Kinnamon J C, Sherman T A, Roper S D
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder 80309-0347.
J Comp Neurol. 1988 Apr 1;270(1):1-10, 56-7. doi: 10.1002/cne.902700102.
We have used serial high voltage electron micrographs and computer-generated, three-dimensional reconstructions to study morphological relationships and patterns of synaptic connectivity in taste buds from the circumvallate papillae of the mouse. The intragemmal arborizations of 40 sensory nerve fibers were examined from 7 taste buds that were sectioned serially. We identified the synaptic connections from taste cells onto the reconstructed nerve fibers and classified the presynaptic taste cells based on previously established ultrastructural criteria. From these data we were able to extract the following information for the reconstructed nerve fibers: (1) the morphology of intragemmal nerve fibers and their arborizations within the taste bud, (2) the total number of synaptic connections from taste bud cells onto the nerve fibers, and (3) the taste cell types associated with each of the synapses. Fifty-six synapses were studied. Synapses were often found to be located at either the branch points or terminations of nerve fiber processes. The maximum number of taste cells observed to synapse onto a single nerve fiber was 5. Several nerve fibers had no apparent synapses. Dark cells (type I), intermediate cells, and light cells (type II) all formed synaptic connections with sensory nerve fibers. In no cases did dark cells and light cells synapse onto the same sensory nerve fiber. Our observation that any given nerve fiber receives its synaptic input from morphologically similar taste cells provides evidence for specificity in taste bud synaptic connections. We speculate that the observed pattern of synaptic connections is related to taste bud function. Since all of the synapses onto a given nerve fiber are from morphologically similar taste cells, we postulate that there is a correlation between taste cell morphology and sensory responsiveness. Intracellular electrophysiological studies on taste cells, in which responses to focally applied chemical stimuli are followed by characterization of the ultrastructural features of the same taste cells, will prove or disprove this hypothesis.
我们利用系列高压电子显微镜照片以及计算机生成的三维重建技术，研究了小鼠轮廓乳头味蕾中突触连接的形态关系和模式。从连续切片的7个味蕾中检查了40条感觉神经纤维的味蕾内分支。我们确定了味觉细胞与重建神经纤维之间的突触连接，并根据先前确立的超微结构标准对突触前味觉细胞进行了分类。从这些数据中，我们能够为重建的神经纤维提取以下信息：（1）味蕾内神经纤维的形态及其分支，（2）味蕾细胞与神经纤维之间突触连接的总数，以及（3）与每个突触相关的味觉细胞类型。共研究了56个突触。突触常常位于神经纤维分支点或末端。观察到单个神经纤维上突触连接的味觉细胞最大数量为5个。有几条神经纤维没有明显的突触。暗细胞（I型）、中间细胞和亮细胞（II型）均与感觉神经纤维形成突触连接。暗细胞和亮细胞从未在同一感觉神经纤维上形成突触。我们观察到任何给定的神经纤维都从形态相似的味觉细胞接收突触输入，这为味蕾突触连接的特异性提供了证据。我们推测观察到的突触连接模式与味蕾功能有关。由于给定神经纤维上的所有突触都来自形态相似的味觉细胞，我们假设味觉细胞形态与感觉反应性之间存在相关性。对味觉细胞进行细胞内电生理研究，即在对局部施加的化学刺激的反应之后对相同味觉细胞的超微结构特征进行表征，将证实或反驳这一假设。
