Responses of the Afferent Nerve from the Medial Gastrocnemius Muscle to the Intra-arterial Algesic Substances in the Cat

Abstract

The afferent nerve fibers from the medial gastrocnemius muscle in the cat were studied and classified according to their conduction velocity and their responses to intraarterial injection of KCl and lactic acid. Among a total of 513 units identified, 101 units were classified as group III and IV. Eighty-six units were tested for algesic substances. In 39 units there were no responses to either KCl or lactic acid. In 30 units which showed increased responses to KCl injections, responses to lactic acid were tested. Among them 11 showed an increase, four showed a decrease, and 15 showed no response. Among five units which showed a decreasing response to KCl, two showed an increased response to lactic acid, two a decreased response, and one showed no response. Eight units showed varying responses to KCI. Among them, four showed an increase, one showed a decrease, and one showed a decrease followed by an increased response to lactic acid. It was concluded from the above results that activation of the muscular afferent nerve fibers by intra-arterial injection of lactic acid, which could be produced during vigorous muscle contraction, might be related to muscle pain.