Effect of ischemia on responses of group III and IV afferents to contraction

Abstract

Static contraction of the hindlimb muscles of cats reflexly increases cardiovascular function, an effect that is potentiated by occlusion of the arterial supply to the working muscles. Although group III and IV afferents are known to be stimulated by and to cause the reflex cardiovascular responses to static muscular contraction, little is known about the responses of these afferents to static contraction when the arterial supply to a working muscle is occluded. We therefore recorded the impulse activity of 24 group III afferents and 30 group IV afferents with endings in the triceps surae while we statically contracted this muscle group, both when the abdominal aorta was occluded and when it was patent. A chi 2 analysis revealed that ischemia increased the responses to static contractions of a significantly higher percentage of group IV afferents than group III afferents (46.7% vs. 12.5%, respectively; P less than 0.02). In addition, two patterns of responses to ischemic contraction were observed. The first pattern was displayed by afferents (n = 10) that were stimulated by nonischemic contraction but were stimulated more by ischemic contraction. The second pattern was displayed by afferents (n = 7) that were not stimulated by nonischemic contraction but were stimulated by ischemic contraction. We conclude that afferents displaying both patterns are likely to contribute to the reflex cardiovascular responses to ischemic contraction.

Effects of sustained stimulation on the excitability of motoneurons innervating paralyzed and control muscles

“…The similar reductions in motoneuron excitability observed here for both SCI and control subjects, even though the paralyzed muscles were fatigued to a much greater extent, also suggest that the F-wave changes are not directly mediated by feedback from small-diameter muscle afferents. Small-diameter afferents that are activated by the accumulation of muscle metabolites during fatigue (19) are considered to be responsible for the decreased H reflexes (14) and decreased motoneuron firing rates associated with fatigue in control muscles (30,41). In contrast, the present data are consistent with other studies that have shown that prolongation of the firing of small-diameter muscle afferents does not decrease motoneuron excitability when tested with short-latency reflex responses (42), responses to transmastoid stimulation during relaxation (34), or during voluntary contractions (Ref.…”

Reliability and Precision of Hip Proprioception Methods in Healthy Individuals

“…55 Some of the metabolites produced by muscle contraction stimulate group III and IV muscle afferents. 60,117,119 These afferents also have potent effect on both the dynamic and static γ motoneurons. 2,3 The γ motor neurons regulate activity in the spindle afferents and particularly these primary muscle spindle afferents have been suggested to be of great importance in the regulation of muscle stiffness and proprioception.…”

Exercise pressor reflex in health and diseases: Animal studies

“…1). Moreover, ischemia of the cat hindlimb potentiated the activity of both group III and IV muscle afferents in response to contraction 9) . This finding may lead us to speculate that metabolic byproducts of muscular contraction not only stimulate chemically sensitive muscle afferents but also sensitize mechanically sensitive afferents in response to contraction (Fig.…”

“…Direct recordings of afferent impulses arising from endings in skeletal muscle while the muscle was contracted in anesthetized cats were taken 8,9) . Continuous contraction of the gastrocnemius muscle to a level equal to or greater than that needed to elevate blood pressure reportedly stimulated 12 of 19 group III afferents and 13 of 19 group IV afferents 8) .…”