Perspectives on the role of serotonergic mechanisms in the pharmacology of schizophrenia

Sex Differences in Brain Disorders

A remarkable feature of the brain is its sexual dimorphism. Sexual dimorphism in brain structure and function is associated with clinical implications documented previously in healthy individuals but also in those who suffer from various brain disorders. Sex-based differences concerning some features such as the risk, prevalence, age of onset, and symptomatology have been confirmed in a range of neurological and neuropsychiatric diseases. The mechanisms responsible for the establishment of sex-based differences between men and women are not fully understood. The present paper provides up-to-date data on sex-related dissimilarities observed in brain disorders and highlights the most relevant features that differ between males and females. The topic is very important as the recognition of disparities between the sexes might allow for the identification of therapeutic targets and pharmacological approaches for intractable neurological and neuropsychiatric disorders.

Obsessive-compulsive symptoms in schizophrenia: a review

OBJECTIVE

To review the available literature on obsessive-compulsive symptom (OCS)/obsessive-compulsive disorder (OCD) in patients with schizophrenia.

METHODOLOGY

Electronic searches were carried out to locate studies reporting various aspects of OCS/OCD in patients with schizophrenia.

RESULTS

Available evidence suggests that prevalence of OCS/OCD in patients with schizophrenia is much higher than prevalence in general population and it is seen in all the stages of schizophrenia, starting from at risk mental state to chronic/stabilisation/deficit phases. Symptom profile of OCS/OCD in schizophrenia is similar to that seen in patients with OCD only. Presence of OCS/OCD is associated with higher severity of symptoms of schizophrenia and more negative outcome. At present there is very limited data on the efficacy/effectiveness of various pharmacological measures and psychological interventions, for management of OCS/OCD in patients with schizophrenia. There is some evidence pointing towards beneficial effect of certain antipsychotics, antidepressants and cognitive behaviour therapy. Management of OCS/OCD in patients with schizophrenia involves proper assessment. If the OCS/OCD is related to use of particular antipsychotic use, initial attempt must be made to reduce the dose of antipsychotics, however, if this is not effective, than addition of a selective serotonin reuptake inhibitor (SSRIs) must be considered. If the OCS/OCD is not related to the use of antipsychotic medication, than depending up on the severity of psychotic symptoms, addition of SSRIs must be considered.

CONCLUSION

This review suggests that OCS/OCD is highly prevalent among patients with schizophrenia and there is limited good quality evidence to make any specific recommendations for management.

Enhancement of 5-HT2A receptor function and blockade of Kv1.5 by MK801 and ketamine: implications for PCP derivative-induced disease models

MK801 and ketamine, which are phencyclidine (PCP) derivative N-methyl-d-aspartate receptor (NMDAr) blockers, reportedly enhance the function of 5-hydroxytryptamine (HT)-2A receptors (5-HT_2ARs). Both are believed to directly affect the pathogenesis of schizophrenia, as well as hypertension. 5-HT_2AR signaling involves the inhibition of Kv conductance. This study investigated the interaction of these drugs with Kv1.5, which plays important roles in 5-HT_2AR signaling and in regulating the excitability of the cardiovascular and nervous system, and the potential role of this interaction in the enhancement of the 5-HT_2AR-mediated response. Using isometric organ bath experiments with arterial rings and conventional whole-cell patch-clamp recording of Chinese hamster ovary (CHO) cells ectopically overexpressing Kv1.5, we examined the effect of ketamine and MK801 on 5-HT_2AR-mediated vasocontraction and Kv1.5 channels. Both ketamine and MK801 potentiated 5-HT_2AR-mediated vasocontraction. This potentiation of 5-HT_2AR function occurred in a membrane potential-dependent manner, indicating the involvement of ion channel(s). Both ketamine and MK801 rapidly and directly inhibited Kv1.5 channels from the extracellular side independently of NMDArs. The potencies of MK801 in facilitating the 5-HT_2AR-mediated response and blocking Kv1.5 were higher than those of ketamine. Our data demonstrated the direct inhibition of Kv1.5 channels by MK801/ketamine and indicated that this inhibition may potentiate the functions of 5-HT_2ARs. We suggest that 5-HT_2AR-Kv1.5 may serve as a receptor-effector module in response to 5-HT and is a promising target in the pathogenesis of MK801-/ketamine-induced disease states such as hypertension and schizophrenia.

The drugs ketamine and MK801, which are derivatives of phencyclidine (PCP, or angel dust), may provide clues to treatment of schizophrenia and hypertension. Both ketamine and MK801 have been reported to induce symptoms of schizophrenia and hypertension, and are used as to study these illnesses. The two drugs are known to affect serotonin receptors, but the mechanism remains unclear. Young Min Bae at Konkuk University School of Medicine, Chungju, South Korea, and colleagues investigated how ketamine and MK801 interact with a type of electrically activated biological switch known as a voltage-gated ion channel to influence serotonin receptors. They found that both ketamine and MK801 blocked the switch and enhanced activity of serotonin receptors, with MK801 having a stronger effect than ketamine. These results may help identify drug targets for treating hypertension and schizophrenia.

Antipsychotic medication and prefrontal cortex activation: a review of neuroimaging findings

Decreased prefrontal activation (hypofrontality) in schizophrenia is thought to underlie negative symptoms and cognitive impairments, and may contribute to poor social outcome. Hypofrontality does not always improve during treatment with antipsychotics. We hypothesized that antipsychotics, which share antagonism at dopamine receptors, with a relatively low dopamine receptor affinity and high serotonin receptor affinity may have a sparing effect on prefrontal function compared to strong dopamine receptor antagonists. We systematically investigated the relation between serotonin and dopamine antagonism of antipsychotics and prefrontal functioning by reviewing neuroimaging studies. The weight of the evidence was consistent with our hypothesis that antipsychotics with low dopaminergic receptor affinity and moderate to high serotonergic affinity were associated with higher activation of the prefrontal cortex. However, clozapine, a weak dopamine and strong serotonin antagonist, was associated with decrease in prefrontal activation. Future studies should further elucidate the link between prefrontal activation and negative symptoms using prospective designs and advanced neuroimaging techniques, which may ultimately benefit the development of treatments for disabling negative symptoms.

Can genetics inform the management of cognitive deficits in schizophrenia?

There is no doubt that schizophrenia has a significant genetic component and a number of candidate genes have been identified for this debilitating disorder. Of note, several of these are implicated in cognition. Cognitive deficits constitute core symptoms of schizophrenia, and while current antipsychotic treatment strategies aim to help psychosis-related symptomatology, the cognitive symptom domain is largely inadequately treated. A number of other pharmacological approaches (e.g. using drugs that target specific neurotransmitter systems) have also been attempted for the amelioration of cognitive deficits in this population; however, these too have had limited success so far. Psychological interventions appear promising, though there has been speculation regarding whether or not these produce long-term functional improvements. Pharmacogenetic studies of the cognitive effects of currently available antipsychotics, although in relatively early stages, suggest that the treatment of cognitive deficits in schizophrenia may be advanced by focusing on genetic variants associated with specific cognitive dysfunctions in the general population and using this to match the most relevant pharmacological and/or psychological interventions with the genetic and cognitive profiles of the target population. Such a strategy would encourage bottom-up advances in drug development and provide a platform for individualised treatment of cognitive deficits in schizophrenia.

