Sensory input and burst firing output of rat and cat thalamocortical cells: The role of NMDA and non-NMDA receptors

J. P. Turner, N. Leresche, A. Guyon, I. Soltesz, V. Crunelli

    Research output: Contribution to journalArticlepeer-review


    Intracellular and patch-clamp recordings were obtained from thalamocortical (TC) cells in the rat and cat dorsal lateral geniculate nucleus (dLGN) in vitro to study the role of N-methyl-D-aspartate (NMDA) and non-NMDA receptors in the synaptic potential and burst firing evoked by electrical stimulation of the optic tract. At membrane potentials more positive than -65 mV, the sensory synaptic potential consisted of a fast EPSP that was followed by a smaller, slower component. At membrane potentials more negative than -65 mV, this slower component became more prominent owing to the presence of a low-threshold (LT) Ca2+ potential, which in turn evoked a high-frequency (> 150 Hz) burst of action potentials. The lower, but not the upper limit of the range of membrane potential over which burst firing occurred was dependent on the amplitude of the fast EPSP. The non-NMDA receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 5-10 μM) and 1-(4-amino-phenyl)-4-methyl-7,8-methylene-dioxy-5H-2,3-benzodiazepine (GYKI 52466, 100 μM) greatly depressed the fast EPSP, abolished the burst firing generated by the LT Ca2+ potential, and left a relatively small, slow EPSP, which was sensitive to the NMDA antagonist DL-2-amino-5-phosphonovaleric acid (DL-AP5, 50-100 μM). In the absence of CNQX or GYKI 52466, DL-AP5 depressed the slow but not the fast EPSP. DL-AP5 also increased the latency of the first action potential evoked by the LT Ca2+ potential or even abolished the LT Ca2+ potential and associated burst firing. The latter effect was only present when this type of firing occurred within a small membrane potential range. DL-AP5 had no effect on the properties of the LT Ca2+ current I(T), indicating that its effect on the burst firing was not mediated by a direct action on I(T) The response of TC cells to high-frequency (100 Hz) stimulation consisted of an initial burst firing response, followed by a sustained depolarization that could reach firing threshold. This sustained depolarization was markedly depressed by DL-AP5 but not by CNQX. These results demonstrate that with low-frequency stimulation of the sensory afferents, the generation of TC cell output in the rat and cat dLGN is mainly controlled by non-NMDA receptors, while the contribution of NMDA receptors is limited to the burst firing generated by the LT Ca2+ potential, and depends on the membrane potential range over which this type of firing occurs. With high-frequency stimulation, the contribution of NMDA receptors is more pronounced, since their activation underlies the sustained depolarization.
    Original languageEnglish
    Pages (from-to)281-295
    Number of pages14
    JournalJournal of Physiology
    Issue number2
    Publication statusPublished - 1994


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