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At least 613 records · Page 34Linked to original sources
PubMed1975

Are we learning what actually goes on when the brain recognizes and controls?

Drawing upon recent advances in neuroscience for examples, the thesis is defended that, in contrast to a Kuhnian view of proress by overturning whole sciences, progress amounting to revolution in our understanding of nervous systems is happening by the accumulation of many discrete discoveries, and that this process may be expected to continue for a long time. Twelve propositions are put forward illustrative of ideas developed during and influenced by C. L. Prosser's career, all in the segment of neuroscience concerned with subsystem organization. They range from the generally accepted to the frankly polemical and the merely heuristic. (1) Ongoing background activity has different forms. (2) Codes, both spike and graded, are several. (3) Integrative variables in neuron function are several. (4) Identifiable cells may be widespread. (5) Neuronal circuits for behavior are known. (6) Redundancy is usually overlap. (7) Reliability can be high. (8) Recognition neurons may be common and complex. (9) Command neurons may be common and complex. (10) Pattern is often central in origin. (11) Hierarchies and switches may be common. (12) Subsystem function is an intellectual challenge. Each of these is briefly elaborated and its logical relation to the others suggested. The role of discrete discovery is thus illustrated--in the generation of new conceptual frameworks that gradually become interrelated and cumulatively change profoundly our picture of what's going on in the brain.

Action Potentials↗
PubMed1976

Evidence for a polyspermy block at the level of sperm-egg plasma membrane fusion in Urechis caupo.

The results of sperm binding experiments reveal no change in the sperm binding properties of the egg surface coat at fertilization of Urechis caupo eggs. When fertilized eggs are reinseminated, sperm continue to attach to the egg surface coat. The acrosomal tubules of supernumerary sperm are observed in the perivitelline space closely apposed to the egg membrane. Thus, the polyspermy block in Urechis eggs involves neither alteration of sperm binding sites nor inhibition of the acrosome reaction. Our results suggest that the block is at the level of sperm-egg membrane fusion.

Acrosome↗
PubMed1985

Blocks to polyspermy in Chaetopterus.

Blocks to polyspermy may act either at the level of the egg plasma membrane to prevent gamete fusion or at the level of egg surface coats to prevent gamete attachment. The present study was undertaken to determine what type(s) of block(s) to polyspermy exist in Chaetopterus. The results showed the existence of both types. A rapid block acts at the plasma membrane level based on independence from detectable changes in the vitelline layer and is dependent on external sodium ions. A vitelline layer block had been predicted on morphological evidence and is supported here by demonstrating an increase in polyspermy following chemical disruption of the vitelline layer. However, the vitelline layer of the fertilized egg retained its ability to initiate the acrosome reaction in sperm and attach sperm which had undergone the acrosome reaction. The vitelline layer block resulted from the retraction of egg microvilli from the vitelline layer, and not from elevation of the vitelline layer per se. Thus the vitelline layer of the fertilized egg could be involved in preventing sperm penetration into the egg without being altered structurally or functionally.

Animals↗
PubMed1987

Invertebrate red blood cell carbonic anhydrase.

This is the first report documenting the presence of carbonic anhydrase (CA) for any invertebrate red cells. CA activity was measured in plasma, hemolysates of blood cells, and in hemolymph of selected species of invertebrates. Annelid red blood cells (RBC) and sipunculid pink blood cells both possessed significant levels of CA activity. Molluscan RBC, on the other hand, lacked CA activity. The distribution appears to have fallen along phylogenetic lines, with CA being present only in blood cells of the two more closely related groups. However, the presence of extracellular CA was confirmed in oyster hemolymph. Oyster hemolymph CA showed a similar affinity (Ki) for the sulfonamide inhibitors acetazolamide and ethoxzolamide, as did the vertebrate RBC CA II isozyme, supporting the idea that this isozyme could be the ancestral form of the enzyme.

Animals↗
PubMed1987

The Chaetopterus vitelline envelope is not necessary for the gamete interactions that lead to fertilization.

It has been recently shown that, in several genera of annelids, including Chaetopterus, fertilizing sperm attach to and fuse with egg microvilli which penetrate the vitelline envelope. This suggests that the annelid vitelline envelope may have no direct or obligatory role in normal fertilization. The present study was undertaken to investigate the involvement of the vitelline envelope in fertilization in Chaetopterus experimentally, by examining the fertilization of vitelline envelope-free eggs quantitatively and qualitatively. Brief exposure of the eggs to isotonic sucrose-EDTA removed the vitelline envelope as determined by both phase-contrast and electron microscopy, rendered the eggs more sensitive to polyspermy and substantially reduced the binding of supernumerary sperm to eggs but did not decrease fertilizability as determined by sperm dilution assay and did not make the eggs more sensitive to cross-fertilization. The events of fertilization were examined by electron microscopy and found to be very similar in vitelline envelope-free eggs to those in intact eggs. We conclude that the vitelline envelope in Chaetopterus has binding sites for sperm but that it has no obligatory role in fertilization and is primarily involved in the prevention of polyspermy.

Animals↗
PubMed2002

Regeneration in planarians and other worms: New findings, new tools, and new perspectives.

Molecular biology, recombinant DNA techniques, and new methods of cell lineage have reignited the interest of planarians and other worms (mainly annelids and nemerteans) as invertebrate model systems of regeneration. Here, the mean results produced in the last five years are reviewed, an update of the genes and molecules involved in planarian regeneration is provided, and a new morphallactic-epimorphic model of pattern formation is suggested. Moreover, and most importantly, we highlight the new strides brought upon by genomic/proteomic analyses, RNA interference (RNAi) to inactivate gene function, and Bromodeoxyuridine (BrdU) cell labelling. The raising hope to obtain transformed neoblasts and transgenic planarians is also stressed. Altogether, such approaches will eventually lead to solve the long-standing open questions on regeneration which still baffles us. Finally, we warn against overlooking the evident links between regeneration processes and those controlling the daily wear and tear of tissues and cells. Both processes act, at least in planarians, upon a unique stem-cell endowed with an unrivaled developmental potential in the animal kingdom-the neoblast. This cell could be considered the forebear and a model system for stem-cell analysis.

Animals↗