Technical note: a procedure for the preparation and quantitative analysis of samples for titanium dioxide.

A procedure was developed for the rapid analysis of titanium dioxide (TiO2) concentrations in feed and fecal samples. Samples were digested in concentrated H2SO4 for 2 h, followed by addition of 30% H2O2, and absorbance was measured at 410 nm. Standards were prepared by spiking blanks with increasing amounts of TiO2, resulting in a linear standard curve. Complete analysis using this procedure can typically be accomplished within 4.5 h. This procedure was compared to a previously published dry-ash procedure for the analysis of TiO2 in bovine fecal samples. Three sources of OM devoid of TiO2 (a forage sample, a bovine fecal sample without Cr2O3, and a bovine fecal sample containing Cr2O3) were spiked with graded amounts (0, 2, 4, 6, 8, or 10 mg) of TiO2. With our procedure, TiO2 recoveries averaged 96.7, 97.5, and 98.5%, for the three OM sources, respectively, vs. 74.3, 83.8, and 53.1% for the same samples analyzed using the dry-ash method. These results suggest that our procedure is a rapid and accurate alternative to dry-ash procedures for the determination of TiO2.

Stability of refraction during four years after radial keratotomy in the prospective evaluation of radial keratotomy study.

The Prospective Evaluation of Radial Keratotomy Study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refraction between -2.00 and -8.00 diopters. We studied the stability of the refractive error during four years after surgery for each of 341 eyes first operated on that had a single surgical procedure. Between baseline and two weeks after surgery, all eyes became less myopic; between two weeks and three months, 161 eyes (59%) lost 1.00 D or more of the initial effect; and between three and six months, 266 eyes (95%) had a stable refraction with less than 1.00 D change. The change from six months to four years was less than 1.00 D for 246 eyes (72%). There was 1.00 D or more decrease in surgical effect (increased minus power) for 13 eyes (4%), and 1.00 D or more increase in surgical effect (decreased minus power) for 82 eyes (24%). Eyes with larger amounts of preoperative myopia and smaller diameter of the clear zone were more likely to have an increasing effect of the surgery. The duration of this continued increasing effect of the surgery is unknown.

Three year results of the Prospective Evaluation of Radial Keratotomy (PERK) study.

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refractive error between -2.00 and -8.00 diopters (D). We report results for one eye of each patient. The surgical technique consisted of eight incisions using a diamond micrometer knife with the blade length determined by intraoperative ultrasonic pachymetry and the diameter of the central clear zone determined by the preoperative refractive error. At three years after surgery, 58% of eyes had refractive error within one diopter of emmetropia; 26% were undercorrected, and 16% were overcorrected by more than one diopter. Uncorrected visual acuity was 20/40 or better in 76% of eyes. The operation was more effective in eyes with a preoperative refractive error between -2.00 and -4.37 diopters. Between one and three years after surgery, the refractive error changed by 1.00 diopter or more in 12% of eyes, indicating a lack of stability in some eyes.

Three-year results of the Prospective Evaluation of Radial Keratotomy (PERK) Study.

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refractive error between -2.00 and -8.00 diopters (D). The authors report results for one eye of each patient. The surgical technique consisted of eight incisions using a diamond micrometer knife with the blade length determined by intraoperative ultrasonic pachymetry and the diameter of the central clear zone determined by the preoperative refractive error. At 3 years after surgery, 58% of eyes had refractive error within 1.00 D of emmetropia; 26% were undercorrected and 16% were overcorrected by more than 1.00 D. Uncorrected visual acuity was 20/40 or better in 76% of eyes. The operation was more effective in eyes with a preoperative refractive error between -2.00 and -4.37 D. Between 1 and 3 years after surgery, the refractive error changed by 1.00 D or more in 12% of eyes, indicating a lack of stability in some eyes. In the 435 eyes, there was a small number of complications including six eyes that lost two or three lines of best-corrected acuity, 16 that experienced vascularization of the incisions, 2 that had delayed bacterial keratitis, and 4 that had recurrent epithelial erosions.

Sex differences in acetaldehyde on body temperature and open-field performance in the rat.

