Internal Nuclear Layer Research Articles

Complementary freeze fracture replication: An example of its use in the study of horizontal cell gap junctions of the carp retina

AbstractDark‐adapted carp retinas were fixed with glutaraldehyde, frozen in liquid nitrogen slush, and their complementary replicas were harvested using a bipolar‐vacuum evaporater. On montage pictures, plasmic (PFF) and ectoplasmic fracture faces (EFF) of the external horizontal cells (EHC) were marked, and PFF of gap junction (GJ) areas were scrutinized by virtue of particulate aggregation visible at relatively low magnification. Summation of digitized values obtained from a complementary pair of replicas was taken to represent all existent GJ areas in an examined EHC surface. A similar method was applied to large horizontal processes (LHP) that are located in the inner‐most part of the internal nuclear layer and currently accepted to be extensions of EHC. The occurrence of fractured faces of plasma membrane was smaller in EHC than LHP. The percentage of GJ areas was about ten times larger in EHC than LHP. Examining complementary replicas at relatively low magnification appears to be useful for facilitating quantitative analysis of intercellular coupling by GJ structures.

Etomidate induced retinal changes.

The author examined the effect of etomidate-anaesthesia of one hour duration on the ultrastructure of the retina in animal experiments. Immediately after the exposure only the Müller's cells were moderately damaged. One day following the narcosis more serious pathological changes developed in the external nuclear layer which were partly irreversible. The changes found in the internal nuclear layer were less serious. The structure of the glial cells also altered. In the specimens taken 48 h following the anaesthesia the pathological changes of the neurons regressed to some degree, the Müller's cells reorganised and masses of glycogen accumulated in them. Further studies are needed to explain the eventual retinal toxic effect of this agent.

OBSERVATIONS ON THE RETINA OF FLORIDA CHAMELEON (ANOLIS CAROLINENSIS)

The structure of the A. carolinensis retina is similar to that of diurnal lacertilians described in the literature. It possesses 10 layers. The visual cell layer is made up of single and double cones. No rods are present. The internal nuclear layer is thicker than the external nuclear layer. The nuclei and ganglion cells of light- and dark-adapted animals do not show any differences in staining. A prominent conus papillaris and a fovea are present. The epithelial pigment layer and the cones do not undergo any photomechanical changes. It was not possible to condition the chameleons to yield any behavioral responses.