Involvement of 5-HT1A receptors in prefrontal cortex in the modulation of dopaminergic activity: role in atypical antipsychotic action

Asenapine induces differential regional effects on serotonin receptor subtypes

Asenapine, a novel psychopharmacologic agent being developed for the treatment of schizophrenia and bipolar disorder, has high affinity for a wide range of receptors, including the serotonergic receptors 5-HT(1A), 5-HT(1B), 5-HT(2A), 5-HT( 2B), 5-HT(2C), 5-HT(5A), 5-HT(6) and 5-HT( 7). We examined the long-term effects in rat brain of multiple doses of asenapine on representative serotonin receptor subtypes: 5-HT(1A), 5-HT(2A) and 5-HT(2C). Rats were given asenapine (0.03, 0.1 or 0.3 mg/kg) subcutaneously twice daily or vehicle for 4 weeks. Brain sections were collected from the medial prefrontal cortex (mPFC), dorsolateral frontal cortex (DFC), caudate putamen, nucleus accumbens, hippocampal CA( 1) and CA(3) regions, and entorhinal cortex and processed for in-vitro receptor autoradiography. Asenapine 0.1 and 0.3 mg/kg significantly increased 5-HT(1A) binding in mPFC (by 24% and 33%, respectively), DFC (27%, 31%) and hippocampal CA(1) region (23%, 25%) (all P < 0.05). All three asenapine doses (0.03, 0.1 and 0.3 mg/kg) significantly decreased 5-HT(2A) binding by a similar degree in mPFC (40%, 44%, 47%, respectively) and DFC (45%, 51%, 52%) (all P < 0.05), but did not alter 5-HT(2A) binding in the other brain regions studied. In contrast to the effects on 5-HT(1A) and 5-HT(2A) receptors, asenapine did not alter 5-HT(2C) binding in any brain region examined at the doses tested. Our results indicate that repeated administration of asenapine produces regional-specific effects on 5-HT(1A) and 5-HT(2A) receptors in rat forebrain regions, which may contribute to the distinctive psychopharmacologic profile of asenapine.

The prefrontal cortex: a target for antipsychotic drugs

OBJECTIVE

At therapeutic doses, classical antipsychotic drugs occupy a large proportion of subcortical dopamine D2 receptors, whereas atypical antipsychotics preferentially occupy cortical 5-HT(2) receptors. However, the exact cellular and network basis of their therapeutic action is not fully understood.

METHOD

To review the mechanism of action of antipsychotic drugs with a particular emphasis on their action in the prefrontal cortex (PFC).

RESULTS

The PFC controls a large number of higher brain functions altered in schizophrenia. Histological studies indicate the presence of a large proportion of PFC neurons expressing monoaminergic receptors sensitive to the action of atypical- and to a lesser extentclassical antipsychotic drugs. Functional studies also indicate that both drug families act at PFC level.

CONCLUSION

Atypical antipsychotic drugs likely exert their therapeutic activity by a preferential action on PFC neurons, thus modulating the PFC output to basal ganglia circuits. Classical antipsychotics also interact with these PFC targets in addition to blocking massively striatal D2 receptors.

Electrophysiological studies in the rat brain on the basis for aripiprazole augmentation of antidepressants in major depressive disorder

RATIONALE

Aripiprazole (ARI) is an atypical antipsychotic approved by the Food and Drug Administration for use in major depressive disorder as an adjunct to antidepressants. However, the precise mechanisms responsible for the effectiveness of ARI augmentation are not fully understood.

OBJECTIVES

The current study was aimed at examining the effects of ARI administration alone and in combination with the selective serotonin reuptake inhibitors (SSRI) escitalopram (ESC) on the firing of serotonin (5-HT), norepinephrine (NE), and dopamine (DA) neurons.

METHODS

Electrophysiological experiments were carried out in anesthetized Sprague-Dawley rats. ESC was delivered via subcutaneously implanted osmotic minipumps at a dose of 10 mg/kg/day. ARI was subcutaneously injected daily at a dose of 2 mg/kg/day. Both drugs were administered for 2 and 14 days alone and in combination. Control rats received physiological saline in analogous regimens.

RESULTS

Two-day ESC administration resulted in a significant decrease in the firing rate of 5-HT, NE, and DA neurons. Following 14 days of ESC administration, 5-HT firing returned to the baseline. The firing rate of NE and DA neurons remained significantly decreased. ARI administered for 2 or 14 days significantly increased the firing rate of 5-HT neurons by 36% and 48%, respectively, but not those of DA and NE neurons. Desensitization of somatodendritic 5-HT autoreceptors was observed after 2 days of ARI administration. The combination of the two drugs reversed the inhibitory action of ESC on the firing rate of 5-HT, NE, and DA neurons.

CONCLUSION

The present study showed that addition of ARI to an SSRI regimen reverses the inhibitory action of the SSRI on monoaminergic neuronal firing.

The effects of antipsychotic drugs administration on 5-HT1A receptor expression in the limbic system of the rat brain

Increasing evidence suggests that 5-HT1A receptors are involved in the pathophysiology and treatment of schizophrenia. This paper investigated 5-HT1A receptor mRNA expression and binding density in female rats treated with aripiprazole (2.25 mg/kg/day), olanzapine (1.5 mg/kg/day), haloperidol (0.3 mg/kg/day) or vehicle (control) orally three times/day for 1 or 12 weeks. Animals were sacrificed 48 h after the last administration. Aripiprazole significantly increased 5-HT1A receptor binding density by 33% in the CA1 region of the hippocampus and by 21% in the medial posterodorsal nuclei of posterior amygdala (MeP) compared to the control group after 1 week of treatment. Olanzapine significantly decreased 5-HT1A receptor binding density by 17-22% in Layers I-IV of the cingulate cortex after 1 week of treatment. Neither of these antipsychotic drugs affected 5-HT1A receptor binding density after 12 weeks drug treatment. As expected, haloperidol treatment did not have any significant effect on 5-HT1A binding density after 1 or 12 weeks of treatment. 5-HT1A receptor mRNA expression was not altered by antipsychotic treatment in any brain region. The results indicate that aripiprazole and olanzapine have differential effects on 5-HT1A receptor expression, which may contribute to their distinct profiles in improving negative symptoms and cognitive deficits in schizophrenia. Aripiprazole and olanzapine may produce adaptation and desensitization of 5-HT1A receptor expression after long term treatment.

Cognitive effects of second-generation antipsychotics: current insights into neurochemical mechanisms

Historically, pharmacotherapy for schizophrenia was mainly focused on finding drugs to treat psychotic symptoms only, without addressing other crucial domains of the disorder such as cognitive impairments. As a result, these domains have remained undertreated. In this review, we discuss recent preclinical research efforts, including investigation of synaptic mechanisms as well as intracellular signalling pathways and mechanisms involved in neuroplasticity and cell resilience, that may represent new mechanisms participating in the pathogenesis of schizophrenia, particularly at the level of the prefrontal cortex and hippocampus, and that might lead to the development of drugs that can counteract, at least partially, the cognitive impairments typical of schizophrenia.