CNS and antimalarial activity of synthetic meridianin and psammopemmin analogs

The marine invertebrate-derived meridianin A, the originally proposed structure for psammopemmin A, and several related 3-pyrimidylindole analogs were synthesized and subsequently investigated for central nervous system, antimalarial, and cytotoxic activity. A Suzuki coupling of an indoleborate ester to the pyrimidine electrophile was utilized to form the natural product and derivatives thereof. The 3-pyrimidineindoles were found to prevent radioligand binding to several CNS receptors and transporters, most notably, serotonin receptors (<0.2 μM K(i) for 5HT(2B)). Two compounds also inhibited the human malaria parasite Plasmodium falciparum (IC(50) <50 μM). Only the natural product was cytotoxic toward A549 cells (IC(50)=15 μM).

5-Hydroxytryptamine Receptor Subtypes and their Modulators with Therapeutic Potentials

5-hydroxytryptamine (5-HT) has become one of the most investigated and complex biogenic amines. The main receptors and their subtypes, e.g., 5-HTI (5-HT1A, 5-HT1B, 5-HTID, 5-HTIE and 5-HT1F), 5-HT2 (5-HT2A, 5-HT2B and 5-HT2C), 5-HT3, 5-HT4, 5-HT5 (5-HT5A, 5-HT5B), 5-HT6 and 5-HT7 have been identified. Specific drugs which are capable of either selectively stimulating or inhibiting these receptor subtypes are being designed. This has generated therapeutic potentials of 5-HT receptor modulators in a variety of disease conditions. Conditions where 5-HT receptor modulators have established their use with distinct efficacy and advantages include migraine, anxiety, psychosis, obesity and cancer therapy-induced vomiting by cytotoxic drugs and radiation. Discovery of 5-HT, its biosynthesis, metabolism, physiological role and the potential of 5-HT receptor modulators in various nervous, cardiovascular and gastrointestinal tract disorders, bone growth and micturition have been discussed in this article.

Neuroanatomical, neurochemical, and neurodevelopmental basis of obsessive-compulsive symptoms in schizophrenia

The prevalence of the obsessive-compulsive symptoms in schizophrenia (OCSS) appears to be higher than that expected on the basis of comorbidity rates. Review of brain abnormalities in schizophrenia and obsessive-compulsive disorder (OCD) reveals involvement of similar regions namely the frontal lobe, the basal ganglia, the thalamus, and the cerebellum, in both the disorders. Neurodevelopmental etiopathogenesis has been proposed to explain schizophrenia as well as OCD. Significant overlap in neurotransmitter dysfunction (serotonin, glutamate, and dopamine) has been documented between schizophrenia and OCD. The New-onset obsessive-compulsive (OC) symptoms have been reported with the use of atypical antipsychotics in the schizophrenia patients In this background, OCSS is an emerging area of recent interests. This article attempts to review the literature on the neurobiology of OCSS. Neuroimaging, neuropsychological, and neuromotor abnormalities in OCSS discussed in the context of neurodevelopmental etiopathogenesis suggest glutamate abnormalities in OCSS. Atypical antipsychotic induced OCSS points towards the possible roles of glutamate and serotonin. Dopamine may be responsible for the beneficial role of antipsychotics in the treatment of OCD. In summary, we propose that glutamate, serotonin, and dopamine abnormalities may be the probable basis for OCSS.

The 5-HT1A receptor active compounds (R)-8-OH-DPAT and (S)-UH-301 modulate auditory evoked EEG responses in rats

Schizophrenics commonly demonstrate abnormalities in central filtering capability following repetitive sensory stimuli. Such sensory inhibition deficits can be mirrored in rodents following administration of psycho-stimulatory drugs. In the present study, male Sprague-Dawley rats were implanted with brain surface electrodes to record auditory evoked EEG potentials in a paired-stimulus paradigm, using 87 dB clicks delivered 0.5 s apart. Amphetamine (1.83 mg/kg, i.p.) produced the expected loss of sensory inhibition, as defined by an increase in the ratio between test (T) and conditioning (C) amplitudes at N40, a mid-latency peak of the evoked potentials. Also, the 5-HT(1A) agonist (R)-8-OH-DPAT caused a significant increase in the TC ratio at the highest dose studied (0.5 mg/kg s.c.), while the 5-HT(1A) antagonist (S)-UH-301 did not significantly affect the TC ratio at any dose studied (0.1-5 mg/kg s.c.). When administered with amphetamine, a lower dose of 8-OH-DPAT (0.1 mg/kg) and the highest dose of UH-301 tested (5 mg/kg, s.c.) were able to reverse the amphetamine-induced increase in TC ratio. The findings suggest that 5-HT(1A) signaling is involved in sensory inhibition and support the evaluation of 5-HT(1A) receptor active compounds in conditions with central filtering deficits, such as schizophrenia.

Serotonin depolarizes the membrane potential in rat mesenteric artery myocytes by decreasing voltage-gated K+ currents

We hypothesized that voltage-gated K+ (Kv) currents regulate the resting membrane potential (Em), and that serotonin (5-HT) causes Em depolarization by reducing Kv currents in rat mesenteric artery smooth muscle cells (MASMCs). The resting Em was about -40 mV in the nystatin-perforated patch configuration, and the inhibition of Kv currents by 4-aminopyridine caused marked Em depolarization. The inhibition of Ca2+-activated K+ (KCa) currents had no effect on Em. 5-HT (1 microM) depolarized Em by approximately 11 mV and reduced the Kv currents to approximately 63% of the control at -20 mV. Similar 5-HT effects were observed with the conventional whole-cell configuration with a weak Ca2+ buffer in the pipette solution, but not with a strong Ca2+ buffer. In the presence of tetraethylammonium (1mM), 5-HT caused Em depolarization similar to the control condition. These results indicate that the resting Em is largely under the regulation of Kv currents in rat MASMCs, and that 5-HT depolarizes Em by reducing Kv currents in a [Ca2+]i-dependent manner.

