Respiratory Metaplasia Research Articles

Integrated age-related immunohistological changes occur in human olfactory epithelium and olfactory bulb.

Olfactory epithelium (OE) is capable of lifelong regeneration due to presence of basal progenitor cells that respond to injury or neuronal loss with increased activity. However, this capability diminishes with advancing age and a decrease in odor perception in older individuals is well established. To characterize changes associated with age in the peripheral olfactory system, an in-depth analysis of the OE and its neuronal projections onto the olfactory bulb (OB) as a function of age was performed. Human olfactory tissue autopsy samples from 36 subjects with an average age of 74.1 years were analyzed. Established cell type-specific antibodies were used to identify OE component cells in whole mucosal sheets and epithelial sections as well as glomeruli and periglomerular structures in OB sections. With age, a reduction in OE area occurs across the mucosa progressing in a posterior-dorsal direction. Deterioration of the olfactory system is accompanied with diminution of neuron-containing OE, mature olfactory sensory neurons (OSNs) and OB innervation. On an individual level, the neuronal density within the epithelium appears to predict synapse density within the OB. The innervation of the OB is uneven with higher density at the ventral half that decreases with age as opposed to stable innervation at the dorsal half. Respiratory metaplasia, submucosal cysts, and neuromata, were commonly identified in aged OE. The finding of respiratory metaplasia and aneuronal epithelium with reduction in global basal cells suggests a progression of stem cell quiescence as an underlying pathophysiology of age-related smell loss in humans. KEY POINTS: A gradual loss of olfactory sensory neurons with age in human olfactory epithelium is also reflected in a reduction in glomeruli within the olfactory bulb. This gradual loss of neurons and synaptic connections with age occurs in a specific, spatially inhomogeneous manner. Decreasing mitotically active olfactory epithelium basal cells may contribute to age-related neuronal decline and smell loss in humans.

Rapid fluorescent vital imaging of olfactory epithelium

SummaryOlfactory epithelium (OE) undergoes degeneration in disorders such as age-related and post-viral olfactory dysfunction. However, methods for real-time in vivo detection of OE and assessment of total extent within the nasal cavity are currently unavailable. We identified two fluorescence probes for rapidly detecting and evaluating the entire extent of mice OE with topical application. Taking advantage of the differential expression of the enzymes cytochrome p450 (CYP) and γ-glutamyltranspeptidase (GGT) in OE relative to respiratory epithelium, we utilized the conversion of coumarin (a substrate of various CYP subtypes) and gGlu-HRMG (a substrate of GGT) by these enzymes to form metabolites with fluorescent emissions in the duct cells and sustentacular cells of neuron-containing OE. In depleted and regenerated OE model, the emission of these probes remained absent in respiratory metaplasia but appeared in regenerated OE. These substrates could be used to monitor OE degeneration and follow regenerative response to therapeutic interventions.

Squamous and Respiratory Metaplasia After Olfactory Mucosal Resection.

Resection of the olfactory mucosa (OM) is sometimes unavoidable during surgery; however, it is not known whether the OM can completely recover thereafter. The aim of this study was to uncover whether the OM fully recovers after mucosal resection and describe the process of OM regeneration. 8-week-old male Sprague–Dawley rats (n = 18) were subjected to OM resection at the nasal septum; six rats were euthanized for histological examination 0, 30, and 90 days after surgery. Immunohistochemistry was performed to identify olfactory receptor neuron (ORN) lineage cells [mature and immature ORNs and ORN progenitors, and olfactory ensheathing cells (OECs)], as well as dividing and apoptotic cells. Squamous and respiratory metaplasia and inflammatory cell infiltration were also assessed. On day 30 after resection, the mucosa had regenerated, and mainly contained thin nerve bundles, basal cells, and immature ORNs, with a few mature ORNs and OECs. On day 90, the repaired nasal mucosa had degenerated into stratified squamous or ciliated pseudostratified columnar epithelia, with reducing ORNs. The lamina propria contained numerous macrophages. Partial regeneration was observed within 1 month after OM resection, whereas subsequent degeneration into squamous and respiratory epithelia occurred within 3 months. Given the poor persistence of ORNs and OECs, OM resection is likely to result in olfactory impairment. Overall, surgeons should be cautious not to injure the OM during surgery.

