Patterns and plasticity of dental afferent inputs to trigeminal (V) brainstem neurons in kittens.

In the young cat, the natural replacement of deciduous teeth with a permanent dentition may be accompanied by extensive peripheral nerve degeneration and reinnervation. Since we have previously reported significant physiological effects of tooth pulp deafferentation on V brainstem neurons, we wished to determine if deafferentation associated with deciduous tooth exfoliation was accompanied by comparable neuroplastic changes in the brainstem of kittens. We have examined the pulpal afferent terminating pattern within the brainstem as well as the electrophysiological properties of V brainstem neurons during this naturally occurring deafferentation phenomenon. The pattern of the HRP-labelled terminals in different parts of V brainstem subnuclei in kittens was similar to that in adult cats. The highest density of labelled terminals was found in the subnucleus oralis. The properties of subnucleus oralis neurons also showed many similarities between kittens at age of 3-4 months old and adult cats, e.g., (1) in the proportions of neurons activated by tactile stimulation of 1-4 teeth (mandibular and maxillary canines and premolars), (2) the ratio of neurons showing fast adapting or slow adapting responses to dental tactile stimulation, (3) the proportions of neurons activated by electrical pulp stimulation of 1-4 teeth, and (4) the minimal latencies of pulp-evoked responses. However, the incidences of pulpal inputs as well as the convergent pattern to oralis neurons of afferent inputs evoked by periodontal stimulation and electrical pulpal stimulation were less common in kittens than adult cats.