Localization of a defect in hypothalamic dopaminergic neurons of the aged brain that results in impaired PKA-dependent activation of tyrosine hydroxylase

N. Aguila-Mansilla, W. Kedzierski, J. C. Porter

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Abstract

Using an in vitro incubation system, the role of the cyclic AMP-dependent protein kinase A (PKA) pathway in the regulation of the in situ activity of tyrosine hydroxylase (TH) was studied in the hypothalamuses of young and aged ovariectomized rats. Hypothalamic tissue was incubated for 60 min in medium containing 3-hydroxybenzylhydrazine dihydrochloride, a dihydroxyphenylalanine (DOPA) decarboxylase inhibitor, and various agents that modify the activity of the PKA pathway. At the end of the incubation, the tissue was homogenized and analyzed for DOPA and TH mass. The in situ molar activity of TH was expressed as the moles of DOPA accumulating in the tissue per mole of TH per hour. Forskolin, an activator of adenylyl cyclase and the cyclic AMP agonist, (Sp)-cyclic adenosine 3',5'-monophosphothioate, significantly (P < .01) increased the in situ molar activity of TH in the hypothalamic dopaminergic (DAergic) neurons of both young and aged rats. Theophylline, a phosphodiesterase inhibitor, did not affect the TH molar activity in the hypothalamuses of aged animals but did significantly (P < .001) increase its activity in those of young rats. When vasoactive intestinal peptide was evaluated, the TH molar activity was significantly (P < .005) increased in the hypothalamuses of young rats but not in those of aged rats. It was suggested that the deficiency of DA secretion by hypothalamic DAergic neurons of aged rats may be the result of insufficient activation of PKA caused by failure of transduction of an extracellular signal to activate adenylyl cyclase and produce cyclic AMP.

Original languageEnglish (US)
Pages (from-to)171-175
Number of pages5
JournalJournal of Pharmacology and Experimental Therapeutics
Volume267
Issue number1
StatePublished - 1993

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Dopaminergic Neurons
Tyrosine 3-Monooxygenase
Cyclic AMP-Dependent Protein Kinases
Brain
Dihydroxyphenylalanine
Adenylyl Cyclases
Cyclic AMP
Phosphodiesterase Inhibitors
Vasoactive Intestinal Peptide
Colforsin
Theophylline
Adenosine
Signal Transduction

ASJC Scopus subject areas

  • Pharmacology

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Localization of a defect in hypothalamic dopaminergic neurons of the aged brain that results in impaired PKA-dependent activation of tyrosine hydroxylase. / Aguila-Mansilla, N.; Kedzierski, W.; Porter, J. C.

In: Journal of Pharmacology and Experimental Therapeutics, Vol. 267, No. 1, 1993, p. 171-175.

Research output: Contribution to journalArticle

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