The purpose of this study was to investigate the role of
oxygen radical-induced
lipid peroxidative mechanisms in trophic deprivation-induced apoptotic motor neuronal degeneration by testing the ability of the 21-aminosteroid
lipid peroxidation inhibitor tirilazad mesylate (U-74006F) to attenuate the
retrograde degeneration of facial motor neurons following
axotomy in 14-day-old rat pups. On day 0, the right facial nerve of each rat was transected at its point of exit from the stylomastoid foramen. Pups were treated orally with either 10 or 30 mg/kg
U-74006F or
cyclodextrin vehicle 10 min before
axotomy, and post-treated once a day from days 1 to 6, and then once every other day from days 8 to 21. The rats were sacrificed 3 weeks post-transection and the surviving motor neurons, identified through
choline acetyltransferase immunocytochemistry, were counted in three regions (planes) in the facial nucleus. In vehicle-treated rats, 56.2% (region A), 50.6% (region B), and 57.4% (region C) of the motor neurons in the ipsilateral facial nucleus survived 21 days following facial nerve
axotomy in comparison to the non-axotomized contralateral nucleus (P < 0.0001). Treatment with 10 mg/kg
U-74006F significantly enhanced motor neuron survival in regions B and C to 72.8% (P < 0.01) and 66.7% (P < 0.02%), respectively. The 30 mg/kg dose level also increased survival rates to 64.2% (P < 0.02) and 67.9% (P < 0.01), respectively. A second experiment demonstrated that oral dosing with
U-74006F (30 mg/kg), when limited to the first 5 days after
axotomy, also significantly blunted
retrograde degeneration measured at 21 days post-
axotomy. The efficacy of the
lipid peroxidation inhibitor U-74006F in protecting a portion of the facial motor neuron pool from post-
axotomy degeneration suggests that lipid peroxidation may play a mechanistic role in trophic deprivation-induced apoptotic neuronal death.