Juusola M, Uusitalo R O, Weckström M
Department of Physiology, University of Oulu, Finland.
J Gen Physiol. 1995 Jan;105(1):117-48. doi: 10.1085/jgp.105.1.117.
To characterize the transfer of graded potentials and the properties of the associated noise in the photoreceptor-interneuron synapse of the blowfly (Calliphora vicina) compound eye, we recorded voltage responses of photoreceptors (R1-6) and large monopolar cells (LMC) evoked by: (a) steps of light presented in the dark; (b) contrast steps; and (c) pseudorandomly modulated contrast stimuli at backgrounds covering 6 log intensity units. Additionally, we made recordings from photoreceptor axon terminals. Increased light adaptation gradually changed the synaptic signal transfer from low-pass to band-pass filtering. This was accompanied by decreased synaptic delay and increased contrast gain, but the overall synaptic gain and the intrinsic noise (i.e., transmission noise) were reduced. Based on these results, we describe a descriptive synaptic model, in which the kinetics of the tonic transmitter (histamine) release from the photoreceptor axon terminals change with mean photoreceptor depolarization. During signal transmission, tonic transmitter release is augmented by voltage-dependent contrast-enhancing mechanisms in the photoreceptor axons that produce fast transients from the rising phases of the photoreceptor responses and add these enhanced voltages to the original photoreceptor responses. The model can predict the experimental findings and it agrees with the recently proposed theory of maximizing sensory information.
为了表征家蝇（Calliphora vicina）复眼光感受器 - 中间神经元突触中分级电位的传递以及相关噪声的特性，我们记录了光感受器（R1 - 6）和大的单极细胞（LMC）的电压响应，这些响应由以下因素诱发：（a）在黑暗中呈现的光阶跃；（b）对比度阶跃；以及（c）在覆盖6个对数强度单位的背景下的伪随机调制对比度刺激。此外，我们还记录了光感受器轴突终末的情况。光适应增强逐渐改变了突触信号传递，从低通滤波变为带通滤波。这伴随着突触延迟的减少和对比度增益的增加，但整体突触增益和内在噪声（即传输噪声）降低。基于这些结果，我们描述了一个描述性突触模型，其中从光感受器轴突终末释放的持续性递质（组胺）的动力学随光感受器平均去极化而变化。在信号传递过程中，持续性递质释放通过光感受器轴突中依赖电压的对比度增强机制增强，这些机制从光感受器响应的上升阶段产生快速瞬变，并将这些增强的电压加到原始光感受器响应上。该模型可以预测实验结果，并且与最近提出的最大化感官信息的理论一致。
