Nervous system responses of rats to subchronic inhalation of n-hexane and n-hexane + methyl-ethyl-ketone mixtures

The effects of long-term continuous and intermittent inhalation exposure to selected concentrations of n-hexane and mixtures of n-hexane and methyl-ethyl-ketone (MEK) on the nervous system of rats were investigated. Animals exposed continuously (24 h/d, 7 d/week) to 500 ppm n-hexane displayed complete hindlimb paralysis after 9 weeks. Histological examination showed hexacarbon-specific axonal lesions in peripheral nerves, particularly tibial branches to calf muscles, and in the gracile tract at cervical levels of the spinal cord. Similar clinical and pathological signs of neuropathy appeared one week earlier in animals treated with a mixture of 500 ppm n-hexane MEK (4:1 or 3:2) and 5 weeks earlier with 700 n-hexane MEK mixture (5:2) or 700 ppm of n-hexane alone. Rats exposed to the latter concentrations intermittently, 8 hours daily for 40 weeks, did not develop clinical or morphological signs of a hexacarbon neuropathy.