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A Verstappen

Publications and source records attributed to A Verstappen.

14 recordsLinked to original sources
PubMed1994

Characterization of alpha 2-adrenoceptor binding sites in rabbit ciliary body membranes.

PURPOSE: This study sought to identify and characterize subtypes of alpha 2-adrenoceptors in rabbit ciliary body. METHODS: Radioligand binding assays were performed with the alpha 2-agonist ligand [125I]-p-iodoclonidine ([125I]PIC) and the antagonist ligand [3H]rauwolscine. RESULTS: Both [125I]PIC and [3H]rauwolscine bound to a single population of receptors in membrane preparations of rabbit ciliary body. The densities for the two ligands were the same (about 640 fmol/mg). However, the affinity of [125I]PIC (dissociation constant, Kd = 1.91 +/- 0.24 nM) was about threefold higher than that of [3H]rauwolscine (dissociation constant = 6.79 +/- 1.5 nM), and binding of [125I]PIC exhibited guanine nucleotide sensitivity. Inhibition of [125I]PIC binding by epinephrine, idazoxan, and amiloride was examined to differentiate between alpha 2-adrenoceptors and the imidazoline-preferring receptor. Epinephrine and idazoxan competed for all of the [125I]PIC binding; relative potency was epinephrine > idazoxan >> amiloride. Subtypes of alpha 2-adrenoceptors were further studied by competition for [125I]PIC binding by subtype-selective compounds. [125I]PIC binding sites showed the pharmacologic characteristics of an alpha 2A-adrenoceptor (oxymetazoline > chlorpromazine >> prazosin), and competition by oxymetazoline and chlorpromazine was best fit by a one-site model. Likewise, the relative potency of inhibition of [3H]rauwolscine binding was oxymetazoline > chlorpromazine. However, inhibition of [3H]rauwolscine-binding by oxymetazoline was better fit by a two-site model, which was converted to a one-site model in the presence of 100 microM 5'-guanylimidodiphosphate. CONCLUSIONS: A large number of alpha 2-adrenoceptors are present in rabbit ciliary body. They are not the imidazoline-preferring receptor but are alpha 2-adrenergic-specific receptors of the alpha 2A subtype.

Affinity Labels↗
PubMed1992

Effects of lofexidine, an alpha 2-adrenoreceptor agonist, on ocular blood flow and ion transport of rabbit iris-ciliary body.

The effect of topical unilateral application of lofexidine, an alpha 2-agonist, on ocular regional blood flow was tested in anesthetized rabbits using radiolabeled microspheres. A significant reduction in blood flow was found only in the ciliary body of the treated eye at 1 hr after lofexidine treatment. However, the IOP of both eyes was decreased significantly at 30 and 60 min post lofexidine treatment. Yohimbine (i.v.) blocked this IOP lowering effect, but only partially prevented the blood flow response. In addition, no significant difference was found in either basal or amphotericin-B stimulated short-circuit current or potential difference of the isolated rabbit iris-ciliary body after 30 minutes of lofexidine treatment. These observations suggest that the IOP lowering effect of lofexidine appears to be mediated by alpha 2-receptors but unrelated to the reduction in the ocular blood flow and net electrogenic ion transport.

Adrenergic alpha-Agonists↗
PubMed1987

Calcium binding protein immunoreactivity in pigeon retina.

Pigeon retina has been mapped immunocytochemically for vitamin D-dependent calcium-binding protein (D-CaBP). Immunoreactivity was found in the cones of the yellow field, but not in photoreceptors of the red field. The D-CaBP-containing cones were a subpopulation of those in the yellow field having straight fibres leading to their synaptic terminals. D-CaBP immunoreactivity was also found in horizontal cells, the amount present varying according to position along the retina, and in some amacrine cells. Immunoblots of pigeon retinal proteins separated by SDS-polyacrylamide gel electrophoresis indicated two D-CaBP forms, having apparent molecular weights of 27000 and 29000. Both these forms of D-CaBP have been found previously in rat and pigeon brain.

