The response of individual sympathetic preganglionic neurones to microelectrophoretically applied endogenous monoamines.

In anaesthetized cats the effect on antidromically identified single sympathetic preganglionic neurones (SPN) in the third thoracic segment of microelectrophoretically applied monoamines, amino acids and acetyl choline was examined. 5-Hydroxytryptamine (5-HT) creatinine sulphate and bimaleate excited a majority of SPN. A few cells were inhibited by 5-HT creatinine sulphate. These effects were observed on spontaneously active SPN (cardiac and non-cardiac type) and on silent SPN. Noradrenaline, adrenaline and dopamine inhibited all 'types' of SPN, including spontaneously active neurons, silent neurones activated by glutamate or DL-homocysteic acid and neurones synaptically activated by electrically stimulating a brain stem excitatory region. Acetyl choline had no effect on different types of SPN.