The Journal of Neurophysiology Vol. 84 No. 3 September 2000, pp. 1361-1368
Copyright ©2000 by the American Physiological Society

Dorsal Column Nuclei Neurons Recorded in a Brain Stem-Spinal Cord Preparation: Characteristics and Their Responses to Dorsal Root Stimulation

Royal Free Hospital School of Medicine, London NW3 2PF, United Kingdom

Deuchars, Susan A., T. Trippenbach, and K. Michael Spyer. Dorsal Column Nuclei Neurons Recorded in a Brain Stem-Spinal Cord Preparation: Characteristics and Their Responses to Dorsal Root Stimulation. J. Neurophysiol. 84: 1361-1368, 2000. Recordings were obtained from dorsal column nucleus (DCN) neurons in a neonatal rat brain stemspinal cord preparation to study their basic electrophysiological properties and responses to stimulation of a dorsal root. Whole-cell patch-clamp recordings were made from 21 neurons that responded to dorsal root stimulation with a fast excitatory postsynaptic potential (EPSP). These neurons were located lateral to, but at the level of, the area postrema at depths of 100-268 µm below the dorsal surface of the brain. The neurons could be divided into groups according to the shape of their action potentials or voltage responses to hyperpolarizing current steps; however, the response profiles of the groups of neurons to dorsal root stimulation were not significantly different and all neurons were considered together. Dorsal root stimulation elicited excitatory postsynaptic potentials (EPSPs) in all neurons with a very low variability in onset latency and an ability to follow 100-Hz stimulation, indicating that they were mediated by activation of a monosynaptic pathway. The peak amplitude of the EPSP increased with membrane hyperpolarization, and applications of the non-NMDA receptor antagonists 6-nitro-7-sulfamoylbenzo[f]quinoxaline-2,3-dione (NBQX) and 6,7-dinitroquinoxaline-2,3-dione (DNQX) decreased the amplitude of the EPSP to 14.2% of the control response (n = 6). The descending phase of the EPSP decreased with membrane hyperpolarization and was reduced by the N-methyl-D-aspartate (NMDA) receptor antagonist AP-5 (n = 2). The EPSPs were also reduced in amplitude by applications of the -aminobutyric acid-B (GABA_B) receptor agonist baclofen, which had no effect on membrane potential or input resistance. These results show that fast EPSPs in DCN neurons elicited by dorsal root stimulation are mediated by an excitatory amino acid acting at both non-NMDA and, to a lesser extent, NMDA receptors. In addition, GABA acting at presynaptic GABA_B receptors can inhibit these responses.