Dystrophic calcification and respiratory metaplasia in the epithelial lining of odontogenic cysts: a study of 362 odontogenic cysts in a Brazilian population and literature review

PurposeMain study: undertake a histological study of odontogenic cysts (OC) to determine the prevalence of dystrophic calcification and metaplasia to respiratory epithelium on a Brazilian population. Literature review: to review the literature for studies that investigated the prevalence of respiratory metaplasia and dystrophic calcification on OC. MethodsMain study: a retrospective histopathological evaluation was made of the archives from a pathology laboratory. A total of 362 cases diagnosed as OC were identified; they were analyzed by two expert observers to determine the presence of dystrophic calcification and respiratory metaplasia. The association with sex, age and anatomic location was performed through statistical analysis. Literature review: a critical literature review was undertaken. Two main electronic databases (PubMed and LILACS) were searched. Retrospective studies of histological evaluation that determined the prevalence of epithelial metaplasia and dystrophic calcification on OC, with at least 10 cases, were included; their findings were summarized and discussed. ResultsMain study: the histological evaluation of OC revealed the presence of respiratory epithelium in 25 cases (6.9%) and dystrophic calcification in 24 cases (6.6%). Positive association was found to dystrophic calcification on residual cyst and age; respiratory metaplasia on OC and sex; respiratory metaplasia on residual cyst and gnatic bone; respiratory metaplasia in OC and gnatic bone; dystrophic calcification in OC and anatomic site of mandible. Literature review: eleven studies were included in the literature review, and respiratory metaplasia ranged from 0.0% to 19.2% while dystrophic calcification ranged from 2.5% to 40.5%. Conclusionsthe histological evaluation of this study found 6.9% of prevalence of respiratory metaplasia and 6.6% of dystrophic calcification, which is in accordance with the literature reviewed. Therefore, these phenomena must be taken into account in routine diagnosis services.

The Neuroregenerative Capacity of Olfactory Stem Cells Is Not Limitless: Implications for Aging.

The olfactory epithelium (OE) of vertebrates is a highly regenerative neuroepithelium that is maintained under normal conditions by a population of stem and progenitor cells, globose basal cells (GBCs), which also contribute to epithelial reconstitution after injury. However, aging of the OE often leads to neurogenic exhaustion, the disappearance of both GBCs and olfactory sensory neurons (OSNs). Aneuronal tissue may remain as olfactory, with an uninterrupted sheet of apically arrayed microvillar-capped sustentacular cell, or may undergo respiratory metaplasia. We have generated a transgenic mouse model for neurogenic exhaustion using olfactory marker protein-driven Tet-off regulation of the A subunit of Diphtheria toxin such that the death of mature OSNs is accelerated. At as early as 2 months of age, the epithelium of transgenic mice, regardless of sex, recapitulates what is seen in the aged OE of humans and rodents. Areas of the epithelium completely lack neurons and GBCs; whereas the horizontal basal cells, a reserve stem cell population, show no evidence of activation. Surprisingly, other areas that were olfactory undergo respiratory metaplasia. The impact of accelerated neuronal death and reduced innervation on the olfactory bulb (OB) was also examined. Constant neuronal turnover leaves glomeruli shrunken and affects the dopaminergic interneurons in the periglomerular layer. Moreover, the acceleration of OSN death can be reversed in those areas where some GBCs persist. However, the projection onto the OB recovers incompletely and the reinnervated glomeruli are markedly altered. Therefore, the capacity for OE regeneration is tempered when GBCs disappear.SIGNIFICANCE STATEMENT A large percentage of humans lose or suffer a significant decline in olfactory function as they age. Therefore, quality of life suffers and safety and nutritional status are put at risk. With age, the OE apparently becomes incapable of fully maintaining the neuronal population of the epithelium despite its well known capacity for recovering from most forms of injury when younger. Efforts to identify the mechanism by which olfactory neurogenesis becomes exhausted with age require a powerful model for accelerating age-related tissue pathology. The current OMP-tTA;TetO-DTA transgenic mouse model, in which olfactory neurons die when they reach maturity and accelerated death can be aborted to assess the capacity for structural recovery, satisfies that need.

Evaluation of the effect of cigarette smoking on the olfactory neuroepithelium of New Zealand white rabbit, using scanning electron microscope.

