Biomedical subjects

R S Baker

Publications and source records attributed to R S Baker.

At least 19 recordsLinked to original sources

PubMed1992

Type-specific changes in fiber morphometry following denervation of canine extraocular muscle.

To investigate the changes that occur in extraocular muscle morphometry following denervation, 12 beagles were subjected to intracranial section of the left oculomotor nerve. The inferior and medial rectus muscles were removed from both orbits of four dogs killed at each 4-week postoperative interval. Fiber diameters and fiber-type ratios of denervated muscles were compared with those from paired muscles in the normal orbit. We found significant, persistent atrophy of the singly innervated fibers in both the global and orbital layers of denervated extraocular muscle. The multiinnervated fibers were predominantly spared from denervation atrophy. We also found a significant increase in the proportion of multiinnervated fibers in the orbital layer only. These results suggest a relative neurotrophic independence of multiinnervated fibers in extraocular muscle.

Animals↗

PubMed1992

Tumorigenicity of cyclopenta[a]phenanthrene derivatives and micronucleus induction in mouse skin.

The most potent carcinogen of the cyclopenta[a]phenanthrene series, 15, 16-dihydro-11-methylcyclopenta[a]phenanthren-17-one and its non-carcinogenic, unmethylated parent compound, were compared for their abilities to induce micronuclei in epidermal keratinocytes after application onto the dorsal skin of Skh/HR-1 hairless mice. Although both substances were shown to be mutagenic in vitro, only the 11-methyl derivative has been proven to initiate cancer in TO and Sencar mouse strains. In the present study, only the 11-methyl derivative was active as a cancer initiator in Skh/HR-1 mice. For studying micronucleus induction, a preliminary experiment was conducted to establish doses of both chemicals that allowed cell survival. Subsequently, micronucleus induction in epidermal keratinocytes was shown to agree with the cancer-initiating potential of the two compounds. Only the carcinogenic derivative induced a statistically significant increase in micronuclei, over the range 10-100 nmol. This is considerably lower than the dose of approximately 1600 nmol commonly used to initiate skin cancer in mice, but is comparable to the active dose range for skin micronucleus induction by benzo[a]pyrene, a chemical of equivalent carcinogenic potency.

Animals↗

PubMed1992

Skin carcinomas and micronucleus induction in epidermal keratinocytes following 12-O-tetradecanoylphorbol-13-acetate and mezerein treatment.

Phorbol esters are chemical compounds which have the ability to promote carcinogenesis in the skin of mice. In the HRA/Skh mouse strain, an initiation-promotion assay substantiated evidence that mezerein acts as a complete promoter. Complete promotion with 9.0 nmol mezerein induced a total of 53 papillomas in 28 mice within 40 weeks, while 1.5 nmol 12-O-tetradecanoylphorbol-13-acetate (TPA), using the same application regime, resulted in a total of 298 papillomas in 58 mice. However, 7.6% of the papillomas in the mezerein group progressed to carcinomas, compared with 0.7% in the TPA group. Approximately the same molar concentrations of TPA and mezerein induced a dose-dependent and reproducible increase in micronuclei in supra-basal cells derived from the epidermis of treated mice. In contrast, the latter compound was less toxic to these cells and induced higher numbers of micronuclei at the higher concentrations.

Animals↗

PubMed1992

Prenatal morphogenesis of primate extraocular muscle: neuromuscular junction formation and fiber type differentiation.

Extraocular muscle represents a distinctive class among mammalian skeletal musculature in exhibiting the full range of muscle fiber type variability found in vertebrate species. To better understand the basis for the unique structural/functional diversity of extraocular muscle, the ontogeny of lateral rectus muscles was studied in Macaca nemestrina fetuses of 62-156 days gestation using light and electron microscopy. At E62, myotubes and myofibers are evident, but fiber-type differentiation has not yet occurred and neuromuscular junctions are primitive. By E92, presumptive singly and multiply innervated fiber types could be distinguished on the basis of myofibril delineation. Like other skeletal muscles, extraocular myogenesis proceeds through at least two generations of myofibers. All primary and secondary myofibers were generated and were maturing by E121. The phylogenetically "old" global multiply innervated fiber type was the first to attain adult form. This was followed by maturation of global layer singly innervated fiber types, which are developed by E156, except for attainment of definitive size and mitochondrial content. Orbital layer fiber types, particularly the orbital singly innervated fiber, are the last to mature. Neuromuscular junction maturation paralleled the changes observed during fiber-type differentiation. In summary, the sequential development of their constituent muscle fiber types may reflect the functional pressures the extraocular muscles are exposed to by maturing visual and visuomotor systems. In particular, ontogenic and phylogenic changes observed in the orbital singly innervated fiber type may have direct implications for the types, range, and precision of eye movements used by different species and at different gestational ages.

