EFFECT OF para-METHOXYPHENYLETHYLAMINE ON POLYSYNAPTIC PATHWAYS AND ON INTERNEURONS IN THE CAT LUMBAR SPINAL CORD

¹ Department of Anatomy, University of Texas Southwestern Medical School, Dallas, Dallas, Texas

The action of para-methoxyphenylethylamine (PMPEA) upon interneuronal pathways in the spinal cord was examined in spinal cats anesthetized with -chloralose. The polysynaptic facilitation or inhibition of the monosynaptic reflex produced by conditioning volleys in cutaneous afferent fibers was reduced by i.v. injections of PMPEA. as were the cord dorsum N wave, the negative dorsal root potential and the cord dorsum P wave. These findings suggest that PMPEA interferes with transmission in interneuronal pahtways in the spinal cord. The antivity of single interneurons was also depressed by PMPEA. However, the drug appearred not to depress the recurrent inhibitory pathway or the discharges of Renshaw cells. Thus. the action was not a generalized suppression of all types of interneuronal activity. Synaptic noise in motoneurons was often reduced by PMPEA, presumably secondarily to the depression of interneurons. Similarities between the actions of PMPEA and of agents which elevate the levels of monoamines in the spinal cord are pointed out. These findings support the concept that PMPEA exerts its effects at monoaminergic synapses.