Biomedical subjects

Ann B Butler

Publications and source records attributed to Ann B Butler.

5 recordsLinked to original sources

PubMed2003

Clustered phylogenetic distribution of nucleus rostrolateralis among ray-finned fishes.

Nucleus rostrolateralis, which was named for its location in the rostrolateral part of the diencephalon of neopterygian fishes, has been identified in a variety of species based on position, cytoarchitecture, hodology, and/or histochemistry. The phylogenetic distribution of the nucleus is highly sporadic, however. Due to this distribution, nucleus rostrolateralis cannot be regarded as phylogenetically homologous, but it might be an example of syngeny, or generative homology, which applies to characters that have the same genetic and/or developmental basis inherited from a common ancestor, whether or not the character itself has a phylogenetic distribution congruent with a monophyletic taxon--i.e., in general terms, an example of either phylogenetic homology or parallelism. To test whether the nucleus occurs in closely related taxonomic clusters, as might be expected for a character with a shared generative basis, a number of species of cyprinids and atherinomorphs (both teleost taxa) were examined for its presence. Many of the species examined appear to lack the nucleus, but a clustered occurrence of it was found within both taxa. Within cyprinids, nucleus rostrolateralis occurs in all three members examined of the Subfamily Rasborinae. Within atherinomorphs, it occurs in both members examined of the Tribe Poeciliini (of the Subfamily Poeciliinae, Family Poeciliidae) and in the one member examined of the Family Anablepidae. The clustered occurrence of nucleus rostrolateralis supports the hypothesis that it is an example of syngeny. Its postulated shared generative basis appears to derive from the common ancestor of the entire neopterygian radiation despite the rare occurrence of the character itself.

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PubMed2002

The corticostriatal junction: a crucial region for forebrain development and evolution.

Most parts of the brain are conserved across reptiles and birds (sauropsids) and mammals. Two major qualitative differences occur in the upper part, or pallium, of the telencephalon, the most rostral part of the brain. Mammals have a six-layered neocortex and also exhibit a different morphological organization in the lateral half, or sector, of their pallium than do sauropsids. These differences of lateral pallial construction may derive from small but crucial differences in migration patterns of neuronal precursors generated at or above the corner of the lateral ventricle, the corticostriatal junction (CS). Sauropsids have a large structure, the dorsal ventricular ridge, that is proliferated from this region, and its anterior part (ADVR) receives ascending projections from the dorsal thalamus. Mammals have multiple structures in this same region-the lateral part of neocortex, amygdala, and claustrum-endopiriform formation. We propose here that, as the degree of development of structures that form the deeper tier of the pallium varies across the stages of embryology and across phylogeny, mutations may have occurred during evolution at the origin of mammals that had profound consequences for the fate of neural populations generated in the region of the CS and its neighboring pallial germinal zone.

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PubMed2002

Neuronal changes during forebrain evolution in amniotes: an evolutionary developmental perspective.

Embryology is the interface of genetic inheritance and phenotypic expression in adult forms, and as such is uniquely positioned to illuminate both. Embryonic cell migration pattern, transient connectivity, axonal growth kinetics and fasciculation patterns can clearly be substantially impacted at the striatocortical junction, which appears to be critical for telencephalic development. Similarly, the big questions concerning pallial evolution in amniotes all involve the pivotal region at the pallial-subpallial boundary, an area where complex developmental cross-currents may be involved in the specification of multiple structures that are thus related to each other. We review some of the positions based on recent genetic data and/or hodology, then suggest that comparative studies of intervening, embryological events may resolve some of the apparent conflicts and illuminate the evolutionary scenario. We propose a new hypothesis, the collopallial field hypothesis, which specifies that the anterior dorsal ventricular ridge of sauropsids and a set of structures in mammals--the lateral neocortex, basolateral amygdalar complex, and claustrum-endopiriform nucleus formation--are homologous to each other as derivatives of a common embryonic field. We propose that in mammals the laterally lying collopallium splits, or differentiates, into deep (claustroamygdalar) and superficial (neocortical) components, whereas in sauropsids, this split does not occur.

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PubMed2002

Apparent absence of claustrum in monotremes: implications for forebrain evolution in amniotes.

The claustrum, which comprises the claustrum proper and the endopiriform nucleus, is generally thought to be present in all mammals. Some previous reports of its possible absence in monotremes have appeared in the literature, but the question of its presence or absence in this clade has not been formally addressed. Whether monotremes have a claustrum is of some importance for formulating and evaluating hypotheses relating to the evolution of the structures in the lateral sector of the pallium across amniotes. Archival sets of sections through the brains of the platypus and the short-beaked echidna were examined and included material stained for seven different histochemical and immunohistochemical protocols. No cytoarchitectonically distinct claustrum could be identified in this material for either monotreme. We thus conclude that if monotremes have any cell population that is homolgous to the claustrum of therian mammals, it is entirely cryptic. A claustrum might have been present in ancestral mammals and lost in the monotreme clade, or it might have been gained at the origin of therian mammals. Nonetheless, its absence as a cytoarchitectonically discrete and identifiable structure in monotremes fails to support homology of the claustrum of therian mammals with any single part of the sauropsid pallium.

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PubMedDate not supplied

Development and evolution of the collopallium in amniotes: a new hypothesis of field homology.

Embryological development is uniquely positioned to illuminate both hodology in adult brains and its inherited genetic bases. The lateral corner of the lateral ventricle in mammals is a particularly crucial region where cell migration patterns, transiently formed connections, axonal growth kinetics, and fasciculation patterns are complex and interactive. Based on hodology, the sauropsid anterior dorsal ventricular ridge (ADVR) has been proposed as the homologue on a one-to-one basis of the mammalian lateral neocortex (LNC), the basolateral amygdalar complex (BLA), or the claustrum-endopiriform nucleus (CE). Data on gene expression patterns during development have indicated ADVR homology with parts of the latter two structures rather than with LNC. Collothalamic nuclei (the set of dorsal thalamic nuclei that receive their predominant input from the midbrain roof) project to part of BLA and to LNC. Recent findings demonstrate a complex pattern of mutually overlapping but noncongruent gene expression territories and collothalamic projections, which suggests a new, collopallial field hypothesis that the ADVR is homologous as a field to all three structures LNC, BLA, and CE. This hypothesis accounts for current hodological and developmental data as well as for lack of a CE in monotremes and for an abnormal subcortical lamina of gray matter that results from a genetic abnormality in humans.

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