Biomedical subjects

R G Jones

Publications and source records attributed to R G Jones.

At least 127 records · Page 7Linked to original sources

PubMed1978

Insemination-induced histolysis of the flight musculature in fire ants (Solenopsis, spp.): an ultrastructural study (1).

The fine structure of the insemination-induced flight muscle degeneration (histolysis) in the queen fire ant (Solenopsis spp.) has been investigated. Within 2 hours post-insemination, degenerative changes are detectable in the most peripheral fasciculi of the fibrillar flight muscle. Histolysis proceeds internally with time. Myofibril (sarcomere) dissolution begins with myofilament breakdown and continues until only free Z-line material remains. The latter subsequently disappears leaving, at the terminal stages, only nuclei, lamellar bodies (myelin figures), and tracheoles as residual myoid elements. Lysosomes and/or phagocytes do not appear to play a primary role in the initiation and continuance of this process.

Animals↗

PubMed1978

Morphological studies on the mantle of the fresh-water mussel Amblema (Unionidae): scanning electron microscopy.

The scanning electron microscope has been used to describe the surface morphology of the mantle in mantle-shell preparations from the fresh-water mussel Amblema. In some regions (adductor muscle insertions), the mantle is firmly attached to the shell. In other areas (along the main course of the mantle), transient adhesions between the outer mantle epithelial cells and the nacre appear to temporally further compartmentalize the extrapallial fluid possibly as a prerequisite for the initial crystallization phenomenon. At the mantle edge, as well as at the isthmus, the periostracum was seen to extrude from the periostracal groove. At the siphonal edge, peculiar finger-like processes were identified; these may represent primitive photoreceptors. The epithelial cells of the outer mantle epithelium are all microvillated whereas those of the inner mantle epithelium are both microvillated and ciliated. Specific differences in surface morphology are described for various regions of the outer mantle epithelium. These may be related to precise regionalized functional differences of this tissue. Several functions of the mantle, in addition to shell formation, and based on its various morphologies, are also discussed.

Animals↗

PubMed1978

The effects cytochalasin B on the surface morphology of the toad urinary bladder epithelium: a scanning electron microscopic study.

Cytochalasin B depresses the hydroosmotic response of the toad urinary bladder to vasopressin without affecting basal (bulk flow) permeability, diffusional permeability, or the hormone induced increase in short circuit current. Fine structural studies demonstrated that this macrolide fungal metabolite, in the presence of both an osmotic gradient and vasopressin, induces the formation of large intracellular vacuoles or 'lakes' in epitelial cells lining the bladder mucosa. Some surface changes (shortening and irregularity of microvilli, clumping of the glycocalyx, etc.) were reported by transmission electron microscopy. Scanning electron microscopy demonstrates that cytochalasin B drastically alters the mucosal surface morphology of the hormone stimulated bladder. Lesser changes were seen in the absence of vasopressin. In the presence of arginine vasopressin, excessive cellular swelling and possible rupturing, as well as surface membrane infolding and rippling, were seen in the cytochalasin treated tissues, The specific entity most affected by this treatment is the granular cell.

Animals↗

PubMed1977

The effect of cytochalasin B on the endosteal lining cells of mammalian bone. A scanning electron microscopic study.

The lining osteoblasts of the rat tibial endosteum were treated for various times (between 1 and 60 min) and increasing doses (3.87-38.7 microgram/ml) with the macrolide fungal metabolite cytochalasin B (CB). Dimethylsulfoxide (DMSO) served as the vehicle for CB and was administered to control tissues. An in vitro incubation system and scanning electron microscopy (SEM) were used to evaluate the effects of CB. The drug initiated cell rounding (contraction), nuclear protrusion, bleb formation, and the subsequent clustering of blebs and microvilli into aggregates. All CB-induced aberrations of the surface structure were readily reversible when tissues were washed with CB-free media. DMSO had no significant effect on cell surface morphology. The reversible structural changes brought about by CB are explained in terms of alterations of the subplasmalemmal cortical microfilament system of osteoblasts. The potential use of CB in evaluating the bone cell cytoskeleton and its relationship to the physiology of the cellular functional membrane (endosteum) of bone is discussed.

Animals↗

PubMed1975

Low dose-response for 2-deoxy-D-glucose-induced feeding, and the involvement of peripheral factors.

Latencies to feed and meal sizes were observed in recently satiated rats injected intraperitoneally with an isotonic solution of 2-deoxyglucose, using 3-0-methyl glucose for the control injection. The feeding response latency shortened monotonically with dose from about 0.3 mmole/kg (50 mg/kg) to 0.5-0.6 mmole/kg, with an extended plateau up to dehilitating doses. At modest doses, the latency to feed was shorter in adrenal demedullated rats than in intact rats, suggesting that the hyperglycemic response to 2DG partially inhibits the feeding response. Food-deprived rats took larger meals following 2DG injection, if there had been recent rapid intestinal absorption of glucose. It is suggested that a major action of 2DG is to block the satiating consequences of the process of absorption, possibly at hepatic receptors.

Adrenal Medulla↗

PubMed1975

Presence of Two Different Membrane-bound, KCl-stimulated Adenosine Triphosphatase Activities in Maize Roots.

Recent publications have indicated that a KCl-stimulated ATPase from cereal roots is specifically associated with plasmalemma-enriched membrane fractions. However, in previous work we found that relatively high specific activities of this enzyme were also associated with a membrane fraction which did not contain plasmalemma. In an attempt to clarify this discrepancy, we have investigated the effect of density gradient composition upon the association of the enzyme with different membrane fractions isolated from the roots of Zea mays L. (WF9 x M14).When roots were fractionated on a single, discontinuous sucrose density gradient the KCl-stimulated ATPase activity was concentrated in membrane fractions of relatively high density (sigma = 1.17-1.22) which were enriched in plasmalemma. When fractions were isolated on both Ficoll and sucrose density gradients, KCl-stimulated ATPase activity was again found associated with plasmalemma and also in a second membrane fraction which did not contain plasmalemma. This fraction was found at relatively low densities (sigma = 1.08) on the Ficoll gradient. The precise identity of the membrane in this fraction could not be determined.A preliminary investigation into the properties of the two KCl-stimulated ATPase activities indicated that both had acid pH maxima and both displayed similar responses to changes in KCl concentration.

Journal Article↗

PubMed1974