MIB-1 labeling indices in benign, aggressive, and malignant meningiomas: a study of 90 tumors

Predicting tumor behavior in meningiomas based on histology alone has been problematic. This study retrospectively compares histology and MIB-1 (cell proliferation marker) labeling indices (LI) in benign, aggressive, and malignant meningiomas. Six histological features, including mitoses, necrosis, loss of pattern, hypervascularity/hemosiderin deposition, prominent nucleoli, and nuclear pleomorphism, were compared in 90 meningiomas (Fisher's exact test). Tumors with two or more of the above features were designated as aggressive meningiomas. Malignant meningiomas were characterized by brain invasion or metastasis. The MIB-1 LIs (% positive tumor cell nuclei) were compared between the three groups (Kruskal-Wallis test, Wilcoxon two-sample test). Of the benign meningiomas (n=37; mean age, 54 years), 41% had one of the six histological features, with nuclear pleomorphism (n=10) being the most frequent. The aggressive tumors (n=29; mean age, 61 years) were characterized by nuclear pleomorphism (n=28), mitoses (n=20), necrosis (n=16), loss of pattern (n=16), prominent nucleoli (n=6), and hypervascularity/hemosiderin deposition (n=5). Malignant tumors (n=24; mean age, 59 years) were characterized by nuclear pleomorphism (n=22), mitoses (n=21), loss of pattern (n=21), necrosis (n=21), nucleoli (n=17), and hypervascularity/hemosiderin deposition (n=3). Significant differences were found between the aggressive and malignant groups with regard to loss of pattern, necrosis, and nucleoli (P=.0043, .011, and .00029, respectively). Mean MIB-1 LIs for the benign, aggressive, and malignant groups were 1.0% (range, 0 to 5.5%),5.5% (range, 0.1 to 32.5%), and 12.0% (range, 0.3 to 32.5%), respectively. Differences in the mean MIB-1 LI between groups were statistically significant, with P values of <.0001 (benign v aggressive) and .0012 (aggressive v malignant). Mean MIB-1 LIs for recurrent versus nonrecurrent tumors were 7.1% (range, 0 to 32.5%) versus 3.8% (range, 0 to 20.9%) (P=.32). The mean MIB-1 LI for patients who were alive with or without tumor was 6.2% (range, 0 to 32.5%) versus a mean MIB-1 LI of 14.2% (range, 2.8% to 32.5%) for patients who died of or with tumor (P=.0013). In conclusion, (1) There is a statistically significant difference in the increasing MIB-1 LI means between benign, aggressive, and malignant meningiomas and between patients who were alive versus those who died; (2) there is some overlap in MIB-1 LI ranges between groups, which warrants caution in interpreting an individual MIB-1 LI in a given tumor.     

Gastric mucosal biopsy via a nasogastric tube: a nonendoscopic method for diagnosing fundic and antral mucosal gastritis and Helicobacter pylori infection in man

Synthesis of poly(gamma-glutamate) metabolites of natural folates and antifolates is a critical process. Folypolyglutamates are essential for cell proliferation. Polyglutamates of glutamate (Glu)-containing antifolates are often critical for their cytotoxic action and are relevant to antifolate resistance. However, the role of polyglutamate synthesis in selectivity is less clear. We have undertaken a research program to further define the significance of polyglutamate metabolism and to devise ways to exploit this metabolism to achieve greater therapeutic selectivity in cancer chemotherapy. This article briefly reviews several approaches tested thus far. Inhibition of folypolyglutamate synthesis should lead to cell death. Current ornithine (Orn)-containing folate-based inhibitors of the enzyme responsible for their synthesis, folypolyglutamate synthetase (FPGS), are poorly transported, apparently because of interference by the protonated delta-amine. Replacement of Orn with 4, 4-difluoroOrn, the delta-amine of which has a much lower pKa and is thus less protonated at physiological pH, was explored. Since it is unclear how polyglutamylation contributes to selectivity, we explored generic means either to eliminate or to enhance polyglutamylation. The data indicate that substitution for Glu in an antifolate by some Glu analogs in which the gamma-COOH is either altered or replaced (e.g., gamma-tetrazole-Glu) leads to loss of both FPGS substrate activity and binding; antifolate target specificity is unchanged, while uptake is actually enhanced. Substitution of 3,3-difluoroGlu for Glu leads to enhanced polyglutamylation (although probably only to the diglutamate), retention of target specificity, and at least equal uptake. Comparative studies of the same antifolate containing different replacements for Glu, such as gamma-tetrazole-Glu (no polyglutamylation) or 3,3-difluoroGlu (enhanced polyglutamylation), will be useful in exploring the role and significance of polyglutamylation.     

