Treating schizophrenia symptoms with an alpha7 nicotinic agonist, from mice to men

Unusual effects of nicotine as a psychostimulant on ambulatory activity in mice

The present study examined the effect of nicotine, alone and in combination with various drugs that act on the CNS, on ambulatory activity, a behavioral index for locomotion, in ICR (CD-1) strain mice. Nicotine at 0.25–2 mg/kg acutely reduced ambulatory activity of ICR mice. The effect of nicotine was similar to that of haloperidol and fluphenazine but distinct from that of bupropion and methylphenidate. ICR mice developed tolerance against the inhibitory effect of nicotine on ambulatory activity when nicotine was repeatedly administered. This effect was also distinct from bupropion and methylphenidate as they produced augmentation of their ambulation-stimulating effects in ICR mice. Nicotine reduced the ambulation-stimulating effects of bupropion and methylphenidate as well as haloperidol and fluphenazine. Taken together, nicotine exhibited unusual effects as a psychostimulant on ambulatory activity in ICR mice.

3-(2,4-dimethoxybenzylidene)-anabaseine: a promising candidate drug for Alzheimer's disease?

3-(2,4-dimethoxybenzylidene)-anabaseine is an analog of the paralytic alkaloid, anabaseine, from the ribbon worms Amphiporus sp., that shows numerous properties, in particular an agonist activity on alpha 7 nicotinic acetylcholine receptors. This article reviews these properties and explains to what extent they could be valuable to control symptomatology and/or neurodegeneration in Alzheimer's disease.

α7 nicotinic ACh receptors as a ligand-gated source of Ca(2+) ions: the search for a Ca(2+) optimum

The spatiotemporal distribution of cytosolic Ca(2+) ions is a key determinant of neuronal behavior and survival. Distinct sources of Ca(2+) ions including ligand- and voltage-gated Ca(2+) channels contribute to intracellular Ca(2+) homeostasis. Many normal physiological and therapeutic neuronal functions are Ca(2+)-dependent, however an excess of cytosolic Ca(2+) or a lack of the appropriate balance between Ca(2+) entry and clearance may destroy cellular integrity and cause cellular death. Therefore, the existence of optimal spatiotemporal patterns of cytosolic Ca(2+) elevations and thus, optimal activation of ligand- and voltage-gated Ca(2+) ion channels are postulated to benefit neuronal function and survival. Alpha7 nicotinic -acetylcholine receptors (nAChRs) are highly permeable to Ca(2+) ions and play an important role in modulation of neurotransmitter release, gene expression and neuroprotection in a variety of neuronal and non-neuronal cells. In this review, the focus is placed on α7 nAChR-mediated currents and Ca(2+) influx and how this source of Ca(2+) entry compares to NMDA receptors in supporting cytosolic Ca(2+) homeostasis, neuronal function and survival.

Occupancy of α7 Nicotinic Acetylcholine Receptors in the Brain by Tropisetron: A Positron Emission Tomography Study Using [(11)C]CHIBA-1001 in Healthy Human Subjects

OBJECTIVE

Agonists of α7-nicotinic acetylcholine receptors (nAChRs) have been developed as potential therapeutic drugs for neuropsychiatric diseases such as schizophrenia and Alzheimer's disease. Positron emission tomography (PET) is a noninvasive brain imaging technique to measure receptor occupancy in the living human brain. Although much effort has been expended to create specific PET radioligands for α7-nAChRs in the brain, only 4-[(11)C]methylphenyl-1,4-diazabicyclo[3.2.2.]nonane-4-carboxylate ([(11)C]CHIBA-1001) is currently available for clinical studies. In contrast, two 5-hydroxytryptamine-3 (5-HT(3)) receptor antagonists, tropisetron and ondansetron, have been used to treat patients with chemotherapy-induced or postoperative nausea and vomiting. Furthermore, tropisetron, but not ondansetron, possesses high affinity for α7-nAChRs. In the present study, we evaluated the receptor occupancy in the human brain after a single oral administration of tropisetron and ondansetron using [(11)C]CHIBA-1001 and PET.

METHODS

Two serial dynamic PET scans using [(11)C]CHIBA-1001 in healthy non-smoking male subjects were performed before and after receiving an oral administration of these medications.

RESULTS

A single oral administration of tropisetron, but not ondansetron, decreased the total distribution volume of [(11)C]CHIBA-1001 in the human brain.

CONCLUSION

This study shows that tropisetron, but not ondansetron, could bind to α7-nAChRs in the human brain after a single oral administration. Therefore, [(11)C]CHIBA-1001 may be a useful PET radioligand to measure the occupancy of α7-nAChRs in the human brain.

Chaperoning α7 neuronal nicotinic acetylcholine receptors

The α7 subtype of nicotinic acetylcholine receptors (AChRs) is one of the most abundant members of the Cys-loop family of receptors present in the central nervous system. It participates in various physiological processes and has received much attention as a potential therapeutic target for a variety of pathologies. The importance of understanding the mechanisms controlling AChR assembly and cell-surface delivery lies in the fact that these two processes are key to determining the functional pool of receptors actively engaged in synaptic transmission. Here we review recent studies showing that RIC-3, a protein originally identified in the worm Caenorhabditis elegans, modulates the expression of α7 AChRs in a subtype-specific manner. Potentiation of AChR expression by post-transcriptional events is also critically assessed.

Synthesis of bridgehead-substituted azabicyclo[2.2.1]heptane and -[3.3.1]nonane derivatives for the elaboration of α7 nicotinic ligands

Azabicyclo[2.2.1]heptane and -[3.3.1]nonane scaffolds (X = Cl, Br) containing a pyridinyl substituent at the bridgehead position were prepared via two complementary chemical pathways, either by the transformation of a methoxy group into a synthetically valuable chlorine atom at the C-6 position of the pyridine moiety or by means of a regioselective C-6 deprotonation/halogenation process of the pyridine moiety exemplified by chlorination or bromination. These newly generated scaffolds were then engaged in Suzuki-Miyaura coupling reactions to provide α7 nicotinic ligands. Both chemical series were evaluated in vitro for their affinity at α7 nicotinic receptors, revealing nanomolar potency with significant selectivity over the α4β2 nicotinic subtype. These approaches offer a general access to these α7 nicotinic scaffolds and ligands.

