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At least 217 records · Page 12Linked to original sources
PubMed1998

Unique HIV type 1 V3 region sequences derived from six different regions of brain: region-specific evolution within host-determined quasispecies.

HIV type 1 viral quasispecies were amplified by polymerase chain reaction (PCR) in the hypervariable V3 region of gp120 from six different regions of the brain (right and left frontal; right and left parietal; and right and left occipital) and from the peripheral blood mononuclear cells (PBMCs) of a patient who died of AIDS dementia complex (ADC). Cloning and sequencing of the entire V3 region suggested the presence of genetically unique sequences in different regions of the brain. In contrast, the blood-derived viral quasispecies carried homogeneous sequences that were characterized by a single octapeptide crest motif (HLGPGSAF), a motif important in viral fusion. The brain-derived viral strains showed extensive sequence heterogeneity and the presence of seven different octapeptide and four different tetrapeptide crest motifs (HIGPGRAF, RIGPGRAF, HIGPGSAI, HLGPGSAF, HIGPESAI, HLGPESAI, and YLRPGSAF). In addition, the brain-derived strains were also characterized by variable net V3 loop charge and hydrophilicity, along with distinct amino acid changes specific to different brain regions. Together, the sequence and phylogenetic analyses are unique in identifying the complexity of a viral quasispecies and its independent regional evolution within the brain compartment. Uniquely divergent viral strains were identified in the frontal regions and their presence was further supported by the presence of multinucleated giant cells (characteristic of HIV encephalopathy) predominantly in the left and right frontal regions. In summary, these analyses suggest that genetically different populations of HIV-1 may be present in different brain compartments and confirm that specific neurotropic variants may exist.

Acquired Immunodeficiency Syndrome↗
PubMed1990

The early development and evolution of the human brain.

THE CHEMISTRY OF THE BRAIN: The brain and nervous system is characterised by a heavy investment in lipid chemistry which accounts for up to 60% of its structural material. In the different mammalian species so far studied, only the 20 and 22 carbon chain length polyenoic fatty acids were present and the balance of the n-3 to n-6 fatty acids was consistently 1:1. The difference observed between species, was not in the chemistry but in the extent to which the brain is developed. This paper discusses the possibility that essential fatty acids may have played a part in it evolution. THE ORIGIN OF AIR BREATHING ANIMALS: The first phase of the planet's existence indulged in high temperature reactions in which oxygen combined with everything feasible: from silicon to make rocks to hydrogen to make water. Once the planet's temperature dropped to a point at which water could condense on the surface allowing chemical reactions to take place in it. The atmosphere was at that time devoid of oxygen so life evolved in a reducing atmosphere. Oxygen was liberated by photolysis of water and as a by-product of the blue-green algae through photosynthesis. When the point was reached at which oxidative metabolism became thermodynamically possible, animal life evolved with all the principle phyla establishing themselves within a relatively short space of geological time. (Bernal 1973). DHA and nerve cell membranes DHA AND NERVE CELL MEMBRANES: From the chemistry of contemporary algae it is likely that animal life evolved in an n-3 rich environment although not exclusively so as smaller amounts of n-6 fatty acids would have been present. A key feature of the first animals was the evolution of the photoreceptor: in examples of marine, amphibian and modern mammalian species, it has been found to use docosahexaenoic acid (DHA) as the principle membrane fatty acid in the phosphoglycerides. It is likely that the first animals did so as well. Coincidentally, the synaptic membranes involved in signal transduction also use high proportions of n-3 fatty acids. However, the n-6 fatty acids also find a place, in the inositol phosphoglyceride (IPG) which appears to be involved with calcium ion transport and hence signal activation and reception. Even in the photoreceptor, the IPG is an arachidonic acid rich phosphoglyceride. THE EVOLUTION OF MAMMALS AND THE LARGE BRAIN: The dominance of n-3 fatty acids in the food chain, persisted until the end of the Cretaceous period when the flowering plants followed on the disappearance of the giant cycads and ferns. A new set of species, the mammals, then evolved with a requirement for n-6 fatty acids for reproduction. This dependance was coincident with the flowering plants which for the first time produced protected seeds: these introduced a rich source of n-6 fatty acids. The brain size of the mammals tended to be relatively larger (that is in relation to body size) by comparison with the previous reptilian or egg laying systems. This process led to the large human brain. A crucial difference between man and other animals, is undoubtedly the extent to which the brain and its peripheral attributes have been developed. This paper will address the possibility that the potential for the evolution of the large human brain may have been released by the evolving human primate occupying an ecological niche which offered a rich source of those nutrients specifically required for the brain. That niche is at the land/water interface.