The development of the adrenal gland zona glomerulosa in the rat. A morphological, immunohistochemical and biochemical study

We have studied the development of the adrenal gland in the rat comprising the ages ranging from 0 to 90 days after birth. The weight of the animals and that of the adrenal glands demonstrated a linear growth with time until 75 days, both in males and females. The area of the zona glomerulosa (ZG) increased in size from birth until approximately 40 days of age. After that, growth had a much smaller slope (females, r=0.84, P < 0.001; males, r=0.81, P < 0.001). Aldosterone secretion had a marked increase until 20 days of age and thereafter demonstrated a tendency for a decrease (females, r=-0.19, P < 0.02: males r=-0.26, P < 0.001). Plasma renin activity followed a trend parallel to that of aldosterone. The steroid precursor 18-OH-deoxycorticosterone (18-OH-DOC) demonstrated a different course as it increased progressively with age especially in the females (females, r=0.57, P < 0.001; males, r=0.40, P <0.001). The expression of the enzyme 3-beta-hydroxysteroid dehydrogenase (3-beta-HSD) was also studied by immunohistochemistry and it was shown to be very low at birth and starting to increase by 10 days of age. After 30/40 days of age the amount of this enzyme existing in the ZG was comparable with that of the outer zona fasciculata (ZF). We conclude that the development of the ZG in the rat has particularities that make it different from that of the rest of the cortex.     

Growth of colorectal polyps: recovery and evaluation of unresected polyps of less than 10 mm, 1 year after detection

BACKGROUND AND METHODS: Colonoscopic 1-year control of polyps of less than 10 mm left in situ was carried out in 103 (89%) of 116 originally examined patients. RESULTS: Analysis showed an 85% recovery: 91% and 81% for polyps of 5-9 mm and < 5 mm, respectively. The recovery was significantly related to size and localization, whereas the growth rate was inversely correlated to the originally measured diameter. A linear relationship was demonstrated between anus-to-polyp distances 1 year apart, with a normalized agreement index of 0.70. In only 1 of 189 polyps, an increase of diameter to > 10 mm was demonstrated. The 79 new polyps in 52 (50%) of the patients were significantly smaller, more often right-sided, and related to multiplicity of polyps at the initial examination but not to growth of recovered polyps or cleansing status. CONCLUSION: An acceptable recovery and growth rate of polyps < 10 mm seems to justify the continuation of the study for the remaining 2 years.     

Proliferation of gemistocytic cells and glial fibrillary acidic protein (GFAP)-positive oligodendroglial cells in gliomas: a MIB-1/GFAP double labeling study

Affinity chromatography using different lytic transglycosylases as a specific ligand revealed an interaction of both murein hydrolases and murein synthases. This interaction is taken as evidence for the assemblage into a multienzyme complex that could function as a murein replicase precisely copying the given three-dimensional structure of the murein sacculus. The sacculus of the mother cell would function as a template, which is identically replicated by copying the lengths of the existing glycan strands and the pattern of crosslinkages. A hypothetical enzyme complex specifically involved in cell division and a complex specifically involved in cell elongation are presented. It is postulated that PBPs 1a and/or 1b are present in both complexes, whereas the presence of PBP2 or PBP3 defines the specificity of the murein-synthesizing machinery as being involved in either cell elongation or septation. Moreover, the proposed "holoenzyme" suprastructure could explain why the specific inhibition of PBPs 1a/1b results in bacteriolysis and why inhibition of PBP2 and PBP3 causes the well-known morphological alterations, spherical growth, and filamentation, respectively.     

