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At least 1,207 records · Page 67Linked to original sources
PubMed2003

Three gonadotropin-releasing hormone neuronal groups with special reference to teleosts.

Gonadotropin-releasing hormone (GnRH) is a decapeptide, which has been isolated from the hypothalamus as a releasing hormone of gonadotropins from the pituitary. However, subsequent morphological studies have demonstrated the presence of multiple GnRH neuronal groups outside the hypothalamus and preoptic area. In most vertebrate lineages studied to date, GnRH neuronal groups are present along the terminal nerve and in the midbrain tegmentum, in addition to a population in the preoptico-hypothalamic areas. The presence of GnRH fibers in extrahypothalamic areas has also been demonstrated, indicating a significance for GnRH neurons in functions other than those that are purely hypophysiotropic. Among vertebrate lineages, GnRH neurons have been most extensively studied in teleost fish through morphological, electrophysiological, behavioral and molecular approaches. To date, studies on differential roles of GnRH neuronal groups have been mostly restricted to teleosts. In the present review, the anatomy and functions of each GnRH neuronal group are reconsidered, based mainly on knowledge from teleosts. Recent findings in teleosts indicate that the preoptico-hypothalamic GnRH neurons are hypophysiotropic and that GnRH neurons of the terminal nerve and midbrain tegmentum regulate neural activities in various regions, including extrahypothalamic areas. The latter populations presumably serve as neuromodulatory systems to control aspects of neural functions such as reproductive behavior. Similar functional differentiation may be generalized to other vertebrate lineages as well.

Animals↗
PubMed2002

The self-perceived survival ability and reproductive fitness (SPFit) theory of substance use disorders.

A new theory of substance use disorders is proposed-the SPFit theory-that is based on evolutionary biology and adaptive systems. Self-perceived survival ability and reproductive fitness (SPFit) is proposed as a human psychobiological construct that prioritizes and organizes (i.e. motivates) behavior, but is highly vulnerable to temporary, artificial activation by drugs of abuse. Autoshaping/sign-tracking/feature positive phenomena are proposed to underlie the development of craving and expectations about drugs as the individual learns that abused drugs will easily and reliably inflate SPFit. The cortico-mesolimbic dopamine system and its modulating interconnections are viewed as the biological substrate of SPFit; it is proposed to be a survival and reproductive motivation system rather than a reward center or reward pathway. Finally, the concept of modularity of mind is applied to the SPFit construct. Although considerable empirical data are consistent with the theory, new research is needed to test specific hypotheses derived from SPFit theory.

Biological Evolution↗
PubMed1999

Organization of visual cortex in the northern quoll, Dasyurus hallucatus: evidence for a homologue of the second visual area in marsupials.

Two visual areas, V1 and V2 (first and second visual areas), appear to be present in the posterior neocortex of all eutherian mammals investigated so far. However, previous studies have not established whether an area homologous to V2 also exists in metatherian mammals (marsupials). Using electrophysiological techniques, we mapped the visual receptive fields of neurons in the striate and peristriate cortices of the northern quoll, an Australian marsupial. We found that neurons in a 2-mm-wide strip of cortex rostrolateral to V1 form a single, relatively simple representation of the complete contralateral hemifield. This area resembles V2 of eutherians in several respects: (i) neurons in the medial half of the peristriate area represent the lower visual quadrant, whereas those in the lateral half represent the upper visual quadrant; (ii) the vertical meridian of the visual field is represented adjacent to V1, while the visual field periphery is represented along the lateral and rostrolateral borders of the peristriate area; (iii) there is a marked anisotropy in the representation, with a larger magnification factor parallel to the V1 border than perpendicular to this border; and (iv) receptive fields of multiunit clusters in the peristriate cortex are much larger than those of cells in V1 at comparable eccentricities. The cortex immediately rostral and lateral to V2 did not respond to visual stimulation under our recording conditions. These results suggest that V1 and V2 together form a 'core' of homologous visual areas, likely to exist in all therian mammals.

Animals↗
PubMedDate not supplied

Early development of the neural plate, neural crest and facial region of marsupials.

