The role of the α7 nicotinic receptor in cognitive processing of persons with schizophrenia

Nicotine Administration Normalizes Behavioral and Neurophysiological Perturbations in the MAM Rodent Model of Schizophrenia

BACKGROUND

The present study utilized the methylazoxymethanol (MAM) neurodevelopmental rodent model of schizophrenia (SCZ) to evaluate the hypothesis that individuals with SCZ smoke in an attempt to "self-medicate" their symptoms through nicotine (NIC) intake.

METHODS

To explore this question, we examined the effects of acute and chronic administration of NIC in 2 established behavioral tests known to be disrupted in the MAM model: prepulse inhibition of startle and novel object recognition. Additionally, we assessed the effects of acute and chronic NIC on 2 indices of the pathophysiology of SCZ modeled by MAM, elevated dopamine neuron population activity in the ventral tegmental area and neuronal activity in the ventral hippocampus, using in vivo electrophysiological recordings.

RESULTS

Our findings demonstrated that both acute and chronic administration of NIC significantly improved deficits in prepulse inhibition of startle and novel object recognition among MAM rats and normalized elevated ventral tegmental area and ventral hippocampal neuronal activity in these animals.

CONCLUSION

Together, these findings of NIC-induced improvement of deficits lend support for a "self-medication" hypothesis behind increased cigarette smoking in SCZ and illustrate the potential utility of nicotinic modulation in future pharmacotherapies for certain SCZ symptoms.

Association of the kynurenine pathway metabolites with clinical, cognitive features and IL-1β levels in patients with schizophrenia spectrum disorder and their siblings

OBJECTIVE

There is evidence suggesting that tryptophan (TRP)-kynurenine (KYN) pathway dysregulation is involved in the pathophysiology of schizophrenia and is regulated by inflammatory cytokines. The study investigate for the first time whether this dysregulation occurs in advanced stages of the disease as a byproduct or emerges as one of the early and inherited manifestations of schizophrenia.

METHOD

Sera of 148 patients with schizophrenia spectrum disorders (SCZ), 139 unaffected siblings (SIB) and 210 controls were investigated. Serum interleukin (IL)-1β levels were measured by ELISA, and TRP, KYN and kynurenic acid (KYNA) levels were measured by a high-performance liquid chromatography system. Also, we collected clinical data by applying Comprehensive Assessment of Symptoms and History in SCZ, and SIS-R in SIB and control groups.

RESULTS

Compared to controls, SCZ and SIB groups had lower TRP and higher KYNA levels. TRP levels showed significant differences only between SCZ and controls (p < 0.01). KYNA levels of both SCZ (p ≤ 0.001) and SIB (p < 0.05) were higher than controls. No statistical significance was found for KYN levels across groups. SCZ and SIB groups had higher serum IL-1β levels than controls (p ≤ 0.001).

CONCLUSIONS

Patients with SCZ and their siblings exhibited similar clinical features and TRP metabolite levels suggesting that TRP-KYN dysregulation may be an inherited component of the disease putatively conferring increased risk to schizophrenia. Elevation of IL-1β is one of the factors promoting overconsumption of the TRP-KYN pathway leading to increased production of neuroregulatory KYNA and presumably to neurodegeneration.

Brain PET Imaging of α7-nAChR with [18F]ASEM: Reproducibility, Occupancy, Receptor Density, and Changes in Schizophrenia

BACKGROUND

The α7 nicotinic acetylcholine receptor increasingly has been implicated in normal brain physiology, as well as in neuropsychiatric disorders. The highly cortical distribution of α7 nicotinic acetylcholine receptor suggests a role in cognition.

METHODS

We expanded the first-in-human PET imaging of α7 nicotinic acetylcholine receptor with [18F]ASEM from 5 to 21 healthy nonsmoking volunteers and added a feasibility study in 6 male patients with schizophrenia. Study aims included: (1) confirmation of test-retest reproducibility of [18F]ASEM binding, (2) demonstration of specificity by competition with DMXB-A, an α7 nicotinic acetylcholine receptor partial agonist, (3) estimation of [18F]ASEM binding potentials and α7 nicotinic acetylcholine receptor density in vivo in humans, and (4) demonstrating the feasibility of studying α7 nicotinic acetylcholine receptor as a target for schizophrenia.

