Johnson Bruce R, Schneider Lauren R, Nadim Farzan, Harris-Warrick Ronald M
Dept. of Neurobiology and Behavior, S.G. Mudd Hall, Cornell Univ., Ithaca, NY 14853, USA.
J Neurophysiol. 2005 Nov;94(5):3101-11. doi: 10.1152/jn.00440.2005. Epub 2005 Jul 13.
The phasing of neuronal activity in a rhythmic motor network is determined by a neuron's intrinsic firing properties and synaptic inputs; these could vary in their relative importance under different modulatory conditions. In the lobster pyloric network, the firing of eight follower pyloric (PY) neurons is shaped by their intrinsic rebound after pacemaker inhibition and by synaptic input from the lateral pyloric (LP) neuron, which inhibits all PY neurons and is electrically coupled to a subset of them. Under control conditions, LP inhibition is weak and has little influence on PY firing. We examined modulation that could theoretically enhance the LP's synaptic contribution to PY firing. We measured the effects of dopamine (DA) on LP-->PY synapses, driving the LP neuron with trains of realistic waveforms constructed from prerecorded control and DA LP oscillations, which differed in shape and duration. Under control conditions, chemical inhibition underwent severe depression and disappeared; in the mixed synapses, electrical coupling dominated. Switching between control and DA LP waveforms (with or without DA present) caused only subtle changes in synaptic transmission. DA markedly enhanced synaptic inhibition, reduced synaptic depression and weakened electrical coupling, reversing the sign of the mixed synapses. Despite this, removal of the LP from the intact network still had only weak effects on PY firing. DA also enhances PY intrinsic rebound properties, which still control the onset of PY firing. Thus in a rhythmic network, the functional importance of synaptic modulation can only be understood in the context of parallel modulation of intrinsic properties.
节律性运动网络中神经元活动的相位由神经元的固有放电特性和突触输入决定；在不同的调节条件下，它们的相对重要性可能会有所不同。在龙虾幽门网络中，八个跟随性幽门（PY）神经元的放电由起搏器抑制后的固有反弹以及来自外侧幽门（LP）神经元的突触输入所塑造，LP神经元抑制所有PY神经元，并与其中一部分PY神经元电耦合。在对照条件下，LP抑制较弱，对PY放电影响很小。我们研究了理论上可增强LP对PY放电突触贡献的调节作用。我们测量了多巴胺（DA）对LP→PY突触的影响，用根据预先记录的对照和DA LP振荡构建的逼真波形序列驱动LP神经元，这些波形在形状和持续时间上有所不同。在对照条件下，化学抑制严重衰退并消失；在混合突触中，电耦合起主导作用。在对照和DA LP波形之间切换（有无DA存在）仅引起突触传递的细微变化。DA显著增强突触抑制，减少突触衰退并削弱电耦合，使混合突触的信号反转。尽管如此，从完整网络中去除LP对PY放电的影响仍然较弱。DA还增强了PY的固有反弹特性，这仍然控制着PY放电的起始。因此，在节律性网络中，只有在固有特性平行调节的背景下，才能理解突触调制的功能重要性。
