The effects of antipsychotic drugs on Fos protein expression in the prefrontal cortex: cellular localization and pharmacological characterization

Clozapine and dopamine D3 receptor antisense reduce cocaine- and amphetamine-regulated transcript expression in the rat nucleus accumbens shell

Cocaine- and amphetamine-regulated transcript (CART) is a neuropeptide highly expressed in the hypothalamus and nucleus accumbens. Hypothalamic CART has been associated with food intake and body weight control, but in the nucleus accumbens the role of CART remains elusive. New generations of antipsychotic drugs show a good efficacy over psychotic symptoms but they induce an important weight gain. The mechanism underlying this unexpected side effect is still unknown. The present results show, for the first time, that acute and chronic treatment with the atypical neuroleptic clozapine, but not the conventional neuroleptic haloperidol, reduced the expression of CART mRNA in the shell of the nucleus accumbens. CART mRNA is colocalized with both dopamine D(2) and D(3) receptor transcripts in the nucleus accumbens shell. However, a dopamine D(3) receptor, but not D(2), antisense oligonucleotide administration reduced CART expression in this brain area. These results suggest that the dopamine D(3) receptor, but not the D(2), is involved in the control of CART expression in the nucleus accumbens and that it may participate in the modulation of CART mRNA levels by clozapine. The modulation of CART, an anorexigenic neuropeptide, in the dopamine mesolimbic pathway may potentially play a role in dysregulated food intake induced by some antipsychotic drugs.

The medial prefrontal cortex in the rat: evidence for a dorso-ventral distinction based upon functional and anatomical characteristics

The prefrontal cortex in rats can be distinguished anatomically from other frontal cortical areas both in terms of cytoarchitectonic characteristics and neural connectivity, and it can be further subdivided into subterritories on the basis of such criteria. Functionally, the prefrontal cortex of rats has been implicated in working memory, attention, response initiation and management of autonomic control and emotion. In humans, dysfunction of prefrontal cortical areas with which the medial prefrontal cortex of the rat is most likely comparable is related to psychopathology including schizophrenia, sociopathy, obsessive-compulsive disorder, depression, and drug abuse. Recent literature points to the relevance of conducting a functional analysis of prefrontal subregions and supports the idea that the area of the medial prefrontal cortex in rats is characterized by its own functional heterogeneity, which may be related to neuroanatomical and neurochemical dissociations. The present review covers recent findings with the intent of correlating these distinct functional differences in the dorso-ventral axis of the rat medial prefrontal cortex with anatomical and neurochemical patterns.

Optimizing limbic selective D2/D3 receptor occupancy by risperidone: a [123I]-epidepride SPET study

Selective action at limbic cortical dopamine D2-like receptors is a putative mechanism of atypical antipsychotic efficacy with few extrapyramidal side effects. Although risperidone is an atypical antipsychotic with high affinity for D2 receptors, low-dose risperidone treatment is effective without inducing extrapyramidal symptoms. The objective was to test the hypothesis that treatment with low-dose risperidone results in 'limbic selective' D2/D3 receptor blockade in vivo. Dynamic single photon emission tomography (SPET) sequences were obtained over 5 hours after injection of [123I]-epidepride (approximately 150 MBq), using a high-resolution triple-headed brain scanner (Marconi Prism 3000XP). Kinetic modelling was performed using the simplified reference region model to obtain binding potential values. Estimates of receptor occupancy were made relative to a normal volunteer control group (n = 5). Six patients treated with low-dose risperidone (mean = 2.6 mg) showed moderate levels of D2/D3 occupancy in striatum (49.9%), but higher levels of D2/D3 occupancy in thalamus (70.8%) and temporal cortex (75.2%). Occupancy values in striatum were significantly different from thalamus (F (1,4) = 26.3, p < 0.01) and from temporal cortex (F (1,4) = 53.4, p < 0.01). This is the first study to evaluate striatal and extrastriatal occupancy of risperidone. Low dose treatment with risperidone achieves a similar selectivity of limbic cortical over striatal D2/D3 receptor blockade to that of atypical antipsychotics with lower D2/D3 affinity such as clozapine, olanzapine and quetiapine. This finding is consistent with the relevance of 'limbic selective' D2/D3 receptor occupancy to the therapeutic efficacy of atypical antipsychotic drugs.

Molecular aspects of glutamate dysregulation: implications for schizophrenia and its treatment

The glutamate system is involved in many aspects of neuronal synaptic strength and function during development and throughout life. Synapse formation in early brain development, synapse maintenance, and synaptic plasticity are all influenced by the glutamate system. The number of neurons and the number of their connections are determined by the activity of the glutamate system and its receptors. Malfunctions of the glutamate system affect neuroplasticity and can cause neuronal toxicity. In schizophrenia, many glutamate-regulated processes seem to be perturbed. Abnormal neuronal development, abnormal synaptic plasticity, and neurodegeneration have been proposed to be causal or contributing factors in schizophrenia. Interestingly, it seems that the glutamate system is dysregulated and that N-methyl-D-aspartate receptors operate at reduced activity. Here we discuss how the molecular aspects of glutamate malfunction can explain some of the neuropathology observed in schizophrenia, and how the available treatment intervenes through the glutamate system.

Antipsychotic drug treatment induces differential gene expression in the rat cortex

Antipsychotic drug treatment is known to modulate gene expression in experimental animals. In this study, candidate target genes for antipsychotic drug action were searched using microarrays after acute clozapine treatment (1, 6 and 24 h) in the rat prefrontal cortex. Microarray data clustering with a self-organizing map algorithm revealed differential expression of genes involved in presynaptic function following acute clozapine treatment. The differential expression of 35 genes most profoundly regulated in expression arrays was further examined using in situ hybridization following acute clozapine, and chronic clozapine and haloperidol treatments. Acute administration of clozapine regulated the expression of chromogranin A, synaptotagmin V and calcineurin A mRNAs in the cortex. Chronic clozapine treatment induced differential cortical expression of chromogranin A, son of sevenless (SoS) and Sec-1. Chronic treatment with haloperidol regulated the mRNA expression of inhibitor of DNA-binding 2 (ID-2) and Rab-12. Furthermore, the expression of visinin-like proteins-1, -2 and -3 was regulated by chronic drug treatments in various brain regions. Our data suggest that acute and chronic treatments with haloperidol and clozapine modulate the expression of genes involved in synaptic function and in regulation of intracellular Ca2+ in cortex.

Induction of differential patterns of local cerebral glucose metabolism and immediate-early genes by acute clozapine and haloperidol

Atypical antipsychotic drugs, such as clozapine, show many differences in their actions as compared to typical antipsychotic drugs, such as haloperidol. In particular, the neuroanatomical substrates responsible for the superior therapeutic profile of clozapine are unknown. In order to identify regions of the CNS which are affected either differentially or in parallel by clozapine and haloperidol, we have used 2-deoxyglucose autoradiography to monitor local cerebral glucose utilisation (LCGU), in parallel with in situ hybridisation to monitor the expression of five immediate-early genes (c-fos, fos B, fra 1, fra 2 and zif 268). Clozapine (20 mg/kg i.p.) caused a reduction in LCGU in many areas of the psychosis-related corticolimbothalamic and Papez circuits, such as the anterior cingulate and retrosplenial cortices and the mammillary body. Haloperidol (1 mg/kg i.p.) showed less ability to modulate LCGU in these regions. Clozapine also increased immediate-early gene expression in these limbic circuits, although the pattern of induction was different for each gene, and also differed from the pattern of effects on LCGU. The only region which displayed similar effects with both antipsychotics was the anteroventral thalamus, with LCGU and c-fos mRNA expression being altered similarly by both drugs. This further supports the hypothesis of the thalamus being a common site of antipsychotic action. Since the Papez circuit has been implicated in emotive learning, and to be involved in mediating the negative symptoms associated with schizophrenia, the greater action of clozapine on regions within this circuit may also provide clues to the atypical antipsychotic's superior efficacy against negative symptoms. This is one of the first studies which provides a direct comparison of regional activity as assessed by LCGU and by a panel of IEGs. The results emphasise the necessity of monitoring a number of different parameters of regional activity in order to identity the neuroanatomical substrate for actions of a drug in the CNS.

