The FESN-sponsored follow-up meeting on neural development highlighted progress toward understanding several central issues in developmental neurobiology with particular emphasis on investigation into the mechanisms of cell fate determination. In systems as diverse as the HSN neurons of C. elegans, the photoreceptor cells of the Drosophila eye, the wide range of cell types within the vertebrate retina and the neurons of the cerebral cortex, hindbrain and spinal cord, the importance of environment in the determination and maintenance of cell fate was clearly established. Advances in cell marking techniques, including fluorescent dye and retroviral tagging, have enabled the fates of cells in normal and heterotypic environments to be followed and have demonstrated the initial plasticity of the progenitor cell population in many systems. The recent establishment of in vitro systems for studying neural development should further define the precise nature and identity of the environmental signals that act to establish and maintain cell fate. Of course, establishment of cell identity is only the initial phase in the formation of the mature nervous system. Once the fate of individual cells is determined, migration of cells to appropriate locations, extension of axons to appropriate targets and refinement of neuronal circuitry must occur. Both the definition of genes that influence these processes in nematodes and recent advances in imaging techniques that provide a means of observing these later, dynamic processes in 'living' brain slices promise to significantly advance understanding of the complexities of development of functional nervous systems.

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Functional architecture of cortex revealed by optical imaging of intrinsic signals.

Optical imaging of cortical activity offers several advantages over conventional electrophysiological and anatomical techniques. One can map a relatively large region, obtain successive maps to different stimuli in the same cortical area and follow variations in response over time. In the intact mammalian brain this imaging has been accomplished with the aid of voltage sensitive dyes. However, it has been known for many years that some intrinsic changes in the optical properties of the tissue are dependent on electrical or metabolic activity. Here we show that these changes can be used to study the functional architecture of cortex. Optical maps of whisker barrels in the rat and the orientation columns in the cat visual cortex, obtained by reflection measurements of the intrinsic signal, were confirmed with voltage sensitive dyes or by electrophysiological recordings. In addition, we describe an intrinsic signal originating from small arteries which can be used to investigate the communication between local neuronal activity and the microvasculature. One advantage of the method is that it is non-invasive and does not require dyes, a clear benefit for clinical applications.

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PubMedDate not supplied

Effects of monocular deprivation on the cat's visual cortex.

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