Lowe D A, Russell I J
Proc R Soc Lond B Biol Sci. 1984 Jun 22;221(1225):437-54. doi: 10.1098/rspb.1984.0043.
In adult Xenopus laevis the mandibular and ophthalmic branches of the trigeminal nerve were backfilled with CoCl2 or cobaltous lysine and whole brains silver intensified to reveal neurons of the mesencephalic Vth nucleus (mes. V). The nucleus contains about 100 cells arranged in a band extending arch-like from the ventrolateral margin of the optic tectum to the midline. Many cells possess a small number of short dendritic processes that arborize in the tectal neuropil; in some cells one dendrite terminates within the ependyma or ventricle. A single axon arises from each cell and courses in layer 7 to the margin of the tectum. Axon collaterals arise close to the cell body to terminate principally within layer 6, but occasionally also in layers 8 and 9. Collaterals occurring more caudally terminate in layer 6. These findings suggest that mes. V cells acts as tectal interneurons as well as conveying somatosensory information to the tectum from the mouth region. In the dorsal roof of the tectum the trajectory of a fibre is related to the distance of the soma from the midline. Mes. V cells located at the lateral end of the nucleus possess axons that course initially in a mediolateral direction before turning along the ventrolateral margin of the tectum. Cells positioned close to the midline have axons that project rostrocaudally the entire length of the tectum. The axons of cells located at intermediate positions within the nucleus course at correspondingly oblique angles through the dorsal roof of the tectum. Thus in this area there is a more or less 90 degrees rang in the orientation of mes. V fibres to the longitudinal axis. It is proposed that this topographical relationship between soma position and axon trajectory arises through a developmental mechanism, in which mes. V fibres grow during larval life sequentially into the medial zone of tectal growth and become subsequently displaced rostrolaterally, owing to the further addition of tectal tissue medially, through an angle dependent upon the parent cell's date of birth.
在成年非洲爪蟾中，用氯化钴或赖氨酸钴对三叉神经的下颌支和眼支进行逆向填充，并对整个大脑进行银增强处理，以显示中脑V核（中脑V）的神经元。该核包含约100个细胞，排列成一条带，从视顶盖的腹外侧边缘呈拱形延伸至中线。许多细胞具有少量短的树突状突起，这些突起在顶盖神经毡中分支；在一些细胞中，一个树突终止于室管膜或脑室内。每个细胞发出一条轴突，在第7层向顶盖边缘延伸。轴突侧支在靠近细胞体处发出，主要终止于第6层，但偶尔也终止于第8层和第9层。在更靠尾侧的部位发出的侧支终止于第6层。这些发现表明，中脑V细胞既作为顶盖中间神经元，又从口部区域向顶盖传递躯体感觉信息。在顶盖的背顶，纤维的轨迹与细胞体到中线的距离有关。位于核外侧端的中脑V细胞的轴突最初沿中外侧方向延伸，然后沿顶盖的腹外侧边缘转向。靠近中线的细胞的轴突在顶盖的整个长度上向头尾方向投射。位于核内中间位置的细胞的轴突以相应的倾斜角度穿过顶盖的背顶。因此，在这个区域，中脑V纤维与纵轴的方向存在或多或少90度的范围。有人提出，细胞体位置与轴突轨迹之间的这种拓扑关系是通过一种发育机制产生的，在这种机制中，中脑V纤维在幼体生活期间依次生长到顶盖生长的内侧区域，随后由于内侧顶盖组织的进一步添加，通过一个取决于母细胞出生日期的角度向 rostrolaterally 移位。