Multimodal neuroimaging studies and neurodevelopment and neurodegeneration hypotheses of schizophrenia

The interpretation of the huge number of results in schizophrenia research using neuroimaging is uncertain. However, the simultaneous use of complimentary data obtained with these techniques may yield more relevant information in this regard. In this paper we present a series of studies performed by our group in two schizophrenic samples with the use of structural (magnetic resonance imaging, MRI), functional [glucose positron emission tomography (PET) and N-acetyl-aspartate (NAA) magnetic resonance spectrocopy] and neurophysiological techniques (the P300 event-related potential). Transversal and longitudinal measurements were performed.The integrated vision of the results so obtained allows us to propose the hypothesis of a neurodevelopmentally determined state of prefrontal disinihibition, in which the degree of atrophy would directly relate to the metabolic rate. This state would already be present in the first stages of illness and could have neurotoxic consequences in the long term. This would explain the findings of an association between sulcal cerebrospinal fluid (CSF) and illness duration and decreased NAA levels in chronic but not in recent-onset cases. The prefrotnal disinhibition would overstimulate the limbic system and the hippocampus would become overactivated, the metabolic rate at this level being inversely related to P300 amplitude. Clozapine showed a more selective and intense action on that hyperactive metabolic tone than haloperidol.

Interaction of dopamine D1 and NMDA receptors mediates acute clozapine potentiation of glutamate EPSPs in rat prefrontal cortex

The atypical antipsychotic drug clozapine effectively alleviates both negative and positive symptoms of schizophrenia via unclear cellular mechanisms. Clozapine may modulate both glutamatergic and dopaminergic transmission in the prefrontal cortex (PFC) to achieve part of its therapeutic actions. Using whole cell patch-clamp techniques, current-clamp recordings in layers V-VI pyramidal neurons from rat PFC slices showed that stimulation of local afferents (in 2 microM bicuculline) evoked mixed [AMPA/kainate and N-methyl-D-aspartate (NMDA) receptors] glutamate receptor-mediated excitatory postsynaptic potentials (EPSPs). Clozapine (1 microM) potentiated polysynaptically mediated evoked EPSPs (V(Hold) = -65 mV), or reversed EPSPs (rEPSP, V(Hold) = +20 mV) for >30 min. The potentiated EPSPs or rEPSPs were attenuated by elevating [Ca(2+)](O) (7 mM), by application of NMDA receptor antagonist 2-amino5-phosphonovaleric acid (50 microM), or by pretreatment with dopamine D1/D5 receptor antagonist SCH23390 (1 microM) but could be further enhanced by a dopamine reuptake inhibitor bupropion (1 microM). Clozapine had no significant effect on pharmacologically isolated evoked NMDA-rEPSP or AMPA-rEPSPs but increased spontaneous EPSPs without changing the steady-state resting membrane potential. Under voltage clamp, clozapine (1 microM) enhanced the frequency, and the number of low-amplitude (5-10 pA) AMPA receptor-mediated spontaneous EPSCs, while there was no such changes with the mini-EPSCs (in 1 microM TTX). Taken together these data suggest that acute clozapine can increase spike-dependent presynaptic release of glutamate and dopamine. The glutamate stimulates distal dendritic AMPA receptors to increase spontaneous EPSCs and enabled a voltage-dependent activation of neuronal NMDA receptors. The dopamine released stimulates postsynaptic D1 receptor to modulate a lasting potentiation of the NMDA receptor component of the glutamatergic synaptic responses in the PFC neuronal network. This sequence of early synaptic events induced by acute clozapine may comprise part of the activity that leads to later cognitive improvement in schizophrenia.

Effects of the adenosine A(1) receptor agonist N(6)-cyclopentyladenosine on phencyclidine-induced behavior and expression of the immediate-early genes in the discrete brain regions of rats

Because of the possible interaction between adenosine receptors and dopaminergic functions, the compound acting on the specific adenosine receptor subtype may be a candidate for novel antipsychotic drugs. To elucidate the antipsychotic potential of the selective adenosine A(1) receptor agonist N(6)-cyclopentyladenosine (CPA), we examined herein the effects of CPA on phencyclidine (PCP)-induced behavior and expression of the immediate-early genes (IEGs), arc, c-fos and jun B, in the discrete brain regions of rats. PCP (7.5 mg/kg, s.c.) increased locomotor activity and head weaving in rats and this effect was significantly attenuated by pretreatment with CPA (0.5 mg/kg, s.c.). PCP increased the mRNA levels of c-fos and jun B in the medial prefrontal cortex, nucleus accumbens and posterior cingulate cortex, while leaving the striatum and hippocampus unaffected. CPA pretreatment significantly attenuated the PCP-induced increase in c-fos mRNA levels in the medial prefrontal cortex and nucleus accumbens. CPA also significantly attenuated the PCP-induced arc expression in the medial prefrontal cortex and posterior cingulate cortex. When administered alone, CPA decreased the mRNA levels of all IEGs examined in the nucleus accumbens, but not in other brain regions. Based on the ability of CPA to inhibit PCP-induced hyperlocomotion and its interaction with neural systems in the medial prefrontal cortex, posterior cingulate cortex and nucleus accumbens, the present results provide further evidence for a significant antipsychotic effect of the adenosine A(1) receptor agonist.

Expression of c-Fos, Fos B, Jun B, and Zif268 transcription factor proteins in rat barrel cortex following apomorphine-evoked whisking behavior

Apomorphine-evoked expression of transcription factor proteins: c-Fos, Fos B, Jun B, and Zif268 (also named Krox-24, NGFI-A, Egr-1), was investigated in rat somatosensory (barrel) cortex. The effect of the N-methyl-D-aspartate receptor antagonist MK-801 on their expression was also analyzed. Apomorphine is a dopamine receptor agonist, eliciting motor activity, including enhanced whisking leading to the activation of vibrissae representation in the barrel cortex. Rats had their whiskers clipped on one side of the snout. The Zif268 levels were markedly reduced by this procedure alone. In contrast, apomorphine (5.0 mg/kg) evoked marked c-Fos elevation, less pronounced changes in Jun B and Zif268 and no change in Fos B. The greatest apomorphine-evoked c-Fos accumulation was observed in layers IV and V/VI of non-deprived barrel cortex and was not significantly influenced by MK-801 injection at 0.1 mg/kg. A higher dose of MK-801 (1.0 mg/kg) produced abnormalities in locomotor behavior and diminished c-Fos levels on the non-deprived side to the ones observed in the sensory stimulus-deprived cortex. We conclude that the response of the somatosensory cortex is selective with respect to both the gene activated and its cortical layer localization. Furthermore, sensory stimulation provides a major but not the only component to apomorphine-evoked barrel cortex gene activation.

Parametric images of the extrastriatal D2 receptor density obtained using a high-affinity ligand (FLB 457) and a double-saturation method

The potential of positron emission tomography for the quantitative estimation of receptor concentration in extrastriatal regions has been limited in the past because of the low density of the D2 receptor sites in these regions and the insufficient affinity of the most widely used radioligands for dopamine receptors. The new method described in this paper permits the estimate of the D2 receptor concentration in the extrastriatal regions using a two-injection protocol and FLB 457, a ligand with a high affinity (20 pmol/L in vitro ) with D2 dopamine receptors. This approach is not valid for the striatal regions because some hypotheses cannot be verified (because of the high receptor concentration in these regions). The experimental protocol includes two injections with ligand doses designed to significantly occupy the extrastriatal receptor sites (approximately 90%), while leaving less than 60% of the receptor sites occupied by the ligand in the striatal regions. The results obtained using this double-saturation method are in line with the concentration estimates previously obtained using the multiinjection approach. The receptor concentration is 2.9 +/- 0.5 pmol/mL in the thalamus, 1.0 +/- 0.2 pmol/mL in the temporal cortex, and 0.35 +/- 0.13 pmol/mL in the occipital cortex. This study provides new arguments supporting the presence of a small receptor-site concentration in the cerebellum, estimated at 0.35 +/- 0.16 pmol/mL The simplicity of the calculation used to estimate the receptor concentration lends itself easily to parametric imaging. The receptor concentration is estimated pixel by pixel, without filtering. This method permits estimation of the extrastriatal D2 receptor concentration using an experimental protocol that can easily be used in patient studies (i.e., single experiment, no blood sampling, short experiment duration).