Neuropathology in cats experimentally infected with feline immunodeficiency virus: a morphological, immunocytochemical and morphometric study

Head flexion and extension movements near the natural head position (NHP) were analysed for the location of the mean instantaneous centre of rotation (ICR). Forty-six healthy young adults (30 women and 16 men) with sound dentitions, free from cranio-cervical disorders, performed habitual movements that were automatically detected and measured by an infrared three-dimensional motion analyser. ICR and curvature radius were calculated for each movement and subject. In both extension and flexion, ICR position changed during the motion. The movement was symmetrical in all subjects. No gender or flexion/extension differences were found for both ICR position and relevant curvature radius. On average, ICR relative to NHP soft-tissue nasion was located at about 150% of the soft-tissue nasion-right tragus distance, with an angle of about 220 degrees relative to the true horizontal. Results suggest that head flexion or extension is always performed with a combination of rotation (atlanto-occipital joint) and translation (cervical spine) even in the first degrees of motion. Moreover, NHP at rest seems to be some degree more flexed and anterior than head position during movements. These relative positions and their muscular determinants could also influence mandibular posture at rest and during functional movements.     

Quantification of mucin in human gallbladder bile: a fast, specific, and reproducible method

It is generally accepted that gallbladder mucin (GBM) plays an important role in the pathogenesis of cholesterol gallstone (ChG) disease. However, it remains unclear whether ChG patients have higher GBM concentrations than controls. Discrepant findings regarding biliary mucin concentrations may be due to methodological problems with the assays commonly used. The methods currently used to quantitate mucin in bile have not been systematically evaluated. To establish a reliable method for mucin quantification in bile, we evaluated three mucin assays: the classic Pearson-PAS (periodic acid Schiff) assay, a direct fluorometric assay, and a new PAS or fluorometric assay with the following modifications of the Pearson assay: preincubation of bile samples with TBS containing KSCN and sodium taurocholate and micellation of biliary lipids during gel chromatographic fractionation using 25 mM sodium taurocholate in the elution buffer. SDS-PAGE and monoclonal anti-human-GBM (GBM59) were used to identify mucin. Highly specific and reproducible mucin isolation was achieved with the modified method. We found considerable loss of mucin during the different purification steps in the Pearson method. The direct fluorometric assay showed unspecific fluorometric signal with low molecular constituents of bile. Our experiments showed that human-GBM can be accurately measured after a simple modified chromatographic fractionation followed by a PAS or fluorometric assay.     

Liposarcoma: a population-based epidemiologic and prognostic study of features of 43 patients, including tumor DNA content

Different conceptions exist regarding the epidemiology and prognosis of liposarcoma, and several classification systems are in use. We analyzed a population-based, 25-year series of 43 patients with liposarcoma of the extremity or trunk wall. Follow-up was complete. The annual incidence was 0.12/10(5). The thigh was the most common location. One of 6 tumors was subcutaneous. Deep-seated tumors were larger than s.c. tumors. Among the 42 surgically treated patients, grade II (4-grade scale) was the most common malignancy grade. Four tumors were well-differentiated, 24 were predominantly myxoid, 4 predominantly round-cell, and 10 were predominantly of pleomorphic type. The 5-year metastasis-free survival rate was 69%. By univariate analysis increasing malignancy grade, tumor necrosis, vascular invasion, mitotic count, subtype other than well-differentiated, and high cellularity were prognostic for metastatic disease. However, in the multivariate analysis only tumor necrosis was an independent risk factor. Tumor necrosis should be considered when prognosis of liposarcoma of the extremity and trunk wall is evaluated.     

Prediction of occult neck metastases in laryngeal carcinoma: role of proliferating cell nuclear antigen, MIB-1, and E-cadherin immunohistochemical determination

The aim of this study is to investigate the predictive value of proliferative activity assessment and E-cadherin expression by means of immunohistochemistry in identifying patients with laryngeal squamous cell carcinoma at a high risk for occult node metastasis. Thirty consecutive patients treated for laryngeal carcinoma with false clinically negative nodes (occult metastases, pN+) between the years 1980 and 1990 were selected for this study. A group of 30 cases with negative cervical lymph nodes (pN-) having a similar anatomic site and tumor size distribution was used as control. In each case, several histological parameters, including grade, pattern of invasion, number of mitosis (x10 high-power field), tumor inflammatory infiltrate, and tumor sclerosis, were assessed. Proliferative activity was determined using immunohistochemical staining for proliferating cell nuclear antigen (PCNA) and MIB-1. Other putative prognostic factors investigated at the immunohistochemical level were the cell adhesion molecule E-cadherin and two oncoproteins, p53 and c-erbB-2. In pN+ cases, the expression of PCNA and MIB-1 was significantly higher than in the pN- group. Moreover, a significant loss of E-cadherin expression was observed in carcinomas with occult metastases. No differences in p53 and c-erbB-2 oncoproteins were found between pN+ and pN- cases. Among the other pathological parameters examined, only histological grade was significantly associated with the presence of occult metastases, but on multivariate analysis, this relationship was lost. We conclude that PCNA, MIB-1, and E-cadherin are independent predictors of occult nodal disease in laryngeal squamous cell carcinoma, and their immunohistochemical determination could be useful in identifying patients with clinically negative lymph nodes who are at considerable risk for occult metastases and who may benefit from elective neck dissection.     

