Clozapine blocks dopamine, 5-HT2 and 5-HT3 responses in the medial prefrontal cortex: an in vivo microiontophoretic study

Computational/in silico methods in drug target and lead prediction

Drug-like compounds are most of the time denied approval and use owing to the unexpected clinical side effects and cross-reactivity observed during clinical trials. These unexpected outcomes resulting in significant increase in attrition rate centralizes on the selected drug targets. These targets may be disease candidate proteins or genes, biological pathways, disease-associated microRNAs, disease-related biomarkers, abnormal molecular phenotypes, crucial nodes of biological network or molecular functions. This is generally linked to several factors, including incomplete knowledge on the drug targets and unpredicted pharmacokinetic expressions upon target interaction or off-target effects. A method used to identify targets, especially for polygenic diseases, is essential and constitutes a major bottleneck in drug development with the fundamental stage being the identification and validation of drug targets of interest for further downstream processes. Thus, various computational methods have been developed to complement experimental approaches in drug discovery. Here, we present an overview of various computational methods and tools applied in predicting or validating drug targets and drug-like molecules. We provide an overview on their advantages and compare these methods to identify effective methods which likely lead to optimal results. We also explore major sources of drug failure considering the challenges and opportunities involved. This review might guide researchers on selecting the most efficient approach or technique during the computational drug discovery process.

Functional Changes of Orexinergic Reaction to Psychoactive Substances

It is becoming increasingly apparent the importance of the central nervous system (CNS) as the major contributor to the regulation of systemic metabolism. Antipsychotic drugs are used often to treat several psychiatric disorders, including schizophrenia and bipolar disorder However, antipsychotic drugs prescription, particularly the second-generation ones (SGAs), such as clozapine and olanzapine, is related to a considerable weight gain which usually leads to obesity. The aim of this paper is to assess the influence of orexin A on sympathetic and hyperthermic reactions to several neuroleptic drugs. Orexin A is a neuropeptide which effects both body temperature and food intake by increasing sympathetic activity. Orexin A-mediated hyperthermia is reduced by haloperidol and is blocked by clozapine and olanzapine. Orexin A-mediated body temperature elevation is increased by risperidone. These hyperthermic effects are delayed by quietapine. In this paper, it is discussed the orexinergic pathway activation by neuroleptic drugs and its influence on human therapeutic strategies. With the aim to determine that neuroleptic drugs mediate body temperature control through to the orexinergic system, we summarized our previously published data. Psychiatric disorders increase the risk of developing metabolic disorders (e.g., weight gain, increased blood pressure, and glucose or lipid levels). Therefore, the choice of antipsychotic drug to be prescribed, based on the relevant risks and benefits of each individual drug, has an essential role in human health prevention.

Clozapine-induced dysphagia with secondary substantial weight loss

Dysphagia is listed as a 'rare' side effect following clozapine treatment. In this case report, we describe how significant clozapine-induced dysphagia has led to significant reduction of nutritional intake with subsequent substantial weight loss. An 18-year-old single man with an established diagnosis of treatment-resistant paranoid schizophrenia recovered well on a therapeutic dose of clozapine. However, he was noted to lose weight significantly (up to 20% of his original weight) as the dose was uptitrated. This was brought about by development of dysphagia, likely to be due to clozapine. Addition of nutritional supplementary liquids and initiation of a modified behavioural dietary/swallowing programme, while repeatedly mastering the Mendelsohn manoeuvre technique, alleviated the swallowing difficulties and restored his weight.

