Alterations of serotonin transmission in schizophrenia

The tryptophan hydroxylase 1 (TPH1) gene, schizophrenia susceptibility, and suicidal behavior: a multi-centre case-control study and meta-analysis

Serotonin (5-hydroxytryptamin; 5-HT) alternations has since long been suspected in the pathophysiology of schizophrenia. Tryptophan hydroxylase (tryptophan 5-monooxygenase; TPH) is the rate-limiting enzyme in the biosynthesis of 5-HT, and sequence variation in intron 6 of the TPH1 gene has been associated with schizophrenia. The minor allele (A) of this polymorphism (A218C) is also more frequent in patients who have attempted suicide and individuals who died by suicide, than in healthy control individuals. In an attempt to replicate previous findings, five single nucleotide polymorphisms (SNPs) were genotyped in 837 Scandinavian schizophrenia patients and 1,473 controls. Three SNPs spanning intron 6 and 7, including the A218C and A779C polymorphisms, were associated with schizophrenia susceptibility (P = 0.019). However there were no differences in allele frequencies of these loci between affected individuals having attempted suicide at least once and patients with no history of suicide attempts (P = 0.84). A systematic literature review and meta-analysis support the A218C polymorphism as a susceptibility locus for schizophrenia (odds ratio 1.17, 95% confidence interval 1.07-1.29). Association studies on suicide attempts are however conflicting (heterogeneity index I(2) = 0.54) and do not support the A218C/A779C polymorphisms being a susceptibility locus for suicidal behavior among individuals diagnosed with a psychiatric disorder (OR = 0.96 [0.80-1.16]). We conclude that the TPH1 A218/A779 locus increases the susceptibility of schizophrenia in Caucasian and Asian populations. In addition, the data at hand suggest that the locus contributes to the liability of psychiatric disorders characterized by elevated suicidal rates, rather than affecting suicidal behavior of individuals suffering from a psychiatric disorder.

Picture representation during REM dreams: a redox molecular hypothesis

A novel molecular hypothesis about visual perception and imagery has recently been proposed (Bókkon, 2009; BioSystems). Namely, external electromagnetic visible photons are converted into electrical signals in the retina and are then conveyed to V1. Next, these retinotopic electrical signals (spike-related electrical signals along classical axonal-dendritic pathways) can be converted into synchronized bioluminescent biophoton signals (inside the neurons) by neurocellular radical reactions (redox processes) in retinotopically organized V1 mitochondrial cytochrome oxidase-rich visual areas. The bioluminescent photonic signals (inside the neurons) generated by neurocellular redox/radical reactions in synchronized V1 neurons make it possible to produce computational biophysical pictures during visual perception and imagery. Our hypothesis is in line with the functional roles of reactive oxygen and nitrogen species in living cells and states that this is not a random process, but rather a strict mechanism used in signaling pathways. Here, we suggest that intrinsic biophysical pictures can also emerge during REM dreams.

Constitutive genetic deletion of the growth regulator Nogo-A induces schizophrenia-related endophenotypes

The membrane protein Nogo-A, which is predominantly expressed by oligodendrocytes in the adult CNS and by neurons mainly during development, is well known for limiting neurite outgrowth and regeneration in the injured mammalian CNS. In addition, it has recently been proposed that abnormal Nogo-A expression or Nogo receptor (NgR) mutations may confer genetic risks for neuropsychiatric disorders of presumed neurodevelopmental origin, such as schizophrenia. We therefore evaluated whether Nogo-A deletion may lead to schizophrenia-like abnormalities in a mouse model of genetic Nogo-A deficiency. Here, we show that systemic, lifelong knock-out of the Nogo-A gene can lead to specific behavioral abnormalities resembling schizophrenia-related endophenotypes: deficient sensorimotor gating, disrupted latent inhibition, perseverative behavior, and increased sensitivity to the locomotor stimulating effects of amphetamine. These behavioral phenotypes were accompanied by altered monoaminergic transmitter levels in specific striatal and limbic structures, as well as changes in dopamine D2 receptor expression in the same brain regions. Nogo-A deletion was further associated with elevated expression of growth-related markers. In contrast, acute antibody-mediated Nogo-A neutralization in adult wild-type mice failed to produce such phenotypes, suggesting that the phenotypes observed in the knock-out mice might be of developmental origin, and that Nogo-A normally subserves critical functions in neurodevelopment. This study provides the first experimental demonstration that Nogo-A bears neuropsychiatric relevance, and alterations in its expression may be one etiological factor in schizophrenia and related disorders.

