Detecting necrotic neurons with fluoro-jade stain

Fluoro-jade, a novel stain for detection of neuropathic lesions by fluorescence microscopy, was validated on the models of toxic neuropathy induced with 3-acetylpyridine (3-AP) or with acrylamide (ACR). Groups of male and female albino rats of Wistar strain were either exposed to a single administration of 80 mg/kg i.p. 3-AP followed 5 hours later by 300 mg/kg of nicotinamide i.p. and examined at days 3 and 15, or to 15 daily doses of 30 mg/kg p.o. ACR and examined at day 15. Following in-life behavioral observations and measurements, the rats were fixed by perfusion with formalin. Additional animals treated with same dose of 3-AP and nicotinamide were submitted to purposeful autolysis for 4 or 16 hours before immersion fixation with formalin on test day 3. In-life observations showed in 3-AP-treated animals signs of severe general toxicity, sensorimotor dysfunction and decreased motor activity starting shortly after the treatment and persisting throughout the observation period. ACR-treated rats started to develop abnormal gait on test day 8 and by day 15 developed reduced grip strength, increased landing footsplay and decreased motor activity. Fluoro-jade, applied to paraffin sections of the nervous system, detected selectively and sensitively the necrotic neurons in the brain, especially those in the inferior olivary nucleus of animals treated with 3-AP, at test day 3, as well as the necrotic Purkinje cells in the cerebellum of ACR-treated animals at test day 15. Chromatolytic neurons in the dorsal root ganglia of ACR-treated animals did not stain positively, indicating that this kind of reversible neuronal remodeling is not detectable using fluoro-jade. Necrotic neurons were still stained by fluoro-jade after 4 hour autolysis, but following 16 hour autolysis the results became false negative. There was no false positive fluorescence in fresh or autolytic tissues, except that emitted by red blood cells in unperfused specimens. The study confirmed the validity of fluoro-jade as a stain suitable for detecting necrotic neurons in toxicological safety studies.