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Marsden CA, Curzon G. 
“Effects of Altered Brain 5-Hydroxytryptaminergic Activity on Brain Tryptophan, 5-Hydroxytryptamine and 5-Hydroxyindoleacetic Acid”. 
Neuropharmacology. 1976;15(II):703-08.
Abstract
The influence of serotonergic activity on tryptophan (TR), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) brain levels was studied. Methods The dorsal raphe nucleus (RN) of male Sprague-Dawley rats (220-240 g) was stimulated at 10 pulse/sec for 60 min. using a 6 V stimulus of 2 msec duration. A further group (180-200 g) were transferred to a chamber at 40 + 3 for 60 min. Before transfer, some rats were given i.p. LSD (Sandoz) at 500 mcg/kg or i.p. probenecid (Merck-USA) at 200 mg/kg (15 min before transfer). Electrolytic lesions were placed in both dorsal and median RN of some animals (220-240 g), under ether anesthesia, using a 2.0 mA currest for 20 sec. Plasma and brain tyrosine, TR, 5-HT, and 5 -HIAA were determined. Results RN stimulation increased 5-HIAA in the hypothalamus, striatum, midbrain, and cortex but not the hippocampus. % Increases were greatest in the hypothalmus and striatum. 5-HT fell slightly in the midbrain and cortex but other regions were unaffected. TR increased significantly in the hypothalamus only (less than 5-HIAA). - High temperature markedly increased brain TR (199%), moderately increased 5-HIAA (29%) but did not alter 5-HT. Plasma total and free TR were both increased 110%. Tyrosine values also increased. LSD did not diminish the rise in plasma and brain TR. Temperatureinduced 5-HIAA increase was unaffected by probenecid but the increase of TR" was much less marked. Raphe lesions markedly reduced brain 5-HT (-66%) and 5-HIAA (-78%) at day 8 but brain and plasma TR were unaffected. Conclusion - Brain TR changes probably do not regulate 5-HT synthesis after alteration of 5-hydroxytryptaminergic activity.
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