Neurochemical imaging in schizophrenia

Recent advances in the development and applications of neurochemical brain imaging methods have improved the ability to study the neurochemistry of the living brain in normal processes as well as psychiatric disorders. In particular, positron emission tomography (PET) and single photon emission computed tomography (SPECT) have been used to determine neurochemical substrates of schizophrenia and to uncover the mechanism of action of antipsychotic medications. The growing availability of radiotracers for monoaminergic neurotransmitter synthesis, transporters and receptors, has enabled the evaluation of hypotheses regarding neurotransmitter function in schizophrenia derived from preclinical and clinical observations. This chapter reviews the studies using neurochemical brain imaging methods for (1) detection of abnormalities in indices of dopamine and serotonin transmission in patients with schizophrenia compared to controls, (2) development of new tools to study other neurotransmitters systems, such as gamma-aminobutyric acid (GABA) and glutamate, and (3) characterization of target occupancy by antipsychotic drugs, as well as its relationship to efficacy and side effects. As more imaging tools become available, this knowledge will expand and will lead to better detection of disease, as well as better therapeutic approaches.

How have developments in molecular imaging techniques furthered schizophrenia research?

Molecular imaging techniques have led to significant advances in understanding the pathophysiology of schizophrenia and contributed to knowledge regarding potential mechanisms of action of the drugs used to treat this illness. The aim of this article is to provide a review of the major findings related to the application of molecular imaging techniques that have furthered schizophrenia research. This article focuses specifically on neuroreceptor imaging studies with PET and SPECT. After providing a brief overview of neuroreceptor imaging methodology, we consider relevant findings from studies of receptor availability, and dopamine synthesis and release. Results are discussed in the context of current hypotheses regarding neurochemical alterations in the illness. We then selectively review pharmacological occupancy studies and the role of neuroreceptor imaging in drug development for schizophrenia.

Pharmacological characterization of senktide-induced tail whips

The tachykinin NK(3) receptor shows promise as a novel target for antipsychotics, but knowledge of downstream activity following tachykinin NK(3) receptor activation is lacking. To determine the practical utility of senktide-induced tail whips in mice as a tool for determining and characterizing downstream activity following tachykinin NK(3) receptor activation, mice were injected with 0.05 nmol of senktide i.c.v. and the number of tail whip bouts was counted for 20 min. Strain differences were observed, with NMRI mice showing a stronger tail whip response than C57Bl/6J mice. Tachykinin NK(3) receptor specificity was confirmed by the absence of the senktide-induced tail whip response in tachykinin NK(3) receptor knockout mice. Effects of tachykinin receptor pharmacological agents were tested by pretreatment with tachykinin NK(3) receptor antagonists (SB222200, talnetant and osanetant), which attenuated senktide-induced tail whips, and the tachykinin NK(1) receptor antagonist MK869, which had no effect on senktide-induced tail whips. Pharmacological interactions with other neurotransmitter systems were determined by pretreatment with dopamine D(1), D(2), and D(3) receptor antagonists, atypical antipsychotics, serotonin 5HT(1a) receptor antagonists, serotonin 5HT(2a/c) receptor antagonists, benzodiazepine and putative anxiolytics, antidepressants, and an anticholinergic. Senktide-induced tail whips were attenuated by dopamine D(2) receptor antagonists, atypical antipsychotics, serotonin 5HT(2a/c) antagonists, and benzodiazepine anxiolytics, but unaffected by drugs from other classes. Thus, the senktide-induced tail whip response is easily quantifiable, specific to the tachykinin NK(3) receptor, and provides valuable information on the downstream pharmacology of tachykinin NK(3) receptor activation.

