L-Dopa-Induced Hypotension: Depression of Spinal Sympathetic Neurons by Release of 5-Hydroxytryptamine
In studies designed to determine the respective functional roles of two bulbospinal monoaminergic pathways to sympathetic preganglionic neurons, both L-dopa and precursors of 5-HT depressed transmission through excitatory spinal reflex and bulbospinal sympathetic pathways. Transmission through spinal reflex pathways was secondarily enhanced after L-dopa. Pharmacological tests indicated mediation of these effects by monoamines. After antagonism or depletion of central 5-HT, L-dopa only enhanced transmission through both pathways. The results indicate that hypotension and other sympathoinhibitory effects of L-dopa are produced at the spinal level by release of 5-HT from terminals of bulbospinal 5-HT pathways that are inhibitory to sympathetic preganglionic neurons. The excitatory effects of L-dopa are apparently mediated by release of catecholamines from bulbospinal noradrenergic pathways that are excitatory.
KeywordsSympathetic Nerve Activity Depressant Effect Excitatory Effect Reflex Pathway Sympathetic Discharge
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