Function and morphology of vertebrate retina

我们对脊椎动物视网膜研究的一个主要目标是通过识别神经元之间的传递函数来解剖神经元回路，即，以恢复将突触前神经元的响应转换为突触后神经元的响应的神经元滤波器。在生物学或工程学中，解剖复杂电路和识别这种滤波器的最直接方法是将测试信号注入一个电路元件，并在另一个元件中记录产生的和转换的信号。在通过光刺激引起的反应识别细胞类型之后，将由脉冲、正弦或高斯白噪声信号调制的外源性电流相继注入一个神经元，并从另一个神经元记录所产生的反应。两个电极的尖端约为0.2-0.4 mm。在高斯白噪声电流的情况下，持续时间为20 s的输入电流与计算一阶和二阶维纳核的响应互相关。通过将电流传递到附近的细胞外空间来控制实验，以验证观察到的结果来自注入神经元的电流。为了研究视网膜神经元的突触结构，我们在电子显微镜下观察了HRP标记的神经元。在自然光环境中，互连的模式可能不是严格固定的;相反，连接的权重可能会根据空间和时间变化的视觉输入进行修改。因此，视网膜中的信号相互作用可能涉及神经生理学迄今未知的新原理。

A major goal of our studies on vertebrate retina is to dissect neuronal circuitry by identifying the transfer function between neurons,i.e., to recover the neuronal filter that transforms the responses of the presynaptic neuron to those of the postsynaptic neuron. The most direct means of dissecting complex circuitry and of identifying such a filter, either in biology or in engineering, is to inject a test signal into one circuit element and to record the resulting and transformed signals in another element.Intracellular recordings were made simultaneously from two neighboring neurons in the eye-cup preparation of the channel catfish, Ictalurus punctatus. After identifying cell types by the responses evoked by light stimuli, an extrinsic current, modulated by pulse, sinusoid or Gaussian white-noise signal, was successively injected into one neuron and the resulting response was recorded from the other neuron. The tips of the two electrodes were about 0.2-0.4 mm part. In the case of Gaussian white-noise current, input current 20s in duration was cross-correlated against the response to compute first-and second-order Wiener kernels. Experiments were controlled by passing a current into nearby extracellular space to verify that the observed results were from the current injected into a neuron. For the study of synaptic organization of the retinal neurons, HRP-marked neurons were examined under an electron microscope.Our results indicate that retinal circuitry is a highly interconnected network. The pattern of interconnections may not be rigidly fixed in natural photic environment; rather the weights of connections may undergo modification as a function of spatially and temporally changing visual inputs. It appears, therefore, that signal interaction in the retina may involve new principles hitherto unknown in neurophysiology.