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Biomedical subjects

A H Neufeld

Publications and source records attributed to A H Neufeld.

At least 55 records · Page 3Linked to original sources
PubMed1986

Maintenance of corneal endothelial cell shape by prostaglandin E2: effects of EGF and indomethacin.

Confluent, cultured, rabbit corneal endothelial cells maintain a polygonal shape which is characteristic of these cells in vivo. When cultured in the presence of EGF (10 ng/ml) and/or indomethacin (1.0 microM), the endothelial cells have markedly different shapes at confluency. By morphometry, untreated cells are polygonal and have a maximum axis of 33 mu; EGF treatment causes a spindle-shaped elongation to 48 mu and indomethacin treatment causes a stellate-shaped elongation to 48 mu. There is a slight increase in cell density. When cells are cultured in the presence of both drugs, elongation is more pronounced to a fibroblastic appearing cell population, with maximum axes of 60 mu and more, but no additive increase in cell density. Continuity of cell borders is often lost. Corneal endothelial cells cultured in the presence of EGF, indomethacin, and PGE2 (0.5 microgram/ml) maintain their polygonal shape; PGF2 alpha is not effective at reversing the drugs' effects. Untreated and EGF-treated cells synthesize and release substantial quantities of PGE2 (2-4 ng/10(4) cells). Indomethacin completely inhibits PGE2 synthesis. It is concluded that PGE2 maintains the polygonal cell shape of the corneal endothelium in vitro and, perhaps, in vivo. The elongated forms of the cell may be related to migration and important in wound closure.

Animals↗
PubMed1985

Cellular migration and morphology in corneal endothelial wound repair.

After a mechanical denudation of rabbit corneal endothelial cells, the healing process was followed with wide-field specular microscopy. Individual cell migration and morphologic changes were analyzed by computer-assisted morphometry. The cells surrounding the wound migrated to cover the defect without producing intercellular gaps. The greatest cellular migration and morphologic alterations occurred close to the wound edge. As the cells migrated toward the wound, they elongated and increased their surface area in the direction of the migration. As the healing proceeded, the cells lost their original hexagonal pattern, which returned after coverage was complete. The wound was covered completely by large, irregularly shaped cells showing mitotic figures between 24 and 48 hr. During this period, cellular migration decreased and normal cellular morphology began to recover. When mitosis decreased, the normal cellular pattern rearranged towards a more hexagonal shape. During the healing process, the degree and direction of cellular migration varied from cell to cell. Additionally, changes in cell-to-cell contact (positional changes of neighboring cells) occurred in one-third of migrating cells. Such cellular migration can account for monolayered cells sliding without producing gaps between individual cells.

Animals↗
PubMed1985

Study of central regulation of intraocular pressure using ventriculocisternal perfusion.

The ability of hypoosmotic solution, prostaglandin E1 (PGE1) and clonidine to influence intraocular pressure (IOP) by a central mechanism was studied using the technique of ventriculocisternal perfusion in conscious rabbits. IOP remained unchanged during the perfusion of 150 mOsm artificial cerebrospinal fluid. IOP rapidly increased by 15 mmHg during the perfusion of PGE1 at the dose of 1 or 3 micrograms/min. However, when PGE1 was perfused intravenously at the dose of 1 microgram/min, a similar IOP response was observed. Furthermore, during the ventriculocisternal perfusion of PGE1 a significant systemic absorption occurred. These observations indicate that the ocular hypertension during the ventriculocisternal perfusion of PGE1 is primarily due to the peripheral action of systematically absorbed PGE1. IOP gradually decreased by 3 mmHg during the ventriculocisternal perfusion of clonidine at the dose of 0.1 or 0.33 micrograms/min. Intravenous perfusion of clonidine at the same doses did not change the IOP. These results indicate that clonidine can lower IOP by a centrally mediated mechanism. Ventriculocisternal perfusion of clonidine (0.1 micrograms/min) in rabbits with unilateral superior cervical ganglionectomy lowered IOP in both eyes, indicating that ocular adrenergic innervation does not participate in this centrally mediated IOP response. However, the cardiovascular parameters of anesthetized rabbits were altered by the ventriculocisternal perfusion of clonidine (0.1 micrograms/min), suggesting that a change in systemic hemodynamics is involved in the central IOP effect of clonidine.

