ANTAGONISM OF SYNAPTIC POTENTIALS IN VENTRAL HORN NEURONS BY 6-CYANO-7-NITROQUINOXALINE-2,3-DIONE - A STUDY IN THE RAT SPINAL-CORD INVITRO

1 The rat spinal cord in vitro has been used to assess the effect of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on the dorsal root evoked extracellular ventral root reflex (DR-VRR) and the intracellular excitatory postsynaptic potential (e.p.s.p.) in ventral horn neurones and motoneurones. 2 CNQX (1 - 5 muM) produces a selective and dose-dependent reduction in the amplitude of the monosynaptic component of the DR-VRR recorded from lumbar spinal segments. 3 With low intensity dorsal root stimulation CNQX selectively attenuates the amplitude of the short latency intracellular e.p.s.p. (70% reduction, P<0.005) and its rise-time (75%, P<0.01) without affecting the half-time to decay. 4 When high intensity stimulation is used CNQX significantly attenuates the amplitude of the e.p.s.p. (56%, P<0.005), rise-time (76%, P<0.01) and abolishes the short latency spike. In addition longer latency synaptic components are attenuated and the half-time to decay significantly reduced (47%, P<0.005). 5 The results with CNQX are compared to D-aminophosphonovalerate and discussed in relation to the recruitment of low versus high threshold afferents. The data supports an involvement of non-NMDA receptors in transmission through both mono- and polysynaptic pathways in the ventral horn.