CHANGES IN ULTRASTRUCTURE AND FUNCTION OF THE SHEEP PIGMENT EPITHELIUM AND RETINA INDUCED BY SODIUM IODATE¹

Abstract

The present investigation shows that the membrane properties of the sheep pigment epithelial cells were very rapidly and severely affected by sodium iodate, whereas the effects concerning the neuroretina were delayed. The c-wave of the ERG was immediately abolished and replaced by a cornea-negative potential, but the a- and b-waves were preserved for about 80-100 min. Ultrastructurally the plasma membranes (particularly the basal plasma membrane) of the pigment epithelial cells were destroyed or less distinct than normally. The cell organelles were swollen and ruptured. There were indications that the pigment epithelium could no longer participate in the receptor outer segment turnover. The photoreceptor cells were morphologically undamaged, and few or no signs of injury were observed in the inner layers of the retina. The effects upon the neuroretinal functions seen after 80-100 min, consisting of a reduction of alpha- and beta-wave amplitudes, were most likely caused by an inability of the pigment epithelium to maintain in the long run its metabolic and barrier properties. It appears that at an early stage after sodium iodate injection, the present preparation may be useful for the study of the effects on the neuroretina proper of drugs and other agents.

Early effects of sodium iodate injection on ERG in mice

“…Using rabbits, Clifton & Makous (1973) showed that the amplitudes of the a-and b-waves were not affected by NaIO, during the first 10 h after injection. Nilsson et al (1977) found decreased aand b-waves in sheep 100 min after NaIO, injection, although the sensory retina showed no or possibly very slight changes. We previously found decreased b-wave sensitivity, while the maximal response dramatically increased at 24 h after injection and lasted for several days.…”

“…Little information has been gathered on chan-ges of a-and b-waves of the ERG within the first hour of recording (Nilsson et al 1977).…”

Paradoxical enhancement of the ERG c‐wave by a small dose of sodium iodate

“…This may explain the transient increase in c-wave amplitude. Histopathological studies in sheep (Nilsson et al 1977) indicated that the earliest ultrastructural change after intravenous injection of 30 mg/kg of NaI03 was the destruction of the basal membrane and a less extent of the apical membrane of the pigment epithelium. Textorius & Welinder (198 1) reported that injection of 30 mg/kg of NaI03 increased the standing potential (SP), whereas injection of 40 mg/'kg NaI03 decreased it in rabbits.…”

“…C previously to abolish the c-wave (Noel1 1953(Noel1 , 1954(Noel1 , 1958(Noel1 , 1959(Noel1 , 1963Nilsson et al 1977). This observation was similar for both pigmented and albino rabbits, suggesting that pigmentation is not involved in the drug induced ERG changes.…”

EARLY EFFECTS OF SODIUM IODATE ON THE SLOW OFF‐EFFECTS, PARTICULARLY THE h‐WAVE, AND ON THE c‐WAVE OF THE DC RECORDED ELECTRORETINOGRAM IN RABBIT

“…The morphology investigated by light microscopy 4 days later showed severe damage to the pigment epithelium, and Noell suggested that the c-wave of the 'on-ERG and the slow negative off-response were related phenomena and that they were generated mainly across the pigment epithelium. Later, Nilsson et al (1977a) observed severe ultrastructural damage to the pigment epithelium 2 h after the injection of NaIO3.…”