[Detection of dual phase of light response of interphotoreceptor matrix]

The postnatal development of light-evoked changes in the interphotoreceptor matrix (IPM), a complex of the extracellular matrix that surrounds the photoreceptors and lies between them and the retinal pigment epithelium, was studied by use of a histochemical probe colloidal iron in rats at various postnatal days of age. In the dark, IPM constituents distributed uniformly throughout the outer segment zone and in the apical region of the inner segment zone; this dark pattern of IPM distribution was commonly observed in animals ranging from postnatal day 12 to one year. In the light, little changes were observed at postnatal day 12, followed by varying light-evoked changes in the IPM with increasing ages. At postnatal day 14, the IPM constituents showed a distribution towards the basal region of the inner segment zone along with the dark pattern. At postnatal day 16, they concentrated in bands at the apical and basal region of the outer segment zone, and also in the inner segment zone with expansion from the apical to basal region with increasing time after light exposure. At age one year, the light-adapted IPM constituents were distributed in a manner similar to that on postnatal day 14. The present results confirm the light-evoked changes in the IPM as revealed by colloidal iron-recognized IPM components and provide evidence for postnatal development of the light-evoked changes in the IPM components, whereby the changes appeared earlier and were preserved longer in the basal region of the inner segment.