In search of allosteric modulators of a7-nAChR by solvent density guided virtual screening

Nicotinic acetylcholine receptors (nAChR) are pentameric ligand gated ion channels whose activity can be modulated by endogenous neurotransmitters as well as by synthetic ligands that bind the same or distinct sites from the natural ligand. The subtype of α7 nAChR has been considered as a potenial therapeutic target for Alzheimer's disease, schizophrenia and other neurological and psychiatric disorders. Here we have developed a homology model of α7 nAChR based on two high resolution crystal structures with Brookhaven Protein Data Bank (PDB) codes 2QC1 and 2WN9 for threading on one monomer and then for building a pentamer, respectively. A number of small molecule binding sites are identified using Pocket Finder (J. An, M. Tortov, and R. Abagyan, Molecular & Cellular Proteomics, 4.6, 752-761 (2005)) of Internal Coordinate Mechanics (ICM). Remarkably, these computer-identified sites match perfectly with ordered solvent densities found in the high-resolution crystal structure of α1 nAChR, suggesting that the surface cavities in the α7 nAChR model are likely binding sites of small molecules. A high throughput virtual screening by flexible ligand docking of 5008 small molecule compounds was performed at three potential allosteric modulator (AM) binding sites of α7 nAChR using Molsoft ICM software (R. Abagyan, M. Tortov and D. Kuznetsov, J Comput Chem 15, 488-506, (1994)). Some experimentally verified allosteric modulators of α7 like CCMI comp-6, LY 7082101, 5-HI, TQS, PNU-120596, genistein, and NS-1738 ranked among top 100 compounds, while the rest of the compounds in the list could guide further search for new allosteric modulators.

Separate and combined effects of low dose ketamine and nicotine on behavioural and neural correlates of sustained attention

Given the cognitive-promoting properties of the nicotinic acetylcholinergic receptor (nAChR) agonist, nicotine, the increased prevalence of smoke-inhaled nicotine in schizophrenia has been interpreted as an attempt to self-correct cognitive deficits, which have been particularly pronounced in the attentional domain. As glutamatergic abnormalities have been implicated in these attentional deficiencies, this study attempted to shed light on the separate and interactive roles of the N-methyl-d-aspartate receptor (NMDAR) and nAChR systems in the modulation of attention by investigating, in healthy volunteers, the separate and combined effects of nicotine and the NMDAR antagonist ketamine on neural and behavioural responses in a sustained attention task. In a randomized, double-blind, placebo controlled study, performance and the P300 event-related brain potential (ERP) in a visual information processing (RVIP) task were examined in 20 smokers and 20 non-smokers (both male and female). Assessment involved intravenous injection of a low subperceptual bolus dose (.04mg/kg) of ketamine or placebo, which was accompanied by acute treatment with nicotine (4mg) or placebo gum. Nicotine-enhanced attentional processing was most evident in nonsmokers, with both performance accuracy and P300 amplitude measures. Ketamine's detrimental effects on these behavioural and electrophysiologic measures were negatively moderated by acute nicotine, the synergistic effects being expressed differently in smokers and nonsmokers. These findings support the view that acute alterations and individual differences in nAChR function can moderate even subtle glutamatergic-driven cognitive deficiencies in schizophrenia and can be important therapeutic targets for treating cognitive impairments in schizophrenia.

P50 sensory gating and smoking in the general population

P50 gating is a major functional biomarker in research on schizophrenia and other psychiatric conditions with high smoking prevalence. It is used as endophenotype for studying nicotinic systems genetics and as surrogate endpoint measure for drug development of nicotinic agonists. Surprisingly, little is known about P50 gating in the general population and the relationship to smoking-related characteristics. In this multicenter study at six academic institutions throughout Germany, n=907 never-smokers (NS<20 cigarettes/lifetime), n=463 light smokers (LS) with Fagerström Test for Nicotine Dependence (FTND)≥4 and n=353 heavy smokers (HS, FTND<4) were randomly selected from the general population. As part of a standardized protocol for investigating the genetics of nicotine dependence (ND), an auditory P50 paradigm was applied. The main outcome measure was P50-amplitude difference followed by time-frequency analyses and functional imaging (sLORETA). Reduced P50 gating was found in HS compared to NS with LS taking an intermediate position-correlating with the degree of ND. sLORETA and time-frequency analyses indicate that high-frequency oscillations in frontal brain regions are particularly affected. With growing age, P50 gating increased in (heavy) smokers. This is the first large-scale study (normative sample data) on P50 sensory gating and smoking in the general population. Diminished gating of P50 and associated high-frequency oscillations in the frontal brain region are indications of a deficient inhibitory cortical function in nicotine-dependent smokers. The suitability and application of sensory P50 gating as functional biomarker with regard to genetic and pharmacological studies is discussed.

Involvement of the cholinergic system in conditioning and perceptual memory

The cholinergic systems play a pivotal role in learning and memory, and have been the centre of attention when it comes to diseases containing cognitive deficits. It is therefore not surprising, that the cholinergic transmitter system has experienced detailed examination of its role in numerous behavioural situations not least with the perspective that cognition may be rescued with appropriate cholinergic 'boosters'. Here we reviewed the literature on (i) cholinergic lesions, (ii) pharmacological intervention of muscarinic or nicotinic system, or (iii) genetic deletion of selective receptor subtypes with respect to sensory discrimination and conditioning procedures. We consider visual, auditory, olfactory and somatosensory processing first before discussing more complex tasks such as startle responses, latent inhibition, negative patterning, eye blink and fear conditioning, and passive avoidance paradigms. An overarching reoccurring theme is that lesions of the cholinergic projection neurones of the basal forebrain impact negatively on acquisition learning in these paradigms and blockade of muscarinic (and to a lesser extent nicotinic) receptors in the target structures produce similar behavioural deficits. While these pertain mainly to impairments in acquisition learning, some rare cases extend to memory consolidation. Such single case observations warranted replication and more in-depth studies. Intriguingly, receptor blockade or receptor gene knockout repeatedly produced contradictory results (for example in fear conditioning) and combined studies, in which genetically altered mice are pharmacological manipulated, are so far missing. However, they are desperately needed to clarify underlying reasons for these contradictions. Consistently, stimulation of either muscarinic (mainly M(1)) or nicotinic (predominantly α7) receptors was beneficial for learning and memory formation across all paradigms supporting the notion that research into the development and mechanisms of novel and better cholinomimetics may prove useful in the treatment of neurodegenerative or psychiatric disorders with cognitive endophenotypes.