Consequences of post-weaning social isolation on anxiety behavior and related neural circuits in rodents

Exposure to adverse experiences in early-life is implicated in the later vulnerability to development of psychiatric disorders, including anxiety and affective disorders in humans. Adverse early-life experiences likely impart their long-term consequences on mental health by disrupting the normal development of neural systems involved in stress responses, emotional behavior and emotional states. Neural systems utilizing the neurotransmitters serotonin, dopamine and the neuropeptide corticotropin-releasing factor (CRF) are implicated in mediating emotive behaviors, and dysfunction of these neurochemical systems is associated with mood/anxiety disorders. These neural systems continue maturing until early or mid-adolescence in humans, thus alterations to their development are likely to contribute to the long-term consequences of adverse early-life experiences. A large body of literature suggests that post-weaning isolation rearing of rodents models the behavioral consequences of adverse early-life experiences in humans. Overall, the majority findings suggest that post-weaning social isolation that encompasses pre-adolescence produces long-lasting alterations to anxiety behavior, while measures of monoaminergic activity in various limbic regions during social isolation suggest alterations to dopamine and serotonin systems. The goal of this review is to evaluate and integrate findings from post-weaning social isolation studies specifically related to altered fear and anxiety behaviors and associated changes in neuroendocrine function and the activity of monoaminergic systems.

F15063, a potential antipsychotic with dopamine D2/D3 receptor antagonist, 5-HT1A receptor agonist and dopamine D4 receptor partial agonist properties: influence on neuronal firing and neurotransmitter release

F15063 (N-[(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)-ethyl]-(3-cyclopenten-1-yl-benzyl)-amine) is a potential antipsychotic with dopamine D2/D3 receptor antagonist, 5-HT1A receptor agonist and dopamine D4 receptor partial agonist properties. Herein, we compared its effects on rat ventral tegmental area dopamine and dorsal raphe serotonin electrical activity with those of the dopamine D2 receptor partial agonist/5-HT1A receptor agonist, SSR181507. Further, we investigated the modulation of extracellular dopamine and noradrenaline in the medial prefrontal cortex and serotonin in the hippocampus of freely moving rats by F15063 using in vivo microdialysis. In the ventral tegmental area, F15063 (200-700 microg/kg, i.v.) did not alter the electrical activity of dopamine neurons whereas SSR181507 (250-1000 microg/kg, i.v.) partially inhibited it, consistent with dopamine D2 receptor partial agonism. Both compounds reduced the inhibition of firing rate induced by the full agonist apomorphine. In the dorsal raphe, both ligands suppressed firing activity, consistent with agonism at 5-HT1A autoreceptors, although SSR181507 (25-75 microg/kg, i.v.) was more potent than F15063 (100-300 microg/kg, i.v.). F15063 (0.63-40 mg/kg, i.p.) dose-dependently increased dopamine levels in the prefrontal cortex and decreased hippocampal 5-HT. These effects were reversed by the selective 5-HT1A receptor antagonist WAY100635 (0.16 mg/kg, s.c.), indicating that they were mediated by 5-HT1A receptors (at post- and pre-synaptic levels, respectively). In the medial prefrontal cortex, noradrenaline levels were moderately but significantly increased by F15063 at 2.5 mg/kg. In conclusion, whereas SSR181507 exhibits (partial) agonism at dopamine D2 and 5-HT1A receptors, F15063 blocks dopamine D2-like receptors whilst activating 5-HT1A receptors. Such a profile distinguishes F15063 from SSR181507 and currently available antipsychotic drugs.

Differential effects of M1 and 5-hydroxytryptamine1A receptors on atypical antipsychotic drug-induced dopamine efflux in the medial prefrontal cortex

Systemic administration of the M(1) receptor agonists N-desmethylclozapine (NDMC) and 4-[3-(4-butylpiperidin-1-yl)-propyl]-7-fluoro-4H-benzo[1,4]oxazin-3-one (AC260584) increase dopamine (DA) efflux in rat medial prefrontal cortex (mPFC). This increase is blocked by systemic administration of both telenzepine, a preferential M(1) receptor antagonist, and N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide (WAY-100635), a 5-hydroxytryptamine(1A) receptor antagonist. The present study sought to determine whether DA efflux in the mPFC induced by the atypical antipsychotic drugs clozapine, risperidone, and olanzapine is also mediated by M(1) receptor stimulation and, specifically, to determine whether these effects are mediated M(1) receptors in the mPFC through use of in vivo microdialysis in awake, freely moving Sprague-Dawley rats. Telenzepine (3 mg/kg) significantly attenuated clozapine- (20 mg/kg), olanzapine- (10 mg/kg), and risperidone- (1.0 mg/kg) induced increases in mPFC DA efflux. Local mPFC perfusion of NDMC, AC260584, clozapine, risperidone, or olanzapine (10-500 microM), significantly increased DA efflux in the mPFC. Local mPFC perfusion of telenzepine (0.1 microM) prevented increases in mPFC DA efflux induced by systemic administration of AC260584 (10 mg/kg), NDMC (20 mg/kg), and clozapine (10 mg/kg), but not by risperidone (1.0 mg/kg) or olanzapine (10 mg/kg). However, local mPFC perfusion of WAY-100635 (0.1 microM) prevented mPFC DA efflux induced by clozapine, risperidone, and olanzapine, but not by AC260584 or NDMC. These results suggest that the AC260584-, NDMC-, and clozapine-induced DA efflux in the mPFC is mediated directly by mPFC M(1) receptors.

The firing activity of pyramidal neurons in medial prefrontal cortex and their response to 5-hydroxytryptamine-1A receptor stimulation in a rat model of Parkinson's disease

The changes in the firing rate and firing pattern of pyramidal neurons in medial prefrontal cortex (mPFC) and the effects of selective 5-hydroxytryptamine-(1A) (5-HT(1A)) receptor agonist (R)-(+)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) and antagonist N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2-pyridylcyclohexane carboxamide maleate salt (WAY-100635) on the firing activity of the neurons were studied in sham-lesioned rats and rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc). The lesion of the SNc increased the firing rate of pyramidal neurons significantly compared to sham-lesioned rats, and the firing pattern of these neurons also changed significantly towards a more burst-firing. The systemic administration of 8-OH-DPAT at doses in the range of 0.5-128 microg/kg showed an excitatory-inhibitory effect on the firing rate of pyramidal neurons in mPFC of sham-lesioned rats. At lower doses, 0.5-32 microg/kg, it evoked excitation of the neurons, and at a high dose, i.e. 128 microg/kg, inhibited the activity of the neurons. In contrast to sham-lesioned rats, 8-OH-DPAT, at the same doses, showed no excitatory effect in the lesioned rats although the inhibitory phase of the effect of 8-OH-DPAT on the firing rate of pyramidal neurons in mPFC was still present. Furthermore, the local application of 8-OH-DPAT, 5 microg, in mPFC inhibited the firing rate of pyramidal neurons in sham-lesioned rats, while having no effect on firing rate in the lesioned rats. The excitatory or inhibitory effects of 8-OH-DPAT were reversed by WAY-100635, indicating that these effects are mediated by 5-HT(1A) receptor. Altogether, these results indicate that the lesion of the SNc leads to hyperactivity of pyramidal neurons in mPFC and the abnormality of response of these neurons to 5-HT(1A) receptor stimulation, suggesting that mPFC may be involved in the pathophysiology of the psychiatric disturbance of Parkinson's disease.

