Visual performance after photorefractive keratectomy with a 6-mm ablation zone.

PURPOSE: To prospectively examine the effect of photorefractive keratectomy with a 6-mm ablation zone on best-spectacle-corrected visual performance. METHODS: A prospective study was conducted of 164 eyes of 164 patients with an average (+/-SD) of -4.02 +/- 1.74 diopters (range, -0.63 to -8.38 diopters spherical equivalent). Best-spectacle-corrected high-contrast and low-contrast visual acuity (18% Weber contrast) was measured with both natural and dilated pupils. Patients were tested preoperatively and at 3, 6, and 12 months after photorefractive keratectomy. Photorefractive keratectomy was performed with an argon fluoride excimer laser. Fifty-five eyes of 55 patients also underwent astigmatic keratotomy. RESULTS: Twelve months after photorefractive keratectomy, best-spectacle-corrected high-contrast visual acuity with natural pupils showed no significant change from preoperative values; mean (+/-SD) change was 0.004 +/- 0.10 logMAR (t = 0.45, P = .65). Best-spectacle-corrected low-contrast visual acuity with natural pupils was significantly reduced compared to baseline; mean (+/-SD) change was 0.04 +/- 0.13 logMAR (t = 3.3, P = .001). The low-contrast loss was larger (1.5 lines) with dilated pupils; mean (+/-SD) change was 0.13 +/- 0.15 logMAR (t = 9.31, P < .001). Greater losses in dilated low-contrast visual acuity were associated with concurrent astigmatic ketatotomy (t = 2.28, P = .025) and corneal haze of grade 1 or greater (t = 2.71, P = .005). CONCLUSIONS: Reductions in visual performance occur after photorefractive keratectomy with a 6-mm zone. These changes are greatest for low-contrast visual acuity with dilated pupils. Corneal haze and concurrent astigmatic keratotomy are associated with greater losses in low-contrast visual acuity. Best-spectacle-corrected low-contrast visual acuity is a sensitive measure for evaluating visual performance after refractive surgery.

Nuclear translocation of prolactin: collaboration of tyrosine kinase and protein kinase C activation in rat Nb2 node lymphoma cells.

Recent evidence has suggested that prolactin (PRL), internalized by lactogen-dependent Nb2 lymphoma cells, is actively translocated to the nucleus where it binds to PRL receptors. Moreover, the mitogenic action of PRL in these cells has been separately linked to protein tyrosyl phosphorylation and activation of protein kinase C (PKC). Therefore, the coupling of PRL internalization and nuclear translocation to the activation of these signal transduction pathways was investigated. Results from control experiments indicated that 30% of internalized and 5% total cell-associated 125I-rat PRL could be recovered within nuclei obtained from Nb2 cells previously incubated with the radiolabel for 3 h at 37 degrees C. Furthermore, internalized PRL was found to be intact and not associated with any carrier proteins. Addition of tyrosine kinase (TK) antagonists, genistein or tyrphostin, significantly reduced cell surface binding, internalization, and nuclear translocation of 125I-rat PRL. In contrast, neither the level of cell-associated nor internalized hormone differed between cells treated with the PKC antagonists, staurosporine or calphostin C, and control cultures. Instead, PKC inhibition significantly reduced nuclear PRL translocation. The inhibitory effects of the TK and PKC antagonists on PRL internalization and nuclear translocation in intact Nb2 cells were verified by immunofluorescence microscopy in parallel experiments. In other experiments, each of the kinase inhibitors blocked PRL-stimulated Nb2 cell proliferation in a concentration-dependent manner. It is concluded that activated TK and PKC collaborate in the process of PRL internalization and translocation to the nucleus. TK activation may participate in PRL receptor binding or hormone internalization while activation of PKC appears to be required for its nuclear targeting. Since TK and PKC activation are required for lactogen-stimulated Nb2 cell proliferation, we suggest that a component of the mitogenic pathway in these cells is a direct nuclear interaction of PRL.

Normal activity-dependent refinement in a compressed retinotectal projection in goldfish.

