Binocular interaction in the formation of specific intertectal neuronal connexions

The mechanisms concerned in the formation of the ipsilateral visual projection in Xenopus have been investigated by examining the results in the adult of various surgical manoeuvres on the embryonic eye: 1. In animals with one double-nasal compound eye, the ipsilateral projection from the compound eye was normal while that from the normal eye was abnormal but internally organized. 2. In animals with one double-temporal compound eye the ipsilateral projection from both operated and normal eyes was normal. 3. In animals with one rotated eye, the ipsilateral projection from the operated eye was normal while that from the normal eye was rotated. 4. In animals reared with only one eye the ipsilateral projection was abnormal in that it was diffuse. The observations are interpreted as indicating that the formation of the retinotopically organized intertectal projection which forms part of the ipsilateral projection is dependent upon a process by which regions of the two tecta that generally receive similar spatiotemporal patterns of excitation become neurally interconnected.

The use of the flush-fitting scleral contact shell after surgical intervention on acoustic neuroma

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The ventral photoreceptor cells of Limulus. I. The microanatomy

The ventral photoreceptor cells of Limulus polyphemus resemble the retinular cells of the lateral eyes both in electrical behavior and in morphology. Because of the great size of the ventral photoreceptor cells they are easy to impale with glass capillary micropipettes. Their location along the length of the ventral eye nerve makes them easy to dissect out and fix for electron microscopy. Each cell has a large, ellipsoidal soma that tapers into an axon whose length depends upon the distance of the cell from the brain. The cell body contains a rich variety of cytoplasmic organelles with an especially abundant endoplasmic reticulum. The most prominent structural feature is the microvillous rhabdomere, a highly modified infolding of the plasmalemma. The microvilli are tightly packed together within the rhabdomere, and quintuple-layered junctions are encountered wherever microvillar membranes touch each other. Glial cells cover the surface of the photoreceptor cell and send long, sheet-like projections of their cytoplasm into the cell body of the photoreceptor cell. Some of these projections penetrate the rhabdomere deep within the cell and form quintuple-layered junctions with the microvilli. Junctions between glial cells and the photoreceptor cell and between adjacent glial cells are rarely encountered elsewhere, indicating that there is an open pathway between the intermicrovillous space and the extracellular medium. The axon has a normal morphology but it is electrically inexcitable.