Haplotype analysis confirms association of the serotonin transporter (5-HTT) gene with schizophrenia in the Han Chinese population

Serotonin transmission has long been suspected as being involved in the pathogenesis of schizophrenia. 5-HTT is a promising candidate gene for schizophrenia due to its critical role in regulating serotonin transmission and role in the mechanism of the atypical antipsychotic drugs. A common polymorphism STin2 VNTR in the 5-HTT gene has been extensively investigated in the genetic association studies, but the results are conflicting. Meanwhile, the SNPs of the 5-HTT gene have been much less explored. We therefore conducted a case-control study of the association between STin2 VNTR and three tagging SNPs in 5-HTT and schizophrenia in the Han Chinese population based on a cohort of 329 schizophrenic patients and 288 control subjects. No association was found in the single locus, but haplotype-based analyses revealed significant association between two haplotypes with schizophrenia even after Bonferroni correction (P=0.00000538 and 0.011).

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

Functional interrelations between nucleus raphé dorsalis and nucleus raphé medianus: a dual probe microdialysis study of glutamate-stimulated serotonin release

Dual-probe in vivo microdialysis was used to explore the relationships between the two midbrain raphé nuclei, raphé dorsalis (DRN) and raphé medianus (MRN). Infusion of the excitatory neurotransmitter glutamate (10 mM) into the dorsal raphé nucleus produced a large increase in the extracellular 5-HT (5-HT(ext)) in the dorsal raphé (1400% of control values) that was limited to the time of infusion. This was followed by a significant decrease in extracellular 5-HT below baseline levels that continued for the duration of the experiment (3 h). Extracellular 5-HT (5-HT(ext)) was also increased to 500% of control values in the median raphé nucleus following infusion of 10 mM glutamate (GLU) into the dorsal raphé nucleus. Infusion of the competitive NMDA receptor antagonist AP5 prior to and during infusion of GLU into the DRN resulted in a decrease in the response to GLU in the DRN and an antagonism of the increase of 5-HT(ext) in the MRN. Infusion of 10mM GLU into the lateral midbrain tegmentum, an area of the brain just lateral to the DRN, also increased 5-HT(ext) in the probe in the lateral midbrain tegmentum (900% of control) but did not alter 5-HT(ext) in the MRN. When glutamate was infused into the MRN, 5-HT(ext) was also increased to 1400% of control in a time course similar to that seen with infusion of GLU into the DRN. Infusion of glutamate into the MRN, however, did not alter the 5-HT(ext) in the DRN. These data suggest a serotonergic innervation of the median raphé nucleus by the dorsal raphé nucleus. A reciprocal innervation from the median raphé to the dorsal raphé is not mediated by glutamate, does not appear to be serotonergic, and does not regulate extracellular serotonin in the dorsal raphé.

Schizophrenia, "Just the Facts": what we know in 2008 part 1: overview

For every disorder, there is a set of established findings and accepted constructs upon which further understanding is built. The concept of schizophrenia as a disease entity has been with us for a little more than a century, although descriptions resembling this condition predate this conceptualization. In 1988, for the inaugural issue of Schizophrenia Research, at the invitation of the founding editors, a senior researcher, since deceased (RJ Wyatt) published a summary of generally accepted ideas about the disorder, which he termed "the facts" of schizophrenia. Ten years later, in conjunction with two of the authors (MSK, RT), he compiled a more extensive set of "facts" for the purpose of evaluating conceptual models or theoretical constructs developed to understand the nature of schizophrenia. On the 20th anniversary of this journal, we update and substantially expand our effort to periodically summarize the current body of information about schizophrenia. We compile a body of seventy-seven representative major findings and group them in terms of their specific relevance to schizophrenia -- etiologies, pathophysiology, clinical manifestations, and treatments. We rate each such "fact" on a 0-3 scale for measures of reproducibility, whether primary to schizophrenia, and durability over time. We also pose one or more critical questions with reference to each "fact", answers to which might help better elucidate the meaning of that finding for our understanding of schizophrenia. We intend to follow this paper with the submission to the journal of a series of topic-specific articles, critically reviewing the evidence.