Regulation of nestin expression after cortical ablation in adult rat brain

During embryogenesis, transient expression of nestin in proliferating neuroepithelial stem cells signals the commitment of progenitor cells to differentiate. Although adult mammalian brain contains very little nestin, significant upregulation of nestin has been reported following cerebral injury, leading to speculation that nestin may be involved in brain repair. In this study, we assessed the temporal profile of nestin expression following ablation injury of the sensory barrel cortex and investigated the influence of contralateral whisker stimulation on nestin expression. Since the adult mammalian brain contains proliferating neuronal progenitor cells that can be labeled with bromodeoxyuridine (BrdU), we also determined the association of nestin reexpression with BrdU-labeled cells. Nestin reexpression was detected predominantly in the ipsilateral cortex 3 days post-ablation. There was no significant nestin upregulation in the subcortical region. Nestin reexpression was most marked surrounding the lesion, but also extended throughout the entire lateral cortex. Nestin in the ipsilateral cortex subsided by day 7, although perilesional nestin expression was still apparent 28 days post-injury. Western blot analysis of nestin expression 3 days post-ablation confirmed a significant two-fold increase in nestin expression (p<0.05). Double immunofluorescence labeling demonstrated that the majority of nestin expression occurred in astrocytes. We were unable to detect any colocalization with neuronal makers. However, BrdU-labeled cells, which were readily detected in the subventricular zone prior to injury, were readily detected in the perilesional area 3 days post-ablation, concomitant with nestin in this area. Confocal microscopy detected several BrdU-positive cells expressing nestin. Taken together, the data support a potential role for nestin reexpression in brain repair.

A collagen-based scaffold for a tissue engineered human cornea: physical and physiological properties

Stabilized collagen-glycosaminoglycan scaffolds for tissue engineered human corneas were characterized. Hydrated matrices were constructed by blending type I collagen with chondroitin sulphates (CS), with glutaraldehyde crosslinking. A corneal keratocyte cell line was added to the scaffolds with or without corneal epithelial and endothelial cells. Constructs were grown with or without ascorbic acid. Wound-healing was evaluated in chemical-treated constructs. Native, noncrosslinked gels were soft with limited longevity. Crosslinking strengthened the matrix yet permitted cell growth. CS addition increased transparency. Keratocytes grown within the matrix had higher frequencies of K+ channel expression than keratocytes grown on plastic. Ascorbic acid increased uncrosslinked matrix degradation in the presence of keratocytes, while it enhanced keratocyte growth and endogenous collagen synthesis in crosslinked matrices. Wounded constructs showed recovery from exposure to chemical irritants. In conclusion, this study demonstrates that our engineered, stabilized matrix is well-suited to function as an in vitro corneal stroma.

Changes in measured intraocular pressure after hyperopic photorefractive keratectomy

PURPOSE

To investigate the effect of hyperopic photorefractive keratectomy (PRK) on intraocular pressure (IOP) measurements.

SETTING

University of Ottawa Eye Institute, Ottawa Hospital, Ottawa, Canada.

METHODS

In this retrospective cohort study, IOP and central corneal thickness (CCT) were measured preoperatively and at 1, 2, 3, 6, 12, 18, and 24 months in 191 eyes that had hyperopic PRK with the VISX Star excimer laser. All corrections applied were between +1.00 and +6.50 diopters (D) of sphere and less than 3.75 D of cylinder.

RESULTS

At all postoperative examinations, the mean IOP in the hyperopic PRK group was 1.0 to 1.8 mm Hg lower than the preoperative IOP (P <.001). A large range of IOP changes was found across the population; eg, at 6 months, 49% of the eyes had a change in IOP from baseline of at least +/-3 mm Hg. A mean reduction of 19 microm of CCT was found with pachymetry after surgery (P < .001). The change in IOP readings postoperatively was not correlated with age, sex, keratometric readings, or applied correction. Changes in IOP were strongly correlated with preoperative IOP at all time points and with preoperative CCT at 18 and 24 months (P < .001). After hyperopic PRK, the measured IOP was more likely to increase in patients with preoperative IOPs less than 14.5 mm Hg and more likely to decrease in patients with preoperative IOPs above 14.5 mm Hg.

