The role of 5-HT1A autoreceptors and alpha1-adrenoceptors in the modulation of 5-HT release--III. Clozapine and the novel putative antipsychotic S 16924

Regulation of neutrophil phagocytosis of Escherichia coli by antipsychotic drugs

Antipsychotic drugs (APDs) have been used to ease the symptoms of schizophrenia. APDs have recently been reported to regulate the immune response. Our previous studies revealed that the atypical APDs risperidone and clozapine and the typical APD haloperidol can inhibit the phagocytic ability of macrophages. Our research next determined the effects of APDs on the phagocytic ability of neutrophils, which are the most abundant type of white blood cells in mammals. Here we provide evidence that clozapine and haloperidol can induce increased phagocytic uptake of Escherichia coli by differentiated HL-60 cells and by purified human neutrophils. Furthermore, clozapine and haloperidol can increase the myeloperoxidase activity and IL-8 production in neutrophils. Our results also show that clozapine can inhibit E. coli survival within differentiated HL-60 cells. Furthermore, clozapine and haloperidol are shown to enhance cell surface Mac-1 expression and the activated AKT signaling pathway in purified neutrophils exposed to E. coli. These results indicate that clozapine and haloperidol can increase the phagocytic ability of neutrophils by increasing AKT activation when cells are exposed to bacteria.

Augmentation of SSRI effects on serotonin by 5-HT2C antagonists: mechanistic studies

The treatment of depression may be improved by using an augmentation approach involving selective serotonin reuptake inhibitors (SSRIs) in combination with compounds that focus on antagonism of inhibitory serotonin receptors. Using microdialysis coupled to HPLC, it has recently been shown that the systemic co-administration of 5-HT(2C) antagonists with SSRIs augmented the acute effect of SSRIs on extracellular 5-HT. In this paper, we have investigated the mechanism through which this augmentation occurs. The increase in extracellular 5-HT was not observed when both compounds were locally infused. However, varying the route of administration for both compounds differentially revealed that an augmentation took place when the 5-HT(2C) antagonist was locally infused into ventral hippocampus and the SSRI given systemically, but not when systemic 5-HT(2C) antagonist was co-administered with the local infusion of citalopram. This suggests that the release of extracellular serotonin in ventral hippocampus may be controlled by (an)other brain area(s). As 5-HT(2C) receptors are not considered to be autoreceptors, this would implicate that other neurotransmitter systems are involved in this process. To investigate which neurotransmitter systems were involved in the interaction, systemic citalopram was challenged with several glutamatergic, GABA-ergic, noradrenergic, and dopaminergic compounds to determine their effects on serotonin release in ventral hippocampus. It was determined that the involvement of glutamate, norepinephrine, and dopamine in the augmentation did not seem likely, whereas evidence implicated a role for the GABA-ergic system in the augmentation.

Differential effects of (R)-, (R, S)- and (S)-8-hydroxy-2-(di-n-propylamino)tetralin on hippocampal serotonin release and induction of hypothermia in awake rats

The effects of (R)- and (S)-optical isomers of 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) and of the racemate (R,S)-8-OH-DPAT on serotonin (5-HT) release in the ventral hippocampus of awake rats and on induction of the whole-body hypothermia were studied. Extracellular 5-HT levels were determined by a newly developed high-sensitive HPLC method based on derivatization with benzylamine and fluorescence detection. The basal levels of 5-HT in 20 min microdialysates from rats perfused with Ringer solution or with Ringer solution containing 1 microM citalopram were 6.3 +/- 1.3 fmol/20 microl and 36.1 +/- 4.2 fmol/20 microl (n=20), respectively. The reduction of hippocampal 5-HT levels induced by subcutaneous (s.c.) administration of (R,S)-8-OH-DPAT (0.3 mg/kg) was significantly attenuated by the presence of 5-HT reuptake inhibitor citalopram in Ringer solution only at its peak value at 40 min (maximal reduction to 60% compared to 46% of control values in Ringer-perfused rats), whereas the overall effects were comparable at both experimental conditions. Injection of (R)-8-OH-DPAT (0.3 mg/kg s.c.) caused further reduction of 5-HT levels, to 49% and 41%, respectively, whereas (S)-8-OH-DPAT (0.3 mg/kg s.c.) caused maximal reduction of 5-HT levels only to 74% of controls in both perfusion groups. Similar pattern and time-courses were observed in rats with hypothermia induced by injection of 8-OH-DPAT enantiomers, where (R,S), (R)-forms were about two-times more potent than the (S)-isomer. It is concluded that the acute systemic dose of (R)-, (S)- and (R,S)-8-OH-DPAT enantiomers exerted enantiomer-specific effects on 5-HT(1A) receptor-mediated function both at the presynaptic and postsynaptic sites as revealed by monitoring hippocampal 5-HT levels and body temperature.

