Response properties of the neurons in the cervical cord to stimulation of the inferior alveolar nerve in the cat

Abstract

The purpose of this study was to investigate the neuronal mechanisms of the clinical symptoms of unusual muscle stiffness and/or pain in the neck and shoulder sometimes observed in patients suffering from chronic pulpal or periodontal diseases. Physiological properties of the neurons responding to the inferior alveolar nerve stimulation (inferior alveolar nerve driven-neurons: IANDNs) were studied by recording single unit activities in the upper cervical cord in cats anesthetized with alpha-chloralose. The results were as follows: (1) IANDNs were widely distributed from the dorsal horn to the ventral horn in the gray matter of the cervical cord (C2 and C3). (2) IANDNs were subdivided into two types of neurons based on the latencies of the spike responses: fast-type (F-type) (n = 60) and slow-type (S-type) (n = 101). (3) Two possible pathways from the inferior alveolar nerve to the cervical spinal cord participating in these spike responses were assumed: one was through the trigeminal spinal nucleus and the other through Probst's tract by way of the trigeminal mesencephalic nucleus. These results suggest that the impulses originating from dental inflammatory loci might drive IANDNs in C2 or C3 and that their activities may evoke contraction of the neck muscles, resulting in their stiffness and cervical back pain.