To detect ultra-structural changes of Rabbit's olfactory neuro-epithelium using scanning electron microscope after exposure to cigarette smoking. Sixty six rabbits (Pathogen free New Zealand white rabbits weighing 1-1.5kg included in the study were randomly assigned into one of three groups: control group did not expose to cigarette smoking, study group 1 was exposed to cigarette smoking for 3 months and study group 2 was exposed to cigarette smoking 3 months and then stopped for 2 months. Olfactory neuro-epithelium from all rabbits were dissected and examined under Philips XL-30 scanning electron microscope. Changes that were found in the rabbits of study group 1 in comparison to control group were loss of microvilli of sustentacular cells (p = 0.016) and decreases in distribution of specialized cilia of olfactory receptor cells (p = 0.046). Also respiratory metaplasia was detected. These changes were reversible in study group 2. Cigarette smoking causes ultra-structural changes in olfactory neuro-epithelium which may explain why smell was affected in cigarette smokers. Most of these changes were reversible after 45 days of cessation of cigarette smoking to the rabbits.

Normal Anatomy, Histology, and Spontaneous Pathology of the Nasal Cavity of the Cynomolgus Monkey (Macaca fascicularis).

The evaluation of inhalation studies in monkeys is often hampered by the scarcity of published information on the relevant nasal anatomy and pathology. We examined nasal cavities of 114 control cynomolgus monkeys from 11 inhalation studies evaluated 2008 to 2013, in order to characterize and document the anatomic features and spontaneous pathology. Compared to other laboratory animals, the cynomolgus monkey has a relatively simple nose with 2 unbranched, dorsoventrally stacked turbinates, large maxillary sinuses, and a nasal septum that continues into the nasopharynx. The vomeronasal organ is absent, but nasopalatine ducts are present. Microscopically, the nasal epithelium is thicker than that in rodents, and the respiratory (RE) and transitional epithelium (TE) rest on a thick basal lamina. Generally, squamous epithelia and TE line the vestibule, RE, the main chamber and nasopharynx, olfactory epithelium, a small caudodorsal region, while TE is observed intermittently along the passages. Relatively high incidences of spontaneous pathology findings, some resembling induced lesions, were observed and included inflammation, luminal exudate, scabs, squamous and respiratory metaplasia or hyperplasia, mucous cell hyperplasia/metaplasia, and olfactory degeneration. Regions of epithelial transition were the most affected. This information is considered helpful in the histopathology evaluation and interpretation of inhalation studies in monkeys.

Mechanisms of permanent loss of olfactory receptor neurons induced by the herbicide 2,6-dichlorobenzonitrile: Effects on stem cells and noninvolvement of acute induction of the inflammatory cytokine IL-6

We explored the mechanisms underlying the differential effects of two olfactory toxicants, the herbicide 2,6-dichlorobenzonitrile (DCBN) and the anti-thyroid drug methimazole (MMZ), on olfactory receptor neuron (ORN) regeneration in mouse olfactory epithelium (OE). DCBN, but not MMZ, induced inflammation-like pathological changes in OE, and DCBN increased interleukin IL-6 levels in nasal-wash fluid to much greater magnitude and duration than did MMZ. At 24h after DCBN injection, the population of horizontal basal cells (HBCs; reserve, normally quiescent OE stem cells) lining the DMM became severely depleted as some of them detached from the basal lamina, and sloughed into the nasal cavity along with the globose basal cells (GBCs; heterogeneous population of stem and progenitor cells), neurons, and sustentacular cells of the neuroepithelium. In contrast, the layer of HBCs remained intact in MMZ-treated mice, as only the mature elements of the neuroepithelium were shed. Despite the respiratory metaplasia accompanying the greater severity of the DCBN lesion, residual HBCs that survived intoxication were activated by the injury and contributed to the metaplastic respiratory epithelium, as shown by tracing their descendants in a K5CreErT2::fl(stop)TdTomato strain of mice in which recombination causes HBCs to express TdTomato in advance of the lesion. But, contrary to published observations with MMZ, the HBCs failed to form ORNs. A role for IL-6 in suppressing ORN regeneration in DCBN-treated mice was rejected by the failure of the anti-inflammatory drug dexamethasone to prevent the subsequent respiratory metaplasia in the DMM, suggesting that other factors lead to HBC neuro-incompetence.