Antipsychotic drugs and neuroplasticity: insights into the treatment and neurobiology of schizophrenia

This paper reviews the evidence that antipsychotic drugs induce neuroplasticity. We outline how the synaptic changes induced by the antipsychotic drug haloperidol may help our understanding of the mechanism of action of antipsychotic drugs in general, and how they may help to elucidate the neurobiology of schizophrenia. Studies have provided compelling evidence that haloperidol induces anatomical and molecular changes in the striatum. Anatomical changes have been documented at the level of regional brain volume, synapse morphology, and synapse number. At the molecular level, haloperidol has been shown to cause phosphorylation of proteins and to induce gene expression. The molecular responses to conventional antipsychotic drugs are predominantly observed in the striatum and nucleus accumbens, whereas atypical antipsychotic drugs have a subtler and more widespread impact. We conclude that the ability of antipsychotic drugs to induce anatomical and molecular changes in the brain may be relevant for their antipsychotic properties. The delayed therapeutic action of antipsychotic drugs, together with their promotion of neuroplasticity suggests that modification of synaptic connections by antipsychotic drugs is important for their mode of action. The concept of schizophrenia as a disorder of synaptic organization will benefit from a better understanding of the synaptic changes induced by antipsychotic drugs.

Prenatal cocaine exposure increases mesoprefrontal dopamine neuron responsivity to mild stress

Children whose mothers used cocaine during pregnancy appear to have an increased incidence of certain neurobehavioral deficits. Rodent models of prenatal cocaine exposure have mimicked these deficits in the offspring, yet the biochemical basis of the behavioral abnormalities is unknown. We have been able to reproduce short-term memory deficits in our rat intravenous model of prenatal cocaine exposure, and as short-term memory is dependent on the function of dopamine neurons innervating the medial prefrontal cortex, we hypothesized that prenatal cocaine induces a dysfunction in the regulation of this pathway. Here we report that mild footshock stress, which preferentially activates the mesoprefrontal dopamine system, leads to an enhanced increase in dopamine turnover in the ventromedial prefrontal cortex of adolescent (postnatal day 35-37) rats exposed to cocaine in utero, suggesting that the dopamine neurons innervating this region are hyperresponsive in these rats. Thus, this biochemical alteration may be central to some of the cognitive deficits exhibited by offspring that were exposed to cocaine during fetal development.

Olanzapine activates the rat locus coeruleus: in vivo electrophysiology and c-Fos immunoreactivity

BACKGROUND

Activation of central noradrenergic pathways by atypical antipsychotics has been hypothesized to play a role in their efficacy in treating the negative symptoms and cognitive impairment of schizophrenia. Because acute administration of the atypical antipsychotic olanzapine has been shown to increase extracellular levels of norepinephrine in the medial prefrontal cortex, we examined the effects of olanzapine on the noradrenergic cells of the locus coeruleus (LC).

METHODS

The effects of olanzapine (0.25-16 mg kg(-1), IV) on the firing rates and patterns of LC neurons were determined by extracellular, single-unit recordings in chloral hydrate-anaesthetized rats. The effects of olanzapine and clozapine on c-Fos expression in the LC, nucleus subcoeruleus part alpha (SubCA), and nucleus A5 (A5) were studied by immunohistochemistry.

RESULTS

Olanzapine increased LC cell firing rates, de-regularized firing, and induced burst firing. Induction of c-Fos expression in the LC by olanzapine and clozapine was confirmed and was also found in the SubCA, but not in A5.

CONCLUSIONS

Acute administration of olanzapine activates the noradrenergic neurons of the rat LC. This increased activity of LC neurons may play an important role in the efficacy of olanzapine and clozapine in treating both the negative symptoms and cognitive impairment observed in schizophrenic patients.

Pharmacology of the atypical antipsychotic remoxipride, a dopamine D2 receptor antagonist

Remoxipride is a substituted benzamide that acts as a weak but very selective antagonist of dopamine D2 receptors. It was introduced by Astra (Roxiam) at the end of the eighties and was prescribed as an atypical antipsychotic. This article reviews its putative selective effects on mesolimbic versus nigrostriatal dopaminergic systems. In animals, remoxipride has minimal cataleptic effects at doses that block dopamine agonist-induced hyperactivity. These findings are predictive of antipsychotic activity with a low likelihood of extrapyramidal symptoms. Remoxipride also appears to be effective in more recent animal models of schizophrenia, such as latent inhibition or prepulse inhibition. In clinical studies, remoxipride shows a relatively low incidence of extrapyramidal side effects and its effects on prolactin release are short-lasting and generally mild. The clinical efficacy of remoxipride is similar to that of haloperidol or chlorpromazine. Although its clinical use was severely restricted in 1993, due to reports of aplastic anemia in some patients receiving remoxipride, this drug has been found to exhibit relatively high selectivity for dopamine D2 receptors making remoxipride an interesting tool for neurochemical and behavioral studies.

Interactions between environmental stimulation and antipsychotic drug effects on forebrain c-fos activation

The immediate-early gene product Fos is differentially induced in the rat brain by the antipsychotic drugs haloperidol and clozapine. It is often claimed that although both drugs induce Fos in the nucleus accumbens, haloperidol but not clozapine increases Fos-like immunoreactivity in the striatum, whereas clozapine but not haloperidol increases Fos-like immunoreactivity in prefrontal cortex. Investigations of antipsychotic drug effects on Fos have typically administered high doses with pronounced sedative effects to behaviorally naive animals. In the present study, we compared the effects of low doses of haloperidol (0.1 mg/kg) and clozapine (5 mg/kg) on Fos-like immunoreactivity in rats which were either behaviorally naive, exposed to a novel environment or tested for two-way active avoidance. We determined that haloperidol increased Fos in the striatum and nucleus accumbens regardless of testing condition whereas clozapine markedly reduced the induction of Fos by behavioral testing in these regions; moreover, haloperidol dramatically increased prefrontal cortical Fos expression in animals placed in a novel environment, but not in testing-naive controls. From these results we suggest that antipsychotic drug-induced patterns of Fos expression in the rat are highly dependent on animals' concurrent behavioral status, perhaps reflecting neuroanatomically specific interactions between antipsychotic drugs and environmental stressors which also may occur in the schizophrenic condition.

The expression of glutamate transporter GLT-1 in the rat cerebral cortex is down-regulated by the antipsychotic drug clozapine

We show here that clozapine, a beneficial antipsychotic, down-regulates the expression of the glutamate transporter GLT-1 in the rat cerebral cortex, thereby reducing glutamate transport and raising extracellular glutamate levels. Clozapine treatment (25--35 mg kg(-1) day(-1) orally) reduced GLT-1 immunoreactivity in several brain regions after 3 weeks; this effect was most prominent after 9 weeks and most evident in the frontal cortex. GLT-1 protein levels were reduced in the cerebral cortex of treated rats compared with controls and were more severely affected in the anterior (71.9 +/- 4.5%) than in the posterior (53.2 +/- 15.4%) cortex. L-[(3)H]-glutamate uptake in Xenopus laevis oocytes injected with mRNA extracted from the anterior cerebral cortex of rats treated for 9 weeks was remarkably reduced (to 30.6 +/- 8.6%) as compared to controls. In addition, electrophysiological recordings from oocytes following application of glutamate revealed a strong reduction in glutamate uptake currents (46.3 +/- 10.2%) as compared to controls. Finally, clozapine treatment led to increases in both the mean basal (8.1 +/- 0.7 microM) and the KCl-evoked (28.7 +/- 7.7 microM) output of glutamate that were 3.1 and 3.5, respectively, higher than in control rats. These findings indicate that clozapine may potentiate glutamatergic synaptic transmission by regulating glutamate transport.

Neuropharmacological profiles of a novel atypical antipsychotic, NRA0562, in rats

Neuropharmacological profiles of 5-(2-[4-(6-fluoro-1H-indole-3-yl) piperidine-1-yl] ethyl)-4-(4-fluorophenyl) thiazole-2-carboxylic acid amide (NRA0562) in rats were examined using electrophysiological and immunohistochemical methods. The firing rates of the substantia nigra pars compacta (A9) and the ventral tegmental area (A10) dopamine neurons were inhibited by methamphetamine (1 mg/kg, i.v.). NRA0562 dose-dependently reversed the inhibitory effects of methamphetamine on A9 and on A10 dopamine neurons. NRA0562 was more potent to reverse the inhibitory effects of methamphetamine on A10 (ED(50)=0.3 mg/kg) than on A9 (ED(50)=0.9 mg/kg) dopamine neurons. NRA0562 produced significant increases in Fos-like immunoreactivity in both the nucleus accumbens and the dorsolateral striatum. The difference between the number of Fos-like immunoreactivity produced by NRA0562 in the nucleus accumbens vs. dorsolateral striatum, referred to as the atypical index, was positive. Similar results could be observed with risperidone, an atypical antipsychotic. These results suggest that NRA0562 may have the atypical antipsychotic activities seen with risperidone, but without the liability of motor side effects typical of classical antipsychotics.