Schizophrenia and tobacco smoking comorbidity: nAChR agonists in the treatment of schizophrenia-associated cognitive deficits

Tobacco smoking is a preventable cause of morbidity and mortality throughout the world. Very high rates of tobacco smoking are seen in patients with schizophrenia. Importantly, smokers with schizophrenia generally have higher nicotine dependence scores, experience more severe withdrawal symptoms upon smoking cessation, have lower cessation rates than healthy individuals, and suffer from significant smoking-related morbidity and premature mortality compared with the general population. Interestingly, significant disturbances in cholinergic function are reported in schizophrenia patients. The high smoking-schizophrenia comorbidity observed in schizophrenia patients may be an attempt to compensate for this cholinergic dysfunction. Cholinergic neurotransmission plays an important role in cognition and is hypothesized to play an important role in schizophrenia-associated cognitive deficits. In this review, preclinical evidence highlighting the beneficial effects of nicotine and subtype-selective nicotinic receptor agonists in schizophrenia-associated cognitive deficits, such as working memory and attention, is discussed. Furthermore, some of the challenges involved in the development of procognitive medications, particularly subtype-selective nicotinic receptor agonists, are also discussed. Amelioration of schizophrenia-associated cognitive deficits may help in the treatment of schizophrenia-smoking comorbidity by promoting smoking cessation and thus help in the better management of schizophrenia patients.

Electrophysiological perspectives on the therapeutic use of nicotinic acetylcholine receptor partial agonists

Partial agonist therapies rely variously on two hypotheses: the partial agonists have their effects through chronic low-level receptor activation or the partial agonists work by decreasing the effects of endogenous or exogenous full agonists. The relative significance of these activities probably depends on whether acute or chronic effects are considered. We studied nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus laevis oocytes to test a model for the acute interactions between acetylcholine (ACh) and weak partial agonists. Data were best-fit to a basic competition model that included an additional factor for noncompetitive inhibition. Partial agonist effects were compared with the nAChR antagonist bupropion in prolonged bath application experiments that were designed to mimic prolonged drug exposure typical of therapeutic drug delivery. A primary effect of prolonged application of nicotine was to decrease the response of all nAChR subtypes to acute applications of ACh. In addition, nicotine, cytisine, and varenicline produced detectable steady-state activation of α4β2* [(α4)(2)(β2)(3), (α4)(3)(β2)(2), and (α4)(2)(β2)(2)α5)] receptor subtypes that was not seen with other test compounds. Partial agonists produced no detectable steady-state activation of α7 nAChR, but seemed to show small potentiation of ACh-evoked responses; however, "run-up" of α7 ACh responses was also sometimes observed under control conditions. Potential off-target effects of the partial agonists therefore included the modulation of α7 responses by α4β2 partial agonists and decreases in α4β2* responses by α7-selective agonists. These data indicate the dual effects expected for α4β2* partial agonists and provide models and insights for utility of partial agonists in therapeutic development.

Nicotine ameliorates NMDA receptor antagonist-induced deficits in contextual fear conditioning through high-affinity nicotinic acetylcholine receptors in the hippocampus

NMDA glutamate receptors (NMDARs) and nicotinic acetylcholine receptors (nAChRs) are both involved in learning and synaptic plasticity. Increasing evidence suggests processes mediated by these receptors may interact to modulate learning; however, little is known about the neural substrates involved in these interactive processes. The present studies investigated the effects of nicotine on MK-801 hydrogen maleate (MK-801) and DL-2-Amino-5-phosphonovaleric acid (APV)-induced disruption of contextual fear conditioning in male C57BL/6J mice, using direct drug infusion and selective nAChR antagonists to define the brain regions and the nAChR subtypes involved. Mice treated with MK-801 showed a deficit in contextual fear conditioning that was ameliorated by nicotine. Direct drug infusion demonstrated that the NMDAR antagonists disrupted hippocampal function and that nicotine acted in the dorsal hippocampus to ameliorate the deficit in learning. The high-affinity nAChR antagonist Dihydro-β-erythroidine hydrobromide (DhβE) blocked the effects of nicotine on MK-801-induced deficits while the α7 nAChR antagonist methyllycaconitine citrate salt hydrate (MLA) did not. These results suggest that NMDARs and nAChRs may mediate similar hippocampal processes involved in contextual fear conditioning. Furthermore, these results may have implications for developing effective therapeutics for the cognitive deficits associated with schizophrenia because a large subset of patients with schizophrenia exhibit cognitive deficits that may be related to NMDAR dysfunction and smoke at much higher rates than the healthy population, which may be an attempt to ameliorate cognitive deficits.

Cholinergic contributions to the cognitive symptoms of schizophrenia and the viability of cholinergic treatments

Effective treatment of the cognitive symptoms of schizophrenia has remained an elusive goal. Despite the intense focus on treatments acting at or via cholinergic mechanisms, little remains known about the dynamic cholinergic abnormalities that contribute to the manifestation of the cognitive symptoms in patients. Evidence from basic neuroscientific and psychopharmacological investigations assists in proposing detailed cholinergic mechanisms and treatment targets for enhancement of attentional performance. Dynamic, cognitive performance-dependent abnormalities in cholinergic activity have been observed in animal models of the disorder and serve to further refine such proposals. Finally, the potential usefulness of individual groups of cholinergic drugs and important issues concerning the interactions between pro-cholinergic and antipsychotic treatments are addressed. The limited evidence available from patient studies and animal models indicates pressing research needs in order to guide the development of cholinergic treatments of the cognitive symptoms of schizophrenia.

Activation of functional α7-containing nAChRs in hippocampal CA1 pyramidal neurons by physiological levels of choline in the presence of PNU-120596

Background

The level of expression of functional α7-containing nicotinic acetylcholine receptors (nAChRs) in hippocampal CA1 pyramidal neurons is believed to be very low compared to hippocampal CA1 interneurons, and for many years this expression was largely overlooked. However, high densities of expression of functional α7-containing nAChRs in CA1 pyramidal neurons may not be necessary for triggering important cellular and network functions, especially if activation of α7-containing nAChRs occurs in the presence of positive allosteric modulators such as PNU-120596.

Methodology/Principal Findings

An approach previously developed for α7-containing nAChRs expressed in tuberomammillary neurons was applied to investigate functional CA1 pyramidal α7-containing nAChRs using rat coronal hippocampal slices and patch-clamp electrophysiology. The majority (∼71%) of tested CA1 pyramidal neurons expressed low densities of functional α7-containing nAChRs as evidenced by small whole-cell responses to choline, a selective endogenous agonist of α7 nAChRs. These responses were potentiated by PNU-120596, a novel positive allosteric modulator of α7 nAChRs. The density of functional α7-containing nAChRs expressed in CA1 pyramidal neurons (and thus, the normalized net effect of activation, i.e., response net charge per unit of membrane capacitance per unit of time) was estimated to be ∼5% of the density observed in CA1 interneurons. The results of this study demonstrate that despite low levels of expression of functional pyramidal α7-containing nAChRs, physiological levels of choline (∼10 µM) are sufficient to activate these receptors and transiently depolarize and even excite CA1 pyramidal neurons in the presence of PNU-120596. The observed effects are possible because in the presence of 10 µM choline and 1–5 µM PNU-120596, a single opening of an individual pyramidal α7-containing nAChR ion channel appears to transiently depolarize (∼4 mV) the entire pyramidal neuron and occasionally trigger action potentials.

