Effects of stress and defence allocation on tree growth: Simulation results at the individual and stand level.

The long life span of trees implies that they are more or less frequently confronted with different biotic and abiotic stress situations during their lives. However, biotic stress such as attacks by herbivores or pathogens and abiotic stress such as frost or drought could strongly vary in frequency, intensity, duration, time of occurrence as well as in the involved tissues. This urged trees to develop flexible defence mechanisms during their evolution ensuring a high probability of survival to regenerate successfully. Based on an analysis of existing literature on plant response to herbivory, McNaughton (1983) concludes that “. . .the yield of the tissue affected and other tissues is not affected in proportion to the amount of tissues damaged by the herbivore”, referring also to Lee and Bazzaz (1980) and Neilsen (1981). McNaughton presents a set of alternative patterns about the eff

Topography of Auditory Nerve Projections to the Cochlear Nucleus in Cats after Neonatal Deafness and Electrical Stimulation by a Cochlear Implant

We previously reported that auditory nerve projections from the cochlear spiral ganglion (SG) to the cochlear nucleus (CN) exhibit clear cochleotopic organization in adult cats deafened as neonates before hearing onset. However, the topographic specificity of these CN projections in deafened animals is proportionately broader than normal (less precise relative to the CN frequency gradient). This study examined SG-to-CN projections in adult cats that were deafened as neonates and received a unilateral cochlear implant at ∼7 weeks of age. Following several months of electrical stimulation, SG projections from the stimulated cochleae were compared to projections from contralateral, non-implanted ears. The fundamental organization of SG projections into frequency band laminae was clearly evident, and discrete projections were always observed following double SG injections in deafened cochleae, despite severe auditory deprivation and/or broad electrical activation of the SG. However, when normalized for the smaller CN size after deafness, AVCN, PVCN, and DCN projections on the stimulated side were broader by 32%, 34%, and 53%, respectively, than projections in normal animals (although absolute projection widths were comparable to normal). Further, there was no significant difference between projections from stimulated and contralateral non-implanted cochleae. These findings suggest that early normal auditory experience may be essential for normal development and/or maintenance of the topographic precision of SG-to-CN projections. After early deafness, the CN is smaller than normal, the topographic distribution of these neural projections that underlie frequency resolution in the central auditory system is proportionately broader, and projections from adjacent SG sectors are more overlapping. Several months of stimulation by a cochlear implant (beginning at ∼7 weeks of age) did not lessen or exacerbate these degenerative changes observed in adulthood. One clinical implication of these findings is that congenitally deaf cochlear implant recipients may have central auditory system alterations that limit their ability to achieve spectral selectivity equivalent to post-lingually deafened subjects