Enhancing the Enrichment of Pharmacophore-Based Target Prediction for the Polypharmacological Profiles of Drugs

PharmMapper is a web server for drug target identification by reversed pharmacophore matching the query compound against an annotated pharmacophore model database, which provides a computational polypharmacology prediction approach for drug repurposing and side effect risk evaluation. But due to the inherent nondiscriminative feature of the simple fit scores used for prediction results ranking, the signal/noise ratio of the prediction results is high, posing a challenge for predictive reliability. In this paper, we improved the predictive accuracy of PharmMapper by generating a ligand-target pairwise fit score matrix from profiling all the annotated pharmacophore models against corresponding ligands in the original complex structures that were used to extract these pharmacophore models. The matrix reflects the noise baseline of fit score distribution of the background database, thus enabling estimation of the probability of finding a given target randomly with the calculated ligand-pharmacophore fit score. Two retrospective tests were performed which confirmed that the probability-based ranking score outperformed the simple fit score in terms of identification of both known drug targets and adverse drug reaction related off-targets.

Are 5-HT3 antagonists effective in obsessive-compulsive disorder? A systematic review of literature

OBJECTIVE

The purpose of this literature database search-based review was to critically consider and evaluate the findings of literature focusing on efficacy and safety of 5-HT3 antagonists in the treatment of obsessive-compulsive disorder (OCD), so as to test whether preclinical data match clinical therapeutic trials.

DESIGN

The PubMed database has been searched for papers on 5-HT3 antagonists and OCD in humans and for animal models of OCD and 5-HT3 receptors.

RESULTS

Of the clinically tested 5-HT3 receptor antagonists, ondansetron has been used to treat OCD in five therapeutic studies, whereas granisetron only in one recent trial. Both showed some efficacy in open studies and superiority to placebo in double-blind studies, along with fair safety. No animal OCD model directly implicated 5-HT3 receptors.

CONCLUSIONS

Overall, results indicate some utility, but the available literature is too scanty to allow for valid conclusions to be drawn. The mismatch between animal models of obsessive-compulsive disorder and clinical data with 5-HT3 antagonists needs more clinical data to ensure that it is not an artefact.

Characterizing the pocketome of Mycobacterium tuberculosis and application in rationalizing polypharmacological target selection

Polypharmacology is beginning to emerge as an important concept in the field of drug discovery. However, there are no established approaches to either select appropriate target sets or design polypharmacological drugs. Here, we propose a structural-proteomics approach that utilizes the structural information of the binding sites at a genome-scale obtained through in-house algorithms to characterize the pocketome, yielding a list of ligands that can participate in various biochemical events in the mycobacterial cell. The pocket-type space is seen to be much larger than the sequence or fold-space, suggesting that variations at the site-level contribute significantly to functional repertoire of the organism. All-pair comparisons of binding sites within Mycobacterium tuberculosis (Mtb), pocket-similarity network construction and clustering result in identification of binding-site sets, each containing a group of similar binding sites, theoretically having a potential to interact with a common set of compounds. A polypharmacology index is formulated to rank targets by incorporating a measure of druggability and similarity to other pockets within the proteome. This study presents a rational approach to identify targets with polypharmacological potential along with possible drugs for repurposing, while simultaneously, obtaining clues on lead compounds for use in new drug-discovery pipelines.

The psychopharmacology of aggressive behavior: a translational approach: part 1: neurobiology

Patients with mental disorders are at an elevated risk for developing aggressive behavior. In the last 19 years, the psychopharmacological treatment of aggression has changed dramatically because of the introduction of atypical antipsychotics into the market and the increased use of anticonvulsants and lithium in the treatment of aggressive patients.Using a translational medicine approach, this review (part 1 of 2) examines the neurobiology of aggression, discussing the major neurotransmitter systems implicated in its pathogenesis, namely, serotonin, glutamate, norepinephrine, dopamine, and γ-aminobutyric acid, and also their respective receptors. The preclinical and clinical pharmacological studies concerning the role of these neurotransmitters have been reviewed, as well as research using transgenic animal models. The complex interaction among these neurotransmitters occurs at the level of brain areas and neural circuits such as the orbitoprefrontal cortex, anterior cortex, amygdala, hippocampus, periaqueductal gray, and septal nuclei, where the receptors of these neurotransmitters are expressed. The neurobiological mechanism of aggression is important to understand the rationale for using atypical antipsychotics, anticonvulsants, and lithium in treating aggressive behavior. Further research is necessary to establish how these neurotransmitter systems interact with brain circuits to control aggressive behavior at the intracellular level.