Role of different monoamine receptors controlling MK-801-induced release of serotonin and glutamate in the medial prefrontal cortex: relevance for antipsychotic action

Several studies have demonstrated that systemically administered N-methyl-d-aspartate (NMDA) receptor antagonists increase serotonin (5-HT) and glutamate release in the medial prefrontal cortex (mPFC). Previously we showed that the perfusion of clozapine in the mPFC prevented the MK-801-induced increase in extracellular glutamate and 5-HT whereas haloperidol blocked only the effect of MK-801 on glutamate. To study the contribution of different monoaminergic receptors (for which clozapine and haloperidol exhibit distinct affinities) to these effects, here we used in-vivo microdialysis to examine the role of local blockade of dopamine D2, 5-HT2A and alpha1-adrenergic receptors as well as agonism at dopamine D1 and 5-HT1A receptors in the mPFC on the increased efflux of glutamate and 5-HT elicited by MK-801. The results show that M100907 (5-HT2A antagonist), BAY x 3702 (5-HT1A agonist) and prazosin (alpha1-adrenergic antagonist) blocked the MK-801-induced increase of 5-HT and glutamate in the mPFC. However, raclopride, eticlopride (dopamine D2 antagonists) and SKF-38393 (dopamine D1 agonist) were able to prevent the increased efflux of glutamate (but not that of 5-HT) elicited by MK-801. We propose that D2 receptor antagonists and D1 agonists would act predominantly on a subpopulation of GABAergic interneurons of the mPFC, thus leading to an enhanced cortical inhibition that would prevent an excessive glutamatergic transmission. On the other hand, atypical antipsychotic drugs might further act upon 5-HT2A, 5-HT1A and alpha1-adrenoceptors present in pyramidal cells (including those projecting to the dorsal raphe nucleus), which would directly inhibit an excessive excitability of these cells.

Acute and chronic effects of citalopram on 5-HT1A receptor-labeling by [18F]MPPF and -coupling to receptors-G proteins

Selective serotonin reuptake inhibitors take several weeks to produce their maximal therapeutic antidepressant effect. This delay has been attributed to the gradual desensitization of somatodendritic serotonin 5-HT(1A) autoreceptors. We evaluated adaptive changes of 5-HT(1A) receptors after acute and chronic citalopram challenges in rat. Small animal positron emission tomography trial and quantitative ex vivo autoradiography studies using [(18)F]MPPF were employed, as well as in vitro 8-OH-DPAT-stimulated [(35)S]-GTPgammaS binding assay. Additionally, 5-HT(1A) receptor knock-out mice were used to assess the specificity of [(18)F]MPPF. Acute treatment with citalopram did not alter [(18)F]MPPF binding in dorsal raphe nucleus (DR), frontal cortex, or hippocampus. The absence of [(18)F]MPPF binding in the brain of 5-HT(1A) knock-out mice demonstrates the specificity of MPPF for 5-HT(1A) receptor brain imaging, but the high affinity of [(18)F]MPPF compared to 5-HT suggests that it would only be displaced by dramatic increases in extracellular 5-HT. Chronic citalopram did not modify 5-HT(1A) receptor density in any of the brain regions studied. In addition, this treatment did not modify 8-OH-DPAT-stimulated [(35)S]-GTPgammaS binding in DR, although a significant increase was observed in frontal cortex and hippocampus. [(18)F]MPPF appears to be an efficient radioligand to quantify specifically 5-HT(1A) receptor density in brain imaging. The delayed therapeutic efficacy of citalopram did not appear to be linked to either a downregulation of 5-HT(1A) receptors or to a 5-HT(1A) receptor-G protein decoupling process in serotonergic neurons, but to increased functional sensitivity of postsynaptic 5-HT(1A) receptors.

Effects of bifeprunox and aripiprazole on rat serotonin and dopamine neuronal activity and anxiolytic behaviour

The atypical antipsychotic bifeprunox is a partial dopamine D(2) and 5-HT(1A) receptor agonist. Using in-vivo electrophysiological and behavioural paradigms in the rat, the effects of bifeprunox and aripiprazole were assessed on ventral tegmental area (VTA) dopamine and dorsal raphe serotonin (5-HT) cell activity and on foot shock-induced ultrasonic vocalisation (USV). In VTA, bifeprunox and aripiprazole decreased (by 20-50%) firing of dopamine neurons. Interestingly, bursting activity was markedly reduced (by 70-100%), bursting being associated with a larger synaptic dopamine release than single spike firing. Both ligands reduced inhibition of firing rate induced by the full dopamine receptor agonist apomorphine, whereas the D(2) receptor antagonist haloperidol prevented these inhibitory effects, confirming partial D(2)-like agonistic properties. On 5-HT neurons, bifeprunox was more potent than aripiprazole to suppress firing activity. The 5-HT(1A) receptor antagonist WAY-100,635 prevented their effects. In the USV test of anxiolytic-like activity, bifeprunox had higher potency than aripiprazole to reduce vocalisations. Both WAY-100,635 and haloperidol reversed the effects of both agonists. The present in-vivo study shows that bifeprunox is a potent partial D(2)-like and 5-HT(1A) receptor agonist reducing preferentially the phasic activity of dopamine neurons. Thus, bifeprunox would be expected to be an effective compound against positive and negative symptoms of schizophrenia.

Electrophysiological characterization of the effects of asenapine at 5-HT(1A), 5-HT(2A), alpha(2)-adrenergic and D(2) receptors in the rat brain

Asenapine is a psychopharmacologic agent being developed for schizophrenia and bipolar disorder. This study electrophysiologically characterized the in vivo effects of asenapine at dorsal raphe nucleus (DRN) and hippocampus serotonin-1A (5-HT(1A)), ventral tegmental area D(2), locus coeruleus 5-HT(2A,) and alpha(2)-adrenergic receptors in anesthetized rats. Asenapine displayed potent antagonistic activity at alpha(2)-adrenoceptors (ED(50), 85+/-2 microg/kg), 5-HT(2A) (ED(50), 75+/-2 microg/kg) and D(2) receptors (ED(50), 40+/-2 microg/kg) as evidenced by its reversal of clonidine-, DOI-, and apomorphine-induced inhibition of norepinephrine and dopamine neurons. In contrast, asenapine acted as a partial agonist at 5-HT(1A) receptors in DRN and hippocampus, as indicated by blockade of its inhibitory effect on neuronal firing by the 5-HT(1A) antagonist WAY 100635 and the partial inhibition of the suppressant action of 5-HT when co-applied by microiontophoresis. These results confirm that asenapine displays potent antagonistic activity at 5-HT(2A), D(2), alpha(2)-adrenergic receptors and provide evidence to support its 5-HT(1A) partial agonistic activity.

Aripiprazole ameliorates phencyclidine-induced impairment of recognition memory through dopamine D1 and serotonin 5-HT1A receptors

RATIONALE

Cognitive deficits, including memory impairment, are regarded as a core feature of schizophrenia. Aripiprazole, an atypical antipsychotic drug, has been shown to improve disruption of prepulse inhibition and social interaction in an animal model of schizophrenia induced by phencyclidine (PCP); however, the effects of aripiprazole on recognition memory remain to be investigated.

OBJECTIVES

In this study, we examined the effect of aripiprazole on cognitive impairment in mice treated with PCP repeatedly.

MATERIALS AND METHODS

Mice were repeatedly administered PCP at a dose of 10 mg/kg for 14 days, and their cognitive function was assessed using a novel-object recognition task. We investigated the therapeutic effects of aripiprazole (0.01-1.0 mg/kg) and haloperidol (0.3 and 1.0 mg/kg) on cognitive impairment in mice treated with PCP repeatedly.

RESULTS

Single (1.0 mg/kg) and repeated (0.03 and 0.1 mg/kg, for 7 days) treatment with aripiprazole ameliorated PCP-induced impairment of recognition memory, although single treatment significantly decreased the total exploration time during the training session. In contrast, both single and repeated treatment with haloperidol (0.3 and 1.0 mg/kg) failed to attenuate PCP-induced cognitive impairment. The ameliorating effect of aripiprazole on recognition memory in PCP-treated mice was blocked by co-treatment with a dopamine D1 receptor antagonist, SCH23390, and a serotonin 5-HT1A receptor antagonist, WAY100635; however, co-treatment with a D2 receptor antagonist raclopride had no effect on the ameliorating effect of aripiprazole.

