Aruna D. Weberg

Ototoxicity of furosemide during development.

The rat is an altricial animal which serves as a useful model for human auditory development. The purpose of the present study was to investigate the effects of furosemide on cochlear function and the stria vascularis ultrastructure at various postnatal ages. Rat pups anesthetized with ketamine hydrochloride/xylazine hydrochloride received furosemide 35 mg/kg intravenously (IV), and the endocochlear potential and compound action potential of the eighth nerve were recorded. The stria vascularis was removed and prepared for transmission electron microscopy. Rat pups 9 to 28 days of age had a much greater reduction of endocochlear potential and elevation of the compound action potential threshold than animals older than 30 days. These physiologic changes were accompanied by edema of the stria on transmission electron microscopy only in animals at susceptible ages. These findings support the concept of a critical period of susceptibility to ototoxic drugs during development and could have important clinical implications in premature infants.

Development of the Stria vascularis in the Rat

The rat is an altricial animal and is thus a useful model for the study of auditory development. The endocochlear potential (EP) undergoes a rapid increase in magnitude from the end of the 1st week to the beginning of the 3rd postnatal week. The purpose of this study was to examine the ultrastructure of the developing stria vascularis in the rat pup in order to correlate functional changes with structural alterations. Rat pups of various ages underwent EP measurement under Rompun anesthesia. The cochleas were rapidly removed under deep pentobarbital anesthesia. The tissues were fixed in 2.5% glutaraldehyde and postfixed in 1.5% osmium tetroxide. Thin sections were viewed and photographed using a Hitachi H7000 transmission electron microscope. A series of distinct developmental changes were observed. Intermediate and basal cells became more distinct from one another, and basal cells became more elongated. Marginal cells underwent progressive development of basolateral infoldings. These cytologic changes may signal the development of ion transport mechanisms necessary for EP development.

Rat as a potential model for hearing loss in biotinidase deficiency.

Biotinidase deficiency is an inborn error of metabolism that is transmitted as an autosomal recessive disorder. Symptoms include hearing loss, ataxia, blindness, mental retardation, and seizures. The metabolic defect is an inability to recycle the vitamin biotin, which is an important cofactor in key enzymes. We therefore sought to develop an animal model for this disorder by inducing biotin deficiency. Rat pups were divided into control and experimental groups. Control rats were fed a normal diet whereas experimental animals were given a diet deficient in biotin. Animals from both groups underwent brain stem auditory evoked potential testing at various ages. Wave I thresholds at various ages were similar in both groups, Latencies for wave I, however, and interpeak latencies (I-IV) were prolonged in the biotin-deficient groups compared to controls. Scanning electron microscopy of the organ of Corti in biotin-deficient animals showed no significant hair cell loss, The biotin-deficient developing rat appears to acquire functional changes in the auditory brain stem. These effects may be caused by defective myelination, since biotin is important in fatty acid metabolism.

Ultrastructural changes in neonatal sciatic nerve tissue: effects of passive maternal smoking.

The dangers of cigarette smoking having already been recognized, this study attempts to delineate findings from a passive smoking study at the ultrastructural level. The project utilized a model of mice subjected to cigarette smoke and encompassed the electron microscopic examination of neonatal tissue for morphological abnormalities. Study of sciatic nerve tissue taken from the offspring of passively smoked females revealed definite toxic effects on the neonatal tissue. This investigation, which concentrated on morphological changes, indicates that passive maternal smoke inhalation may result in abnormal changes to the fine structure of fetal tissue although further investigation in this area is necessary to broaden our knowledge and understanding of the mechanisms involved.

The effect of maternal smoke exposure on the ultrastructure of fetal peripheral blood vessels in the mouse

Ultrastructural changes have been found in umbilical blood vessels, placental blood vessels, and peripheral blood vessels of human fetuses whose mothers smoked during pregnancy. This study was undertaken to determine if similar changes could be found in peripheral blood vessels of mice fetuses whose mothers were exposed to cigarette smoke during pregnancy. Breeding mice of the C57BL/KsJ strain were placed in a smoking box similar to that described by Younoszai and exposed to cigarette smoke intermittently. This produces carbon monoxide levels in the adult mice similar to that found in human adults smoking one pack of cigarettes per day. Similarly caged mice of the same strain were used as controls. The female mice were not removed from their cage from pre-conception time until after delivery. Upon delivery each pup was sacrificed via neck fracture and the entire pup was immersed in a solution of 2.5% glutaraldehyde in 0.1 M cacodylate buffer at pH 7.3. While still under solution, the rear leg muscles were dissected free, sliced, and immersed in the same preservative for four to five hours. They were then placed in fresh 2.5% glutaraldehyde mixture overnight. The tissues were post-fixed in osmium ferrocyanide and en-block stained with uranyl acetate in a graded series of alcohol. The tissues were infiltrated with and embedded in Spurr. Sections were taken via an ultramicrotome and post-stained with uranyl acetate and lead citrate. The sections were examined in a Philips 201 electron microscope at 60 KV. In the peripheral vessels of the fetuses from smoke-exposed mothers, endothelial blebbing (both surface-type and vacuole-type) was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of organic acids on stria vascularis ultrastructure and function in the chinchilla

