Clozapine and haloperidol differently suppress the MK-801-increased glutamatergic and serotonergic transmission in the medial prefrontal cortex of the rat

The administration of noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists such as phencyclidine and ketamine has been shown to increase the extracellular concentration of glutamate and serotonin (5-HT) in the medial prefrontal cortex (mPFC). In the present work, we used in vivo microdialysis to examine the effects of the more potent noncompetitive NMDA receptor antagonist, MK-801, on the efflux of glutamate and 5-HT in the mPFC, and whether the MK-801-induced changes in the cortical efflux of both transmitters could be blocked by clozapine and haloperidol given systemically or intra-mPFC. The systemic, but not the local administration of MK-801, induced an increased efflux of 5-HT and glutamate, which suggests that the NMDA receptors responsible for these effects are located outside the mPFC, possibly in GABAergic neurons that tonically inhibit glutamatergic inputs to the mPFC. The MK-801-induced increases of extracellular glutamate and 5-HT were dependent on nerve impulse and the activation of mPFC AMPA/kainate receptors as they were blocked by tetrodotoxin and NBQX, respectively. Clozapine and haloperidol blocked the MK-801-induced increase in glutamate, whereas only clozapine was able to block the increased efflux of 5-HT. The local effects of clozapine and haloperidol paralleled those observed after systemic administration, which emphasizes the relevance of the mPFC as a site of action of these antipsychotic drugs in offsetting the neurochemical effects of MK-801. The ability of clozapine to block excessive cortical 5-HT efflux elicited by MK-801 might be related to the superior efficacy of this drug in treating negative/cognitive symptoms of schizophrenia.This work was supported by the Spanish Ministry of Education and Science Grants SAF 2004-05525 and SAF 2003-04930 and by the Generalitat de Catalunya (SGR2005/00758 and SGR2005/00826). XL-G, ZB, and MA-B were recipients of predoctoral fellowships from the Consejo Superior de Investigaciones Científicas (CSIC), Spanish Ministry of Education and Science, and Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), respectively.Peer reviewe

Cytoarchitectonic and chemoarchitectonic characterization of the prefrontal cortical areas in the mouse

This study describes cytoarchitectonic criteria to define the prefrontal cortical areas in the mouse brain (C57BL/6 strain). Currently, well-illustrated mouse brain stereotaxic atlases are available, which, however, do not provide a description of the distinctive cytoarchitectonic characteristics of individual prefrontal areas. Such a description is of importance for stereological, neuronal tracing, and physiological, molecular and neuroimaging studies in which a precise parcellation of the prefrontal cortex (PFC) is required. The present study describes and illustrates: the medial prefrontal areas, i.e., the infralimbic, prelimbic, dorsal and ventral anterior cingulate and Fr2 area; areas of the lateral PFC, i.e., the dorsal agranular insular cortical areas and areas of the ventral PFC, i.e., the lateral, ventrolateral, ventral and medial orbital areas. Each cytoarchitectonically defined boundary is corroborated by one or more chemoarchitectonic stainings, i.e., acetylcholine esterase, SMI32, SMI311, dopamine, parvalbumin, calbindin and myelin staining

Differential Regulation of the Excitability of Prefrontal Cortical Fast-Spiking Interneurons and Pyramidal Neurons by Serotonin and Fluoxetine

Serotonin exerts a powerful influence on neuronal excitability. In this study, we investigated the effects of serotonin on different neuronal populations in prefrontal cortex (PFC), a major area controlling emotion and cognition. Using whole-cell recordings in PFC slices, we found that bath application of 5-HT dose-dependently increased the firing of FS (fast spiking) interneurons, and decreased the firing of pyramidal neurons. The enhancing effect of 5-HT in FS interneurons was mediated by 5-HT2 receptors, while the reducing effect of 5-HT in pyramidal neurons was mediated by 5-HT1 receptors. Fluoxetine, the selective serotonin reuptake inhibitor, also induced a concentration-dependent increase in the excitability of FS interneurons, but had little effect on pyramidal neurons. In rats with chronic fluoxetine treatment, the excitability of FS interneurons was significantly increased, while pyramidal neurons remained unchanged. Fluoxetine injection largely occluded the enhancing effect of 5-HT in FS interneurons, but did not alter the reducing effect of 5-HT in pyramidal neurons. These data suggest that the excitability of PFC interneurons and pyramidal neurons is regulated by exogenous 5-HT in an opposing manner, and FS interneurons are the major target of Fluoxetine. It provides a framework for understanding the action of 5-HT and antidepressants in altering PFC network activity

