Friedman B, Price J L
J Comp Neurol. 1984 Feb 10;223(1):88-109. doi: 10.1002/cne.902230108.
The structure of the olfactory bulb and cortex of rats is described using the Timm method, in which endogenous transition or "heavy" metals are precipitated with sulfide and then stained with silver. With the light microscope, two types of staining, a fine, "colored" reaction and a coarse, "granular" reaction, are found in the neuropil of the adult forebrain; neuronal somata, fiber tracts, and some specific areas of the neuropil are almost unstained. With the electron microscope the Timm method consists of small silver granules, which are associated with axon terminals. These granules are located over the external surface of the presynaptic membrane, facing the synaptic cleft, and over synaptic vesicles, especially the internal surface of the vesicle membrane. This localization suggests that the reactive metals are related to a membrane component which is recycled during secretion of synaptic transmitters. The colored and granular reactions seen with the light microscope appear to be correlated with different intensities of staining of different types of axon terminals. The full extent of the olfactory cortex can be delineated by a bilaminar staining pattern in layer I, which coincides with the pattern of termination of fiber systems to the cortex demonstrated by axonal tracing experiments. The superficial part of layer I is very palely stained; this corresponds precisely to layer Ia, the zone of termination of fibers from the olfactory bulb. In contrast, the deep part of the layer is stained with an intense colored reaction; this corresponds precisely to layer Ib, the zone of termination of the major association fiber system within the olfactory cortex. A prominent granular reaction, which does not correspond to any known long axon system, is found in all layers of the cortex, although it is concentrated at the superficial edge of layer Ib and in layer II. Variations in staining in the several subdivisions of the olfactory cortex are illustrated and described. In the olfactory bulb, the most prominent staining is a relatively fine, granular reaction in the glomerular formations, which apparently corresponds to the olfactory nerve terminals. In immature rats, the Timm method stains the neuropil throughout the olfactory system, although the patterns and quality of staining differ from that found in adults. Before birth, the best-differentiated reaction is seen in glomeruli of the olfactory bulb and correlates well with the pattern of olfactory nerve ingrowth.(ABSTRACT TRUNCATED AT 400 WORDS)
采用Timm法描述大鼠嗅球和皮质的结构，该方法利用硫化物沉淀内源性过渡金属或“重金属”，然后用银染色。在光学显微镜下，在成年前脑的神经毡中发现两种染色类型，一种是精细的“显色”反应，另一种是粗糙的“颗粒状”反应；神经元胞体、纤维束和神经毡的一些特定区域几乎未被染色。在电子显微镜下，Timm法由与轴突终末相关的小银颗粒组成。这些颗粒位于突触前膜的外表面，面向突触间隙，也位于突触小泡上，尤其是小泡膜的内表面。这种定位表明反应性金属与一种在突触递质分泌过程中循环利用的膜成分有关。光学显微镜下看到的显色和颗粒状反应似乎与不同类型轴突终末的不同染色强度相关。嗅皮质的全貌可通过I层的双分层染色模式勾勒出来，这与轴突追踪实验所显示的纤维系统向皮质的终止模式一致。I层的浅层染色很浅；这恰好对应于Ia层，即来自嗅球的纤维的终止区。相比之下，该层的深层有强烈的显色反应；这恰好对应于Ib层，即嗅皮质内主要联合纤维系统的终止区。在皮质的所有层中都发现了一种突出的颗粒状反应，它与任何已知的长轴突系统都不对应，尽管它集中在Ib层的浅表边缘和II层。文中展示并描述了嗅皮质几个亚区染色的变化。在嗅球中，最显著的染色是在小球状结构中呈现相对精细的颗粒状反应，这显然对应于嗅神经终末。在未成熟大鼠中，Timm法可对整个嗅觉系统的神经毡进行染色，尽管染色模式和质量与成年大鼠不同。出生前，在嗅球的小球中可看到分化最好的反应，且与嗅神经向内生长的模式密切相关。（摘要截取自400字）
