New approaches to the management of schizophrenia: focus on aberrant hippocampal drive of dopamine pathways

Association of HTR1A Gene Polymorphisms with Efficacy and Plasma Concentrations of Atypical Antipsychotics in the Treatment of Male Patients with Schizophrenia

Purpose

We investigate the association of HTR1A rs10042486 and rs6295 with efficacy and plasma concentrations of atypical antipsychotics in the treatment of male patients with schizophrenia.

Patients and Methods

A total of 140 male patients diagnosed with schizophrenia who were treated with any single atypical antipsychotic between May 2020 and May 2022 were retrospectively included. Clinical symptoms were assessed using Positive and Negative Syndrome Scale (PANSS). All SNPs were typed using Agena Bioscience MassARRAY DNA mass spectrometry. Plasma concentrations of antipsychotics at week 3, 6 and 12 after treatment commence were analyzed using mass spectrometry.

Results

For efficacy of atypical antipsychotics, we observed no significant difference between HTR1A rs10042486, rs6295 and positive symptom improvement, where the patients with heterozygous mutant at the rs10042486 and rs6295 locus were superior to those with wild-type or homozygous mutant genotypes on negative symptom improvement, especially at 12 weeks of follow-up when the difference between genotypes at the rs6295 locus have statistical significance (P = 0.037). For plasma concentration, we found that quetiapine plasma concentrations were significantly lower in patients with mutation-heterozygous types than in wild-type and homozygous mutation genotypes at week 6. In contrast, higher plasma concentrations were found for mutant heterozygous than wild genotypes in the risperidone monotherapy analysis, and the difference among genotypes at the rs6295 locus was statistically significant at 6 weeks of follow-up.

Conclusion

The assessment of the correlation of genetic polymorphisms of HTR1A rs6295 and rs10042486 in male patients with schizophrenia with the monitoring of therapeutic drug concentrations and therapeutic efficacy provides a constructive foundation for the clinical individualization of antipsychotics, such as quetiapine and risperidone, which is important in selecting the dose of the medication and improving the improvement of negative symptoms.

Effects of tamoxifen alone and in combination with risperidone on hyperlocomotion, hippocampal structure and bone in ketamine-induced model of psychosis in rats

Background and aim of the work

Protein kinase C activation with subsequent increase in oxidative stress (OXS) and reduction in brain derived neurotrophic factor (BDNF) are implicated in the pathophysiology of psychotic disorders and in osteoporosis. Accordingly PKC inhibitors such as tamoxifen could be a novel approach to psychotic illness and may reduce progression of osteoporosis. Since current antipsychotics such as risperidone have inconsistent effects on OXS and BDNF, combination with tamoxifen could be beneficial. Accordingly in this work, tamoxifen was used to investigate the impact of changes in OXS and BDNF on behavioral, hippocampus structural changes in a ketamine induced model of psychosis in rats. The impact of tamoxifen on the antipsychotic effects of risperidone and on its bone damaging effects was also determined.

Ketamine was chosen, because it is a valid model of psychosis. Hippocampus was chosen, since hippocampal overactivity is known to correlate with the severity of symptoms in psychosis. Hippocampal overactivity contributes to hyperdopaminergic state in ventral tegmental area and increase in DA release in nucleus accumbens, these are responsible for positive symptoms of schizophrenia and hyperlocomotion in rodents. Hyperlocomotion is considered a corelate of positive symptoms of psychotic illness in rodents and is considered primary outcome to assess manic-like behavior.

Methods

Rats were divided into seven groups (ten rats each (1) non-ketamine control and (2) ketamine treated groups (a ketamine control, b risperidone/ketamine, c tamoxifen/ketamine, d Risp/Tamox/ketamine risperidone, tamoxifen/risperidone) to test if TAM exhibited behavioral changes or potentiated those of risperidone); (e clomiphene/ketamine and f clomiphene/risperidone/ketamine) to verify that estrogen receptor modulators do not exhibit behavioral changes or potentiates those of risperidone. In addition, thus, the effects of tamoxifen are not due to estrogen effects but rather due to protein kinase c inhibition. Drugs were given for 4 weeks and ketamine was given daily in the last week. Effects of drugs on ketamine-induced hyperlocomotion (open field test) and hippocampus and bone biochemical (MDA, GSH, BDNF) and histological changes (Nissel granules, GFAP positive astrocytes in hippocampus were determined).

