DESCRIPTION (provided by applicant): The development and maintenance of neuronal form depends on an array of molecular and activity-based cues. While developing neurons are highly susceptible to such cues, this flexible responsiveness appears to wane as neuronal systems age. One of the more striking examples of adult plasticity is the denervationinduced dendritic sprouting of auditory interneurons in the cricket. Unilateral removal of the ear induces interneuron dendrites to aberrantly cross the midline and become innervated by auditory afferents from the contralateral ear (Hoy et al., 1985; Schildberger et al., 1986). This reinnervation is remarkably precise, reinstating interneuron-specific threshold and intensity responses. What factors trigger and guide this compensatory regeneration? The combination of confocal microscopy and modern fluorescent tracers or genetic markers will be used to gain a qualitative and quantitative three-dimensional understanding of the compensatory regeneration of auditory interneurons. In addition, the development of auditory interneurons and their innervating afferents will be described. Standard molecular and cellular techniques, including cloning, in situ hybridization, and immunohistochemistry will be used to search for molecular factors whose expression patterns correlate with stages of development. Since neuronal regeneration may rely on cues utilized during development, these experiments will yield information valuable to the examination of neuronal regeneration. Regeneration experiments, informed by development, will examine how alterations in molecular expression patterns might induce or allow dendritic regeneration. It is hoped that an investigation of this invertebrate regeneration phenomenon will advance the fundamental understanding of the development and plasticity of dendrites, and reveal principles governing neuronal regeneration that may be applicable to all neuronal systems, including mammals.