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PubMed1989

Taxonomic differences in the scaling of brain on body weight among mammals.

Theories for the evolution of brain weight in mammals suggest that closely related species have diverged largely as a result of selection for differences in body weight, but that differences among more distantly related species have arisen due to greater net directional selection on brain weight. This pattern of changing selection causes brain weight to evolve more slowly than body weight among closely related species, such as those in the same genus, than among more distantly related species, such as those from different families or orders; a phenomenon known as the "taxon-level effect." Thus, brain weight differs more for a given difference in body weight as the species compared are more distantly related. An alternative explanation for the taxon-level effect is proposed. Distantly related species are more likely to inhabit different ecological conditions than are more closely related species. Where the taxon-level effect occurs, brain weight appears to have evolved in response to the demands of these different ecological conditions. As a consequence, brain weight differs more among distantly related species, for any given difference in body weight, than among closely related species. This effect, rather than a progressive pattern of changing selection pressures, may account for the taxon-level effect in mammals.

Animals↗
PubMed2001

Ruminant brain ribonucleases: expression and evolution.

Molecular evolutionary analyses of mammalian ribonucleases have shown that gene duplication events giving rise to three paralogous genes occurred in ruminant ancestors. One of these genes encodes a ribonuclease identified in bovine brain. A peculiar feature of this enzyme and orthologous sequences in other ruminants are C-terminal extensions consisting of 17-27 amino acid residues. Evidence was obtained by Western blot analysis for the presence of brain-type ribonucleases in brain tissue not only of ox, but also of sheep, roe deer and chevrotain (Tragulus javanicus), a member of the earliest diverged taxon of the ruminants. The C-terminal extension of brain-type ribonuclease from giraffe deviates much in sequence from orthologues in other ruminants, due to a change of reading frame. However, the gene encodes a functional enzyme, which could be expressed in heterologous systems. The messenger RNA of bovine brain ribonuclease is not only expressed at a high level in brain tissue but also in lactating mammary gland. The enzyme was isolated and identified from this latter tissue, but was not present in bovine milk, although pancreatic ribonucleases A and B could be isolated from both sources. This suggests different ways of secretion of the two enzyme types, possibly related to structural differences. The sequence of the brain-type RNase from chevrotain suggests that the C-terminal extensions of ruminant brain-type ribonucleases originate from deletions in the ancestral DNA (including a region with stop codons), followed by insertion of a 5-8-fold repeated hexanucleotide sequence, coding for a proline-rich polypeptide.

Amino Acid Sequence↗
PubMed1995

Lateralization of predator-evasion response in a teleost fish (Girardinus falcatus).

Evidence of lateral asymmetries in the direction of turning during escape behaviour in a species of poeciliid fish, Girardinus falcatus, is reported. When repeatedly faced with a simulated predator (in five successive sessions, spaced 7 days apart), immature Girardinus falcatus exhibited a significant population bias to turn right on the first session and a progressive bias to turn left in subsequent sessions. Mature Girardinus were then tested to check whether the shift in the direction of turn with repeated sessions depended on maturation or habituation. It was found that adult Girardinus showed a slight population bias to turn right in the first session and a strong subsequent bias to turn left after repeated sessions. The implications of these findings to our current understanding of the evolution of brain lateralization are discussed.

Animals↗
PubMedDate not supplied

[2 types of generalization in the evolution of the visual brain].

It has been shown that mechanism of generalization with respect to the size (shift of differentiation of the size from objects of one form to other forms) is located in dogs within the suprasylvian convolution, in cats--within the median part of the lateral suprasylvian region. After removal of these parts of the brain, other visual functions including the invariant description of the image, remain unaffected. The latter is disturbed after extirpation of the field 21; however, the shift with respect to the size does not undergo any significant changes. Therefore, two types of visual generalization, i.e. phylogenetically less ancient generalization of the detected properties and evolutionary more ancient subject generalization (invariant image), are located in different parts of the visual brain.

