School of Biosciences, Cardiff University, Cardiff, UK.
Curr Mol Pharmacol. 2008 Nov;1(3):181-90. doi: 10.2174/1874467210801030181.
The olfactory bulb is located at the start of a hierarchical chain of sensory processing mechanisms. The relative ease of its isolation allows the possibility that models of these mechanisms might be integrated to develop a detailed understanding of function. In this sensory processing chain odour molecules evoke signal transduction in the olfactory receptor neurons. These signals represent the diverse range of molecular binding affinities of the olfactory receptor proteins. The first level of processing of this sensory input is performed by the neurons of the olfactory bulb. The olfactory system needs to filter the vast amount of sensory input it receives to be able to select the subset of biological significance. The importance of the olfactory bulb in this filtering process is suggested by its wide range of modulatory mechanisms. These mechanisms include an array of centrifugal inputs from other regions of the brain as well as numerous intrinsic feedback circuits. Given the complexity of the olfactory bulb and the range of its modulatory activity, the process of isolation of its components produces some difficulties of interpretation. This is mainly due to the removal of some of the effects of interaction and the change in balance that results. We present a summary of the current understanding of the interacting modulatory elements that are found in the olfactory bulb and a detailed account of the properties of mitral/tufted cells, the projection neurons of the olfactory bulb. This is followed by a discussion of the intrinsic and extrinsic modulatory systems acting on these cells. A consideration of the integration of the effects of these modulatory systems allows an understanding of how the output of the mitral/tufted cells is controlled. While significant progress has been made in the elucidation of the individual components as a result of advances in techniques over the last decade we suggest that there is a need for computational studies as a further aid to the understanding and interpretation of the weight of individual modulatory components in this dynamic interacting system.
嗅球位于感觉处理机制的层级链的起始端。其相对容易被分离出来，这使得整合这些机制的模型以深入了解其功能成为可能。在这个感觉处理链中，气味分子会引发嗅球中的感觉神经元的信号转导。这些信号代表了嗅觉受体蛋白的多种分子结合亲和力。这种感觉输入的第一级处理是由嗅球中的神经元完成的。嗅觉系统需要过滤其接收到的大量感觉输入，以便能够选择具有生物学意义的子集。嗅球在这个过滤过程中的重要性是由其广泛的调制机制所提示的。这些机制包括来自大脑其他区域的大量离心输入以及许多内在反馈回路。鉴于嗅球的复杂性及其广泛的调制活性，其组成部分的分离过程产生了一些解释上的困难。这主要是由于去除了一些相互作用的影响，以及由此产生的平衡变化。我们总结了当前对嗅球中相互作用的调制元件的理解，并详细介绍了嗅球中的投射神经元——僧帽细胞和丛状细胞的特性。接下来讨论了作用于这些细胞的内在和外在调制系统。考虑这些调制系统的影响的整合，可以理解僧帽细胞和丛状细胞的输出是如何被控制的。虽然由于过去十年中技术的进步，在阐明各个组成部分方面已经取得了重大进展，但我们认为，作为对这个动态相互作用系统中单个调制成分的权重的理解和解释的进一步辅助，还需要进行计算研究。