Animals↗
PubMed1987

[Differential diagnosis between retinoblastoma and ocular toxocariasis].

We studied the sensitivity for Toxocara Canis (ELISA technique) in 5 cases of retinoblastoma confirmed by anatomopathological examination. Some presented with a positive reaction in serum and/or in aqueous. Now that surgical technique are available that permit to functionally save eyes affected by toxocariasis, we felt that a safe and reliable differential diagnosis between toxocariasis and retinoblastoma is of major importance. A positive ELISA test even in the aqueous fluid does'nt seem reliable enough for that purpose. We concluded to the necessity to include in preoperative tests some more invasive techniques such as aqueous tap for dosage of lactico-dehydrogenases or vitreous biopsy for cytological examination, at least for the most difficult cases with a positive ELISA test.

Aqueous Humor↗
PubMed1986

Demonstration of a neuropeptide Y (NPY)-like immunoreactivity in the pigeon retina.

The distribution of neuropeptide Y (NPY)-like immunoreactivity in the pigeon retina was investigated by fluorescence immunohistochemistry. NPY-positive cells were found in central and peripheral retina. NPY somata were located in the proximal portion of the inner nuclear layer and their processes directed to the inner plexiform layer where they ramified in 3 immunoreactive bands. NPY might play a role as a neurotransmitter or neuromodulator in the pigeon retina.

Animals↗
PubMed1986

Vitamin D-dependent calcium binding protein immunoreactivity in human retina.

Using immunohistochemistry, vitamin D-dependent calcium binding protein (D-CaBP) has been detected in human retina. In the photoreceptor layer the cones are positive but the rods are negative. In the inner nuclear layer, horizontal cells and some bipolar cells are D-CaBP. In the ganglion cell layer both small and large somata are immunoreactive for D-CaBP. Beaded fibres from the outer plexiform, inner plexiform and fibre layers are also positive.

Cells↗
PubMed1983

Clinicopathological study of the visual pathways, eyes, and cerebral hemispheres in 32 cases of disseminated sclerosis.

The pathological study of the cerebral hemispheres and visual pathways in 32 cases of disseminated sclerosis, including 15 cases in which the retinal structures were investigated, lead us to point out: 1) the high frequency of histological lesions of the optic nerves, tracts and radiations; 2) the lack of correlation between the extent of demyelination of the optic nerves and the impairment of visual acuity that is mainly related to axonal lesions; 3) the relative high frequency of pathological sheathing of retinal veins; and 4) the high proportion of shadow plaques in the cerebral hemispheres in cases with clear-cut relapses and remissions.

Adult↗
PubMedDate not supplied

Distribution of neuropeptide Y immunoreactivity in human visual cortex and underlying white matter.

Immunocytochemical techniques have been used to study neuropeptide Y (NPY) distribution in the human visual cortex (Brodman's areas 17, 18 and 19) NPY cell bodies belong mostly to inhibitory (multipolar and bitufted) but also to excitatory (bipolar and some pyramidal) neuronal types. Their distribution is similar in the three cortical areas studied: 20 to 40% of the NPY perikarya are located in the cortical gray matter, mostly in the deep layers, while the remaining 60 to 80% are located in the underlying white matter. Immunoreactive NPY processes form a rich network of intersecting fibers throughout the entire visual cortex. A superficial plexus (layers I and II) and a deep plexus (deep layer V and layer VI) of NPY fibers are present in areas 17, 18 and 19. In area 17, an additional well developed plexus is present in layers IVb and IVc. These plexuses receive branches from long parallel fibers arising from deep cortical layers or underlying white matter and terminating in superficial layers. Local or extrinsic NPY terminals wind around vessels in the cortex as well as in the white matter, and either penetrate them or form clusters of club endings on their walls. Our results suggest a role for NPY in human visual circuitry and in cortical blood flow regulation.

Aged↗