Animals↗

PubMed1991

Use of bioerodible polymers impregnated with mitomycin in glaucoma filtration surgery in rabbits.

A prospective, randomized, double-masked, and placebo-controlled study was performed to evaluate the effects of a localized and sustained release of mitomycin on the success of glaucoma filtration surgery in rabbits. A bioerodible polymer was used as the drug carrier. Full-thickness filtration surgeries were performed and data from 22 rabbits were collected. One eye received a polymer impregnated with mitomycin (0.02 mg or 0.06 mg), while the fellow eye received a drug-free polymer. Intraocular pressure, bleb survival, and postoperative complications were investigated. Intraocular pressures remained lower for a longer period of time (P less than 0.004) and filtration blebs lasted longer (P less than 0.05) in experimental eyes than in control eyes. Conjunctivitis and sectorial corneal haze occurred more frequently in eyes treated with the higher dosage mitomycin compared with control eyes. The use of mitomycin-C in a polymer delivery system appeared to promote the success of glaucoma filtration surgery in rabbits. With the lower dosage of mitomycin, clinically significant ocular toxicity was not noted.

Animals↗

PubMed1991

Evaluation of optic nerve sheath fenestration in pseudotumor cerebri using automated perimetry.

Evaluation of the efficacy of optic nerve sheath fenestration in pseudotumor cerebri has been hindered by a lack of quantitative indicators of visual function before and after treatment. Nine patients (14 eyes) were treated who had pseudotumor with optic nerve sheath fenestration, in whom automated perimetry was used as a major parameter in the decision to undertake surgery and in evaluating the results. Visual field results demonstrated significant improvement in this group of patients. Seven of 8 eyes with total loss less than 1500 dB had improvement or no further deterioration. Using results of the last preoperative examination as baseline, it was found that six of the eight had improvement over 150 dB. In one patient, a slight deterioration occurred postoperatively. Those eyes with total loss above 1500 dB demonstrated stabilization of fields postoperatively. Statistical analysis of total loss preoperatively and postoperatively for this group of patients demonstrated significant improvement for five of the six comparisons investigated. Average preoperative total loss and average postoperative total loss were not significantly different. Comparisons of results of the last preoperative examination to those of the first postoperative and most recent follow-up examinations, and evaluation of average total loss postoperatively showed significant improvement had occurred. Results of the first postoperative examination and those of the most recent follow-up examination showed significant improvement from the average preoperative total loss.

Adult↗

PubMed1991

The effects of topical mitomycin on glaucoma filtration surgery in rabbits.

A prospective, randomized, double-masked, and placebo controlled study was performed to examine the effects of topically applied mitomycin on the success of full thickness filtration surgery in 23 rabbits. Both eyes of each rabbit had surgery by the same surgeon. After surgery, the experimental eye received a single subconjunctival injection of mitomycin (0.2 mg), and 50 microliters of a 0.2 mg/cc solution of mitomycin topically four time daily. The fellow control eyes were treated with sterile water. The mean intraocular pressure reduction from baseline exhibited by the experimental eyes was greater than that observed for the control eyes. The difference in intraocular pressure reduction between the two groups was statistically significant from post-operative day three through day 21 (p less than .05). With survival analysis, fewer failures were noted in the experimental eyes compared to control eyes for each time period throughout the study (p less than .005). The experimental eyes also demonstrated a longer time to bleb failure although this difference did not achieve statistical significance (p less than .10). An additional five rabbits were treated with the experimental drop in one eye and sterile water in the fellow eye but underwent no surgery. No differences between eyes were noted with regard to intraocular pressure change or anterior segment pathology. These data demonstrated the efficacy of mitomycin in promoting filtration surgical success in rabbits.

Administration, Topical↗

PubMed1991

Micronuclei induction by dichlorvos in the mouse skin.

Micronucleus (MN) induction in cultured keratinocytes was investigated following skin painting of HRA/Skh mice with the pesticide, dichlorvos. Whole skin and partially-purified epidermal cells from 5-6 week old male animals were cultured for 4 days in vitro after single topical applications of various concentrations of dichlorvos in vivo. Appropriate doses, allowing optimum survival of keratinocytes, were selected following an initial range-finding experiment. To evaluate MN induction in dividing cells, the cytokinesis-block method was employed. Results showed statistically significant MN at all dose levels in partially-purified epidermal cells and a positive trend with respect to dose from 51 to 1033 nmol dichlorvos. A significant increase in MN was also detectable in cultured cells from whole skin, dissociated within as little as 1 h after application of dichlorvos. Although a number of technical difficulties are associated with the skin micronucleus method, it has been used successfully in this laboratory to detect several skin carcinogens of both high and low potency. Since dichlorvos is rapidly absorbed through the skin, and can induce MN in skin cells of treated mice, this compound may therefore be considered to pose a contact hazard for exposed humans.