Electron microscopy scanning of the femur bone was done. Histomorphometric parameters measuring the: 1. Trabecular bone thickness and 2. The trabecular bone volume percentage.

Results

Tamoxifen reduced hyperlocomotion, and improved hippocampus structure in ketamine-treated rats, by reducing OXS (reduced malondialdehyde and increased glutathione) and increasing BDNF. These effects might be related to (PKC) inhibition, rather than estrogen modulation, since the anti-estrogenic drug clomiphene had no effect on hyperlocomotion. Tamoxifen enhanced the beneficial effects of risperidone on hippocampal OXS and BDNF, augmenting its effectiveness on hyperlocomotion and hippocampal structure. It also reduced risperidone-induced OXS and the associated bone damage.

Conclusions

PKC inhibitors, particularly tamoxifen, might be potential adjuncts to antipsychotics, by reducing OXS and increasing BDNF increasing their effectiveness while reducing their bone damaging effects.

Increased Presynaptic Dopamine Synthesis Capacity Is Associated With Aberrant Dopamine Neuron Activity in the Methylazoxymethanol Acetate Rodent Model Used to Study Schizophrenia-Related Pathologies

Aberrant dopamine system function is thought to contribute to the positive symptoms of schizophrenia. Clinical imaging studies have demonstrated that the largest dopamine abnormality in patients appears to be an increase in presynaptic dopamine activity. Indeed, studies utilizing [ 18 F]DOPA positive emission tomography reliably report increases in presynaptic dopamine bioavailability in patients and may serve as a biomarker for treatment response. The mechanisms contributing to this increased presynaptic activity in human patients is not yet fully understood, which necessitates the use of preclinical models. Dopamine system function can be directly examined in experimental animals using in vivo electrophysiology. One consistent finding from preclinical studies in rodent models used to study schizophrenia-like neuropathology is a 2-fold increase in the number of spontaneously active dopamine neurons in the ventral tegmental area (VTA), termed population activity. We posit that increased striatal dopamine synthesis capacity is attributed to an augmented VTA dopamine neuron population activity. Here, we directly test this hypothesis using [3H]DOPA ex vivo autoradiography, to quantify striatal dopamine synthesis capacity, in the methylazoxymethanol acetate (MAM) model, a validated rodent model displaying neurophysiological and behavioral alterations consistent with schizophrenia-like symptomatologies. Consistent with human imaging studies, dopamine synthesis capacity was significantly increased in dorsal and ventral striatal subregionis, including the caudate putamen and nucleus accumbens, of MAM-treated rats and associated with specific increases in dopamine neuron population activity. Taken together, these data provide a link between mechanistic studies in rodent models and clinical studies of increased presynaptic dopamine function in human subjects.

The Perspectives of Early Diagnosis of Schizophrenia Through the Detection of Epigenomics-Based Biomarkers in iPSC-Derived Neurons

The lack of early diagnostic biomarkers for schizophrenia greatly limits treatment options that deliver therapeutic agents to affected cells at a timely manner. While previous schizophrenia biomarker research has identified various biological signals that are correlated with certain diseases, their reliability and practicality as an early diagnostic tool remains unclear. In this article, we discuss the use of atypical epigenetic and/or consequent transcriptional alterations (ETAs) as biomarkers of early-stage schizophrenia. Furthermore, we review the viability of discovering and applying these biomarkers through the use of cutting-edge technologies such as human induced pluripotent stem cell (iPSC)-derived neurons, brain models, and single-cell level analyses.

