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Biomedical subjects

D A Riley

Publications and source records attributed to D A Riley.

At least 73 records · Page 4Linked to original sources
PubMed1985

Flexible memory processing by rats: use of prospective and retrospective information in the radial maze.

Four experiments investigated the content of the memory used by rats in mediating retention intervals interpolated during performance in a 12-arm radial maze. The delay occurred following either the 2nd, 4th, 6th, 8th, or 10th choice. A 15-min delay had the greatest disruptive effect when interpolated in the middle of the choice sequence and less of an effect when it occurred either earlier or later. This pattern of results was obtained when either a free- or forced-choice procedure was used prior to the delay and regardless of whether postdelay testing consisted of completion of the maze or two-alternative forced-choice tests. Assuming that the disruptive effect of a delay is a function of memory load, this implies that the rats used information about previously visited arms (retrospective memory) following an earlier interpolated delay but information about anticipated choices (prospective memory) following a delay interpolated late in the choice sequence. There appeared to be a recency effect only in the early and middle delay conditions. This provides converging evidence for the dual-code hypothesis. No evidence for prospective memory was obtained following a 60-min delay.

Animals↗
PubMed1984

Ultrastructural cytochemical localization of carbonic anhydrase activity in rat peripheral sensory and motor nerves, dorsal root ganglia and dorsal column nuclei.

Some of the myelinated axons in rat peripheral nerves possess marked axoplasmic carbonic anhydrase activity [Riley, Ellis and Bain (1982) J. Histochem. Cytochem. 30, 1275-1288; Riley and Lang (1984) J. Hand Surg. 9A, 112-120]. A mixture of reactive and nonreactive neurons was a general observation in cervical, thoracic and lumbar ganglia. Nonmyelinated axons in lumbar dorsal roots were nonreactive; this was consistent with the lack of carbonic anhydrase in small sensory neurons. The carbonic anhydrase cytochemical method marked the larger afferent or sensory neurons and distinguished them from the smaller sensory neurons which were devoid of carbonic anhydrase activity. Nonmyelinated axons in the lumbar ventral roots were also nonreactive. Examination of muscle spindle innervation revealed staining of the primary sensory and gamma motor endings. This was strongly suggestive that some of the reactive sensory neurons were primary afferents and a portion of the reactive ventral root axons were gamma motor. The reactive central processes of spinal neurons sent collaterals into the grey matter of the spinal cord, entered the dorsal funiculi, and terminated in synaptic glomeruli in the cuneate and gracilis nuclei. Oligodendroglial cells appeared to be the only intrinsic cellular elements of the brain stem and spinal cord that exhibited high carbonic anhydrase activity. Both oligodendroglial and Schwann cells exhibited intense carbonic anhydrase activity in thin pockets of cytoplasm internal to compact myelin. The subcellular distribution of reaction product within sensory neurons and oligodendroglial cells agreed with biochemical reports of cytosol and membrane-bound forms of carbonic anhydrase. A general staining of the cytoplasm was suggestive of soluble carbonic anhydrase fixed in situ by the glutaraldehyde. Clumps of reaction product on the cytoplasmic surface of the endoplasmic reticulum possibly represented membrane-bound enzyme. Most of the membrane-bound carbonic anhydrase was associated with the internal membranes rather than the axolemma or limiting plasma membrane of the axon. In contrast to biochemical reports, a small fraction of neuronal mitochondria exhibited staining in the intracristal spaces. We suggest that the association of carbonic anhydrase with endoplasmic reticulum and mitochondria implicates the enzyme in regulating intracellular calcium because both organelles are known to sequester calcium.

Animals↗
PubMed1984

Carbonic anhydrase activity of human peripheral nerves: a possible histochemical aid to nerve repair.

The return of usable function after injury of peripheral nerves depends upon the appropriate regeneration of axons to their end organs. Debridement trimmings of severed nerves harvested during surgery were stained to demonstrate carbonic anhydrase activity. This histochemical method can be accomplished within 3 to 4 hours of receiving the tissue. Nerve fascicles were readily discriminated from one another by the individual staining patterns of their constituent axons. Axoplasmic staining was predominantly a feature of sensory fibers, and myelin staining was characteristic of skeletal motor axons. Carbonic anhydrase histochemistry may provide a means of accurately matching fascicles in cut nerve ends.

Adult↗
PubMed1983

Research on the adaptation of skeletal muscle to hypogravity: past and future directions.

Our current understanding of hypogravity-induced atrophy of skeletal muscles is based primarily on studies comparing pre- and post-flight properties of muscles. Interpretations are necessarily qualified by the assumption that the stress of reentry and readjustment to terrestrial gravity do not alter the parameters being analyzed. The neuromuscular system is highly responsive to changes in functional demands and capable of rapid adaptation, making this assumption questionable. A reexamination of the changes in the connective tissue and synaptic terminals of soleus muscles from rats orbited in biosatellites and sampled postflight indicates that these structural alterations represent adaptative responses of the atrophic muscles to the increased workload of returning to 1 G, rather than hypogravity per se. The atrophy of weightlessness is postulated to result because muscles are both underloaded and used less often. Proper testing of this hypothesis requires quantitation of muscle function by monitoring electromyography, force output and length changes during the flight. Experiments conducted in space laboratories, like those being developed for the Space Shuttle, will avoid the complications of reentry before tissue sampling and allow time course atudies of the rate of development of adaptive changes to zero gravity. Another area of great importance for future studies of muscle atrophy is inflight measurement of plasma levels of hormones and tissue receptor levels. Glucocorticoids, thyroid hormone and insulin exert dramatic regulatory influences on muscle structure. Prevention of neuromuscular atrophy becomes increasingly more important as spaceflights increase in duration. Definition of the atrophic mechanism is essential to developing means of preventing neuromuscular atrophy.