M100907, a selective 5-HT(2A) receptor antagonist, attenuates phencyclidine-induced Fos expression in discrete regions of rat brain

5-HT and dopamine receptor antagonists have become widely used as atypical antipsychotics. Although 5-HT(2A) receptor antagonistic activity is thought to contribute to the atypical aspects of these agents, the precise mechanism remains unknown. M100907 (R(+)-alpha(2,3-dimethoxyphenyl)-1-[2(4-fluorophenyl)ethyl)]-4-piperidine -methanol), a selective 5-HT(2A) receptor antagonist, is reported to attenuate phencyclidine (PCP)-induced locomotion in rodents. For the purpose of identifying regions in which M100907 exerts its effect, we investigated the effects of M100907 on PCP-induced Fos expression in rat brain. PCP (5 mg/kg, subcutaneously, s.c.) induced Fos expression in the cingulate cortex area 3, the agranular insular cortex, the piriform cortex, the nucleus accumbens, the anterior paraventricular thalamic nucleus and the ventral lateral septal nucleus. Pretreatment with M100907 (0.5 mg/kg, s.c.) attenuated Fos expression induced by PCP in the nucleus accumbens core, the shell, the agranular insular cortex and the piriform cortex. M100907 did not induce Fos expression in any of the regions investigated including the dorsolateral caudate/putamen when given alone. These results indicate that 5-HT(2A) receptor antagonism attenuates Fos expression in a regionally specific manner in rat brain in the PCP model of psychosis.

Pharmacology and behavioral pharmacology of the mesocortical dopamine system

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

deltaFosB: a molecular switch underlying long-term neural plasticity

Numerous chronic perturbations have been shown to induce highly stable isoforms of the transcription factor deltaFosB in the brain in a region-specific manner. This review examines the functional consequences of the induction of deltaFosB in particular neuronal populations as well as its possible role in behavioral abnormalities such as drug addiction and movement disorders.

Limited participation of 5-HT(1A) and 5-HT(2A/2C) receptors in the clozapine-induced Fos-protein expression in rat forebrain regions

Through the development of tolerance following long-term clozapine treatment, we investigated whether 5-HT(1A) and 5-HT(2A/2C) receptors participate in the clozapine-induced Fos-protein expression in the rat forebrain. Tolerance exists when the acutely increased Fos responses to a challenge dose of the 5-HT(1A) and 5-HT(2A/2C) agonists 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane-hydrochloride (DOI) and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), respectively, given simultaneously to rats, are attenuated after 3-week clozapine (20 mg kg(-1) day(-1) i.p.) pretreatment. As compared to the acute effects of clozapine, the Fos responses to concomitant administration of the 5-HT receptor agonists DOI (2.5 mg kg(-1) i.p. ) and 8-OH-DPAT (2.5 mg kg(-1) i.p.) were more pronounced in the prefrontal cortex, the nucleus accumbens core and the dorsomedial and ventromedial striatum, areas in which clozapine (20 mg kg(-1) i. p.) exhibited marginal effects. In the hypothalamic paraventricular nucleus, both clozapine and DOI/8-OH-DPAT induced a remarkably high number of Fos-positive nuclei. Long-term clozapine pretreatment attenuated the acutely induced Fos expression of the 5-HT receptor agonists in the nucleus accumbens core, the dorsomedial and ventromedial parts of the striatum and the lateral septum, indicating (partial) common sites of action of the agents in these brain regions. No tolerance was found in the nucleus accumbens shell and the hypothalamic paraventricular nucleus and the central amygdala, suggesting that the clozapine-induced Fos responses, though distinct in these regions, are independent of 5-HT receptors. The prefrontal cortex and the dorsolateral striatum indicated only a tendency towards tolerance. In addition, the involvement of the tested 5-HT receptor agonists in the clozapine-enhanced release of plasma corticosterone became apparent. The present results indicate that the clozapine-induced patterns of Fos expression in the rat forebrain can only be in part attributed to an interaction with 5-HT(1A/2A/2C) receptors.

Effect of amphetamine on extrastriatal D2 dopamine receptor binding in the primate brain: a PET study

[(11)C]raclopride binding to D2 dopamine receptors in the striatum is sensitive to drug-induced changes of endogenous dopamine concentration. We recently developed the new radioligand [(11)C]FLB 457, which is suitable for positron emission tomography (PET) studies of extrastriatal D2 dopamine receptors. The purpose of this PET study was to examine the effect of amphetamine on [(11)C]FLB 457 binding in extrastriatal regions. Each of three cynomolgus monkeys was examined at baseline conditions, 15 min and 3 h after I.V. injection of amphetamine (2 mg/kg). The effect of amphetamine was calculated from the ratio of specific [(11)C]FLB 457 binding to the binding in the cerebellum, a region which was used as reference for free and nonspecific binding in the brain. The changes of the ratio in the striatum, the thalamus, and the neocortex were between -1.2% and -15.5% at 15 min and -2.1% and -16.3% at 3 h, respectively, after amphetamine administration. The reductions of the binding ratios in the extrastriatal regions are similar to those reported for [(11)C]raclopride binding in the striatum. These data in a limited series of monkeys suggest that [(11)C]FLB 457 binding to D2 dopamine receptors in extrastriatal regions is sensitive to changes in the concentration of endogenous dopamine.

Contrasting patterns and cellular specificity of transcriptional regulation of the nuclear receptor nerve growth factor-inducible B by haloperidol and clozapine in the rat forebrain

This study was designed to investigate the possible involvement of members of the nuclear receptor family of transcription factors in the effects of antipsychotic drugs used in the treatment of schizophrenia. We have identified, using RT-PCR screening, an important modulation of nerve growth factor-inducible B (NGFI-B) mRNA levels by typical and atypical neuroleptics in the rat forebrain. NGFI-B, a member of the nuclear receptor family, can be observed in target structures of dopaminergic pathways. Using in situ hybridization, we also demonstrate that typical and atypical antipsychotics induced contrasting patterns of expression of NGFI-B after both acute and chronic administration. An acute treatment with clozapine or haloperidol induces high NGFI-B mRNA levels in the prefrontal and cingulate cortices and in the nucleus accumbens shell. However, haloperidol, but not clozapine, dramatically increases NGFI-B expression in the dorsolateral striatum. In contrast, chronic treatment with clozapine reduces NGFI-B expression below basal levels in the rat forebrain, whereas haloperidol still induces high NGFI-B mRNA levels in the dorsolateral striatum. Finally, using a double in situ hybridization technique, we show that acute administration of both neuroleptics increases NGFI-B expression in neurotensin-containing neurons in the nucleus accumbens shell, whereas the effects of haloperidol in the dorsolateral striatum are mainly observed in enkephalin-containing neurons. These results are the first demonstration that members of the nuclear receptor family of transcription factors could play an important role in the effects of antipsychotic drugs.

Changes in CArG-binding protein A expression levels following injection(s) of the D1-dopamine agonist SKF-82958 in the intact and 6-hydroxydopamine-lesioned rat

We recently characterized the rat brain homolog of mouse muscle CArG-binding protein A initially identified in C2 myogenic cells and showed an inverse temporal correlation between increased expression levels of this messenger RNA, c-fos and zif268 messenger RNA levels following the addition of nerve growth factor to PC12 cells. In addition, we found an inverse correlation between c-Fos protein and CArG-binding protein A messenger RNA levels in the lateral caudate-putamen of rats treated acutely and chronically with the D2 receptor antagonist fluphenazine (phenothiozine typical psychotic). To determine whether D1 receptor stimulation is also capable of inducing CArG-binding protein A up-regulation, drug naive or dopamine-depleted (i.e. 6-hydroxydopamine-lesioned) D1 hypersensitized rats (i.e. rats given repeated daily injections of SKF-82958 for 14days) were acutely injected with the D1 agonist SKF-82958 and examined using a combination of in situ hybridization for CArG binding protein A and immunocytochemistry for c-Fos. Both acutely treated animals and dopamine-depleted hypersensitized animals showed increases in CArG-binding protein A. Moderate increases were found in the medial caudate-putamen and nucleus accumbens core and shell regions following acute treatment whereas large increases in CArG-binding protein A expression levels were found in the medial and lateral caudate-putamen and the shell and core of the nucleus accumbens following hypersensitization. No change in CArG-binding protein A expression level was found in the dopamine-depleted, drug naive animals relative to controls. Regions of the basal ganglia where increases in CArG-binding protein A were detected following each treatment correlated perfectly with c-Fos protein induction. The results demonstrate that CArG-binding protein A responds to SKF-82958 and that the changes in CArG-binding protein A match perfectly with the pattern of c-Fos induction induced by the D1 agonist.

