Effects of 2,5-hexanedione on deefferented muscle spindle position sensitivity

2,5-Hexanedione (HD) produces a neurofilamentous axonpathy in humans and experimental animals. The present study was carried out to determine the time course of the effects of HD on muscle spindle position sensitivity to permit comparisons with similar effects of other toxicants which produce a neurofilamentous axonopathy. Cats were administered HD either via their drinking water or via osmotic minipumps. Muscle spindle position sensitivity was tested after a total HD dose of 2.43 or 4.85 g/kg via the drinking water or 0.96, 1.91, or 4.78 g/kg via an osmotic minipump. The position sensitivities of both primary and secondary endings were depressed regardless of the route of administration. However, secondary muscle spindle afferents in the animals intoxicated with HD via the minipumps were affected to a greater extent than primary muscle spindle afferents at all doses studied. These data show that HD alters muscle spindle function and lends support to the suggestion that the largest diameter fibers are not the most vulnerable to HD.