Distinct functional profiles of aripiprazole and olanzapine at RNA edited human 5-HT2C receptor isoforms

In this study we have functionally characterized aripiprazole (OPC-14597; 7-(4-[4-(2,3-dichlorophenyl)-1-piperazinyl]butyloxy-3,4-dihydro-2-(1H)-quinolinone), the prototype of a new generation antipsychotic drug termed dopamine-serotonin-system stabilizer, in cells expressing 5-hydroxytryptamine2 (5-HT2) receptor subtypes in comparison with olanzapine. In Chinese hamster ovary (CHO) cells stably expressing 5-HT2 receptors, aripiprazole displayed a dual agonist/antagonist profile for 5-HT2C receptor (VNI isoform) mediated calcium signaling (EC50 1070 nM, IC50 281 nM). It exhibited no appreciable 5-HT2A or 5-HT2B agonism, whereas it antagonized 5-HT-stimulated calcium increase at either 5-HT2A or 5-HT2B receptor expressed in CHO cells (IC50s of 369 and 0.46 nM, respectively). In comparison, olanzapine was devoid of agonism but was an antagonist at all three subtypes, with a potency rank order of 5-HT2A (IC50, 2.5 nM)>5-HT2B (47 nM)>5-HT2C (69 nM). In human embryonic kidney (HEK) cells transiently expressing 5-HT2C receptor isoforms, aripiprazole exhibited full agonism at the unedited INI, but partial agonism at the partially edited VNI and fully edited VSV isoforms (EC50s of 571, 1086 and 2099 nM, respectively). A partial antagonism was also observed for aripiprazole at the two edited isoforms (IC50s of 1138 and 1000 nM, respectively). In contrast, while lacking agonist activity at the VNI and VSV, olanzapine showed inverse agonism at the INI isoform (IC50 594 nM), reaching a maximal attenuation of 20%. In addition, olanzapine was a full antagonist at all three isoforms, with a rank order of potency of VNI (IC50, 79 nM)>VSV (101 nM)>INI (3856 nM). The modest 5-HT2A antagonism and 5-HT2C partial agonism, along with reported D2 and 5-HT1A partial agonism, may allow aripiprazole to stabilize the disturbed dopamine-serotonin interplay in schizophrenia with a moderate yet adequate pharmacological intervention. 5-HT2C agonism may also underlie the minimal weight gain seen with aripiprazole.

Novel oral drug administration in an animal model of neuroleptic therapy

A novel method of oral drug administration was used in a neuroleptic animal study. Seventy male Sprague-Dawley rats were randomly subdivided into four groups, which were treated with clozapine, haloperidol, diazepam or a vehicle solution (5% sucrose solution). Oral drug treatment was achieved by training the rats to drink the drug of choice mixed with five percent sucrose or vehicle solution from a syringe. Within 3-4 weeks the haloperidol group developed vacuous chewing movement, which did not disappear with discontinuation of the drug. Significant weight gain was observed for all drug groups in relation to the control group, whereas only the diazepam group showed a significant increase in response latency on the disengage test of sensorimotor function, which disappeared with drug withdrawal. A novel means of testing the motivational status showed that all drug-treated groups engaged in eating chocolate before grooming (t=11.69, p<0.001), whereas the control group showed no specific tendency towards either task. Furthermore, there was a significant delay in grooming for the haloperidol group compared to the other drug groups and controls. In conclusion, a novel method of oral drug administration with minimum stress was introduced that was sufficient to cause the described changes in behavioural parameters. Additionally, the combination of tests used provided an efficient discrimination between the behavioural effects of clozapine, haloperidol and diazepam in rodents.

The dorsal raphe nucleus in schizophrenia: a post mortem study of 5-hydroxytryptamine neurones

The 5-hydroxytryptamine (5-HT, serotonin) system has been implicated in the pathophysiology and treatment of schizophrenia. In this study, we addressed the hypothesis that a deficit of 5-HT neurones, either inherited or acquired, is central to the developmental pathology of the disorder. We examined putative 5-HT neurones of the dorsal raphe nucleus (DRN) in post mortem, formalin-fixed tissue from 15 schizophrenic patients and 20 control subjects matched for age and gender. No significant difference was detected between these groups in the number or size (cross-sectional area or diameter) of tryptophan-hydroxylase-immunoreactive cell profiles viewed in transverse sections collected from the level of the trochlear decussation to the emergence of the trigeminal nerve. Profile number was not affected by age, gender, side of the brainstem (left or right) or post mortem interval; however, time in formalin correlated negatively with the number of neurones counted. Moreover, a significant negative correlation was detected between time in formalin and the levels of immunoreaction product (optical density), which in turn correlated positively with our profile counts. A positive correlation was found between the age of subjects and our estimates of cell size. Our results do not support the proposal that an abnormality in the number and/or size of DRN 5-HT neurones is central to the aetiopathology of schizophrenia.

Anxiolytic-like effect of a serotonergic ligand with high affinity for 5-HT1A, 5-HT2A and 5-HT3 receptors

S-(-)-2-[[4-(napht-1-yl)piperazin-1-yl]methyl]-1,4-dioxoperhydropyrrolo[1,2-alpha]-pyrazine (CSP-2503) is a serotonin (5-HT) receptor ligand with selectivity and high affinity for 5-HT1A, 5-HT2A and 5-HT3 receptors. CSP-2503 reduced rectal temperature and 5-HT neuronal hypothalamic activity in mice, decreased electrical activity of raphe nuclei cells in rats and blocked the enhancement of adenylate cyclase activity induced by forskolin in HeLa cells transfected with the human 5-HT1A receptor. This compound also blocked head-twitches induced by the 5-HT(2A/2C) receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI). Contractions of guinea pig ileum induced by the 5-HT3 receptor agonist 2-methyl-5-HT were prevented by CSP-2503. Moreover, it reduced the bradycardia reflex induced by 2-methyl-5-HT in anaesthetized rats. In the light/dark box and social interaction tests, CSP-2503 presented anxiolytic activity, an action shared by 5-HT1 agonists and 5-HT3 antagonists. Taken together, these results suggest that CSP-2503 is a new 5-HT1 receptor agonist with 5-HT2A and 5-HT3)receptor antagonist activities that might be useful in a number of conditions associated with anxiety.

Pharmacogenetics as a tool in the therapy of schizophrenia

AIM

This review summarises the present knowledge of associations between pharmacogenetics and therapeutic efficacy and side effects of antipsychotics to enable pharmacists to judge the applicability for a more tailor made therapy in patients with schizophrenia. Polymorphisms of Cytochrome P450 isoenzymes and neurotransmitter receptors involved in the efficacy and side effects of antipsychotics are highlighted in this review.

METHOD

A search was performed in Medline and EMBASE for the period 1995-August 2002. Also relevant references from the selected papers were incorporated.