Using the open field, for making an overall assessment of behavioural change in response to acetaldehyde (AcH) treatment, the results from the present study demonstrate that AcH produces behavioural and physiological effects similar to those of ethanol. High doses of AcH produced a similar degree of change as high doses of ethanol. Both compounds render the animal incapable of locomotor activities, such as ambulation and rearing and both produce a decrease of 2-3 degrees C in body temperature. AcH, however, appears to be a much more potent compound as behavioural and physiological changes are exhibited even after a dose of 10 mg/kg, while the dose of ethanol necessary to produce a decrease in open-field behaviour is at least 10 times as much. Females were more sensitive to the effects of AcH at the 100 mg/kg dose.

Dopamine and salsolinol levels in rat hypothalami and striatum after schedule-induced self-injection (SISI) of ethanol and acetaldehyde.

Endogenous levels of salsolinol and dopamine were measured by a gas chromatography/mass spectrometry (GC/MS)--selected ion monitoring technique using deuterated internal standards in rats allowed to self-inject either acetaldehyde, ethanol or saline control solution over 20 days for 1 h/day. Significant increases in medial basal hypothalamic (MBH) and striatal salsolinol concentrations were found in animals exposed to acetaldehyde but not ethanol, whereas dopamine concentrations for these animals did not differ significantly from rats exposed to control conditions. The data provides further support for the in vivo formation of salsolinol following acetaldehyde exposure in experimental animals.

The use of a laser for debridement of incipient caries.

The mode-locked YAG laser effectively removes debris and/or stains from incipient carious lesions in pits and fissures. Prior investigations inferred that the energy levels used in this study would not cause pulpal injury or remove sound intact enamel. This would be a desirable step in sealant therapy and could provide an improved method of debridement in treating precarious lesions.

Results of the prospective evaluation of radial keratotomy (PERK) study one year after surgery.

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center, self-controlled clinical trial of a standardized technique of radial keratotomy in 435 patients who had physiologic myopia with a preoperative refraction between -2.00 and -8.00 diopters. The surgical technique consisted of eight incisions using a diamond micrometer knife with blade length determined by intraoperative ultrasonic pachymetry and the diameter of central clear zone determined by preoperative refraction. At one year after surgery, myopia was reduced in all eyes; 60% were within +/- 1.00 diopter of emmetropia; 30% were undercorrected and 10% were overcorrected by more than 1.00 diopter (range of refraction, -4.25 to +3.38 D). Uncorrected visual acuity was 20/40 or better in 78% of eyes. The operation was most effective in eyes with a refraction between -2.00 and -4.25 diopters. Thirteen percent of patients lost one or two Snellen lines of best corrected visual acuity. However, all but three eyes could be corrected to 20/20. Ten percent of patients increased astigmatism more than 1.00 diopter. Disabling glare was not detected with a clinical glare tester, but three patients reduced their driving at night because of glare. Between six months and one year, the refraction changed by greater than 0.50 diopters in 19% of eyes.

Intraocular lens design for the neodymium:YAG laser.

Phacoemulsification was performed on both lenses of 24 rabbits. One eye received a lens implant with a convex-plano optic; the fellow eye received an implant with a convex-concave optic which separated the posterior surface of the implant from the posterior capsule by 0.2 mm, 0.3 mm, or 0.4 mm. A YAG laser capsulotomy was performed on all eyes immediately following surgery and an assessment of both microscopic and macroscopic YAG-induced lens damage was made. The meniscus optics with their capsule-implant separation showed significantly less YAG-induced damage than their convex-plano counterparts without this separation. Increasing the amount of capsule-implant separation beyond 0.2 mm did not enhance the degree of protection from YAG-induced damage.

Salsolinol and dopamine in rat medial basal hypothalamus after chronic ethanol exposure.

Endogenous levels of salsolinol and dopamine were measured by a gas chromatography/mass spectrometry (GC/MS) - selected ion monitoring technique using deuterated internal standards in Long Evans rats chronically exposed to ethanol for ten months. Chronic ethanol exposure produced significant increases of dopamine and salsolinol concentrations in the medial basal hypothalamus but not striatum. The data suggest that the occurrence of salsolinol in rat brain tissue is a consequence of an in vivo Pictet-Spengler cyclization.

Effects of naloxone and buprenorphine on intravenous acetaldehyde self-injection in rats.