Salivary gland malignant myoepithelioma: a clinicopathologic and immunohistochemical study of ten cases

BACKGROUND: Malignant myoepithelioma (MME) of the salivary gland, also known as myoepithelial carcinoma, is rare and its biologic behavior has not been clarified fully. METHODS: Ten cases of MME were analyzed for their clinicopathologic features and immunohistochemical characteristics, focusing on prognostic factors and tumor differentiation. In addition, six cases of benign myoepithelioma (BME) also were examined for comparison. RESULTS: The ten patients with MME (3 men and 7 women) ranged in age from 48-81 years (mean, 61.9 years). Seven cases of MME arose in the parotid salivary gland, two in the submandibular salivary gland, and one in minor salivary glands of the soft palate. In the current series, the incidence of MME was 0.45% among 1945 cases of major salivary gland tumors. Seven cases of MME developed from a benign preexisting tumor (six in pleomorphic adenoma and one in BME). Four of nine patients with MME died of the disease and two patients developed a recurrence. It was shown that MMEs were comprised of one cell type or a combination of two cell populations; these included, in order of incidence, epithelioid, spindle, and plasmacytoid cells. Patients with MME with marked cellular pleomorphism and perineural invasion had a poor prognosis. Immunohistochemically, putative myoepithelial markers such as muscle actins, cytokeratin 14, vimentin, and calponin, and S-100 protein were expressed highly in MME. High and low molecular weight cytokeratins and epithelial membrane antigen also frequently were positive in MME. p53 expression was observed in five MME cases, four of which either recurred or were fatal. Cellular proliferative activity assessed by mitotic count and the Ki-67 labeling index was significantly higher in MME cases than in BME cases. In limited cases, such cellular proliferative activity was shown to have prognostic value. Ultrastructurally, the tumor cells displayed certain myoepithelial characteristics. CONCLUSIONS: MME is a rare salivary gland tumor showing clinicopathologic diversity and presenting with various stages of myoepithelial differentiation. Histologic aggressiveness, marked cellular pleomorphism, p53 expression, and high cell proliferative activity were found to be correlated with a poor clinical outcome.     

Reactive astroglia-neuron relationships in the human cerebellar cortex: a quantitative, morphological and immunocytochemical study in Creutzfeldt-Jakob disease

In order to investigate the role of neuron-glia interactions in the response of astroglial to a non-invasive cerebellar cortex injury, we have used two cases of the ataxic form of Creutzfeldt-Jakob disease (CJD) with distinct neuronal loss and diffuse astrogliosis. The quantitative study showed no changes in cell density of either Purkinje or Bergmann glial cells in CJ-1, whereas in the more affected CJ-2 a loss of Purkinje cells and an increase of Bergmann glial cells was found. The granular layer in both CJD cases showed a similar loss of granule cells (about 60%) in parallel with the significant increase in GFAP+ reactive astrocytes. GFAP immunostaining revealed greater reactivity of Bergmann glia in CJ-2 than in CJ-1, as indicated by the thicker glial processes and the higher optical density. Granular layer reactive astrocytes were regularly spaced. In both CJD cases there was strict preservation of the spatial arrangement of all astroglial subtypes--Fa?anas cells, Bergmann glia and granular layer astrocytes. Reactive Fa?anas and Bergmann glial cells and microglia/macrophages expressed vimentin, while only a few vimentin+ reactive astrocytes were detected in the granular layer. Karyometric analysis showed that the increase in nuclear volume in reactive astroglia was directly related with the level of glial hypertrophy. The number of nucleoli per nuclear section was constant in astroglial cells of human controls and CJD, suggesting an absence of polyploidy in reactive astroglia. Ultrastructural analysis revealed junctional complexes formed by the association of macula adherens and gap junctions. In the molecular layer numerous vacant dendritic spines were ensheathed by lamellar processes of reactive Bergmann glia. Our results suggest that quantitative (neuron/astroglia ratio) and qualitative changes in the interaction of neurons with their region-specific astroglial partners play a central role in the astroglial response pattern to the pathogenic agent of CJD.     