Subchronic toxicity and carcinogenicity studies of 1,2-dichloropropane inhalation to mice

The subchronic toxicity and carcinogenicity of 1,2-dichloropropane (DCP) in male and female B6D2F1 mice exposed to DCP by inhalation for 13 weeks or for 2 years was investigated. The DCP concentrations used were 50, 100, 200, 300 or 400 ppm (v/v) in the 13-week study, and 32, 80 or 200 ppm (v/v) in the 2-year study. Thirteen weeks inhalation exposure of mice to DCP caused death in the mice exposed to 300 ppm and above, and was found to induce hemolytic anemia and lesions of the liver, forestomach and heart. Two years exposure to DCP significantly increased the combined incidence of bronchiolo-alveolar adenomas and carcinomas in females and marginally increased the incidence of Harderian gland adenomas in males. As non-neoplastic lesion, atrophy and respiratory metaplasia in the olfactory epithelium, and respiratory metaplasia in the submucosal gland of the nasal cavity were increased. Thus, two years inhalation exposure to DCP is carcinogenic in female mice and there is a marginal evidence of carcinogenicity in males.

Assessment of Lung Cytological Atypia among Shisha Smokers

Objectives. The aim of this study was to assess frequency of lung epithelial atypia among Shisha users.Methods. Sputum samples were collected from 200 subjects (100 Shisha users (cases) and 100 nontobacco users (controls)). Cytological smears were prepared and demonstrated using Papanicolaou and silver nucleolar organizer region (AgNORs) methods.Results. Cytological atypia was identified among 2/100 (2%) of the cases, and no cytological atypia was found among controls. Respiratory squamous metaplasia was significantly higher among cases 42/100 (42%), compared to controls 7/100 (7%) (P<0.001). Shisha users were found more susceptible for bacterial infections 34 (34%) compared to controls 3/100 (3%), (P<0.0001). The mean AgNOR dots count was higher among cases (2.3±.23) than among controls (1±.2),P<0.001.Conclusion. In view of these findings, the consumption of Shisha is a risk factor for cellular proliferation activity in respiratory epithelium. The mean AgNORs count is a useful indicator for prediction of the risk of exposure to certain carcinogenic elements that may induce lung cancer.

Immunohistochemical characterization of human olfactory tissue

The pathophysiology underlying human olfactory disorders is poorly understood because biopsying the olfactory epithelium (OE) can be unrepresentative and extensive immunohistochemical analysis is lacking. Autopsy tissue enriches our grasp of normal and abnormal olfactory immunohistology and guides the sampling of the OE by biopsy. Furthermore, a comparison of the molecular phenotype of olfactory epithelial cells between rodents and humans will improve our ability to correlate human histopathology with olfactory dysfunction. An immunohistochemical analysis of human olfactory tissue using a comprehensive battery of proven antibodies. Human olfactory mucosa obtained from 21 autopsy specimens was analyzed with immunohistochemistry. The position and extent of olfactory mucosa was assayed by staining whole mounts (WMs) with neuronal markers. Sections of the OE were analyzed with an extensive group of antibodies directed against cytoskeletal proteins and transcription factors, as were surgical specimens from an esthesioneuroblastoma. Neuron-rich epithelium is always found inferior to the cribriform plate, even at advanced age, despite the interruptions in the neuroepithelial sheet caused by patchy respiratory metaplasia. The pattern of immunostaining with our antibody panel identifies two distinct types of basal cell progenitors in human OE similar to rodents. The panel also clarifies the complex composition of esthesioneuroblastoma. The extent of human olfactory mucosa at autopsy can easily be delineated as a function of age and neurologic disease. The similarities in human versus rodent OE will enable us to translate knowledge from experimental animals to humans and will extend our understanding of human olfactory pathophysiology.

Olfactory mucosa in nasal polyposis: Implications for FESS outcome

This study investigates olfactory epithelium biopsies from patients with nasal polyposis, in correlation with olfactory test results and ratings of olfactory dysfunction pre- and postoperatively. Twenty-seven patients with nasal polyposis were included. Olfactory function was tested with the "Sniffin Sticks" test. Biopsies from the olfactory region performed at the end of endoscopic surgery and studied with immunohistochemistry. Patients used a visual analogue scale to report their olfactory dysfunction when re-examined one year postoperatively. Subjects with little or no inflammation in olfactory and respiratory biopsies had short-er duration of disease and better olfactory function. Pathological changes of olfactory mucosa included replacement by respiratory metaplasia, degenerated epithelium, rupture of epithelial surface and infiltration by inflammatory cells. Postoperative olfactory test results showed improvement of olfaction in 74% of patients. Although this improvement seemed to be better in subjects with little or no inflammation, this was not significant. Preoperative and postoperative olfactory test results were positively correlated. The disease process includes loss of structural organization and inflammatory infiltration of the olfactory epithelium. The inflammation severity is related to the olfactory test results; however, it cannot be the only predictive factor postoperatively.