Marsupial mammals have a distinctive reproductive strategy. The young are born after an exceptionally short period of organogenesis and are consequently extremely altricial. Yet because they must be functionally independent in an essentially embryonic condition, the marsupial neonate exhibits a unique suite of adaptations. In particular, certain bones of the facial region, most cranial musculature and a few additional structures are accelerated in their development. In contrast, central nervous system structures, especially the forebrain, are markedly premature at birth, resembling an embryonic d 11 or 12 mouse. This review examines the developmental processes that are modified to produce these evolutionary changes. The focus is on the early development of the neural plate, neural crest and facial region in the marsupial, Monodelphis domestica, compared with patterns reported for rodents. Neural crest begins differentiation and migration at the neural plate stage, which results in large accumulations of neural crest in the facial region at an early stage of development. The early accumulation of neural crest provides the material for the accelerated development of oral and facial structures. The first arch region is massive in the early embryo, and the development of the olfactory placode and frontonasal region is advanced relative to the forebrain region. The development of the forebrain is delayed in marsupials relative to the hindbrain or facial region. These observations illustrate how development may be modified to produce evolutionary changes that distinguish taxa. Further, they suggest that development is not necessarily highly conserved, but instead may be quite plastic.

Adaptation, Physiological↗
PubMed2004

Toward an evolutionary perspective on conceptual representation: species-specific calls activate visual and affective processing systems in the macaque.

Non-human primates produce a diverse repertoire of species-specific calls and have rich conceptual systems. Some of their calls are designed to convey information about concepts such as predators, food, and social relationships, as well as the affective state of the caller. Little is known about the neural architecture of these calls, and much of what we do know is based on single-cell physiology from anesthetized subjects. By using positron emission tomography in awake rhesus macaques, we found that conspecific vocalizations elicited activity in higher-order visual areas, including regions in the temporal lobe associated with the visual perception of object form (TE/TEO) and motion (superior temporal sulcus) and storing visual object information into long-term memory (TE), as well as in limbic (the amygdala and hippocampus) and paralimbic regions (ventromedial prefrontal cortex) associated with the interpretation and memory-encoding of highly salient and affective material. This neural circuitry strongly corresponds to the network shown to support representation of conspecifics and affective information in humans. These findings shed light on the evolutionary precursors of conceptual representation in humans, suggesting that monkeys and humans have a common neural substrate for representing object concepts.

Acoustic Stimulation↗
PubMed2005

Morphological affinities of the Sahelanthropus tchadensis (Late Miocene hominid from Chad) cranium.

The recent reconstruction of the Sahelanthropus tchadensis cranium (TM 266-01-60-1) provides an opportunity to examine in detail differences in cranial shape between this earliest-known hominid, African apes, and other hominid taxa. Here we compare the reconstruction of TM 266-01-60-1 with crania of African apes, humans, and several Pliocene hominids. The results not only confirm that TM 266-01-60-1 is a hominid but also reveal a unique mosaic of characters. The TM 266-01-60-1 reconstruction shares many primitive features with chimpanzees but overall is most similar to Australopithecus, particularly in the basicranium. However, TM 266-01-60-1 is distinctive in having the combination of a short subnasal region associated with a vertical upper face that projects substantially in front of the neurocranium. Further research is needed to determine the evolutionary relationships between Sahelanthropus and the known Miocene and Pliocene hominids.

Animals↗
PubMed1976

Rates, patterns, and effectiveness of evolution in multi-level situations.

Evolution is a multi-level process. Both actual evidence and theoretical considerations suggest as a first generalization that evolution both at single levels and in series of increasingly complex levels decelerates with time. Additional evidence, the expected difference between rapid nonadaptive speciation in small populations and effective adaptation in large ones, and analysis of explosive evolution suggest further that effective adaptive evolution occurs primarily in large populations, and that segments of such evolution tend to begin slowly; accelerate, sometimes explosively; and then decelerate. The segments are irregular, and do not occur at regular intervals. However, the explosive evolution of a general adaptation pre-adapts to and is often followed by an explosive radiation of derivative lineages. This description seems to fit the origin and initial radiation of mammals, and the evolutionary history of man and man's cultures.