Alprostadil↗
PubMed1984

Effects of timolol on intraocular pressure following ocular adrenergic denervation.

The effects of timolol on the elevation of intraocular pressure induced by orogastric water-loading were studied in conscious pigmented rabbits which had undergone unilateral, superior cervical ganglionectomy. Each rabbit was studied without timolol treatment and with unilateral 2% timolol treatment, either to the innervated eye or to the denervated eye, 90 min before water-loading. Timolol, applied to the innervated eye, significantly reduced the elevation of intraocular pressure in that eye, but not in the fellow eye. Timolol, applied to the denervated eye, did not affect the elevated intraocular pressure in either the denervated or the fellow eye. These results demonstrate that ocular adrenergic innervation participates in the mechanism of ocular hypotensive action of timolol in water-loaded pigmented rabbits.

Animals↗
PubMed1984

Beta-adrenergic and serotonergic stimulation of rabbit corneal tissues and cultured cells.

The adult rabbit cornea synthesizes cyclic AMP in response to both serotonin and isoproterenol. The authors have examined the postnatal development of these pathways and attempted to localize the responsive cell type(s) by dissection, cell culture, and surgical denervation. Full thickness corneas of neonatal rabbits have beta-adrenergic responses similar to the adult but fail to respond to serotonin until the animals are 9-12 weeks old. When adult corneas are separated into epithelia, stromal, and endothelial layers, only the stromal layer synthesizes cyclic AMP in response to serotonin, whereas all layers respond to isoproterenol. When grown in tissue culture, keratocytes, epithelial, and endothelial cells are unresponsive to serotonin but respond to isoproterenol. Neither adrenergic nor sensory denervation abolishes the corneal adrenergic or serotonergic response pathways. These results indicate that the epithelial cells do not contain the serotonin stimulated, cyclic AMP-mediated pathway as originally postulated. The cell population that does contain this pathway is within the stroma and may be the Schwann cells.

Animals↗
PubMed1984

Corneal endothelial function and structure following cryo-injury in the rabbit.

Wide-field specular microscopy, fluorophotometry, pachymetry, and scanning electron microscopy are used to characterize a reproducible, in vivo model of corneal endothelial injury and recovery in the rabbit. Following an 8-mm central cryo-injury, the cornea remains thickened for as long as 3 weeks. Mean endothelial permeability to fluorescein is above normal for 10 days following injury, but by 14 days postinjury the endothelial permeability to fluorescein is not statistically significantly different from preinjury control values, thus indicating that endothelial permeability probably returns to normal by approximately 2 weeks postinjury. Cell morphology, as determined by scanning electron microscopy, is also essentially normal by 2 weeks postinjury. Endothelial permeability appears to recover before stromal thickness normalizes, suggesting a lag in recovery of endothelial pump function.

Animals↗
PubMed1983

Laboratory and clinical studies on the mechanism of action of timolol.

Timolol is now widely used in the treatment of glaucoma but its mechanism of action is unclear. The drug decreases aqueous humor formation by the ciliary processes and is a potent beta-adrenergic antagonist. However, the physiological basis for such a drug to decrease intraocular pressure has not been clearly demonstrated.

Adrenergic Fibers↗
PubMed1983

Changes in responsiveness of the beta-adrenergic and serotonergic pathways of the rabbit corneal epithelium.

