Tryptophan hydroxylase. Purification and some properties of the enzyme from rabbit hindbrain. (17/424)

Tryptophan hydroxylase from rabbit hindbrain has been extensively purified. It is estimated that the enzyme is between 85 and 90% pure and has a molecular weight of 230, 000. Sodium dodecyl sulfate gel electrophoresis shows that the enzyme is composed of two subunits very close in molecular weight (57, 500 and 60, 900). The substrate specificity and the reaction stoichiometry catalyzed by the enzyme in the presence of 6, 7-dimethyltetrahydropterin, 6-methyltetrahydropterin, and tetrahydrobiopterin have been determined. The effect of some natural occurring phospholipids on the purified enzyme was investigated.  (+info)

Biological activity of the rolB-like 5' end of the A4-orf8 gene from the Agrobacterium rhizogenes TL-DNA. (18/424)

The iaaM gene from different plant-associated bacteria encodes a tryptophan monooxygenase (IaaM) that catalyzes the synthesis of indole-3-acetamide (IAM), a precursor of indole-3-acetic acid (IAA). Unlike the IaaM proteins from other bacteria, Agrobacterium spp. T-DNA-encoded IaaM proteins carry a 200 amino acid N-terminal extension with low homology to various members of the RolB protein family. This family is composed of 18 highly divergent T-DNA-encoded proteins, the basic functions of which are still largely undetermined. Deletion of the 5' rolB-like extension of the iaaM gene from Agrobacterium tumefaciens strain Ach5 did not lead to a reduction in IAM synthesis in plants. When expressed in tobacco, the rolB-like fragment did not affect growth or morphology. An iaaM homolog (A4-orf8) from the TL-DNA of Agrobacterium rhizogenes strain A4 also was investigated. Neither the full-size A4-orf8 gene nor the 5'-truncated form induced detectable IAM synthesis. Plants expressing the rolB-like part of the A4-orf8 gene, however, were dwarfed and mottled to various extents and synthesized abnormally high amounts of glucose, fructose, sucrose, and starch.  (+info)

The neurobiology and genetics of suicide and attempted suicide: a focus on the serotonergic system. (19/424)

Numerous abnormalities have been found in the serotonergic system in suicide attempters and completers. There is considerable evidence that the serotonergic system is partly under genetic control and that as yet unknown genetic factors mediate the risk for suicidal behavior independently of the genetic factors responsible for the heritability of major psychiatric conditions associated with suicide. An argument is made that there is a relationship of genetic variants to intermediate phenotypes, such as impulsivity, psychomotor change, pathological aggression and biological abnormalities including specific gene products. A variety of biological indices have been generated by new approaches using postmortem tissue and in vivo imaging that will provide a rich substrate for further genetic studies.  (+info)

Autoregulation of cell-specific MAP kinase control of the tryptophan hydroxylase promoter. (20/424)

The neurotransmitter serotonin controls a wide range of biological systems, including its own synthesis and release. As the rate-limiting enzyme in serotonin biosynthesis, tryptophan hydroxylase (TPH) is a potential target for this autoregulation. Using the serotonergic neuron-like CA77 cell line, we have demonstrated that treatment with a 5-hydroxytryptamine autoreceptor agonist, CGS 12066A, can lower TPH mRNA levels and promoter activity. We reasoned that this repression might involve inhibition of MAP kinases, since 5-HT1 receptors can increase mitogen-activated protein (MAP) kinase phosphatase levels. To test this hypothesis, we first showed that the TPH promoter can be activated 20-fold by mitogen-activated extracellular-signal regulated kinase kinase kinase (MEKK), an activator of MAP kinases. This activation was then blocked by CGS 12066A. The maximal MAP kinase and CGS repression regulatory region was mapped to between -149 and -45 base pairs upstream of the transcription start site. The activation by MEKK appears to be cell-specific, because MEKK did not activate the TPH promoter in nonneuronal cell lines. At least part, but not all, of the MAP kinase responsiveness was mapped to an inverted CCAAT box that binds the transcription factor NF-Y. These data suggest a model for the autoregulation of serotonin biosynthesis by repression of MAP kinase stimulation of the TPH promoter.  (+info)

Family-based association studies of monoaminergic gene polymorphisms among North Indians with schizophrenia. (21/424)

Associations between schizophrenia and four candidate genes were tested among Indian patients with schizophrenia and their parents (DSM-IV criteria, n = 179 families). Polymorphisms within the genes encoding the serotonin 2A receptor (HT2A), tryptophan hydroxylase (TPH), catechol-O-methyl transferase (COMT) and dopamine transporter (DAT) were thus investigated. Two polymorphisms each were analyzed at HT2A and TPH, enabling haplotype-based analyses using the transmission disequilibrium test (TDT) for these genes. No significant associations were detected. Pooled analysis of samples like ours may be necessary to definitively exclude putative allelic associations at these loci.  (+info)