RESULTS

Test-retest PET confirmed reproducibility (>90%) (variability ≤7%) of [18F]ASEM volume of distribution (VT) estimates in healthy volunteers. Repeated sessions of PET in 5 healthy subjects included baseline and effect of inhibition after oral administration of 150 mg DMXB-A. From reduction of binding potentials, we estimated the dose-dependent occupancy of α7 nicotinic acetylcholine receptor by DMXB-A at 17% to 49% for plasma concentrations at 60 to 200 nM DMXB-A. In agreement with evidence postmortem, α7 nicotinic acetylcholine receptor density averaged 0.67 to 0.82 nM and inhibitor affinity constant averaged 170 to 385 nM. Median VT in a feasibility study of 6 patients with schizophrenia was lower than in healthy volunteers in cingulate cortex, frontal cortex, and hippocampus (P = 0.02, corrected for multiple comparions, Mann-Whitney test).

CONCLUSIONS

The current results confirm the reproducibility of [18F]ASEM VT estimates and the specificity of the tracer for α7 nicotinic acetylcholine receptor. Preliminary findings from our feasibility study of [18F]ASEM binding in patients with schizophrenia are suggestive and provide guidance for future studies with more subjects.

PET tracers for imaging brain α7 nicotinic receptors: an update

Positron emission tomography (PET) molecular imaging of brain targets is a powerful tool to diagnose, follow up, and develop treatments and personalized medicine for a number of acute and chronic brain disorders. The availability of β+ emitter tracers labelled with [(11)C] or [(18)F] having optimal characteristics of affinity and selectivity for alpha-7 nicotinic receptors (α7R) has received considerable attention, due to the major implication of these receptors in brain functions. The aim of this review is to identify the interest and need for the in vivo exploration of α7R by PET molecular imaging, which tools are currently available for this and how to progress.

Melatonin regulates the autophagic flux via activation of alpha-7 nicotinic acetylcholine receptors

Our previous study suggested that melatonin-mediated neuroprotective effects are related with the activation of autophagy. However, the mechanism of melatonin-mediated autophagic activation in prion-mediated mitochondrial damage is not reported. Alpha-7 nicotinic acetylcholine receptors (α7nAchR) is a member of nicotinic acetylcholine receptors, and α7nAchR activation regulates via melatonin. Thus, we hypothesized that melatonin-mediated neuroprotective effect related with to autophagy pathway as a result of α7nAchR regulation. Inactivation of α7nAchR inhibited melatonin-mediated autophagic activation and protective effect against prion-mediated mitochondrial neurotoxicity. Also, knockdown of ATG5 blocked the melatonin-mediated neuroprotection and did not influence to the activation of α7nAchR caused by melatonin. This report is the first study demonstrating that melatonin-mediated autophagic activation regulates via modulation of α7nAchR signals, and upregulation of α7nAchR signals induced by melatonin plays a pivotal role in neuroprotection of prion-mediated mitochondrial neurotoxicity. Our results suggested that regulator of α7 nAChR signals including melatonin may have used for neuroprotective strategies for the neurodegenerative disorders including prion diseases.

cAMP-dependent protein kinase inhibits α7 nicotinic receptor activity in layer 1 cortical interneurons through activation of D1/D5 dopamine receptors

KEY POINTS

Protein kinases can modify the function of many proteins including ion channels. However, the role of protein kinase A in modifying nicotinic receptors in the CNS has never been investigated. We showed through whole-cell recordings of layer 1 prefrontal cortical interneurons that α7 nicotinic responses are negatively modulated by protein kinase A. Furthermore, we show that stimulation of dopamine receptors can similarly attenuate α7 nicotinic responses through the activation of protein kinase A. These results suggest how the interaction of the cholinergic and dopaminergic systems may influence neuronal excitability in the brain.