Towards Novel Treatments for Schizophrenia: Molecular and Behavioural Signatures of the Psychotropic Agent SEP-363856

Schizophrenia is a complex psychopathology whose treatment is still challenging. Given the limitations of existing antipsychotics, there is urgent need for novel drugs with fewer side effects. SEP-363856 (SEP-856) is a novel psychotropic agent currently under phase III clinical investigation for schizophrenia treatment. In this study, we investigated the ability of an acute oral SEP-856 administration to modulate the functional activity of specific brain regions at basal levels and under glutamatergic or dopaminergic-perturbed conditions in adult rats. We found that immediate-early genes (IEGs) expression was strongly upregulated in the prefrontal cortex and, to a less extent, in the ventral hippocampus, suggesting an activation of these regions. Furthermore, SEP-856 was effective in preventing the hyperactivity induced by an acute injection of phencyclidine (PCP), but not of d-amphetamine (AMPH). The compound effectively normalized the PCP-induced increase in IEGs expression in the PFC at all doses tested, whereas only the highest dose determined the major modulations on AMPH-induced changes. Lastly, SEP-856 acute administration corrected the cognitive deficits produced by subchronic PCP administration. Taken together, our data provide further insights on SEP-856, suggesting that modulation of the PFC may represent an important mechanism for the functional and behavioural activity of this novel compound.

Hippocampal Hyperactivity as a Druggable Circuit-Level Origin of Aberrant Salience in Schizophrenia

The development of current neuroleptics was largely aiming to decrease excessive dopaminergic signaling in the striatum. However, the notion that abnormal dopamine creates psychotic symptoms by causing an aberrant assignment of salience that drives maladaptive learning chronically during disease development suggests a therapeutic value of early interventions that correct salience-related neural processing. The mesolimbic dopaminergic output is modulated by several interconnected brain-wide circuits centrally involving the hippocampus and key relays like the ventral and associative striatum, ventral pallidum, amygdala, bed nucleus of the stria terminalis, nucleus reuniens, lateral and medial septum, prefrontal and cingulate cortex, among others. Unraveling the causal relationships between these circuits using modern neuroscience techniques holds promise for identifying novel cellular-and ultimately molecular-treatment targets for reducing transition to psychosis and symptoms of schizophrenia. Imaging studies in humans have implicated a hyperactivity of the hippocampus as a robust and early endophenotype in schizophrenia. Experiments in rodents, in turn, suggested that the activity of its output region-the ventral subiculum-may modulate dopamine release from ventral tegmental area (VTA) neurons in the ventral striatum. Even though these observations suggested a novel circuit-level target for anti-psychotic action, no therapy has yet been developed along this rationale. Recently evaluated treatment strategies-at least in part-target excess glutamatergic activity, e.g. N-acetyl-cysteine (NAC), levetiracetam, and mGluR2/3 modulators. We here review the evidence for the central implication of the hippocampus-VTA axis in schizophrenia-related pathology, discuss its symptom-related implications with a particular focus on aberrant assignment of salience, and evaluate some of its short-comings and prospects for drug discovery.

Effect fingerprints of antipsychotic drugs on neural networks in vitro

We compared the acute effect of typical (haloperidol) and atypical (aripiprazole, clozapine, olanzapine) antipsychotic drugs (APDs) on spontaneous electrophysiological activity of in vitro neuronal networks cultured on microelectrode arrays (MEAs). Network burst analysis revealed a "regularizing" effect of all APDs at therapeutic concentrations, i.e., an increase of network-wide temporal synchronization. At supratherapeutic concentrations, all APDs but olanzapine mediated a decrease of burst and spike rates, burst duration, number of spikes in bursts, and network synchrony. The rank order of potency of APDs was: haloperidol > aripiprazole > clozapine > olanzapine (no suppression). Disruption of network function was not due to enhanced cell death as assessed by trypan blue staining. APDs promoted distinct concentration-dependent alterations yielding acute effect fingerprints of the tested compounds. These effects were rather characteristic for individual compounds than distinctive for typical vs. atypical APDs. Thus, this dichotomy may be of value in distinguishing clinical features but has no apparent basis on the network or local circuitry level.

Distinct Time-Course of Alterations of Groups I and II Metabotropic Glutamate Receptor and GABAergic Receptor Expression Along the Dorsoventral Hippocampal Axis in an Animal Model of Psychosis