Signaling pathways responsible for the rapid antidepressant-like effects of a GluN2A-preferring NMDA receptor antagonist

In a previous study we found that the preferring GluN2A receptor antagonist, NVP-AAM077, elicited rapid antidepressant-like effects in the forced swim test that was related to the release of glutamate and serotonin in the medial prefrontal cortex. In the present work we sought to examine the duration of this behavioral effect as well as the molecular readouts involved. Our results showed that NVP-AAM077 reduced the immobility in the forced swim test 30?min and 24?h after its administration. However, this effect waned 7 days later. The rapid antidepressant-like response seems to be associated with increases in the GluA1 subunit of ?-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, mammalian target of rapamycin (mTOR) signaling, glia markers such as glial fibrillary acidic protein (GFAP) and excitatory amino acid transporter 1 (EAAT1), and a rapid mobilization of intracellular stores of brain-derived neurotrophic factor (BDNF) in the medial prefrontal cortex.Acknowledgements: M.G.-S. was recipient of a contract from the Sistema Nacional de Garantía Juvenil co-funded by the European Social Fund. We also thank Novartis for the generous gift of NVP-AAM077. This work was supported by the Instituto de Salud Carlos III, Subdirección General del Evaluación y Fomento de la Investigación (FIS Grants PI13/00038 and PI16/00217) that were co-funded by the European Regional Development Fund (‘A way to build Europe’). Funding from the Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Instituto de Salud Carlos III is also acknowledged

Acció de fàrmacs antipsicòtics sobre el circuit escorça prefrontal-nuclis del rafe