CONCLUSION

Changes in IOP after hyperopic PRK were similar to changes after myopic PRK, despite only minimal changes in the CCT. This suggests that hyperopic PRK results in biomechanical effects that modify the elastic properties of the cornea beyond the changes in rigidity expected from central corneal thinning. There was a strong negative correlation between the measured preoperative IOP and the change in IOP postoperatively that was likely the result of regression of the mean effect.

New Paradigm for the Treatment of Myopia By Refractive Surgery

It is proposed that refractive surgery visual outcomes will be significantly improved when using refractive surgery profiles that maintain preoperative corneal aberrations following surgery. An equation to calculate postoperative corneal shapes is presented.

Acute hyperinsulinemia and very-low-density and low-density lipoprotein subfractions in obese subjects

BACKGROUND

The influence of hyperinsulinemia on concentrations of lipoprotein subfractions in obese, nondiabetic persons has not been clarified.

OBJECTIVE

We analyzed VLDL and LDL subfractions before and after a euglycemic, hyperinsulinemic clamp.

DESIGN

Lipoprotein subfractions were isolated from plasma samples obtained in the basal state and after a 4-h clamp from obese patients, obese patients with type 2 diabetes, and nonobese control subjects.

RESULTS

Hyperinsulinemia tended to reduce concentrations (&xmacr;: 20%) of large, triacylglycerol-rich VLDL(1) in obese patients but had a minor effect on VLDL(2) and VLDL(3). Placing obese patients into insulin-sensitive and insulin-resistant subgroups revealed distinct effects of the degree of insulin sensitivity on VLDL. VLDL(1) concentrations decreased by a mean of 38% (P < 0.05) in insulin-sensitive patients after the clamp, similar to but less marked than the decrease observed in control subjects (&xmacr;: 62%; P < 0.01). VLDL(1) concentrations did not change significantly after the clamp in insulin-resistant patients (and patients with type 2 diabetes), whereas VLDL(3) concentrations decreased in both groups, in contrast with the changes seen in the insulin-sensitive patients and control subjects. Acute hyperinsulinemia modified the LDL subfraction profile toward a greater prevalence of small, dense LDLs in insulin-resistant patients and patients with type 2 diabetes.

CONCLUSIONS

Insulin resistance appears to be the primary determinant of the modifications to VLDL subfraction concentrations. Our results suggest a continuum of impaired insulin action on VLDL, ranging from that in healthy persons to that in patients with type 2 diabetes, in which obese patients occupy a transition state. Insulin resistance may also play a role in detrimental modifications to the LDL profile by allowing the development of hypertriglyceridemia.

Functional human corneal equivalents constructed from cell lines

Human corneal equivalents comprising the three main layers of the cornea (epithelium, stroma, and endothelium) were constructed. Each cellular layer was fabricated from immortalized human corneal cells that were screened for use on the basis of morphological, biochemical, and electrophysiological similarity to their natural counterparts. The resulting corneal equivalents mimicked human corneas in key physical and physiological functions, including morphology, biochemical marker expression, transparency, ion and fluid transport, and gene expression. Morphological and functional equivalents to human corneas that can be produced in vitro have immediate applications in toxicity and drug efficacy testing, and form the basis for future development of implantable tissues.

Positive correlation between Tono-Pen intraocular pressure and central corneal thickness

OBJECTIVE

To examine the relationship between intraocular pressure (IOP) readings taken by the Tono-Pen tonometer (Mentor O&O, Norwell, MA) and central corneal thickness (CCT).

DESIGN

Prospective cross-sectional population study.

PARTICIPANTS

There were 651 eyes of 332 healthy subjects.

MAIN OUTCOME MEASURES

A questionnaire was given to each subject requesting information on gender, age, race, and other factors that can influence IOP. The IOP then was measured using the Tono-Pen followed by measurements of CCT using an ultrasonic pachymeter.

RESULTS

The IOP was found to increase by 2.9 mmHg/100 microns CCT in males and 1.2 mmHg/100 microns in females. For males, CCT was found to be statistically significant in predicting IOP (P < 0.001 in the right and left eyes) and diabetes was of borderline significance (P = 0.012 in the right eye, P = 0.089 in the left eye). For females, CCT was of borderline significance (P = 0.064 in the right eye, P = 0.019 in the left eye). In females, a family history of glaucoma (P = 0.021 in the right eye, P = 0.022 in the left eye) and hypertension (P = 0.010 in the right eye, P = < 0.001 in the left eye) were also significant in the prediction of IOP. Race was found to be a significant predictor of CCT (P < 0.001 in both right and left eyes) for both males and females.

