Department of Zoology, University of Cambridge, Cambridge, UK.
Sensapex Ltd, Oulu, Finland.
PLoS Comput Biol. 2018 Nov 6;14(11):e1006566. doi: 10.1371/journal.pcbi.1006566. eCollection 2018 Nov.
Modulation is essential for adjusting neurons to prevailing conditions and differing demands. Yet understanding how modulators adjust neuronal properties to alter information processing remains unclear, as is the impact of neuromodulation on energy consumption. Here we combine two computational models, one Hodgkin-Huxley type and the other analytic, to investigate the effects of neuromodulation upon Drosophila melanogaster photoreceptors. Voltage-dependent K+ conductances in these photoreceptors: (i) activate upon depolarisation to reduce membrane resistance and adjust bandwidth to functional requirements; (ii) produce negative feedback to increase bandwidth in an energy efficient way; (iii) produce shunt-peaking thereby increasing the membrane gain bandwidth product; and (iv) inactivate to amplify low frequencies. Through their effects on the voltage-dependent K+ conductances, three modulators, serotonin, calmodulin and PIP2, trade-off contrast gain against membrane bandwidth. Serotonin shifts the photoreceptor performance towards higher contrast gains and lower membrane bandwidths, whereas PIP2 and calmodulin shift performance towards lower contrast gains and higher membrane bandwidths. These neuromodulators have little effect upon the overall energy consumed by photoreceptors, instead they redistribute the energy invested in gain versus bandwidth. This demonstrates how modulators can shift neuronal information processing within the limitations of biophysics and energy consumption.
调制对于调整神经元以适应当前状态和不同需求至关重要。然而，对于调制如何调整神经元特性以改变信息处理，我们仍不清楚，也不清楚神经调制对能量消耗的影响。在这里，我们结合了两种计算模型，一种是 Hodgkin-Huxley 型，另一种是分析型，来研究神经调制对黑腹果蝇光感受器的影响。这些光感受器中的电压依赖性 K+电导：(i) 在去极化时激活，以降低膜电阻并调整带宽以满足功能要求；(ii) 以节能的方式产生负反馈，增加带宽；(iii) 产生分流峰化，从而增加膜增益带宽产物；(iv) 失活以放大低频。通过对电压依赖性 K+电导的影响，三种调节剂——血清素、钙调蛋白和 PIP2——在对比度增益和膜带宽之间进行权衡。血清素使光感受器的性能朝着更高的对比度增益和更低的膜带宽方向转变，而 PIP2 和钙调蛋白则使性能朝着更低的对比度增益和更高的膜带宽方向转变。这些神经调节剂对光感受器消耗的总能量几乎没有影响，而是重新分配了在增益与带宽之间投入的能量。这表明了调制如何在生物物理和能量消耗的限制内改变神经元的信息处理。
