TULLIDORA (KARWINSKIA HUMBOLDTIANA) TOXIN MAINLY AFFECTS FAST CONDUCTING AXONS

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Abstract
Cats were given a single oral dose of ether extracts from tullidora (K. humboldtiana) fruit which contains an identified neurotoxin. Acute experiments were performed 4-7 wk after toxin administration when flaccid limb paralysis was evident. Normal cats were used as controls. The medial gastrocnemius, the soleus and the sural nerves were electrically stimulated and the unitary potentials evoked by the stimuli were extracellularly recorded from spinal root filaments to measure the conduction velocity of single fibers. In control cats, the average conduction velocity .**GRAPHIC**. was greater in medial gastrocnemius motor fibers than in the afferent ones of the same nerve and the soleus motor axons, whereas in the sural nerve .**GRAPHIC**. was less than in these cases. The .**GRAPHIC**. values and the proportion of fast conducting fibers (> 80 m/s) in each nerve were directly related (r = 0.99). In treated cats, .**GRAPHIC**. diminished in all the nerves studied, but the conduction velocity was further reduced in the faster fibers. The motor division of the medial gastrocnemius nerve, normally composed of a high proportion (57%) of fast fibers, was more affected by tullidora; the sural nerve, which has the lowest proportion (0.7%) of these type of fibers, was the less affected. The preferential involvement of motor nerves in the experimental tullidora (buckthorn) neuropathy, as well as the preservation of somatic sensation in quadriplegic children accidentally poisoned with tullidora, are related to the distribution of axonal diameters in peripheral nerves.