CONCLUSION

Clinicians should be aware that, as with the Goldmann applanation tonometer, the Tono-Pen has a systematic error in IOP readings caused by its dependence on CCT. Tono-Pen IOP readings are positively correlated to CCT in males and, to a lesser extent, in females as well. The CCT measurements should be considered to ensure proper interpretation of IOP measurements in the diagnosis and management of disorders in which the CCT or IOP readings are outside normal limits.

Comparative study of the elevation topography of complex shapes

PURPOSE

To compare the accuracy and precision of the elevation topography from two commercially available instruments using videokeratoscopy or rasterstereography.

SETTING

University of Ottawa Eye Institute, Ottawa General Hospital, Ontario, Canada.

METHODS

Repeated measurements of elevation topography of six calibrated surfaces were done with the PAR Corneal Topography System (CTS) and the Tomey Topographic Modeling System (TMS-1). The shapes simulated normal (A: aspheric, B: spherocylindric) and postsurgical corneas (C: hyperopic, D: myopic, E: central island, F: phototherapeutic keratectomy). Surface shapes were described by parametric equations. Equation parameters associated with each elevation measurement were determined by best-fit analysis. Measurement precision was assessed by the standard deviation of the difference between the fitted and the measured data. Fitted parameters were compared with nominal values obtained from an independent calibration of each surface. The root mean square error (RMSE) of the deviation of the fitted from the nominal surfaces was used to evaluate the accuracy of each instrument.

RESULTS

The accuracy of the CTS exceeded that of the TMS-1 for all surfaces measured. The RMSE values (micron) were (A: 0.1, 6.5), (B: 0.3, 3.8), (C: 1.1, 11.8), (D: 5.0, 43.0), (E: 1.2, 3.2) and (F: 2.2, 17.5) for the CTS and TMS-1, respectively. The differences in the measured data from the fit surface were generally smaller with the TMS-1.

CONCLUSION

Quantitative analysis of elevation measurements showed that the CTS represented surface topography more accurately than the TMS-1.

Correction of intraocular pressure for changes in central corneal thickness following photorefractive keratectomy

OBJECTIVE

To investigate the relation between measurements of intraocular pressure (IOP) and central corneal thickness (CCT) in myopic patients undergoing photorefractive keratectomy (PRK).

DESIGN

Descriptive study.

SETTING

University-affiliated eye care centre in Ottawa.

PATIENTS

A total of 481 consecutive eyes of 318 patients with a mean preoperative refractive error of -6.50 dioptres treated with excimer PRK between March 1993 and December 1996.

OUTCOME MEASURES

IOP measured by Goldmann applanation tonometry and CCT before and 3, 6, 12, 18 and 24 months after surgery.

RESULTS

CCT was a significant predictor of IOP only before PRK and 6 months after PRK (p < or = 0.05). The relation between IOP and CCT suggests corrections for CCT that are not clinically significant (0.81 mm Hg [standard error (SE) 0.33 mm Hg] and 1.00 mm Hg [SE 0.38 mm Hg] per 100 microns of corneal thinning preoperatively and at 6 months respectively). On average, there was a significant decrease in IOP after PRK (0.96 mm Hg and 1.24 mm Hg at 12 and 24 months respectively) (p < 0.05). There was a significant correlation between change in IOP and change in CCT (decrease of 2.1 mm Hg per 100 microns of corneal thinning) (p < 0.05). For a given change in CCT, individual changes in IOP were variable, with increases or decreases of more than 5 mm Hg in some cases.

CONCLUSIONS

There are individual differences in IOP changes following PRK. Until further data are available we propose that the change in IOP between the preoperative visit (or the fellow eye, if healthy or untreated) and the 12-month visit be used as an individual correction factor to be applied to IOP measurements in the operated eye.