ABSTRACT

Phosphorylation of ion channels, including nicotinic acetylcholine receptors (nAChRs), by protein kinases plays a key role in the modification of synaptic transmission and neuronal excitability. α7 nAChRs are the second most prevalent nAChR subtype in the CNS following α4β2. Serine 365 in the M3-M4 cytoplasmic loop of the α7 nAChR is a phosphorylation site for protein kinase A (PKA). D1/D5 dopamine receptors signal through the adenylate cyclase-PKA pathway and play a key role in working memory and attention in the prefrontal cortex. Thus, we examined whether the dopaminergic system, mediated through PKA, functionally interacts with the α7-dependent cholinergic neurotransmission. In layer 1 interneurons of mouse prefrontal cortex, α7 nicotinic currents were decreased upon stimulation with 8-Br-cAMP, a PKA activator. In HEK 293T cells, dominant negative PKA abolished 8-Br-cAMP's effect of diminishing α7 nicotinic currents, while a constitutively active PKA catalytic subunit decreased α7 currents. In brain slices, the PKA inhibitor KT-5720 nullified 8-Br-cAMP's effect of attenuating α7 nicotinic responses, while applying a PKA catalytic subunit in the pipette solution decreased α7 currents. 8-Br-cAMP stimulation reduced surface expression of α7 nAChRs, but there was no change in single-channel conductance. The D1/D5 dopamine receptor agonist SKF 83822 similarly attenuated α7 nicotinic currents from layer 1 interneurons and this attenuation of nicotinic current was prevented by KT-5720. These results demonstrate that dopamine receptor-mediated activation of PKA negatively modulates nicotinic neurotransmission in prefrontal cortical interneurons, which may be a contributing mechanism of dopamine modulation of cognitive behaviours such as attention or working memory.

Neurocognitive effects of acute choline supplementation in low, medium and high performer healthy volunteers

Novel pharmacological treatments targeting alpha 7 nicotinic acetylcholine receptor (α7 nAChR) hypofunction in schizophrenia have shown mixed success in ameliorating cognitive impairments associated with this disorder. Choline, a selective agonist at α7 receptors is increased with oral administration of cytidine 5'-diphosphocholine (CDP-choline), the cognitive effects of which were assessed in healthy volunteers. Using the CogState test battery, behavioral performance in schizophrenia-relevant cognitive domains was assessed in 24 male participants following a single low (500mg) and moderate (1000mg) dose of CDP-choline. Relative to placebo, CDP-choline improved processing speed, working memory, verbal learning, verbal memory, and executive function in low baseline performers, while exerting no effects in medium baseline performers, and diminishing cognition in high baseline performers. Dose effects varied with cognitive domain but were evident with both the 500mg and 1000mg doses. These preliminary findings of cognitive enhancement in relatively impaired performers are consistent with the α7 receptor mechanism and support further trials with CDP-choline as a potential pro-cognitive strategy for cognitive impairment in schizophrenia.

Wnt and lithium: a common destiny in the therapy of nervous system pathologies?

Wnt signaling is required for neurogenesis, the fate of neural progenitors, the formation of neuronal circuits during development, neuron positioning and polarization, axon and dendrite development and finally for synaptogenesis. This signaling pathway is also implicated in the generation and differentiation of glial cells. In this review, we describe the mechanisms of action of Wnt signaling pathways and their implication in the development and correct functioning of the nervous system. We also illustrate how a dysregulated Wnt pathway could lead to psychiatric, neurodegenerative and demyelinating pathologies. Lithium, used for the treatment of bipolar disease, inhibits GSK3β, a central enzyme of the Wnt/β-catenin pathway. Thus, lithium could, to some extent, mimic Wnt pathway. We highlight the possible dialogue between lithium therapy and modulation of Wnt pathway in the treatment of the diseases of the nervous system.

