Antón P S, Granger R, Lynch G
Center for the Neurobiology of Learning and Memory, University of California, Irvine 92717.
Brain Res. 1993 Nov 19;628(1-2):157-65. doi: 10.1016/0006-8993(93)90951-i.
Whereas many theories have been proposed for the function of dendritic spines in axodendritic processing, the influence of spines on reciprocal dendrodendritic processing has received relatively little attention. Mitral cells in the olfactory bulb, for example, synapse on granule cell spines (gemmules) which are in turn presynaptic to reciprocal inhibitory synapses back onto the same mitral cells. The postulate that these synapses respond with synaptic strengths graded by presynaptic depolarization results in a sensitivity of the reciprocal response to the local depolarization in the spine head. A biophysical computer simulation was performed to study this effect and the effect of changing the spine neck diameter and cytoplasmic resistance on the reciprocal and lateral inhibitory responses given graded dendrodendritic synapses. Since spine head local potentials are larger than similar inputs on dendritic shafts, spines facilitate the graded reciprocal response even for low levels of activity. Spine heads also reduce the synaptic current, lowering the contribution to the rest of the granule dendritic tree and thus reducing lateral inhibition. In addition, an increase in the effective spine neck axial resistance further increases the reciprocal synaptic response and decreases the lateral inhibitory response. Short-term, reversible, and long-term methods of implementing this resistance-based dendrodendritic plasticity are discussed as well as the partial dependence of the reciprocal increase/lateral decrease effect on a broad synaptic gradation. Candidate memory operations by the bulb are also discussed, including a possible recognition memory pass/block function.
尽管已经提出了许多关于树突棘在轴突 - 树突加工中功能的理论，但棘突对相互的树突 - 树突加工的影响却相对较少受到关注。例如，嗅球中的二尖瓣细胞与颗粒细胞的棘突（小芽）形成突触，而这些棘突反过来又成为与相同二尖瓣细胞形成相互抑制性突触的突触前结构。这些突触以由突触前去极化分级的突触强度做出反应的假设导致相互反应对棘突头部局部去极化的敏感性。进行了生物物理计算机模拟，以研究这种效应以及改变棘突颈部直径和细胞质电阻对给定分级树突 - 树突突触的相互和侧向抑制反应的影响。由于棘突头部的局部电位大于树突轴上的类似输入，即使在低活动水平下，棘突也有助于分级的相互反应。棘突头部还会降低突触电流，减少对颗粒树突其余部分的贡献，从而减少侧向抑制。此外，有效棘突颈部轴向电阻的增加会进一步增加相互突触反应并降低侧向抑制反应。还讨论了实现这种基于电阻的树突 - 树突可塑性的短期、可逆和长期方法，以及相互增加/侧向减少效应在广泛突触分级上的部分依赖性。还讨论了嗅球可能的记忆操作，包括可能的识别记忆通过/阻断功能。