When the optic nerve in a goldfish is crushed, regenerating fibers can reform a normal retinotopic projection. Two processes are thought to generate this retinotopic order. One is an activity-independent process, presumed to be some form of substrate-directed growth, which generates rough retinotopy as seen in the early formed projection. The other is an activity-dependent process that generates fine retinotopy during a protracted period of refinement. This projection also displays two other behaviors. One is retinotopic plasticity, in which optic fibers can compensate for retinal or tectal ablations by expanding or compressing into the available tectal space while preserving retinotopic order. These plasticities can dramatically alter the scale of the projection. The other behavior is the formation of fixed synaptic sites in tectum. Optic fibers make a characteristic number of synaptic connections in tectum, which is not changed by increasing the number of invading optic fibers. This has been interpreted to mean that fibers compete for limited synaptic sites. How the two processes that generate order, substrate-directed growth, and activity-dependent refinement might each be affected by the expression of retinotopic plasticity and altered synaptic competition is largely unknown. In particular, it is not known how fine retinotopic order (activity-dependent refinement) might be affected by altering the scale of the projection. Would optic fibers from neighboring ganglion cells converge into the same-sized area of tectum, or would they expand or compress in proportion to the altered scale of the overall map? To explore this issue, the posterior half of tectum of goldfish was removed, and the optic nerve was crushed, thereby forcing regenerating fibers to form a compressed retinotopic projection onto the anterior half of tectum. Under these conditions, optic fibers are also forced to compete for half the normal number of synaptic sites. The effect on retinotopy was monitored at various times during regeneration by making a small spot injection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into nasal retina corresponding to fibers that would normally terminate in the missing posterior half of tectum. To distinguish between activity-dependent and activity-independent processes, retinal impulse activity was blocked in some animals by repeated intraocular injections of tetrodotoxin. The initial projection was found to be unaffected by impulse activity. Regardless of activity, nasal fibers failed initially to grow to the most posterior available regions, but instead were dispersed across much of the "incorrect" anterior half of tectum at 30 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity-dependent retinotopic refinement in a low-density retinotectal projection in the goldfish: evidence favoring synaptic cooperation over competition.

During optic nerve regeneration in goldfish, the label from a small retinal spot injection of WGA-HRP has been previously reported to be initially widely dispersed in the tectum and subsequently to condense into a small patch in the retinotopically appropriate location of tectum. This refinement involves two separate processes: one is activity independent and generates gross retinotopy; the other is activity dependent and mediates the formation of fine retinotopy. Since the number of synapses remains constant during this refinement, one or both of these processes may involve some form of competition for a limited number of synaptic sites. To clarify the role of synaptic competition, we created a low-density retinotectal projection in goldfish by deflecting about 20% of the optic fibers from one tectum into the opposite tectum, which was denervated of all other optic fibers. Under this condition, it was previously shown that less than half the normal density of synapses is formed. If competition for synaptic sites is a requirement of refinement, refinement should be prevented or significantly hindered. To monitor refinement during regeneration, 2 nl spot injections of WGA-HRP were made into the retina at various times after deflection. To distinguish between activity-dependent and activity-independent refinement, retinal impulse activity was blocked in some fish with repeated injections of TTX into the eye for the duration of the experiment. It was found that considerable activity-independent refinement occurred under continuous TTX blockade although the fibers remained more dispersed than in previous TTX studies when normal numbers of fibers were present. Surprisingly, in fish with normal impulse activity, the degree of activity-dependent refinement was almost normal. Labeled fibers condensed into a small area roughly comparable in size to that observed when the full complement of fibers was regenerating into tectum. These results suggest that competition for limited synaptic sites is not essential for activity-dependent refinement, which may, instead, be mediated by a cooperative process that actively promotes convergence. The findings further suggest that if synaptic competition plays a role in this system, it is in regulating activity-independent mechanisms that determine the large-scale distribution of fibers within tectum.

Nuclear co-localization of prolactin and the prolactin receptor in rat Nb2 node lymphoma cells.