Serotonergic dysfunction in schizophrenia assessed by the loudness dependence measure of primary auditory cortex evoked activity

Increased serotonergic activity is discussed as an important pathogenetic factor in schizophrenia. Further support for this hypothesis is difficult to obtain due to the lack of valid indicators of the brain's serotonin system. A great deal of evidence discovered through human and animal studies suggests that a weak loudness dependence of auditory evoked potentials (LDAEP) indicates high serotonergic activity and vice versa. The LDAEP is a measure of auditory cortex activity, reflecting increase or decrease of auditory evoked potential amplitudes with increasing tone loudness, which is probably modulated by the serotonergic innervation there. This is true only for the LDAEP of the primary auditory cortex, since this region is more highly innervated by serotonergic fibers than the secondary auditory cortex. The LDAEP (N1/P2 component) of 25 inpatients with schizophrenia free of medication and 25 healthy controls matched by age and gender, were recorded. Using dipole source analysis, the LDAEP of primary (tangential dipole) and this of secondary auditory cortex (radial dipole) was separately analyzed. Following a 4-week treatment with the 5-HT(2) antagonists clozapine or olanzapine, patients were once again studied. The LDAEP of the primary, but not of the secondary auditory cortex, was significantly weaker in the patients with schizophrenia than in healthy volunteers, indicating enhanced serotonergic neurotransmission. After treatment with the 5-HT(2) antagonists, the LDAEP (of the right hemisphere) tended to be increased, indicating normalization of serotonergic function in the patients with schizophrenia. These results suggest that the loudness dependence of primary auditory cortex evoked activity is well suitable to assess serotonergic dysfunction in schizophrenia.

Modified synthesis of 11-[14C]-clozapine

The reported synthetic pathway of 8-chloro-11-(4-methyl-1-piperazinyl)-11-[14C]-5H-dibenzo[b,e][1,4]diazapine (clozapine) was modified in several steps. The synthetic pathway was shortened by 60% and the total yield was increased from 6% to 23%.

MS-377, a novel selective sigma(1) receptor ligand, reverses phencyclidine-induced release of dopamine and serotonin in rat brain

A novel selective sigma(1) receptor ligand, (R)-(+)-1-(4-chlorophenyl)-3-[4-(2-methoxyethyl)piperazin-1-yl]methyl-2-pyrrolidinone L-tartrate (MS-377), inhibits phencyclidine (1-(1-phenylcyclohexyl)piperidine; PCP)-induced behaviors in animal models. In this study, we measured extracellular dopamine and serotonin levels in the rat brain after treatment with MS-377 alone, using in vivo microdialysis. We also examined the effects of MS-377 on extracellular dopamine and serotonin levels in the rat medial prefrontal cortex after treatment with PCP. MS-377 itself had no significant effects on dopamine release in the striatum (10 mg/kg, p.o.) nor on dopamine or serotonin release in the medial prefrontal cortex (1 and 10 mg/kg, p.o.). PCP (3 mg/kg, i.p.) markedly increased dopamine and serotonin release in the medial prefrontal cortex. MS-377 (1 mg/kg, p.o.), when administered 60 min prior to PCP, significantly attenuated this effect of PCP. These results suggest that the inhibitory effects of MS-377 on PCP-induced behaviors are partly mediated by inhibition of the increase in dopamine and serotonin release in the rat medial prefrontal cortex caused by PCP.

The effect of tandospirone, a serotonin(1A) agonist, on memory function in schizophrenia

BACKGROUND

The purpose of this study was to test the hypothesis that the addition of tandospirone, a 5-HT(1A) partial agonist, to ongoing treatment with typical antipsychotic drugs, would improve memory function in patients with schizophrenia.

METHODS

Eleven outpatients (male/female = 7/4) with schizophrenia who had been on stable doses of haloperidol and biperiden were given tandospirone, 30 mg/day, for 4 weeks. The Wechsler Memory Scale-Revised (WMS-R) was administered at baseline and 4 weeks after the addition of tandospirone. The Brief Psychiatric Rating Scale (BPRS; Total, Positive, and Negative subscale scores) and the Simpson-Angus Scale for Extrapyramidal Symptoms (SAS) were also completed on the two occasions. To exclude the possibility of a practice effect on the WMS-R test, 11 age-matched patients with schizophrenia (M/F = 7/4) were tested at baseline and after a 4-week interval.

RESULTS

Repeated measures analysis of variance revealed a significant time by group (patients with or without tandospirone) effect for the Verbal-, but not the Visual Memory composite scores of the WMS-R test; no significant change was observed in patients without tandospirone, whereas improvement in the Verbal Memory score was noted in patients receiving tandospirone. Moreover, there was improvement in the Inclusion score, an index of memory organization as measured by the Logical Memory subtest of WMS-R, only in patients with tandospirone. Scores on the BPRS and SAS were improved during treatment with tandospirone, but the effects did not reach statistical significance.