CONCLUSIONS

These results suggest that the ameliorative effect of aripiprazole on PCP-induced memory impairment is associated with dopamine D1 and serotonin 5-HT1A receptors.

Role of medial prefrontal, entorhinal, and occipital 5-HT in cocaine-induced place preference and hyperlocomotion: evidence for multiple dissociations

RATIONALE

Application of cocaine or exposure to cocaine-related stimuli induces widespread activation of the cortex in neuroimaging studies with human subjects. In accordance to these findings, it was reported in previous microdialysis experiments that cocaine increased serotonin (5-HT) and dopamine in various cortical brain areas. The present series of studies set out to investigate the functional role of the observed increases in 5-HT in the medial prefrontal cortex (mPFC), the entorhinal cortex (EC), and the occipital cortex (OccC) in the mediation of cocaine-induced conditioned place preference (CPP) and hyperactivity.

MATERIALS AND METHODS

To reduce 5-HTergic neurotransmission in circumscribed brain areas, bilateral local infusions of the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), were made into the mPFC, EC, or OccC. Two weeks following surgery, cocaine-induced (10 mg/kg; i.p.) CPP was measured in an unbiased design.

RESULTS

The 90% depletion of 5-HT in the mPFC significantly attenuated the preference for the cocaine-associated environment and the hyperlocomotor response to cocaine. A 61% depletion of 5-HT in the EC reduced conditioned place preference without modulation of hyperactivity, while a 78% 5-HT depletion of the OccC cortex had no effect on cocaine-induced CPP and hyperactivity. No lesion affected general activity, habituation learning, or visual stimulation-induced behavioral activation.

CONCLUSION

These results indicate an important role of cortical 5-HT in the mediation of cocaine-induced CPP and specify the region-dependent contribution of a neurochemical response to cocaine-mediated behavior.

Blockade of NMDA receptors in the prefrontal cortex increases dopamine and acetylcholine release in the nucleus accumbens and motor activity

OBJECTIVES

The present study investigates the effects of injections of a specific N-methyl-D-aspartic acid (NMDA) antagonist 3-[(R)-2-carboxypiperazin-4-yl]-propyl-1-phophonic acid (CPP) into the prefrontal cortex (PFC) on the extracellular concentrations of dopamine and acetylcholine in the nucleus accumbens (NAc) and on motor activity in the freely moving rat.

MATERIALS AND METHODS

Sprague-Dawley male rats were implanted with guide cannulas into the medial PFC and NAc to perform bilateral microinjections and microdialysis experiments. Spontaneous motor activity was monitored in the open field.

RESULTS

Injections of CPP (1 microg/0.5 microL) into the PFC produced a significant increase of the baseline extracellular concentrations of dopamine (up to 130%), dihydroxyphenylacetic acid (DOPAC; up to 120%), homovanillic acid (HVA; up to 130%), and acetylcholine (up to 190%) in the NAc as well as motor hyperactivity. In the NAc, perfusion of the NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate antagonists CPP (50 microM)+6,7-dinitroquinoxaline-2,3-dione (DNQX; 50 microM) through the microdialysis probe blocked acetylcholine release, but not DOPAC and HVA increases produced by CPP injections into the PFC. Also, increases in motor activity produced by prefrontal injections of CPP were significantly reduced by bilateral injections into the NAc of a mixed D1/D2 antagonist, flupenthixol (5 and 25 microg/0.5 microL). Injections into the NAc of the muscarinic antagonist scopolamine (1 and 10 microg/0.5 microL) further increased, and of the nicotinic antagonist mecamylamine (1 and 10 microg/0.5 microL) did not change, the increases in motor activity produced by prefrontal CPP injections.

CONCLUSIONS

These results suggest that the dysfunction of NMDA receptors in the PFC could be a key factor in the neurochemical and motor effects associated with corticolimbic hyperactivity.

The --1019 C/G polymorphism of the 5-HT(1)A receptor gene is associated with negative symptom response to risperidone treatment in schizophrenia patients

The application of pharmacogenetics is currently one of the most promising developments in anti-psychotic treatment and is attracting more and more attention. Although risperidone belongs to the first-line atypical anti-psychotics, there have been relatively few risperidone pharmacogenetic studies, especially in Asian populations. We investigated the relationship between the C825T polymorphism of GBN3 (rs5443) and the -1019 C/G polymorphism of 5-HT(1)A (rs6295) and response to risperidone treatment. One-hundred and thirty schizophrenia patients were recruited. They were treated with risperidone monotherapy for eight weeks. Clinical response was assessed on the Positive and Negative Syndrome Scale (PANSS) on the day of admission and was subsequently assessed after eight weeks following the treatment. Patients were genotyped for two functional polymorphisms: C825T of GBN3 (rs5443) and -1019 C/G of HT(1)A (rs6295). Association tests between genotypes and percentage improvement in total PANSS scores, as well as positive symptom scores and negative symptom scores, were performed using analyses of variance (ANOVA). The -1019 C/G polymorphism of HT(1)A (rs6295) was associated with negative symptom response to treatment. Patients with the CC genotype showed substantial improvement as regards negative symptom response (F = 4.177, df = 2, P = 0.019), compared with the patients with the CG and GG genotypes. No association was observed between C825T of GBN3 (rs5443) and changes in PANSS scores. The results suggest that the -1019 C/G polymorphism (rs6295) in the 5-HT(1)A gene may be a useful predictor of reduction in negative symptoms in schizophrenic patients treated with risperidone.

Asenapine increases dopamine, norepinephrine, and acetylcholine efflux in the rat medial prefrontal cortex and hippocampus

Atypical antipsychotic drugs, which are more potent direct acting antagonists of brain serotonin (5-HT)(2A) than dopamine (DA) D(2) receptors, preferentially enhance DA and acetylcholine (ACh) efflux in the rat medial prefrontal cortex (mPFC) and hippocampus (HIP), compared with the nucleus accumbens (NAc). These effects may contribute to their ability, albeit limited, to improve cognitive function and negative symptoms in patients with schizophrenia. Asenapine (ASE), a new multireceptor antagonist currently in development for the treatment of schizophrenia and bipolar disorder, has complex serotonergic properties based upon relatively high affinity for multiple serotonin (5-HT) receptors, particularly 5-HT(2A) and 5-HT(2C) receptors. In the current study, the effects of ASE on DA, norepinephrine (NE), 5-HT, ACh, glutamate, and gamma-aminobutyric acid (GABA) efflux in rat mPFC, HIP, and NAc were investigated with microdialysis in awake, freely moving rats. ASE at 0.05, 0.1, and 0.5 mg/kg (s.c.), but not 0.01 mg/kg, significantly increased DA efflux in the mPFC and HIP. Only the 0.5 mg/kg dose enhanced DA efflux in the NAc. ASE, at 0.1 and 0.5 mg/kg, significantly increased ACh efflux in the mPFC, but only the 0.5 mg/kg dose of ASE increased HIP ACh efflux. ASE did not increase ACh efflux in the NAc at any of the doses tested. The effect of ASE (0.1 mg/kg) on DA and ACh efflux was blocked by pretreatment with WAY100635, a 5-HT(1A) antagonist/D(4) agonist, suggesting involvement of indirect 5-HT(1A) agonism in both the actions. ASE, at 0.1 mg/kg, increased NE, but not 5-HT, efflux in the mPFC and HIP. ASE, at 0.1 mg/kg (s.c.), had no effect on glutamate and GABA efflux in either the mPFC or NAc. These findings indicate that ASE is similar to clozapine and other atypical antipsychotic drugs in preferentially increasing the efflux of DA, NE, and ACh in the mPFC and HIP compared with the NAC, and suggests that, like these agents, it may also improve cognitive function and negative symptoms in patients with schizophrenia.