Functional dysconnectivity in schizophrenia and its relationship to neural synchrony

Schizophrenia is a debilitating disorder of unknown cause. There is increasing momentum to consider functional dysconnectivity as an endophenotype of schizophrenia, and in particular, how it relates to cognition as a core feature of the disorder. Here, the authors review the conceptual models of functional dysconnectivity in schizophrenia to date, the evidence they are based on and some of the limitations of these models. The authors then propose 'neural synchrony' as a potential mechanism for functional dysconnectivity and review the current state of evidence for a link between neural synchrony and cognition in schizophrenia across behavioral, physiological, brain imaging, neurochemical and neurogenetic units of enquiry. The authors conclude by outlining the unmet needs in this field and give an outlook on how to fill these gaps.

Central Executive Dysfunction and Deferred Prefrontal Processing in Veterans with Gulf War Illness

Gulf War Illness is associated with toxic exposure to cholinergic disruptive chemicals. The cholinergic system has been shown to mediate the central executive of working memory (WM). The current work proposes that impairment of the cholinergic system in Gulf War Illness patients (GWIPs) leads to behavioral and neural deficits of the central executive of WM. A large sample of GWIPs and matched controls (MCs) underwent functional magnetic resonance imaging during a varied-load working memory task. Compared to MCs, GWIPs showed a greater decline in performance as WM-demand increased. Functional imaging suggested that GWIPs evinced separate processing strategies, deferring prefrontal cortex activity from encoding to retrieval for high demand conditions. Greater activity during high-demand encoding predicted greater WM performance. Behavioral data suggest that WM executive strategies are impaired in GWIPs. Functional data further support this hypothesis and suggest that GWIPs utilize less effective strategies during high-demand WM.

Rivastigmine reverses cognitive deficit and acetylcholinesterase activity induced by ketamine in an animal model of schizophrenia

Schizophrenia is one of the most disabling mental disorders that affects up to 1 % of the population worldwide. Although the causes of this disorder remain unknown, it has been extensively characterized by a broad range of emotional, ideational and cognitive impairments. Studies indicate that schizophrenia affects neurotransmitters such as dopamine, glutamate and acetylcholine. Recent studies suggest that rivastigmine (an acetylcholinesterase inhibitor) is important to improve the cognitive symptoms of schizophrenia. Therefore, the present study evaluated the protective effect of rivastigmine against the ketamine-induced behavioral (hyperlocomotion and cognitive deficit) and biochemical (increase of acetylcholinesterase activity) changes which characterize an animal model of schizophrenia in rats. Our results indicated that rivastigmine was effective to improve the cognitive deficit in different task (immediate memory, long term memory and short term memory) induced by ketamine in rats. Moreover, we observed that rivastigmina reversed the increase of acetylcholinesterase activity induced by ketamine in the cerebral cortex, hippocampus and striatum. However, rivastigmine was not able to prevent the ketamine-induced hyperlocomotion. In conslusion, ours results indicate that cholinergic system might be an important therapeutic target in the physiopathology of schizophrenia, mainly in the cognition, but additional studies should be carried.

Nicotinic modulation of intrinsic brain networks in schizophrenia

The nicotinic receptor is a promising drug target currently being investigated for the treatment of cognitive symptoms in schizophrenia. A key step in this process is the development of noninvasive functional neuroimaging biomarkers that can be used to determine if nicotinic agents are eliciting their targeted biological effect, ideally through modulation of a fundamental aspect of neuronal function. To that end, neuroimaging researchers are beginning to understand how nicotinic modulation affects "intrinsic" brain networks to elicit potentially therapeutic effects. An intrinsic network is a functionally and (often) structurally connected network of brain areas whose activity reflects a fundamental neurobiological organizational principle of the brain. This review summarizes findings of the effects of nicotinic drugs on three topics related to intrinsic brain network activity: (1) the default mode network, a group of brain areas for which activity is maximal at rest and reduced during cognitive tasks, (2) the salience network, which integrates incoming sensory data with prior internal representations to guide future actions and change predictive values, and (3) multi-scale complex network dynamics, which describe these brain's ability to efficiency integrate information while preserving local functional specialization. These early findings can be used to inform future neuroimaging studies that examine the network effects of nicotinic agents.