Dual cytoarchitectonic trends: an evolutionary model of frontal lobe functioning and its application to psychopathology

OBJECTIVE

To introduce and discuss an evolutionary model of frontal lobe functioning (the dual cytoarchitectonic trends theory [DTT]) and its application to understanding the neurobiology of schizophrenia and anxiety disorders.

METHOD

An introduction to the DTT with respect to neural architecture, connectivity, and function is presented. In addition, neurobiologic, neuropathologic, clinical, and cognitive research supporting the application of this model to schizophrenia and anxiety disorders is reviewed.

RESULTS

Traditional neuropsychologic models of acquired brain damage have been limited in their ability to explain frontal lobe dysfunction and its consequences in relation to psychopathology. The DTT offers an appropriately general neural-systems framework that may be better able to account for the diversity of symptoms, widespread neuropathology, and developmental abnormalities that are associated with most forms of psychopathology.

CONCLUSIONS

Research investigating the neurobiology of psychopathology would benefit from adopting models of brain dysfunction that are consistent with neurodevelopmental pathology and evolution. Such efforts would likely lead to a greater understanding of neurobiologic mechanisms and, ultimately, better treatment strategies.

Effects of age, medication, and illness duration on the N-acetyl aspartate signal of the anterior cingulate region in schizophrenia

The authors performed a MRSI study of the anterior cingulate gyrus in 19 schizophrenic patients under stable medication and 16 controls in order to corroborate previous findings of reduced NAA in the anterior cingulate region in schizophrenia. Furthermore, correlations between NAA in the anterior cingulate gyrus and age or illness duration have been determined. A decreased NAA signal was found in the anterior cingulate gyrus of patients compared to controls. Subdividing the patient group into two groups depending on medication revealed that the group of patients receiving a typical neuroleptic medication showed a lower mean NAA in comparison to the group of patients receiving atypical antipsychotic drugs. No significant group differences in the creatine and phosphocreatine signal or the signal from choline-containing compounds were found. The NAA signal significantly correlated with age, and therefore, individual NAA values were corrected for the age effect found in the control group. The age-corrected NAA signal in schizophrenia correlated significantly with the duration of illness. The detected correlations of NAA decrease with age and illness duration are consistent with recent imaging studies where progressing cortical atrophy in schizophrenia was found. Further studies will be needed to corroborate a possible favorable effect of atypical antipsychotics on the NAA signal.

Cortically driven Fos induction in the striatum is amplified by local dopamine D2-class receptor blockade

Dopamine D2-class receptors have been shown to control the excitability of striatal neurons in response to cortical activation. It has been unclear, however, whether such receptors could regulate the number of striatal neurons activated by cortical stimulation, and thus affect the population response of the striatum to its cortical inputs. We used Fos induction as a readout to measure the ensemble response of striatal neurons to localized stimulation of the frontal cortex and tested for the effects of D2-class dopamine receptor blockade on this response. In freely moving rats, we stimulated the frontal cortex by local epidural application of a dose of a GABAA receptor antagonist (picrotoxin) just threshold for inducing Fos in the striatum. We combined this treatment with D2-class dopamine receptor antagonist treatments at dose levels also just threshold for inducing Fos, using either (i) systemic haloperidol or (ii) intrastriatal (-)sulpiride. Both systemic and intrastriatal blockade of D2-class receptors sharply increased the numbers of striatal neurons exhibiting cortically evoked Fos induction. These findings suggest that local activation of intrastriatal D2-class dopamine receptors can regulate the number of striatal neurons responsive to cortical inputs, thus dynamically shaping the flow of information through the striatum.

Quantification of [11C]FLB 457 binding to extrastriatal dopamine receptors in the human brain

Positron emission tomography (PET) has hitherto been used to examine D2 dopamine receptor binding in the striatum, a region with a high density of receptors. Research has been hampered by the lack of suitable radioligands for detection of the low-density D2 dopamine receptor populations in the limbic and cortical dopamine systems that are implicated in the pathophysiology of schizophrenia. [11C]FLB 457 is a new radioligand with the very high affinity of 20 pmol/L (K(i)) for the D2 and D3 dopamine receptor subtypes. This study in eight healthy subjects was designed to evaluate the suitability of [11C]FLB 457 for quantification of extrastriatal D2/D3 dopamine receptors. PET-data were acquired in the three-dimensional mode and the arterial input function was corrected for labeled metabolites. The standard three-compartment model and four derived approaches were applied to calculate and compare the binding potentials. Besides the striatum, conspicuous radioactivity was found in extrastriatal regions such as the thalamus, the anterior cinguli, and the temporal and frontal cortices. The time activity curves could be described by the three compartment model. The different approaches gave similar binding potential values and the rank order between regions was consistent with that found in vitro. The short time of a PET measurement using [11C]FLB 457 (63 minutes) seemed not to be sufficient for reliable determination of the high binding potential in the striatum. These results are of principal importance because they show the potential for PET quantification of minute receptor populations in the human brain.

Region-specific induction of deltaFosB by repeated administration of typical versus atypical antipsychotic drugs

Whereas acute administration of many types of stimuli induces c-Fos and related proteins in brain, recent work has shown that chronic perturbations cause the region-specific accumulation of novel Fos-like proteins of 35-37 kD. These proteins, termed chronic FRAs (Fos-related antigens), have recently been shown to be isoforms of DeltaFosB, which accumulate in brain due to their enhanced stability. In the present study, we sought to extend earlier findings that documented the effects of acute administration of antipsychotic drugs (APDs) on induction of Fos-like proteins by investigating the ability of typical and aytpical APDs, after chronic administration, to induce these DeltaFosB isoforms in several brain regions implicated in the clinical actions of these agents. By Western blotting we found that chronic administration of the typical APD, haloperidol, dramatically induces DeltaFosB in caudate-putamen (CP), a brain region associated with the extrapyramidal side effects of this drug. A smaller induction was seen in the nucleus accumbens (NAc) and prefrontal cortex (PFC), brain regions associated with the antipsychotic effects of the drug. In contrast, chronic administration of the prototype atypical APD clozapine failed to significantly increase levels of DeltaFosB in any of the three brain regions, and even tended to reduce DeltaFosB levels in the NAc. Two putative atypical APDs, risperidone and olanzapine, produced small but still significant increases in the levels of DeltaFosB in CP, but not NAc or PFC. Studies with selective receptor antagonists suggested that induction of DeltaFosB in CP and NAc is most dependent on antagonism of D2-D3 dopamine receptors, with antagonism of D1-like receptors most involved in the PFC. Immunohistochemical analysis confirmed the greater induction of DeltaFosB in CP by typical versus atypical APDs, with no significant induction seen in PFC with either class of APD. Together, these findings demonstrate that repeated administration of APDs results in the induction of long-lasting Fos-like transcription factors that could mediate some of the persistent and region-specific changes in brain function associated with chronic drug exposure. Synapse 33:118-128, 1999.

Blockade of cannabinoid receptors by SR141716 selectively increases Fos expression in rat mesocorticolimbic areas via reduced dopamine D2 function

The present study investigated, in rats, whether blockade of cannabinoid CB1 receptors may alter Fos protein expression in a manner comparable to that observed with antipsychotic drugs. Intraperitoneal administration of the selective CB1 receptor antagonist, SR141716, dose-dependently (1.0, 3.0 and 10 mg/kg) increased Fos-like immunoreactivity in mesocorticolimbic areas (prefrontal cortex, ventrolateral septum, shell of the nucleus accumbens and dorsomedial caudate-putamen), while motor-related structures such as the core of the nucleus accumbens and the dorsolateral caudate-putamen were unaffected. In the ventrolateral septum, taken as a representative structure, the Fos-inducing effect of SR141716 (10 mg/kg) was maximal 2 h after injection and returned to near control levels by 4 h. Within the prefrontal cortex, SR141716 increased the number of Fos-positive cells predominantly in the infralimbic and prelimbic cortices, presumptive pyramidal cells being the major cell types in which Fos was induced. The D1-like receptor antagonist, SCH23390 (0.1 mg/kg), did not prevent the Fos-inducing effect of SR141716 in any brain region examined (prefrontal cortex, nucleus accumbens, ventrolateral septum and dorsomedial caudate-putamen), although SCH23390 significantly reduced Fos expression induced by cocaine (20 mg/kg) in all these regions. By contrast, the dopamine D2-like agonist, quinpirole (0.25 mg/ kg), counteracted SR141716-induced Fos-like immunoreactivity in the ventrolateral septum, the nucleus accumbens and the dorsomedial caudate-putamen, while no antagonism was observed in the prefrontal cortex. Microdialysis experiments in awake rats indicated that SR141716, at doses which increased Fos expression (3 and 10 mg/kg), did not alter dopamine release in the shell of the nucleus accumbens. Finally, SR141716 increased the levels of neurotensin-like immunoreactivity in the nucleus accumbens, but not in the caudate-putamen. Collectively, the present results show that blockade of cannabinoid receptors increases Fos- and neurotensin-like immunoreactivity with characteristics comparable to those reported for atypical neuroleptic drugs.

