title: Prolonged synaptic currents increase relay neuron firing at the developing retinogeniculate synapse.
abstract: The retinogeniculate synapse, the connection between retinal ganglion cells (RGC) and thalamic relay neurons, undergoes robust changes in connectivity over development. This process of synapse elimination and strengthening of remaining inputs is thought to require synapse specificity. Here we show that glutamate spillover and asynchronous release are prominent features of retinogeniculate synaptic transmission during this period. The immature excitatory postsynaptic currents exhibit a slow decay time course that is sensitive to low-affinity glutamate receptor antagonists and extracellular calcium concentrations, consistent with glutamate spillover. Furthermore, we uncover and characterize a novel, purely spillover-mediated AMPA receptor current from immature relay neurons. The isolation of this current strongly supports the presence of spillover between boutons of different RGCs. In addition, fluorescence measurements of presynaptic calcium transients suggest that prolonged residual calcium contributes to both glutamate spillover and asynchronous release. These data indicate that, during development, far more RGCs contribute to relay neuron firing than would be expected based on predictions from anatomy alone.
authors: Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts.
authors: Jessica L
authors: JL
authors: Hauser
authors: Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts.
authors: Xiaojin
authors: X
authors: Liu
authors: Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts.
authors: Elizabeth Y
authors: EY
authors: Litvina
authors: Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts chinfei.chen@childrens.harvard.edu.
authors: Chinfei
authors: C
authors: Chen
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D019706:Excitatory Postsynaptic Potentials; D005829:Geniculate Bodies / Q000254:growth & development*; D005971:Glutamates / Q000502:physiology; D008810:Mice, Inbred C57BL; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D018091:Receptors, AMPA / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000502:physiology*; D013569:Synapses / Q000502:physiology*
chemical_list: D005971:Glutamates; D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D002118:Calcium
keywords: asynchronous release; development; glutamate spillover; retinogeniculate synapse; visual system