional neurotransmitter receptors and few studies have specifically (and prospectively) tested the hypothesis that 5HT(2A) antagonism alone results in enhanced cognitive function.

OBJECTIVES

The purpose of this study was to evaluate the selective 5-HT(2A) antagonist, 7-{4-[2-(4-fluoro-phenyl)-ethyl]-piperazine-1-carbonyl}-1H-indole-3-carbonitrile HCl (EMD 281014) in young and aged monkeys in a test designed to assess working memory function.

METHODS

Four oral doses (0.1, 1.0, 3.0, and 10.0 mg/kg) of EMD 281014 were evaluated in six young adult (mean age=9.2 years) and eight aged rhesus macaques (mean age=24.9 years) trained to perform a computer-assisted delayed matching-to-sample (DMTS) task.

RESULTS

Depending on dose, EMD 281014 improved DMTS accuracy in young and aged monkeys primarily at either the medium or long retention intervals. While the latencies associated with incorrect color selections (choices latencies) tended to be longer than those associated with correct selections (particularly in the aged subjects) under baseline conditions, there were no significant effects of EMD 281014 on either sample or choice latencies in either age group. In addition, no adverse effects were observed across the range of doses evaluated in either cohort of animals.

CONCLUSION

These experiments, conducted in a non-human primate model, suggest that selective 5HT(2A) antagonists such as EMD 281014 could offer therapeutic benefit to younger and older psychiatric patients by improving working memory function.

CB1 cannabinoid receptors mediate anxiolytic effects: convergent genetic and pharmacological evidence with CB1-specific agents

Cannabinoids are known to modulate GABAergic and glutamatergic transmission in cortical areas, the former via CB1 and the latter via a novel receptor. Pharmacological data demonstrate that several widely used cannabinoid ligands bind to both receptors, which may explain the inconsistencies in their behavioural effects. Earlier we showed that the cannabinoid antagonist SR-141716A affected behaviour in both CB1 knockout and wild-type animals, and its effect (anxiolysis) was different from that of CB1 gene disruption (anxiogenesis). In the present experiments, we studied the effects of the CB1 antagonist AM-251, and the cannabinoid agonist WIN-55,212-2 in wild-type as well as in CB1 knockout mice. CB1 knockout mice showed higher scores of anxiety-like behaviour than the wild-type animals in the elevated plus-maze. Selective blockade of CB1 receptors by AM-251 (0.3, 1 and 3 mg/kg) increased anxiety-like behaviour dose-dependently in the wild-type mice but had no effect in the knockouts. In wild types, the cannabinoid agonist WIN-55,212-2 (1 and 3 mg/kg) caused a decrease in anxiety-like behaviour, which was abolished by the CB1-selective antagonist AM-251 (3 mg/kg). The same agonist did not change plus-maze behaviour in CB1 knockout animals. These data demonstrate at the behavioural level that AM-251 and, at low concentrations, WIN-55,212-2, are selective ligands of the CB1 cannabinoid receptor in mice. Our studies on the behavioural effects of the cannabinoid antagonist SR-141716A and the CB1 antagonist AM-251 show that the CB1 and the novel cannabinoid receptor mediate anxiolytic and anxiogenic effects, respectively. This suggests that agonists of the former, or antagonists of the latter, are promising new compounds in the pharmacotherapy of anxiety.

[123I]AM281 single-photon emission computed tomography imaging of central cannabinoid CB1 receptors before and after Delta9-tetrahydrocannabinol therapy and whole-body scanning for assessment of radiation dose in tourette patients

BACKGROUND

The cannabinoid CB1 receptor agonist Delta9-THC has been suggested for treatment of Tourette syndrome (TS). Based on animal studies, the CB1 antagonist [123I]AM281 (N-(Morpholin-4-yl)-1-(2,4-dichlorophenyl)-5-(4-[123I]iodophenyl)-4-methyl-1H-pyrazole-3-carboxamide) has been proposed for single photon emission computed tomography (SPECT) in humans. Our aims were to 1) evaluate specific binding of [123I]AM281 to CB1 receptors in TS patients and 2) assess radiation exposure associated with the use of AM281 labeled with 123I for SPECT and 124I for positron emission tomography.