[cat] L'esquizofrènia és un trastorn cerebral crònic, greu i incapacitant que afecta l'1% de la població i s'expressa en funcions mentals anormals i alteracions en el comportament. La causa de l'esquizofrènia és desconeguda, ara bé, la vulnerabilitat de patir aquesta malaltia psiquiàtrica està clarament relacionada amb factors genètics. Existeixen evidències que suggereixen que aquest trastorn es relaciona amb una activitat i connectivitat alterada de l'escorça prefrontal (EPF) i àrees relacionades anatòmicament i funcional com el tàlem i els nuclis del mesencèfal (nuclis del rafe-NR, locus coeruleus-LC i l'àrea tegmental ventral-ATV). S'han elaborat nombroses hipòtesis sobre l'etiologia de l'esquizofrènia que inclouen una hiperactivació de la neurotransmissió dopaminèrgica i una hipofunció glutamatèrgica. Ara bé, recentment s'ha suggerit que la hipofunció del receptor NMDA pot originar un excés compensatori d'alliberació de glutamat i incrementar l'activitat de les neurones piramidals de l'EPF. Endemés, en models de desconnexió neonatal de l'hipocamp s'ha observat una més elevada activitat excitadora de dopamina sobre neurones piramidals corticals. En la present Tesi Doctoral hem caracteritzat el paper que exerceixen receptors corticals excitadors i inhibitoris sobre l'activitat del circuit EPF-NR, i hem estudiat l'acció dels fàrmacs antipsicòtics sobre aquests receptors per tal de conèixer millor les bases neurobiològiques de la seva acció terapèutica. L'EPF medial (EPFm) expressa abundantment receptors serotoninèrgics 5-HT1A (inhibitoris) i 5-HT2A (excitadors). Els nostres treballs han mostrat que l'activació farmacològica d'aquests receptors corticals modula de manera oposada l'alliberació local de 5-HT mitjançant canvis en l'excitabilitat de les neurones piramidals que coexpressen àmpliament ambdós receptors i que projecten als nuclis serotoninèrgics. Antecents del grup mostren que l'administració de DOI (al.lucinogen, agonista 5-HT2A/2C) incrementa la freqüència de descàrrega de les neurones piramidals i l'alliberació cortical de serotonina (5-HT), activació circuit EPFm-NR. Així hem estudiat l'alliberació de 5-HT cortical, mitjançant la tècnica de microdiàlisi intracerebral in vivo, com a mesura indirecta de l'activitat de les neurones piramidals. Hem descrit també que l'estimulació dels receptors excitadors adrenèrgics 1 corticals incrementa l'alliberació local i al NDR de 5-HT, possiblement a través del mateix mecanisme que l'activació dels receptors 5-HT2A (estimulació de les vies excitadores descendents cap al NDR). De la mateixa manera, l'augment de la neurotransmissió glutamatèrgica a l'EPFm, mitjançant i) l'aplicació local de S-AMPA, ii) la desinhibició de les aferències glutamatèrgiques talàmiques o bé iii) l'administració sistèmica d'antagonistes glutamatèrgics dels receptors NMDA, estimula l'alliberació de 5-HT a l'EPF, fet que és probablement degut a una major activitat de les neurones piramidals que projecten al NDR i al conseqüent increment de l'activitat serotoninèrgica. Amdós efectes (adrenèrgic-1 i glutamatèrgic) són revertits pel bloqueig de receptors adrenèrgics 1 i 5-HT2A. Endemés hem observat que l'estimulació del receptor 5-HT1A a l'EPFm reverteix l'increment de l' alliberació local de 5-HT induït per l'agonista 5-HT2A/2C DOI, l'agonista adrenèrgic 1 cirazolina i S-AMPA. La implicació dels receptors 5-HT1A postsinàptics a EPFm en aquesta inhibició es fa palesa perquè i) és comuna a cinc agonistes diferents, ii) és revertida per la inactivació prèvia i el bloqueig dels receptors 5-HT1A, i iii) està totalment absent en ratolins genoanul·lats d' aquest receptor. Finalment, hem descrit que els fàrmacs antipsicòtics reverteixen l'increment de l'alliberació de 5-HT a l'EPFm induït per l' estimulació de receptors excitadors corticals. Aquesta acció és possiblement deguda a la seva capacitat de bloquejar in vivo els receptors 1 adrenèrgics (típics i atípics) i 5-HT2A (atípics) pels quals presenten una elevada afinitat. Aquestes dades suggereixen que els fàrmacs antipsicòtics exercirien en part la seva acció terapèutica disminuint una possible hiperactivitat de les neurones de l'EPF. Ara bé, la incapacitat de l'haloperidol de bloquejar l'efecte dels antagonistes NMDA indica possiblement diferències d'acció entre antipsicòtics típics i atípics sobre les neurones corticals.[eng] The prefrontal cortex (PFC) plays a crucial role in higher brain functions which are altered in schizophrenic patients. Pyramidal neurons in medial PFC (mPFC) integrate excitatory inputs from cortex and thalamus, and modulatory inputs from brainstem aminergic nuclei like raphe nuclei (RN). In turn, mPFC controls the activity of raphe serotonergic neurons. Previous reports showed that the stimulation of prefrontal 5-HT2A or AMPA receptors increases pyramidal and serotonergic cell firing, and 5-hydroxytryptamine (5-HT) release in mPFC. We use 5-HT release (microdialysis technique) as an indirect measure of pyramidal activity. In this Doctoral Thesis we have examined the role of cortical excitatory and inhibitory receptors in the mPFC-RN circuit, which has been implicated in schizophrenia. Given the similar laminar distribution of 5-HT2A receptors and a1-adrenoceptors in mPFC and their excitatory action on pyramidal neuron activity, we tested the hypothesis that a1-adrenoceptors might also modulate 5-HT release. Antipsychotics exhibit high affinity for receptors expressed in pyramidal neurons such as 5-HT2A and a1-adrenoceptors. Therefore, we have also examined the effects of antipsychotics, as well as selective antagonists for these receptors, on the increased mPFC 5-HT release induced by cirazoline (a1-adrenoceptor agonist), DOI (5-HT2A/2C agonist), and the increase in glutamatergic transmission. The results showed that the stimulation of prefrontal a1-adrenoceptors and the increase in mPFC glutamatergic transmission (exogenous stimulation of AMPA receptors, disinhibition of thalamic afferents to mPFC or acute administration of NMDA antagonists) activate pyramidal afferents to ascending serotonergic neurons (measured as an increase in 5-HT release in RN and mPFC) possibly in a manner similar to that observed for 5-HT2A receptors. This effect was reversed by antipsychotics and antagonists of excitatory receptors located in pyramidal neurons. The PFC contains high density of serotonin 5-HT1A (inhibitory) and 5-HT2A (excitatory) receptors. Likewise, we report that the activation of cortical 5-HT1A receptors reverse the increase in local 5-HT release induced by cirazoline, DOI and S-AMPA. Finally, our results suggest that antipsychotics may exert their therapeutic action by reducing the increased excitability of prefrontal pyramidal neurons. The effect of classical antipsychotics may involve blockade of a1-adrenoceptors, whereas that of atypical may also involve blockade of 5-HT2A receptors