Genetic deletion of the adenosine A(2A) receptor prevents nicotine-induced upregulation of α7, but not α4β2* nicotinic acetylcholine receptor binding in the brain

Considerable evidence indicates that adenosine A(2A) receptors (A(2A)Rs) modulate cholinergic neurotransmission, nicotinic acetylcholine receptor (nAChR) function, and nicotine-induced behavioural effects. To explore the interaction between A(2A) and nAChRs, we examined if the complete genetic deletion of adenosine A(2A)Rs in mice induces compensatory alterations in the binding of different nAChR subtypes, and whether the long-term effects of nicotine on nAChR regulation are altered in the absence of the A(2A)R gene. Quantitative autoradiography was used to measure cytisine-sensitive [¹²⁵I]epibatidine and [¹²⁵I]α-bungarotoxin binding to α4β2* and α7 nAChRs, respectively, in brain sections of drug-naïve (n = 6) or nicotine treated (n = 5-7), wild-type and adenosine A(2A)R knockout mice. Saline or nicotine (7.8 mg/kg/day; free-base weight) were administered to male CD1 mice via subcutaneous osmotic minipumps for a period of 14 days. Blood plasma levels of nicotine and cotinine were measured at the end of treatment. There were no compensatory developmental alterations in nAChR subtype distribution or density in drug-naïve A(2A)R knockout mice. In nicotine treated wild-type mice, both α4β2* and α7 nAChR binding sites were increased compared with saline treated controls. The genetic ablation of adenosine A(2A)Rs prevented nicotine-induced upregulation of α7 nAChRs, without affecting α4β2* receptor upregulation. This selective effect was observed at plasma levels of nicotine that were within the range reported for smokers (10-50 ng ml⁻¹). Our data highlight the involvement of adenosine A(2A)Rs in the mechanisms of nicotine-induced α7 nAChR upregulation, and identify A(2A)Rs as novel pharmacological targets for modulating the long-term effects of nicotine on α7 receptors.

Effects of L-arginine and N(ω)-nitro-L-arginine methylester on learning and memory and α7 nAChR expression in the prefrontal cortex and hippocampus of rats

Nitric oxide (NO) is a novel type of neurotransmitter that is closely associated with synaptic plasticity, learning and memory. In the present study, we assessed the effects of L-arginine and N(ω)-nitro-L-arginine methylester (L-NAME, a nitric oxide synthase inhibitor) on learning and memory. Rats were assigned to three groups receiving intracerebroventricular injections of L-Arg (the NO precursor), L-NAME, or 0.9% NaCl (control), once daily for seven consecutive days. Twelve hours after the last injection, they underwent an electric shock-paired Y maze test. Twenty-four hours later, the rats' memory of the safe illuminated arm was tested. After that, the levels of NO and α7 nicotinic acetylcholine receptor (α7 nAChR) in the prefrontal cortex and hippocampus were assessed using an NO assay kit, and immunohistochemistry and Western blots, respectively. We found that, compared to controls, L-Arg-treated rats received fewer foot shocks and made fewer errors to reach the learning criterion, and made fewer errors during the memory-testing session. In contrast, L-NAME-treated rats received more foot shocks and made more errors than controls to reach the learning criterion, and made more errors during the memory-testing session. In parallel, NO content in the prefrontal cortex and hippocampus was higher in L-Arg-treated rats and lower in L-NAME rats, compared to controls. Similarly, α7 nAChR immunoreactivity and protein expression in the prefrontal cortex and hippocampus were higher in L-Arg-treated rats and lower in L-NAME rats, compared to controls. These results suggest that the modulation of NO content in the brain correlates with α7 nAChR distribution and expression in the prefrontal cortex and hippocampus, as well as with learning and memory performance in the Y-maze.