Psychosis is a clinical state that encompasses a range of abnormal conditions, including distortions in sensory information processing and the resultant delusional thinking, emotional discordance and cognitive impairments. Upon developing this condition, the rate at which cognitive and behavioral deteriorations progress steadily increases suggesting an active contribution of the first psychotic event to the progression of structural and functional abnormalities and disease establishment in diagnosed patients. Changes in GABAergic and glutamatergic function, or expression, in the hippocampus have been proposed as a key factor in the pathophysiology of psychosis. However, little is known as to the time-point of onset of putative changes, to what extent they are progressive, and their relation to disease stabilization. Here, we characterized the expression and distribution patterns of groups I and II metabotropic glutamate (mGlu) receptors and GABA receptors 1 week and 3 months after systemic treatment with an N-methyl-D-aspartate receptor (NMDAR) antagonist (MK801) that is used to model a psychosis-like state in adult rats. We found an early alteration in the expression of mGlu1, mGlu2/3, and GABA_B receptors across the hippocampal dorsoventral and transverse axes. This expanded to include an up-regulation of mGlu5 levels across the entire CA1 region and a reduction in GABA_B expression, as well as GAD67-positive interneurons particularly in the dorsal hippocampus that appeared 3 months after treatment. Our findings indicate that a reduction of excitability may occur in the hippocampus soon after first-episode psychosis. This changes, over time, into increased excitability. These hippocampus-specific alterations are likely to contribute to the pathophysiology and stabilization of psychosis.

Ventral hippocampal overexpression of Cannabinoid Receptor Interacting Protein 1 (CNRIP1) produces a schizophrenia-like phenotype in the rat

Adolescent cannabis use has been implicated as a risk factor for schizophrenia; however, it is neither necessary nor sufficient. Previous studies examining this association have focused primarily on the role of the cannabinoid receptor 1 (CB1R) with relatively little known about a key regulatory protein, the cannabinoid receptor interacting protein 1 (CNRIP1). CNRIP1 is an intracellular protein that interacts with the C-terminal tail of CB1R and regulates its intrinsic activity. Previous studies have demonstrated aberrant CNRIP1 DNA promoter methylation in post-mortem in human patients with schizophrenia, and we have recently reported decreased methylation of the CNRIP1 DNA promoter in the ventral hippocampus (vHipp) of a rodent model of schizophrenia susceptibility. To examine whether augmented CNRIP1 expression could contribute to the pathology of schizophrenia, we performed viral-mediated overexpression of CNRIP1 in the vHipp of Sprague Dawley rats. We then tested these rats for behavioral correlates of schizophrenia symptoms, followed by electrophysiology to determine the effects on the dopamine system, known to underlie psychosis. Here, we report that overexpression of vHipp CNRIP1 induces impairments in latent inhibition and social interaction, similar to those observed in individuals with schizophrenia and in rodent models of the disease. Furthermore, rats overexpressing vHipp CNRIP1 displayed a significant increase in ventral tegmental area (VTA) dopamine neuron population activity, a putative correlate of psychosis. These data provide evidence that alterations in CNRIP1 may contribute to the pathophysiology of schizophrenia, as overexpression is sufficient to produce neurophysiological and behavioral correlates consistently observed in rodent models of the disease.

Convergent Inputs from the Hippocampus and Thalamus to the Nucleus Accumbens Regulate Dopamine Neuron Activity

Aberrant hippocampal activity is observed in individuals with schizophrenia and is thought to underlie the augmented dopamine system function associated with psychosis. The pathway by which the ventral hippocampus (vHipp) regulates dopamine neuron activity has been demonstrated previously and involves a glutamatergic projection to the nucleus accumbens (NAc). Recent postmortem studies have confirmed glutamatergic abnormalities in the NAc of individuals with schizophrenia. Specifically, an increase in vesicular glutamate transporter 2 (vGlut2) expression was reported. Although projections from the hippocampus do express vGlut2, inputs from the thalamus are more likely to account for this alteration; however, the role of thalamic inputs to the NAc in the regulation of dopamine neuron activity has not been elucidated. Here, using male Sprague Dawley rats, we demonstrate that a subset of NAc medium spiny neurons receive convergent inputs from the vHipp and paraventricular nucleus of the thalamus (PVT), with both regions working synergistically to regulate dopamine neuron activity. Activation of either the vHipp or PVT increases the number of spontaneously active dopamine neurons in the ventral tegmental area. Moreover, this regulation requires simultaneous activity in both regions because PVT inactivation can reverse vHipp-induced increases in dopamine neuron population activity and vHipp inactivation can reverse PVT-induced increases. This is relevant to schizophrenia because inactivation of either the vHipp or PVT is sufficient to reverse aberrant dopamine system function in two distinct rodent models. These data suggest that thalamic abnormalities may contribute to the aberrant dopamine system function observed in schizophrenia and that the PVT represents a novel site of intervention for psychosis.SIGNIFICANCE STATEMENT Current treatments for schizophrenia are far from adequate and a more complete understanding of the pathophysiology underlying this disease is warranted if we are to discover novel therapeutic targets. We have previously demonstrated that the aberrant dopamine system function observed in individuals with schizophrenia and rodent models is driven by increases in hippocampal activity. We now demonstrate that thalamic (paraventricular nucleus, PVT) and ventral hippocampal afferents converge in the nucleus accumbens to regulate dopamine system function. Such information provides a potential site for therapeutic intervention for schizophrenia. Indeed, inactivation of the PVT can effectively reverse aberrant dopamine system function in two distinct rodent models displaying circuit level alterations and corresponding behavioral deficits relevant to schizophrenia.