Two-year inhalation study of carcinogenicity and chronic toxicity of 1,4-dioxane in male rats

Carcinogenicity and chronic toxicity of 1,4-dioxane were examined by inhalation exposure of 50 male F344 rats to 1,4-dioxane vapor at 0 (clean air), 50, 250, or 1250 ppm (v/v) for 6 h/day, 5 days/wk, and 104 wk. Survival rates of 250 and 1250 ppm-exposed groups were decreased near the end of the 2-yr exposure period, due probably to the occurrence of malignant tumors. A statistically significant but marginal decrement of terminal body weight (<10%) was found in the 1250 ppm-exposed group, suggesting slight systemic toxicity. Significant changes in plasma levels of AST, ALT, ALP, and γ-GTP and relative weight of the liver occurred in the 1250 ppm-exposed group. Dose-dependent and statistically significant increases in incidences of nasal squamous cell carcinomas, hepatocellular adenomas, and peritoneal mesotheliomas were found primarily in the 1250 ppm-exposed group. The incidences of renal cell carcinomas, fibroadenomas in the mammary gland, and adenomas in the Zymbal gland were also increased dose-dependently. Preneoplastic lesions occurred in the nasal cavity and liver of the 1,4-dioxane-exposed groups. As nonneoplastic lesions, the significantly increased incidences of nuclear enlargement, atrophy, and respiratory metaplasia in the nasal cavity were noted at 50 ppm and above. A LOAEL (lowest observed adverse effect level) was determined at 50 ppm for the nasal endpoint of general chronic toxicity. This study provides clear evidence of carcinogenicity for 1,4-dioxane in male rats. A cytotoxic-proliferative and in vivo genotoxic mode of action is suggested to operate in 1,4-dioxane-induced carcinogenesis.

Abnormalities of Axon Growth in Human Olfactory Mucosa

Random biopsies of the human adult olfactory mucosa often demonstrate degenerative changes in the olfactory epithelium (OE) in both dysosmic and normosmic patients and, consequently, have limited diagnostic usefulness. However, detailed analysis of the subepithelial tissue with specific attention to the fascicles of the olfactory nerve and abnormalities of axonal growth may improve the correlation of histopathology with sensory function. Retrospective review of human OE biopsies. Mucosal biopsies from the olfactory area obtained from 27 subjects were examined by light and electron microscopy, with particular attention to the olfactory nerve fascicles; results were correlated with clinical status. Immunohistochemical analysis was used to characterize the extent of axonal depletion, relative maturity of the parent population, and aberrant axonal growth. As expected, there are areas of respiratory metaplasia and neuronal depletion in normosmic as well as dysosmic patients. The degree of axon degeneration within the fascicles correlates better with individual olfactory status. Immature neurons predominate, and re-entrant neuromas develop in patients with olfactory loss caused by disconnection from the olfactory bulb. Individuals with olfactory loss caused by epithelial damage as with chronic rhinosinusitis display evidence of nerve fascicle degeneration and intraepithelial neuromas. The status of olfactory axons provides useful information on the overall condition of the olfactory periphery and improves the diagnostic usefulness of mucosal biopsies. In addition to an assessment of the epithelium per se, the fascicles of the olfactory nerve need to be characterized for a complete analysis of the olfactory mucosa.