Effects of NRA0045, NRA0160, and NRA0215 on regional Fos-like immunoreactivity in the rat brain

Pharmacological characteristics of NRA compounds, novel atypical antipsychotics, were compared with those of clozapine and haloperidol, in regard to modification of Fos-like immunoreactivity (FLI) in rats. (R)-(+)-2-Amino-4-(4-fluorophenyl)-5-[1-[4-(4-fluorophenyl)-4-oxobutyl] pyrrolidin-3-yl] thiazole (NRA0045) and 2-carbamoyl-4-phenyl-5-[2-[4-(4-fluorobenzylidene) piperidin-1-yl] ethyl] thiazole (NRA0215) have a high affinity for dopamine D4 receptors, serotonin2A receptors, and the alpha1 adrenoceptor. 2-Carbamoyl-4-(4-fluorophenyl)-5-[2-[4-(3-fluorobenzylidene) piperidin-1-yl] ethyl] thiazole (NRA0160) has a selective and high affinity for dopamine D4 receptors. NRA0045 and clozapine (10 and 30 mg/kg, IP) produced significant increases in FLI in both the nucleus accumbens (N. Acc.) and the medial prefrontal cortex (mPFC) but not in the dorsolateral striatum (DLS). In contrast, NRA0160 and NRA0215 (10 and 30 mg/kg, IP) significantly increased FLI in the mPFC but not in the N. Acc. and the DLS. Haloperidol (0.1 and 1 mg/kg, IP) significantly produced FLI in the N. Acc., the DLS, and the mPFC. These data indicate that the antagonistic effects of dopamine D4 receptors may contribute, at least in part, to the actions of NRA0045, NRA0160, and NRA0215 in the mPFC.

Quantitation of extrastriatal D2 receptors using a very high-affinity ligand (FLB 457) and the multi-injection approach

The multi-injection approach has been used to study in baboon the in vivo interactions between the D2 receptor sites and FLB 457, a ligand with a very high affinity for these receptors. The model structure was composed of four compartments (plasma, free ligand, and specifically and unspecifically bound ligands) and seven parameters (including the D2 receptor site density). The arterial plasma concentration, after correction for metabolites, was used as the input function. The experimental protocol, which consisted of three injections of labeled and/or unlabeled ligand, allowed the evaluation of all model parameters from a single positron emission tomography experiment. In particular, the concentration of receptor sites available for binding (B'max) and the apparent in vivo FLB 457 affinity were estimated in seven brain regions, including the cerebellum and several cortex regions, in which these parameters are estimated in vivo for the first time (B'max is estimated to be 4.0+/-1.3 pmol/mL in the thalamus and from 0.32 to 1.90 pmol/mL in the cortex). A low receptor density was found in the cerebellum (B'max = 0.39+/-0.17 pmol/mL), whereas the cerebellum is usually used as a reference region assumed to be devoid of D2 receptor sites. In spite of this very small concentration (1% of the striatal concentration), and because of the high affinity of the ligand, we demonstrated that after a tracer injection, most of the PET-measured radioactivity in the cerebellum results from the labeled ligand bound to receptor sites. The estimation of all the model parameters allowed simulations that led to a precise knowledge of the FLB 457 kinetics in all brain regions and gave the possibility of testing the equilibrium hypotheses and estimating the biases introduced by the usual simplified approaches.

Differential effects of acute and chronic treatment with typical and atypical neuroleptics on c-fos mRNA expression in rat forebrain regions using non-radioactive in situ hybridization

The regional difference in the expression of c-fos mRNA in rat forebrain after either acute or chronic administration of typical (haloperidol and fluphenazine) and atypical neuroleptics (clozapine and (+/-)-sulpiride) was investigated. Rats were injected intraperitoneally with vehicle or neuroleptics daily for 14 days. Twenty-four hours after the last injection, the rats were challenged with vehicle or neuroleptics. C-fos mRNA expression was determined by non-radioactive in situ hybridization. Acute treatment with typical neuroleptics induced a remarkable induction of c-fos mRNA in the dorsolateral striatum, whereas this induction was greatly attenuated by chronic administration. All neuroleptics examined induced c-fos mRNA in the shell region of N. accumbens by acute administration and this expression was still elevated after chronic treatment. Since chronic neuroleptics do not induce tolerance to their antipsychotic activities, our study suggests that the shell region of N. accumbens is an important target site for antipsychotic effects of neuroleptics.

mRNAs for clozapine-sensitive receptors co-localize in rat prefrontal cortex neurons

The clinical efficacy of clozapine in treating schizophrenia may stem from its lack of receptor selectivity. If true, several clozapine-sensitive receptors may be co-expressed by neurons dysfunctional in schizophrenia. To test this hypothesis, neurons from the rat medial prefrontal cortex were acutely isolated and subjected to single cell RT-PCR analysis. The co-ordinated expression of five clozapine-sensitive receptors (D4, m1, 5-HT2a, 5-HT2c, 5-HT7) was examined in interneurons and pyramidal neurons. Profiling of GABAergic interneurons commonly revealed the co-expression of two or more clozapine-sensitive receptor mRNAs. Although co-expression of these receptors was less extensive in pyramidal neurons, it was also commonly found. These results suggest that clozapine's therapeutic effects may be mediated by antagonism of dopaminergic, cholinergic and serotoninergic signaling pathways at the single cell level.

Modification of haloperidol-induced pattern of c-fos expression by serotonin agonists

Acute challenge with clozapine and haloperidol produce different anatomical patterns of c-fos expression in the forebrain. The pharmacological profile of atypical antipsychotics suggests that serotonin might contribute to the unique therapeutic benefits of these drugs. In order to test this possibility, we examined the abilities of 5-HT1A and 5-HT2A/2c agonists to modify the pattern of c-fos expression induced by haloperidol and clozapine. Various groups of rats were pretreated with either saline, DOI, 8-OH-DPAT, and 8-OH-DPAT + DOI 30 min prior to haloperidol or clozapine administration. Rats were killed 90 min after antipsychotic administration. In saline-pretreated rats, haloperidol produced intense Fos-LI in all four striatal quadrants while the effect of clozapine was restricted to the medial part of the striatum. Prior administration of 8-OH-DPAT significantly reduced haloperidol-induced Fos-LI in all four striatal quadrants while DOI and 8-OHDPAT + DOI significantly reduced Fos-LI only in dorso- and ventrolateral quadrants. In the nucleus accumbens, haloperidol induced intense Fos-LI in the core and the shell regions whereas clozapine induced c-fos expression only in the shell. Pretreatment with 8-OHDPAT in haloperidol treated rats reduced Fos-LI in the core region yielding to a c-fos pattern similar to that induced by clozapine. In the prefrontal cortex of saline-pretreated rats, haloperidol produced a moderate c-fos expression compared with the intense expression produced by clozapine. Pretreatment with serotonin agonists before haloperidol brought the number of FOS-positive neurons to the same level as in clozapine treated rats. These results show the ability of 5-HT agonists to transform the typical pattern of c-fos expression induced by haloperidol into a pattern resembling that of clozapine.

