Temporal Analysis of Increases in c-Fos Expression in Rat Spinal Trigeminal Nucleus Complex by Selective Stimulation of C-afferent Fibers.

Abstract

This study evaluates temporal increases in the expression of Fos-like immunoreactive labeled neurons (FLI-labeled neurons) in the spinal trigeminal nucleus complex (STNC) following selective stimulation of C-fibers. Selective stimulating C-fibers were obtained using low doses (10 mg/kg b.w.) of capsaicin injection.Under sodium pentobarbital anaesthesia, 1% capsaicin was administered into the rats left infraorbital region. At periods of 30 min, 1, 3, 6, 9 and 12 hr after capsaicin injection, rats were anesthetized and killed for immunohistochemical examination of Fos-like protein products.The results showed that FLI-labeled neurons in the STNC appeared within 30 min after induction of capsaicin injection into the rat trigeminal region, reached peak increases at 3 hr, and disappeared between 9 and 12 hr.This time course was similar to dental treatment results which probably stimulated both A-delta and C fibers. According to previous studies, both A-delta and C fibers are essential to conduct impulses of nociceptive stimulation. But, this theory does not apply to the time course of FLI-labeled neuron expression in the STNC. In conclusion, this study showed that the time course of FLI-labeled neuron expression in the STNC was unchanged in stimulated or non-stimulated A-delta fibers.