Time-Dependent Alterations in the Expression of NMDA Receptor Subunits along the Dorsoventral Hippocampal Axis in an Animal Model of Nascent Psychosis

Psychosis is a mental condition that is characterized by hallucinations, delusions, disordered thought, as well as socio-emotional and cognitive impairments. Once developed, it tends to progress into a chronic psychotic illness. Here, the duration of untreated psychosis plays a crucial role: the earlier the treatment begins, relative to the first episode of the disease, the better the patient's functional prognosis. To what extent the success of early interventions relate to progressive changes at the neurotransmitter receptor level is as yet unclear. In fact, very little is known as to how molecular changes develop, transform, and become established following the first psychotic event. One neurotransmitter receptor for which a specific role in psychosis has been discussed is the N-methyl-d-aspartate receptor (NMDAR). This receptor is especially important for information encoding in the hippocampus. The hippocampus is one of the loci of functional change in psychosis, to which a role in the pathophysiology of psychosis has been ascribed. Here, we examined whether changes in NMDAR subunit expression occur along the dorsoventral axis of the hippocampus 1 week and 3 months after systemic treatment with an NMDAR antagonist (MK801) that initiates a psychosis-like state in adult rats. We found early (1 week) upregulation of the GluN2B levels in the dorso-intermediate hippocampus and late (3 month) downregulation of GluN2A expression across the entire CA1 region. The ventral hippocampus did not exhibit subunit expression changes. These data suggest that a differing vulnerability of the hippocampal longitudinal axis may occur in response to MK801-treatment and provide a time-resolved view of the putative development of pathological changes of NMDAR subunit expression in the hippocampus that initiate with an emulated first episode and progress through to the chronic stabilization of a psychosis-like state in rodents.

Optogenetic induction of the schizophrenia-related endophenotype of ventral hippocampal hyperactivity causes rodent correlates of positive and cognitive symptoms

Pathological over-activity of the CA1 subfield of the human anterior hippocampus has been identified as a potential predictive marker for transition from a prodromal state to overt schizophrenia. Psychosis, in turn, is associated with elevated activity in the anterior subiculum, the hippocampal output stage directly activated by CA1. Over-activity in these subfields may represent a useful endophenotype to guide translationally predictive preclinical models. To recreate this endophenotype and study its causal relation to deficits in the positive and cognitive symptom domains, we optogenetically activated excitatory neurons of the ventral hippocampus (vHPC; analogous to the human anterior hippocampus), targeting the ventral subiculum. Consistent with previous studies, we found that vHPC over-activity evokes hyperlocomotion, a rodent correlate of positive symptoms. vHPC activation also impaired performance on the spatial novelty preference (SNP) test of short-term memory, regardless of whether stimulation was applied during the encoding or retrieval stage of the task. Increasing dopamine transmission with amphetamine produced hyperlocomotion, but was not associated with SNP impairments. This suggests that short-term memory impairments resulting from hippocampal over-activity likely arise independently of a hyperdopaminergic state, a finding that is consistent with the pharmaco-resistance of cognitive symptoms in patients.

