Tsau Y, Wu J Y, Höpp H P, Cohen L B, Schiminovich D, Falk C X
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
J Neurosci. 1994 Jul;14(7):4167-84. doi: 10.1523/JNEUROSCI.14-07-04167.1994.
We examined two aspects of the response to siphon stimulation in an attempt to test the hypothesis that the Aplysia CNS functions as a distributed system. First, we estimated the number of central neurons that respond to a light touch to the siphon skin. We made voltage-sensitive dye recordings from the abdominal, pleural, pedal, and cerebral ganglia. From these recordings we estimated that 220 abdominal neurons, 110 pleural neurons, and 650 pedal neurons were affected by the light touch. Thus, the information about this mild and localized stimulus is very widely distributed within the Aplysia CNS. This result allows the possibility that the Aplysia CNS functions as a distributed system. If only a small number of neurons had responded to the touch, it would have supported the conclusion that the gill-withdrawal reflex could be generated by a small, dedicated circuit. Second, we searched for correlations between the spike times of the individual abdominal ganglion neurons. Two time scales were examined: a millisecond time scale corresponding to the duration of a fast synaptic potential and a seconds time scale corresponding to the duration of the gill-withdrawal movement. Neuron pairs with highly correlated spike activity on a millisecond time scale must be connected by (or have a common input that uses) relatively powerful, fast, excitatory synapses. We expected that this kind of synaptic interaction would be relatively rare in nervous systems that functioned in a distributed manner. Indeed, only 0.3% of the neuron pairs had correlation coefficients of 0.15 or greater. These correlations accounted for approximately 2% of the action potentials generated in response to siphon stimulation. Thus, large, fast excitatory synaptic interactions appear to be relatively unimportant. This result is consistent with the hypothesis that the abdominal ganglion functions as a distributed system. When the longer time scale was used for the cross-correlograms, a large fraction of the cell pairs had correlated activity because many neurons are activated by the stimulus. It was not possible to interpret the slow correlations in terms of actual synaptic interactions between individual neurons. Our results are consistent with the possibility that the abdominal ganglion functions in a distributed manner. However, this evaluation is indirect and thus only tentative conclusions can be drawn. Evidence from several sources suggests that the neuronal interactions for generating the Aplysia gill-withdrawal reflex are complex.
我们研究了海兔对虹吸管刺激反应的两个方面，试图检验海兔中枢神经系统作为一个分布式系统发挥功能的假说。首先，我们估计了对虹吸管皮肤进行轻触时做出反应的中枢神经元数量。我们从腹神经节、胸膜神经节、足神经节和脑神经节进行了电压敏感染料记录。从这些记录中我们估计，220个腹神经节神经元、110个胸膜神经节神经元和650个足神经节神经元受到了轻触的影响。因此，关于这种轻微且局部的刺激的信息在海兔中枢神经系统内分布得非常广泛。这一结果使得海兔中枢神经系统作为一个分布式系统发挥功能成为可能。如果只有少数神经元对触碰做出反应，那就会支持鳃收缩反射可能由一个小型的专用回路产生的结论。其次，我们寻找单个腹神经节神经元的放电时间之间的相关性。研究了两个时间尺度：一个是对应快速突触电位持续时间的毫秒时间尺度，另一个是对应鳃收缩运动持续时间的秒时间尺度。在毫秒时间尺度上具有高度相关放电活动的神经元对必须通过（或有一个共同的使用）相对强大、快速的兴奋性突触连接。我们预计这种突触相互作用在以分布式方式发挥功能的神经系统中相对较少见。事实上，只有0.3%的神经元对的相关系数为0.15或更高。这些相关性约占对虹吸管刺激产生的动作电位的2%。因此，大型、快速的兴奋性突触相互作用似乎相对不重要。这一结果与腹神经节作为一个分布式系统发挥功能的假说一致。当在互相关图中使用较长的时间尺度时，很大一部分细胞对具有相关活动，因为许多神经元被刺激激活。不可能根据单个神经元之间实际的突触相互作用来解释这种缓慢的相关性。我们的结果与腹神经节以分布式方式发挥功能的可能性一致。然而，这种评估是间接的，因此只能得出初步结论。来自多个来源的证据表明，产生海兔鳃收缩反射的神经元相互作用是复杂的。