Conclusions

1) The majority of hippocampal CA1 pyramidal neurons express functional α7-containing nAChRs. In the absence of PNU-120596, a positive allosteric modulator of α7 nAChRs, a lack of responsiveness of some hippocampal CA1 pyramidal neurons to focal application of 0.5–1 mM choline does not imply a lack of expression of functional α7-containing nAChRs in these neurons. Rather, it may indicate a lack of detection of α7-containing nAChR-mediated currents by patch-clamp electrophysiology. 2) PNU-120596 can serve as a powerful tool for detection and enhancement of responsiveness of low densities of functional α7-containing nAChRs such as those present in hippocampal CA1 pyramidal neurons. 3) In the presence of PNU-120596, physiological concentrations of choline activate functional CA1 pyramidal α7-containing nAChRs and produce step-like currents that cause repetitive step-like depolarizations, occasionally triggering bursts of action potentials in CA1 pyramidal neurons. Therefore, the results of this study suggest that in the presence of PNU-120596 and possibly other positive allosteric modulators, endogenous choline may persistently activate CA1 pyramidal α7-containing nAChRs, enhance the excitability of CA1 pyramidal neurons and thus act as a potent therapeutic agent with potential neuroprotective and cognition-enhancing properties.

Acute nicotine alteration of sensory memory impairment in smokers with schizophrenia

CONTEXT

Patients with schizophrenia have a high rate of cigarette smoking and also exhibit profound deficits in sensory processing, which may in part be ameliorated by the acute actions of smoke-inhaled nicotine. The mismatch negativity (MMN), a preattentive event-related potential index of auditory sensory memory, is diminished in schizophrenia. The MMN is increased in healthy controls with acute nicotine.

OBJECTIVE

To utilize the MMN to compare auditory sensory memory in minimally tobacco-deprived (3 hours) patients and matched tobacco-deprived smoking controls and to assess the effects of acute nicotine on MMN-indexed sensory memory processing in the patients.

DESIGN

Event-related potentials were recorded in 2 auditory oddball paradigms, one involving tone frequency changes (frequency MMN) and one involving tone duration changes (duration MMN). Controls were assessed once under nontreatment conditions, and patients were assessed twice under randomized double-blind treatment conditions involving placebo and nicotine (8 mg) gum.

SETTING

Outpatient mental health center.

PATIENTS

Twelve smokers with schizophrenia and twelve control smokers.

RESULTS

Compared with the controls, the patients showed reduced frequency-MMN (P < 0.001) and duration-MMN (P < 0.04) amplitudes. In addition to prolonging peak latency in duration MMN (P < 0.01), nicotine, relative to placebo, increased the amplitude of the patients' duration MMN (P < 0.01), but not their frequency MMN, to a level comparable with that seen in the controls.

CONCLUSIONS

These preliminary findings demonstrate for the first time that acute nicotine can normalize temporal aspects of sensory memory processing in patients with schizophrenia, an effect that may be mediated by activation of α7 nicotinic acetylcholine receptors, the function of which is diminished in schizophrenia. These ameliorating actions of nicotine may have implications for understanding the close relationship between tobacco smoking and schizophrenia and for developing nicotinic pharmacotherapies to alleviate sensory memory impairments in schizophrenia.

Continuous administration of a selective alpha7 nicotinic partial agonist, DMXBA, improves sensory inhibition without causing tachyphylaxis or receptor upregulation in DBA/2 mice

Stimulation of nicotinic receptors, specifically the alpha7 subtype, improves sensory inhibition and cognitive function in receptor deficient humans and rodents. However, stimulation with a full agonist, such as nicotine, produces rapid tachyphylaxis of the P20N40-measured sensory inhibition process. 3-(2,4-dimethoxybenzylidine) anabaseine (DMXBA, also GTS-21) selectively activates the alpha7 nicotinic receptor, and in acute administration studies, has been shown to improve deficient sensory inhibition in both humans and rodents with repeated dosing. Unlike nicotine, this partial agonist acted without inducing tachyphylaxis. Here, we assessed the ability of DMXBA to improve sensory inhibition in DBA/2 mice after 7 days of continuous administration via a subcutaneously implanted osmotic minipump. When assessed on day 8, mice receiving saline showed the characteristic deficient sensory inhibition seen with untreated DBA/2 mice. The 25- and 50-mg/ml infusion concentrations of DMXBA, but not the 100-mg/ml, produced significantly improved sensory inhibition in the mice, exclusively through a decrease in test amplitude. No concentration significantly upregulated hippocampal alpha7 receptor levels. DMXBA levels in the brain were higher than plasma at 2 of the 3 concentrations infused. These data suggest that continuous exposure to DMXBA does not significantly affect the underlying responsiveness of the sensory inhibition pathway to this partial agonist, nor cause receptor upregulation, at these relatively low brain concentrations. The ability of DMXBA to maintain its effectiveness during constant administration conditions may be due to an ability to activate alpha7 receptors at low concentrations, and consequently low fractional occupancy of the five possible binding sites on this homomeric receptor.

Behavioral effects of PNU-282987, an alpha7 nicotinic receptor agonist, in mice

The cholinergic system is closely related to learning and memory processes, and its neurodegeneration seems to be involved in neurodegenerative and neuropsychiatric cognitive disorders in the elderly. Alpha7 nicotinic acetylcholine receptors (nAChRs) have recently been shown to mediate neuroprotection and enhance cognitive performance in a variety of tasks, suggesting that there may be a new target for the pharmacotherapy of cognitive deficiencies. In this study, we investigated the behavioral effects of the acute and sub-chronic administration of 0, 1, 3, and 5 mg/kg of PNU-282987 (PNU) on motor activity, anxiety and learning in open-field and Morris water maze tasks in mice. Our results showed that the highest dose of PNU (5 mg/kg) diminished motor activity in the open-field following 5 and 12 days of administration (acute and sub-chronic, respectively). No effects on the acquisition of the Morris water maze were observed. However, only 1 mg/kg of PNU administered just before training trials over a period of 5 days showed beneficial effects on the retention of the water maze when evaluated 4 h after water maze acquisition. Further studies are needed to clarify the effects on the cognitive performance and potential neuroprotection of these agents in an elderly population with slight or severe deficiency in learning and memory processes, and/or in animal models vulnerable to neurodegenerative disorders.

