QUANTITATIVE AND QUARITATIVE STUDY OF PERIGLOMERULR CELLS IN THE MAIN OLFACTORY BULB

近年来对嗅觉系统的研究进展使其成为理解信息处理的神经机制的一个有用的感觉模型系统。在嗅觉系统的主要中枢嗅球中，肾小球被认为是传递气味信号和处理嗅觉信息的重要功能单位，但一直被认为仅由少数神经元类型组成，因此其神经元和突触组织简单。然而，越来越多的形态学数据显示，每种类型的神经元可能进一步由几个不同的亚群组成，这表明肾小球的组织可能不像人们认为的那么简单。我们对大鼠OB的神经元组织进行免疫细胞化学分析，发现肾小球周围细胞的化学和结构异质性，提出将其分为1型和2型。1型肾小球周围细胞将其肾小球内树突同时送入嗅神经区和非嗅神经区，而2型肾小球周围细胞仅将其肾小球内树突送入非嗅神经区。1型细胞可能包括gaba能神经元，2型细胞显然包括CB-IR和CR-IR神经元。两类肾小球周围细胞树突投射的差异，特别是它们在嗅觉神经末梢突触输入上的显著差异，使我们推测它们在局部回路中可能存在的功能差异。1型细胞可能在投射神经元接收ON传入信号的同时也接收到ON传入信号的激活，而2型细胞只有在投射神经元被激活后才能通过来自投射神经元的突触被激活。由于这两种类型都与投射神经元形成许多突触，包括相互突触，这些突触连接的差异可能导致投射神经元对单个气味分子的不同生理反应。

Recent progress in the studies of the olfactory system makes it one of useful sensory model systems for understanding neural mechanisms for the information processing. In the olfactory bulb, the primary center of the olfactory system, glomeruli are regarded as important functional units in the transmission of odorant signals and in processing the olfactory information, but have been believed to be composed by only a small number of neuronal types and thus to be simple in their neuronal and synaptic organization. However, accumulating morphological data reveal that each type of neurons might further consist of several different subpopulations, indicating that the organization of glomeruti might not be so simple as it was believed.We analyzed the neuronal organization of the rat OB immunocytochemically and found the chemical and structural heterogeneity of the periglomerular cells, proposing to classify them into two types, type 1 and 2. Type 1 periglomerular cells send their intraglomerular dendrites both into the olfactory nerve (ON) zone and non-ON zone, whereas type 2 periglomerular cells send their intraglomerular dendrites only into the non-ON zone. Type 1 cells might include GABAergic neurons and type 2 cells apparently include CB-IR and CR-IR neurons. The differences in dendritic projection of two categories of periglomerular cells, especially their prominent differences in the synaptic inputs from the olfactory nerve terminals, lead us to speculate their possible functional differences in the local circuit. Type 1 cells are likely to receive activation from ON afferents at the same time when projection neurons receive them, whereas type 2 cells are activated via synapses from projection neurons only after projection neurons are activated. As both types make many synapses, including reciprocal ones, with projection neurons, these differences in synaptic connections might cause various physiological responses of projection neurons to single odorant molecules.