N-methyl-D-aspartate (NMDA) and non-NMDA receptor antagonists suppress the superior sagittal sinus-evoked activity of C1 spinal neurons responding to tooth pulp electrical stimulation in rats.

The aim of the present study was to determine whether there is a convergence of inputs from tooth pulp (TP) and the superior sagittal sinus (SSS) on rat C1 spinal neurons, and to examine the effects of iontophoretically applied N-methyl-d-aspartate (NMDA) and non-NMDA receptor antagonists on the SSS-evoked activity of C1 neurons. Extracellular single unit-recordings were made from 20 C1 units responding to TP electrical stimulation with a constant temporal relationship to a digastric electromyogram signal, using a multibarrel electrode in pentobarbital-anesthetized rats. Ninety percent of C1 neurons (18/20) responding to TP stimulation also responded to the SSS stimulation. These neurons were considered to be SSS-afferent inputs from Aδ-fibers (5.8 ± 0.6 m/s; n = 18), based on the calculation of nerve conduction velocity. After the iontophoretic application (30, 50, and 70 nA) of an NMDA receptor blocker (5R-10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cycloheptene-5,10-imine hydrogen maleate (MK801) or a non-NMDA receptor blocker (6-cyano-7-nitroquinoxaline-2,3-dione) (CNQX), the mean number of spikes responding to the SSS stimulation significantly decreased (30, 50, and 70 nA; P < 0.05). These results suggest that there is a convergence of inputs from SSS and TP afferents on C1 neurons; it is possible that both NMDA and non-NMDA receptors located on C1 neurons may be targets for the treatment of the trigeminal referred pain associated with migraine.