A randomised, double-blind, placebo-controlled trial of tropisetron in patients with schizophrenia

BACKGROUND

Cognitive deficits in schizophrenia are associated with psychosocial deficits that are primarily responsible for the poor long-term outcome of this disease. Auditory sensory gating P50 deficits are correlated with neuropsychological deficits in attention, one of the principal cognitive disturbances in schizophrenia. Our studies suggest that the alpha7 nicotinic acetylcholine receptor (alpha7 nAChR) agonist tropisetron might be a potential therapeutic drug for cognitive deficits in schizophrenia. Therefore, it is of particular interest to investigate the effects of tropisetron on the cognitive deficits in patients with schizophrenia.

METHODS

A randomised, placebo-controlled trial of tropisetron in patients with schizophrenia was performed. A total of 40 patients with chronic schizophrenia who had taken risperidone (2 to 6 mg/day) were enrolled. Subjects were randomly assigned to a fixed titration of tropisetron (n = 20, 10 mg/day) or placebo (n = 20) in an 8-week double-blind trial. Auditory sensory gating P50 deficits and Quality of Life Scale (QLS), Cambridge Neuropsychological Test Automated Battery (CANTAB), and Positive and Negative Syndrome Scale (PANSS) scores were measured.

RESULTS

In all, 33 patients completed the trial. Tropisetron was well tolerated. Administration of tropisetron, but not placebo, significantly improved auditory sensory gating P50 deficits in non-smoking patients with schizophrenia. The score on the rapid visual information processing (sustained visual attention) task of CANTAB was significantly improved by tropisetron treatment. Total and subscale scores of PANSS were not changed by this trial. QLS scores in the all patients, but not non-smoking patients, were significantly improved by tropisetron trial.

CONCLUSIONS

This first randomised, double-blind, placebo-controlled trial supports the safety and efficacy of adjunctive tropisetron for treatment of cognitive deficits in schizophrenia.

Role of the central cholinergic system in the therapeutics of schizophrenia

The therapeutic agents currently used to treat schizophrenia effectively improve psychotic symptoms; however, they are limited by adverse effects and poor efficacy when negative symptoms of the illness and cognitive dysfunction are considered. While optimal pharmacotherapy would directly target the neuropathology of schizophrenia neither the underlying neurobiological substrates of the behavioral symptoms nor the cognitive deficits have been clearly established. Abnormalities in the neurotransmitters dopamine, serotonin, glutamate, and GABA are commonly implicated in schizophrenia; however, it is not uncommon for alterations in the brain cholinergic system (e.g., choline acetyltransferase, nicotinic and muscarinic acetylcholine receptors) to also be reported. Further, there is now considerable evidence in the animal literature to suggest that both first and second generation antipsychotics (when administered chronically) can alter the levels of several cholinergic markers in the brain as well as impair memory-related task performance. Given the well-established importance of central cholinergic neurons to information processing and cognition, it is important that cholinergic function in schizophrenia be further elucidated and that the mechanisms of the chronic effects of antipsychotic drugs on this important neurotransmitter system be identified. A better understanding of these mechanisms would be expected to facilitate optimal treatment strategies for schizophrenia as well as the identification of novel therapeutic targets. In this review, the following topics are discussed: 1) the central cholinergic system in schizophrenia 2) effects of antipsychotic drugs on central cholinergic neurons 3) important neurotrophins in schizophrenia, especially those that support central cholinergic neurons; 4) novel strategies to optimize the therapeutics of schizophrenia via the use of cholinergic compounds as primary (i.e., antipsychotic) treatments as well as adjunctive, pro-cognitive agents.

α7 Nicotinic Receptor Agonists: Potential Therapeutic Drugs for Treatment of Cognitive Impairments in Schizophrenia and Alzheimer's Disease

Accumulating evidence suggests that α7 nicotinic receptors (α7 nAChRs), a subtype of nAChRs, play a role in the pathophysiology of neuropsychiatric diseases, including schizophrenia and Alzheimer's disease (AD). A number of psychopharmacological and genetic studies shown that α7 nAChRs play an important role in the deficits of P50 auditory evoked potential in patients with schizophrenia, and that (α nAChR agonists would be potential therapeutic drugs for cognitive impairments associated with P50 deficits in schizophrenia. Furthermore, some studies have demonstrated that α7 nAChRs might play a key role in the amyloid-β (Aβ)-mediated pathology of AD, and that α7 nAChR agonists would be potential therapeutic drugs for Aβ deposition in the brains of patients with AD. Interestingly, the altered expression of α7 nAChRs in the postmortem brain tissues from patients with schizophrenia and AD has been reported. Based on all these findings, selective α7 nAChR agonists can be considered potential therapeutic drugs for cognitive impairments in both schizophrenia and AD. In this article, we review the recent research into the role of α7 nAChRs in the pathophysiology of these diseases and into the potential use of novel α7 nAChR agonists as therapeutic drugs.

Mouse behavioral endophenotypes for schizophrenia

An endophenotype is a heritable trait that is generally considered to be more highly, associated with a gene-based neurological deficit than a disease phenotype itself. Such, endophenotypic deficits may therefore be observed in the non-affected relatives of disease patients. Once endophenotypes have been established for a given illness, such as schizophrenia, mechanisms of, action may then be established and treatment options developed in order to target such measures. The, current paper describes and assesses the merits and limitations of utilizing behavioral and, electrophysiological endophenotypes of schizophrenia in mice. Such endophenotypic deficits include: decreased auditory event related potential (ERP) amplitude and gating (specifically, that of the P20, N40, P80 and P120); impaired mismatch negativity (MMN); changes in theta and gamma frequency, analyses; decreased pre-pulse inhibition (PPI); impaired working and episodic memories (for instance, novel object recognition [NOR], contextual and cued fear conditioning, latent inhibition, Morris and, radial arm maze identification and nose poke); sociability; and locomotor activity. A variety of, pharmacological treatments, including ketamine, MK-801 and phencyclidine (PCP) can be used to, induce some of the deficits described above, and numerous transgenic mouse strains have been, developed to address the mechanisms responsible for such endophenotypic differences. We also, address the viability and validity of using such measures regarding their potential clinical implications, and suggest several practices that could increase the translatability of preclinical data.

