Shumway C A
Neurobiology Unit, Scripps Institution of Oceanography, UCSD, La Jolla, California 92093.
J Neurosci. 1989 Dec;9(12):4400-15. doi: 10.1523/JNEUROSCI.09-12-04400.1989.
Both wave- and pulse-type species of weakly electric gymnotiform fish have 3 topographic maps of electroreceptive information in the electrosensory lateral line lobe (ELL). These maps receive identical input from trifurcating axons of phase- and amplitude-coding primary afferents (Carr et al., 1982; Heiligenberg and Dye, 1982). Physiological experiments in the ELL of the wave-type fish Eigenmannia show that the amplitude-coding pyramidal cells differ among maps with respect to receptive field size, sensitivity, rate of adaptation, and temporal-frequency response (Shumway, 1989). This study investigated morphological correlates of the physiological differences among maps. Estimates of primary afferent convergence in Eigenmannia, based on map size, cell counts, and areas of terminal fields from intracellularly filled P-type primary afferents, suggest a 2-fold increase in convergence in the lateral map relative to the centromedial map. Similar differences in convergence between maps are found in the wave-type species Apteronotus leptorhynchus and the pulse-type fish Hypopomus occidentalis. The lateral and centrolateral maps in Hypopomus, however, show an even greater difference in convergence. Comparison of the efferent projections of pyramidal cells among the different maps of Eigenmannia indicates that cells from the 3 maps terminate in the same laminae of the torus semicircularis, but the maps differ in the strength of projection to particular laminae. In both wave-type species, the abundance of a class of interneurons which receives descending input and inhibits pyramidal cells (interneurons of the ventral molecular layer) differs among maps; the centromedial map has 10 times fewer neurons of this type than the other 2 maps. Cytochrome oxidase studies in all 3 species demonstrated increased levels of activity in the lateral map, within the region receiving descending input from the cerebellum. These results suggest that the primary anatomical bases of the physiological differences among maps are differences in the amount of primary afferent convergence, coupled with differences in descending input.
弱电裸背电鳗目鱼类的波型和脉冲型物种在电感受侧线叶（ELL）中都有3种电感受信息的地形图。这些地图从相位和幅度编码初级传入神经元的三叉分支轴突接收相同的输入（Carr等人，1982年；Heiligenberg和Dye，1982年）。对波型鱼类艾氏电鳗ELL的生理学实验表明，幅度编码锥体细胞在不同地图之间在感受野大小、敏感性、适应率和时间频率响应方面存在差异（Shumway，1989年）。本研究调查了不同地图之间生理差异的形态学相关性。基于地图大小、细胞计数以及细胞内填充的P型初级传入神经元终末场面积，对艾氏电鳗初级传入神经元汇聚的估计表明，外侧地图的汇聚相对于中央内侧地图增加了2倍。在波型物种细吻无臀电鳗和脉冲型鱼类西方低臀电鳗的地图之间也发现了类似的汇聚差异。然而，低臀电鳗的外侧和中央外侧地图在汇聚方面显示出更大的差异。对艾氏电鳗不同地图中锥体细胞传出投射的比较表明，来自这3个地图的细胞终止于半规管环面的相同层，但不同地图向特定层的投射强度不同。在这两种波型物种中，一类接收下行输入并抑制锥体细胞的中间神经元（腹侧分子层中间神经元）在不同地图中的丰度不同；中央内侧地图中这种类型的神经元比其他两个地图少10倍。对所有3个物种的细胞色素氧化酶研究表明，在接收来自小脑下行输入的区域内，外侧地图的活性水平增加。这些结果表明，不同地图之间生理差异的主要解剖学基础是初级传入神经元汇聚量的差异，以及下行输入的差异。
