DEVELOPMENT OF WHISKER-RELATED PATTERNS IN MARSUPIALS - FACTORS CONTROLLING TIMING

In mature rodents, whisker-related patterns are known to be present in three levels of the brain: the brainstem trigeminal nuclei,the ventro basal thalamus and the somatosensory cortex. These patterns have been demonstrated using neuroanatomical tracing techniques, histological an d histochemical staining methods and electrophysiological recordings. The development and topography of these patterns are dependent on an i ntact periphery. But what governs when patterns form at the three leve ls! Possibilities include a controlling signal from the periphery or l ocal mechanisms at each site, such as the arrival of afferent inputs o r the maturation of target tissue. ln this review, we report on the ma turation of the whisker pathway in a marsupial, the wallaby, where the slow tempo of development is a feature. At each level, afferent fibre s grow into the region of termination many weeks before the whisker-re lated pattern emerges. The results suggest that the maturity of the ta rget tissue as well as signals from the periphery combine to trigger p attern formation at each level of the pathway.