Animals↗
PubMed2001

A comparative analysis of relative brain size in waterfowl (Anseriformes).

Variation in relative brain size was examined in 55 species of waterfowl (Anseriformes). Using both conventional statistics and phylogenetically based comparative methods, the extent of variation in relative brain size and possible relationships with mode of foraging and diet were examined. The results indicate that although brain size does vary considerably between closely related species of waterfowl, it is not reliably related to either foraging mode or diet. There are a number of possible reasons for the lack of relationships between brain size and foraging mode and diet. Firstly, subtle changes in foraging mode and diet may favor relatively large changes in brain size. Secondly, foraging mode and diet could be correlated with the expansion of an individual brain region without affecting overall brain size. Thirdly, other behavioral/ecological traits may be more important with respect to brain size evolution in waterfowl. For example, the relatively large brain of the musk duck (Biziura lobata) and altriciality of their young in comparison to other stiff-tailed ducks (Oxyura spp.) indicates that developmental rate plays a significant role in the evolution of brain size. Given the difference between our results and that reported in inter-order comparisons of brain size in birds, further research is required into other avian orders to assess how brain size and behavior might be related within orders as well as between them.

Animals↗
PubMedDate not supplied

'Brain-specific' transcription and evolution of the identifier sequence.

A recent model for the transcriptional control of gene expression in neural cells involves a dispersed repetitive DNA sequence termed the identifier (ID) sequence. However, the model is based on circumstantial evidence from studies on rat brain gene expression. Furthermore, available data are complicated by observations from several laboratories which suggest that the ID sequence is a family of mobile genetic elements. Although this does not preclude a role for some family members in regulating gene expression, the contention that these sequences are transcribed tissue-specifically is not proof of such a role. We have now measured the genomic copy number and tissue pattern of transcription of ID sequences in the rat, mouse and hamster, and have found that ID-homologous, BC1-like RNAs are restricted to brain in all three species, but that ID-homologous transcripts occur in total cellular RNAs of brain, liver and kidney of all three organisms. The genomic copy number of the ID sequences varies over two orders of magnitude between these species. Our data suggest that most ID sequences in these genomes are dispersed at random with respect to transcription units. A cis-acting, transcriptional-level controlling role for the ID therefore seems unlikely.

Animals↗
PubMed1985

Cellular location of cytosolic triiodothyronine binding protein in primary cultures of fetal rat brain.

The evolution of a cytosolic triiodothyronine (T3) binding protein was studied in primary cultures of fetal rat brain. These cultures exhibited neuronal characteristics during the first week. T3 binding activity in cell supernatants increased during this period from 39 +/- 7 (mean +/- SD) to 159 +/- 24 fmoles T3/culture flask. A similar increase was observed in the soluble proteins. After day 8, neuronal death occurred and glial cells multiplied and differentiated. On day 11 an 86% drop in the binding activity was observed (24 +/- 7 fmoles T3/culture flask); the pool of soluble proteins remained stable. Scatchard analysis revealed two types of binding site in both 7- and 14-day cultured cell cytosols. Binding affinities were similar in both cytosols (KA1 approximately 1.5 X 10(9) M-1, KA2 approximately 1 X 10(8) M-1); in contrast, the number of sites was 4-fold smaller in 14-day cytosols. In subcultures mostly composed of glial cells, almost the same affinities were measured, but the numbers of both types of sites were 20 times smaller than in 7-day cells. These results show that in cell cultures from embryonic rat telencephalon, cytosolic T3 binding protein is mainly located in the neurons.

Animals↗
PubMed1998

Evolution of the human brain: is bigger better?

1. The hominid brain has increased approximately three times in size since the Pliocene, but so has the brain of equids. The tripling of hominid brain size has been considered as an indicator of increased mental abilities, as it coincided with the production of tools, weapons and other artefacts of increasing sophistication. No indicators of the increase in equid intelligence are known. Intraspecific correlation between brain size and variously measured 'intelligence' is, in modern humans, very weak if not completely absent. With the exception of size, there are no major differences between the anatomy of ape and human brains. 2. A study of 297 estimates of body height, 626 estimates of bodyweight and 276 estimates of the cranial capacity of hominids dated at various periods over the past 5 million years shows that the increase in hominid brain size was paralleled by an increase in body size. 3. In a sample of 45 variously dated fossil hominids, brain size correlates isometrically with body size. 4. Since the Late Pleistocene (approximately 30,000 years ago), human brain size decreased by approximately 10%; yet again, this decrease was paralleled by a decrease in body size. 5. Therefore, it may be concluded that the gross anatomy of the hominid brain is not related to its functional capabilities. The large human brain:body size ratio may be a result of the structural reduction of the size of the gastrointestinal tract and, consequently, its musculoskeletal supports. It is related to richer, meat-based diets and extra-oral food processing rather than the exceptional increase in the size of the cerebrum. The exceptional mental abilities of humans may be a result of functional rather than anatomical evolution.