Carcinogenicity and Chronic Toxicity in Mice and Rats Exposed by Inhalation to para-Dichlorobenzene for Two Years

Carcinogenicity and chronic toxicity of para-dichlorobenzene (p-DCB) were examined by exposing 50 BDF1 mice and 50 F344 rats of both sexes by inhalation to p-DCB vapor at a target concentration of 0 (control), 20, 75 or 300 ppm for 6 hr/day, 5 days/week and 2 years. Incidences of hepatocellular carcinomas, hepatoblastomas and hepatic histiocytic sarcomas in the 300 ppm-exposed male mice, and hepatocellular adenomas and carcinomas and hepatoblastomas in the 300 ppm-exposed female mice were increased. An increase in the incidences of most of those liver tumors was dose-related. No increase in tumor incidence was found in any p-DCB-exposed rat of either sex. Centrilobular hypertrophy of hepatocytes and papillary mineralization and pelvic urothelial hyperplasia of the kidney were noted in the 300 ppm-exposed male rats. Treatment- and age-related increases in incidences of the eosinophilic globules of the respiratory and olfactory epithelia in female rats and incidences of the respiratory metaplasia of the nasal gland epithelium in mice and rats and the olfactory epithelium in mice were noted. The nasal lesion was the most sensitive endpoint of chronic inhalation toxicity. Induction of the mouse hepatocarcinogenicity and lack of the rat nephrocarcinogenicity found in the present study were compared with the mouse liver tumors and the rat renal tumors reported by the NTP gavage study, and discussed in light of the estimated p-DCB uptake into the body through the inhalation and the oral administration.

Globose basal cells are required for reconstitution of olfactory epithelium after methyl bromide lesion

Despite a remarkable regenerative capacity, recovery of the mammalian olfactory epithelium can fail in severely injured areas, which subsequently reconstitute as aneuronal respiratory epithelium (metaplasia). We contrasted the cellular response of areas of the rat epithelium that recover as olfactory after methyl bromide lesion with those undergoing respiratory metaplasia in order to identify stem cells that restore lesioned epithelium as olfactory. Ventral olfactory epithelium is at particular risk for metaplasia after lesion and patches of it are rendered acellular by methyl bromide exposure. In contrast, globose basal cells (GBCs, marked by staining with GBC-2) are preserved in surrounding ventral areas and uniformly throughout dorsal epithelium, which consistently and completely recovers as olfactory after lesion. Over the next few days, neurons reappear, but only in those areas in which GBCs are preserved and multiply. In contrast, parts of the epithelium in which GBCs are destroyed are repopulated in part by Bowman's gland cells, which pile up above the basal lamina. Electron microscopy confirms the reciprocity between gland cells and globose basal cells. By 14 days after lesion, the areas that are undergoing metaplasia are repopulated by typical respiratory epithelial cells. As horizontal basal cells are eliminated from all parts of the ventral epithelium, the data suggest that GBC-2(+) cells are ultimately responsible for regenerating olfactory neuroepithelium. In contrast, GLA-13(+) cells may give rise to respiratory metaplastic epithelium where GBCs are eliminated. Thus, we support the idea that a subpopulation of GBCs is the neural stem cell of the olfactory epithelium.

Progression of alachlor-induced olfactory mucosal tumours.

Alachlor is an herbicide used primarily in the production of corn (maize), peanuts, and soybeans and is associated with cancer of the nasal cavity, thyroid, and stomach in rats. Previous work from our laboratory demonstrated that the nasal cavity tumours originate from the olfactory mucosa, and that neoplasms were present following 6 months of exposure (126 mg/kg/day in the diet). The studies presented herein were conducted to determine more precisely the earliest time point at which alachlor-induced tumours were present, and to describe the histological changes that occur en route to tumour formation. We determined that dramatic histological changes, including respiratory metaplasia of the olfactory mucosa, were present following 3 months of exposure, and the earliest alachlor-induced olfactory mucosal tumours were detected following 5 months of treatment. Because alachlor is positive in short-term mutagenicity assays with olfactory mucosal activation, and because of the relatively short time-to-tumour formation observed with alachlor, we also conducted a 'stop' study in which rats were treated with alachlor for 1 month and then held without further treatment for an additional 5 months. This study demonstrated that abbreviated alachlor exposure did not result in subsequent tumour formation within the 6-month observation period.

Surgical (implantation) cyst of the mandible with ciliated respiratory epithelial lining: A case report

Although respiratory metaplasia is occasionally observed in the squamous epithelial lining of mandibular odontogenic cysts, mandibular cystic lesions that feature linings composed exclusively of respiratory epithelium are extremely rare. This phenomenon may be attributed to entrapment of respiratory epithelium during surgical procedures. Two such cases were reported in which the cystic lesions occurred in the region of the chin after augmentation genioplasty after the use of nasal bone and cartilage.1,2 We present the case of a patient with a history of maxillary and mandibular osteotomies in whom a large cystic lesion of the left mandible developed. The cyst was lined exclusively with ciliated respiratory epithelium.