The correlation between neuron counts and optical density of NADPH-diaphorase histochemistry in the rat striatum: a quantitative study

NADPH diaphorase (NADPH-d) histochemistry is a useful technique for examining select neuronal populations in both experimental studies and human neuropathology and also provides a simple method to localize nitric oxide synthase in the central nervous system. However, no established method exists for detecting quantitative changes of NADPH-d histochemistry under different experimental conditions. To develop a quantitative procedure, we systematically examined the properties of NADPH-d histochemistry and then investigated the correlation between the number of NADPH-d positive cells and the optical density of NADPH-d histochemistry in the rat striatum. NADPH-d activity was sensitive to specific experimental conditions, such as incubation time, fixation, and high temperature. In the striatum NADPH-d activity of neuropil was more sensitive to these conditions than were the somata. The different staining patterns of NADPH-d between the neuropil of the striatum and white matter, such as the optic tract suggest neuropil staining in the striatum is not just unspecific background staining. Increasing incubation time only increased the optical density of NADPH-d staining, in contrast, the number of NADPH-d positive cells counted was relatively consistent across incubation times. Therefore, little correlation existed between the optical density and cell number. These results indicate that when using NADPH-d histochemistry, the number of NADPH-d positive neurons is independent of the optical density of the staining, and these two parameters should be considered and treated separately when conducting quantitative analysis related to an experimental treatment.     

Gliofibromas (including malignant forms), and gliosarcomas: a comparative study and review of the literature

The presence of connective tissue elements in gliomas necessitates in every case a thorough analysis of the character and derivation of such elements to allow the formulation of an appropriate diagnosis. Four cases are presented in this paper. In cases 1 and 2 (anaplastic astrocytomas in two children, 9 and 4 years old, respectively) all the neoplastic elements were astrocytes and their ability to produce or indirectly promote the production of reticulin and collagen fibers accounted for the presence of such elements in close association with the tumor cells. The term "gliofibroma" has been coined for such tumors, but "desmoplastic astrocytoma", (low grade or anaplastic) or in highly malignant cases "desmoplastic glioblastoma", as the case may be, also seem to be appropriate terms for such neoplasms. In contrast, cases 3 and 4 represented composite tumors in adults (66 and 58 years old, respectively) and the neoplasms of these patients consisted of glioblastoma and sarcoma, the latter component demonstrably being of vascular origin. This is the type of tumor usually referred to as gliosarcoma or "Feigin tumor". Although some apparent similarities between the two groups may exist at times, the histogenesis of the latter group's sarcomatous or sarcoma-like portions is different from that of the first group and, therefore, warrants separate diagnostic terms and placement in brain tumor classification.     

CSF-1 stimulation induces the formation of a multiprotein complex including CSF-1 receptor, c-Cbl, PI 3-kinase, Crk-II and Grb2

Recently c-Cbl has been reported to be phosphorylated upon CSF-1 stimulation. The product of the c-cbl proto-oncogene (c-Cbl) is a 120 kDa protein harboring several docking sites for Src homology 2 (SH2) domain containing proteins and proline-rich regions that have been shown to allow its constitutive association with the SH3 domains of Grb2. We demonstrate here that CSF-1 exposure of stable transfectant CHO cells expressing the CSF-1 receptor induced the sustained tyrosine phosphorylation of c-Cbl and its subsequent association with Crk-II and the p85 kDa subunit of the PI 3-kinase, while it constitutively associates with Grb2. We demonstrate by in vitro experiments that these associations require the SH2 domain of Crk-II and both the C- and N-terminal SH2 domains of the p85 subunit of the PI 3-kinase. cCbl is the major PI 3-kinase-containing protein in c-Fms expressing CHO cells upon CSF-1 stimulation. Thus c-Cbl behaves as a core protein, allowing the formation of a quaternary complex including, Crk-II, PI 3-kinase and Grb2. We provide evidence that this multiprotein complex can interact with the tyrosine phosphorylated CSF-1 receptor through the unoccupied SH2 domain of Grb2.     