Rats can be induced to self-inject acetaldehyde under an appropriate operant conditioning schedule. The narcotic antagonist naloxone (30 mg/kg) is shown to produce a decrease in schedule-induced acetaldehyde self-injection, but was without effect on both barpress responding and spontaneous activity in rats tested individually for fine, gross and total activity. On the other hand buprenorphine (0.3 and 3 mg/kg), the mixed agonist-antagonist derived from the opium alkaloid thebaine, also produced a significant decrease in acetaldehyde self-injection. However, a significant effect of buprenorphine on barpressing in otherwise drug naive rats indicated that this finding should not be dissociated from a possible involvement of buprenorphine on motor responding. While the findings are consistent with the hypothesis of opiate involvement in acetaldehyde self-administration, caution must be exercised when drawing conclusions about the participation of endogenous opiates in acetaldehyde-mediated behavior.

Psychosocial characteristics of candidates for the prospective evaluation of radial keratotomy (PERK) study.

The National Eye Institute Prospective Evaluation of Radial Keratotomy (PERK) Study is a multicenter clinical trial for the evaluation of radial keratotomy. This article describes the questionnaire data collected on PERK patients and compares them with a similar group of myopic persons studied during the Rand Health Insurance Experiment (heretofore referred to as the Rand study). The PERK patients are young, white myopes who dislike being dependent on corrective lenses but perceive themselves to be more visually impaired than do comparable Rand study myopes. Most female subjects and a plurality of the male subjects have tried contact lenses and quit wearing them mainly because use of the lenses was inconvenient or bothersome. There is no evidence that patients are psychologically or socially deviant. Both male and female subjects expressed a fear of being without vision and cited impatience with the lenses as their major motivation for wanting surgery.

Alteration of alcohol drinking in the rat by peripherally self-administered acetaldehyde.

The effects of intravenous acetaldehyde or saline self-injection and feeding regimes on oral alcohol consumption in rats was examined. The alcohol solutions offered to the animals was increased systematically in concentrations from 3 to 30%, according to a three-bottle, two-choice technique. Results suggest that (1) acetaldehyde pre-treatment using a self-injection procedure induces increased consumption of alcohol, the effect being particularly marked when coupled with conditions of food-deprivation (2) food-deprivation alone may be capable of inducing increased alcohol intake and this effect may persist even when deprivation is terminated (3) the combination of acetaldehyde and food-deprivation is most effective when food-deprivation follows a period of free-feeding. These findings provide support for an involvement of acetaldehyde in the development of an animal's preference for alcohol.

Rationale for and design of the National Eye Institute Prospective Evaluation of Radial Keratotomy (PERK) Study.

A five-year, multicenter, collaborative clinical trial of radial keratotomy for myopia is being carried out at nine clinical centers. The study, funded by the National Eye Institute, is recruiting approximately 500 patients aged 21 years or older with -2.00 to -8.00 diopters of physiologic myopia who also meet other clearly defined eligibility criteria. Surgeons use a diamond-bladed micrometer knife to make eight radial incisions in the anterior cornea. The diameter of the central clear zone is determined by the amount of myopia and the depth of the incisions by intraoperative ultrasonic pachymetry. Investigators other than the surgeon gather all pre- and post-operative data. Examinations include measurement of visual acuity with standardized charts, verification of refractions by a second observer, measurement of corneal curvature by keratometry and photokeratoscopy, quantitation of glare with a glare tester, and measurement of the size of individual endothelial cells from specular photomicrographs with a computerized digitizer. A formal psychometric questionnaire is used to evaluate the patients' subjective response. Physician monitors insure adherence to the protocol during site visits and members of the Data and Safety Monitoring Board oversee the progress of the study. Biostatisticians at the Coordinating Center insure complete data collection, process the data, and assist in the interpretation of results.

Intravenous self-administration of acetaldehyde in the rat as a function of schedule, food deprivation and photoperiod.

The present series of experiments were conducted to discover whether rats would self-administer acetaldehyde (AcH) intravenously. The first study establishes the basic parameters for AcH self-injection in rats at 80% reduced body weight on a fixed-time 1 min (FT-1) food delivery schedule tested in the dark phase of a 12:12 light/dark cycle. The results show a dose-dependent effect with 1.3% AcH being the preferred dose as measured by the number of infusions. In the second experiment rats were on 100% free-feeding and at 80% reduced body weight, both conditions either with or without the influence of a FT-1 min schedule. The findings indicate that an interaction between dose, food deprivation and a FT-1 min schedule appears to initiate and maintain high levels of AcH self-injection in the dark. In a further experiment using 1.3% AcH the self-injection rates of animals at 80% body weight with a FT-1 min schedule reveal that the time of day of testing may be an important variable for inducing AcH intake. The results suggest that under altered environmental conditions AcH may have both an aversive and reinforcing effect.