Conduction block and functional denervation caused by Tullidora ( Karwinskia humboldtiana)

Abstract

Cats treated with ether extracts from the fruit of Tullidora ( Karwinskia humboldtiana) developed paralysis of the hind limbs starting 3 to 6 weeks after a single oral dose. The purpose of these experiments was to elucidate the mechanisms underlying the paralysis. The medial gastrocnemius and soleus muscles of paralyzed hind limbs showed mechanical properties similar to those observed after denervation. When motor nerves of treated animals were stimulated close to their muscles, the twitch tensions were as large as the twitch tension produced by direct stimulation of the muscles. In contrast, the twitches elicited by stimulation of the ventral roots were considerably reduced. These findings suggested conduction block in peripheral nerves. The postulated conduction block was investigated in cutaneous (sural) and motor (medial gastrocnemius) nerves. Potentials elicited in the sural nerve decreased in amplitude and area as the distance between stimulating and recording electrodes increased. This potential reduction was more prominent toward the periphery. The action potentials produced in the medial gastrocnemius nerve by ventral root stimulation were also reduced compared to control animals. Electron microscopy revealed intense demyelination in motor nerves and increased density of neurofilaments. Demyelination was not observed in the ventral roots. It is postulated that the observed conduction block is a consequence of demyelination.