The role of nicotine on respiratory sensory gating measured by respiratory-related evoked potentials

Respiratory perception can be altered by changes in emotional or psychological states. This may be due to affective (i.e., anxiety) modulation of respiratory sensory gating. Nicotine withdrawal induces elevated anxiety and decreased somatosensory gating. Respiratory sensory gating is evidenced by decreased amplitude of the respiratory-related evoked potentials (RREP) N1 peak for the second occlusion (S2) when two 150-ms occlusions are presented with a 500-ms interval during an inspiration. The N1 peak amplitude ratio of the S2 and first occlusion (S1) (S2/S1) is <0.5 and due to central neural sensory gating. We hypothesized that withdrawal from nicotine is anxiogenic and reduces respiratory gating in smokers. The RREP was recorded in smokers with 12-h withdrawal from nicotine and nonsmokers using a paired occlusion protocol. In smokers, the RREP was measured after nicotine withdrawal, then with either nicotine or placebo gum, followed by the second RREP trial. Nonsmokers received only placebo gum. After nicotine withdrawal, the smokers had a higher state anxiety compared with nonsmokers. There was a significant interaction between groups (nonsmokers vs. smokers with nicotine vs. smokers with placebo) and test (pre- vs. posttreatment) in RREP N1 peak amplitude S2/S1. The S2/S1 in the smokers were larger than in nonsmokers before treatment. After gum treatment, the smoker-with-placebo group had a significantly larger S2/S1 than the other two groups. The S2/S1 was significantly decreased after the administration of nicotine gum in smokers due to significantly decreased S2 amplitudes. The RREP Nf and P1 peaks were unaffected. These results demonstrated that respiratory sensory gating was decreased in smokers after nicotine withdrawal. Nicotine increased respiratory sensory gating in smokers with a S2/S1 similar to that of the nonsmokers. Nicotine did not change respiratory sensory information arrival, but secondary information processing in respiratory sensation.

Physiological concentrations of choline activate native alpha7-containing nicotinic acetylcholine receptors in the presence of PNU-120596 [1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)-urea]

The use of PNU-120596 [1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)-urea], a positive allosteric modulator of alpha7 nicotinic acetylcholine receptor (nAChR), may be beneficial for enhancing cholinergic therapies. However, the effects of PNU-120596 on activation of native alpha7-containing nAChRs by physiological concentrations of choline are not known and were investigated in this study using patch-clamp electrophysiology and histaminergic tuberomammillary neurons in hypothalamic slices. In the presence of PNU-120596, subthreshold (i.e., inactive) physiological concentrations of choline ( approximately 10 microM) elicited repetitive step-like whole-cell responses reminiscent of single ion channel openings that were reversibly blocked by 20 nM methyllycaconitine, a selective alpha7 nAChR antagonist. The effects of choline and PNU-120596 were synergistic as administration of 10 to 40 microM choline or 1 to 4 muM PNU-120596 alone did not elicit responses. In voltage clamp at -60 mV, the persistent activation of alpha7-containing nAChRs by 10 microM choline plus 1 microM PNU-120596 was estimated to produce a sustained influx of Ca(2+) ions at a rate of 8.4 pC/min ( approximately 0.14 pA). In the presence of PNU-120596 in current clamp, transient step-like depolarizations ( approximately 5 mV) enhanced neuronal excitability and triggered voltage-gated conductances; a single opening of an alpha7-containing nAChR channel appeared to transiently depolarize the entire neuron and facilitate spontaneous firing. Therefore, this study tested and confirmed the hypothesis that PNU-120596 enhances the effects of subthreshold concentrations of choline on native alpha7-containing nAChRs, allowing physiological levels of choline to activate these receptors and produce whole-cell responses in the absence of exogenous nicotinic agents. In certain neurological disorders, this activation may be therapeutically beneficial, more efficacious, and safer than treatments with nAChR agonists.

Ketamine-induced deficit of auditory gating in the hippocampus of rats is alleviated by medial septal inactivation and antipsychotic drugs

RATIONALE

Gating of sensory responses is impaired in schizophrenic patients and animal models of schizophrenia. Ketamine, an N-methyl-D-aspartate receptor antagonist, is known to induce schizophrenic-like symptoms including sensory gating deficits in humans.

OBJECTIVE

This study aims to investigate the mechanisms underlying ketamine's effect on gating of auditory evoked potentials in the hippocampus of freely moving rats.

METHODS

Gating was measured by the ratio of the test-click response (T) to the conditioning-click response (C), or T/C, with T and C measured as peak amplitudes.

RESULTS

Ketamine (1, 3, or 6 mg/kg s.c.) injection dose-dependently increased T/C ratio as compared to saline injection (s.c.). T/C ratio was 0.48 +/- 0.05 after saline injection and 0.73 +/- 0.17 after ketamine (3 mg/kg s.c.) injection. The increase in T/C ratio after ketamine was blocked by prior inactivation of the medial septum with GABA(A) receptor agonist muscimol or by systemic administration of antipsychotic drugs, including chlorpromazine (5 mg/kg i.p.), haloperidol (1 mg/kg i.p.), or clozapine (7.5 mg/kg i.p.). Infusion of muscimol into the medial septum or injection of an antipsychotic drug alone did not affect the T/C ratio. However, rats with selective lesion of the septohippocampal cholinergic neurons by 192 IgG-saporin showed a significantly higher T/C ratio (0.86 +/- 0.10) than sham lesion rats (0.26 +/- 0.07), and ketamine did not further increase T/C ratio in rats with septohippocampal cholinergic neuron lesion.

CONCLUSIONS

Ketamine's disruption of hippocampal auditory gating was normalized by inactivation of the medial septum; in addition, septal cholinergic neurons participate in normal auditory gating.

Differential contribution of genetic variation in multiple brain nicotinic cholinergic receptors to nicotine dependence: recent progress and emerging open questions

Nicotine dependence (ND), a major public health challenge, is a complex, multifactorial behavior, in which both genetic and environmental factors have a role. Brain nicotinic acetylcholine receptor (nAChR)-encoding genes are among the most prominent candidate genes studied in the context of ND, because of their biological relevance as binding sites for nicotine. Until recently, most research on the role of nAChRs in ND has focused on two of these genes (encoding the alpha4- and beta2-subunits) and not much attention has been paid to the possible contribution of the other nine brain nAChR subunit genes (alpha2-alpha3, alpha5-alpha7, alpha9-alpha10, beta3-beta4) to the pathophysiology and genetics of ND. This situation has changed dramatically in the last 2 years during which intensive research had addressed the issue, mainly from the genetics perspective, and has shown the importance of the CHRNA5-CHRNA3-CHRNB4 and CHRNA6-CHRNB3 loci in ND-related phenotypes. In this review, we highlight recent findings regarding the contribution of non-alpha4/beta2-subunit containing nAChRs to ND, based on several lines of evidence: (1) human genetics studies (including linkage analysis, candidate-gene association studies and whole-genome association studies) of several ND-related phenotypes; (2) differential pharmacological and biochemical properties of receptors containing these subunits; (3) evidence from genetically manipulated mice; and (4) the contribution of nAChR genes to ND-related personality traits and neurocognitive profiles. Combining neurobiological genetic and behavioral perspectives, we suggest that genetic susceptibility to ND is not linked to one or two specific nAChR subtype genes but to several. In particular, the alpha3, alpha5-6 and beta3-4 nAChR subunit-encoding genes may play a much more pivotal role in the neurobiology and genetics of ND than was appreciated earlier. At the functional level, variants in these subunit genes (most likely regulatory) may have independent as well as interactive contributions to the ND phenotype spectrum. We address methodological challenges in the field, highlight open questions and suggest possible pathways for future research.