CONCLUSIONS

The results suggest that adjunctive treatment with 5-HT(1A) agonists may improve some types of memory function in schizophrenia.

5-HT(1A) receptor mutant mice exhibit enhanced tonic, stress-induced and fluoxetine-induced serotonergic neurotransmission

Mutant mice that lack serotonin(1A) receptors exhibit enhanced anxiety-related behaviors, a phenotype that is hypothesized to result from impaired autoinhibitory control of midbrain serotonergic neuronal firing. Here we examined the impact of serotonin(1A) receptor deletion on forebrain serotonin neurotransmission using in vivo microdialysis in the frontal cortex and ventral hippocampus of serotonin(1A) receptor mutant and wild-type mice. Baseline dialysate serotonin levels were significantly elevated in mutant animals as compared with wild-types both in frontal cortex (mutant = 0.44 +/- 0.05 n M; wild-type = 0.28 +/- 0.03 n M) and hippocampus (mutant = 0.46 +/- 0.07 n M; wild-type = 0.27 +/- 0.04 n M). A stressor known to elicit enhanced anxiety-like behaviors in serotonin(1A) receptor mutants increased dialysate 5-HT levels in the frontal cortex of mutant mice by 144% while producing no alteration in cortical 5-HT in wild-type mice. There was no phenotypic difference in the effect of this stressor on serotonin levels in the hippocampus. Fluoxetine produced significantly greater increases in dialysate 5-HT content in serotonin(1A) receptor mutants as compared with wild-types, with two- and three-fold greater responses being observed in the hippocampus and frontal cortex, respectively. This phenotypic effect was mimicked in wild-types by pretreatment with the serotonin(1A) antagonist 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide (p-MPPI). These results indicate that deletion of central serotonin(1A) receptors results in a tonic disinhibition of central serotonin neurotransmission, with a greater dysregulation of serotonin release in the frontal cortex than ventral hippocampus under conditions of stress or increased interstitial serotonin levels.

Lack of association between the T-->C 267 serotonin 5-HT6 receptor gene (HTR6) polymorphism and prediction of response to clozapine in schizophrenia

The affinity of clozapine for 5-HT2A, 5-HT2C, 5-HT6, 5-HT7, and 5-HT1A receptors has been suggested to contribute to various aspects of its complex clinical actions. This study examined the hypothesis that genetic variation in 5-HT1A, 5-HT6, and 5-HT7 receptor genes is involved in the variability observed in response to clozapine. We employed a pharmacogenetic approach in a group (n=185) of schizophrenia patients that have been clinically well characterized for clozapine response. Polymorphisms in the 5-HT6 (HTR6), 5-HT1A (HTR1A) and 5-HT7 (HTR7) receptor genes were genotyped. No evidence for either an allelic or genotypic association of the T-->C 267 HTR6 polymorphism with response to clozapine was found in our sample (allele: chi(2)=0.06, 1 df, P=0.80; genotype: chi(2)=1.21, 2 df, P=0.55). The pro16leu HTR1A polymorphism was not observed in our sample; all individuals genotyped were pro/pro 16 homozygotes. With respect to the pro279leu HTR7 polymorphism, one Caucasian male responder to clozapine was observed to be heterozygous (pro/leu 279 genotype). This individual was clinically similar to the other clozapine responders. Overall, our findings do not support a role for the T-->C 267 polymorphism of the 5-HT6 receptor gene in response to clozapine, although replication is required to confirm this finding.

Design, synthesis and biological evaluation of new 3-[(4-aryl)piperazin-1-yl]-1-arylpropane derivatives as potential antidepressants with a dual mode of action: serotonin reuptake inhibition and 5-HT1A receptor antagonism

It has been suggested that the combination of a selective serotonin reuptake inhibitor (SSRI) and a 5-HT1A receptor antagonist may facilitate the onset of the SSRIs antidepressant action. Accordingly, we describe the synthesis of a series of new 3-[(4-aryl)piperazin-1-yl]-1-arylpropane derivatives with structural modifications performed in Ar1, Ar2 and Z (Z is different functional groups) to obtain the sought dual activity. Compounds were evaluated for in vitro affinity at 5-HT1A receptors and 5-HT transporter. The antidepressant-like activity of derivatives with the higher affinity was assessed initially using the forced swimming test (FST). Compound 1-(2,4-dimethylphenyl)-3-[(2-methoxyphenyl)piperazin-1-il]-1-propa none (III.1.a) showed the best antidepressant-like activity which was further confirmed in the learned helplessness test.