Differential effects of 5-HT(2A) and 5-HT(2C) receptor blockade on strategy-switching

Recent experiments indicate that blockade of serotonin (5-HT) 2A and 2C receptors have differential effects on reversal learning. The present experiments investigated the effects of the 5-HT(2A) receptor antagonist, ketanserin and 5-HT(2C) receptor antagonist, SB242084 on acquisition and strategy-switching in a visual cue-response paradigm. Long-Evans rats were trained in a cross-maze to enter an arm based on color (visual cue version) or a specific turn response (response version). Systemic treatment with ketanserin did not affect initial learning of a visual cue or response discrimination, but ketanserin at 0.5 mg/kg significantly enhanced a switch between visual cue and response strategies. Ketanserin facilitated strategy-switching by inhibiting responses to a previously relevant strategy without affecting choices to never-reinforced strategies. Treatment with SB242084 (0.5, 1.0 or 2.0 mg/kg) did not affect acquisition of a visual cue or response discrimination. SB242084 treatment also did not affect strategy-switching. The present findings suggest that blockade of 5-HT(2A), but not 5-HT(2C), receptors enhance strategy switching.

Clozapine but not haloperidol treatment reverses sub-chronic phencyclidine-induced disruption of conditional discrimination performance

Abusers of phencyclidine (PCP) often present with a symptom profile similar to that exhibited by schizophrenic patients. Animal models utilising such psychotomimetics are currently informing research into the condition. Accumulating evidence suggests that a central cognitive deficit in schizophrenia is the inability to use task-setting cues to guide goal directed behaviour and that this ability is mediated by prefrontal dopamine (DA). The current study used the non-competitive NMDA antagonist phencyclidine (PCP) and Haloperidol (typical antipsychotic) and Clozapine (atypical antipsychotic) in order to further investigate the influence of DAergic manipulation on a task that requires the use of conditional information to inform goal-directed performance. An instrumental conditional discrimination task was employed in which rats learn to respond appropriately according to the presence of specific auditory conditional stimuli. Probe test 1 showed impaired conditional discrimination performance following sub-chronic PCP administration (seven twice-daily injection protocol) compared to control which was reversed by acute treatment with clozapine (5 mg/kg) but not haloperidol (0.1 mg/kg) both administered 60 min pre-test. Probe test 2 (8 days post-treatment) showed enduring deficits to conditional discrimination performance that were again reversed by clozapine but not haloperidol (injection procedures as above). These results show that tasks dependent upon conditional relationships are particularly sensitive to manipulation of DAergic systems as prolonged treatment with PCP has been shown to selectively reduce prefrontal cortex (PFC) DA activity and treatment with clozapine (known to ameliorate cognitive deficits) but not haloperidol has been shown to selectively restore PFC DA levels.

Sodium- and magnesium-valproate in vivo modulate glutamatergic and GABAergic synapses in the medial prefrontal cortex

RATIONALE

Valproic acid (VPA) is a psychoactive drug currently used for the treatment of epilepsy. Recently it has been introduced in psychiatry for the treatment of bipolar disorders, aggression, impulsivity, and resistant schizophrenia, although the mechanism by which VPA acts on these psychiatric diseases remains still unknown.

OBJECTIVES

The aim of this study was to analyze the distinct effects of sodium-(Na-) and magnesium-valproate (Mg-VPA) in pyramidal neurons of the medial prefrontal cortex (mPFC) and their interactions with gamma-aminobutyric acid (GABA) and excitatory amino acid responses.

MATERIALS AND METHODS

In vivo electrophysiology and microiontophoresis techniques were used to attend these goals.