METHODS

We employed [123I]AM281 in six TS patients before and after Delta9-THC treatment. Dynamic SPECT, plasma measurements (including metabolite analysis with thin layer chromatography), and whole-body imaging were performed. Regions of interest derived from magnetic resonance images were used to extract from SPECT uptake in an area with high CB1 density (lentiform nuclei) and reference regions. Specific over nonspecific partition coefficients V3" were calculated. Whole-body images were carried out for dosimetric analysis. Data obtained with [123I]AM281 were used to predict doses from [124I]AM281.

RESULTS

Mean V3" ranged from .19 to .31 and did not change significantly after Delta9-THC treatment. Nevertheless, in the only patient with a marked clinical response, V3" clearly declined. Thin layer chromatography revealed biexponential kinetics of tracer metabolism; about 60% remained nonmetabolized after 3 hours. Effective doses of .011 mSv/MBq for [123I]AM281 and .34 for [124I]AM281 were computed.

CONCLUSIONS

This study suggests that specific binding of [123I]AM281 to CB1 receptors can be detected in patients using SPECT. Radiation exposure with [123I]AM281 is low; that with [124I]AM281 is higher but acceptable for single investigations.

The selective serotonin-2A receptor antagonist M100907 reverses behavioral deficits in dopamine transporter knockout mice

A hyperdopaminergic state in humans has been hypothesized to contribute to the pathology of a number of psychiatric illnesses, including schizophrenia, bipolar disorder, and attention deficit hyperactivity disorder. Mice that display elevated synaptic levels of dopamine due to a genetically engineered deletion of the dopamine transporter (DAT) model behavioral deficits that simulate the above conditions. As novel treatment strategies for these disorders have focused on the serotonin (5-HT) 2A receptor, we determined the capacity of the highly selective 5-HT(2A) receptor antagonist M100907 to reverse behavioral deficits in DAT knockout (KO) mice. Prior to drug treatment, DAT KO mice exhibited increased levels of locomotor activity and highly linearized movement in a novel environment, as well as reduced prepulse inhibition (PPI) of acoustic startle, compared to wild-type littermates. Treatment with M100907 (0.3-1.0 mg/kg, but not 0.1 mg/kg) reversed locomotor deficits in DAT KO mice. Similarly, treatment with 1.0 mg/kg M100907 reversed the PPI deficits in DAT KO mice. These data indicate that selective 5-HT(2A) receptor antagonists, such as M100907, may represent a class of drugs that can be used to treat conditions in which a chronic, elevated dopaminergic tone is present and contributes to abnormal behavior and sensorimotor gating deficits.

SSR181507, a dopamine D(2) receptor antagonist and 5-HT(1A) receptor agonist. I: Neurochemical and electrophysiological profile

SSR181507 ((3-exo)-8-benzoyl-N-[[(2S)7-chloro-2,3-dihydro-1,4-benzodioxin-1-yl]methyl]-8-azabicyclo[3.2.1]octane-3-methanamine monohydrochloride) is a novel tropanemethanamine benzodioxane derivative that possesses high and selective affinities for D2-like and 5-HT(1A) receptors (K(I)=0.8, 0.2, and 0.2 nM for human D(2), D(3), and 5-HT(1A), respectively). In vivo, SSR181507 inhibited [(3)H]raclopride binding to D(2) receptors in the rat (ID(50)=0.9 and 1 mg/kg, i.p. in limbic system and striatum, respectively). It displayed D(2) antagonist and 5-HT(1A) agonist properties in the same concentration range in vitro (IC(50)=5.3 nM and EC(50)=2.3 nM, respectively, in the GTPgammaS model) and in the same dose range in vivo (ED(50)=1.6 and 0.7 mg/kg, i.p. on striatal DA and 5-HT synthesis, respectively, and 0.03-0.3 mg/kg, i.v. on dorsal raphe nucleus firing rate). It selectively enhanced Fos immunoreactivity in mesocorticolimbic areas as compared to the striatum. This regional selectivity was confirmed in electrophysiological studies where SSR181507, given acutely (0.1-3 mg/kg, i.p.) or chronically (3 mg/kg, i.p., o.d., 22 days), increased or decreased, respectively, the number of spontaneous active DA cells in the ventral tegmental area, but not in the substantia nigra. Moreover, SSR181507 increased both basal and phasic DA efflux (as assessed by microdialysis and electrochemistry) in the medial prefrontal cortex and nucleus accumbens, but not in the striatum. This study shows that the combination of D(2) receptor antagonism and 5-HT(1A) agonism, in the same dose range, confers on SSR181507 a unique neurochemical and electrophysiological profile and suggests the potential of this compound for the treatment of the main dimensions of schizophrenia.

