Dopamine produced from L-DOPA is degraded by endogenous monoamine oxidase in neurons of the dorsal raphe nucleus of the rat: an immunohistochemical study.
The aim of the present study is to examine by immunohistochemistry whether dopamine produced from L-DOPA in serotonin neurons of the rat brain is degraded by endogenous monoamine oxidase (MAO). In rats that received intraperitoneally L-DOPA plus a peripheral decarboxylase inhibitor, carbidopa, a cluster of dopamine-immunoreactive neurons was found in the dorsal raphe nucleus (DR). In L-DOPA/carbidopa-injected rats that were pretreated with an intraperitoneal injection of a MAO inhibitor, pargyline, when compared with the L-DOPA/carbidopa-injected rats without the pargyline pretreatment, neurons of the cluster of the DR became much darker in dopamine staining. The distribution of dopamine-stained neurons in the DR of these rats corresponded very closely to the previously reported distribution of serotonin-immunoreactive neurons of normal rats. In normal or only pargyline-injected rats, dopamine-stained neurons were scarcely observed in the DR. We previously showed that serotonin neurons of the rat DR were induced to contain dopamine by the injection of L-DOPA plus carbidopa. These findings suggest that the newly produced dopamine from L-DOPA in serotonin neurons of the rat DR is degraded by endogenous MAO.
Arai
R
R
Department of Anatomy, Fujita Health University School of Medicine, Aichi, Japan.
Karasawa
N
N
Nagatsu
I
I
D000818:Animals; D002230:Carbidopa / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D007980:Levodopa / Q000378:metabolism*; D008297:Male; D008995:Monoamine Oxidase / Q000378:metabolism*; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010293:Pargyline / Q000494:pharmacology; D011903:Raphe Nuclei / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D004791:Enzyme Inhibitors; D008996:Monoamine Oxidase Inhibitors; D007980:Levodopa; D010293:Pargyline; D008995:Monoamine Oxidase; D002230:Carbidopa; D004298:Dopamine