Disinhibition of the mediodorsal thalamus induces fos-like immunoreactivity in both pyramidal and GABA-containing neurons in the medial prefrontal cortex of rats, but does not affect prefrontal extracellular GABA levels

Stimulation of the mediodorsal and midline thalamic nuclei excites cortical neurons and induces c-fos expression in the prefrontal cortex. Data in the literature data suggest that pyramidal neurons are the most likely cellular targets. In order to determine whether cortical interneurons are also impacted by activation of mediodorsal/midline thalamic nuclei, we studied the effects of thalamic stimulation on (1) Fos protein expression in gamma-aminobutyric acid (GABA)-immunoreactive neurons and on (2) extracellular GABA levels in the prefrontal cortex of rats. Perfusion of the GABA-A receptor antagonist bicuculline for 20 minutes through a dialysis probe implanted into the mediodorsal thalamus induced Fos-like immunoreactivity (IR) approximately 1 hour later in the thalamus and in the medial prefrontal cortex of freely moving rats. Immunohistochemical double-labeling for Fos-like IR and GABA-like IR showed that about 8% of Fos-like IR nuclei in the prelimbic and infralimbic areas were located in GABA-like IR neurons. Fos-like IR was detected in three major subsets of GABAergic neurons defined by calbindin, parvalbumin, or vasoactive intestinal peptide (VIP)-like IR. Dual probe dialysis showed that the extracellular levels of GABA in the prefrontal cortex did not change in response to thalamic stimulation. These data indicate that activation of thalamocortical neurons indeed affects the activity of GABAergic neurons as shown by the induction of Fos-like IR but that these metabolic changes are not reflected in changes of extracellular GABA levels that are sampled by microdialysis.

Olanzapine-induced Fos expression in the rat forebrain; cross-tolerance with haloperidol and clozapine

Acute administration of the atypical antipsychotic drug olanzapine (5 mg kg(-1 i.p.) increased the number of Fos-positive cells moderately in the prefrontal cortex and the striatum; more pronounced were the effects in the nucleus accumbens, the lateral septum, the hypothalamic paraventricular nucleus and the amygdala. The acutely-induced Fos responses of olanzapine were significantly reduced in all brain areas investigated after a 3-week treatment period, indicating the development of tolerance. Through evaluation of cross-tolerance we investigated whether the effects of olanzapine, haloperidol and clozapine on Fos expression and on plasma corticosterone are mediated by the same or by different mechanisms. Cross-tolerance between olanzapine and either haloperidol or clozapine was assessed by the administration of a challenge dose of olanzapine to rats, that were pretreated for 3 weeks with either the same drug, with saline (1 ml kg(-1) day(-1), haloperidol (1 mg kg(-1) day(-1) or clozapine (20 mg kg(-1) day(-1). A competitive dose of olanzapine in long-term haloperidol-treated rats showed cross-tolerance in the rostral part of the cingulate cortex, the dorsomedial and the dorsolateral striatum, the nucleus accumbens and the lateral septum. Cross-tolerance between olanzapine and clozapine, however, was limited to limbic nuclei, including the prefrontal cortex, the lateral septum, the hypothalamic paraventricular nucleus and the amygdala, with minor effects in the mid- and caudal parts of the cingulate cortex. Interesting are the common effects in the lateral septum, possibly an important target for antipsychotic efficacy. Olanzapine administration induced elevated levels of plasma corticosterone and cross-tolerance was seen in haloperidol- and clozapine-pretreated rats.

Subpopulations of cortical GABAergic interneurons differ by their expression of D1 and D2 dopamine receptor subtypes

D1 and D2 receptors have been described in different populations of efferent pyramidal neurons of the rat frontal cortex. Combined in situ hybridization and immunocytochemistry show here that these two subtypes are expressed in cortical GABAergic interneurons, with D1 and D2 mainly found in a subpopulation containing parvalbumin, whereas only 10% of the calbindin neurons express D1 receptors. These data indicate that various DA agonists may influence inhibitory circuits by distinct dopamine receptor subtypes.

The antisense strategy applied to the study of dopamine D3 receptor functions in rat forebrain

1. The authors have investigated the effects of a dopamine D3 receptor antisense oligodeoxynucleotide (ODN), on neuropeptides (neurotensin and dynorphin) and transcription factor (c-fos) mRNA levels in rat forebrain. 2. Intracerebroventricular injections of ODNs were made into the lateral ventricle (5 and 10 micrograms/h, for 5 days). Effect of antisense administration on dopamine D2 and D3 receptor binding were measured by means of receptor autoradiography. Neuropeptides and c-fos mRNA levels were evaluated by in situ hybridization using specific complementary RNA probes. 3. Dopamine D3 receptor densities were dose-dependently reduced in the shell of nucleus accumbens of rats that received the D3 antisense ODN. Sense and missense controls remained without effect. No significant effect was observed on D2 receptor binding in any of the ODN groups studied, as measured with [3H]raclopride binding. Concomitant reductions of dynorphin and neurotensin mRNA levels were observed in the shell of nucleus accumbens after D3 antisense ODN administration. Interestingly, the D3 antisense administration also reduced c-fos mRNA levels in the cingulate cortex of these animals. 4. The results show that D3 receptors may tonically regulate basal transcription factor, as well as neuropeptides, gene expression in the rat forebrain. These results clearly demonstrate that an antisense strategy could be useful to identify molecular targets under control of specific dopamine receptor subtypes.

Widespread expression of Fos protein induced by acute haloperidol administration in the rat brain

The effect of acute haloperidol administration on Fos protein expression was examined immunohistochemically in discrete regions of the rat brain. Male Wistar rats were injected subcutaneously (s.c.) with 0.1, 0.25, or 1.0 mg/kg of haloperidol. Two h after the injection, the rats were perfused, and the numbers of Fos immunoreactive neurons were counted in 24 brain regions. In contrast to the limited changes in Fos immunoreactivity at the low dose of haloperidol (0.1 mg/kg), the moderate dose (0.25 mg/kg) induced widespread increases in Fos-positive neurons in the rat brain. Large increases were produced in the caudate-putamen, nucleus accumbens, central amygdaloid nucleus, dorsomedial hypothalamic nucleus, hippocampus CA1 and substantia nigra pars compacta. Moderate increases were observed in the entorhinal cortex, lateral septum, lateral habenula, lateral amygdaloid nucleus, dentate gyrus, and mesencephalic central grey. Mild increases were induced in the anterior cingulate, temporal, occipital and perirhinal cortex, and central medial thalamic nucleus. The distribution of changes in Fos immunoreactivity at the high dose of haloperidol (1.0 mg/kg) were comparable to their distribution at the moderate dose. These findings indicate that the effect of acute haloperidol on Fos expression is widely distributed in the rat brain beyond the previously known dopamine-rich areas at the dose which produces plasma levels equivalent to those within the therapeutic range used clinically in humans. Further studies on the effects of chronic antipsychotic treatment are needed in order to identify the sites of the therapeutic action of antipsychotic drugs.

Expression of Fos protein in the limbic regions of the rat following haloperidol decanoate

To identify sites of antipsychotic drug action, the effects of acute and chronic haloperidol treatment on Fos protein expression in rat brain regions were examined by immunohistochemical methods. Male Wistar rats were injected with haloperidol decanoate (40 mg/kg, i.m. ) or vehicle. Fourteen days after injection, each rat was given an acute subcutaneous injection of haloperidol (0.25 mg/kg) or vehicle, and was transcardially perfused 2 h after the second injection. A single dose of haloperidol to chronic vehicle-treated rats produced significant increases in Fos-positive neurons in 18 of 21 brain regions examined including the several cortical areas, caudate-putamen, nucleus accumbens, lateral septum, thalamic nuclei, amygdala, hippocampus CA1, mesencephalic dopaminergic nuclei, and periaqueductal grey. The rats treated with acute vehicle after chronic haloperidol showed persistent Fos increases in confined brain regions comprising the lateral and central amygdala, lateral septum, and entorhinal cortex. Additional haloperidol injection to the chronic haloperidol-treated rats induced significant increases in Fos immunoreactivity in more widespread limbic-thalamo-cortical areas, whereas no significant increase was seen in the dorsolateral caudate-putamen. The persisting effects of haloperidol in the limbic and related structures, especially the amygdala, lateral septum, and entorhinal area may be of significance to the efficacy of long-term haloperidol treatment.

Clozapine in bipolar disorder: treatment implications for other atypical antipsychotics

Traditional neuroleptics are often utilized clinically for the management of bipolar disorder. Although effective as antimanic agents, their mood stabilizing properties are less clear. Additionally, their acute clinical side effect profile and long term risk of tardive dyskinesia, particularly in mood disorder patients, portend significant liability. This review focuses on the use of atypical antipsychotics in the treatment of bipolar disorder focusing on clozapine as the prototypical agent. Although, preclinical research and clinical experience suggest that the atypical antipsychotics are distinctly different from typical antipsychotics, they themselves are heterogeneous in profiles of neuropharmacology, clinical efficacy, and tolerability. The early clinical experience of clozapine as a potential mood stabilizer suggests greater antimanic than antidepressant properties. Conversely, very preliminary clinical experience with risperidone suggests greater antidepressant than antimanic properties and some liability for triggering or exacerbating mania. Olanzapine and sertindole are under investigation in psychotic mood disorders. The foregoing agents and future drugs with atypical neuroleptic properties should come to play an increasingly important role, compared to the older classical neuroleptics, in the acute and long term management of bipolar disorder.

