Temporary and Permanent Hearing Loss

Long-term exposure to the dust of fiber glass used for insulation causes no demonstrable gross or microscopic pulmonary damage. This conclusion is based on the results of a postmortem study of the lungs of 20 fiber glass workers, who had had exposures to the dust of fibrous glass which ranged from slight to severe and for periods which ranged from 16 to 32 years, and a comparison of this study’s results with those obtained in a similar study of the lungs of 26 urban dwellers of both sexes, who presumably had not been exposed occupationally to fibrous glass dust, which showed that the average total amount of dust, the average total number of fibers per gram of dry lung, and the average dimensions of the fibers found in the lungs were not significantly different.     

Compromised first permanent molars: an orthodontic perspective

The first permanent molar (FPM) is commonly subject to significant compromise which may arise due to caries or endodontic complication, or from developmental anomalies such as hypoplasia. Compromised teeth with questionable prognosis may result in short and long-term clinical dilemmas. This review article highlights the factors that require careful consideration when a compromised FPM is detected and the importance of timely FPM extraction. Several clinical cases are described in detail to discuss possible treatment options from the orthodontic perspective.     

Perinatal changes in bombesin-stimulated muscle contraction in rabbit stomach and colon

Bombesin and its mammalian homologue, gastrin-releasing peptide, stimulate smooth muscle contraction and may promote the growth of gastrointestinal tissues. Isometric contraction of strips from circular muscle of the gastric fundus and longitudinal muscle of the distal colon were used to compare changes in the response to bombesin in newborn and weanling rabbits. There was an age-related qualitative change in gastric muscle from biphasic contractions including phasic and tonic components in the newborn to phasic contractions alone in the weanling. The colon contractions were tonic at both ages. In both tissues there was an age-related fivefold increase in stress in response to maximally effective concentrations of bethanechol (P less than 0.05). In contrast, in the stomach age-related decreases in the response to maximally effective concentrations of bombesin were observed, from 2930 +/- 179 mN/cm2 (98% of the maximal response to bethanechol) in the newborn to 565 +/- 81 mN/cm2 (4% of the maximal response to bethanechol) in the weanling (P less than 0.005). In the colon, a twofold increase in response to bombesin was observed, from 446 +/- 59 mN/cm2 (82% of the response to bethanechol) in the newborn to 862 +/- 11 mN/cm2 (29% of the response to bethanechol) in the weanling (P less than 0.05). No age-related changes were observed in the potency of bombesin in either tissue. Neither atropine nor tetrodotoxin altered the contractions in either tissue, suggesting that bombesin interacted directly with myocytes. There was three times as much bombesinlike immunoreactivity in the stomach compared with the colon, but no age-related changes in either tissue. In summary, by the age of weanling the stomach lost the tonic component of contraction and 80% of the efficacy of bombesin-stimulated phasic contraction that had been present in the newborn. The loss of efficacy, absolute in the stomach and relative to bethanechol in the colon, suggest that bombesin may be most important in stimulating motility in the neonatal period.     

Deleterious effects of irradiation and bone marrow transplantation therapy in the genetically anemic an/an mouse

The efficacy and outcome of bone marrow transplantation therapy following lethal irradiation were examined in syngeneic mice that had a hereditary macrocytic anemia (an/an) or were genotypically normal (+/+). Successful RBC and WBC replacement, based on blood cell parameters and donor genetic markers, were observed in all combinations of transplant therapy. Nevertheless, the an/an mice died prematurely several months after treatment, whether they received +/+ or an/an marrow cells. In contrast, the +/+ recipients of either +/+ or an/an marrow cells survived for at least 1 year after transplantation. Premature death of the an/an mice was associated with lymphopenia, anemia, kidney lesions, and severe pathogen-free pneumonitis. On the basis of our results, we hypothesize that the premature deaths of an/an mice are caused by a kind of chronic irradiation damage to which an/an mice are especially susceptible.     

Expression of specific granule markers on the cell surface of neutrophil cytoplasts

The widespread assumption that cytoplasts generated from human polymorphonuclear leukocytes (PMNs) are vesicles consisting solely of cytoplasm surrounded by plasma membrane and devoid of granule activity remains to be tested. PMN cytoplasts were prepared by centrifugation of intact cells on a Ficoll step gradient in the presence of cytochalasin B. Two granule membrane markers, Mol, a fluorometrically detectable antigen, and cytochrome b, both of which have been shown to translocate to the plasma membrane during granule release, were compared for their activity in cytoplasts and intact PMNs. We found that the amount of Mol detected on the plasma membrane of intact PMNs, as compared with other membrane markers (such as antigens LFA-1 and beta 2m), increased 1.6- fold upon exposure of PMNs to Ficoll plus cytochalasin B prior to centrifugation. Another twofold increase in Mol expression occurred upon cytoplast preparation. Release of the granule enzymes, vitamin B12- binding protein, and lysozyme were also followed and correlated well (r = .78 and .92) with the amount of Mol antigen present on the cell surface. Cytochrome b was also found to be higher (1.4-fold) on plasma membranes isolated from cytoplasts than on plasma membranes isolated from intact control cells. These results indicate that some fusion of granule membranes and plasma membranes occurred during treatment of PMNs with Ficoll plus cytochalasin b and during cytoplast preparation.