ABSTRACT
The response properties of tooth pulp neurons that respond to noxious thermal stimulation of the dental pulp have been not well-studied. The present study was designed to characterize the response properties of tooth pulp neurons to noxious thermal stimulation of the dental pulp. Experiments were conducted on 25 male ferrets, and heat stimulation was applied by a computer-controlled thermode. Only 15% of tooth pulp neurons (n = 39) responded to noxious thermal stimulation of the teeth. Tooth pulp neurons were found in both the superficial and deep nuclear regions of the subnucleus caudalis (Vc) and in the interface between the nucleus caudalis and interpolaris (Vc/Vi). Thirty-seven neurons had cutaneous receptive fields and were classified as either NS (16) or WDR (21) neurons. Repeated heat stimulation of the dental pulp sensitized and increased the number of electrically evoked potentials of tooth pulp neurons. These results provide evidence that both the Vc and Vc/Vi regions contain neurons that respond to noxious thermal stimulation of the dental pulp, and that these cells may contribute to the sensitization process associated with symptomatic pulpitis.
Subject(s)
Dental Pulp/innervation , Neurons/physiology , Thermosensing/physiology , Animals , Cold Temperature , Cuspid/innervation , Electric Stimulation , Evoked Potentials, Somatosensory/physiology , Ferrets , Gingiva/innervation , Hot Temperature , Lip/innervation , Male , Mechanoreceptors/physiology , Mouth Mucosa/innervation , Neural Conduction/physiology , Neurons/classification , Nociceptors/physiology , Physical Stimulation/methods , Reaction Time/physiology , Sensory Receptor Cells/physiology , Skin/innervation , Thermoreceptors/physiology , Trigeminal Caudal Nucleus/cytology , Trigeminal Caudal Nucleus/physiologyABSTRACT
Renal afferent neurons were retrogradely labeled with FluoroGold in Sprague-Dawley rats at 50, 60, 70, 80, 90, 110, 130 and 200 days of age. Recordings of afferent renal nerve activity (ARNA) and immunofluorescent assessment of calcitonin gene-related peptide (CGRP)-like immunoreactivity (LI) and substance P (SP)-LI in spinal ganglia T10-L1 were obtained in the same rats. The frequency of renal afferent neurons positive for CGRP-LI declined abruptly from 88% in animals younger than 100 days of age (342 of 388 total cells) to 63% in rats older than 100 days of age (223 of the 353 total cells). The intensity of CGRP-LI (scaled 1-3) in renal afferent CGRP-positive neurons also declined significantly from a mean of 2.23 +/- 0.04 before 100 days to 1.48 +/- 0.05 in older rats (P < 0.001 in each age group). SP-LI positive neurons declined from 44% to 28% (P < 0.001). These changes in neuropeptide immunofluorescence coincided with an altered pattern of ARNA in which the excitatory response to complete renal ischemia increased from 274 +/- 69% above background to 1167 +/- 124% after the age of 100 days. Previous studies have shown that this alteration in the ARNA response to renal ischemia is due to the appearance of activity from R1 chemoreceptor nerves in ARNA. These data demonstrated that this transition in the electrophysiologic characteristics of ARNA is accompanied by profound alterations in CGRP-LI and SP-LI levels in renal afferent nerve cell bodies.