RESULTS

Poor metabolism with respect to CYP2D6 seems to be related with more pronounced extrapyramidal symptoms and more specifically with a higher incidence of tardive dyskinesia. The C/C-genotype for CYP1A2 results in smokers in a reduction of enzyme activity, but an effect on the incidence of tardive dyskinesia is controversial. For dopamine D2 receptors the effect of the -141C Ins/Del polymorphism on efficacy is not clear yet, although the Taq I polymorphism is associated with greater improvement of positive, but not negative symptoms in acute psychosis. The Gly9-allele of the dopamine D3 receptor is associated with the response to clozapine, but in studies in which the choice of antipsychotics is not restricted, the role of this polymorphism is unclear. The reverse is applicable to the dopamine D(4.2/4.7) polymorphism. For the 5-HT2A receptor the His452Tyr polymorphism is associated with response to clozapine, the 102 T/C polymorphism leads to equivocal results. The polymorphism studied for 5-HT5A, 5-HT6, alpha1A- and alpha2A-receptors give no clear associations with the response to clozapine. The polymorphism studied of the dopamine D2 and D4 receptor are not related to extrapyramidal adverse effects and side effects, respectively. The 9Gly-variant of the dopamine D3 receptor, the 102C-variant, but not the His452Tyr polymorphism of the 5-HT2A-receptor and the 23Ser-variant (for females only) of the 5-HT2C receptor seem to increase the susceptibility to tardive dyskinesia. Weight gain induced by antipsychotics seems to be associated with the -759C-allele of the 5-HT2C receptor.

CONCLUSION

The results show the first careful steps toward application of pharmacogenetics in a more individualised, tailor-made, pharmacotherapy. A pre-condition seems to be a multifactorial approach, as can be expected for multifactorial processes.

Regulation of GABAergic inhibition by serotonin signaling in prefrontal cortex: molecular mechanisms and functional implications

Serotonergic neurotransmission in prefrontal cortex (PFC) plays a key role in regulating emotion and cognition under normal and pathological conditios. Increasing evidence suggests that serotonin receptors are involved in the complex regulation of GABAergic inhibitory transmission in PFC. Activation of postsynaptic 5-HT2 receptors in PFC pyramidal neurons inhibits GABAA-receptor currents via phosphorylation of GABAA receptor gamma2 subunits by RACK1-anchored PKC. In contrast, activation of postsynaptic 5-HT4 receptors produces an activity-dependent bi-directional regulation of GABA-evoked currents in PFC pyramidal neurons, which is mediated through phosphorylation of GABAA-receptor beta subunits by anchored PKA. On the presynaptic side, GABAergic inhibition is regulated by 5-HT through the activation of 5-HT2, 5-HT1, and 5-HT3 receptors on GABAergic intereneurons. These data provide a molecular and cellular mechanism for serotonin to dynamically regulate synaptic transmission and neuronal excitability in the PFC network, which may underlie the actions of many antidepressant and antipsychotic drugs.

Serotonin 5-HT1A receptors regulate AMPA receptor channels through inhibiting Ca2+/calmodulin-dependent kinase II in prefrontal cortical pyramidal neurons

We have studied the regulation of AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) receptor channels by serotonin signaling in pyramidal neurons of prefrontal cortex (PFC). Application of serotonin reduced the amplitude of AMPA-evoked currents, an effect mimicked by 5-HT(1A) receptor agonists and blocked by 5-HT(1A) antagonists, indicating the mediation by 5-HT(1A) receptors. The serotonergic modulation of AMPA receptor currents was blocked by protein kinase A (PKA) activators and occluded by PKA inhibitors. Inhibiting the catalytic activity of protein phosphatase 1 (PP1) also eliminated the effect of serotonin on AMPA currents. Furthermore, the serotonergic modulation of AMPA currents was occluded by application of the Ca(2+)/calmodulin-dependent kinase II (CaMKII) inhibitors and blocked by intracellular injection of calmodulin or recombinant CaMKII. Application of serotonin or 5-HT(1A) agonists to PFC slices reduced CaMKII activity and the phosphorylation of AMPA receptor subunit GluR1 at the CaMKII site in a PP1-dependent manner. We concluded that serotonin, by activating 5-HT(1A) receptors, suppress glutamatergic signaling through the inhibition of CaMKII, which is achieved by the inhibition of PKA and ensuing activation of PP1. This modulation demonstrates the critical role of CaMKII in serotonergic regulation of PFC neuronal activity, which may explain the neuropsychiatric behavioral phenotypes seen in CaMKII knockout mice.

An RT-PCR study of 5-HT(6) and 5-HT(7) receptor mRNAs in the hippocampal formation and prefrontal cortex in schizophrenia

5-Hydroxytryptamine (5-HT; serotonin) 5-HT(6) receptors (5-HT(6)R) and 5-HT(7) receptors (5-HT(7)R) have been implicated in schizophrenia and as targets of atypical antipsychotic drugs. We have studied the expression of these receptors in the hippocampal formation and dorsolateral prefrontal cortex (DLPFC) of 17 subjects with schizophrenia and 17 controls using reverse transcription-polymerase chain reaction (RT-PCR) with cyclophilin co-amplification. In schizophrenia, 5-HT(6)R mRNA was decreased in the hippocampal formation, and 5-HT(7)R mRNA was decreased in the dorsolateral prefrontal cortex. The mRNAs were unchanged in rats treated for 2 weeks with haloperidol, chlorpromazine, risperidone, olanzapine or clozapine. Regional decreases in 5-HT(6)R and 5-HT(7)R expression in schizophrenia may contribute to the overall serotonergic alterations which occur in the disorder, in part through their interactions with other neurotransmitter systems including glutamate and acetylcholine.

Prepulse inhibition of the startle response in risperidone-treated patients: comparison with typical antipsychotics

Individuals with schizophrenia are known to show deficits in prepulse inhibition (PPI) of the startle response. PPI refers to a response suppression in reaction to a strong startling stimulus, if preceded briefly by a weak non-startling stimulus and represents a well-established animal model to investigate information processing deficits in schizophrenia. This study examined PPI of the startle acoustic response in schizophrenic patients given typical antipsychotics or a second generation atypical antipsychotic, risperidone, using a naturalistic between-subjects design. Two groups of male schizophrenic patients: (i) stable on a range of typical antipsychotics (n = 20), and (ii) stable on risperidone (n = 10) were tested for PPI (prepulse-to-pulse intervals: 30, 60, and 120 ms, prepulses 15 dB above the background) of the acoustic startle response, and compared with a group of healthy male subjects (n = 20). Patients on typical antipsychotics showed significantly less PPI with 30 and 60 ms prepulse trials than healthy subjects. Risperidone-treated patients did not differ from healthy subjects for PPI with any prepulse trials. Further longitudinal within-subject studies are now required to examine whether risperidone is superior to typical antipsychotics in improving information processing functions, as assessed by PPI of the acoustic startle response, in treatment-responsive male patients with schizophrenia.