Administration, Topical↗

PubMed1991

Extraocular muscle regeneration in freeze-treated extraocular muscle autografts.

New growth of extraocular muscle has been demonstrated in degenerating peripheral nerve autografts implanted between two extraocular muscles. This suggests that extraocular muscle may be lengthened for therapeutic purposes if a suitable matrix can be found to support this new growth. Investigators of peripheral nerve regeneration have found that the basal lamina of freeze-killed skeletal muscle remains intact and supports axonal regeneration. This study was designed to investigate the feasibility of inducing regenerative growth of extraocular muscle in freeze-treated extraocular muscle autografts. In six beagles the inferior oblique muscle was removed from both orbits, frozen in liquid nitrogen, and allowed to thaw at room temperature. The freeze-thaw cycle was repeated. The freeze-treated grafts were then sewn in an end-to-end fashion between the cut end of the lateral rectus and the globe. At both 4 and 8 weeks postoperatively, three dogs were killed, and the grafts were removed from both orbits. These were prepared for light and electron microscopic examination. This revealed robust growth of mature-appearing, innervated muscle fibers in the proximal graft that could be differentiated by adenosine triphosphatase histochemistry. Rare, immature fibers were seen in the distal graft. These results demonstrate that freeze-treated extraocular muscle autografts support regenerative growth of extraocular muscle.

Animals↗

PubMed1990

Effects of beta-carotene on chemically-induced skin tumors in HRA/Skh hairless mice.

In order to evaluate the role of beta-carotene as an inhibitor of skin carcinogenesis, hairless female HRA/Skh mice were treated with the initiator 7,12-dimethylbenz[a]anthracene (DMBA) and with the promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), and were fed a balanced diet free from vitamin A either with or without gavage-administered beta-carotene. There was no evidence of avitaminosis A or differences in body weight in mice deprived of beta-carotene and vitamin A, compared with those given 290 or 1430 IU beta-carotene/kg per day. Mice fed with normal animal feed pellets displayed a significantly higher body weight (28.5 +/- 1.95 g) compared with mice on the special diet (25.7 +/- 1.9 g), and also displayed a higher papilloma yield. However animals on the special diet, fed with beta-carotene from weaning, displayed significantly lower numbers of papillomas per mouse. This lower papilloma yield was evident particularly between 12-24 weeks after commencement of the study, which coincided with the period of maximum tumor yield in DMBA/TPA-treated mice. The characteristic regression of papillomas after that time points to the reversibility of many earlier papillomas, and their dependence on continued TPA administration. Evaluation of carcinomas in mice on the various dietary regimes showed there was no significant difference between any group, including those fed with beta-carotene continuously from weaning. The present results demonstrate that a sustained dietary intake of beta-carotene from 3 weeks of age partially suppressed the growth of papillomas, but did not affect the course of malignant progression in DMBA/TPA-treated HRA/Skh mice. It is evident that beta-carotene predominantly affects TPA-dependent papillomas, which possess reversible properties and have a low probability of progression to form carcinomas.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1990

Selective cloning of hybridoma cells for enhanced immunoglobulin production using flow cytometric cell sorting and automated laser nephelometry.

Techniques for selective cloning of murine hybridoma cells by flow cytometric cell sorting and use of automated laser nephelometry to determine the resultant clones' immunoglobulin secretion levels are described. Using a commercially available attachment to a fluorescence-activated cell sorter, individual hybridoma cells were successfully distributed into microtiter wells in an automated manner based on their forward angle light scatter properties and their reaction to fluorescein-conjugated anti-mouse-IgG. The techniques were used to estimate successfully the frequency of immunoglobulin-secreting cells in established cultures. In addition, heterogeneity of cell surface immunoglobulin expression was observed and utilized as a criterion for flow sorting of new hybridoma variants. In these studies, clones derived from high (anti-IgG) intensity sorting regions yielded cultures with enhanced immunoglobulin secretion levels, as determined by automated laser nephelometry. Furthermore, the surface immunoglobulin phenotype of the derived clones was conserved in subsequent progeny. Finally, it was established that inclusion of propidium iodide in the hybridoma cell sorting mixtures improved cloning efficiency by facilitating enhanced discrimination and elimination of nonviable cells. Our results indicate that flow cytometric-assisted single cell deposition provides positive attributes of several traditional hybridoma cloning techniques and, in addition, furnishes a tool for steering the cloning process toward selection of enhanced immunoglobulin producing cultures.