Animals↗
PubMed2002

Inactivation of CMP-N-acetylneuraminic acid hydroxylase occurred prior to brain expansion during human evolution.

Humans are genetically deficient in the common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc) because of an Alu-mediated inactivating mutation of the gene encoding the enzyme CMP-N-acetylneuraminic acid (CMP-Neu5Ac) hydroxylase (CMAH). This mutation occurred after our last common ancestor with bonobos and chimpanzees, and before the origin of present-day humans. Here, we take multiple approaches to estimate the timing of this mutation in relationship to human evolutionary history. First, we have developed a method to extract and identify sialic acids from bones and bony fossils. Two Neanderthal fossils studied had clearly detectable Neu5Ac but no Neu5Gc, indicating that the CMAH mutation predated the common ancestor of humans and the Neanderthal, approximately 0.5-0.6 million years ago (mya). Second, we date the insertion event of the inactivating human-specific sahAluY element that replaced the ancestral AluSq element found adjacent to exon 6 of the CMAH gene in the chimpanzee genome. Assuming Alu source genes based on a phylogenetic tree of human-specific Alu elements, we estimate the sahAluY insertion time at approximately 2.7 mya. Third, we apply molecular clock analysis to chimpanzee and other great ape CMAH genes and the corresponding human pseudogene to estimate an inactivation time of approximately 2.8 mya. Taken together, these studies indicate that the CMAH gene was inactivated shortly before the time when brain expansion began in humankind's ancestry, approximately 2.1-2.2 mya. In this regard, it is of interest that although Neu5Gc is the major sialic acid in most organs of the chimpanzee, its expression is selectively down-regulated in the brain, for as yet unknown reasons.

Animals↗
PubMedDate not supplied

[Brain insulin receptors in the evolution of vertebrates].

Studies have been made on 125I-insulin binding for brain membranes from cyclostomes (the lamprey Lampetra fluviatilis), fish (pink salmon Oncorhynchus gorbuscha) and mammals (rats). The species studied differed by the level of binding (the highest in the rat and the lowest in the lamprey), which was due mainly to differences in the number of binding sites per membrane protein. Qualitative properties of the receptors in the species studied were found to be very similar. All three types of the receptors were capable of differentiating between the insulins from pig, pink salmon and lamprey, all of them binding porcine insulin more readily than the salmon one and the latter better than the insulin from the lamprey. It means that these insulins reacted not to the species specific properties of the hormone, but to biological activity of the insulin. The data obtained indicate that functionally mature insulin receptor may be found already in the brain of cyclostomes and that in the course of animal evolution from cyclostomes to mammals functional properties of this receptor did not undergo any significant changes.

Animals↗
PubMed2000

How does evolution build a complex brain?

To understand how complex brains evolve one can examine a variety of the products of the evolutionary process and then infer the mechanisms that generate the differences observed. We address this issue using a number of techniques. We combine neurophysiological recording techniques with neuroanatomical tracing techniques and histochemical methods in an effort to accurately determine the functional subdivisions of the neocortex in a variety of mammals. By using these techniques we can determine common features of neocortical organization, or common cortical areas, which are considered homologous. We can observe modifications to patterns of cortical organization, or to cortical fields specifically, that are independently evolved and generally related to morphological and behavioural specializations. Comparative studies have led us to consider the development of the neocortex and the specific changes in developmental mechanisms that might account for the observed changes in extant adults. Both comparative studies and developmental studies allow us to formulate hypotheses regarding how the neocortex is constructed in the life of an individual, and in a lineage over time.

Animals↗
PubMed2003

Have brain dynamics evolved? Should we look for unique dynamics in the sapient species?

Ongoing "spontaneous" electrical field potentials of assemblies of neurons in the brains of diverse animal groups differ widely in character and amplitude without obvious explanation. There may be correlates with other measures of brain complexity, such as histological differentiation, but so far there are no known differences between the EEGs of humans and other mammals or between mammals and reptiles, amphibians or fish, apart from amplitude. The proposition is defended that further search for descriptors or statistical, probably nonlinear features of the time series will reveal consistent differences, meaning that we have so far missed major features of the natural history of EEGs, just as we have thus far relatively neglected the identification of features of the physiology of the brain relevant to its evolution of complexity through major grades of phyla, classes, and orders.

Animals↗