Receptor profile of P88-8991 and P95-12113, metabolites of the novel antipsychotic iloperidone

Iloperidone is a novel atypical antipsychotic compound currently under clinical development for the treatment of psychotic disorders. In radioligand binding studies, iloperidone binds with high affinity to serotonin (5-HT) 5-HT2A and noradrenaline alpha1 and alpha2C receptors [Neuropsychopharmacology (2001) 25, 904-914]. The human metabolism of iloperidone generates two major metabolites, P88-8991 and P95-12113. The aim of this study was to compare the receptor affinity profile of P88-8991 and P95-12113 with that of the parent compound. The receptor affinity profile of P88-8991 is comparable to that of iloperidone. This metabolite binds to the following monoamine receptors (pKi values in nM): serotonin 5-HT2A receptors (9.56), adrenergic alpha1 (8.08) and alpha2C (7.79) receptors, and D2A receptors (7.80). Lower affinity is seen for other dopamine, serotonin, alpha2-adrenergic and histamine H1 receptors. In contrast, P95-12113 shows affinity for 5-HT2A receptors (pKi 8.15; which is 60-fold lower than that of iloperidone), adrenergic alpha1 (7.67), alpha2C (7.32) and alpha2B (7.08) receptors. Given this affinity profile, and the observation that P95-12113 does not readily cross the blood-brain barrier, it is unlikely that this metabolite contributes to the therapeutic effect of iloperidone in patients with schizophrenia. However, the comparable receptor binding profile of P88-8991 indicates that it is likely to contribute to the clinical profile of iloperidone.

Effects of the 5HT antagonist cyproheptadine on neuropsychological function in chronic schizophrenia

This study tests the hypothesis that the ability of atypical neuroleptics to improve negative symptoms is due to 5HT-receptor antagonism and enhanced frontal lobe function. We investigated the effects of cyproheptadine (a 5HT2 antagonist) on neuropsychological tests of frontal lobe functions in chronic schizophrenic patients. Eighteen stable schizophrenic patients on depot neuroleptic medication participated in a 4-week double blind crossover study. Outcome measures were clinical symptoms rating scales, neuropsychological tests (verbal fluency, Stroop colour word task, trail making) and antisaccade eye movements. During the cyproheptadine phase statistically significant improvement was seen on Stroop colour word task, verbal fluency and Trail B tests. The ability to suppress reflexive eye movement to a target light in an anti saccade task was also significantly enhanced. The patients had low clinical ratings of negative symptoms and they were unaffected by cyproheptadine. The results indicate that 5HT2C receptors selectively modulate speed and motor control mechanisms related to frontal lobe functions but this was not associated with changes in symptoms.

Expression of serotonin 5-HT(2A) receptors in the human cerebellum and alterations in schizophrenia

The occurrence of human cerebellar serotonin 5-HT(2A) receptors (5-HT(2A)R) is equivocal and their status in schizophrenia unknown. Using a range of techniques, we investigated cerebellar 5-HT(2A)R expression in 16 healthy subjects and 16 subjects with schizophrenia. Immunocytochemistry with a monoclonal antibody showed labelling of Purkinje cell bodies and dendrites, as well as putative astrocytes. Western blots showed a major band at approximately 45 kDa. Receptor autoradiography and homogenate binding with [(3)H]ketanserin revealed cerebellar 5-HT(2A)R binding sites present at levels approximately a third of that in prefrontal cortex. 5-HT(2A)R mRNA was detected by reverse transcriptase-polymerase chain reaction, with higher relative levels in men than women. Several aspects of 5-HT(2A)R expression were altered in schizophrenia. 5-HT(2A)R immunoreactivity in Purkinje cells was partially redistributed from soma to dendrites and was increased in white matter. 5-HT(2A)R mRNA was decreased in the male patients. 5-HT(2A)R measured by dot blots and [(3)H]ketanserin binding (B(max) and K(d)) were not significantly altered in schizophrenia. These data show that 5-HT(2A)R gene products (mRNA, protein, binding sites) are expressed in the human cerebellum at nonnegligible levels; this bears upon 5-HT(2A)R imaging studies which use the cerebellum as a reference region. 5-HT(2A)R expression is altered in schizophrenia; the shift of 5-HT(2A)R from soma to dendrites is noteworthy since atypical antipsychotics have the opposite effect. Finally, the results emphasise that expression of a receptor gene is a mutifaceted process. Measurement of multiple parameters is necessary to give a clear picture of the normal situation and to show the profile of alterations in a disease.

Are atypical antipsychotic drugs also atypical antidepressants?

OBJECTIVE

To report a case series and review the psychopharmacology of the neuroleptic drugs to suggest that the atypical antipsychotic drugs may have an antidepressant action, at least for those patients with the melancholic subtype.

METHOD

We note the literature suggesting that the older (or typical) antipsychotic drugs were established as having antidepressant activity, describe an open study of some two dozen patients with a treatment-resistant melancholic depression, describe rapid resolution of depression and augmentation benefits associated with commencing an atypical antipsychotic drug in a percentage of subjects, and then review relevant psychopharmacological studies to consider whether there is a rationale for use of antipsychotic drugs to treat depression.

RESULTS

Of some two dozen patients treated with an atypical antipsychotic drug, almost immediate improvement was noted in four patients, and evidence of augmentation benefit obtained in another three patients.

CONCLUSIONS

Impressions from this case series are encouraging. However, as open clinical observational studies are problematic, controlled studies are required to establish whether the atypical antipsychotic drugs have a role in the management of certain expressions of depression, and, in particular, treatment-resistant melancholic depression.

Serotonin receptors modulate GABA(A) receptor channels through activation of anchored protein kinase C in prefrontal cortical neurons

Serotonergic neurotransmission in prefrontal cortex (PFC) has long been known to play a key role in regulating emotion and cognition under normal and pathological conditions. However, the cellular mechanisms by which this regulation occurs are unclear. In this study, we examined the impact of serotonin on GABA(A) receptor channels in PFC pyramidal neurons using combined patch-clamp recording, biochemical, and molecular approaches. Application of serotonin produced a reduction of postsynaptic GABA(A) receptor currents. Although multiple 5-HT receptors were coexpressed in PFC pyramidal neurons, the serotonergic modulation of GABA-evoked currents was mimicked by the 5-HT(2)-class agonist (-)-2,5-dimethoxy-4-iodoamphetamine and blocked by 5-HT(2) antagonists risperidone and ketanserin, indicating the mediation by 5-HT(2) receptors. Inhibiting phospholipase C blocked the 5-HT(2) inhibition of GABA(A) currents, as did dialysis with protein kinase C (PKC) inhibitory peptide. Moreover, activation of 5-HT(2) receptors in PFC slices increased the in vitro kinase activity of PKC toward GABA(A) receptor gamma2 subunits. Disrupting the interaction of PKC with its anchoring protein RACK1 (receptor for activated C kinase) eliminated the 5-HT(2) modulation of GABA(A) currents, suggesting that RACK1-mediated targeting of PKC to the vicinity of GABA(A) receptors is required for the serotonergic signaling. Together, our results show that activation of 5-HT(2) receptors in PFC pyramidal neurons inhibits GABA(A) currents through phosphorylation of GABA(A) receptors by the activation of anchored PKC. The suppression of GABAergic signaling provides a novel mechanism for serotonergic modulation of PFC neuronal activity, which may underlie the actions of many antidepressant drugs.