Glutamatergic dysfunction in schizophrenia: from basic neuroscience to clinical psychopharmacology

The underlying cellular mechanisms leading to frontal cortical hypofunction (i.e., hypofrontality) in schizophrenia remain unclear. Both hypoactive and hyperreactive prefrontal cortical (PFC) states have been reported in schizophrenia patients. Recent proton magnetic resonance spectroscopy studies revealed that antipsychotic-naïve patients with first psychotic episode exhibit a hyperactive PFC. Conversely, PFC activity seems to be diminished in patients chronically exposed to conventional antipsychotic treatments, an effect that could reflect the therapeutic action as well as some of the impairing side effects induced by long-term blockade of dopamine transmission. In this review, we will provide an evolving picture of the pathophysiology of schizophrenia moving from dopamine to a more glutamatergic-centered hypothesis. We will discuss how alternative antipsychotic strategies may emerge by using drugs that reduce excessive glutamatergic response without altering the balance of synaptic and extrasynaptic normal glutamatergic neurotransmission. Preclinical studies indicate that acamprosate, a FDA approved drug for relapse prevention in detoxified alcoholic patients, reduces the glutamatergic hyperactivity triggered by ethanol withdrawal without depressing normal glutamatergic transmission. Whether this effect is mediated by a direct modulation of NMDA receptors or by antagonism of metabotropic glutamate receptor remains to be determined. We hypothesize that drugs with similar pharmacological actions to acamprosate may provide a better and safer approach to reverse psychotic symptoms and cognitive deficits without altering the balance of excitation and inhibition of the corticolimbic dopamine-PFC system. It is predicted that schizophrenia patients treated with acamprosate-like compounds will not exhibit progressive cortical atrophy associated with the anti-dopaminergic effect of classical antipsychotic exposure.

The absence of 5-HT(1A) receptors has minor effects on dopamine but not serotonin release evoked by MK-801 in mice prefrontal cortex

RATIONALE

Non-competitive NMDA receptor antagonists markedly increase neuronal activity in medial prefrontal cortex (mPFC), an effect which partly underlies their schizomimetic actions. Projection pyramidal neurons and local GABAergic interneurons in mPFC express 5-HT(1A) receptors, whose activation modulates dopaminergic (DA) and serotonergic (5-HT) activity in midbrain and the cortical release of both monoamines.

OBJECTIVE

To examine whether the presence of 5-HT(1A) receptors can modulate the effect of NMDA receptor blockade with MK-801 (dizocilpine) on DA and 5-HT release in mouse mPFC.

MATERIALS AND METHODS

Brain microdialysis and locomotor activity measures in wild-type and 5-HT(1A) receptor knockout mice.

RESULTS

Systemic MK-801 administration (0.125, 0.25, 0.50, and 1 mg/kg i.p.) induced a dose-dependent increase in mPFC 5-HT output, which was independent of the genotype. MK-801 increased DA output in a dose-dependent manner with a significant effect of genotype on low doses (0.125, 0.25 mg/kg). These differences were not paralleled by differences in gross locomotor activity. Overall, MK-801 increased more markedly DA than 5-HT output in both genotypes. Finally, the local perfusion of MK-801 in mPFC (30, 100, 300 muM) by reverse dialysis did not elevate dialysate DA or 5-HT concentrations in mPFC.

CONCLUSION

5-HT(1A) receptors partly modulate the increase in mPFC DA (but not 5-HT) release produced by NMDA receptor blockade. The lack of effect observed after the local MK-801 application suggests that the change in cortical monoamines is mainly driven by subcortical NMDA receptor blockade, without a significant involvement of PFC 5-HT(1A) receptors.

Serotonin1A receptors in the pathophysiology of schizophrenia: development of novel cognition-enhancing therapeutics

Serotonin (5-HT) receptors have been suggested to play key roles in psychosis, cognition, and mood via influence on neurotransmitters, synaptic integrity, and neural plasticity. Specifically, genetic evidence indicates that 5-HT(1A), 5-HT(2A), and 5-HT(2C) receptor single-nucleotide polymorphisms (SNPs) are related to psychotic symptoms, cognitive disturbances, and treatment response in schizophrenia. Data from animal research suggest the role of 5-HT in cognition via its influence on dopaminergic, cholinergic, glutamatergic, and GABAergic function. This article provides up-to-date findings on the role of 5-HT receptors in endophenotypic variations in schizophrenia and the development of newer cognition-enhancing medications, based on basic science and clinical evidence. Imaging genetics studies on associations of polymorphisms of several 5-HT receptor subtypes with brain structure, function, and metabolism suggest a role for the prefrontal cortex and the parahippocampal gyrus in cognitive impairments of schizophrenia. Data from animal experiments to determine the effect of agonists/antagonists at 5-HT(1A), 5-HT(2A), and 5-HT(2C) receptors on behavioral performance in animal models of schizophrenia based on the glutamatergic hypothesis provide useful information. For this purpose, standard as well as novel cognitive tasks provide a measure of memory/information processing and social interaction. In order to scrutinize mixed evidence for the ability of 5-HT(1A) agonists/antagonists to improve cognition, behavioral data in various paradigms from transgenic mice overexpressing 5-HT(1A) receptors provide valuable insights. Clinical trials reporting the advantage of 5-HT(1A) partial agonists add to efforts to shape pharmacologic perspectives concerning cognitive enhancement in schizophrenia by developing novel compounds acting on 5-HT receptors. Overall, these lines of evidence from translational research will facilitate the development of newer pharmacologic strategies for the treatment of cognitive disturbances of schizophrenia.

Serotonin 1A receptors in human and monkey prefrontal cortex are mainly expressed in pyramidal neurons and in a GABAergic interneuron subpopulation: implications for schizophrenia and its treatment

Serotonin 1A (5-HT(1A)) receptors are found in high densities in prefrontal cortex. However, their distribution within cortical cell populations is unknown in both humans and primates. We used double in situ hybridization histochemistry to quantify the percentage of glutamatergic and GABAergic neurons expressing 5-HT(1A) receptors in human and monkey prefrontal cortex. Moreover, in the case of the monkey, we also quantified the parvalbumin and calbindin GABAergic subpopulations expressing this receptor. 5-HT(1A) receptor mRNAs were expressed in about 80% of glutamatergic neurons in external layers II and upper III, and in around 50% in layer VI; they were also present in approximately 20% of GABAergic neurons in both species. Although they were found in up to 43% of the calbindin cell subpopulation they were rarely present in parvalbumin cells in monkey prefrontal cortex. The knowledge of the phenotype of the prefrontal cortex (PFC) cells expressing 5-HT(1A) will help understanding serotonin actions in PFC.

The hallucinogen DOI reduces low-frequency oscillations in rat prefrontal cortex: reversal by antipsychotic drugs

BACKGROUND

Perceptual and psychic alterations and thought disorder are fundamental elements of schizophrenia symptoms, a pathology associated with an abnormal macro- and microcircuitry of several brain areas including the prefrontal cortex (PFC). Alterations in information processing in PFC may partly underlie schizophrenia symptoms.