Adaptation, Physiological↗
PubMed1982

Carbonic anhydrase activity in skeletal muscle fiber types, axons, spindles, and capillaries of rat soleus and extensor digitorum longus muscles.

Carbonic anhydrase (CA) activities were studied in soluble extracts and cryostat sections of skeletal muscles from prepubertal and postpubertal rats. Acetazolamide inhibition was utilized to distinguish between activities of the acetazolamide-sensitive (CA I and II) and acetazolamide-resistant (CA III) forms of the enzyme. The inhibition studies indicated that fast-twitch oxidative-glycolytic muscle fibers contained both the sensitive and resistant forms of CA. Acetazolamide-sensitive activity was localized within muscle fibers, axons, myelin, and capillaries. Axoplasmic staining was restricted to subpopulations of myelinated axons in both the dorsal and ventral roots. Soleus muscles exhibited significantly greater activity of CA III than extensor digitorum longus muscles at all ages examined. CA III was richest in slow-twitch oxidative and intrafusal fibers. During puberty, soleus muscle fibers matured and converted from fast-twitch oxidative-glycolytic to slow-twitch oxidative fibers. There was a shift from the sensitive to the resistant form of CA; CA III activity increased about sevenfold. This activity peaked earlier in the muscles of female rats than male rats. These results demonstrated a complex distribution of CA isozymes in the neuromuscular system and pointed out that isozyme content depends on both the type of muscle and the age and sex of the animal.

Acetazolamide↗
PubMed1981

31P nuclear magnetic resonance spectroscopy of lipopolysaccharides from Pseudomonas aeruginosa.

Intact lipopolysaccharide antigens isolated from seven different immunotypes of Pseudomonas aeruginosa have been examined by 31P-NMR spectroscopy. These macromolecular complexes contain phosphorus covalently attached to the carbohydrate residues present in the lipid A moiety and the 'core' oligosaccharide region. The spectral signals for various ortho- and pyrophosphoric esters were observed. All phosphate groups appeared to be monoesterified. Certain shifts characteristic for phosphate diester groups, observed in lipopolysaccharide complexes from other Gram-negative bacteria, were absent. Furthermore, no evidence was found to indicate that phosphate groups are involved in the covalent linkage of individual lipopolysaccharide complexes to form dimers or trimers.

Diphosphates↗
PubMed1981

Ultrastructural evidence for axon retraction during the spontaneous elimination of polyneuronal innervation of the rat soleus muscle.

This study provides morphological evidence for axon retraction during the elimination of polyneuronal innervation in postnatal rat soleus muscle. The motor innervation of muscles from animals 7-15 days and two months of age was examined in silver-stained preparations at the light microscopic level and in serial sections with the electron microscope. Transection of the soleus nerve in immature muscles revealed that the pattern of terminal and preterminal degeneration was similar to, but much more rapid than, that reported for adult muscles. During normal development, less than 1% of the preterminal axons sampled exhibited a denervation-like morphology and none of the neuromuscular junctions exhibited dense terminal degeneration. This indicates that autotomy and phagocytosis of the excess axons play a minor role in the development of connections. From estimates of the number of axons lost per day, about 20% of the endplates in 14-day-old muscles would be expected to have involuting axons associated with them. Slender axons terminating in vesicle-laden enlargements were associated with 18% of the endplates examined ultrastructurally which is consistent with the predicted rate of axon removal. These structures are interpreted as morphological manifestations of axon retraction because they were not present in adult material and they were not produced by nerve transection. Furthermore, they are comparable in shape and location to the putative retraction fibres identified in silver-stained sections at the light microscopic level. The present results indicate that retraction is the major means by which all but one of the multiple inputs per endplate are removed during the establishment of the adult pattern of motor innervation.

Animals↗
PubMed1977

Spontaneous elimination of nerve terminals from the endplates of developing skeletal myofibers.

The development of the motor innervation of a skeletal muscle was examined in the soleus muscles of young rats. At 11 days after birth, nearly three-quarters of the endplates of individual myofibers were innervated by more than one silver stained axon. Four days later, only about 9% of the endplates remained innervated by two or more terminals. The dramatic reduction in the number of axon terminals appeared to result in large measure from the retraction of all but one of the multiple terminals. An axon interpreted as undergoing retraction was characterized by a terminal oval enlargement believed to be the site of disassembly of the fiber.

Aging↗
PubMed1977

Silver staining the caveolae intracellularis of smooth muscle.

Bodian silver staining of guinea-pig Taenia coli produces a regular distribution of silver at the periphery of the smooth muscle cells. Electron microscopic analysis of this precipitate revealed that the membrane of the caveolae intracellularis was the only structure at the periphery of the cells that consistently exhibited a high affinity for silver. Thus, this staining method demonstrates that caveolae are distributed over most of the cell surface in an orderly pattern.

Animals↗