Blocking interactions between brain-stem reflex facilitation and sympathetic reflex enhancement

¹ Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana

In cats anesthetized with Nembutal the integrity of the lumbar sympathetic chain is necessary for the maintenance of the normal basal height of the patellar reflex. The centrally activated sympathetic component of brain stem enhancement of the patellar reflex is consistently and totally abolished by either surgical or chemical interference with the sympathetic supply to the hind leg. Although the use of sympatholytic drugs does not affect (presumably) synaptic facilitation of reflex activity resulting from brain stem reticular stimulation, mechanical stimulation of either the lumbar sympathetic or splanchnic nerves will cause a temporary but marked depression of this facilitation. Simultaneous stimulation of either the lumbar sympathetic or splanchnic nerves completely and consistently blocks the facilitatory effects of brain stem reticular stimulation. Conversely, simultaneous stimulation of the brain stem reticular formation consistently and totally blocks the enchancement of the patellar reflex which results from stimulation of the peripheral lumbar sympathetic or splanchnic nerves. The former phenomenon does not result from any peripheral locus of interaction between adrenaline and the innervation of the quadriceps muscle. Cross perfusion experiments indicate that the locus of interaction may involve the brain stem reticular formation.