METHODS

The 5-HT(2A/2C) agonist DOI and antipsychotic drugs were administered to anesthetized rats. Single unit and local field potential (LFP) extracellular recordings were made in medial PFC (mPFC). Electrolytic lesions were performed in the thalamic nuclei.

RESULTS

DOI markedly disrupts cellular and network activity in rat PFC. DOI altered pyramidal discharge in mPFC (39% excited, 27% inhibited, 34% unaffected; n = 51). In all instances, DOI concurrently reduced low-frequency oscillations (.3-4 Hz; power spectrum: .25 +/- .02 and .14 +/- .01 microV(2) in basal conditions and after 50-300 microg/kg intravenous (i.v.) DOI, respectively; n = 51). Moreover, DOI disrupted the temporal association between the active phase of LFP and pyramidal discharge. Both effects were reversed by M100907 (5-HT(2A) receptor antagonist) and were not attenuated by thalamic lesions, supporting an intracortical origin of the effects of DOI. The reduction in low-frequency oscillations induced by DOI was significantly reversed by the antipsychotic drugs haloperidol (.1-.2 mg/kg i.v.) and clozapine (1 mg/kg i.v.).

CONCLUSIONS

DOI disorganizes network activity in PFC, reducing low-frequency oscillations and desynchronizing pyramidal discharge from active phases of LFP. These effects may underlie DOI's psychotomimetic action. The reversal by clozapine and haloperidol indicates that antipsychotic drugs may reduce psychotic symptoms by normalizing an altered PFC function.

MicroPET imaging of 5-HT 1A receptors in rat brain: a test-retest [18F]MPPF study

PURPOSE

Earlier studies have shown that positron emission tomography (PET) imaging with the radioligand [(18)F]MPPF allows for measuring the binding potential of serotonin 5-hydroxytryptamine(1A) (5-HT(1A)) receptors in different regions of animal and human brain, including that of 5-HT(1A) autoreceptors in the raphe nuclei. In the present study, we sought to determine if such data could be obtained in rat, with a microPET (R4, Concorde Microsystems).

METHODS

Scans from isoflurane-anaesthetised rats (n = 18, including six test-retest) were co-registered with magnetic resonance imaging data, and binding potential, blood to plasma ratio and radiotracer efflux were estimated according to a simplified reference tissue model.

RESULTS

Values of binding potential for hippocampus (1.2), entorhinal cortex (1.1), septum (1.1), medial prefrontal cortex (1.0), amygdala (0.8), raphe nuclei (0.6), paraventricular hypothalamic nucleus (0.5) and raphe obscurus (0.5) were comparable to those previously measured with PET in cats, non-human primates or humans. Test-retest variability was in the order of 10% in the larger brain regions (hippocampus, medial prefrontal and entorhinal cortex) and less than 20% in small nuclei such as the septum and the paraventricular hypothalamic, basolateral amygdaloid and raphe nuclei.

CONCLUSIONS

MicroPET brain imaging of 5-HT(1A) receptors with [(18)F]MPPF thus represents a promising avenue for investigating 5-HT(1A) receptor function in rat.

Switching schizophrenia patients from typical neuroleptics to olanzapine: effects on BOLD response during attention and working memory

Dysfunctional activation of the dorsolateral prefrontal cortex (DLPFC) during working memory (WM) in schizophrenia patients has repeatedly been observed, however little is known about specific medication effects on the modulation of DLPFC activation. We measured activation of DLPFC during a WM task in a longitudinal fMRI study in ten schizophrenia patients first when they received conventional antipsychotics (T1) and a second time after they had been switched to olanzapine (T2). A healthy control group matched for age, handedness and gender was investigated at two corresponding time points. We analyzed the fMRI data with SPM5 in a 2 x 2 x 2 design (group x session x task). Schizophrenia patients showed fewer correct responses compared to healthy controls at both time points. The fMRI data revealed a significant group by task interaction in the bilateral DLPFC and the right parietal cortex, indicating a reduced BOLD response in the patient group. After switching to olanzapine, schizophrenia patients displayed a significant increase in the BOLD response during the 0-back condition in the DLPFC. This study showed that switching patients from conventional neuroleptics to olanzapine did not significantly alter the frontal or parietal BOLD response during working memory task. However, medication status had influences on the activation during attentional task (0-back), emphasizing the importance of baseline selection in pharmacological fMRI studies.

Functional interactions between dopamine, serotonin and norepinephrine neurons: an in-vivo electrophysiological study in rats with monoaminergic lesions

Anatomical studies have established the existence of reciprocal relationships between the main population of monoamine, serotonin (5-HT), norepinephrine (NE) and dopamine (DA) neurons in the brain. The present study was thus conducted to examine the firing activity of 5-HT and NE neurons in DA-depleted rats, as well as the firing activity of DA neurons in 5-HT- or NE-depleted rats. The selective lesion of DA neurons elicited by 6-hydroxydopamine (6-OHDA) decreased the spontaneous firing activity of dorsal raphe (DR) nucleus 5-HT neurons by 60%, thus revealing the excitatory effect of the DA input on these 5-HT neurons. In contrast, the selective lesion of 5-HT neurons produced by 5,7-dihydroxytryptamine (5,7-DHT) enhanced by 36% the firing activity of VTA DA neurons, thereby indicating an inhibitory effect of the 5-HT input on these DA neurons. With regard to the reciprocal interaction between DA and NE neurons, it was observed that the selective loss of DA neurons achieved by the intra-ventral tegmental area (VTA) injection of 6-OHDA increased the firing activity of a subset of locus coeruleus (LC) NE neurons by 47%. The selective loss of NE neurons in response to the intra-LC injection of 6-OHDA enhanced the firing activity of VTA DA neurons by 70%, demonstrating a net inhibitory role of the NE input on VTA DA neurons. These findings have important consequences for antidepressant treatments aimed at enhancing simultaneously 5-HT, NE and DA transmission. Indeed, based on the understanding of such interactions, it may be possible to develop strategies to improve the effectiveness of antidepressant drugs by preventing counter-productive negative feedback actions.

The antipsychotics clozapine and olanzapine increase plasma glucose and corticosterone levels in rats: comparison with aripiprazole, ziprasidone, bifeprunox and F15063

Several novel antipsychotics activate serotonin 5-HT1A receptors as well as antagonising dopamine D2/3 receptors. Such a pharmacological profile is associated with a lowered liability to produce extrapyramidal side effects and enhanced efficacy in treating negative and cognitive symptoms of schizophrenia. However, 5-HT1A receptor agonists increase plasma corticosterone and many antipsychotics disturb the regulation of glucose. Here, we compared the influence on plasma glucose and corticosterone of acute treatments with 'new generation' antipsychotics which target dopamine D2/3 receptors and 5-HT1A receptors, with that of atypical antipsychotics, and with haloperidol. Olanzapine and clozapine, antipsychotics that are known to produce weight gain and diabetes in humans, both at 10 mg/kg p.o., substantially increased plasma glucose (from 0.8 to 1.7 g/l) at 1 h after administration, an effect that returned to control levels after 4 h. In comparison, F15063 (40 mg/kg p.o.) was without effect at any time point. Olanzapine and clozapine dose-dependently increased plasma glucose concentrations as did SLV313 and SSR181507. Haloperidol and risperidone had modest effects whereas aripiprazole, ziprasidone and bifeprunox, antipsychotics that are not associated with metabolic dysfunction in humans, and F15063 had little or no influence on plasma glucose. The same general pattern of response was found for plasma corticosterone levels. The present data provide the first comparative study of conventional, atypical and 'new generation' antipsychotics on glucose and corticosterone levels in rats. A variety of mechanisms likely underlie the hyperglycemia and corticosterone release observed with clozapine and olanzapine, whilst the balance of dopamine D2/3/5-HT1A interaction may contribute to the less favourable impact of SLV313 and SSR181507 compared with that of bifeprunox and F15063.