RNA editing of the 5-HT(2C) receptor is reduced in schizophrenia

5-HT(2C) receptor (5HT(2C)R, serotonin-2C) RNA undergoes editing to produce several receptor variants, some with pharmacological differences. This investigation comprised two parts: the characterisation of 5-HT(2C)R RNA editing in a larger human control sample than previously examined, and a comparative study in subjects with schizophrenia. Secondary structure analysis of the putative edited region of the human 5-HT(2C)R gene predicted the existence of a double stranded (ds) RNA loop, essential for RNA editing in this receptor. RNA was then extracted from frontal cortex of five controls and five subjects with schizophrenia. RT-PCR products of the edited region were cloned and sequenced (n = 100). Reduced RNA editing, increased expression of the unedited 5-HT(2C-INI) isoform in schizophrenia (P = 0.001) and decreased expression of the 5-HT(2C-VSV) and 5-HT(2C-VNV) isoforms were detected in the schizophrenia group. In addition, two novel mRNA edited variants were identified: 5-HT(2C-MNI) and 5-HT(2C-VDI). Screening of the 5-HT(2C)R gene did not reveal any mutations likely to disrupt the dsRNA loop, suggesting that the reduced RNA editing in schizophrenia may instead be caused by altered activity of the editing enzyme(s). Since the unedited 5-HT(2C-INI) is more efficiently coupled to G proteins than the other isoforms, its increased expression in schizophrenia may lead to enhanced 5-HT(2C)R-mediated effects. The results also illustrate that potentially important receptor alterations may occur in schizophrenia which are not detectable merely in terms of receptor abundance.

Antipsychotic drug use in neurodegenerative disease in the elderly: problems and potential from a pharmacological perspective

The past decade has seen the introduction of several new antipsychotics for the treatment of schizophrenia. These drugs demonstrate substantially lower levels of extrapyramidal side effects (EPS) than the classical antipsychotics, as well as having (often poorly supported) claims of increased efficacy at ameliorating certain schizophrenic syndromes. Increasingly, these 'atypical' drugs are being used in the treatment of psychotic or related behavioural disturbances in patients with neurodegenerative disease. Thus, some newer antipsychotics are particularly valuable in ameliorating the L-dopa-induced psychosis in Parkinson's disease, while behavioural problems in dementing disorders, such as those occurring in Alzheimer's disease, are also frequently treated by antipsychotic drugs. The relationship between drug pharmacology and neurotransmitter pathology is essential to understanding the relative efficacy of individual antipsychotic drugs in treating the psychotic and behavioural disturbances of neurodegenerative disorders.

The 5-HT1A receptor in schizophrenia: a promising target for novel atypical neuroleptics?

Increasing attention is being directed towards the role of the serotonergic system in the neurochemistry of schizophrenia and antipsychotic drug treatment. This review considers the 5-HT1A receptor in this context. In patients with schizophrenia, the majority of post-mortem studies have reported increases in 5-HT1A receptor density in the prefrontal cortex in the approximate range 15-80%. Although the pathophysiological significance of this finding is unclear, given the location of a major proportion of these receptors on pyramidal cells, it may reflect an abnormal glutamatergic network. In terms of drug treatment, 5-HT1A agonists clearly display anticataleptic activity in rats. In addition, 5-HT1A agonists consistently increase dopamine release in the prefrontal cortex in rodents, which is an effect that might be predicted to improve negative symptoms. 5-HT1A agonists augment classical neuroleptics in some rat models of antipsychotic action and may be capable of modulating the glutamatergic network therapeutically. Despite the encouraging preclinical data, there is a paucity of clinical studies of 5-HT1A agonist augmentation of neuroleptics in the treatment of schizophrenia. However, the clinical relevance may be clarified by the atypical antipsychotic drugs clozapine, quetiapine and ziprasidone which combine D2 receptor antagonism and 5-HT1A agonism. In conclusion, given the increased prefrontal 5-HT1A receptor density in the illness, and the anticataleptic activity of 5-HT1A agonists combined with their ability to evoke prefrontal dopamine release, there is now a sufficient rationale to examine thoroughly the role of the 5-HT1A receptor in schizophrenia and antipsychotic drug treatment.

Monoaminergic synapses and schizophrenia: 45 years of neuroleptics

In 1952 Delay and Deniker introduced the first antipsychotic, chlorpromazine, into the treatment of mental patients. They subsequently defined the word 'neuroleptic' to describe drugs as different as reserpine and chlorpromazine which seemed to have similar effects on the mental life of patients. In the 1960s the hypothesis was developed, mainly due to Carlsson, that the principal mode of action of neuroleptics was to interfere with synaptic transmission mediated by dopamine (DA) in the brain. This concept was given substantial credence with the discovery by Seeman and Snyder in the 1970s that many of the neuroleptics acted as DA receptor blockers. Subsequently two different classes of DA receptor were defined on the basis of their coupling to adenylate cyclase by Kebabian. In the 1980s molecular biology led to the cloning of five different DA receptors, and at the end of this period vanTol and his colleagues cloned the D4 DA receptor, which has been of considerable interest in the 1990s as it is greatly elevated in the brains of schizophrenics. This historical review ends with a consideration of the possibility that in addition to DA receptors, serotonin and perhaps other transmitter receptors are involved in the aetiology of schizophrenia.

Serotonin 5-HT2 receptors in schizophrenic patients studied by positron emission tomography

Using positron emission tomography (PET) and [11C]N-methylspiperone (NMSP), we examined 5-HT2 receptors in the cortex of schizophrenic patients in whom we previously observed decreased prefrontal D1 receptor binding. The subjects were 10 neuroleptic-naive schizophrenic patients, 7 schizophrenic patients who were drug-free but had previously been treated with neuroleptics, and 12 normal controls. A non-significant trend towards decreased prefrontal [11C]NMSP binding was observed in the neuroleptic-treated patients, suggesting a possible effect of previous neuroleptic treatment on the alteration in cortical 5-HT2 function. However, the neuroleptic-naive patients showed no noticeable difference in cortical [11C]NMSP binding compared to controls. Our results do not rule out the role of 5-HT2 function as a crucial site of therapeutic activity of schizophrenia, but they do suggest that cortical 5-HT2 receptors might not be primarily involved in the pathophysiology of schizophrenia.

