Tryptophan hydroxylase (TrpH), the rate limiting enzyme in the synthesis of 5-hydroxytryptamine (5-HT) in CNS, converts tryptophan to 5-hydroxytryptophan (5-HTP) in a reaction that also requires molecular oxygen and reduced pterin cofactor. The project focusses on factors that may regulate the activity of this enzyme and hence 5-HT synthesis in brain in vivo with particular emphasis on the contribution that changes in its kinetic behaviour may make. 5-HT neuronal impulse flow increases both the hydroxylation of tryptophan in vivo, and the in vitro activity of cortical TrpH and an analysis of the effects of neuronal firing on the kinetic properties of the enzyme is thus a major focus of the project. These studies will be extended to other 5-HT projection areas, particularly spinal cord where evidence exists that regulatory properties of TrpH may be different. The effects on enzyme activity of blockade of 5-HT impulse flow will also be examined. Comparisons will be made of the properties of enzyme activated in vivo with those of enzyme activated in vitro under phosphorylating conditions. The possibility will also be explored that administration into the 5-HT neuronal nuclei of other substances (largely peptides) that may serve a transmitter/modulator role there can influence enzyme activity in the terminal projections of 5-HT neurons e.g. through effects on 5-HT neuronal activity. Finally regulation of enzyme activity in terminal regions versus the cell body and between different terminal fields will be compared. This study is prompted by evidence that various peptides can alter enzyme activity in slices or synaptosomes presumably as a result of direct receptor mediated interactions rather than via effects on 5-HT neuronal firing rate. Enzyme activity will be measured in vitro under subsaturating concentrations of artificial reduced pterin cofactor, 6-methyl-5,6,7,8-tetrahydropterin (6MPH4) or the natural cofactor tetrahydrobiopterin and also in vivo, by the accumulation of 5-HTP in the presence of a decarboxylase inhibitor in order to determine whether increases in activity detected in vitro are expressed in vivo. The 5-HTP formed in each case will be isolated by high performance liquid chromatography (HPLC) and quantitated by electrochemical detection (EC). This study should enhance our understanding of the regulation of 5-HT synthesis, a central monoamine transmitter, which is known to be involved in modulating or regulating a wide variety of functions including mood or affect.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS014090-05
Application #
3395390
Study Section
Neurological Sciences Subcommittee 1 (NLS)
Project Start
1979-12-01
Project End
1986-11-30
Budget Start
1984-12-01
Budget End
1985-11-30
Support Year
5
Fiscal Year
1985
Total Cost
Indirect Cost
Name
Virginia Commonwealth University
Department
Type
Overall Medical
DUNS #
City
Richmond
State
VA
Country
United States
Zip Code
23298
Corley, Karl C; Phan, Tam-Hao; Daugherty, Wilson P et al. (2002) Stress-induced activation of median raphe serotonergic neurons in rats is potentiated by the neurotensin antagonist, SR 48692. Neurosci Lett 319:1-4
Dilts, R P; Novitzki, M R; Phan, T H et al. (1996) Neurotensin inhibits the activation of midbrain serotonergic neurons produced by random inescapable sound. Brain Res 742:294-8
Dilts, R P; Boadle-Biber, M C (1995) Differential activation of the 5-hydroxytryptamine-containing neurons of the midbrain raphe of the rat in response to randomly presented inescapable sound. Neurosci Lett 199:78-80
Singh, V B; Kalimi, M; Phan, T H et al. (1994) Intracranial dehydroepiandrosterone blocks the activation of tryptophan hydroxylase in response to acute sound stress. Mol Cell Neurosci 5:176-81
Singh, V B; Corley, K C; Krieg, R J et al. (1994) Sound stress activation of tryptophan hydroxylase blocked by hypophysectomy and intracranial RU 38486. Eur J Pharmacol 256:177-84
Boadle-Biber, M C (1993) Regulation of serotonin synthesis. Prog Biophys Mol Biol 60:1-15
Boadle-Biber, M C; Singh, V B; Corley, K C et al. (1993) Evidence that corticotropin-releasing factor within the extended amygdala mediates the activation of tryptophan hydroxylase produced by sound stress in the rat. Brain Res 628:105-14
Corley, K C; Singh, V B; Phan, T H et al. (1992) Effect of gepirone on increases in tryptophan hydroxylase in response to sound stress. Eur J Pharmacol 213:417-25
Singh, V B; Hao-Phan, T; Corley, K C et al. (1992) Increase in cortical and midbrain tryptophan hydroxylase activity by intracerebroventricular administration of corticotropin releasing factor: block by adrenalectomy, by RU 38486 and by bilateral lesions to the central nucleus of the amygdala. Neurochem Int 20:81-92
Singh, V B; Onaivi, E S; Phan, T H et al. (1990) The increases in rat cortical and midbrain tryptophan hydroxylase activity in response to acute or repeated sound stress are blocked by bilateral lesions to the central nucleus of the amygdala. Brain Res 530:49-53

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