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The effects of deafferentation of the tooth pulps of mandibular or maxillary teeth were investigated on the functional properties of single neurons recorded in the subnucleus oralis of the trigeminal (V) spinal tract nucleus of adult cats. Deafferentation was produced by endodontic removal, under sterile conditions, of the coronal pulp of the canine, premolar, and molar teeth. The subnucleus oralis of each animal was then studied electrophysiologically in a series of microelectrode penetrations of the subnucleus at a single postoperative time that varied between 3 days and 2 yr. Data from deafferented cats were compared with those obtained from control (unoperated) animals. The study was based on an examination of over 2,000 single units recorded on the side ipsilateral to the pulp deafferentation. In animals deafferented 7-15 days prior to brain stem neuron recording, tooth pulp deafferentation was associated with a statistically significant decrease compared with control animals in the incidence of neurons having a mechanoreceptive field localized within the mandibular or maxillary division; this decrease in incidence was coincident with a significant increase in the occurrence of neurons having a mechanoreceptive field involving two or three V divisions. Linear trend analysis indicated a progressive return to control values from the 7- to 15-day postoperative period. In deafferented cats there were also statistically significant increases in the incidence of neurons having spontaneous activity or showing rapidly habituating responses to brisk tap stimuli applied to the orofacial region; neurons having a receptive field consisting of discontinuous zones of mechanosensitivity were also encountered. The mean impulse frequency of spontaneous activity was not, however, significantly different between control and deafferented animals. The responsiveness of the habituating tap-sensitive neurons was further quantified and compared with neurons showing normal rapidly adapting (RA) features of their responses to mechanical orofacial stimuli. Whereas most (85%) of the RA neurons could faithfully follow stimuli applied by a mechanical stimulator at a mean maximal following frequency of 6.6 Hz and showed entrainment and 'turning curve' profiles comparable to those previously described for oralis neurons in normal animals, most of the habituating tap-sensitive neurons could not follow mechanical stimulus frequencies greater than 1 Hz (mean maximal following frequency 0.3 Hz) and none could be entrained sufficiently to allow for a determination of their tuning curve.(ABSTRACT TRUNCATED AT 400 WORDS)

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