Previous studies have indicated that prolactin (PRL) interacts with specific, high affinity, immunoreactive binding sites within isolated rat hepatocyte nuclei. Moreover, endogenous PRL appears to be bound to this site. However, it remained important to demonstrate nuclear PRL receptors and hormonal translocation in an intact cell system. Therefore, we sought nuclear translocation of PRL and its receptor in the nucleus of PRL-dependent Nb2 node lymphoma cells. Utilizing immunofluorescence (IF) microscopy, growth-arrested cells were found to constitutively express the PRL receptor in the nucleus and in the membrane/cytosol compartments. Addition of PRL stimulated rapid hormone internalization followed by translocation to the nucleus within 6-12 hrs. The translocation of PRL was found to be reversible and dependent upon ATP. These results indicate that an early event coupled to the mitogenic action of PRL in Nb2 cells is hormone transport to the nucleus during the G1 and S phases of cell cycle. Once in the nucleus, PRL bound to its receptor may directly influence gene transcription.

Short-term dietary copper deficiency does not inhibit angiogenesis in tumours implanted in striated muscle.

The effect of dietary copper deficiency on tumour growth, neovascularisation and microvascular integrity was studied in the rat cremaster muscle. Male, weanling Sprague-Dawley rats were fed purified diets which were copper deficient (< 0.5 micrograms g-1 of diet) or copper adequate (5 micrograms g-1 of diet). Seven days after initiation of diets, a chondrosarcoma was implanted in the cremaster muscle of each rat. Five, 10 or 20 days after tumour implantation, rats were anesthetised and their cremasters prepared for observation by intravital microscopy. Intraarterial injection of fluorescein isothiocyanate-conjugated albumin and subsequent observation of fluorescence in the perivascular space indicated no difference in microvascular albumin leakage between the tumour vasculature of copper deficient and copper adequate rats. Neither tumour growth (assessed by wet weight), vascular density (assessed by light microscopy), nor any ultrastructural characteristics of the tumour or its vasculature (assessed by electron microscopy) were affected by copper deficiency. In view of findings by others which indicate changes in tumour characteristics with copper deficiency, we conclude that the copper dependency of tumour growth and vascularisation is a function of the type of tumour, the host tissue, or the conditions of copper depletion.

The effect of TTX-activity blockade and total darkness on the formation of retinotopy in the goldfish retinotectal projection.

In the normal goldfish, neighboring retinal ganglion cells terminate in one small tectal locus to produce the precise retinotopy characteristic of this projection. This can be directly demonstrated by labeling neighboring ganglion cells with small "spot" injections of WGA-HRP, which yield a single small patch of product at the retinotopically appropriate part of the tectum. When the optic nerve is crushed, label from these spot injections was previously found to be widely dispersed during the early phase of regeneration. With time, label subsequently condensed, typically into several discrete patches reminiscent of ocular dominance columns. In this study, we tested whether the formation of these patches required impulse activity by injecting tetrodotoxin (TTX) into the eye during regeneration. We found that impulse blockade completely inhibited the formation of discrete patches while permitting considerable condensation of the label. This implies that these patches are generated by activity but that some map "refinement" utilized cellular processes that are activity independent. This activity-independent condensation progressed at a noticeably slower rate than the equivalent condensation seen with activity, thus suggesting that activity normally participates as a "helper factor," even though it is not strictly required. Since the formation of discrete patches during regeneration provides a sensitive measure of activity-dependent refinement, this was used to further address two controversial questions concerning the role of impulse activity. One is whether there is a chronologically defined critical period for activity-dependent refinement. This was tested by blocking impulse activity for 2 to 4 months, much longer than the activity-dependent refinement is thought to last, and then permitting activity to resume. We found that multiple patches were formed following this period of late activity, thus indicating that synaptic plasticity extends for several months beyond the supposed critical period. The other question was whether spontaneous retinal activity was sufficient for activity-dependent ordering. To test this, fish were kept in constant darkness during optic nerve crush and labelled with retinal spot injections at various times during regeneration. Condensation of label with the final formation of multiple patches formed at about the same time as fish with normal visual experience. This implies that the amount and extent of correlation of spontaneous activity in retina is adequate for driving activity-dependent refinement.

Surface coat material associated with the developing otic placode/vesicle in the chick.