Modulation of neuroleptic activity of 9,10-didehydro-N-methyl-(2-propynyl)-6-methyl-8-aminomethylergoline bimaleinate (LEK-8829) by D1 intrinsic activity in hemi-parkinsonian rats

Parkinsonism, a common unwanted side effect of typical antipsychotic (neuroleptic) drugs, is induced by the blockade of striatal dopamine D2 receptors. In rats with hemi-parkinsonism induced by unilateral lesion of dopaminergic nigrostriatal neurons with 6-hydroxydopamine, D2 antagonists inhibit contralateral turning induced by D2 agonists and augment the levels of neurotensin mRNA in dopaminergically intact striatum. By contrast, D1 agonists induce contralateral turning and augment neurotensin mRNA levels in dopamine-depleted striatum. These effects could be inhibited by D1 but not by D2 antagonists. Here we used a hemi-parkinsonian model to investigate the effects of putative D1 agonist/D2 antagonist LEK-8829 (9,10-didehydro-N-methyl-(2-propynyl)-6-methyl-8-aminomethylergoline bimaleinate), an experimental antipsychotic, on turning behavior and the expression of striatal neurotensin, preprotachykinin and neurotransmitter-induced early gene protein 4 (ania-4) mRNAs. We found that LEK-8829 inhibited contralateral turning induced by D2 agonist quinpirole, but only if the rats were cotreated with D1 antagonist SCH-23390. In situ hybridization showed that LEK-8829 induced the expression of neurotensin and ania-4 mRNAs in dopamine-intact striatum that could be completely blocked only by the combined treatment with SCH-23390 and quinpirole. In addition, LEK-8829 augmented the expression of neurotensin, preprotachykinin and ania-4 mRNAs in dopamine-depleted striatum that could be completely blocked by SCH-23390. This study clearly demonstrates that in hemi-parkinsonian rats D1 agonistic activity of LEK-8829 confers its anti-parkinsonian drug-like properties and modulates its neuroleptic drug-like properties, which are dependent on the blockade of dopamine D2 receptors. These findings imply that atypical antipsychotics with D1 intrinsic activity might have a reduced propensity for the induction of extrapyramidal syndrome.

Comparison of clozapine and haloperidol on some autonomic and psychomotor functions, and on serum prolactin concentration, in healthy subjects

AIMS

To compare the autonomic, neuroendocrine and psychomotor effects of single doses of the 'atypical' antipsychotic clozapine and the 'classical' antipsychotic haloperidol, in healthy male volunteers.

METHODS

Clozapine (50 mg), haloperidol (3 mg) and placebo were administered to 12 healthy male volunteers at weekly intervals, according to a balanced double-blind design. Resting pupil diameter, salivary output, heart rate, blood pressure, plasma prolactin concentration, critical flicker fusion frequency and subjective 'alertness', 'contentedness' and 'anxiety' were measured at baseline and 2, 3, 4 and 5 h after drug ingestion. Data were analysed by analysis of variance with individual comparisons (Dunnett's test) with a significance criterion of P < 0.05.

RESULTS

Significant treatment effects (difference from placebo [mean, 95% CI] 5 h after drug ingestion) were as follows: clozapine reduced pupil diameter (mm; -3.02 [-3.56, -2.47]), salivary output (g; -0.34 [-0.60, -0.08]), mean arterial blood pressure (mm Hg; -8.7 [-14.3, -3.1]), critical flicker fusion frequency (Hz; -3.26 [-3.94, -2.58]), and subjectively-rated 'alertness' (mm; -20.94 [-29.21, -12.67]) and 'contentedness' (mm; -12.98 [-17.90, -8.06]), whereas haloperidol increased prolactin concentration (mU l(-1); 301.3 [196.7, 405.8]) and caused small reductions in pupil diameter (mm; -0.68 [-1.23, -0.14]), mean arterial blood pressure (mm Hg; -7.0 [-12.6, -1.4]) and critical flicker fusion frequency (Hz; -1.15 [-1.83, -0.47]).

CONCLUSIONS

The effects of the antipsychotics are in agreement with their receptor binding profiles: alpha(1)-adrenoceptor blockade by clozapine may contribute to reductions in pupil diameter, salivation, mean arterial blood pressure and sedation, and muscarinic cholinoceptor blockade by the drug may underlie the reduction in salivation. Conversely, D(2) dopamine receptor blockade by haloperidol is likely to be responsible for the increase in prolactin secretion evoked by the drug.