Changes in retinal fine structure induced in the crab Libinia by light and dark adaptation.

Abstract

The cytological influence of light and dark adaptation (LA and DA) on the retinular cells of the spider crab Libinia emarginata has been studied by light and electron microscopy in four adaptive states: 17 hours darkness, 5 hours darkness, 5 hours diffuse light and 17 hours diffuse light. The rhabdom's fine structure is typical of decapods but its dual overall form and position mingle certain features of both apposition and superposition compound eye types. Distal and proximal retinal pigments both showed adaptive migration, but the distal pigment cells moved over a restricted range, and DA separated the retinular cell pigment granules into two groups, perinuclear and basilar. In the rhabdom no changes in its position, dimensions or microvillus fine structure were observed with LA or DA. But at the base of the rhabdom microvilli the rate of pinocytosis was strongly affected by the eye's adaptive state, being lowest after 17 hours DA and greatest after 17 hours LA; the wall of the 0.1 μ microvesicles so formed, looked like the membrane of the rhabdom microvillus and they were the same size as the vesicles in multivesicular bodies and in vesicular lamellar bodies. Three categories of complex cytoplasmic particles about 1 μ in diameter (multivesicular bodies, vesicular lamellar bodies and purely lamellar bodies) were all increased in number by decreased DA and by increased LA; similar quantitative effects occurred in the endoplasmic reticulum and in the ribosomes. The pinocytotic vesicles and the complex cytoplasmic bodies may represent part of an intracellular system to dispose of rhabdom metabolites whose production was initiated or increased by light absorption. Cytoplasmic and perirhabdomal vacuoles mainly distal in location, were also affected by light, but inversely; their maximal extent occurred after 17 hours DA; less DA or any LA significantly decreased their presence and aggregation. The data reported are of interest not only because they correlate retinal fine structure with the metabolism of vision but also because they provide a new and specific tool for distinguishing active from inactive neurosensory cells in the optic pathway.