Gahtan Ethan, O'Malley Donald M
Department of Biology, Northeastern University, Boston, Massachusetts 02115, USA.
J Comp Neurol. 2003 Apr 28;459(2):186-200. doi: 10.1002/cne.10621.
We report here the pattern of axonal branching for 11 descending cell types in the larval brainstem; eight of these cell types are individually identified neurons. Large numbers of brainstem neurons were retrogradely labeled in living larvae by injecting Texas-red dextran into caudal spinal cord. Subsequently, in each larva a single identified cell was injected in vivo with Alexa 488 dextran, using fluorescence microscopy to guide the injection pipette to the targeted cell. The filling of cells via pressure pulses revealed distinct and often extensive spinal axon collaterals for the different cell types. Previous fills of the Mauthner cell had revealed short, knob-like collaterals. In contrast, the two segmental homologs of the Mauthner cell, cells MiD2cm and MiD3cm, showed axon collaterals with extensive arbors recurring at regular intervals along nearly the full extent of spinal cord. Furthermore, the collaterals of MiD2cm crossed the midline at frequent intervals, yielding bilateral arbors that ran in the rostral-caudal direction. Other medullary reticulospinal cells, as well as cells of the nucleus of the medial longitudinal fasciculus (nMLF), also exhibited extensive spinal collaterals, although the patterns differed for each cell type. For example, nMLF cells had extensive collaterals in caudal medulla and far-rostral spinal cord, but these collaterals became sparse more caudally. Two cell types (CaD and RoL1) showed arbors projecting ventrally from a dorsally situated stem axon. Additional cell-specific features that seemed likely to be of physiological significance were observed. The rostral-caudal distribution of axon collaterals was of particular interest because of its implications for the descending control of the larva's locomotive repertoire. Because the same individual cell types can be identified from fish to fish, these anatomical observations can be directly linked to data obtained in other kinds of experiments. For example, 9 of the 11 cell types examined here have been shown to be active during escape behaviors.
我们在此报告了幼体脑干中11种下传细胞类型的轴突分支模式；其中8种细胞类型是可单独识别的神经元。通过将德克萨斯红葡聚糖注入尾侧脊髓，在活体幼体中对大量脑干神经元进行了逆行标记。随后，在每只幼体中，使用荧光显微镜将注射移液管引导至目标细胞，在体内向单个已识别细胞注射Alexa 488葡聚糖。通过压力脉冲填充细胞，揭示了不同细胞类型独特且通常广泛的脊髓轴突侧支。先前对莫特纳尔细胞的填充显示出短的、瘤状的侧支。相比之下，莫特纳尔细胞的两个节段同源物，即MiD2cm细胞和MiD3cm细胞，显示出轴突侧支具有广泛的分支，沿着脊髓几乎整个长度以规则间隔重复出现。此外，MiD2cm细胞的侧支频繁穿过中线，产生沿头尾方向延伸的双侧分支。其他延髓网状脊髓细胞以及内侧纵束核（nMLF）的细胞也表现出广泛的脊髓侧支，尽管每种细胞类型的模式有所不同。例如，nMLF细胞在延髓尾部和脊髓远头部有广泛的侧支，但这些侧支在更靠尾侧的部位变得稀疏。两种细胞类型（CaD和RoL1）显示分支从位于背侧的主干轴突腹侧伸出。还观察到了其他可能具有生理意义的细胞特异性特征。轴突侧支的头尾分布特别令人感兴趣，因为它对幼体运动行为的下行控制有影响。由于在不同鱼类中可以识别出相同的个体细胞类型，这些解剖学观察结果可以直接与其他类型实验中获得的数据联系起来。例如，这里检查的11种细胞类型中有9种已被证明在逃避行为期间是活跃的。