Nicotine modulates the long-lasting storage of fear memory

Late post-training activation of the ventral tegmental area (VTA)-hippocampus dopaminergic loop controls the entry of information into long-term memory (LTM). Nicotinic acetylcholine receptors (nAChR) modulate VTA function, but their involvement in LTM storage is unknown. Using pharmacological and behavioral tools, we found that α7-nAChR-mediated cholinergic interactions between the pedunculopontine tegmental nucleus and the medial prefrontal cortex modulate the duration of fear-motivated memories, maybe by regulating the activation state of VTA-hippocampus dopamine connections.

Alpha7 neuronal nicotinic receptors as a drug target in schizophrenia

INTRODUCTION

Schizophrenia is a profoundly debilitating disease that represents not only an individual, but a societal problem. Once characterized solely by the hyperactivity of the dopaminergic system, therapies directed to dampen dopaminergic neurotransmission were developed. However, these drugs do not address the significant impairments in cognition and the negative symptoms of the disease, and it is now apparent that disequilibrium of many neurotransmitter systems is involved. Despite enormous efforts, minimal progress has been made toward the development of safer, more effective therapies to date.

AREAS COVERED

The high preponderance of smoking in schizophrenics suggests that nicotine may provide symptomatic improvement, which has led to investigation for selective molecules targeted to individual nicotinic receptor (nAChR) subtypes. Of special interest is activation of the homomeric α7nAChR, which is widely distributed in the brain and has been implicated in the pathophysiology of schizophrenia through numerous approaches.

EXPERT OPINION

Preclinical and clinical data suggest that neuronal α7nAChRs play an important role in cognitive functions. Moreover, some, but not all, early clinical trials conducted with α7nAChR agonists show cognitive benefits in schizophrenics. These encouraging results suggest that development of compounds targeting α7nAChRs will represent a valuable tool to mitigate symptoms associated with schizophrenia, and open new strategies for better pharmacological treatment of these patients.

α7 nicotinic acetylcholine receptors and their role in cognition

The precise role of nicotinic acetylcholine receptors (nAChRs) in central cognitive processes still remains incompletely understood almost 150 years after its initial discovery. Central nAChRs are activated by acetylcholine, which functions in the extracellular space as a nonsynaptic messenger. Recently, a novel concept in the nAChR mode of operation has been described as a fast-type nonsynaptic transmission. In this review, we attempt to summarise the experimental findings that support the role of one of the most distributed receptor subtypes, the α7 nAChRs, and particularly focus on its procognitive effects following receptor activation. The basic characteristics of α7 nAChRs are discussed, from receptor homology to cellular-level functions. Synaptic plasticity is often implicated with α7 nAChRs on the basis of several diverse studies. Here, we provide a summary of the plastic features of the α7 receptor subtype and its role in higher level cognitive function. Finally, recent clinical evidence is reviewed, which demonstrates with increasing confidence the promise α7 nAChRs as a molecular target in future pharmacotherapy to prevent cognitive decline in various types of dementia, specifically, via the development of positive allosteric modulator compounds.

