Synthesis of Serotonin by a Second Tryptophan Hydroxylase Isoform

The present study on rat examined the role of galanin receptor subtypes in regulation of depression-like behavior as well as potential molecular mechanisms involved in the locus coeruleus (LC) and dorsal raphe (DR). The effect of intracerebroventricular (i.c.v.) infusion of galanin or galanin receptor GalR1-and GalR2-selective ligands was studied in the forced swim test, followed by quantitative in situ hybridization studies. Naive control, non-treated (swim control), saline-and fluoxetine-treated rats were used as controls in the behavioral and in situ hybridization studies. Subchronic treatment with fluoxetine reduced immobility and climbing time. Intracerebroventricular infusion of galanin, the GalR1 agonist M617 or the GalR2 antagonist M871 increased, while the GalR2(R3) agonist AR-M1896 decreased, immobility time compared to the aCSF-treated animals. Galanin also decreased the time of climbing. Galanin mRNA levels were upregulated by the combination of injection + swim stress in the saline-and the fluoxetine-treated groups in the LC, but not in the DR. Also tyrosine hydroxylase levels in the LC were increased following injection + swim stress in the saline-and fluoxetine-treated rats. Tryptophan hydroxylase 2 and serotonin transporter mRNAs were not significantly affected by any treatment. 5-HT 1A mRNA levels were downregulated following i.c.v. galanin, M617 or AR-M1896 infusion. These results indicate a differential role of galanin receptor subtypes in depression-like behavior in rodents: GalR1 subtype may mediate 'prodepressive' and GalR2 'antidepressant' effects of galanin. Galanin has a role in behavioral adaptation to stressful events involving changes of molecules important for noradrenaline and/or serotonin transmission.

Section: In Situ Hybridizationmentioning

confidence: 99%

Differential Role of Galanin Receptors in the Regulation of Depression-Like Behavior and Monoamine/Stress-Related Genes at the Cell Body Level

Kuteeva

Wardi

Lundström

et al. 2008

“…mRNA was reverse transcribed into cDNA using SuperScript II Reverse Transcriptase (Invitrogen, Carlsbad, CA), which was subsequently used for PCR. TPH2-specific primers for PCR were generated from the published human cDNA sequence (Walther et al, 2003) available on Genbank (accession number: AY098914). The forward primer sequence was 5 0 -CTCTCCAAACTCTATCCCACT-3 0 and the reverse primer sequence was 5 0 -AGGCATCAAATCCCC AGA-3 0 .…”

Section: Tph2 Mrna In Depressed Suicidesmentioning

confidence: 99%

“…Until the recent discovery of TPH2 (Walther et al, 2003), quantitative studies of TPH gene expression in brain had been hampered by the seemingly almost undetectable level of transcript expression in the raphe (Austin and O'Donnell, 1999;Clark and Russo, 1997). These studies were unknowingly measuring peripheral TPH (TPH1), the non-neuronal isoform of the enzyme (Walther et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Neuronal Tryptophan Hydroxylase mRNA Expression in the Human Dorsal and Median Raphe Nuclei: Major Depression and Suicide

Bach-Mizrachi

Underwood

Kassir

et al. 2005

171

125

Major depressive disorder (MDD) and suicide are associated with deficient serotonergic neurotransmission. Tryptophan hydroxylase (TPH) is the rate-limiting biosynthetic enzyme for serotonin. Previously, we reported elevated levels of TPH protein in the dorsal raphe nucleus (DRN) of depressed suicides and now examine expression of neuronal TPH2 mRNA in a cohort of matched controls and depressed suicides (n ¼ 11 pairs). DRN TPH2 mRNA was measured by densitometric analysis of autoradiograms from in situ hybridization histochemistry experiments. TPH2 mRNA is confirmed as the raphe-specific isoform of TPH in human brain, and is expressed in neurons throughout the anteroposterior extent of the DRN and median raphe nucleus (MRN). TPH2 mRNA expression correlates with TPH protein distribution in the DRN, and has a negative correlation with age. In drug-free suicides, TPH2 expression is 33% higher in the DRN and 17% higher in the MRN as compared to matched nonpsychiatric controls. Higher levels of TPH2 mRNA were found throughout the entire extent of the rostrocaudal axis of the DRN, and were not specific to any single subnucleus. Higher TPH2 mRNA expression may explain more TPH protein observed in depressed suicides and reflect a homeostatic response to deficient brain serotonergic transmission.

“…TPH is the rate-limiting enzyme for the synthesis of serotonin and TPH protein is translated from two mRNA transcripts, TPH-1 and TPH-2, with a large degree of homology in the coding regions (Walther et al, 2003). Commercially available antibodies do not discriminate between the translated proteins and provide an indication of total TPH.…”

Section: Introductionmentioning

confidence: 99%

Effects of Ovarian Steroids and Raloxifene on Proteins that Synthesize, Transport, and Degrade Serotonin in the Raphe Region of Macaques

Smith

Henderson

Abell

et al. 2004

150

127

In the monkey dorsal raphe, we reported that 1-month (mo) of estrogen replacement, with or without progesterone supplementation for 14 days, significantly increased tryptophan hydroxylase-1 (TPH-1) mRNA; decreased serotonin reuptake transporter (SERT) mRNA and decreased monoamine oxidase (MAO)-A mRNA, but had no effect on MAO-B mRNA. Here, we questioned what effect would 1 or 5 mo of ovarian hormones or the selective estrogen receptor modulator (SERM), raloxifene, have on TPH protein and phosphorylation, and on protein expression of SERT, MAO-A or MAO-B? Raloxifene antagonizes estrogen in breast or uterus, but estrogen-like activities in the brain have been reported. Cytoplasmic and membrane extracts of the dorsal raphe region were processed for Western blotting. TPH, phosphoserine, SERT, MAO-A, and MAO-B were detected with specific antibodies. The optical densities of the signals were measured with NIH image and analyzed by ANOVA. Both 1 and 5 mo of estrogen, with or without progesterone, and 5 mo of raloxifene significantly increased TPH protein. Administration for 5 mo of estrogen plus progesterone and raloxifene also increased TPH phosphorylation. Estrogen, with or without progesterone, for 1 mo had no effect on SERT protein. However, 5 mo of estrogen and 5 mo of raloxifene increased SERT protein. Estrogen alone or combined with progesterone for 1 mo caused a significant reduction in MAO-A. Yet, after 5 mo of the same treatments, MAO-A was not different from spayed controls. Estrogen alone had no effect on MAO-B. However, the addition of progesterone significantly increased MAO-B. Raloxifene for 5 mo had no effect on MAO-A or MAO-B. Thus, to various extents, estrogen, progesterone, and raloxifene may increase serotonin production and transport. The expression of the degradative enzymes suggests a complex combination of gene transcription, post-transcriptional processing, and substrate feedback mechanisms.