Decreased brain serotonin 5-HT1A receptor availability in medication-naive patients with major depressive disorder: an in-vivo imaging study using PET and [carbonyl-11C]WAY-100635

Serotonin (5-HT) is involved in the pathophysiology of major depressive disorder (MDD). Among the numerous serotonergic receptors, the 5-HT1A receptor subtype is of interest because of its involvement in cognition, hippocampal neurogenesis, and mechanism of action of antidepressant drugs. Previous imaging studies have suggested altered availability of 5-HT1A receptors in MDD but prior antidepressant medication and chronicity of the illness may confound the interpretation. We examined 21 drug-naive primary-care patients with MDD using positron emission tomography (PET) imaging with [carbonyl-11C]WAY-100635, a radioligand for 5-HT1A receptors, along with 15 healthy control subjects. Binding to receptors was assessed both regionally and at voxel level with the binding potential (BP) that was estimated using arterial blood input. Compared with healthy controls, the BP of [carbonyl-11C]WAY-100635 was reduced in patients with MDD in most brain regions, ranging from -9% to -25%. Voxel-level analysis confirmed this finding by showing a widespread reduction of [carbonyl-11C]WAY-100635 BP. No statistically significant associations were observed between BP and total HAMD scores in the patients, but lower BP was associated with higher likelihood of insomnia. This study demonstrated a widespread reduction in the availability of serotonin 5-HT1A receptors in a relatively large sample of drug-naive primary-care patients with MDD, suggesting the involvement of this receptor subtype in the pathophysiology of the illness. Lack of correlation with overall severity of the illness may relate to a largely trait-like nature of this abnormality in depressive disorders.

Prefrontal cortex lesions cause only minor effects on the hyperlocomotion induced by MK-801 and its reversal by clozapine

The non-competitive NMDA receptor antagonist MK-801 elicits a behavioural syndrome in rodents characterized by hyperlocomotion and stereotypies, which is antagonized by antipsychotic drugs. NMDA receptor antagonists increase prefrontal cortex (PFC) activity in rodents, as assessed by electrophysiological and neurochemical measures. The increase in glutamate outflow induced by systemic MK-801 administration in the medial PFC (mPFC) is prevented by the local administration of clozapine (Clz). In the present study, we examine whether a PFC lesion alters the behavioural syndrome induced by MK-801 in rats and the Clz-induced antagonism of MK-801 actions. We evaluated the hyperlocomotion, stereotypies and other behavioural changes induced by MK-801 in the open field and the effect of electrolytic lesions of the mPFC, and of cortical transection on the behavioural syndrome induced by MK-801 and its reversal by Clz. MK-801 (0.1-0.2 mg/kg i.p.) reduced rearings but only the higher dose induced hyperlocomotion. At this dose, MK-801 also increased disorganized movements, head weavings, and induced ataxia signs. An electrolytic lesion of the mPFC markedly reduced the number of rearings pre-treatment but caused a very slight attenuation of MK-801-induced hyperlocomotion. Cortical transection did not significantly alter MK-801 effects. Clz administration (1 mg/kg s.c.) significantly attenuated hyperlocomotion, head weavings and ataxia signs induced by MK-801 but did not prevent the decrease in rearings. The effect of Clz was essentially unaffected by electrolytic lesions of the mPFC. These results show that MK-801-induced motor syndrome and its reversal by Clz are mostly independent on PFC integrity.

Serotonin, inhibition, and negative mood

Pavlovian predictions of future aversive outcomes lead to behavioral inhibition, suppression, and withdrawal. There is considerable evidence for the involvement of serotonin in both the learning of these predictions and the inhibitory consequences that ensue, although less for a causal relationship between the two. In the context of a highly simplified model of chains of affectively charged thoughts, we interpret the combined effects of serotonin in terms of pruning a tree of possible decisions, (i.e., eliminating those choices that have low or negative expected outcomes). We show how a drop in behavioral inhibition, putatively resulting from an experimentally or psychiatrically influenced drop in serotonin, could result in unexpectedly large negative prediction errors and a significant aversive shift in reinforcement statistics. We suggest an interpretation of this finding that helps dissolve the apparent contradiction between the fact that inhibition of serotonin reuptake is the first-line treatment of depression, although serotonin itself is most strongly linked with aversive rather than appetitive outcomes and predictions.

Serotonin is an evolutionarily ancient neuromodulator probably best known for its role in psychiatric disorders. However, that role has long appeared contradictory to its role in normal function, and indeed its various roles in normal affective behaviors have been hard to reconcile. Here, we model two predominant functions of normal serotonin function in a highly simplified reinforcement learning model and show how these may explain some of its complex roles in depression and anxiety.

Emotional decision-making and its dissociable components in schizophrenia and schizoaffective disorder: a behavioural and MRI investigation

Cognitive decision-making is known to be deficient, but relatively less is known about emotional decision-making in schizophrenia. The Iowa gambling task (IGT) is considered a reliable probe of emotional decision-making and believed to reflect orbitofrontal cortex (OFC) function. The expectancy-valence model of IGT performance implicates three dissociable components, namely, attention to reward, memory for past, relative to recent, outcomes and impulsivity in emotional decision-making. We examined IGT performance, its three components, and their grey matter volume (GMV) correlates in 75 stable patients with schizophrenia, relative to 25 healthy individuals. Patients, relative to controls, showed impaired IGT performance and poor memory for past, relative to recent, outcomes. IGT performance correlated with GMV in the OFC in controls, but not patients. There were associations between (a) attention to reward and GMV in the frontal, temporal, parietal and striatal regions in controls, and in the temporal and thalamic regions in patients, (b) memory for past outcomes and GMV in the temporal region in controls, and the frontal and temporal regions in patients, and (c) low impulsivity and greater GMV in the frontal, temporal, posterior cingulate and occipital regions in controls, and in the frontal, temporal and posterior cingulate regions in patients. Most IGT-GMV associations were stronger in controls. It is concluded that (i) poor memory, rather than less attention to reward or impulsivity, contributes to IGT performance deficit, and (ii) the relationship of IGT performance and its components with GMVs especially in the frontal and temporal lobes is lost or attenuated in schizophrenia.

Reciprocal effects of combined administration of serotonin, noradrenaline and dopamine reuptake inhibitors on serotonin and dopamine levels in the rat prefrontal cortex: the role of 5-HT1A receptors

The purpose of the present study was to examine, by in vivo microdialysis technique, the effects of triple acting monoamine reuptake inhibitors, constructed by combinations of a selective serotonin reuptake inhibitor citalopram with a noradrenaline/dopamine reuptake inhibitor methylphenidate and a serotonin/noradrenaline reuptake inhibitor venlafaxine with a dopamine reuptake inhibitor GBR12909, on extracellular levels of serotonin (5-HT), noradrenaline (NA) and dopamine (DA) in the prefrontal cortex (PFC) of anaesthetized rats. At the highest dose tested, adjunctive methylphenidate (10 mg/kg s.c.) to citalopram markedly attenuated by 63% the extracellular levels of 5-HT as compared to the levels induced by citalopram (5 mg/kg i.p.) alone, whereas the overall DA concentrations significantly increased to about 149% of those induced by methylphenidate alone. Similarly, the combination of venlafaxine with GBR12909 (10 mg/kg s.c.) caused a reduction of 5-HT levels to 66% of the levels induced by venlafaxine (10 mg/kg i.p.) alone, whereas the overall DA levels increased to 151% of the venlafaxine-treated group. The extracellular levels of NA were only marginally affected by the treatments with combined reuptake inhibitors compared to the effects induced by methylphenidate or venlafaxine alone. The modulatory effects of combined administration of the DA/NA reuptake inhibitors with the 5-HT reuptake inhibitors (citalopram and venlafaxine) on potentiation of DA and attenuation of 5-HT efflux were completely reversed by a pre-treatment with the 5-HT(1A) receptor antagonist WAY-100635. These findings suggest a crucial role played by the 5-HT(1A) receptors in balancing the reuptake inhibitory efficacy for the enhancement of 5-HT and DA transmission in the PFC by the drugs combining the reuptake inhibition of all three monoamines.

