cytochalasin-d and Retinal-Detachment

Mechanisms that maintain the close coupling between the formation of photoreceptor disk membranes and the displacement of disk membranes toward the pigment epithelium are poorly understood. This study was designed to determine whether the axial displacement of disk membranes requires the assembly and insertion of new disk lamellae.. Retinal detachment and treatment with cytochalasin D were employed to interrupt the normal formation of disk membranes in cultured Xenopus laevis retinas. The effect of disrupting disk initiation and assembly upon disk displacement was documented and quantified.. Isolating retinas from the retinal pigment epithelium prevented the normal morphogenesis of disks, but previously formed disks moved distally at a rate that is greater than or equal to the rate in attached retinas or in vivo. Treatment of attached retinas in eyecups with cytochalasin D blocked initiation of new disks and resulted in the formation of ectopic, disk-like membranes, but it did not stop axial displacement of previously formed disks. Rod cells in retinas that were cultured while slightly elevated from the retinal pigment epithelium sometimes formed disks of a smaller diameter than normal, even though the rate of initiation and displacement of disks was the same as in vivo.. Observations on detached retinas and or retinas treated with cytochalasin D suggest that disk displacement does not depend upon normal disk formation and that the motive mechanism does not involve filamentous actin. The formation of small diameter disks in elevated retinas suggests that disk initiation and displacement is independent of the completion of normal diameter disks.

Topics: Animals; Cytochalasin D; Fluorescent Dyes; Intracellular Membranes; Isoquinolines; Morphogenesis; Organ Culture Techniques; Retinal Detachment; Rod Cell Outer Segment; Xenopus laevis

This study asks whether retinal adhesiveness is affected by cytochalasin D, a drug that is known to alter the apical morphology of the retinal pigment epithelium (RPE). Cytochalasin D was injected intravitreally in Dutch rabbits and retinal adhesiveness measured 0.5 to 72 h later by two methods: in vitro peeling of the retina from retinal pigment epithelium to observe the amount of adherent pigment, and in vivo measurement of the pressure needed to achieve retinal separation. Electroretinograms were recorded, and RPE apical morphology was examined by scanning electron microscopy. The injection of 60 microM cytochalasin D caused in vitro retinal adhesiveness to fall within 3 h to 10% of normal although the electroretinogram (a, b, and c-waves) remained normal. Smaller doses of cytochalasin D had a lesser effect. The RPE apical surface at 3 h showed large bullet-like microvilli, swollen cone sheaths, and an absence of filamentous microvilli. The severity of these changes was dose-related. At 72 h after cytochalasin D, retinal adhesiveness had largely recovered, and RPE apical morphology appeared normal again. Thus, cytochalasin D weakens retinal adhesiveness acutely but reversibly, and both the initial effect and recovery correlate with changes in RPE microvillar morphology. This suggests that actin microfilaments may be involved in mechanisms of retinal adhesion.

Topics: Adhesiveness; Animals; Cytochalasin D; Dose-Response Relationship, Drug; Electroretinography; Microscopy, Electron, Scanning; Microvilli; Pigment Epithelium of Eye; Rabbits; Retina; Retinal Detachment; Time Factors

The morphology of the apical surface of rabbit retinal pigment epithelium was studied by scanning electron microscopy from the first minute to several hours after making small nonrhegmatogenous retinal detachments (blebs). From 0 to 5 min, there were only slight changes in the homogeneous, dense mat of filamentous microvilli. From 5 to 30 min, filamentous microvilli retracted exposing larger processes. From 30 to 60 min blunt processes became completely exposed and sheet-like processes disappeared. At about 60 min, cone sheaths were no longer identifiable in most specimens. Between 60 min and the time of retinal reapposition (several hours), the apical surface became highly rounded. Colchicine and cytochalasin-D had no effect on the time required for fluid resorption, but colchicine greatly accelerated and enhanced cell rounding, while cytochalasin-D produced prominent apical tufts.

Topics: Animals; Cell Membrane; Colchicine; Cytochalasin D; Cytochalasins; Cytoskeleton; Microscopy, Electron, Scanning; Pigment Epithelium of Eye; Rabbits; Retinal Detachment; Time Factors