Studies on appearance of light responses and generation of synapses during retinal formation.

In the present study，using a newt retinal regeneration system，we attempted describing the process of synapse formation between retinal neurons and appearance of light responses。We first analyzed light responses of neurons in the normal retina by a slice-patch technique as a control for investigating those in regenerating retinas.Spike-generating(Spiking)neurons including amacrine and ganglion cells had non-NMDA and NMDA types of glutamate，GABAA and glycine receptors。Light-evoked post-synaptic currents in amacrine cells were the sum of excitatory and inhibitory components。The inhibitory post-synaptic currents were mostly glycinergic.Then，we examined development of intrinsic membrane properties of cells during retinal regeneration.Retinal progenitor cells in1-to-2cells thick regenerating retinas(Early Stage)strongly coupled to each other through gap junctions。Voltage-activated Na I D1+I D1 currents underlying excitability of neurons were first detected from cells(possibly…More ganglion cells)along the most proximal margin of several cells thick regenerating retinas before apparent segregation of synaptic layers(intermediate-II stage)。Properties of the Na I D1+ii D1 currents were，however，different from those in the normal retina.Subsequently，we examined expression of neurotransmitter receptors in spiking neurons during regeneration。Non-NMDA type of glutamate，GABAA and glycine receptors expressed at the intermediate-II stage，and increased during further regeneration。On the other hand，NMDA type of glutamate receptors expressed at the beginning of synaptic segregation(intermediate-III stage)。Appearance of a neurotransmitter，glutamate，was examined by immunohistochemistry.It appeared in ganglion cells and photoreceptors at the intermediate-II stage，and in bipolar cells at the intermediate-III stage。Amount of glutamate in ganglion cells and photoreceptors seemed to increase temporarily at the intermediate-III stage。In future，we will determine when synaptic transmissions occur between neurons and light responses restore.Less：Less

In the present study, using a newt retinal regeneration system, we attempted describing the process of synapse formation between retinal neurons and appearance of light responses. We first analyzed light responses of neurons in the normal retina by a slice-patch technique as a control for investigating those in regenerating retinas. Spike-generating (spiking) neurons including amacrine and ganglion cells had non-NMDA and NMDA types of glutamate, GABAA and glycine receptors. Light-evoked post-synaptic currents in amacrine cells were the sum of excitatory and inhibitory components. The inhibitory post-synaptic currents were mostly glycinergic.Then, we examined development of intrinsic membrane properties of cells during retinal regeneration. Retinal progenitor cells in 1-to-2 cells thick regenerating retinas (early stage) strongly coupled to each other through gap junctions. Voltage-activated NaィイD1+ィエD1 currents underlying excitability of neurons were first detected from cells (possibly … More ganglion cells) along the most proximal margin of several cells thick regenerating retinas before apparent segregation of synaptic layers (intermediate-II stage). Properties of the NaィイD1+ィエD1 currents were, however, different from those in the normal retina.Subsequently, we examined expression of neurotransmitter receptors in spiking neurons during regeneration. Non-NMDA type of glutamate, GABAA and glycine receptors expressed at the intermediate-II stage, and increased during further regeneration. On the other hand, NMDA type of glutamate receptors expressed at the beginning of synaptic segregation (intermediate-III stage). Appearance of a neurotransmitter, glutamate, was examined by immunohistochemistry. It appeared in ganglion cells and photoreceptors at the intermediate-II stage, and in bipolar cells at the intermediate-III stage. Amount of glutamate in ganglion cells and photoreceptors seemed to increase temporarily at the intermediate-III stage. In future, we will determine when synaptic transmissions occur between neurons and light responses restore. Less