SummaryThe purpose of this study was to compare the effects of several organic acids (probenecid, sodium salicylate and penicillin G) on the endocochlear potential (EP) and the ultrastructure of the stria vascularis of the chinchilla with the effects of furosemide on these parameters. chinchillas received 50 mg/kg i.v. doses of probenecid, sodium salicylate or penicillin G, or 25 mg/kg i.v. furosemide. The EP was monitored continuously before and for 60 min afterwards. The stria vascularis was removed at 10-min intervals from animals and from 10 to 60 min after the injection of these agents. Specimens were then processed for transmission electron microscopy. Only furosemide had an effect on the EP, causing a reversible reduction. The reduction of the EP was accompanied by the appearance of edema in the intercellular spaces of the stria vascularis. No significant edema was found after probenecid, sodium salicylate or penicillin G. This was consistent with the finding that none of these latter three agents affected the endocochlear potential.

Ultrastructural Changes in Preputial Neural Tissues: Effects of Maternal Smoking

The fetal prepuce was studied for neural changes due to maternal smoking during pregnancy. Prepuces from 10 newborns whose mothers smoked throughout pregnancy and from 4 newborns of nonsmoking mothers were examined by transmission electron microscope. Significant ultrastructural changes were seen in the neural tissues of the newborns of smoking mothers. The ultrastructural changes observed were: (1) local aggregation of mitochondria; (2) many myelin bodies, and (3) dilated Golgi apparatus and dilated endoplasmic reticulum of the Schwann cell. Similar changes have been reported in neuropathies due to various drugs, chemicals and deficiency states. These findings suggest adverse effects on fetal preputial neural tissue due to maternal smoking.

Ultrastructural changes in preputial neural tissues: effects of maternal drinking

Peripheral nerves in the prepuces of eight newborns were studied in this investigation. The mothers of four of these newborns were alcohol abusers but did not smoke or take coffee. The other four mothers did not drink alcohol or coffee, nor did they smoke. Using a transmission electron microscope, the peripheral nerves in preputial specimens were studied for pathological changes. In samples taken from the prepuces of those newborns with drinking mothers, the neuropathological changes seen were mainly in the unmyelinated axons. These demonstrated increased vesicular and tubular elements of agranular endoplasmic reticulum and dense bodies not found in the specimens taken from the non-drinking group. Other significant findings in the fetal preputial specimens from the alcohol group were aggregations of mitochondria and collagen entrapment.

Kinocilia in the developing stria vascularis of the rat pup

The mammalian stria vascularis undergoes certain developmental changes in the postnatal rat. The present study was designed to examine the ultrastructure of the stria vascularis in rat pups from immediately after birth to 20 days postpartum. The cochlea were removed with the animals under xylazine (Rompun) anesthesia and were prepared for transmission electron microscopy. Each of the three cell types in the stria were found to contain kinocilia up until 12–17 days of age. The presence of kinocilia in the intermediate and basal cells has not been previously described. Findings suggest that these organelles may serve a motile and/or sensory function to assist in the maturation of cell functions, particularly ion transport, during early stages of development.

Ultrastructural Changes in Neonatal Liver Tissue: Effects of Maternal Drinking

There is already sufficient evidence in the literature that alcohol abuse during pregnancy has a toxic effect upon the developing fetus; however, previous studies have not revealed any morphological changes in fetal or newborn liver specimens from animals exposed to alcohol in utero. As it is known that alcohol freely crosses the placental barrier, this investigation was an attempt to demonstrate that structural abnormalities can indeed be identified in neonatal mouse liver specimens from pups exposed to alcohol in utero. Chosen as a model for this study was the C57BL/KsJ mouse strain as this particular animal demonstrates an alcohol preference paralleling that of the human alcoholic. Findings appear to indicate the presence of abnormal changes on the morphological level in these study animals.