Biomedical subjects

J van der Want

Publications and source records attributed to J van der Want.

9 recordsLinked to original sources

PubMed2005

Perovskites in the comb roof base of hornets: their possible function.

On the ceiling of the Oriental hornet comb cell, there are mineral granules of polycrystalline material known to belong to the group of perovskites. In a comb cell intended to house a worker hornet, the roof base usually carries one or several such perovskite granules containing titanium (Ti), whereas in the roof base of a cell housing a developing queen, there are usually several granules containing a high percentage of silicon (Si), aluminum (Al), calcium (Ca), and iron (Fe), but very little if any Ti. In worker comb cells, Ti usually appears as ilmenite (FeTiO3). Besides documenting the above-mentioned facts, this report discusses possible reasons for the appearance of ilmenite crystals in worker cells only and not in queen cells.

Aluminum↗

PubMed2001

Preservation of endothelial integrity and function in experimental vascular anastomosis with non-penetrating clips.

BACKGROUND: Vascular repair with sutures is associated with disruption of the endothelial lining and subsequent thrombus formation on the intraluminal lesions. This experimental study was designed to determine whether the use of non-penetrating clips improved endothelial preservation. METHODS: In ten female pigs, 25-mm arteriotomies were made in both carotid arteries. The arteriotomies were repaired with jugular vein patches. On the left side, the repair was done with 1.4-mm titanium clips, and on the right side with two running 6/0 polypropylene sutures. Next, the aorta was divided and subsequently repaired with 2-mm clips in five of these pigs, and with two running 5/0 polypropylene sutures in the remaining five pigs. Endothelial function was studied at the anastomotic site in the carotid arteries by determination of endothelium-dependent and -independent relaxatory responses. Morphometric examination of the carotid arteries and inspection of the aortic endothelium were performed by means of scanning electron microscopy. RESULTS: Maximal endothelium-dependent relaxation to adenosine 5'-diphosphate was less in sutured than in clipped carotid arteries (P < 0.05), while there was no difference in maximal endothelium-independent relaxation to sodium nitrite. This result in clipped carotid arteries was not accompanied by less intimal hyperplasia. Screening of the aortic anastomotic line showed better preservation of endothelial architecture after clip anastomosis. Mean cross-clamp time for carotid patch repair was significantly less when using clips than with sutures. CONCLUSION: The use of non-penetrating clips for vascular anastomoses preserved endothelial function and structural integrity better than running sutures, although the degree of intimal hyperplasia was similar.

Anastomosis, Surgical↗

PubMed2000

Nonpenetrating vascular clips for small-caliber anastomosis.

In the search for better anastomosing techniques, an improved vascular stapler device (VCS clip applier system(R)) has been introduced. The system uses nonpenetrating clips to approximate everted vessel walls. The objective of this study was to determine the effects of nonpenetrating vascular clips on endothelial wound healing. Aortic end-to-end anastomoses were performed in male Wistar rats. A comparison was made between clipped (n = 12) and conventional hand-sewn (n = 6) anastomoses. Patency rates were verified at different time intervals (after 1, 4, and 8 weeks), after which the anastomotic sites were removed. Morphological evaluation was carried out using scanning electron microscopy. All rats survived the procedure. Closure with clips took less time than closure with conventional sutures, with decreasing aortic clamping times for the clipped procedures during the course of the experiments. Patency rates were 100% in both the "clipped" and "sutured" groups. Microscopic examination showed favorable endothelial healing at the clipped anastomotic sites, with less inflammatory reaction at 1 week, and a more complete endothelial regeneration at 4 and 8 weeks follow-up, as compared with the sutured anastomoses. The clip applier holds the promise of a useful device in anastomosing small-caliber vessels, since clip closure takes less time than suturing, while patency rates are identical, and morphological results are favorable. Training is mandatory to obtain technical skills and to achieve optimal results.

Anastomosis, Surgical↗

PubMed1994

Ultrastructural organization of GABA in the rabbit superior colliculus revealed by quantitative postembedding immunocytochemistry.

