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J C de Groot

Publications and source records attributed to J C de Groot.

At least 37 records · Page 2Linked to original sources
PubMed1999

A follow-up study of blood pressure and cerebral white matter lesions.

White matter lesions are often observed on cerebral magnetic resonance imaging scans of elderly people and may play a role in the pathogenesis of dementia. Cross-sectional studies have shown an association between elevated blood pressure and white matter lesions. We prospectively studied the relation between blood pressure and white matter lesions in 1,077 subjects aged 60 to 90 years who were randomly sampled from two prospective population-based studies. One study had blood pressure measurements 20 years before, the other 5 years before. Overall response for the magnetic resonance imaging study was 63%, and declined from 73% among 60- to 70-year-olds to 48% for 80- to 90-year-olds. Diastolic and systolic blood pressure levels assessed 20 years before were significantly associated with subcortical and periventricular white matter lesions. The association between 20-year change in diastolic blood pressure and subcortical white matter lesions was J-shaped (relative risk, 2.2; 95% confidence interval, 1.0-5.2; and relative risk, 3.2; 95% confidence interval, 1.4-7.4, for decrease or increase of more than 10 mm Hg, respectively). The association between concurrent diastolic blood pressure level and white matter lesions was linear in subjects without, and J-shaped in subjects with, a history of myocardial infarction. Our results indicate that the J-shape relationship of diastolic blood pressure is not restricted to cardiovascular disease, but is also manifest in cerebrovascular disease.

Age Factors↗
PubMed1999

The ototoxic effects of ethyl benzene in rats.

Exposure to organic solvents has been shown to be ototoxic in animals and there is evidence that these solvents can induce hearing loss in humans. In this study, the effects of inhalation of the possibly ototoxic solvent ethyl benzene on the cochlear function and morphology were evaluated using three complementary techniques: (1) reflex modification audiometry (RMA), (2) electrocochleography and (3) histological examination of the cochleas. Rats were exposed to either ethyl benzene (800 ppm, 8 h/day for 5 days) or to control conditions. The RMA threshold increased significantly by about 25 dB, 1 and 4 weeks after the exposure, irrespective of the stimulus frequency tested (4-24 kHz). Electrocochleography was performed between 8 and 11 weeks after exposure to the organic solvent. The threshold for the compound action potential increased significantly by 10-30 dB at all frequencies tested (1-24 kHz). Histological examination of the cochlea showed outer hair cell (OHC) loss, especially in the upper basal and lower middle turns (corresponding to the mid-frequency region) to an extent of 65%. We conclude that exposure to 800 ppm ethyl benzene for 8 h/day during 5 days induces hearing loss in rats due to OHC loss.

Administration, Inhalation↗
PubMed1999

Cerebral vasomotor reactivity and cerebral white matter lesions in the elderly.

OBJECTIVE: The pathogenesis of white matter lesions is still uncertain, but an ischemic-hypoxic cause has been suggested. Cerebral vasomotor reactivity reflects the compensatory dilatory mechanism of the intracerebral arterioles to a vasodilatory stimulus and provides a more sensitive hemodynamic index than the level of resting flow. METHODS: The authors determined the association between vasomotor reactivity and white matter lesions in 73 consecutive individuals from the Rotterdam Scan Study who also participated in the Rotterdam Study, a large population-based prospective follow-up study of individuals > or =55 years old. Vasomotor reactivity was measured by means of CO2-enhanced transcranial Doppler, and in all individuals axial T1*-, T2*-, and proton density (PD)-weighted MRI scans (1.5 T) were obtained. White matter lesions were scored according to location, size, and number by two independent readers. RESULTS: Vasomotor reactivity was inversely associated with the deep subcortical and total periventricular white matter lesions (OR 0.5, 95% CI 0.3 to 1.1; and OR 0.7, 95% CI 0.4 to 1.1, respectively). A strong association was found between impaired vasomotor reactivity and periventricular white matter lesions adjacent to the lateral ventricular wall (OR 0.6, 95% CI 0.4 to 1.0; p = 0.001). No association was found with periventricular white matter lesions near the frontal and occipital horns. CONCLUSIONS: Our data confirm the association between vasomotor reactivity and white matter lesions and support the hypothesis that some white matter lesions may be associated with hemodynamic ischemic injury to the brain.