Animals↗
PubMed1981

Uric acid provides an antioxidant defense in humans against oxidant- and radical-caused aging and cancer: a hypothesis.

During primate evolution, a major factor in lengthening life-span and decreasing age-specific cancer rates may have been improved protective mechanisms against oxygen radicals. We propose that one of these protective systems is plasma uric acid, the level of which increased markedly during primate evolution as a consequence of a series of mutations. Uric acid is a powerful antioxidant and is a scavenger of singlet oxygen and radicals. We show that, at physiological concentrations, urate reduces the oxo-heme oxidant formed by peroxide reaction with hemoglobin, protects erythrocyte ghosts against lipid peroxidation, and protects erythrocytes from peroxidative damage leading to lysis. Urate is about as effective an antioxidant as ascorbate in these experiments. Urate is much more easily oxidized than deoxynucleosides by singlet oxygen and is destroyed by hydroxyl radicals at a comparable rate. The plasma urate levels in humans (about 300 microM) is considerably higher than the ascorbate level, making it one of the major antioxidants in humans. Previous work on urate reported in the literature supports our experiments and interpretations, although the findings were not discussed in a physiological context.

Adult↗
PubMed1984

Structure linkage, and sequence of the two genes encoding the delta and gamma subunits of the nicotinic acetylcholine receptor.

We have cloned and sequenced a fragment of the chicken genome approximately 9 kilobases in length that comprises the genes encoding the delta and gamma subunits of the nicotinic acetylcholine receptor. The two genes are homologous and have identical structures: both consist of 12 exons, some of which precisely correspond to predicted structural domains of the receptor subunits. The delta and gamma subunit genes are encoded by the same DNA strand and are very closely linked, there being only 740 base pairs between the last codon of delta and the initiator codon of gamma. Blot analysis demonstrates that the genes we describe are unique in the genome. Comparison of the predicted protein sequence for the corresponding subunits of chicken and of the elasmobranch Torpedo reveals a high degree of conservation in some but not all of the protein domains.

Amino Acid Sequence↗
PubMed1990

Phylogeny and evolution of antlered deer determined from mitochondrial DNA sequences.

Mitochondrial DNA sequences of both ribosomal RNA genes and three adjacent transfer RNA genes were obtained for the three extant subfamilies of antlered deer (Cervinae, Muntiacinae, and Odocoileinae) as well as for their antlerless sister group Hydropotinae (family Cervidae). Phylogenetic analysis of these sequences (each nearly 2.7 kilobase pairs in length) supports a cervine/muntiacine clade to the exclusion of odocoileines. These results are statistically significant, stable, and congruent with some independent data. Our mitochondrial DNA sequences, when coupled with other information, indicate that the earliest fossil antlered deer are not closely related to living muntiacines or any other contemporary subfamily. From this information, we hypothesize an Old World, Late Miocene origin of Odocoileinae.

Animals↗
PubMed1992

Strong evolutionary conservation of neuropeptide Y: sequences of chicken, goldfish, and Torpedo marmorata DNA clones.

Neuropeptide Y (NPY) is an abundant and widespread neuropeptide in the nervous system of mammals. NPY belongs to a family of 36-amino acid peptides that also includes pancreatic polypeptide and the endocrine gut peptide YY as well as the fish pancreatic peptide Y. To study the evolution of this peptide family, we have isolated clones encoding NPY from central nervous system cDNA libraries of chicken, goldfish, and the ray Torpedo marmorata, as well as from a chicken genomic library. The predicted chicken NPY amino acid sequence differs from that of rat at only one position. The goldfish sequence differs at five positions and shows that bony fishes have a true NPY peptide in addition to their pancreatic peptide Y. The Torpedo sequence differs from that of rat at three positions. As Torpedo NPY has no unique positions when compared with the other sequences, it seems to be identical to the NPY of the common ancestor of cartilaginous fishes, bony fishes, and tetrapods after 420 million years of evolution. The 30-amino acid carboxyl-terminal extension of the NPY precursor also displays considerable sequence conservation. These results show that NPY is one of the most highly conserved neuroendocrine peptides.

Amino Acid Sequence↗