Adrenergic agonists stimulate the synthesis of cyclic AMP by incubated rabbit corneas with the following order of potency: isoproterenol greater than epinephrine greater than norepinephrine. These agonists have the same order of potency when displacing the specific, beta-adrenergic radioligand, 3H-dihydroalprenolol, from beta-adrenergic receptors on membranes prepared from corneal epithelium. At another locus, serotonin stimulates cyclic AMP synthesis. Inhibition of stimulation in vitro by lysergic acid diethylamide, methysergide, cyproheptadine, and spiroperidol demonstrates the specificity of this pathway for serotonin. Topical epinephrine causes subsensitivity or decreased responsiveness of the beta-adrenergic pathway. There is loss of approximately half the beta-adrenergic receptors from the cornea and a similar loss of epinephrine-stimulated cyclic AMP synthesis, both of which return to control levels in 96 hrs. There is no change in affinity for catecholamines and no loss of responsiveness to prostaglandin E2 or serotonin. Pretreatment with nialamide or subsequent treatment with additional epinephrine does not cause further loss of responsiveness. Supersensitivity or increased responsiveness of this pathway occurs following superior cervical ganglionectomy. Topical serotonin causes decreased responsiveness of the serotonergic pathway. When potentiated by nialamide, serotonin causes almost complete loss of serotonin-stimulated cyclic AMP synthesis for 24-48 hrs. There is no loss of responsiveness to epinephrine. Increased responsiveness of this pathway does not occur following superior cervical ganglionectomy. The authors conclude that the corneal epithelium has both beta 2-adrenergic and serotonin-2 pathways, and each pathway exhibits altered responsiveness by similar mechanisms. In response to exogenous or endogenous stimulation, the beta-adrenergic responsive cells and the serotonergic responsive cells apparently regulate the total number of pathway-specific receptors on their surfaces. Furthermore, the authors postulate that two populations of beta-adrenergic responsive cells exist; those on the apical surface of the epithelium that respond to catecholamine in the tears and those near the basal surface that respond to neuronal catecholamine.

Adrenergic beta-Agonists↗
PubMed1983

Beta-adrenergic and serotonergic responsiveness of rabbit corneal epithelial cells in culture.

Rabbit corneal epithelial cell cultures were established from Dispase-treated anterior corneas. In culture medium containing cholera toxin, insulin and epidermal growth factor, these cells proliferated in vitro in the absence of any contaminating cells. Following subculture, cells retained epithelial morphology and the ability to synthesize cAMP in response to beta-adrenergic stimulation, but lacked the ability to respond to serotonergic stimulation. Retention of the beta-adrenergic system in culture serves as a functional epithelial cell marker; whereas expression of serotonergic responsiveness may be regulated by developmental or extrapithelial systems that are absent in these cell cultures.

Adrenergic beta-Agonists↗
PubMed1983

Effects of l- and d-timolol on cyclic AMP synthesis and intraocular pressure in water-loaded, albino and pigmented rabbits.

Topical 2% l- or d-timolol reduced the elevation of intraocular pressure induced by water-loading in conscious rabbits. This drug effect appeared on the peak elevation (in pigmented eyes) and on the down-phase (in albino and pigmented eyes) of elevated intraocular pressure. The contralateral eye and the treated eye responded similarly. In urethane anesthetized, water-loaded rabbits, a greater inhibitory effect of l-timolol was observed in pigmented eyes than in albino eyes. Two per cent l-timolol caused alterations of heart rate and arterial blood pressure in water-loaded anesthetized rabbits, but time courses of these alterations did not correlate with the inhibitory effect on the elevation of intraocular pressure. The beta-adrenergic antagonistic activity of l-timolol and d-timolol were compared by their ability to inhibit l-isoproterenol-stimulated cyclic AMP synthesis in the rabbit iris-ciliary body preparation in vitro. The I50S for l- and d-timolol differ by about 1.5 log units. In our studies, d-timolol has little of the intraocular pressure lowering and the beta-adrenergic antagonistic activity of l-timolol. Thus, the conscious, water-loaded, pigmented rabbit can be used as a model for studying the effects of beta-adrenergic antagonists on intraocular pressure.

Animals↗
PubMed1982

Neural serotonin stimulates chloride transport in the rabbit corneal epithelium.

