Motor nerve dysfunction in delayed DFP neuropathy

A localized neuropathy was produced in cats by an intra-arterial injection of diisopropyl fluorophosphate (DFP). The soleus nerve-muscle system, and especially the motor nerve endings, were functionally evaluated during the following 1–56 days. Nerve conduction velocities remained unchanged. At 24–72 hr after DFP, the indirectly evoked but not directly evoked contractile strength of muscle fell to about 20% of normal; recovery had commenced by the 7th day. Motor nerve ending function was assessed by measurement of the neurogenic post-tetanic potentiation (PTP) of soleus muscle. PTP was initially unaffected, even though indirectly evoked contractile strength was severely attenuated. However, at day 7, a PTP reduction was evident and reached a loss of 62% on day 21. The underlying post-tetanic repetition (PTR) was lost at this time. Recovery of PTP and PTR occured over the next 5 weeks. These findings indicate that there is an initial functional damage of nerve endings in delayed organophosphate neuropathy. The pattern of nerve ending impairment suggests a trophic deprivation.