Masino T, Grobstein P
Department of Anatomy, University of Chicago, Illinois 60637.
J Comp Neurol. 1990 Jan 1;291(1):103-27. doi: 10.1002/cne.902910108.
Recent studies of visually elicited orienting in the frog Rana pipiens suggest that tectofugal signals important in this behavior relay in the midbrain tegmentum before descending to the spinal cord. They also suggest that the high degree of topographic organization displayed by the retinotectal projection may be less characteristic of other tectal afferent and efferent pathways. To explore these possibilities, we have studied patterns of retrograde and anterograde labelling following multiple and single injections of horseradish peroxidase into the tectum. We have found that the midbrain tegmentum is a major terminal zone for tectal efferent projections. Our material also provided a description of the boundaries of other structures which project to and receive input from the tectum. With this background, we studied topographic organization by analyzing for each structure the distribution of labelling following multiple injections, and comparing it with the label distribution following single injections at tectal loci with known visual field input. Multiple injections produced patchy anterograde and retrograde labelling in the nucleus isthmi, with the number of patches corresponding to the number of tectal sites injected. Single injections produced labelling in restricted regions of the nucleus isthmi, the location of which varied systematically with the location of the tectal injection site. In all other structures studied, labelling was more evenly distributed following multiple injections. In none of these structures could we detect systematic variations in the location of labelling associated with variations in the location of single tectal injection sites, and the labelling following single injections was frequently coextensive with that following multiple injections. We also found no evidence that there exist structures which project to or receive input from particular tectal regions and not others. We conclude that there exist adequate neuroanatomical substrates for a tectotegmentospinal pathway believed to be important for visually elicited orienting in the frog. We also conclude that a high degree of topographic organization is more the exception than the rule in considering tectal connections generally in the frog. Topographic organization was readily apparent in connections related to the nucleus isthmi but not in connections related to any other nonretinal structure.
最近对豹蛙视觉诱发定向的研究表明，在这种行为中起重要作用的顶盖离中信号在下行至脊髓之前，会在中脑被盖中继。这些研究还表明，视网膜顶盖投射所显示的高度拓扑组织，可能在其他顶盖传入和传出通路中不太典型。为了探究这些可能性，我们研究了将辣根过氧化物酶多次和单次注入顶盖后逆行和顺行标记的模式。我们发现中脑被盖是顶盖传出投射的主要终末区。我们的材料还描述了其他投射到顶盖并从顶盖接收输入的结构的边界。在此背景下，我们通过分析每个结构在多次注射后标记的分布，并将其与在具有已知视野输入的顶盖位点单次注射后的标记分布进行比较，来研究拓扑组织。多次注射在峡核中产生了斑片状的顺行和逆行标记，斑块数量与注入顶盖的位点数量相对应。单次注射在峡核的受限区域产生标记，其位置随顶盖注射位点的位置而系统变化。在所有其他研究的结构中，多次注射后标记分布更均匀。在这些结构中，我们均未检测到与单个顶盖注射位点位置变化相关的标记位置的系统变化，并且单次注射后的标记通常与多次注射后的标记共延。我们也没有发现证据表明存在只投射到特定顶盖区域或只从特定顶盖区域接收输入的结构。我们得出结论，存在足够的神经解剖学基础来支持一条被认为对青蛙视觉诱发定向很重要的顶盖 - 被盖 - 脊髓通路。我们还得出结论，在考虑青蛙顶盖连接时，高度的拓扑组织更多是例外而非普遍规律。拓扑组织在与峡核相关的连接中很明显，但在与任何其他非视网膜结构相关的连接中则不明显。