Neurodevelopmental mechanisms of schizophrenia: understanding disturbed postnatal brain maturation through neuregulin-1-ErbB4 and DISC1

Schizophrenia (SZ) is primarily an adult psychiatric disorder in which disturbances caused by susceptibility genes and environmental insults during early neurodevelopment initiate neurophysiological changes over a long time course, culminating in the onset of full-blown disease nearly two decades later. Aberrant postnatal brain maturation is an essential mechanism underlying the disease. Currently, symptoms of SZ are treated with anti-psychotic medications that have variable efficacy and severe side effects. There has been much interest in the prodromal phase and the possibility of preventing SZ by interfering with the aberrant postnatal brain maturation associated with this disorder. Thus, it is crucial to understand the mechanisms that underlie the long-term progression to full disease manifestation to identify the best targets and approaches towards this goal. We believe that studies of certain SZ genetic susceptibility factors with neurodevelopmental implications will be key tools in this task. Accumulating evidence suggests that neuregulin-1 (NRG1) and disrupted-in-schizophrenia-1 (DISC1) are probably functionally convergent and play key roles in brain development. We provide an update on the role of these emerging concepts in understanding the complex time course of SZ from early neurodevelopmental disturbances to later onset and suggest ways of testing these in the future.

Smoking, nicotine and neuropsychiatric disorders

Tobacco smoking is an extremely addictive and harmful form of nicotine (NIC) consumption, but unfortunately also the most prevalent. Although disproportionately high frequencies of smoking and its health consequences among psychiatric patients are widely known, the neurobiological background of this epidemiological association is still obscure. The diverse neuroactive effects of NIC and some other major tobacco smoke constituents in the central nervous system may underlie this association. This present paper summarizes the pharmacology of NIC and its receptors (nAChR) based on a systematic review of the literature. The role of the brain's reward system(s) in NIC addiction and the results of functional and structural neuroimaging studies on smoking-related states and behaviors (i.e. dependence, craving, withdrawal) are also discussed. In addition, the epidemiological, neurobiological, and genetic aspects of smoking in several specific neuropsychiatric disorders are reviewed and the clinical relevance of smoking in these disease states addressed.

A reversible model of the cognitive impairment associated with schizophrenia in monkeys: potential therapeutic effects of two nicotinic acetylcholine receptor agonists

In monkeys proficient in the performance of a computer-assisted delayed response task, administration of sub-sedative doses of ketamine significantly impaired task performance after the 2mg/kg dose, producing a decrease in accuracies across all four delay intervals. Ketamine elicited occasional and inconsistent increases in task latencies. But in general processing speed was not dramatically affected by the test dose. Pretreatment with the alpha7 nicotinic receptor agonist GTS-21 (DMXB-A) [3-[(3E)-3-[(2,4-dimethoxyphenyl) methylidene]-5,6-dihydro-4H-pyridin-2-yl]pyridine] produced a dose-dependent attenuation of ketamine-induced decreases in task accuracies. In fact, the best dose of GTS-21 completely reversed the effects of ketamine. The nicotine metabolite cotinine is a cognitive-enhancer, and active in models predictive of antipsychotic activity. Pretreatment with cotinine did not reverse the task deficits produced by ketamine, and selection of a best dose was necessary to show the activity of cotinine. However, the best dose of cotinine, like GTS-21, completely reversed the ketamine-induced task deficits. Task accuracies were increased relative to their non-ketamine baselines during sessions run 24h later. The cotinine-ketamine order of administration was reversed to provide a more clinically relevant model, and cotinine post-treatment regimen produced a clear reversal of the ketamine-induced task deficits. The protracted task improvement also was still evident. The DMTS task impairment induced by ketamine was capable of being completely reversed by two compounds that are known to improve working memory and cognition. The model could provide a means of late stage preclinical evaluation of new compounds that address the cognitive impairment associated with major psychotic disease.

Astrocyte-derived kynurenic acid modulates basal and evoked cortical acetylcholine release

We tested the hypothesis that fluctuations in the levels of kynurenic acid (KYNA), an endogenous antagonist of the alpha7 nicotinic acetylcholine (ACh) receptor, modulate extracellular ACh levels in the medial prefrontal cortex in rats. Decreases in cortical KYNA levels were achieved by local perfusion of S-ESBA, a selective inhibitor of the astrocytic enzyme kynurenine aminotransferase II (KAT II), which catalyses the formation of KYNA from its precursor L-kynurenine. At 5 mm, S-ESBA caused a 30% reduction in extracellular KYNA levels, which was accompanied by a two-threefold increase in basal cortical ACh levels. Co-perfusion of KYNA in the endogenous range (100 nm), which by itself tended to reduce basal ACh levels, blocked the ability of S-ESBA to raise extracellular ACh levels. KYNA perfusion (100 nm) also prevented the evoked ACh release caused by d-amphetamine (2.0 mg/kg). This effect was duplicated by the systemic administration of kynurenine (50 mg/kg), which resulted in a significant increase in cortical KYNA formation. Jointly, these data indicate that astrocytes, by producing and releasing KYNA, have the ability to modulate cortical cholinergic neurotransmission under both basal and stimulated conditions. As cortical KYNA levels are elevated in individuals with schizophrenia, and in light of the established role of cortical ACh in executive functions, our findings suggest that drugs capable of attenuating the production of KYNA may be of benefit in the treatment of cognitive deficits in schizophrenia.