Evidence is presented that serotonin acts as a neurotransmitter in the cornea of the adult rabbit. Serotonin was localized to granules in a sparse population of subepithelial corneal nerves by an electron microscopic histochemical procedure. Significant endogenous levels of serotonin and its principal metabolite, 5-hydroxyindoleacetic acid, were detected in the central cornea by a fluorometric assay. Exogenous serotonin stimulated ion transport by corneal epithelium. This effect was potentiated by monoamine oxidase inhibition and was unaffected by an alpha-adrenergic receptor antagonist. Serotonin-stimulated ion transport was inhibited by the specific antagonist, methysergide, and by the replacement of Cl- with an impermeable anion. In tracer experiments, the serotonin-stimulated ion transport was shown to be caused by increased epithelial Cl- secretion. The serotonin response was partially inhibited by the beta-adrenergic antagonist, timolol. In a companion article, assay of corneal cyclic AMP showed stimulation of cyclic AMP synthesis by serotonin, inhibition by the specific antagonist, lysergic acid diethylamide, and potentiation by monoamine oxidase inhibition. We postulate that specific serotonergic receptors are present in the corneal epithelium and that activation of these receptors by serotonin released from serotonergic neurons increases the level of cyclic AMP, which stimulates active Cl- secretion by the corneal epithelium.

Animals↗
PubMed1982

Serotonin-stimulated cyclic AMP synthesis in the rabbit corneal epithelium.

Serotonin increases the level of cyclic AMP in incubated rabbit corneas; the concentration of agonist producing half-maximal stimulation is approximately 1.5 microM. Nialamide, an inhibitor of monoamine oxidase, potentiates the response to serotonin but not to epinephrine. Amitriptyline, an inhibitor of neuronal uptake of serotonin, does not potentiate the stimulation of cyclic AMP synthesis. Lysergic acid diethylamide, but not timolol, antagonizes the response to serotonin; the half-maximal inhibitory concentration is approximately 6 nM lysergic acid diethylamide. A comparison of the time course of the increase in cyclic AMP synthesis after addition of serotonin or epinephrine to the incubation media indicates that serotonin, but not epinephrine, must penetrate a barrier to its free diffusion. We conclude that the corneal epithelium contains specific serotonergic receptors that, upon activation, cause the synthesis of cyclic AMP, which mediates the stimulation of chloride transport (c.f. companion article, Klyce et al.). The serotonergic receptors must be at a location posterior to the beta-adrenergic receptors, which are on the anterior-surface of the apical cells.

1-Methyl-3-isobutylxanthine↗
PubMed1981

Effects of intravitreal cholera toxin on adenosine 3',5'-monophosphate, intraocular pressure, and outflow facility in rabbits.

Catecholamines, prostaglandins, and various hormones may influence aqueous humor dynamics via the second messenger, adenosine 3',5'-monophosphate (cyclic AMP). To test this hypothesis in rabbit ocular tissues, we have investigated the effects of cholera toxin (CTX), a specific, irreversible activator of adenylate cyclase. CTX (5 x 10(-4) to 5 x 10(2) microgram/ml) in both the presence and absence of isobutylmethylxanthine (IBMX) increased cyclic AMP production in the isolated iris-ciliary body. The effects of CTX were dependent on its concentration, duration of exposure, and presence of IBMX. Furthermore, iris-ciliary bodies and scleral-trabecular rings exercised after intravitreal injection of 10 microgram of CTX and incubated in vitro produced significantly more cyclic AMP than contralateral control tissues. Thus significant binding of CTX to both iris-ciliary body and scleral-trabecular ring occurred within 5 hr after intravitreal injection. Intraocular pressure (IOP) and outflow facility were measured by intraocular cannulation. Five hours after intravitreal injection of CTX, the IOP was lower than in control eyes. At this time, the outflow facility was threefold greater in the CTX-treated eyes than in control eyes. On the basis of these results, we conclude that (1) CTX stimulates cyclic AMP production in iris-ciliary body and scleral-trabecular ring of rabbits, (2) IOP decreases and outflow facility increases after intravitreal injection of CTX, and (3) the hypotensive effect of CTX is apparently mediated, at least partially, by outflow mechanisms.

Animals↗
PubMed1980

Diurnal rhythm of mitosis in rabbit corneal epithelium.

Incorporation of 3H-thymidine by rabbit corneal epithelium during the course of a one-hour incubation in vitro varies according to the time of day, suggesting a diurnal rhythm of mitotic activity. Adrenergic decentralization of the cornea does not affect this rhythm. Furthermore, there is no diurnal variation in the basal or sympathomimetically-stimulated cyclic AMP production by freshly excised rabbit corneas, incubated in vitro. Therefore, the diurnal rhythm of corneal epithelial mitotsis in the rabbit is not paced by catecholamines.

Animals↗