Cannabinoids elicit antidepressant-like behavior and activate serotonergic neurons through the medial prefrontal cortex

Preclinical and clinical studies show that cannabis modulates mood and possesses antidepressant-like properties, mediated by the agonistic activity of cannabinoids on central CB1 receptors (CB1Rs). The action of CB1R agonists on the serotonin (5-HT) system, the major transmitter system involved in mood control and implicated in the mechanism of action of antidepressants, remains however poorly understood. In this study, we demonstrated that, at low doses, the CB1R agonist WIN55,212-2 [R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl) methanone mesylate] exerts potent antidepressant-like properties in the rat forced-swim test (FST). This effect is CB1R dependent because it was blocked by the CB1R antagonist rimonabant and is 5-HT mediated because it was abolished by pretreatment with the 5-HT-depleting agent parachlorophenylalanine. Then, using in vivo electrophysiology, we showed that low doses of WIN55,212-2 dose dependently enhanced dorsal raphe nucleus 5-HT neuronal activity through a CB1R-dependent mechanism. Conversely, high doses of WIN55,212-2 were ineffective in the FST and decreased 5-HT neuronal activity through a CB1R-independent mechanism. The CB1R agonist-induced enhancement of 5-HT neuronal activity was abolished by total or medial prefrontocortical, but not by lateral prefrontocortical, transection. Furthermore, 5-HT neuronal activity was enhanced by the local microinjection of WIN55,212-2 into the ventromedial prefrontal cortex (mPFCv) but not by the local microinjection of WIN55,212-2 into the lateral prefrontal cortex. Similarly, the microinjection of WIN55,212-2 into the mPFCv produced a CB1R-dependent antidepressant-like effect in the FST. These results demonstrate that CB1R agonists possess antidepressant-like properties and modulate 5-HT neuronal activity via the mPFCv.

Differential effects of adjunctive methylphenidate and citalopram on extracellular levels of serotonin, noradrenaline and dopamine in the rat brain

Several clinical studies have suggested that the combined treatment with methylphenidate and citalopram may accelerate the onset of antidepressant action and induce an improvement even in treatment-refractory patients. In the present study, in vivo microdialysis was used to monitor the extracellular levels of serotonin, noradrenaline and dopamine in the prefrontal cortex, hippocampus, nucleus accumbens and striatum of the rat. Administration of methylphenidate (2.5 mg/kg s.c.) with citalopram (5 mg/kg i.p.) compared to methylphenidate alone caused a marked enhancement of dopamine levels in the prefrontal cortex, n. accumbens and hippocampus, but not in the striatum. Citalopram-induced increase in serotonin levels was strongly enhanced by adjunctive methylphenidate in the hippocampus, but attenuated in the cortex. These findings suggest that the proposed augmentation effects of adjuvant methylphenidate to citalopram are most likely associated with enhanced dopamine transmission in the corticolimbic areas, whereas serotonin and noradrenaline levels show differential and region specific responses.

Effect of buspirone, a serotonin1A partial agonist, on cognitive function in schizophrenia: a randomized, double-blind, placebo-controlled study

In previous studies, we demonstrated that tandospirone, a serotonin-5-HT1A partial agonist, added to ongoing treatment with small to moderate doses of typical antipsychotic drugs, improved executive function and verbal learning and memory. However, tandospirone is not available in most countries, and atypical antipsychotic drugs (AAPDs) have largely replaced typical antipsychotic drugs as the primary treatment for schizophrenia. Therefore, the goal of this randomly assigned placebo-controlled double-blind study was to determine if the addition of buspirone, a widely available 5-HT1A partial agonist, would enhance cognitive function, in subjects with schizophrenia treated with AAPDs. Seventy-three patients with schizophrenia, who had been treated with an AAPD for at least three months, were randomly assigned to receive either buspirone, 30 mg/day, or matching placebo. All other medications remained unchanged. Attention, verbal fluency, verbal learning and memory, verbal working memory, and executive function, as well as psychopathology, were assessed at baseline, and 6 weeks, and 3 and 6 months after baseline. A significant Time x Group interaction effect was noted on the Digit Symbol Substitution Test, a measure of attention/speeded motor performance, due to better performance of the buspirone group compared to the placebo group at 3 months. No significant interaction effects were noted for other domains of cognition. Scores on the Brief Psychiatric Rating Scale (Total, Positive) were improved during treatment with buspirone but not placebo, but the effects did not reach statistical significance. The results of this study showed a possible benefit of buspirone augmentation of AAPDs to enhance attention. However, we did not replicate the results of the previous study with tandospirone, which may be due to the differences between tandospirone and buspirone, between typical antipsychotics and AAPDs, or a combination of the above. Further study to determine the usefulness of 5-HT1A agonist treatment in schizophrenia is indicated.

5-HT1A receptor agonist properties of antipsychotics determined by [35S]GTPgammaS binding in rat hippocampal membranes

1. 5-Hydroxytryptamine 1A (5-HT1A) receptors have attracted increasing attention as a promising target for antipsychotic therapy. Although many atypical antipsychotic drugs, including the prototype clozapine, have been reported to be partial agonists at 5-HT1A receptors, these results are often fragmental and derived mainly from experiments that used cultured cells. 2. In the present study, [35S]guanosine 5'-O-(3-thiotriphosphate) ([35S]GTPgammaS) binding assay in rat hippocampal membranes was applied to a series of antipsychotic drugs, especially atypical antipsychotics. 3. Most, but not all, of atypical antipsychotic drugs and the classical antipsychotic drug nemonapride behaved as partial agonists at 5-HT1A receptors with varied potencies and relative efficacies. The most potent compound was perospirone with a mean EC50 of 27 nmol/L, followed by aripiprazole (45 nmol/L) > ziprasidone (480 nmol/L) > nemonapride (790 nmol/L) > clozapine (3900 nmol/L) > quetiapine (26,000 nmol/L). The maximal percentage increases over the basal binding (%Emax) for these antipsychotic drugs were 30-50%, with the exception of perospirone (approximately 15%), whereas 5-HT stimulated the binding to a mean %Emax of 105%. 4. Increasing concentrations of the selective and neutral 5-HT1A antagonist WAY100635 shifted the concentration-response curve of nemonapride-stimulated [35S]GTPgammaS binding to the right and in parallel. 5. The relative efficacy or intrinsic activity of a compound was affected differently by the differing concentrations of guanosine diphosphate (GDP) in the assay buffer, which should be taken into consideration when determining the relative efficacies of these antipsychotics as 5-HT1A receptor agonists. 6. These results provide important information concerning the relevance of 5-HT1A receptor partial agonist properties in the treatment for schizophrenic patients with most, if not all, of atypical antipsychotic drugs.