Philippides Andrew, Ott Swidbert R, Husbands Philip, Lovick Thelma A, O'Shea Michael
Sussex Centre for Neuroscience, School of Life Sciences, University of Sussex, Brighton BN1 9QG, United Kingdom.
J Neurosci. 2005 Jul 13;25(28):6520-32. doi: 10.1523/JNEUROSCI.1264-05.2005.
In vertebrate and invertebrate brains, nitric oxide (NO) synthase (NOS) is frequently expressed in extensive meshworks (plexuses) of exceedingly fine fibers. In this paper, we investigate the functional implications of this morphology by modeling NO diffusion in fiber systems of varying fineness and dispersal. Because size severely limits the signaling ability of an NO-producing fiber, the predominance of fine fibers seems paradoxical. Our modeling reveals, however, that cooperation between many fibers of low individual efficacy can generate an extensive and strong volume signal. Importantly, the signal produced by such a system of cooperating dispersed fibers is significantly more homogeneous in both space and time than that produced by fewer larger sources. Signals generated by plexuses of fine fibers are also better centered on the active region and less dependent on their particular branching morphology. We conclude that an ultrafine plexus is configured to target a volume of the brain with a homogeneous volume signal. Moreover, by translating only persistent regional activity into an effective NO volume signal, dispersed sources integrate neural activity over both space and time. In the mammalian cerebral cortex, for example, the NOS plexus would preferentially translate persistent regional increases in neural activity into a signal that targets blood vessels residing in the same region of the cortex, resulting in an increased regional blood flow. We propose that the fineness-dependent properties of volume signals may in part account for the presence of similar NOS plexus morphologies in distantly related animals.
在脊椎动物和无脊椎动物的大脑中，一氧化氮（NO）合酶（NOS）经常在极其纤细的纤维构成的广泛网络（丛）中表达。在本文中，我们通过对不同细度和分散度的纤维系统中的NO扩散进行建模，来研究这种形态的功能意义。由于尺寸严重限制了产生NO的纤维的信号传递能力，细纤维占主导地位似乎自相矛盾。然而，我们的建模显示，许多个体效能较低的纤维之间的协作可以产生广泛而强烈的体积信号。重要的是，这样一个由协作的分散纤维组成的系统产生的信号在空间和时间上比由较少的较大来源产生的信号更加均匀。由细纤维丛产生的信号也更好地集中在活动区域，并且对其特定的分支形态依赖性更小。我们得出结论，超细丛被配置为用均匀的体积信号靶向大脑的一个体积区域。此外，通过仅将持续的区域活动转化为有效的NO体积信号，分散的来源在空间和时间上整合了神经活动。例如，在哺乳动物的大脑皮层中，NOS丛会优先将神经活动中持续的区域增加转化为一个靶向位于皮层同一区域的血管的信号，从而导致区域血流量增加。我们提出，体积信号的细度依赖性特性可能部分解释了在远缘动物中存在类似的NOS丛形态的原因。