Stimulation of α1-adrenoceptors in the rat medial prefrontal cortex increases the local in vivo 5-hydroxytryptamine release: reversal by antipsychotic drugs

Pyramidal neurons of the medial prefrontal cortex (mPFC) project to midbrain serotonergic neurons and control their activity. The stimulation of prefrontal 5-HT2A and AMPA receptors increases pyramidal and serotonergic cell firing, and 5-hydroxytryptamine (5-HT) release in mPFC. As the mPFC contains abundant α1-adrenoceptors whose activation increases the excitability of pyramidal neurons, we examined the effects of their stimulation on local 5-HT release, using microdialysis. The application of the α1-adrenoceptor agonist cirazoline by reverse dialysis increased the prefrontal 5-HT release in a concentration-dependent manner, an effect antagonized by coperfusion of TTX, prazosin (α1-adrenoceptor antagonist), BAY × 3702 (5-HT1A agonist), NBQX (AMPA/KA antagonist) and 1S,3S-ACPD (mGluR II/III agonist), but not by MK-801 (NMDA antagonist). Cirazoline also enhanced the increase in 5-HT release induced by DOI (5-HT2A/2C agonist) and AMPA. In addition, M100907 (5-HT2A antagonist) but not SB-242084 (5-HT2C antagonist) reversed the cirazoline- and AMPA-induced 5-HT release. These results suggest that the stimulation of prefrontal α1-adrenoceptors activates pyramidal afferents to ascending serotonergic neurons. The effect of cirazoline was also reversed by coperfusion of classical (chlorpromazine, haloperidol) and atypical (clozapine, olanzapine) antipsychotics, which suggests that a functional antagonism of the α1-adrenoceptor-mediated activation of prefrontal neurons may partly underlie their therapeutic action.Peer reviewe

Clozapine and olanzapine, but not haloperidol, suppress serotonin efflux in the medial prefrontal cortex elicited by phencyclidine and ketamine

N-methyl-D-aspartate (NMDA) receptor antagonists such as phencyclidine (PCP) and ketamine can evoke psychotic symptoms in normal individuals and schizophrenic patients. Here, we have examined the effects of PCP (5 mg/kg) and ketamine (25 mg/kg) on the efflux of serotonin (5-HT) in the medial prefrontal cortex (mPFC) and their possible blockade by the antipsychotics, clozapine, olanzapine and haloperidol, as well as ritanserin (5-HT2A/2C receptor antagonist) and prazosin (alpha1-adrenoceptor antagonist). The systemic administration, but not the local perfusion, of the two NMDA receptor antagonists markedly increased the efflux of 5-HT in the mPFC. The atypical antipsychotics clozapine (1 mg/kg) and olanzapine (1 mg/kg), and prazosin (0.3 mg/kg), but not the classical antipsychotic haloperidol (1 mg/kg), reversed the PCP- and ketamine-induced increase in 5-HT efflux. Ritanserin (5 mg/kg) was able to reverse only the effect of PCP. These findings indicate that an increased serotonergic transmission in the mPFC is a functional consequence of NMDA receptor hypofunction and this effect is blocked by atypical antipsychotic drugs.Peer reviewe