Differential effects of olfactory toxicants on olfactory regeneration.

The aim was to study the long-term response in the olfactory mucosa of NMRI mice after exposure to the olfactory toxicants dichlobenil (a herbicide) or methimazole (an antithyroid drug). Three and six months after exposure to dichlobenil (2x or 1 x 25 mg/kg i.p.), the dorsomedial part of the olfactory region showed a respiratory metaplasia with abundant invaginations and a fibrotic lamina propria. In contrast, 3 months after exposure to a toxic dose of methimazole (2 x 50 mg/kg i.p.), the olfactory neuroepithelium and lamina propria had been restored. To study the regenerative events, we used an antibody derived against growth-associated protein 43 (GAP-43), which stains immature neurons. To study epithelial differentiation and horizontal basal cells (HBCs) we used an antibody derived against some cytokeratins. Two weeks after methimazole treatment, there was a marked increase of GAP-43-stained cells in the whole olfactory region, which correlated with the observed regeneration at that time. Two weeks after dichlobenil treatment, the damaged atypical epithelium in the olfactory region showed a distinct keratin staining of basal and columnar cells whereas GAP-43-stained cells were not found. Despite a transient increase of GAP-43-stained cells in the border zone between damaged and undamaged olfactory mucosa, an expansion of a normal neuroepithelium into the damaged olfactory region was not detected in the dichlobenil-treated mice. An intact lamina propria is suggested as a prerequisite for repopulation of the neuroepithelium after toxicant-induced injury.

Chronic toxicity/oncogenicity study of styrene in CD-1 mice by inhalation exposure for 104 weeks.

Groups of 70 male and 70 female Charles River CD-1 mice were exposed whole body to styrene vapor at 0, 20, 40, 80 or 160 ppm 6 h per day 5 days per week for 98 weeks (females) or 104 weeks (males). The mice were observed daily; body weights, food and water consumption were measured periodically, a battery of hematological and clinical pathology examinations were conducted at weeks 13, 26, 52, 78 and 98 (females)/104 (males). Ten mice of each gender per group were pre-selected for necropsy after 52 and 78 weeks of exposure and the survivors of the remaining 50 of each gender per group were necropsied after 98 or 104 weeks. An extensive set of organs from the control and high-exposure mice were examined histopathologically, whereas target organs, gross lesions and all masses were examined in all other groups. Styrene had no effect on survival in males. Two high-dose females died (acute liver toxicity) during the first 2 weeks; the remaining exposed females had a slightly higher survival than control mice. Levels of styrene and styrene oxide (SO) in the blood at the end of a 6 h exposure during week 74 were proportional to exposure concentration, except that at 20 ppm the SO level was below the limit of detection. There were no changes of toxicological significance in hematology, clinical chemistry, urinalysis or organ weights. Mice exposed to 80 or 160 ppm gained slightly less weight than the controls. Styrene-related non-neoplastic histopathological changes were found only in the nasal passages and lungs. In the nasal passages of males and females at all exposure concentrations, the changes included respiratory metaplasia of the olfactory epithelium with changes in the underlying Bowman's gland; the severity increased with styrene concentration and duration of exposure. Loss of olfactory nerve fibers was seen in mice exposed to 40, 80 or 160 ppm. In the lungs, there was decreased eosinophilia of Clara cells in the terminal bronchioles and bronchiolar epithelial hyperplasia extending into alveolar ducts. Increased tumor incidence occurred only in the lung. The incidence of bronchioloalveolar adenomas was significantly increased in males exposed to 40, 80 or 160 ppm and in females exposed to 20, 40 and 160 ppm. The increase was seen only after 24 months. In females exposed to 160 ppm, the incidence of bronchiolo-alveolar carcinomas after 24 months was significantly greater than in the controls. No difference in lung tumors between control and styrene-exposed mice was seen in the intensity or degree of immunostaining, the location of tumors relative to bronchioles or histological type (papillary, solid or mixed). It appears that styrene induces an increase in the number of lung tumors seen spontaneously in CD-1 mice.