[87]

Rod Photoreceptor Damage Induced By Hypergravity.   A.J. Barnstable1, A.R. Tink1,2, S. Viviano1, L. Baer3, C. Wade3, C.J. Barnstable J. Tombran-Tink.  1Dept. Ophthalmology, Yale Univ. School of Medicine, New Haven, CT, 2Pharmaceutical Sciences, UMKC, Kansas City, MO 3Ames Research Ctr, Moffett Field, CA.

   Retinal rod photoreceptor degeneration can result from a variety of environmental and genetic factors. We have shown that the microgravity environment encountered in space shuttle flight can disrupt normal retinal development and mimic stimuli that induce similar retinal degenerations  (this meeting).  We have now examined eyes from animals maintained in a hypergravity environment and find that these show signs of rod degeneration degeneration as well.

   Groups of pregnant rats were maintained at 2.0 xG for approximately 14 days by centrifugation with a normal lighting schedule. Age- and weight-matched stationary controls were housed in the centrifuge rotunda, which allows them to be exposed to the same environmental conditions as the hypergravity animals.  Eyes from the adult rats were fixed in formalin, cryoprotected, frozen and cryosectioned.  Sections were labeled with a variety of cell type-specific antibodies including those recognizing rod photoreceptor cell bodies, inner segments and outer segments.

Eyes from rats maintained at 2.0 xG showed loss of rod photoreceptors with varying degrees of severity.  In the most extreme cases the cell body layer was reduced to approximately 20% of its normal thickness.  The outer segments were shorter and much more disorganized although inner segments showed less change.  Other cell layers across the retina showed no detectable change.  Stationary control retinas showed normal photoreceptor morphology.

This study shows that extended periods of hypergravity can lead to deleterious changes in rod photoreceptors.  The results are unlikely to be due to changes in intraocular pressure since this usually affects retinal ganglion cells but not rod photoreceptors. Although these changes in gravitational forces could be transient,  understanding how prolonged exposure to altered gravitational fields damage photoreceptors is important for future manned space flight to other planets.  The study  may also provide clues to the mechanisms underlying earth-based retinal degenerative diseases.  (Supported by NIH and RPB Inc.)