Surface coat material (SCM) has been illustrated in association with the apical surfaces of numerous epithelia during morphogenesis. This study investigates the development of a SCM associated with the invaginating otic placode/vesicle in the chick. Glycoconjugate containing SCM was retained by the inclusion of cetylpyridinium chloride (CPC) in the fixative, histochemically visualized by using ruthenium red (RR) staining, and viewed by scanning (SEM) or transmission (TEM) electron microscopy. Initial characterization of the glycoconjugates present in this material was elucidated by using lectins conjugated to fluorescein isothiocyanate. Lectins utilized included concanavalin A (Con A), wheat germ agglutinin (WGA), and soybean agglutinin (SBA). Invagination of the otic placode was apparent as early as stage 12. By stage 15 the vesicle was beginning to separate from the surface ectoderm as evidenced by its aperture, which was altered in shape and reduced in size. All embryos fixed with glutaraldehyde containing either CPC or RR were shown to possess SCM associated with the surface ectoderm, particularly in the area of the otic placode/vesicle. Additional embryos were processed by cryofixation without prior aldehyde fixation; these also exhibited SCM. All lectins labelled the epithelium of the otic placode/vesicle. However, their binding patterns were not identical. The binding of Con A and WGA remained constant over the stages studied, while SBA increased as the otic vesicle developed. The data clearly indicate that otic placode morphogenesis is accompanied by the synthesis of SCM rich in glycoconjugates.

A real-time data-logger system using an optical disk WORM for archiving continuous 12-lead ECG data during exercise testing.

An exercise ECG analysis program was developed over 15 years on a number of mainframes, minicomputers and, most recently, microcomputer-based systems. It has been rehosted into both Motorola MC68000 and Intel 80286 microprocessor-based development systems and is currently used with a removable 200 Mbyte optical disk (Write-Once-Read-Many, WORM) based data-logger system that can record and store all 12 leads simultaneously and continuously for an entire exercise test (up to 38 minutes). Data is acquired with 12-bit A/D resolution at 500 samples/sec. All ECG data and patient information are archived on the optical disk for later off-line recall and analysis on a PC or real-time replay through a D/A converter. Recorded ECG signals are at patient levels so they can be replayed through the patient cable box on any commercial system. Current development includes both simultaneous on-line processing and storage of 12-lead ECG data and off-line processing and development performed on the long-term, continuous ECG data being archived on optical disk. Patient medical histories and clinical information are separately entered into an applications database, where ECG measures and test results are later included. This new optical disk based exercise ECG database contains more than 600 complete exercise tests and is projected to increase to nearly 3,000 within 2 years.

Problems and limitations of ECG baseline estimation and removal using a cubic spline technique during exercise ECG testing: recommendations for proper implementation.

One common variety of exercise-induced artifact is baseline wander resulting from movement, respiration, and poor electrode contact. Although filters can be designed to remove much of this baseline variation, they will distort the low-frequency components of the ECG complex, such as the TP-segment, the PR-segment, and, most problematically, the ST-segment. The ST-segment is the most diagnostically relevant measure of the ECG taken during exercise. While linear baseline interpolation and removal may be adequate at lower heart rates, they also will introduce significant distortions. This is particularly evident when excessive nonlinear wander is present, as seen at higher heart rates and respiration rates. A nonlinear, third-order, polynomial estimator of baseline wander, known as the cubic spline, has been used for nearly 15 years. It is a very robust technique applied to exercise ECG recordings. Since the cubic spline is not a filter and use an a priori knowledge of the shape of the ECG signal, it estimates the true baseline and avoids distortion better. The more common implementations of this technique use relatively short ECG recordings. With the advent of increasing power in computerized ECG systems, the implementation of the cubic spline algorithm for removing baseline wander in continuous, longer-duration ECG records and in real-time processing is being attempted. However, the correct application of the cubic spline to continuous recordings is not straightforward and involves a number of previously unforeseen difficulties. The accuracy and resolution of both floating point and integer operations is critical during long-term application of the cubic spline function.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of histamine on cardiac sarcolemmal calcium binding as indicated by use of ionic lanthanum.