We have studied the organization of gamma-aminobutyric acid (GABA)ergic profiles in the superior colliculus of the rabbit to determine whether the synaptic types found in cat and monkey also exist in a mammalian species whose visual system has a different organization. Ultrastructure of GABAergic profiles was examined by use of a polyclonal antibody to GABA and quantitative postembedding immunocytochemistry. Three distinct types of vesicle-containing profiles were labeled by the GABA antibody in the rabbit superior colliculus. One type was a putative presynaptic dendrite (PSD profile) that received synaptic input from other profiles and contained pleomorphic synaptic vesicles scattered throughout the profile. These PSD profiles frequently received retinal input and formed dendrodendritic synapses. A second type of profile was a large caliber dendrite, often horizontal in orientation (H profile), that had one or more discrete clusters of pleomorphic synaptic vesicles at sites of synaptic contact with conventional dendrites. These H profiles received few synaptic contacts. A third profile type was a putative axon terminal (F profile) with smaller, more flattened synaptic vesicles that densely and uniformly filled the profile. Quantitative analysis of gold particle density revealed that F profiles had a significantly higher gold particle density (14.3/microns 2) than did PSD or H profiles (10.4 and 10.2/microns 2), suggesting that GABAergic profile types contain different concentrations of GABA. The vesicle density of these profile types also differed, but no obvious relationship between vesicle and particle distributions was observed. We conclude that the profiles labeled by GABA in rabbit superior colliculus are similar to those in cat and monkey and must represent a phylogenetically conserved organization common to many mammals, and that particle density analysis of postembedding immunocytochemistry can distinguish different GABAergic profile types.

Animals↗

PubMed1993

Segregation of direction selective neurons and synaptic organization of inhibitory intranuclear connections in the medial terminal nucleus of the rat: an electrophysiological and immunoelectron microscopical study.

A combined electrophysiological and morphological investigation of the medial terminal nucleus (MTN) in the rat was undertaken, aimed at a better understanding of the relationship between structure and function in this nucleus. The locations of upward and downward direction selective units in the MTN were documented with extracellular electrophysiological recording. By means of tracer experiments, with Phaseolus vulgaris-leucoagglutinin, biocytin, and cholera toxin subunit B-horseradish peroxidase, the internal connections of the MTN, its retinal afferents, and the projection neurons to the inferior olive were visualized. Terminals originating from the retina and from internal connections were characterized at the ultrastructural level. Their termination pattern on cells in the MTN, including identified inferior olive projection neurons, were determined. Additionally, postembedding GABA immunocytochemistry was performed to identify GABAergic elements. From reconstructions of the positions of electrophysiologically recorded units in the MTN, a local segregation between upward and downward direction selective units was revealed. Upward direction selective units were found in the dorsal part and ventromedially, whereas downward direction selective units were found ventral and laterally in the MTN. The MTN receives optic fibers via two separate routes which, based on their trajectory, presumably terminate in different parts of the MTN: the inferior fascicle of the accessory optic tract in the dorsal part, and the posterior fiber bundle of the superior fascicle in the ventral part of the MTN. A correspondence has been found between the segregation of direction selective units and the areas in the MTN where the retinal fibers from the two pathways distribute. It is, therefore, proposed that the inferior fasciculus conveys upward direction selectivity and the posterior fiber bundle downward direction selectivity, and that the two fiber bundles terminate segregated in the MTN. After anterograde tracing from the eye, retinal terminals were found evenly distributed throughout the MTN. They are characterized as GABA negative R-type terminals. After retrograde tracing from the inferior olive, identified MTN-inferior olive projection neurons were found in the dorsal MTN and medially in the ventral MTN. Their location in the MTN suggests that MTN-inferior olive projection neurons are upward direction selective. MTN-inferior olive projection neurons are large non-GABAergic cells, with a variable form. A majority of both F- and R-type terminals were found to make synaptic contacts on the dendrites of MTN cells. MTN-inferior olive projection neurons did not differ from other neurons in this respect.

Animals↗

PubMed1993

Glutamate immunoreactivity in terminals of the retinohypothalamic tract of the brown Norwegian rat.

The mammalian circadian pacemaker of the suprachiasmatic nucleus (SCN) is entrained to the environmental light-dark cycle via a retinal projection, the retinohypothalamic tract (RHT). Several studies suggest that an excitatory amino acid, possibly glutamate, is involved in photic entrainment. However, it has not yet been established whether glutamate is a transmitter of the RHT itself. We have now identified terminals of the RHT in the SCN of brown Norwegian rats by intravitreous injections of horse radish peroxidase conjugated to cholera toxin. To detect glutamate immunoreactivity (IR), post-embedding immunocytochemistry was performed with polyclonal antibodies which were visualized for electron microscopy with colloidal gold particles. Retinal terminals had a significantly 82% higher glutamate-IR than their post-synaptic dendrites and a significantly 76% higher glutamate-IR than non-retinal terminals. These observations provide ultrastructural evidence that glutamate is a transmitter of the RHT.

Animals↗

PubMed1992

Variation in form and axonal termination in the nucleus of the optic tract of the rat: the medial terminal nucleus input on neurons projecting to the inferior olive.

