Wang-Bennett L T, Glantz R M
J Comp Physiol A. 1987 Jun;161(1):131-45. doi: 10.1007/BF00609461.
The light responses of the second order lamina monopolar neurons were examined in the crayfish compound eye. Single cartridge monopolar neurons (M1-M4) exhibited nonspiking hyperpolarizing light responses; for M1, M3 and M4 the transient 'on' response operated over the same intensity range as the receptor, 3.5 log units. M2 operated in a much narrower intensity range (1.5 log unit). The 'on' responses were associated with a 19% increase in conductance. The hyperpolarizing 'on' response can be reversed at 18 mV below the resting membrane potential. The half-angular sensitivity width of monopolar cells (in partially dark-adapted eyes) is 15 degrees X 8 degrees (horizontal by vertical). Off axis stimuli elicit attenuated hyperpolarizing responses associated with a diminished conductance increase or depolarizing responses associated with a net decrease in conductance. The latter result is consistent with the presynaptic inhibition of a 'back-ground' transmitter release which normally persists in the dark. Lateral inhibition is elicited from the area immediately surrounding the excitatory field, and it is associated with diminished transient responses and an accelerated decay of the response. Inhibitory stimuli decrease the conductance change associated with the hyperpolarizing response. The surround stimuli can also elicit depolarizing 'off' responses with reversal potentials positive to the membrane resting potential. It is concluded that the rapidly repolarizing monopolar cell response is modulated by both pre- and postsynaptic inhibitory mechanisms. A compartment model indicates that signal attenuation along a 500 microns length of monopolar cell axon is 22-34%. Simulation of steady-state signal transmission suggests that passive (decremental) conduction is sufficient to convey 66 to 78% of the monopolar cell signal from lamina to medulla. The current-voltage relation in current clamp is linear over the physiological operating range, and there is no evidence for rectification. Hyperpolarization of single monopolar cells (M1-M4) provides a polysynaptic excitatory signal to the medullary sustaining fibers.
在小龙虾复眼中研究了二级板层单极神经元的光反应。单个柱单极神经元（M1 - M4）表现出非尖峰超极化光反应；对于M1、M3和M4，瞬态“开”反应在与感受器相同的强度范围内起作用，为3.5对数单位。M2在更窄的强度范围内起作用（1.5对数单位）。“开”反应伴随着电导增加19%。超极化“开”反应可在静息膜电位以下18 mV时反转。单极细胞（在部分暗适应眼中）的半角敏感度宽度为15度×8度（水平×垂直）。离轴刺激引发衰减的超极化反应，伴随着电导增加减少，或引发与电导净减少相关的去极化反应。后一结果与通常在黑暗中持续存在的“背景”递质释放的突触前抑制一致。侧向抑制从兴奋场周围的区域引发，并且与瞬态反应减弱和反应的加速衰减相关。抑制性刺激减少与超极化反应相关的电导变化。周围刺激也可引发去极化“关”反应，其反转电位正于膜静息电位。得出的结论是，快速复极化的单极细胞反应受到突触前和突触后抑制机制的调节。一个隔室模型表明，沿着500微米长的单极细胞轴突的信号衰减为22 - 34%。稳态信号传输的模拟表明，被动（递减）传导足以将66%至78%的单极细胞信号从板层传递到髓质。电流钳中的电流 - 电压关系在生理工作范围内是线性的，并且没有整流的证据。单个单极细胞（M1 - M4）的超极化向髓质维持纤维提供多突触兴奋性信号。
