Muscle spindle function in organophosphorus neuropathy

Abstract

The contribution of muscle spindle dysfunction to the neurological signs odelayed organophophorus neuropathy was investigated in the hindlimbs of cats intraf arterially injected with 2 mg/kg of diisopropylfluorophosphate (DFP). In this model of a delayed peripheral neuropathy, the animals exhibit a peculiar high-step gait and a sluggish response to noxious stimuli. These signs initially appear 14 days and are maximum 21–28 days after DFP administration. The position sensitives of secondary but not primary soleus muscle spindles were depressed at 14 days after DFP.At 21 days after DFP, both primary and secondary endings had attenuated position sensitivities and significantly elevated thresholds. Spindle functions was normal at 56 days after DFP exposure. The onset, peak and recovery of soleus muscle spindle dysfunction corresponded to those in α-motor axons, indicating the mixed sensory motor nature of organophophorus neuropathy. Thus impairment of both sensory and motor functions contributes to the neurological signs of this neuropathy.