Intrauterine growth retardation in Iowa communities with herbicide-contaminated drinking water supplies

In a statewide survey of 856 Iowa municipal drinking water supplies in 1986-1987 the Rathbun rural water system was found to contain elevated levels of triazine herbicides. Rates of low birth weight, prematurity, and intrauterine growth retardation (IUGR) in live singleton births during the period 1984-1990 by women living in 13 communities served by the Rathbun water system were compared to other communities of similar size in the same Iowa counties. The Rathbun communities had a greater risk of IUGR than southern Iowa communities with other surface sources of drinking water (relative risk = 1.8; 95% CI = 1.3, 2.7). Multiple linear regression analyses revealed that levels of the herbicides atrazine, metolachlor, and cyanzinc were each significant predictors of community IUGR rates in southern Iowa after controlling for several potentially confounding factors including maternal smoking and socioeconomic variables. The association with IUGR was strongest for atrazine, but all three herbicides were intercorrelated and the independent contributions of each to IUGR risk could not be determined. We conclude that communities in southern Iowa with drinking water supplies contaminated with herbicides have elevated rates of IUGR compared to neighboring communities with different water supplies. Because of the limitations of the ecologic design of this study, including aggregate rather than individual measures of exposure and limited ability to control for confounding factors related to source of drinking water and risk of IUGR, a strong causal relationship between any specific water contaminant and risk of IUGR cannot yet be inferred. The association between the water supplied to the Rathbun communities and the increased risk of IUGR should be considered a preliminary finding that needs to be verified by more detailed epidemiologic studies.

Intrauterine growth retardation in Iowa communities with herbicide-contaminated drinking water supplies

In a statewide survey of 856 Iowa municipal drinking water supplies in 1986-1987 the Rathbun rural water system was found to contain elevated levels of triazine herbicides. Rates of low birth weight, prematurity, and intrauterine growth retardation (IUGR) in live singleton births during the period 1984-1990 by women living in 13 communities served by the Rathbun water system were compared to other communities of similar size in the same Iowa counties. The Rathbun communities had a greater risk of IUGR than southern Iowa communities with other surface sources of drinking water (relative risk = 1.8; 95% CI = 1.3, 2.7). Multiple linear regression analyses revealed that levels of the herbicides atrazine, metolachlor, and cyanzinc were each significant predictors of community IUGR rates in southern Iowa after controlling for several potentially confounding factors including maternal smoking and socioeconomic variables. The association with IUGR was strongest for atrazine, but all three herbicides were intercorrelated and the independent contributions of each to IUGR risk could not be determined. We conclude that communities in southern Iowa with drinking water supplies contaminated with herbicides have elevated rates of IUGR compared to neighboring communities with different water supplies. Because of the limitations of the ecologic design of this study, including aggregate rather than individual measures of exposure and limited ability to control for confounding factors related to source of drinking water and risk of IUGR, a strong causal relationship between any specific water contaminant and risk of IUGR cannot yet be inferred. The association between the water supplied to the Rathbun communities and the increased risk of IUGR should be considered a preliminary finding that needs to be verified by more detailed epidemiologic studies.

Clinical and epidemiologic studies of cleft lip and palate in the Philippines

Clinical and epidemiologic studies of defined geographic populations can serve as a means of establishing data important for genetic counseling and as a first step in identifying strategies best suited for identification of causes. Under the sponsorship of Operation Smile International, clinical, genetic, and epidemiologic studies were carried out at six sites within the Philippines between 1989 and 1996. Patients who were being evaluated for surgical repair of craniofacial anomalies (primarily clefts of the lip and palate) were briefly examined for the presence of associated anomalies, and a family history was obtained to look for the frequency of cleft lip and palate in siblings. Birth records of 47,969 newborns over an 8-year period at one hospital in Bacolod City in the province of Negros Occidental were reviewed. Medical records of infants born with clefts of the lip and/or palate and other major anomalies were reviewed and birth prevalence rates calculated. Findings include a birth prevalence of 1.94 per 1000 live births for cleft lip with/without palate in the Philippines. Recurrence rates in siblings for nonsyndromic clefts of the lip and palate were 23 per 1000 for cleft lip with or without cleft palate, and 14 per 1000 for cleft palate only. The percentage of clefts associated with multiple anomalies was 21% at birth and 6% for individuals examined during the screening process, providing evidence for a high postnatal death rate. These data provide groundwork for additional etiologic studies including segregation analysis and molecular genetic studies involving linkage or association, as well as for studies of environmental contributions to clefting such as vitamin deficiencies. Preliminary molecular analysis using an association approach is reported in a companion paper. The findings suggest a high incidence of cleft lip and palate in native-born Filipinos.