In vivo efflux of serotonin in the dorsal raphe nucleus of 5-HT1A receptor knockout mice

In the dorsal raphe nucleus (DR), extracellular serotonin (5-HT) regulates serotonergic transmission through 5-HT1A autoreceptors. In this work we used in vivo microdialysis to examine the effects of stressful and pharmacological challenges on DR 5-HT efflux in 5-HT1A receptor knockout (5-HT1A-/-) mice and their wild-type counterparts (5-HT1A+/+). Baseline 5-HT concentrations did not differ between both lines of mice, which is consistent with a lack of tonic control of 5-HT1A autoreceptors on DR 5-HT release. (R)-(+)-8-Hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT, 0.5 mg/kg) reduced 5-HT levels to 30% of basal values in 5-HT1A+/+ mice, but not in 5-HT1A-/- mice. The selective 5-HT1B receptor agonist 1,4-dihydro-3-(1,2,3,6-tetrahydro-4-pyridinyl)-5H-pyrrolo[3,2-b]pyridin-5-one dihydrochloride (CP 93129, 300 micro m) reduced dialysate 5-HT to the same extent (30-40% of baseline) in the two genotypes, which suggests a lack of compensatory changes in 5-HT1B receptors in the DR of such mutant mice. Both a saline injection and handling for 3 min increased DR dialysate 5-HT in mutants, but not in 5-HT1A+/+ mice. Fluoxetine (5 and 20 mg/kg) elevated 5-HT in a dose-dependent manner in both genotypes. However, this effect was markedly more pronounced in the 5-HT1A-/- mice. The increased responsiveness of the extracellular 5-HT in the DR of 5-HT1A receptor knockout mice reflects a lack of the autoinhibitory control exerted by 5-HT1A autoreceptors.Peer reviewe

Antipsychotic drugs reverse the AMPA receptor-stimulated release of 5-HT in the medial prefrontal cortex

The prefrontal cortex (PFC) is involved in the pathophysiology of schizophrenia. PFC neuronal activity is modulated by monoaminergic receptors for which antipsychotic drugs display moderate-high affinity, such as 5-HT2A and α1-adrenoceptors. Conversely, PFC pyramidal neurons project to and modulate the activity of raphe serotonergic neurons and serotonin (5-HT) release. Under the working hypothesis that atypical antipsychotic drugs may partly exert their action in PFC, we assessed their action on the in vivo 5-HT release evoked by increasing glutamatergic transmission in rat medial PFC (mPFC). This was achieved by applying S-AMPA in mPFC (reverse dialysis) or by disinhibiting thalamic excitatory afferents to mPFC with bicuculline. The application of haloperidol, chlorpromazine, clozapine and olanzapine in mPFC by reverse dialysis (but not reboxetine or diazepam) reversed the S-AMPA-evoked local 5-HT release. Likewise, the local (in mPFC) or systemic administration of these antipsychotic drugs reversed the increased prefrontal 5-HT release produced by thalamic disinhibition. These effects were shared by the 5-HT2A receptor antagonist M100907 and the α1-adrenoceptor antagonist prazosin. However, raclopride (DA D2 antagonist) had very modest effects. These results suggest that, besides their action in limbic striatum, antipsychotic drugs may attenuate glutamatergic transmission in PFC, possibly by interacting with 5-HT2A and/or α1-adrenoceptors.Work supported by grant SAF 2004-05525. Support from the Generalitat de Catalunya (2005SGR00758s) also acknowledged. Support from the Spanish Ministry of Health, Instituto de Salud Carlos III, Red de Enfermedades Mentales (REM-TAP Network) is also acknowledged. MAB was recipient of a predoctoral fellowship from IDIBAPS.Peer reviewe