Butler A B
Ivory Tower Neurobiology Institute, Arlington, VA 22207.
Brain Res Brain Res Rev. 1994 Jan;19(1):29-65. doi: 10.1016/0165-0173(94)90003-5.
The evolution of the dorsal thalamus in various vertebrate lineages of jawed vertebrates has been an enigma, partly due to two prevalent misconceptions: the belief that the multitude of nuclei in the dorsal thalamus of mammals could be meaningfully compared neither with the relatively few nuclei in the dorsal thalamus of anamniotes nor with the intermediate number of dorsal thalamic nuclei of other amniotes and a definition of the dorsal thalamus that too narrowly focused on the features of the dorsal thalamus of mammals. The cladistic analysis carried out here allows us to recognize which features are plesiomorphic and which apomorphic for the dorsal thalamus of jawed vertebrates and to then reconstruct the major changes that have occurred in the dorsal thalamus over evolution. Embryological data examined in the context of Von Baerian theory (embryos of later-descendant species resemble the embryos of earlier-descendant species to the point of their divergence) supports a new 'Dual Elaboration Hypothesis' of dorsal thalamic evolution generated from this cladistic analysis. From the morphotype for an early stage in the embryological development of the dorsal thalamus of jawed vertebrates, the divergent, sequential stages of the development of the dorsal thalamus are derived for each major radiation and compared. The new hypothesis holds that the dorsal thalamus comprises two basic divisions--the collothalamus and the lemnothalamus--that receive their predominant input from the midbrain roof and (plesiomorphically) from lemniscal pathways, including the optic tract, respectively. Where present, the collothalamic, midbrain-sensory relay nuclei are homologous to each other in all vertebrate radiations as discrete nuclei. Within the lemnothalamus, the dorsal lateral geniculate nucleus of mammals and the dorsal lateral optic nucleus of non-synapsid amniotes (diapsid reptiles, birds and turtles) are homologous as discrete nuclei; most or all of the ventral nuclear group of mammals is homologous as a field to the lemniscal somatosensory relay and motor feedback nuclei of non-synapsid amniotes; the anterior, intralaminar and medial nuclear groups of mammals are collectively homologous as a field to both the dorsomedial and dorsolateral (including perirotundal) nuclei of non-synapsid amniotes; the anterior, intralaminar, medial and ventral nuclear groups and the dorsal lateral geniculate nucleus of mammals are collectively homologous as a field to the nucleus anterior of anamniotes, as are their homologues in non-synapsid amniotes. In the captorhinomorph ancestors of extant land vertebrates, both divisions of the dorsal thalamus were elaborated to some extent due to an increase in proliferation and lateral migration of neurons during development.(ABSTRACT TRUNCATED AT 400 WORDS)
有颌脊椎动物各谱系中背侧丘脑的演化一直是个谜，部分原因在于两个普遍存在的误解：一是认为哺乳动物背侧丘脑中众多的核既无法与无羊膜动物背侧丘脑中相对较少的核进行有意义的比较，也无法与其他羊膜动物背侧丘脑核数量居中的情况相比较；另一个是对背侧丘脑的定义过于狭隘地聚焦于哺乳动物背侧丘脑的特征。本文所进行的分支系统分析使我们能够识别出哪些特征是有颌脊椎动物背侧丘脑的祖征，哪些是衍征，进而重构背侧丘脑在演化过程中发生的主要变化。在冯·拜尔理论（后代物种的胚胎在其分化点之前类似于早期后代物种的胚胎）背景下研究的胚胎学数据，支持了基于这种分支系统分析产生的背侧丘脑演化的新“双重细化假说”。从有颌脊椎动物背侧丘脑胚胎发育早期阶段的形态类型出发，推导出每个主要类群背侧丘脑发育的不同连续阶段并进行比较。新假说认为，背侧丘脑由两个基本部分组成——丘脑下部和丘脑上部——它们分别从中脑顶盖以及（祖征上）从包括视束在内的lemniscal通路接收主要输入。在存在的情况下，丘脑下部的中脑感觉中继核在所有脊椎动物类群中作为离散核彼此同源。在丘脑上部内，哺乳动物的背外侧膝状核与非合弓纲羊膜动物（双孔亚纲爬行动物、鸟类和龟类）的背外侧视核作为离散核同源；哺乳动物腹侧核群的大部分或全部作为一个区域与非合弓纲羊膜动物的lemniscal躯体感觉中继核和运动反馈核同源；哺乳动物的前核、板内核和内侧核群作为一个区域共同与非合弓纲羊膜动物的背内侧核和背外侧核（包括周边圆形核）同源；哺乳动物的前核、板内核、内侧核群、腹侧核群以及背外侧膝状核作为一个区域共同与无羊膜动物的前核同源，它们在非合弓纲羊膜动物中的同源物也是如此。在现存陆地脊椎动物的杯鼻龙类祖先中