Vinpocetine halts ketamine-induced schizophrenia-like deficits in rats: impact on BDNF and GSK-3β/β-catenin pathway

There are increasing evidences supporting the involvement of oxidative stress and neuroinflammation in schizophrenia. Vinpocetine, a nootropic phosphodiesterase-1 inhibitor, was proven to possess anti-oxidant and anti-inflammatory potentials. This research aimed to reveal the likely protective features of vinpocetine against ketamine-induced schizophrenia-like deficits in rats. Additionally, the probable mechanisms contributing to this neuroprotection were also elucidated. Vinpocetine was given (20 mg/kg, i.p.) once a day for 14 days commencing 7 days before administrating ketamine (25 mg/kg i.p.). Risperidone was applied as a reference antipsychotic. Vinpocetine pre-treatment revealed a marked amendment in the hyperlocomotion, anxiety, and short-term memory deficits induced by ketamine in rats. In rats' hippocampus, ketamine induced a drastic increase in tissue levels of dopamine, lipid peroxidation, and pro-inflammatory cytokines along with a significant decrease in glutamate, GABA, SOD, and total anti-oxidant capacity. Also, ketamine induced a reduced level of BDNF together with the potentiation of GSK-3β/β-catenin pathway that led to the destruction of β-catenin. Pre-treatment of ketamine-challenged animals with vinpocetine significantly attenuated oxidative stress, inflammation, and neurotransmitter alterations. Vinpocetine also elevated BDNF expression and prevented ketamine-induced stimulation of the GSK-3β/β-catenin signaling. This research presents enlightenments into the role of vinpocetine in schizophrenia. This role may be accomplished through its effect on oxidative stress, inflammation as well as modulating BDNF and the GSK-3β/β-catenin pathway.

Cortical high gamma network oscillations and connectivity: a translational index for antipsychotics to normalize aberrant neurophysiological activity

Oscillatory activity in the gamma frequency range is a critical mechanism, which integrates neural networks within and across brain structures during cognitive processes. In schizophrenia, abnormalities in high gamma oscillations are ubiquitous and most likely reflect dysfunction in neuronal networks. In conscious rats, disturbed network oscillations associated with positive symptoms and cognitive deficits were modeled in different cortical areas by the dopaminergic agonist (amphetamine) and the N-methyl-D-aspartate (NMDA) receptor antagonists (PCP and MK801). Subsequently, the efficacies of marketed atypical antipsychotics (olanzapine, risperidone, and clozapine) to normalize dysfunctional oscillations and network connectivity were examined. Acute NMDA antagonists elicited aberrant synchrony in the gamma frequency oscillations. In addition, coherent slow alpha network activity was observed with MK801 and amphetamine, both of whose oscillatory rhythms were correlated with pronounced locomotor activity. All antipsychotics commonly decreased slow alpha and high gamma network oscillations in different cortical regions as well as motion behavior. In the combined treatments, antipsychotics attenuated NMDA antagonist-induced abnormalities in functional network oscillations and connectivity, whose effects on motor behavior is mechanistically related. These results suggest that pharmacologically induced disruption of cortical gamma oscillations and network connectivity in rats is a candidate model to study dysfunctional oscillatory patterns described in positive and negative symptoms of schizophrenia. The efficacy of antipsychotics to rescue cortical network oscillatory patterns is in line with the idea that glutamatergic and dopaminergic systems play a role in maintaining the integrity of cortical circuits. Thus, gamma oscillations could provide a powerful translational index to assess the integrity of neural networks and to evaluate the efficacy of drugs with potential antipsychotic properties.

The antipsychotic drugs olanzapine and haloperidol modify network connectivity and spontaneous activity of neural networks in vitro

Impaired neural synchronization is a hallmark of psychotic conditions such as schizophrenia. It has been proposed that schizophrenia-related cognitive deficits are caused by an unbalance of reciprocal inhibitory and stimulatory signaling. This supposedly leads to decreased power of induced gamma oscillations during the performance of cognitive tasks. In light of this hypothesis an efficient antipsychotic treatment should modify the connectivity and synchronization of local neural circuits. To address this issue, we investigated a model of hippocampal neuronal networks in vitro. Inhibitory and excitatory innervation of GABAergic and glutamatergic neurons was quantified using immunocytochemical markers and an automated routine to estimate network connectivity. The first generation (FGA) and second generation (SGA) antipsychotic drugs haloperidol and olanzapine, respectively, differentially modified the density of synaptic inputs. Based on the observed synapse density modifications, we developed a computational model that reliably predicted distinct changes in network activity patterns. The results of computational modeling were confirmed by spontaneous network activity measurements using the multiple electrode array (MEA) technique. When the cultures were treated with olanzapine, overall activity and synchronization were increased, whereas haloperidol had the opposite effect. We conclude that FGAs and SGAs differentially affect the balance between inhibition and excitation in hippocampal networks.