Pro-cognitive and antipsychotic efficacy of the alpha7 nicotinic partial agonist SSR180711 in pharmacological and neurodevelopmental latent inhibition models of schizophrenia

Schizophrenia symptoms can be segregated into positive, negative and cognitive, which exhibit differential sensitivity to drug treatments. Accumulating evidence points to efficacy of alpha7 nicotinic receptor (nAChR) agonists for cognitive deficits in schizophrenia but their activity against positive symptoms is thought to be minimal. The present study examined potential pro-cognitive and antipsychotic activity of the novel selective alpha7 nAChR partial agonist SSR180711 using the latent inhibition (LI) model. LI is the reduced efficacy of a previously non-reinforced stimulus to gain behavioral control when paired with reinforcement, compared with a novel stimulus. Here, no-drug controls displayed LI if non-reinforced pre-exposure to a tone was followed by weak but not strong conditioning (2 vs 5 tone-shock pairings). MK801 (0.05 mg/kg, i.p.) -treated rats as well as rats neonatally treated with nitric oxide synthase inhibitor L-NoArg (10 mg/kg, s.c.) on postnatal days 4-5, persisted in displaying LI with strong conditioning, whereas amphetamine (1 mg/kg) -treated rats failed to show LI with weak conditioning. SSR180711 (0.3, 1, 3 mg/kg, i.p.) was able to alleviate abnormally persistent LI produced by acute MK801 and neonatal L-NoArg; these models are believed to model cognitive aspects of schizophrenia and activity here was consistent with previous findings with alpha7-nAChR agonists. In addition, unexpectedly, SSR180711 (1, 3 mg/kg, i.p.) potentiated LI with strong conditioning in no-drug controls and reversed amphetamine-induced LI disruption, two effects considered predictive of activity against positive symptoms of schizophrenia. These findings suggest that SSR180711 may be beneficial not only for the treatment of cognitive symptoms in schizophrenia, as reported multiple times previously, but also positive symptoms.

Discovery of 4-(5-(4-chlorophenyl)-2-methyl-3-propionyl-1H-pyrrol-1-yl)benzenesulfonamide (A-867744) as a novel positive allosteric modulator of the alpha7 nicotinic acetylcholine receptor

The discovery of a series of pyrrole-sulfonamides as positive allosteric modulators (PAM) of alpha7 nAChRs is described. Optimization of this series led to the identification of 19 (A-867744), a novel type II PAM with good potency and selectivity. Compound 19 showed acceptable pharmacokinetic profile across species and brain levels sufficient to modulate alpha7 nAChRs. In a rodent model of sensory gating, 19 normalized gating deficits. These results suggest that 19 represents a novel class of molecules capable of allosteric modulation of the alpha7 nAChRs.

Role of beta2-containing nicotinic acetylcholine receptors in auditory event-related potentials

RATIONALE

Nicotine improves sensory processing in schizophrenic individuals, as measured by changes in auditory event-related potentials (ERPs). Nicotine administration also alters ERPs in mice by increasing the amplitude and gating of the P20 ERP component while decreasing the amplitude of the N40 ERP component. Less is known about the role of specific nicotinic acetylcholine receptor (nAChR) subtypes.

OBJECTIVES

In this study, we examined whether nAChRs containing the beta2 subunit contribute to nicotine's effects on auditory ERPs.

MATERIALS AND METHODS

We tested the effect of nicotine in wild-type mice and mice lacking the beta2 nAChR subunit. Mice underwent stereotaxic implantation of stainless steel electrodes located in the CA3 region of the hippocampus, and 50 paired click stimuli were delivered during each drug condition.

RESULTS

There was no significant difference in P20 or N40 amplitude or gating between genotypes during the control condition, suggesting that beta2-containing receptors are not essential for the baseline auditory ERP response. Nicotine increased P20 amplitude and enhanced gating in wild-type and beta2 knockout mice, but only decreased N40 amplitude in wild-type mice. There was no effect of nicotine on N40 gating in either genotype.

CONCLUSIONS

beta2-containing receptors are necessary for nicotine's effects on the N40 component of the mouse auditory ERP. These results suggest that beta2-containing nAChRs modulate sensory processing and may serve as a therapeutic target in schizophrenic individuals.

Targeting the hippocampal mossy fiber synapse for the treatment of psychiatric disorders

It is widely known that new neurons are continuously generated in the dentate gyrus of the hippocampus in the adult mammalian brain. This neurogenesis has been implicated in depression and antidepressant treatments. Recent evidence also suggests that the dentate gyrus is involved in the neuropathology and pathophysiology of schizophrenia and other related psychiatric disorders. Especially, abnormal neuronal development in the dentate gyrus may be a plausible risk factor for the diseases. The synapse made by the mossy fiber, the output fiber of the dentate gyrus, plays a critical role in regulating neuronal activity in its target CA3 area. The mossy fiber synapse is characterized by remarkable activity-dependent short-term synaptic plasticity that is established during the postnatal development and is supposed to be central to the functional role of the mossy fiber. Any defects, including developmental abnormalities, in the dentate gyrus and drugs acting on the dentate gyrus can modulate the mossy fiber-CA3 synaptic transmission, which may eventually affect hippocampal functions. In this paper, I review recent evidence for involvement of the dentate gyrus and mossy fiber synapse in psychiatric disorders and discuss potential importance of drugs targeting the mossy fiber synapse either directly or indirectly in the therapeutic treatments of psychiatric disorders.

Rats and humans paying attention: cross-species task development for translational research

Substantial gains have been made on the neurobiology of attention from systems neuroscience work in animal models and human cognitive neuroscience. However, the integration of rodent-based research on the specific neurotransmitter systems that subserve attention with the results from human behavioral and neuroimaging studies has been hampered by the lack of tasks that validly assess attention in both species. To address this issue, an operant sustained attention task that has been extensively used in research on the neurobiology of attention in rats was redesigned and validated for use in humans. Although humans showed better performance overall, the two species showed similar effects of several attention-related variables, including the introduction of distractor-related challenge. This task provides a useful tool for integrative, cross-species research and may help to determine how specific neurotransmitter systems contribute to the hemodynamic changes observed in human functional neuroimaging experiments.

[Development of antipsychotic drug: new directions]

The treatment of psychotic disorders has been dramatically changed by the discovery, in 1952, of antipsychotic activity of chlorpromazine and the definition of criteria for a new therapeutic class. Since then, although major improvements were done in terms of neurological tolerance and easiness to handle, today's antipsychotics are highly similar to former ones. Those treatments do not answer to all expectations of patients or practitioners, in particular regarding their metabolic or cardiologic side effects and potency to reduce cognitive deficit. Moreover, despite increasing understanding of the pathophysiology of schizophrenic disorders, this new knowledge is not or very little used in the field of therapeutics, justifying to resume research efforts to improve therapeutics in psychotic disorders. The development of a new medication follows several steps, based on precise strategies and regulations. The main streams of research concern compounds that act on dopaminergic, serotoninergic or peptidergic systems.

Natural products to drugs: natural product-derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or are in registration (as at 31st December 2007) have been reviewed, as well as natural product-derived compounds for which clinical trials have been halted or discontinued since 2005. Also discussed are natural product-derived drugs launched since 2005, new natural product templates and late-stage development candidates.