Aged↗
PubMed1998

Induction of endolymphatic hydrops in the guinea pig by perisaccular deposition of sepharose beads carrying and not carrying immune complexes.

We tried to induce endolymphatic hydrops in guinea pig cochleas by unilateral, perisaccular deposition of sepharose beads carrying immune complexes. Controls consisted of the deposition of sepharose beads without immune complexes and the contralateral, untreated ear. The effects of the treatment were studied by light microscopy and electrophysiological recordings of the gross cochlear potentials 1, 2, and 6 weeks after treatment. Each condition included six animals. Analysis of variance of the morphometric data concerning the ears treated with deposition of the beads showed a statistically significant difference (P = 0.04) between the degree of hydrops found for the beads with immune complexes and for those without. The difference between the treated ears and the contralateral untreated ears was significant (P = 0.01) for the beads with immune complexes and not significant (P = 0.8) for those without immune complexes while there was no significant effect of post-treatment time interval. Analysis of variance of the electrophysiological data, collected in response to tone bursts at the apex of the cochlea, showed no significant differences between the results for the beads with and without immune complexes. Therefore these results were pooled. One week after treatment the pooled results for the compound action potential showed a small decrease in amplitude, just significant at 2 kHz, but not at 4 and 8 kHz. This decrease disappeared completely after 6 weeks. The pooled results for the negative summating potential (SP) showed a significant increase in magnitude at all frequencies decreasing with post-treatment interval. The cochlear microphonics did not demonstrate any change in amplitude after treatment. The results indicate that deposition of sepharose beads with immune complexes induces endolymphatic hydrops. Also, deposition of the sepharose beads itself may have induced hydrops together with enhancement of the SP. SP enhancement may be related to the development of endolymphatic hydrops rather than to the presence of hydrops as such. This may be based on pressure build-up while hydrops develops.

Action Potentials↗
PubMed1998

Circle of Willis: morphologic variation on three-dimensional time-of-flight MR angiograms.

PURPOSE: To establish normal reference values for the presence of the anatomic variants of the circle of Willis and average diameters for its component vessels by using three-dimensional time-of-flight magnetic resonance (MR) angiography and to determine whether age- or sex-related differences exist in the circle's anatomy. MATERIALS AND METHODS: One hundred fifty volunteers were grouped according to age: those aged 20-25 years (n = 50) and those aged 60-88 years (n = 100). All subjects underwent three-dimensional time-of-flight MR angiography of the arterial circle at 1.5 T. The anatomic variants of the anterior and posterior parts of the circle were determined separately, the completeness of the entire circle was assessed, and the diameters of all component vessels were measured. RESULTS: On MR angiograms, 111 (74%) subjects demonstrated a complete anterior part of the circle, 78 (52%) demonstrated a complete posterior part of the circle, and 63 (42%) demonstrated an entirely complete circle of Willis (complete anterior and posterior parts of the circle combined). The presence of an entirely complete circle of Willis was slightly higher in younger persons and in women. Most vessel diameters were smaller in women, except for the diameter of the posterior communicating artery. Statistically significant differences were found in vessel diameters between the younger and the older age groups. CONCLUSION: The authors determined normal reference values for morphologic variants and diameter measurements of the circle of Willis specific to three dimensional time-of-flight MR angiography.

Adult↗
PubMed1997

Co-administration of the neurotrophic ACTH(4-9) analogue, ORG 2766, may reduce the cochleotoxic effects of cisplatin.