Animals↗

PubMed1990

SCE induction and cell-cycle delay by toxaphene.

Toxaphene is genotoxic in mammalian cell systems and also inhibits cell replication. It was therefore used to investigate possible masking of SCE induction due to cell-cycle delay. In this study, toxaphene-treated Chinese hamster lung (Don) cells exhibited a dose-dependent decrease in cell-cycle progression compared with untreated cells. At high, nontoxic toxaphene levels (15 micrograms/ml), cell cycling also slowed as the toxaphene treatment time was increased. Toxaphene induced significantly higher numbers of SCEs in treated cells, demonstrating a dose- and treatment time-relationship. Slopes of dose-response curves were 0.29, 0.43 and 0.77 SCE/micrograms toxaphene for 20.5 h, 24.5 h and 28.5 h incubation, respectively. There were no changes in SCE values in control cultures even when slower dividing cells were sampled e.g. at longer incubation times. Thus, higher SCE values in Chinese hamster cells were not associated per se with slower or more delayed cells. The results demonstrate that longer toxaphene treatment times were not necessary for obtaining sufficient harlequin-stained cells for SCE analysis, but that higher numbers of SCEs occurred in slower dividing cells, following prolonged incubation of cultures treated with toxaphene.

Animals↗

PubMed1990

Mutagenicity of basic fractions derived from lamb and beef cooked by common household methods.

Mutagen production was examined in lamb and beef in relation to certain common household cooking methods. Mutagenicity was assessed, after extraction of the basic fraction of cooked meat samples, using Salmonella typhimurium strain TA1538 with added rat-liver S-9 homogenate. Little or no mutagenicity was found in barbecued lamb chops, in microwave-cooked lamb chops, sirloin steak, leg of lamb, or rolled beef loaf, in roasted leg of lamb or rolled beef loaf, in stewed blade steak or in boiled chuck steak. However, the basic fraction from well-done, edible fried or grilled meat contained mutagenic activity equivalent to approximately 30,000 TA1538 revertants/100 g cooked meat. It was found tht the mutagenic activity of grilled lamb chops, sirloin and rump steaks was directly related to the average surface temperatures attained during cooking. Use of butter as a frying medium was particularly associated with higher mutagenicity in meat samples. Fried meats (rump and fillet steaks) generally yielded higher mutagenic activity than did grilled meats (rump steak, lamb chops) at comparable temperatures of the cooking medium. Using similar cooking procedures, lamb did not differ markedly from beef in mutagenic activity.

Animals↗

PubMed1990

Limb muscle regeneration in peripheral nerve autografts.

In a previous study we demonstrated regenerative growth of extraocular muscle within transplanted peripheral nerve autografts. The present study addresses the feasibility of inducing regeneration of limb muscle within autologous peripheral nerve implants in the gluteus medius of beagles. In six anesthetized animals, a 2-cm segment of the left infraorbital sensory nerve was removed from the nose and implanted between the cut ends of several muscle fascicles in the left gluteus medius. After 4 weeks, the nerve grafts were removed and examined by light and electron microscopy. Muscle fibers were seen surrounded by the epineurium of the implanted nerve along its entire length, growing in parallel with the long axis of the nerve. The regenerating fibers were closely associated with the basal lamina of degenerating myelinated and unmyelinated axons. This study suggests that limb muscle, like extraocular muscle, is capable of organized regenerative growth within peripheral nerve autografts.

Animals↗

PubMed1990

A quantitative assessment of extraocular muscle growth in peripheral nerve autografts.

In previous studies, we have documented new growth of extraocular muscle fibers within axon-depleted motor neurons of denervated muscle. This study was designed to quantitate the regenerative growth of extraocular muscle within autologous peripheral sensory nerve transplants and to determine whether acutely denervated extraocular muscle affects this growth. Fifteen anesthetized beagles were subjected to an intracranial lesion of the left third cranial nerve. Segments of the infraorbital sensory nerve were removed from the nose and implanted between the lateral rectus and inferior oblique muscles in both orbits. At 2, 4 and 8 weeks postoperatively, five dogs were killed and the nerve grafts were removed. Muscle fibers were counted at four levels along each nerve segment. Fiber number increased significantly at each successive postoperative interval in implanted nerve segments on both the denervated and nondenervated side. At 8 weeks, fiber number was significantly greater on the denervated side. These results indicate that autologous peripheral sensory nerve is capable of supporting regenerative growth of extraocular muscle and that denervation has a significant positive influence on muscle fiber growth.