The nucleus of the optic tract (NOT) and the medial terminal nucleus (MTN) are two primary visual nuclei that take part in circuits sustaining the optokinetic reflex. The morphology of rat NOT cells projecting to the inferior olive (NOT-IO neurons) and their terminal input, specifically terminals originating from the MTN, have been studied in the rat at the light and electron microscopical level. This has been done by means of combined retrograde tracing from the inferior olive and anterograde tracing from the MTN to the NOT. The area containing MTN terminal fibers and the area occupied by NOT-IO neurons has been found to match. This matched distribution provides a more detailed description of the NOT, with possible functional implications. Identified NOT-IO neurons demonstrate considerable variability in their dendritic branching pattern and have been found to include all neuronal cell types described for the NOT. The dendritic branching pattern of NOT-IO cells could be related to the orientation and distribution of the NOT's major afferent fiber systems. NOT-IO neurons receive a variable MTN and retinal input onto their somata, comparable to other cells in the NOT. With exception of the superficial part of the NOT, NOT-IO neurons with the most MTN terminals were found dorsally in areas containing large numbers of MTN terminals. In conclusion, although NOT-IO neurons are uniform with respect to their receptive field properties, they vary considerably with respect to the shape of the cell body, dendritic branching pattern, and terminal input. This means that morphological characteristics of NOT-IO neurons have no predictive value with regard to their receptive field properties.

Animals↗

PubMed1991

Medial terminal nucleus terminals in the nucleus of the optic tract contain GABA: an electron microscopical study with immunocytochemical double labeling of GABA and PHA-L.

In this study the medial terminal nucleus (MTN) projection to the nucleus of the optic tract (NOT) was investigated in pigmented rats at the light and electron microscopical levels with a new combination of techniques. MTN terminals were anterogradely labeled with Phaseolus vulgaris-leucoagglutinin (PHA-L). Preembedding immunocytochemistry, followed by gold intensification, was used to visualize PHA-L. Postembedding immunocytochemistry with 15 nm immunogold particles was carried out to demonstrate the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Both PHA-L and GABA labeling can be easily discriminated at the electron microscopical level even when present in the same neuronal profiles. Light microscopically MTN-NOT fibers proved to have several branches with many varicosities. MTN terminals were found concentrated in terminal fields. Electron microscopically, it was shown that MTN boutons display characteristics resembling F-type terminals, i.e., terminals with dark mitochondria, pleomorphic vesicles, and symmetrical synapses. All NOT afferents originating from the MTN contained GABA and made multiple contacts exclusively with GABA negative NOT somata and dendrites. These results indicate the existence of a strong and direct inhibitory input onto GABA negative projection neurons in the NOT. This substantiates earlier physiological and morphological reports. It was further demonstrated that the location and organization of MTN terminals in the neuropil differ from that of the retinal input: MTN terminals are largely separated from retinal terminals. MTN terminal fields contain large amounts of GABA positive F terminals in contrast to retinal terminal areas. MTN terminals take part in irregularly shaped agglomerations of terminals, which contain many F terminals and dendritic processes and are surrounded by a glial sheet. Retinal terminals are found grouped together in small circular arrangements contacting a central dendrite.

Animals↗

PubMed1980

The presynaptic grid: a new approach.

A new electron microscopic facility is described which enables systematic visualization of E-PTA-stained presynaptic grids in full en face position. This EM-facility is used to analyze the size and the number of dense projections of synaptic grids in different brain areas of the rabbit. The observations support the view that dense projections form an intrinsic part of all central synapses and are organized in a hexagonal or triangular pattern. The observation of annulate and horseshoe-shaped synaptic grids is in agreement with previous observations on synaptic connections with subsynaptic plate perforations. A non-normal frequency distribution of dense projections per synaptic grid with distinct peaks is suggestive for the existence of distinct size classes of synaptic contacts. Analyses of the frequency distribution of dense projections in different areas and at different levels below the pial surface in adult animals point to a specificity of the distinct size classes related to the afferent origin or the target cell they are projecting on. Investigation of grid size and number of dense projections during a period of rapid synaptogenesis reveals that newly formed synapses also have a specific size. The complementarity of dense projections and vesicle attachment sites implicit in the model of Akert et al. has been used to calculate the number of vesicle attachment sites per sq. micrometer on account of the density of projections per grid. The agreement between our values and those of Akert and Peper, based on the analyses of vesicle attachment sites in freeze-etch specimen, is striking. The possible implications of these observations in relation to synaptic efficacy and neuronal microcicuitry are discussed.

Animals↗