Wind-up of tooth pulp-evoked responses and its suppression in rat trigeminal caudal neurons

Abstract

Induction and suppression of wind-up were studied in 97 tooth pulp-driven neurons in the trigeminal subnucleus caudalis, using Wistar albino rats anesthetized with urethane and alpha-chloralose. Tooth pulp stimulation applied to an ipsilateral lower incisor evoked early discharges, indicating excitatory inputs from A-delta fibers and subsequent late discharges from C-fiber volleys in caudal neurons. Wind-up was efficiently evoked by stimulation delivered at 0.3–1 Hz, with current intensity sufficient to evoke late discharges. Conditioning stimulation of the arcuate nucleus of the hypothalamus (ARH) suppressed late discharges, including wind-up, without affecting the A-fiber response. Focal cooling of the periaqueductal gray (PAG) abolished the suppression by the ARH and further enhanced the wind-up of the caudal neurons. These results suggest: 1. 1) Temporal summation of depolarization evoked by C-fiber volleys builds wind-up in caudal neurons; 2. 2) ARH stimulation suppresses late discharges by blocking synaptic transmission from C-fiber inputs, and this interrupts prolonged facilitation of the neurons; 3. 3) the ARH is involved in induction of inhibitory controls descending from the PAG to the trigeminal caudalis.