D1 dopamine receptors mediate neuroleptic-induced Fos expression in the islands of Calleja

Systemic injections of the selective, full, D1 agonists A-77636 and SKF-82958 induced pronounced Fos-like immunoreactivity in the islands of Calleja in the olfactory tubercle of intact rats. Fos expression in this region could also be induced by injections of the D2-like dopamine antagonist raclopride (0.5 mg/kg). Pretreatment with the selective D1 dopamine antagonist SCH-23390 (0.2 mg/kg) completely abolished this response, but was without significant effect on raclopride-induced Fos expression in the dorsolateral region of the striatum. SCH-23390 was also able to prevent the atypical neuroleptic clozapine (30 mg/kg) from inducing Fos expression in the islands of Calleja. These findings demonstrate that stimulation of D1 dopamine receptors plays an essential role in neuroleptic induction of Fos-like immunoreactivity in the islands of Calleja, but not in the dorsal striatum, and thus suggest that different mechanisms underlie neuroleptic stimulation of immediate early gene expression in these two structures.

The significance of the expression of Fos protein in the brain for the classification of antipsychotics

Samenvatting In de afgelopen zes jaar is veel onderzoek verficht naar de effecten van antipsychotica op de regionale c-fos-expressie in de hersenen. Deze benadering biedt in een dierexperimentele proefopzet de mogelijkheid op cellulair niveau de effecten van psychofarmaca te bestuderen. Het fos-gen behoort tot de groep 'immediate early genes'. Dit zijn genen die de transcriptie van andere, vaak onbekende genen reguleren. Een aantal aspecten van dit mechanisme wordt in deze bijdrage beschreven. Het onderzoek naar de effecten van antipsychotica op c-fos-expressie wordt samengevat en de betekenis voor de classificatie van antipsychotica benadrukt. Het blijkt dat deze farmaca effectief zijn in zowel de (meso)limbische gebieden (als nucleus accumbens, septum en amygdala) als ook in de basale ganglia. De relatieve effecten, wat betreft de c-fos-reactie, van de atypische antipsychotica (als clozapine en risperidon) zijn hoger in de limbische structuren, vergeleken met de effecten van de typische (als haloperidol). De potentie van de c-fos-methodiek voor verdere ontwikkelingen in dit gebied wordt aangegeven.

Differing influences of dopamine agonists and antagonists on Fos expression in identified populations of globus pallidus neurons

Dopamine agonists increase the activity of globus pallidus neurons, as shown electrophysiologically and with Fos expression. More recently it has been shown that decreased D2 receptor activity also causes pallidal Fos expression. Similar responses occur in the striatum, where both dopamine agonists and D2 blockade induce Fos, although in separate neuronal populations (i.e. striatonigral and -pallidal). The present experiments investigate the possible differential dopaminergic regulation of Fos within pallidal neuronal populations, which were classified as parvalbumin-positive or -negative (with parvalbumin immunostaining), or as projecting to various target nuclei (with retrograde transport of FluoroGold iontophoresed into these nuclei). Rats with prior nigrostriatal lesions received saline, D1 agonist, or D2 agonist. Rats with no lesions received saline, combined D1/D2 agonists, or the D2 antagonist eticlopride. Two hours after drug injection, rats were perfused and their brains processed for double-labeling: either Fos staining with parvalbumin staining, or Fos or parvalbumin staining in FluoroGold-labeled sections. Overall, dopamine drug treatments induced more Fos in parvalbumin-negative than -positive cells. However, unlike dopamine agonists, eticlopride induced significant Fos only in the parvalbumin-negative cells. Dopamine agonist-induced Fos was found in pallidal neurons projecting to each of the target nuclei examined, in both normal and nigrostriatal-lesioned rats. Eticlopride-induced Fos occurred only in pallidal neurons projecting to the striatum, providing functional evidence for pallidostriatal cells without axon collaterals to other nuclei. It was also found that pallidostriatal neurons were distinguished from other projection populations by a relative lack of parvalbumin immunoreactivity. Pallidal cells respond heterogeneously to dopaminergic treatments based on their projection target and expression of parvalbumin. The smaller Fos responses in parvalbumin-containing cells may be due largely to the calcium buffering by the parvalbumin itself. Also, the pattern of Fos expression in pallidostriatal neurons suggests that dopamine regulates activity in these cells differently than in other projection populations.

Neurocognitive impairment in schizophrenia and how it affects treatment options

OBJECTIVE

To review the roles played by neurocognitive assessment in the treatment of schizophrenia and in the design of treatment research strategies.

METHOD

A review of the literature and summaries of clinical and research implications are presented, with directions for future research.

RESULTS

Neurocognitive deficits are now targets of antipsychotic drug treatment and should increasingly be used to refine both theory and clinical practice by considering the effects of treatments at the level of neural systems.

CONCLUSION

Efforts to bridge the gaps between preclinical and clinical assessments should yield large rewards in drug development and individualized treatment strategies. Functional neuroimaging may play a major role in these developments.

Regulation of c-Fos and NGF1-A by antidepressant treatments

The influence of antidepressant treatments on the expression of c-Fos and NGF-1A, two immediate early gene (IEG) transcription factors, was examined. Administration of electroconvulsive seizures (ECS), tranylcypromine, or imipramine, three different classes of antidepressants, increased the expression of c-Fos mRNA and immunoreactivity in rat frontal cortex, but the magnitude of the increase for each treatment differed and the effect of imipramine was preceded by inhibition of c-Fos expression. Expression of NGF-1A was increased by acute or chronic administration of ECS or tranylcypromine, and by chronic (21 d), but not acute, administration of imipramine. To study the mechanisms underlying these differences, we examined the neurotransmitter receptors that regulate the expression of c-Fos. ECS- and tranylcypromine induction of c-Fos immunoreactivity in frontal cortex was partially inhibited by pretreatment with specific antagonists for alpha 1-adrenergic, beta-adrenergic, and 5-HT2A/2C, but not D2-dopamine receptors. ECS induction of c-Fos was also inhibited by D1-dopamine and NMDA glutamate receptor antagonists, suggesting that the greater induction of c-Fos by ECS results from activation of these, and possibly other, neurotransmitter receptors. In the hippocampus, antagonism of tranylcypromine was similar to that in frontal cortex, except the D1-dopamine receptor antagonist also blocked the c-Fos response. In contrast, antagonism of the ECS response in hippocampus was only blocked by the NMDA receptor antagonist. The results demonstrate that ECS- and tranylcypromine induction of c-Fos is mediated by activation of several different neurotransmitter receptors, but that the exact pharmacological profile is different for each treatment and brain region.

Modulatory role of catecholamines in the transsynaptic expression of c-fos in the rat medial prefrontal cortex induced by disinhibition of the mediodorsal thalamus: a study employing microdialysis and immunohistochemistry

We studied the interaction of catecholaminergic and thalamic afferents of the medial prefrontal cortex (PFC) by analyzing the effects of catecholamine depletion on thalamus-induced c-fos expression in the PFC of freely moving rats. Thalamic projections to the PFC were pharmacologically activated by perfusing the GABA-A receptor antagonist bicuculline (0.03 mM or 0.1 mM) through a dialysis probe implanted into the mediodorsal thalamic nucleus. Bicuculline perfusion induced Fos-like immunoreactivity in the thalamic projection areas, including the PFC, and in the thalamic nuclei surrounding the dialysis probe. 6-Hydroxydopamine lesions of the ventral tegmental area causing a 70-80% depletion of catecholamines in the PFC did not influence the increase in the number of Fos-like immunoreactive nuclei in the prefrontal cortex in response to thalamic stimulation. However, densitometric image analysis revealed that the intensity of Fos-like immunoreactivity in the PFC of lesioned rats perfused with 0.1 mM bicuculline was higher than in correspondingly treated controls. The behavioral activity to bicuculline perfusion, an increase of non-ambulatory activity (0.03 mM) followed by locomotion and rearing (0.1 mM), was not changed in 6-hydroxydopamine-lesioned rats. It is suggested that the thalamically induced c-fos response is directly mediated by excitatory, presumably glutamatergic, transmission and not indirectly by an activation of catecholaminergic afferents of the PFC. The increase in the intensity of Fos-like immunostaining in strongly stimulated, catecholamine-depleted rats suggests that catecholamines modulate the degree to which thalamic activity can activate the PFC of awake animals.