Effects of acrylamide and botulinum toxin on horseradish peroxidase labelling of trigeminal motor neurons in the rat.

The extent of neuronal labelling with horseradish peroxidase (HRP) was examined in rat trigeminal motor neurons at various stages of acrylamide intoxication, following HRP uptake by motor nerve endings in the anterior digastric muscle. After 7 days of acrylamide (5 daily injections of 30 mg acrylamide/kg body weight), the pattern of HRP labelling was altered from normal, and this changed pattern persisted without further alteration when survival time and dosage were increased to 14 and 21 days (equivalent to 10 X 30 mg/kg and 15 X 30 mg/kg respectively). Six hours after HRP injection, the number of labelled cells in the ipsilateral trigeminal motor nucleus was reduced in treated animals compared to controls. By 18 hours, cells containing label were present in similar numbers to controls; but by 24 hours, the number in treated animals had fallen again, unlike controls in which labelling remained constant between 6 and 24 hours. At longer intervals, this reduction in labelling continued, but more slowly, so that by 96 hours after HRP injection, numbers of labelled cells were again similar in poisoned and control animals. One and three days after a single intramuscular injection of 0.05 microgram botulinum toxin type A, HRP labelling in the trigeminal motor neurons was unaffected, although at three days after toxin, mild chromatolytic changes could be seen in a few of the neurons.