Biomedical subjects

S B Cox

Publications and source records attributed to S B Cox.

4 recordsLinked to original sources

PubMed2006

Evidence that miRNAs are different from other RNAs.

An examination of 513 known pre-miRNAs and 237 other RNAs (tRNA, rRNA, and mRNA) revealed that miRNAs were significantly different from other RNAs (p < 0.001). miRNA genes were less conserved than other RNA genes, although their mature miRNA sequences were highly conserved. The A+U content of pre-miRNAs was higher than non-coding RNA (p < 0.001), but lower than mRNAs. The nucleotides in pre-miRNAs formed more hydrogen bonds and base pairs than in other RNAs. miRNAs had higher negative adjusted minimal folding free energies than other RNAs except tRNAs (p < 0.001). The MFE index (MFEI) was a sufficient criterion to distinguish miRNAs from all coding and non-coding RNAs (p < 0.001). The MFEI for miRNAs was 0.97, significantly higher than tRNAs (0.64), rRNAs (0.59), or mRNAs (0.65). Our findings should facilitate the prediction and identification of new miRNAs using computational and experimental strategies.

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PubMed1993

Localized dynamic changes in cortical blood flow with whisker stimulation corresponds to matched vascular and neuronal architecture of rat barrels.

The hypothesis that functional groups of neurons in whisker barrels are linked to a modular organization of cortical vessels was tested. Endovascular casts demonstrated cortical capillary networks resembling the whisker barrel pattern that were fed from the middle cerebral artery. In histological sections, dense capillaries apparently were confined to single barrels and were supplied by one or a few penetrating arterioles. The barrel field in cortical layer IV was localized in relation to surface arteriovenous patterns. Living vessels were imaged through a closed cranial window under anesthesia with a fluorescence microscope and SIT or ICCD cameras. After intracarotid injections of fluorescein isothiocyanatedextrans, saline, or 3 microns latex beads, changes in arteriolar diameter, arteriovenous transit times (AVTTs), and bead velocities were measured. When row C whiskers were stroked at 4-5 Hz for 1 min, blood flow increased in arterioles that supplied contralateral row C barrels as demonstrated by postmortem histology. AVTTs slowed significantly in vessels supplying adjacent cortex. We hypothesize that cerebral vascular units supply individual whisker barrels and are functionally linked to them for precise focal regulation of cerebral blood flow.

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PubMed1992

The effect of pancreatic polypeptide on glucose disposal after surgical alterations of the pancreas.

Surgical alterations of the pancreas result in anatomic changes that can affect postoperative glucose metabolism. Pancreas transplantation results in reduction of beta-cell mass, systemic release of insulin, and denervation. The authors hypothesized that such alterations affect peripheral glucose disposal to induce an "insensitivity" to endogenously (systemically) released insulin. Additionally, they hypothesized that surgically induced deficiency of the postprandial hormone, pancreatic polypeptide, might contribute to altered glucose disposal. The authors studied two surgical models in dogs known to be devoid of pancreatic polypeptide--70% proximal pancreatectomy (PPx) and PPx plus distal pancreas autotransplantation (PAT/B). Oral glucose challenge and euglycemic hyperinsulinemic clamp studies were performed before and after a 16-day "pulsed" infusion of pancreatic polypeptide. Both surgical procedures resulted in elevations in the integrated glucose response after oral glucose, which was not affected by pancreatic polypeptide infusion. Euglycemic clamp studies showed decreased hepatic glucose output (Ra) and overall glucose disposal (Rd) in the fasted state for both surgical groups. The transplant animals demonstrated significant decreases in Rd during the hyperinsulinemic challenge (3.2 +/- 0.01 versus 5.7 +/- 0.01 mg/kg/minute at 60 to 120 minutes for PAT/B versus control). After 16 days of pancreatic polypeptide infusion, however, basal Ra, as well as basal and 60- to 120-minute Rd values, were returned to control values in the transplant group. The authors conclude that pancreas transplantation results in altered glucose disposal, possibly due to an altered effectiveness of systemically released insulin. They conclude that pancreatic polypeptide is an important modulator of peripheral insulin action. Therefore, the role of pancreatic polypeptide must be taken into account when evaluating postoperative glucose metabolism in canine models of pancreas transplantation.

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PubMedDate not supplied

Neuronal units linked to microvascular modules in cerebral cortex: response elements for imaging the brain.

How neuronal activity changes cerebral blood flow is of biological and practical importance. The rodent whisker-barrel system has special merits as a model for studies of changes in local cerebral blood flow (LCBF). Stimulus-evoked changes in neural firing and 'intrinsic signals' recorded through a cranial window were used to define regions of interest for repeated flow measurements. Whisker-activated changes in flow were measured with intravascular markers at the pia. LCBF changes were always prompt and localized over the appropriate barrel. Stimulus-related changes in parenchymal flow monitored continuously with H2 electrodes recorded short latency flow changes initiated in middle cortical layers. Activation that increased flow to particular barrels often led to reduced flow to adjacent cortex. Dye was injected into single penetrating arterioles from the pia of the fixed brain and injected into arterioles in slices of cortex where barrels were evident without stains. Arteriolar and venular domains at the surface were not directly related to underlying barrels. Capillary tufts in layer IV were mainly coincident with barrels. The matching between a capillary plexus (a vascular module) and a barrel (a functional neuronal unit) is a spatial organization of neurons and blood vessels that optimizes local interactions between the two. The paths of communication probably include: neurons to neurons, neurons to glia, neurons to vessels, glia to vessels, vessels to vessels and vessels to brain. Matching a functional grouping of neurons with a vascular module is an elegant means of reducing the risk of embarrassment for energy-expensive neuronal activity (ion pumping) while minimizing energy spent for delivery of the energy (cardiac output). For imaging studies this organization sets biological limits to spatial, temporal and magnitude resolution. Reduced flow to nearby inactive cortex enhances local differences.

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