Kononenko N I
A. A. Bogomoletz Institute of Physiology, Bogomoletz Street, 4, Kiev, Ukraine.
Neuroscience. 2000;96(2):399-406. doi: 10.1016/s0306-4522(99)00543-6.
The purpose of this study was to determine the role of the axodendritic tree in the generation of bursting pacemaker activity in the identified Helix RPa1 neuron, which is homologous to the Aplysia R15 cell, and propagation of action potentials along the axons. In doing so, I used recording of RPa1 neuron electrical activity after cutting off the right or left parietovisceral connections, the two-electrode voltage-clamp technique, registration of electrical activity of visceral nerve containing RPa1 axon branches, isolation of the RPa1 neuron and puff application of oxytocin on it. Cutting of the right (but not left) parietovisceral connection in all cases (more than 15 preparations) evoked complete disappearance of bursting pacemaker activity in the RPa1 neuron and hyperpolarization of its membrane potential up to -65 to -67 mV. Such silent state of the RPa1 neuron was maintained after its complete isolation from the ganglion. The described cutting did not result in a change of bursting activity of the pacemaker neuron V7 located in the visceral ganglion, although isolation of the V7 neuron also eliminated its own activity. Puff application of oxytocin (10 microM in a micropipette) on to the RPa1 neuron both after cutting the right parietovisceral connection or isolation of the neuron from the ganglion resulted in all cases (more than 10 cells) in transient depolarization with development of beating, oscillatory or bursting activity. Voltage clamping of RPa1 soma in the intact ganglion at a level close to zero membrane current sometimes, and, as a rule, at a more depolarized level, revealed bursting-like oscillations of membrane current, reflecting electrical bursting activity in the unclamped remote region of a neuron, most likely in the dendritic tree. Voltage clamping of RPa1 soma possessing bursting activity reveals bursting-like oscillation of membrane current and prevents propagation of corresponding axon action potentials in the visceral nerve. Controversially, clamping of RPa1 soma possessing beating activity exhibits a beating-like oscillation of membrane current and does not prevent propagation of corresponding action potentials in the nerve. Within the framework of the developed hypothesis that persistent bursting pacemaker activity of the RPa1 neuron is due to a constant activation of its peptidergic synaptic inputs [Kononenko N. I. (1993) Comp. Biochem. Physiol. 106A, 135-147], the experimental results were interpreted in the manner that these synapses and, correspondingly, the locus of electrical bursting activity generation, are localized on the dendritic tree of the RPa1 neuron mainly or possibly exclusively in the visceral ganglion. It is hypothesized that bursting and beating neuronal activities are due to functioning of different loci of the dendritic tree, regarding their electrical relations with axon branches.
本研究的目的是确定轴突树突在已鉴定的与海兔R15细胞同源的耳螺RPa1神经元中爆发性起搏活动的产生以及动作电位沿轴突的传播中所起的作用。为此，我采用了以下方法：切断右侧或左侧壁脏连接后记录RPa1神经元的电活动、双电极电压钳技术、记录含有RPa1轴突分支的内脏神经的电活动、分离RPa1神经元并对其微量注射催产素。在所有情况下（超过15个标本），切断右侧（而非左侧）壁脏连接均会导致RPa1神经元的爆发性起搏活动完全消失，其膜电位超极化至 -65至 -67 mV。RPa1神经元从神经节完全分离后，这种静息状态仍会持续。上述切断操作并未导致位于内脏神经节的起搏神经元V7的爆发性活动发生改变，不过V7神经元的分离也消除了其自身的活动。在切断右侧壁脏连接或神经元从神经节分离后，对RPa1神经元微量注射催产素（微量移液管中为10 microM），在所有情况下（超过10个细胞）均会导致短暂去极化，并产生搏动、振荡或爆发性活动。在完整神经节中，将RPa1胞体电压钳制在接近零膜电流的水平，有时（通常在更去极化的水平）会显示膜电流的爆发样振荡，这反映了神经元未钳制的远端区域（很可能是树突树）的电爆发活动。对具有爆发性活动的RPa1胞体进行电压钳制，会显示膜电流的爆发样振荡，并阻止相应的轴突动作电位在内脏神经中传播。相反，对具有搏动性活动的RPa1胞体进行钳制，会显示膜电流的搏动样振荡，且不会阻止相应动作电位在神经中的传播。在已提出的假说框架内，即RPa1神经元持续的爆发性起搏活动是由于其肽能突触输入的持续激活[Kononenko N. I. (1993) Comp. Biochem. Physiol. 106A, 135 - 147]，实验结果被解释为这些突触以及相应的电爆发活动产生位点主要或可能仅位于RPa1神经元位于内脏神经节的树突树上。据推测，神经元的爆发性和搏动性活动是由于树突树的不同位点发挥作用，这涉及它们与轴突分支的电关系。