Gastric metaplasia of regenerating duodenal mucosa and deformity of duodenal bulb: a correlative study

Women's opinion on the maternal serum screening programme offered at one maternity unit in East Northumberland (1991-1992) was evaluated. The responses from 1,774/2,633 women showed a general acceptance of the test but 722/1,774 (40%) wanted more information and a third, more explanation. Recommendations, which included a 'gold standard' protocol, a video to complement revised patient information literature and a coordinator to facilitate interdisciplinary communication and training with support for midwives, were introduced. The audit cycle was completed by a repeat questionnaire survey of 2,489 women from the postnatal ward (1992-1994) with a 67.3% response. An overall improvement in levels of satisfaction with reduction in, but not eradication of, the need for more information and explanation had occurred. These findings have relevance to the current controversy surrounding the counselling implications of maternal serum screening and have led to the formation of a network of professionals to develop the programme in our region.     

Proton pump inhibitor-associated gastric polyps: a retrospective analysis of their frequency, and endoscopic, histologic, and ultrastructural characteristics

Activation of Kupffer cells by lipopolysaccharide (LPS) plays a pivotal role in the onset of pathophysiological events that occur during endotoxemia and intracellular calcium ([Ca2+]i) is involved in LPS-stimulated cytokine production. Recently, it was shown that Kupffer cells contain a glycine-gated chloride channel. Because taurine, a ubiquitous sulfur-containing beta-amino acid, acts similarly to glycine in neurons by causing hyperpolarization, it was hypothesized that taurine would act via a similar mechanism, blunting the LPS-induced increase in [Ca2+]i in Kupffer cells. To test this hypothesis, Kupffer cells were isolated from female Sprague-Dawley rats and cultured for 24 h. LPS-induced changes in [Ca2+]i were monitored fluorometrically in single cells, whereas levels of tumor necrosis factor alpha (TNF-alpha) released by Kupffer cells after exposure to LPS were measured by enzyme-linked immunosorbent assay. Taurine significantly blunted the LPS-induced increase in [Ca2+]i in a dose-dependent manner (IC50, 0.1 mM). This effect was reversed by strychnine (1 microM) and was prevented when chloride was removed from the extracellular media. Moreover, taurine increased 36Cl- uptake by Kupffer cells in a dose-dependent manner (EC50, 0.2 mM). Furthermore, strychnine (1 microM) reversed the effect of taurine on 36Cl- uptake. These results indicate that taurine activates a glycine-gated chloride channel in Kupffer cells causing chloride influx. In addition, LPS-induced TNF-alpha production was reduced by more than 40% by taurine, an effect that was also reversed by strychnine. In conclusion, taurine blocks the increase in [Ca2+]i due to LPS and significantly reduces TNF-alpha production by mechanisms involving chloride influx into the Kupffer cell.     

Mesocosm study of Mytilus edulis larvae and postlarvae, including the settlement phase, exposed to a gradient of tributyltin

In a mesocosm study, the effects of a gradient of tributylin (TBT) (nominal TBT concentrations of 0.3, 2.3, 18.5, 146, and 1150 ng Sn liter-1) on Mytilus edulis larvae and postlarvae, including the settlement phase, were investigated over 15 days. Effects of TBT on mortality, growth measured as increase in shell length, shell dimensions, and settlement were evaluated. In general, mortality was high in all mesocosms including the control; during the first 24 h of the experiment, mortality was 63% at the highest TBT concentration (26% in the control). An LC50 (24 h) of 254 ng Sn liter-1 was estimated. The mortality rate of larvae/postlarvae increased 40% at 18.5 ng Sn liter-1 (0.41 day-1) compared with the control (0.30 day-1). For postlarvae, the growth rate decreased with increasing TBT concentration. The mean shell length at 2.3 ng Sn liter-1 was significantly reduced in comparison to the control on Day 15. Then EC10 (15 days) for shell growth was estimated to be 5.4 ng Sn liter-1. This is the lowest effect concentration ever reported in the literature. For postlarvae, shell dimensions in terms of shell length-shell width relations were affected by TBT at 1150 ng Sn liter-1, because the reduced growth led to the failure of adult mussels to secret a dissochonch shell. During the first days of exposure, the settlement monitored on polyethylene settling strips was stimulated by TBT, after which the settlement decreased due to the high mortality. Only a small portion of the population survived to the end of the test period. By comparison of the biotic conditions (in terms of larval abundance and particle concentration reflecting larval food) in the control mesocosm with those in the cove where the experiment was conducted, it was concluded that the mesocosm had successfully simulated the field conditions.