In this study the effect of the neurotrophic ACTH(4-9) analogue, ORG 2766, on cisplatin cochleotoxicity was investigated with both light- and transmission electron microscopy. Guinea pigs were treated with either cisplatin+ORG 2766 (n = 11) or cisplatin + physiological saline (n = 9). All animals treated with cisplatin + physiological saline showed complete loss of outer hair cells (OHC) and degeneration of the organ of Corti in the basal cochlear turns, while partial OHC loss was found in the middle and apical turns. The inner hair cells (IHC) and other cochlear tissues were not affected. Eight animals from the group treated with cisplatin + ORG 2766 demonstrated similar pathological changes, but to a lesser degree, especially in the middle turns. The three remaining animals demonstrated no cochlear alterations at all, light-microscopically, and only minor subcellular changes in the OHCs at the ultrastructural level. Electrophysiologically, these three animals showed normals compound action potential (CAP) amplitudes at stimulus frequencies from 0.5 to 16 kHz and normal cochlear microphonics (CM) in the frequency range from 0.5 to 8 kHz. The other animals treated with cisplatin + ORG 2766 showed a severe loss in their CAPs and CM, except for one showing intermediate loss. All animals from the group treated with cisplatin alone showed a severe loss in their CAPs and CM. Endolymphatic hydrops was present in all animals from the cisplatin- and the cisplatin + ORG 2766-treated groups. These data indicate that daily, concomitant administration of ORG 2766 may reduce OHC loss and subsequent degeneration of the organ of Corti in cisplatin-treated guinea pig cochleas.

Acoustic Stimulation↗
PubMed1993

Structure and composition of stereocilia cross-links in normal and hydropic cochleas of the guinea pig.

Structure and composition of stereocilia cross-links were investigated cytochemically in normal and hydropic cochleas of the guinea pig. The electron-dense markers colloidal thorium and cationized ferritin were used for visualization. Side links as well as tip links were visualized using both markers. Cationized ferritin allowed a better visualization of the delicate cross-link substructure than did colloidal thorium. Following digestion with neuraminidase, cross-link reactivity for colloidal thorium was virtually abolished. However, the basic structure of the cross-links could still be observed as a result of routine post-fixation and contrast staining. In both 3- and 6-month hydropic cochleas glycocalyx reactivity of the stereocilia appeared to be unaltered, provided that stereocilia were still present. However, loss of cross-links of the outer hair cells - resulting in disarrangement of the stereociliary bundles - was observed in hydropic cochleas. Our results suggest that cross-links are a separate morphological and cytochemical entity, which is different from the glycocalyx. Furthermore, loss of stereocilia cross-links, with concomitant disarrangement of the outer hair cell stereociliary bundle, appears to be one of the early pathological features of surgically induced endolymphatic hydrops, which might be responsible for permanent sensorineural hearing loss.

Animals↗
PubMed1992

Cell membrane polarity of the epithelial cells in the endolymphatic sac of the guinea pig.

The epithelial cells of the endolymphatic sac (ES) were studied in order to characterize their glycocalyx composition. Colloidal thorium and cationized ferritin were used as electron-dense markers to visualize the glycocalyx as well as the basement membrane. In addition, enzymatic digestions were performed to identify the reactive components of the glycocalyx responsible for colloidal thorium labeling. The results indicate that the glycocalyx of the ES epithelial lining is very rich in sialic acid. Furthermore, a marked polarity in glycocalyx reactivity is present between the apical and basolateral membranes, whereas difference in glycocalyx reactivity between the light and the dark cells are not obvious. We speculate that the specific composition and the apparent polarity of the ES epithelial cell glycocalyx are of importance to the equilibrium of electrolytes in the ES lumen.

Animals↗
PubMed1992

[Localization of Na/K ATP-ase in the inner ear].

The perilymphatic compartment of the inner ear resembles plasma ultrafiltrate, whereas the endolymphatic compartment is characterized by a high potassium and low sodium concentration. Perilymph is considered to be the precursor of endolymph. The chemical composition of endolymph and the generation of the transepithelial potential is regulated by Na-K-activated adenosine triphosphatase. The cytochemical localization of Na/K ATP-ase is demonstrated in the guinea pig inner ear. The mechanism for cation regulation in the endolymphatic compartment is discussed.

Animals↗
PubMed1990

Ultrastructural localization of gentamicin in the cochlea.

The ultrastructural distribution of gentamicin in the cochlea was investigated immunocytochemically. Specific labeling was restricted to the organ of Corti, in particular to the outer and inner hair cells, the Deiters' cells, Hensen's cells and the tympanic layer cells of the basilar membrane. Other cochlear tissues did not demonstrate any labeling. At the subcellular level, gentamicin was found in lysosomes, multivesicular bodies and small tubules and vesicles. A model is proposed in which it is hypothesized that gentamicin is internalized by endocytotic vesicles and is transferred to the lysosomal compartment as well as to the endoplasmic reticulum and Golgi complex.

