Alpha 2-adrenoceptor modulation of 5-HT biosynthesis in the rat brain.
The purpose of the present study is to clarify the modulation of the biosynthesis of serotonin (5-HT) via the alpha 2-adrenoceptors in the brain. For this purpose, 5-hydroxytryptophan (5-HTP) accumulation was determined using an HPLC-ECD system in the presence of the inhibition of aromatic L-amino acid decarboxylase. Administration of alpha 2-adrenoceptor agonist, clonidine, produced a reduction of the in vivo 5-HTP accumulation in both the rat hippocampus and dorsal raphe nucleus. In addition, alpha 2-adrenoceptor antagonist, idazoxan, increased the 5-HTP accumulation in both the hippocampus and the dorsal raphe nucleus. In rats with catecholaminergic neurons denervated by pretreatment with 6-hydroxydopamine, clonidine failed to produce a reduction of 5-HTP accumulation in the dorsal raphe nucleus. On the other hand, hippocampal 5-HTP accumulation was decreased significantly. Brain tryptophan levels were unaffected by either clonidine or idazoxan. These results suggest that alpha 2-adrenoceptors might modulate serotonin biosynthesis and this modulation might be related to the neuroanatomical differences in the rat brain.
First Department of Pharmacology, Hokkaido University School of Medicine, Sapporo, Japan.
M
M
Yoshioka
M
M
Matsumoto
H
H
Togashi
C B
CB
Smith
H
H
Saito
D006916:5-Hydroxytryptophan / Q000378:metabolism; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects*; D003000:Clonidine / Q000494:pharmacology; D004146:Dioxanes / Q000494:pharmacology; D019329:Idazoxan; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D016627:Oxidopamine / Q000494:pharmacology; D011903:Raphe Nuclei / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012701:Serotonin / Q000096:biosynthesis*; D014364:Tryptophan / Q000378:metabolism
D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D011942:Receptors, Adrenergic, alpha; D012701:Serotonin; D014364:Tryptophan; D016627:Oxidopamine; D006916:5-Hydroxytryptophan; D003000:Clonidine; D009638:Norepinephrine; D019329:Idazoxan