Enkephalinergic and Monoaminergic Control of Segmental Pathways from Flexor Reflex Afferents (FRA)
The influence of DOPA, μ- and δ-agonistic enkephalins and naloxone on short- and long latency FRA pathways and spinal rhythm generation was comparatively analyzed in high spinal cats. The results showed that DOPA and the enkephalins are synergistic with respect to a depression of short latency FRA pathways but antagonistic with respect to long latency FRA pathways and spinal rhythm generation which are facilitated by DOPA but depressed by the enkephalins. DOPA and naloxone, on the other hand, are synergistic with respect to a facilitation of long latency FRA pathways and rhythm generation, but antagonistic with respect to the short latency FRA pathways, which are depressed by DOPA but not by naloxone. Without prior DOPA application naloxone may induce high frequency (up to 5.9 cycles/sec) rhythmic activity. The results support the hypothesis that the long latency FRA pathways and their release by DOPA form the basis for a rhythmic motor activity and that spinal motor functions of the enkephalinergic systems go beyond a plain nocifensive engagement. They may subserve a mechanism which blocks the influence of the afferent FRA feed back and its spinal motor actions during the performance of specific movements.
KeywordsDepression Dopamine Morphine Clonidine Naloxone
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