Wind-up of tooth pulp-evoked responses and its suppression in rat trigeminal caudal neurons.
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) Temporal summation of depolarization evoked by C-fiber volleys builds wind-up in caudal neurons; 2) ARH stimulation suppresses late discharges by blocking synaptic transmission from C-fiber inputs, and this interrupts prolonged facilitation of the neurons; 3) the ARH is involved in induction of inhibitory controls descending from the PAG to the trigeminal caudalis.
Hamba
M
M
Department of Physiology, School of Dentistry, Showa University, Tokyo, Japan.
Hisamitsu
H
H
Muro
M
M
D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000502:physiology*; D003782:Dental Pulp / Q000294:innervation*; D004558:Electric Stimulation; D005071:Evoked Potentials; D005260:Female; D007180:Incisor / Q000294:innervation; D009412:Nerve Fibers / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D010487:Periaqueductal Gray / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission; D014275:Trigeminal Caudal Nucleus / Q000502:physiology*