Wnt signaling: role in Alzheimer disease and schizophrenia

Wnt signaling function starts during the development of the nervous system and is crucial for synaptic plasticity in the adult brain. Clearly Wnt effects in synaptic and plastic processes are relevant, however the implication of this pathway in the prevention of neurodegenerative diseases that produce synaptic impairment, is even more interesting. Several years ago our laboratory found a relationship between the loss of Wnt signaling and the neurotoxicity of the amyloid-β-peptide (Aβ), one of the main players in Alzheimer's disease (AD). Moreover, the activation of the Wnt signaling cascade prevents Aβ-dependent cytotoxic effects. In fact, disrupted Wnt signaling may be a direct link between Aβ-toxicity and tau hyperphosphorylation, ultimately leading to impaired synaptic plasticity and/or neuronal degeneration, indicating that a single pathway can account for both neuro-pathological lesions and altered synaptic function. These observations, suggest that a sustained loss of Wnt signaling function may be a key relevant factor in the pathology of AD. On the other hand, Schizophrenia remains one of the most debilitating and intractable illness in psychiatry. Since Wnt signaling is important in organizing the developing brain, it is reasonable to propose that defects in Wnt signaling could contribute to Schizophrenia, particularly since the neuro-developmental hypothesis of the disease implies subtle dys-regulation of brain development, including some core components of the Wnt signaling pathways such as GSK-3β or Disrupted in Schizophrenia-1 (DISC-1). This review focuses on the relationship between Wnt signaling and its potential relevance for the treatment of neurodegenerative and neuropsychiatric diseases including AD and Schizophrenia.

An expanding range of targets for kynurenine metabolites of tryptophan

The kynurenine pathway of tryptophan metabolism accounts for most of the tryptophan that is not committed to protein synthesis and includes compounds active in the nervous and immune systems. Kynurenine acts on the aryl hydrocarbon receptor, affecting the metabolism of xenobiotics and promoting carcinogenesis. Quinolinic acid is an agonist at N-methyl-D-aspartate receptors (NMDARs), but is also pro-oxidant, has immunomodulatory actions, and promotes the formation of hyperphosphorylated tau proteins. Kynurenic acid blocks NMDARs and α7-homomeric nicotinic cholinoceptors and is also an agonist at the orphan G-protein-coupled receptor GPR35. 3-Hydroxykynurenine and 3-hydroxyanthranilic acid have pronounced redox activity and regulate T cell function. Cinnabarinic acid can activate metabotropic glutamate receptors. This review highlights the increasing range of molecular targets for components of the kynurenine pathway in both the nervous and immune systems in relation to their relevance to disease and drug development.

Cotinine: Beyond that Expected, More than a Biomarker of Tobacco Consumption

A greater incidence of tobacco consumption occurs among individuals with psychiatric conditions including post-traumatic stress disorder (PTSD), bipolar disorder, major depression, and schizophrenia, compared with the general population. Even when still controversial, it has been postulated that smoking is a form of self-medication that reduces psychiatric symptoms among individuals with these disorders. To better understand the component(s) of tobacco-inducing smoking behavior, greater attention has been directed toward nicotine. However, in recent years, new evidence has shown that cotinine, the main metabolite of nicotine, exhibits beneficial effects over psychiatric symptoms and may therefore promote smoking within this population. Some of the behavioral effects of cotinine compared to nicotine are discussed here. Cotinine, which accumulates in the body as a result of tobacco exposure, crosses the blood-brain barrier and has different pharmacological properties compared with nicotine. Cotinine has a longer plasma half-life than nicotine and showed no addictive or cardiovascular effects in humans. In addition, at the preclinical level, cotinine facilitated the extinction of fear memory and anxiety after fear conditioning, improved working memory in a mouse model of Alzheimer’s disease (AD) and in a monkey model of schizophrenia. Altogether, the new evidence suggests that the pharmacological and behavioral effects of cotinine may play a key role in promoting tobacco smoking in individuals that suffer from psychiatric conditions and represents a new potential therapeutic agent against psychiatric conditions such as AD and PTSD.

From antipsychotic to anti-schizophrenia drugs: role of animal models

Current drugs for treating schizophrenia are mostly variations on a theme that was started over 50 years ago. Sadly, clinical efficacy has not improved substantially over the years. We argue that both clinical and preclinical researchers have focused too much on psychosis, which is only one of the hallmarks of schizophrenia. This narrow focus has hampered the development of relevant animal models and human experimental medicine paradigms. Other fields in psychiatry, most notably in the realms of addiction and anxiety, have prospered from results obtained in parallel studies using animal models and experimental human studies. Lessons to be learned from those models and recent genetic and cognitive insights in schizophrenia can be utilized to develop better animal and human models and, potentially, novel treatment strategies.