Animals↗
PubMed1988

Early effects of gentamicin on inner ear glycocalyx cytochemistry.

The early effects of gentamicin treatment on the inner ear glycocalyx were investigated using two cationic probes, colloidal thorium and cationized ferritin. Gentamicin treatment resulted in a diminished thorium reactivity of both the endolymphatic and perilymphatic glycocalyx of the hair cells after 1 day and complete abolishment of reactivity after 5 days. Cationized ferritin reactivity of the perilymphatic and endolymphatic glycocalyx was not significantly influenced. The cytochemistry of the inner ear glycocalyx and the possible biochemical changes induced by gentamicin are discussed.

Animals↗
PubMed1987

Effects of endolymphatic sac obliteration on the cochlear duct glycocalyx.

The ultrastructural effects of surgical obliteration of the endolymphatic duct and sac on the cochlear duct glycocalyx were investigated using osmium tetroxide-potassium rutheniumcyanide postfixation. After 2 and 3 months a less prominent glycocalyx contrast staining was observed, together with disappearance of interconnecting material between the stereocilia of the inner and outer hair cells. Possible factors involved in this phenomenon are discussed.

Animals↗
PubMed1987

Human cochlear pathology in aminoglycoside ototoxicity--a review.

The pathological findings due to aminoglycoside ototoxicity in man, as reported in the literature, is reviewed. 21 cases (40 ears) have been studied after serial sectioning, 8 cases (12 ears) have been investigated by the microdissection and surface preparation technique. The combination of both methods provides maximal information. OHCs are primarily affected, followed by IHC loss. Degeneration starts at the basal coil and proceeds towards the apex. The stria vascularis becomes involved in all turns. It is not clear whether stria degeneration is primary or secondary. Supporting cells, nerve fibres and ganglion cells degenerate secondary to hair cell loss. In some cases ingrowth of myelinated nerve fibres in areas with complete destruction of the organ of Corti has been observed. Ototoxic lesions can be asymmetric. Attention is drawn to the audiometric Z-curve in moderate lesions.

Aminoglycosides↗
PubMed1984

Immunobiology of Langerhans' cells migrating into aural cholesteatomas.

Immunohistochemical and submicroscopic analyses of human cholesteatoma matrices reveal the presence of Langerhans' cells and T lymphocytes. Through cell-to-cell interaction, Langerhans' cells probably play a key role in skin-related disorders, including cholesteatomas. They originate from a mobile cell population of monocyte origin and migrate into and out of the body's lining. Their custodial function is always carried out in close relation with T lymphocytes. Various monoclonal antibodies directed against Langerhans' cell and T lymphocyte membrane receptors reveal the presence of these cell populations in cholesteatoma matrices but not in the tympanic membrane. Langerhans' cell and T cell traffic through cholesteatomas are discussed in relation to the pathogenesis, natural course, and recurrence rate of cholesteatomas. Through immunopathologic evaluation the clinical aggressiveness of a cholesteatoma will probably become predictable. Medical manipulation of Langerhans' cell and T cell functions- as an adjuvant to surgery - may have consequences for the future handling of cholesteatomas.

Adolescent↗
PubMedDate not supplied

Ultrastructure of the stria vascularis and Reissner's membrane in experimental hydrops.

A time-sequence study was made of the early ultrastructural changes of the stria vascularis and Reissner's membrane in the guinea pig after obliteration of the endolymphatic sac and duct. Pathological alterations of both the stria vascularis and Reissner's membrane were found to start in the apex of the cochlea. The morphological changes of the stria vascularis were characterized by an increase of vesicles in the marginal cells and by intercellular edema, followed by vacuolization and atrophy of marginal and intermediate cells. In Reissner's membrane extensive gaps in the mesothelial cell layer were observed together with intracellular pathology of the epithelial cells. The significance of these ultrastructural changes in the stria vascularis and Reissner's membrane with regard to the pathophysiology of the endolymphatic hydrops is discussed.

Animals↗