To determine whether the inotropic effect of histamine might be associated with enhanced calcium binding to the sarcolemmal-glycocalyx complex, the effect of histamine on lanthanum binding to the cell membrane in the presence of verapamil was assessed. Rabbit hearts were perfused firstly with histamine, secondly with histamine and verapamil, and subsequently with histamine in the presence of lanthanum and verapamil. Subsequent transmission electron microscopy showed the presence of bound lanthanum on both the cellular surface and cytoplasmic vesicles of most cardiac myocytes, which is in contrast to the absence of lanthanum binding that occurs in the presence of verapamil alone. Furthermore, this histamine mediated enhancement of lanthanum binding is not affected by the H1 antagonist diphenhydramine but is reduced by the H2 antagonist cimetidine. This visual evidence of an apparent enhancement of lanthanum binding under histamine and subsequent attenuation with cimetidine supports the hypothesis that histamine may exert its positive inotropic effect by causing increased calcium binding to the sarcolemmal-glycocalyx complex of cardiac muscle and that the effect is mediated at least in part by H2 receptors.

Histamine induced alteration of calcium binding to microvascular endothelium as indicated by use of ionic lanthanum.

To determine whether histamine's effect on microvascular permeability might be associated with altered calcium binding, the influence of histamine on lanthanum binding to vascular endothelium was assessed in the presence of verapamil. Isolated rabbit hearts were perfused firstly with histamine, secondly with histamine and verapamil, and subsequently with histamine in the presence of lanthanum and verapamil. Examination by transmission electron microscopy showed that 92% of microvessels examined contained bound lanthanum on plasma membranes, plasmalemmal vesicles, or endothelial clefts of vascular endothelium, or all three, in both atria and ventricles, which is in contrast to the low proportion (4%) of microvessels containing bound lanthanum found in the presence of verapamil alone. The enhancement of lanthanum binding was reduced by both H1 and H2 receptor antagonists. This evidence supports the hypothesis that the increase in vascular permeability with histamine may be associated with increased calcium binding to vascular endothelial membranes and that both H1 and H2 receptors play a part in this activity.

The effects of zinc deficiency on developing photoreceptors in the rat retina: a scanning microscopic study.

A study was undertaken to observe the effects of dietary zinc deficiency on the topographical morphology of developing photoreceptor (rod) cells in the sensory retina of the rat. Observations were made by means of scanning electron microscopy (SEM). Pups were utilized from three groups including (1) zinc deficient (2) pair-fed controls and (3) ad libitum controls. Animals ranged in age from birth to twenty days. Femur zinc levels were measured by flame atomic absorption spectrophotometry. A statistically significant increase in the number of photoreceptor cells continued through the 6th day, however, no morphological differences were noted among cells during the first 13 days. By day 14, outer segments appeared more elongated in ad libitum control tissues. No differences in outer segment length were apparent by day 20.

Surface coat material associated with the cells of the developing lens vesicle in the chick embryo.

Ruthenium red (RR) and cetylpyridinium chloride (CPC) were used to demonstrate the distribution of cell surface coat material (SCM) on the free epithelial surface of the developing lens vesicle in stages 14-17 (50-64 hours) chick embryos. Observations were made by light microscopy and transmission. (TEM) and scanning (SEM) electron microscopy. A progressive increase in SCM is observed on cellular apices within the epithelium of the lens vesicle by means of RR staining, particularly at the margins of the aperture which are the sites of presumptive fusion. In contrast, a relatively thin layer of SCM persist on the adjacent surface ectoderm. Ruthenium red-positive SCM extends across the aperture of the lens vesicle prior to initial contact between the advancing epithelial surfaces. The presence of abundant SCM is interpreted as a possible significant prerequisite to invagination and to epithelial adhesion and fusion prior to detachment of the lens from surface ectoderm. When CPC is added to the fixative, a flocculent precipitate over the aperture of the lens vesicle and an associated band of modified surface ectoderm which extends ventrally from its lower margin are observed. The modified ectoderm and associated SCM likely represent a presumptive region of active coordinated cellular migration.

The case for self-insurance.

Faced with escalating costs for primary professional liability insurance, many hospitals are considering self-insuring at least part of their professional liability risk. Self-insurance offers advantages over commercial insurance in several areas. The most important corollary of self-insurance from the perspective of the board is the need for more intimate involvement in the quality of medical practice in the institution.