Evans C G, Alexeeva V, Rybak J, Karhunen T, Weiss K R, Cropper E C
Department of Physiology and Biophysics, The Mt. Sinai Medical Center, New York, New York 10029, USA.
J Neurosci. 1999 Jan 15;19(2):845-58. doi: 10.1523/JNEUROSCI.19-02-00845.1999.
Previous studies have shown that each buccal ganglion in Aplysia contains two B52 neurons, one in each hemiganglion. We now show that there are two B52 neurons in a single buccal hemiganglion and four cells in an animal. We also show that the B52 neurons are histamine-immunoreactive and use reverse phase HPLC to show that the histamine-immunoreactive substance is authentic histamine. Previous studies have shown that the B52 neurons make numerous inhibitory synaptic connections with neurons active during the radula closing/retraction phase of ingestive motor programs. A computational model of the Aplysia feeding central pattern generator has, therefore, suggested that the B52 neurons play a role in terminating closing/retraction. Consistent with this idea we show that both B52 neurons fire at the beginning of radula opening/protraction. We also show that both B52 neurons are sensory neurons. They are depolarized when a flap of connective tissue adjacent to the buccal commissural arch is stretched. During ingestive feeding this is likely to occur at the peak of closing/retraction as opening/protraction begins. In the course of this study we compare the two ipsilateral B52 neurons and show that these cells are virtually indistinguishable; e.g., they use a common neurotransmitter, make the same synaptic connections, and are both sensory as well as premotor neurons. Nevertheless we show that the B52 neurons are reciprocally inhibitory. Our results, therefore, strikingly confirm theoretical predictions made by others that neurons that inhibit each other will not necessarily participate in antagonistic phases of behavior.
以往的研究表明，海兔的每个颊神经节都包含两个B52神经元，每个半神经节各有一个。我们现在发现，单个颊半神经节中有两个B52神经元，而一只动物体内共有四个这样的细胞。我们还发现，B52神经元具有组胺免疫反应性，并使用反相高效液相色谱法证明，具有组胺免疫反应性的物质是真正的组胺。以往的研究表明，B52神经元与摄食运动程序中齿舌闭合/回缩阶段活跃的神经元形成大量抑制性突触连接。因此，海兔摄食中枢模式发生器的计算模型表明，B52神经元在终止闭合/回缩过程中发挥作用。与这一观点一致的是，我们发现两个B52神经元都在齿舌张开/前伸开始时放电。我们还发现，两个B52神经元都是感觉神经元。当颊连合弓附近的结缔组织瓣被拉伸时，它们会发生去极化。在摄食过程中，这种情况可能发生在闭合/回缩的峰值，此时张开/前伸开始。在这项研究过程中，我们比较了同侧的两个B52神经元，发现这些细胞几乎无法区分；例如，它们使用共同的神经递质，形成相同的突触连接，既是感觉神经元也是运动前神经元。然而，我们发现B52神经元之间存在相互抑制作用。因此，我们的结果显著证实了其他人做出的理论预测，即相互抑制的神经元不一定参与行为的拮抗阶段。