RESULTS

Both VPA salts decreased spontaneous neuronal firing activity in greater than 60% of recorded pyramidal neurons as well as potentiated GABA inhibitions. When injected at equal concentrations and currents, Mg-VPA blocked the excitatory responses induced by N-methyl-D-aspartate (NMDA) more frequently than Na-VPA. Both VPA salts equally blocked the excitatory responses of quisqualate and kainate.

CONCLUSIONS

These data suggest that VPA salts significantly modulate the activity of excitatory amino acid at mPFC pyramidal neurons and this mechanism should explain the therapeutic effects of valproate in psychiatric diseases involving NMDA, AMPA, and kainate receptors at the mPFC level.

A simulation model for compensatory plasticity in the prefrontal cortex inducing a cortico-cortical dysconnection in early brain development

In the present work, an abstract prefrontal cortex simulation model is used to predict compensatory structural alterations of the cortico-cortical connectivity pattern in the normal and pathologic forebrain maturation. The simulation network shows different representative courses of morphogenesis when developing undisturbed or when suffering from disturbing excitatory afferences. The simulative results could be affirmed by an immuno-histochemical study, revealing a qualitatively comparable development of the glutamatergic projection fibre density in gerbils (Meriones unguiculatus) after juvenile and adult methamphetamine intoxication. The simulation model further allows to consider different rearing conditions (enriched-environment model), and claims contradictory effects of an equal disturbance after enriched or impoverished rearing which are in accordance with the experimental findings.

Hyperlocomotive and discriminative stimulus effects of cocaine are under the control of serotonin(2C) (5-HT(2C)) receptors in rat prefrontal cortex

The serotonin2C (5-hydroxytryptamine2C; 5-HT2C) receptor (5-HT2CR) is found in abundance in dopamine (DA) mesocorticolimbic pathways and is one of the important target proteins that modulates the behavioral effects of cocaine. In the present study, the hypothesis was tested that the 5-HT2CR in the prefrontal cortex (PFC) may control either spontaneous or cocaine-evoked locomotor activity as well as the discriminative stimulus properties of cocaine. In male Sprague-Dawley rats implanted with bilateral cannulae aimed at the PFC, local microinjections of the preferential 5-HT2CR agonist 6-chloro-2-(1-piperazinyl)pyrazine hydrochloride (MK 212) (0.05-0.5 microg/side) did not alter spontaneous activity, but dose-dependently decreased horizontal hyperactivity evoked by cocaine (10 mg/kg i.p.). Given alone, the selective 5-HT2CR antagonist 8-[5-(2,4-dimethoxy-5-(4-trifluorophenylsulfonamido)phenyl-5-oxopentyl]-1,3,8-triazo-spiro[4.5]decane-2,4-dione hydrochloride (RS 102221) (5 microg/side) increased basal locomotor activity of rats expressed in the vertical plane. Microinjections of RS 102221 (5 microg/side, but not 0.15-1.5 microg/side) significantly enhanced the horizontal activity induced by cocaine (10 mg/kg). In rats trained to discriminate cocaine (10 mg/kg i.p.) from saline (i.p.) in a two-lever, water-reinforced fixed ratio 20 task, intra-PFC microinjections of MK 212 (0.05 and 0.5 microg/side) did not substitute for cocaine, but attenuated the stimulus effects of cocaine. However, intra-PFC microinjections of RS 102221 (1.5 and 5 microg/side) evoked 13 and 40% cocaine-lever responding when tested alone and enhanced the recognition of cocaine. These data indicate that the PFC is a brain site at which the 5-HT2CR exerts an inhibitory control over the hyperactive and discriminative stimulus effects of cocaine known to be dependent upon activation of the DA mesoaccumbens circuit.