Contrasting mechanisms of action and sensitivity to antipsychotics of phencyclidine versus amphetamine: importance of nucleus accumbens 5-HT2A sites for PCP-induced locomotion in the rat

In the present study, the comparative mechanisms of action of phencyclidine (PCP) and amphetamine were addressed employing the parameter of locomotion in rats. PCP-induced locomotion (PLOC) was potently blocked by the selective serotonin (5-HT)2A vs. D2 antagonists, SR46349, MDL100,907, ritanserin and fananserin, which barely affected amphetamine-induced locomotion (ALOC). In contrast, the selective D2 vs. 5-HT2A antagonists, eticlopride, raclopride and amisulpride, preferentially inhibited ALOC vs. PLOC. The potency of these drugs and 12 multireceptorial antipsychotics in inhibiting PLOC vs. ALOC correlated significantly with affinities at 5-HT2A vs. D2 receptors, respectively. Amphetamine and PCP both dose dependently increased dialysate levels of dopamine (DA) and 5-HT in the nucleus accumbens, striatum and frontal cortex (FCX) of freely moving rats, but PCP was proportionally more effective than amphetamine in elevating levels of 5-HT vs. DA in the accumbens. Further, whereas microinjection of PCP into the accumbens elicited locomotion, its introduction into the striatum or FCX was ineffective. The action of intra-accumbens PCP, but not intra-accumbens amphetamine, was abolished by SR46349 and clozapine. Parachloroamphetamine, which depleted accumbens pools of 5-HT but not DA, likewise abolished PLOC without affecting ALOC. In contrast, intra-accumbens 6-hydroxydopamine (6-OHDA), which depleted DA but not 5-HT, abolished ALOC but only partially attenuated PLOC. In conclusion, PLOC involves (indirect) activation of accumbens-localized 5-HT2A receptors by 5-HT. PLOC is, correspondingly, more potently blocked than ALOC by antipsychotics displaying marked affinity at 5-HT2A receptors.

Differences in frontal cortical activation by a working memory task after substitution of risperidone for typical antipsychotic drugs in patients with schizophrenia

Antipsychotic drug treatment of schizophrenia may be complicated by side effects of widespread dopaminergic antagonism, including exacerbation of negative and cognitive symptoms due to frontal cortical hypodopaminergia. Atypical antipsychotics have been shown to enhance frontal dopaminergic activity in animal models. We predicted that substitution of risperidone for typical antipsychotic drugs in the treatment of schizophrenia would be associated with enhanced functional activation of frontal cortex. We measured cerebral blood oxygenation changes during periodic performance of a verbal working memory task, using functional MRI, on two occasions (baseline and 6 weeks later) in two cohorts of schizophrenic patients. One cohort (n = 10) was treated with typical antipsychotic drugs throughout the study. Risperidone was substituted for typical antipsychotics after baseline assessment in the second cohort (n = 10). A matched group of healthy volunteers (n = 10) was also studied on a single occasion. A network comprising bilateral dorsolateral prefrontal and lateral premotor cortex, the supplementary motor area, and posterior parietal cortex was activated by working memory task performance in both the patients and comparison subjects. A two-way analysis of covariance was used to estimate the effect of substituting risperidone for typical antipsychotics on power of functional response in the patient group. Substitution of risperidone increased functional activation in right prefrontal cortex, supplementary motor area, and posterior parietal cortex at both voxel and regional levels of analysis. This study provides direct evidence for significantly enhanced frontal function in schizophrenic patients after substitution of risperidone for typical antipsychotic drugs, and it indicates the potential value of functional MRI as a tool for longitudinal assessment of psychopharmacological effects on cerebral physiology.

A review of central 5-HT receptors and their function

It is now nearly 5 years since the last of the currently recognised 5-HT receptors was identified in terms of its cDNA sequence. Over this period, much effort has been directed towards understanding the function attributable to individual 5-HT receptors in the brain. This has been helped, in part, by the synthesis of a number of compounds that selectively interact with individual 5-HT receptor subtypes--although some 5-HT receptors still lack any selective ligands (e.g. 5-ht1E, 5-ht5A and 5-ht5B receptors). The present review provides background information for each 5-HT receptor subtype and subsequently reviews in more detail the functional responses attributed to each receptor in the brain. Clearly this latter area has moved forward in recent years and this progression is likely to continue given the level of interest associated with the actions of 5-HT. This interest is stimulated by the belief that pharmacological manipulation of the central 5-HT system will have therapeutic potential. In support of which, a number of 5-HT receptor ligands are currently utilised, or are in clinical development, to reduce the symptoms of CNS dysfunction.

Normalization of information processing deficits in schizophrenia with clozapine

OBJECTIVE

The authors tested the hypothesis that the use of an atypical drug, clozapine, for patients with schizophrenia is related to less impairment in information processing deficits (assessed by prepulse inhibition of the startle response) than is the use of typical antipsychotics.

METHOD

Two groups of schizophrenic patients--receiving either clozapine or a range of typical antipsychotics--were tested for prepulse inhibition (a reduction in response to a starting stimulus, if preceded briefly by a weak, nonstartling stimulus; measured at prepulse-to-pulse intervals of 30 msec, 60 msec, and 120 msec) of the acoustic startle response and compared with a group of healthy volunteers.

RESULTS

Patients receiving typical antipsychotics showed less prepulse inhibition with 30-msec and 60-msec prepulse trials than did comparison subjects. Clozapine-treated patients showed normal levels of prepulse inhibition.

CONCLUSIONS

Clozapine is superior to typical antipsychotics in normalizing prepulse inhibition, presumably because of its pharmacological effects on prefrontal regions of the brain or its effects on a broader range of neuroreceptors.

Identification of a new polymorphism in the 3'-untranslated region of the human serotonin receptor 2C (5-HT2C) gene

We identified a polymorphism (2831T > G) in the 3'-untranslated region of 5-HT2C receptor gene, approximately 100 kb from a previously reported coding sequence polymorphism, 796G > C (C23S). Allele frequencies were 0.90 (T) and 0.10 (G) and cosegregation analysis of the alleles at the two loci demonstrated frequencies of 0.82 (GT), 0.08 (CT), 0.10 (GG), and 0 (CC). The increased informativity gained by analysis of both polymorphisms will prove useful for future studies of this gene in X-linked neuropsychiatric disorders.

Serotonin transporter gene is not associated with symptomatology of schizophrenia

The serotonin transporter gene is a primary candidate for involvement in major psychoses. A functional polymorphism in the upstream regulatory region of the serotonin transporter gene (5-HTTLPR) has recently been reported to be associated with a variety of psychopathological conditions. In the present study, we investigated the potential influence of the 5-HTTLPR on the psychopathology of schizophrenia. One hundred and sixty-one inpatients affected by schizophrenia (DSMIII-R) were assessed by the Operational Criteria checklist for psychotic illness (OPCRIT) and were typed for their 5-HTTLPR variants by PCR techniques. Mania, Depression, Delusion and Disorganization were the four symptomatologic factors used to define phenotype. 5-HTTLPR variants were not associated with these symptomatologic factors, and consideration of possible stratification effects such as sex, and age of onset did not reveal any association either. The serotonin transporter gene is not a liability factor for the symptomatology of schizophrenia.

