An excitatory action of 5-Hydroxytryptamine on sympathetic preganglionic neurones

Summary Preganglionic neurones in the fourth thoracic segment of anaesthetized cats fired spontaneously at a rate of about 2/sec. The effects of micro-electrophoretic administration of 5-hydroxytryptamine, noradrenaline, acetylcholine and DL-homocysteic acid on this spontaneous firing were determined. Many cells were excited by 5-hydroxytryptamine (5HT) and DL-homocysteic acid (DLH), a few were depressed by noradrenaline (NAdr), but acetylcholine (ACh) was inactive. The data are consistent with the view that 5HT and NAdr may function as excitatory and inhibitory transmitters which are released from the terminals of descending pathways in the spinal cord.National Science Foundation Postdoctoral Fellow, Riker Fellow.