Activation of presynaptic D1 dopamine receptors by dopamine increases the frequency of spontaneous excitatory postsynaptic currents through protein kinase A and protein kinase C in pyramidal cells of rat prelimbic cortex

To determine the effect of dopamine on the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in pyramidal cells of layers V-VI of the prelimbic cortex, whole-cell patch-clamp recordings were made from 92 pyramidal cells of layers V-VI of the rat prelimbic cortex. In normal buffer, dopamine 100 microM apparently increased the frequency of spontaneous EPSCs. Decreasing the concentration of dopamine from 100 to 50 microM was accompanied by a decreased effect of dopamine. Further decreasing the dopamine concentration to 10 and 1 microM had no effects on the frequency of spontaneous EPSCs. In the presence of tetrodotoxin or cadmium, the increasing effect of dopamine was eliminated. The increasing effect of dopamine was blocked by the dopamine D1 receptor antagonist SCH23390, but not by the dopamine D2 receptor antagonist sulpiride. The D1 receptor agonist SKF38393 partially mimicked the increasing effect, but the D2 receptor agonist quinpirole did not. The alpha(1)-adrenoceptor antagonist prazosin could not block the increasing effect of dopamine on the frequency of spontaneous EPSCs in most cells tested. The protein kinase A inhibitor H-89 and the protein kinase C inhibitor chelerythrine could antagonize the effect of dopamine. The protein kinase A activator forskolin and the protein kinase C activator phorbol 12,13-dibutyrate could mimic the effect of dopamine. These results indicate that dopamine, presynaptically acting on dopamine D1 receptors, increases the frequency of spontaneous EPSCs via intracellular protein kinase A and protein kinase C signaling pathways in pyramidal cells of layers V-VI of the prelimbic cortex.

Prefrontal cortical sulcal widening associated with poor treatment response to clozapine

Increased sulcal widening in the prefrontal cortex of patients with schizophrenia may be associated with a poor treatment response to clozapine. To further evaluate this, we examined data from patients treated with clozapine in our center. Patients with the greatest degree of improvement (n=26) and those with no improvement (n=10) were compared. Computerized tomography (CT) scans were rated blindly on a visual scale of prefrontal sulcal widening. Patients with the greatest degree of functional improvement had significantly less prefrontal sulcal widening than those whose symptoms remained unchanged. There was no relationship between clozapine response and general sulcal widening. These data support the link between the superior therapeutic efficacy of clozapine and the integrity of the prefrontal cortex.

Pharmacology and behavioral pharmacology of the mesocortical dopamine system

The prefrontal cortex (PFC) has long been known to be involved in the mediation of complex behavioral responses. Considerable research efforts are directed towards refining the knowledge about the function of this brain area and the role it plays in cognitive performance and behavioral output. In the first part, this review provides, from a pharmacological perspective, an overview of anatomical, electrophysiological and neurochemical aspects of the function of the PFC, with an emphasis on the mesocortical dopamine system. Anatomy of the mesocortical system, basic physiological and pharmacological properties of neurotransmission within the PFC, and interactions between dopamine and glutamate as well as other transmitters within the mesocorticolimbic circuit are included. The coverage of these data is largely restricted to what is relevant for the second part of the review which focuses on behavioral studies that have examined the role of the PFC in a variety of phenomena, behaviors and paradigms. These include reward and addiction, locomotor activity and sensitization, learning, cognition, and schizophrenia. Although the focus of this review is on the mesocortical dopamine system, given the intricate interactions of dopamine with other transmitter systems within the PFC and the importance of the PFC as a source of glutamate in subcortical areas, these aspects are also covered in some detail where appropriate. Naturally, a topic as complex as this cannot be covered comprehensively in its entirety. Therefore this review is largely limited to data derived from studies using rats, and it is also specifically restricted to data concerning the medial PFC (mPFC). Since in several fields of research the findings concerning the function or role of the mPFC are relatively inconsistent, the question is addressed whether these inconsistencies might, at least in part, be related to the anatomical and functional heterogeneity of this brain area.