Changes in Impulse Discharge of Muscular Afferent Fiber Activated by Lactic Acid

Kim, Yong Ju; Jeong, Dong Won; Hong, Seung Kil

Abstract

In anesthetized cats the effects of lactate-activated muscle spindle upon the group Ia muscular afferent fibers were studied. Laminectomy was done from L5 to Sl spinal cord level. Extracellular recording was done at dorsal root to record the impulse discharge from group Ia muscular afferent fibers. 1) Muscle spindle of Gastrocnemius-Soleus muscle were activated by lactate injection and exhibited increased impulse discharge through group Ia muscular afferent fibers. 2) There was latency of 7-12 seconds before muscle spindle is activated by lactate injection. But the whole response was not dose related. 3) The response pattern after lactate injection was divided into three groups which were excitation, inhibition and inhibition with preceding excitation. 4) Some responses were similar to those of bradykinin, sympathetic stimulation (adrenaline injection) and succinylcholine injection. 5) It was suggested that muscle spindle has characteristics of polymodal receptor which has responses to not only mechanical stimulation but also chemical stimulation.