Effect of lipid oxidation on the regulation of glucose utilization in obese patients

The effect of changes in lipid oxidation on glucose utilization (storage and oxidation) was studied in seven nondiabetic obese patients. They participated in three protocols in which: (1) Intralipid (to raise plasma FFA concentrations), (2) beta-pyridylcarbinol [a precursor of nicotinic acid, to lower plasma free fatty acids (FFA) concentrations], or (3) isotonic saline were infused over 2 h. Thereafter, these infusions were discontinued, and a 2-h euglycemic, hyperinsulinemic clamp was performed to measure glucose uptake. All studies were carried out in combination with indirect calorimetry to measure oxidative and nonoxidative glucose disposal (glucose storage). The high plasma FFA concentrations (1024 +/- 57 mumol/l) and lipid oxidation rates (1.1 +/- 0.1 mg/kg.min) found at the end of the Intralipid infusion and the low plasma FFA concentrations (264 +/- 26 mumol/l) and lipid oxidation rates (0.7 +/- 0.1 mg/kg.min) found at the end of the beta-pyridylcarbinol infusions resulted in significantly different rates of total and nonoxidative glucose disposal during the insulin clamp. The values were 2.6 +/- 0.6 mg/kg.min after Intralipid and 4.1 +/- 1.0 mg/kg.min after beta-pyridylcarbinol for total glucose disposal, and 0.4 +/- 0.4 and 1.6 +/- 0.8, respectively for nonoxidative glucose disposal. In conclusion, these observations show that changes in lipid oxidation rates preceding a glucose load influence glucose disposal and glycogen storage in obese subjects.

CARBONIC ANHYDRASE INJECTION PROVIDES EVIDENCE FOR THE ROLE OF BLOOD ACID-BASE STATUS IN STIMULATING VENTILATION AFTER EXHAUSTIVE EXERCISE IN RAINBOW TROUT

This study tests the hypothesis that the increase in blood PCO2 and associated respiratory acidosis after exhaustive exercise play an important role in stimulating ventilation during post-exercise recovery in fish. Injection of bovine carbonic anhydrase (10 mg kg-1) into the bloodstream of rainbow trout caused a persistent 40 % increase in the HCO3- dehydration capacity of the blood. The treatment was designed to increase CO2 excretion and therefore to reduce PCO2 build-up and acidosis after exercise. Aerobic and anaerobic swimming performance were not affected by carbonic anhydrase, and there were only very minor effects on arterial blood acid&shy;base status in resting fish. However, carbonic anhydrase attenuated post-exercise increases in PaCO2 and decreases in pHa by about 50 % without altering arterial O2 variables, red cell swelling or the intracellular pH of the brain or muscle tissues. The effects on arterial pH (pHa) resulted largely from alleviation of the increase in PaCO2. In accordance with the original hypothesis, normal post-exercise hyperventilation was greatly attenuated, through reductions in both ventilatory stroke volume and frequency, and excess post-exercise O2 consumption was reduced. Post-exercise increases in plasma levels of adrenaline and noradrenaline were also reduced by the carbonic anhydrase treatment. Overall, there was a strong correlation between increases in relative ventilation and decreases in pHa after exhaustive exercise. The results provide functional significance for the phenomenon of PaCO2 elevation and associated respiratory acidosis after exercise and are consistent with other recent studies indicating an important secondary drive to ventilation in fish based on arterial acid&shy;base status, in addition to the primary drive based on arterial O2 levels.

Refractive index distribution and spherical aberration in the crystalline lens of the African cichlid fish Haplochromis burtoni

Refractive index distribution in the teleost crystalline lens was measured with a nondestructive method in freshly excised lenses of the African teleost fish Haplochromis burtoni. Independently, spherical aberration was measured in a parallel set of lenses. The measured refractive index profiles show a continual decrease of refractive index from the center to the surface of the lens. The H. burtoni lens is of high optical quality and slightly overcorrected for spherical aberration. Details of the small residual spherical aberration were accurately predicted by ray-tracing model calculations based on the measured refractive index profile. The refractive index profile and the spherical aberration both show more complex characteristics than suggested by earlier measurements and lens models.