title: Melatonin increases the in situ activity of tyrosine hydroxylase in the mediobasal hypothalamus of male Syrian hamsters.
abstract: The effects of daily late afternoon injections of melatonin on the in situ activity of tyrosine hydroxylase (TH) were examined in the median eminence/arcuate region of the mediobasal hypothalamus (MBH) and the neurointermediate lobe (NIL) of the male Syrian hamster. TH activity was determined in tissue extracts by measuring the accumulation of L-DOPA following administration of the dopa decarboxylase inhibitor, NSD-1015. After 9 weeks of melatonin treatment, highly significant increases in the activity of MBH TH were demonstrated over a 24 hr period, compared to saline-treated controls. Melatonin-induced elevations in TH occurred concomitantly with decreases in tuberoinfundibular dopamine (TIDA) and tuberohypophyseal dopamine (THDA) concentrations. Similar findings were observed in castrated hamsters, indicating that the melatonin-induced increase in TH was not secondary to melatonin-induced changes in circulating levels of gonadal hormones. These data led to the interpretation that melatonin treatment elevated TIDA synthesis either through a direct action on the arcuate nuclei or on neurons impinging on these nuclei.
authors: Department of Anatomy, University of Manitoba, Winnipeg, Canada.
authors: N A
authors: NA
authors: Alexiuk
authors: M
authors: M
authors: Uddin
authors: J
authors: J
authors: Vriend
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000201:enzymology*; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D006224:Cricetinae; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006834:Hydrazines / Q000494:pharmacology; D007033:Hypothalamus, Middle / Q000187:drug effects / Q000378:metabolism*; D007980:Levodopa / Q000378:metabolism; D008297:Male; D008473:Median Eminence / Q000201:enzymology*; D008550:Melatonin / Q000494:pharmacology*; D008647:Mesocricetus; D012016:Reference Values; D013997:Time Factors; D014446:Tyrosine 3-Monooxygenase / Q000494:pharmacology*
chemical_list: D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D004791:Enzyme Inhibitors; D006834:Hydrazines; D007980:Levodopa; C004297:3-hydroxybenzylhydrazine; D014446:Tyrosine 3-Monooxygenase; D008550:Melatonin