Zaghloul Kareem A, Manookin Michael B, Borghuis Bart G, Boahen Kwabena, Demb Jonathan B
Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
J Neurophysiol. 2007 Jun;97(6):4327-40. doi: 10.1152/jn.01091.2006. Epub 2007 Apr 25.
A retinal ganglion cell receptive field is made up of an excitatory center and an inhibitory surround. The surround has two components: one driven by horizontal cells at the first synaptic layer and one driven by amacrine cells at the second synaptic layer. Here we characterized how amacrine cells inhibit the center response of on- and off-center Y-type ganglion cells in the in vitro guinea pig retina. A high spatial frequency grating (4-5 cyc/mm), beyond the spatial resolution of horizontal cells, drifted in the ganglion cell receptive field periphery to stimulate amacrine cells. The peripheral grating suppressed the ganglion cell spiking response to a central spot. Suppression of spiking was strongest and observed most consistently in off cells. In intracellular recordings, the grating suppressed the subthreshold membrane potential in two ways: a reduced slope (gain) of the stimulus-response curve by approximately 20-30% and, in off cells, a tonic approximately 1-mV hyperpolarization. In voltage clamp, the grating increased an inhibitory conductance in all cells and simultaneously decreased an excitatory conductance in off cells. To determine whether center response inhibition was presynaptic or postsynaptic (shunting), we measured center response gain under voltage-clamp and current-clamp conditions. Under both conditions, the peripheral grating reduced center response gain similarly. This result suggests that reduced gain in the ganglion cell subthreshold center response reflects inhibition of presynaptic bipolar terminals. Thus amacrine cells suppressed ganglion cell center response gain primarily by inhibiting bipolar cell glutamate release.
视网膜神经节细胞的感受野由一个兴奋性中心和一个抑制性周边组成。周边有两个组成部分：一个由第一突触层的水平细胞驱动，另一个由第二突触层的无长突细胞驱动。在这里，我们描述了无长突细胞如何在体外豚鼠视网膜中抑制ON型和OFF型中心Y型神经节细胞的中心反应。一个超出水平细胞空间分辨率的高空间频率光栅（4 - 5周/毫米）在神经节细胞感受野周边漂移，以刺激无长突细胞。周边光栅抑制了神经节细胞对中心光斑的放电反应。放电抑制在OFF细胞中最强且最一致地观察到。在细胞内记录中，光栅以两种方式抑制阈下膜电位：刺激 - 反应曲线的斜率（增益）降低约20 - 30%，并且在OFF细胞中，有一个约1毫伏的持续性超极化。在电压钳制中，光栅增加了所有细胞的抑制性电导，同时降低了OFF细胞的兴奋性电导。为了确定中心反应抑制是突触前还是突触后（分流）的，我们在电压钳制和电流钳制条件下测量了中心反应增益。在两种条件下，周边光栅对中心反应增益的降低相似。这一结果表明，神经节细胞阈下中心反应增益的降低反映了突触前双极终末的抑制。因此，无长突细胞主要通过抑制双极细胞谷氨酸释放来抑制神经节细胞的中心反应增益。
