Specific enhancement of neuronal responses to catecholamine by p-tyramine

Extracellular recording and iontophoresis techniques were used to study the interactions of the trace amine, p-tyramine (p-TA) with putative neurotransmitters on single neurones in the cerebral cortex and caudate nucleus of the rat. p-TA, when applied with weak iontophoretic currents which did not result in any change in neuronal firing rate, caused a pronounced potentiation of depressant responses to iontophoretically applied dopamine (DA). Depressant responses of cortical neurones to noradrenaline were also markedly potentiated by weak background application of p-TA. This potentiating action of p-TA was related to the amount of the trace amine applied and was apparently specific for catecholamines, since depressant responses to 5-hydroxytryptamine and gamma-aminobutyric acid were unaffected. Excitatory responses to iontophoretically applied glutamate were also unaltered by weak application of p-TA. Excitatory responses to iontophoretically applied glutamate were also unaltered by weak applications of p-TA. Excitatory responses of most neurones to acetylcholine (ACh) were also unaffected by p-TA in the cortex and caudate nucleus. However, responses to ACh of a small number of cells in both brain areas were reduced in size during weak applications of p-TA. It is suggested that p-TA may act as a modulator of neurotransmission, particularly that mediated by DA in the central nervous system.