5-HT2A receptor blockade in patients with schizophrenia treated with risperidone or clozapine. A SPET study using the novel 5-HT2A ligand 123I-5-I-R-91150

BACKGROUND

5-HT2A receptor antagonism may be crucial to the action of atypical antipsychotics. Previous work has related 5-HT2A receptor blockade to clinical efficacy and protection from extrapyramidal side-effects.

METHOD

We developed a SPET imaging protocol for assessing 5-HT2A receptor binding using the selective ligand 123I-5-I-R91150. Six healthy volunteers, five clozapine- and five risperidone-treated subjects with DSM-IV schizophrenia were studied. Multi-slice SPET was performed on each subject.

RESULTS

Cortex:cerebellum ratios were significantly lower in both clozapine- and risperidone-treated subjects compared with the healthy volunteers in all cortical regions. There was no difference in occupancy between the two drug-treated groups. No correlation was found between the percentage change in the Global Assessment Scale (GAS) and 5-HT2A receptor binding indices in the drug-treated groups.

CONCLUSIONS

Clozapine and risperidone potently block 5-HT2A receptors in vivo. The lack of relationship between receptor binding indices and change in GAS suggests that 5-HT2A receptor blockade may be unrelated to clinical improvement. Future studies will substantiate this finding by studying 5-HT2A receptor binding in large groups of patients treated with both typical and novel atypical antipsychotics.

Meta-analysis of studies on genetic variation in 5-HT2A receptors and clozapine response

Serotonin (5-HT) neurotransmitter receptors are targeted by atypical antipsychotic drugs. We hypothesized that genetic variation in these receptors may affect clinical response to the drugs targeting them. This hypothesis has been tested by several studies in which the correlation between polymorphic variants in the 5-HT2A receptor gene and clinical response to the atypical antipsychotic clozapine was investigated. The results of these studies either found association between 5-HT2A genetic variants and clozapine response or found differences in the same direction which did not reach statistical significance. Meta-analysis of these studies including 373 patients who responded to the treatment and 360 non-responders showed association between two 5-HT2A polymorphisms, 102-T/C and His452Tyr, and clozapine response. Statistical analysis of extreme responders showed a clearer association of the 102-T/C with clozapine response. These results reinforce the hypothesis and strengthen the candidacy of these receptors as important therapeutic targets.

New atypical antipsychotic medications

Conventional antipsychotics were the first treatments effective in controlling psychotic symptomatology and revolutionized management of psychotic disorders when introduced in the 1950's. The use of these agents has, however, been marked by several shortcomings, including limited efficacy in treating the negative and cognitive symptoms of schizophrenia, and by significant extrapyramidal and other side-effects. There appears to be justifiable excitement about the introduction of the newer atypical antipsychotics, which may represent the second pharmacological revolution in the treatment of psychotic disorders. But how are these agents really different from their neuroleptic predecessors? How is their pharmacological profile different? Are there clear differences in efficacy? How do side-effect profiles differ? These issues are reviewed in this manuscript. Atypical agents are pharmacologically distinct from their neuroleptic predecessors. Their primary advantage is their superior side effect profiles, particularly with regard to EPS. The implications of EPS reduction touch virtually every domain of pathology in schizophrenia, including short- and long-term movement disorders, negative symptoms, noncompliance, relapse rate, cognitive dysfunction, and dysphoria. It should be emphasized that while atypical antipsychotics share some clinical attributes, there are substantial clinical differences between them as well. These differences are reviewed in this article as well. The drugs' unique profiles with regard to other side effects may make it possible to tailor treatment more individually to patients. Further refinement of our understanding of the clinical utility of these drugs awaits their widespread use in mainstream clinical settings. Controlled studies comparing them to one another should be of particular interest.

The new antipsychotics, and their potential for early intervention in schizophrenia

Over almost four decades, few fundamentally different antipsychotic drugs evolved to challenge classical neuroleptics as the mainstay of the pharmacotherapy of schizophrenia. However, the recent re-emergence of clozapine, together with the emergence of risperidone, portends an increasing number of new antipsychotics which are now either traversing the stages of regulatory approval or else well-advanced in clinical development. This article first evaluates the significance of clozapine and risperidone; it then reviews some of the new antipsychotics and how they might be classified vis-a-vis potential advantages for patients, outlines putative mechanisms and new therapeutic targets, and considers whether such agents may act on any disease process inherent to schizophrenia. One fundamental issue is the extent to which the new antipsychotics might shift materially the risk benefit balance towards intervention, not just at the earliest possible stage following the onset of psychosis but at a yet earlier, 'prodromal' phase of the disorder where there is a considerably greater likelihood of 'treating' behavioural disturbances that prove not to be the harbingers of psychotic illness.

Antisense inhibition of 5-hydroxytryptamine2a receptor induces an antidepressant-like effect in mice

Treatment with different antidepressants is invariably accompanied by the down-regulation of the 5-hydroxytryptamine2A (5-HT2A) receptor. To determine whether receptor down-regulation is an essential part of antidepressant action, we manipulated levels of the 5-HT2A receptor by using a nonpharmacological approach. Here, we report that down-regulation of the 5-HT2A receptor by intracerebroventricular injection of antisense oligonucleotides resulted in an antidepressant-like effect in mice. Animals with 5-HT2A receptor deficiency showed less immobility in the Porsolt's forced swim test, a well established animal model that is used to identify drugs with an antidepressant effect. The overall locomotor activity of the receptor-deficient animals was not altered, demonstrating the specificity of the behavioral change in the Porsolt's forced swim test. Reduced immobility in this test was accompanied by a greater c-Fos response in piriform cortex. Because 5-HT2A receptors have been localized on gamma-aminobutyric acid interneurons, the inhibitory activity of these neurons may be impaired at low receptor levels, leading to a greater c-Fos response in the piriform cortex and increased mobility in the Porsolt's forced swim test. These experiments demonstrate that down-regulation of the 5-HT2A receptor alone is sufficient to achieve an antidepressant-like effect in mice and suggest that receptor down-regulation may be an essential part of the antidepressant drug action.

What is an atypical antipsychotic?

This is an exciting time for research into the drug treatment of schizophrenia. Modern techniques in imaging and molecular biology have contributed to our understanding of the receptor mechanisms of antipsychotic drug action. Several new antipsychotics are, or will shortly be, available and each of these new drugs promise improvements over classical antipsychotics. This review will discuss the concept of atypicality in antipsychotic drugs, and will describe some of the models for identification of improved antipsychotic action. The various receptor mechanisms proposed to underlie atypical antipsychotic action, several of which have featured in recent debates in this journal, will be considered in the light of the pharmacology of some of the newly-emerging antipsychotic drugs.