Clinical Management of Antipsychotic-Induced Hyperprolactinemia

PURPOSE

This article describes the physiology and mechanisms of prolactin and the assessment and clinical management strategies of antipsychotic-induced hyperprolactinemia.

CONCLUSIONS

Hyperprolactinemia is a disorder of the hypothalamic-pituitary axis which can be caused by several mechanisms. Typical antipsychotic agents are more likely to cause hyperprolactinemia than atypical antipsychotic agents, with the exception of amisulpride, paliperidone, and risperidone.

PRACTICE IMPLICATIONS

Switching from prolactin-elevating to prolactin-sparing agents is recommended. Providing adjunctive treatment and prescribing substitutive hormones are alternatives. Education and lifestyle modification should be a major health promotion strategy. Taking patients' history and conducting physical examinations should be done during follow-up.

Focus on psychosis

The concept of psychosis has been shaped by traditions in the concepts of mental disorders during the last 170 years. The term "psychosis" still lacks a unified definition, but denotes a clinical construct composed of several symptoms. Delusions, hallucinations, and thought disorders are the core clinical features. The search for a common denominator of psychotic symptoms points toward combinations of neuropsychological mechanisms resulting in reality distortion. To advance the elucidation of the causes and the pathophysiology of the symptoms of psychosis, a deconstruction of the term into its component symptoms is therefore warranted. Current research is dealing with the delineation from "normality", the genetic underpinnings, and the causes and pathophysiology of the symptoms of psychosis.

Cerebral Toxocariasis: Silent Progression to Neurodegenerative Disorders?

Toxocara canis and T. cati are highly prevalent nematode infections of the intestines of dogs and cats. In paratenic hosts, larvae do not mature in the intestine but instead migrate through the somatic tissues and organs of the body. The presence of these migrating larvae can contribute to pathology. Toxocara larvae can invade the brains of humans, and while case descriptions of cerebral toxocariasis are historically rare, improved diagnosis and greater awareness have contributed to increased detection. Despite this, cerebral or neurological toxocariasis (NT) remains a poorly understood phenomenon. Furthermore, our understanding of cognitive deficits due to toxocariasis in human populations remains particularly deficient. Recent data describe an enhanced expression of biomarkers associated with brain injury, such as GFAP, AβPP, transforming growth factor β1 (TGF-β1), NF-L, S100B, tTG, and p-tau, in mice receiving even low doses of Toxocara ova. Finally, this review outlines a hypothesis to explore the relationship between the presence of T. canis larvae in the brain and the progression of Alzheimer's disease (AD) due to enhanced AD-associated neurodegenerative biomarker expression.

Functional alterations of astrocytes in mental disorders: pharmacological significance as a drug target

Astrocytes play an essential role in supporting brain functions in physiological and pathological states. Modulation of their pathophysiological responses have beneficial actions on nerve tissue injured by brain insults and neurodegenerative diseases, therefore astrocytes are recognized as promising targets for neuroprotective drugs. Recent investigations have identified several astrocytic mechanisms for modulating synaptic transmission and neural plasticity. These include altered expression of transporters for neurotransmitters, release of gliotransmitters and neurotrophic factors, and intercellular communication through gap junctions. Investigation of patients with mental disorders shows morphological and functional alterations in astrocytes. According to these observations, manipulation of astrocytic function by gene mutation and pharmacological tools reproduce mental disorder-like behavior in experimental animals. Some drugs clinically used for mental disorders affect astrocyte function. As experimental evidence shows their role in the pathogenesis of mental disorders, astrocytes have gained much attention as drug targets for mental disorders. In this paper, I review functional alterations of astrocytes in several mental disorders including schizophrenia, mood disorder, drug dependence, and neurodevelopmental disorders. The pharmacological significance of astrocytes in mental disorders is also discussed.