Animals↗

PubMed1989

Initiating carcinogen, triethylenemelamine, induces micronuclei in skin target cells.

Keratinocytes from mouse skin were cultured for a short period in vitro following single or multiple treatments at low dose levels in vivo with the known chromosome-damaging agent triethylenemelamine (TEM). The chemical was applied to the skin of HRA/Skh hairless mice at concentrations corresponding to those reported to initiate cancer in initiation-promotion assays. A significant dose-related depression in keratinocyte cell recovery occurred over the dose range 0.3-1 mg TEM/mouse (single or multiple treatments). Under the same conditions, a dose-related induction of micronuclei was observed using the cytokinesis-block method with cytochalasin B. A similar frequency of micronuclei was detected in binucleate cells from mice treated with single or multiple applications of TEM. Mice held for 12-48 h post-treatment, before removal of skin for in vitro culture, yielded highest micronuclei frequencies. These results indicate that the same target cell population, skin keratinocytes, can be used to investigate both genotoxicity and carcinogenesis, and that micronucleus induction in these cells may be a sensitive signal of skin cancer initiation.

Animals↗

PubMed1989

Clinical photon correlation spectroscopy evaluation of human diabetic lenses.

Clinical research on cataract prevention requires an in vivo assessment of the lens of the eye that is non-invasive, quantitative and detects lens changes that precede lens opacification or cataract formation. The method of photon correlation spectroscopy or quasi-elastic light scattering spectroscopy provides such a non-invasive probe. The measurement, based on fluctuations in scattered light intensity caused by translational Brownian motion of the lens proteins, allows a determination of a protein diffusion coefficient and hence information on quaternary conformational changes of these protein scatterers. These protein changes have been observed in association with the presence of lens opacification. The occurrence of these changes prior to opacification, however, has still to be established. The analyses performed in this study were aimed at testing the hypothesis of an association between subclinical molecular changes in the lens as measured by quasi-elastic light scattering and the presence of selected risk factors for cataract. Measurements were made from 393 diabetics attending the Joslin Diabetes Center Eye Unit and 38 non-diabetic volunteers. Measurements at two different instrument sample times, 1.5 microseconds and 150 microseconds, allowed characterization of two different protein size distributions contributing to the quasi-elastically light scattered signal. Measurements performed at the 1.5 microseconds sample time demonstrated significantly decreased lens protein diffusivity in association with older age, higher grade of nuclear sclerosis and presence of diabetes. Statistically significant associations were also observed between lens protein diffusivity and diabetes related factors such as glycosylated hemoglobin level (diabetes control), duration of diabetes, age at onset of diabetes and type of diabetic therapy. The pattern of association exhibited between decreased protein diffusion coefficient and risk factor status is consistent with the patterns of increased risk previously demonstrated in cataract formation. Measurements performed at the 150 microseconds sample time demonstrated significantly decreased lens protein diffusivity in association with increasing age, female sex and glycosylated hemoglobin level. These associations differed significantly from those observed at the 1.5 microsecond sample time, thereby suggesting that these two sample times assess different species of lens proteins. The results of this analysis demonstrate the clinical utility of quasi-elastic light scattering as a rapid, non-invasive method to quantitate lens changes and assess methods of cataract prevention and treatment.

Adolescent↗

PubMed1989

New growth of extraocular muscle in peripheral nerve autografts. Ultrastructural relationships.

We assessed the ultrastructural relationships of extraocular muscle (eom) fibers grown in a nonmuscle, extracellular matrix. Free sections of autogenous, extraorbital, peripheral nerve were implanted between the cut edge of a healthy eom and a denervated eom in four dogs. Light microscopy at 4 and 8 weeks demonstrated muscle fiber growth throughout the length of the implanted segments. Electron microscopy showed muscle fibers surrounded by collagen, frequently beside degenerating myelinated nerve fibers, but never growing within Schwann tubes or completely surrounded by the basal lamina of one nerve or Schwann cell. The muscle fibers were, however, bordered by abundant fibroblast processes (always separated by collagen), which often partially encircled the fiber. All muscle fiber growth occurred in parallel with the nerve axis. These findings indicate that peripheral nerve may contain factors conducive to the growth and orderly alignment of eom fibers. The identification of these factors may be helpful in the development of a synthetic matrix for eom graft growth.

Animals↗