Suicide attempts and the tryptophan hydroxylase gene. (22/424)

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme of serotonin synthesis. In this case-control study, we investigated whether the TPH gene was a susceptibility factor for suicidal behavior. Seven polymorphisms spanning the entire gene were studied in a case-control study including 231 individuals who had attempted suicide and 281 controls. Significant associations were found between variants in introns 7, 8 and 9 (chi(2) = 11.2, df = 1, P< 0.0008 for the allele distribution; these loci are in complete linkage disequilibrium) and in the 3' noncoding region (chi(2) = 30.94, P = 0.0014) and suicide attempt. The association was strongest for subjects who had attempted suicide by violent means and who had a history of major depression. No significant association was observed between suicide attempts and polymorphisms in the promoter, intron 1 and intron 3. The results presented here, and those of previous studies, suggest that a genetic variant of the 3' part of the TPH gene may be a susceptibility factor for a phenotype combining suicidal behavior, mood disorder and impulsive aggression.  (+info)

Acidosis-stimulated neurons of the medullary raphe are serotonergic. (23/424)

Neurons of the medullary raphe project widely to respiratory and autonomic nuclei and contain co-localized serotonin, thyrotropin-releasing hormone (TRH), and substance P, three neurotransmitters known to stimulate ventilation. Some medullary raphe neurons are highly sensitive to pH and CO(2) and have been proposed to be central chemoreceptors. Here it was determined whether these chemosensitive neurons are serotonergic. Cells were microdissected from the rat medullary raphe and maintained in primary cell culture for 13-70 days. Immunoreactivity for serotonin, substance P, and TRH was present in these cultures. All acidosis-stimulated neurons (n = 22) were immunoreactive for tryptophan hydroxylase (TpOH-IR), the rate-limiting enzyme for serotonin biosynthesis, whereas all acidosis-inhibited neurons (n = 16) were TpOH-immunonegative. The majority of TpOH-IR medullary raphe neurons (73%) were stimulated by acidosis. The electrophysiological properties of TpOH-IR neurons in culture were similar to those previously reported for serotonergic neurons in vivo and in brain slices. These properties included wide action potentials (4.55 +/- 0.5 ms) with a low variability of the interspike interval, a postspike afterhyperpolarization (AHP) that reversed 25 mV more positive than the Nernst potential for K(+), prominent A current, spike frequency adaptation and a prolonged AHP after a depolarizing pulse. Thus the intrinsic cellular properties of serotonergic neurons were preserved in cell culture, indicating that the results obtained using this in vitro approach are relevant to serotonergic neurons in vivo. These results demonstrate that acidosis-stimulated neurons of the medullary raphe contain serotonin. We propose that serotonergic neurons initiate a homeostatic response to changes in blood CO(2) that includes increased ventilation and modulation of autonomic function.  (+info)

Functional implications of neurotransmitter expression during axonal regeneration: serotonin, but not peptides, auto-regulate axon growth of an identified central neuron. (24/424)

We studied the regenerative properties of one of two electrically coupled molluscan neurons, the serotonergic cerebral giant cells (CGCs) of Lymnaea stagnalis, after axotomy. The CGCs play a crucial role in feeding behavior, and when both cells are disconnected from their target neurons, animals no longer feed. When one CGC was permanently disconnected from its targets and the other was reversibly damaged by a nerve crush, the latter one regenerated over a period of 2 weeks to reform functional synapses with specific target neurons. At the same time, recovery of the feeding behavior was observed. After the crush, neuropeptide gene expression in the CGC was downregulated to approximately 50%. Serotonin synthesis, on the other hand, remained unaffected, suggesting that serotonin might have an active role in regeneration. In primary neuron culture, CGCs failed to extend neurites in the presence of serotonin; in cells that extended neurites in the absence of serotonin, focally applied serotonin, but not neuropeptides, induced growth cone collapse. Using serotonin-sensitive sniffer cells, we show that CGC neurites and growth cones release serotonin in culture. Finally, both the spontaneous and stimulation-induced release of serotonin from CGCs in culture resulted in growth cone collapse responses that could be blocked by the serotonin receptor antagonist methysergide. Our data suggest that auto-released serotonin is inhibitory to CGC neurite outgrowth in vitro. During regeneration in vivo, serotonin release might fine-tune axon guidance and branching by inducing local collapse responses in extending neurites.  (+info)