Animals↗
PubMed1985

Electron microscopic study of central axons degeneration in traumatic human brain edema.

Cortical axonal degeneration was studied in seven cortical biopsies taken from patients with traumatic brain injuries. After one day of evolution of brain injury, myelinated axons underwent axonal swelling, myelin sheath vacuolization and distortion, rupture of axolemma and phagocytosis of myelin ovoids by neuroglial cells. After 8 days, the brain trauma induced an increased number of neurofilaments and augmented volume of oligodendroglial ad-axonal cytoplasm. Fifteen days after brain lesion, varicose fiber swelling and retraction of axoplasm were found with disappearance of axoplasmic organelles. After 21 days, the dark type of degeneration was observed in two cases. At this time, hypertrophic oligodendrocytes invaded the myelin sheath and phagocyted the axoplasmic content. After a long evolution time (2 years) the complete sequence of degeneration events could be followed from the initial axoplasmic changes to the advanced degeneration with phagocytosis by neuroglial and invading cells.

Adolescent↗
PubMed1984

Brain traits through phylogeny: evolution of neural characters.

We have previously derived a hypothetical tree of the lines of mammalian descent, based upon a comprehensive numerical taxonomic cross-analysis of primitive and derived states of 15 brain traits in 38 representative species. In this communication we use this tree to describe the probable sequence of changes that have taken place in phylogenetic history. 2 characters proved to be multiply convergent, occurring in parallel in several disparate lines of descent. The remaining 9 characters each appeared in ancestors of one or another of the lineages and characterize related progeny.

Animals↗
PubMed1984

Comparative neuroscience holds promise for quiet revolutions.

The brain has diversified and advanced in evolution more than any other organ; the variety of nervous systems and behaviors among animal species is thus available for our exploitation. Comparative neuroscience is likely to reach insights so novel as to constitute revolutions in understanding the structure, functions, ontogeny, and evolution of nervous systems. This promise requires pursuit on a wide front, in respect to disciplines and in respect to the species, stages, and states compared. It also requires deliberate concentration on the differences among animals, in addition to the prevailing concern for the basic and common. Neglect of these challenges would be costly. Without due consideration of the neural and behavioral correlates of differences between higher taxa and between closely related families, species, sexes, and stages, we cannot expect to understand our nervous systems or ourselves.

Animals↗
PubMed1981

Neuropathological and computerized tomographic findings in experimental brain abscess.

The neuropathological progression of brain abscess formation was studied experimentally at sequential stages in dogs, and the findings correlated with the appearance on computerized tomographic (CT) brain scans. The evolution of brain-abscess formation was divided into four stages based on histological criteria: early cerebritis (Days 1 to 3); late cerebritis (Days 4 to 9); early capsule (Days 10 to 13); and late capsule (Days 14 and later). The cerebritis stage was characterized by prominent perivascular cuffing by inflammatory cells in the area adjacent to the developing necrotic center. However, the early elements of capsule formation appeared with the presence of fibroblasts by Day 5. The CT scans showed ring-shaped contrast enhancement by Day 3. Delayed scans at 30 minutes revealed diffusion of the contrast material into the developing necrotic center, forming a solid lesion. In lesions that were well encapsulated (14 days and older), five distinct histological zones were apparent: 1) a well formed necrotic center; 2) a peripheral zone of inflammatory cells, macrophages, and fibroblasts; 3) the dense collagenous capsule; 4) a layer of neovascularity associated with continuing cerebritis; and 5) reactive astrocytes, gliosis, and cerebral edema external to the capsule. The CT appearance of well encapsulated abscesses showed a typical ring-shaped contrast-enhancing lesion. On the delayed scans, the "ring" did not fill in with contrast enhancement. The diameter of the ring correlated best with the presence of cerebritis (perivascular infiltrates in the adventitial sheaths of vessels surrounding the abscess). The discussion focuses on the relevance of this study to the current management of patients with brain abscess.

Animals↗