This subproject proposes to investigate the potential role of macrophage-derived cytokines in regulating cellular kinetics of neurosensory epithelia in the cochlea and vestibular system. The Specific Aims have not changed substantially in this second revision. A first goal is to determine which cytokines, from a group of seven, affect cell proliferation rates in isolated epithelial cultures from the avian utricle and cochlea using BrdU labeling techniques. A second aim will examine the potential role of resident macrophages in regulating cell turnover in explants of the avian saccule and utricle via the application of 3 pharmacological agents (L-phenylalanine methyl ester, dexamethasone, interleukin-10) that have been shown to selectively inhibit cytokine production by macrophages in other systems. Cell proliferation and apoptosis-mediated cell death will be assessed by BrdU labeling and application of the TUNEL assay, respectively. Aim 3 will explore the influence of resident macrophages on the proliferation of hair cells in the noise-damaged avian cochlea by examining the effects of administrating in vivo the immunosuppressive agents dexamethasone and cyclosporine-A. A final aim seeks to determine whether macrophages are present in the utriculus of normal mice and/or are recruited to sites of gentamycin-induced damage in mammalian utricular neurosensory epithelium. These experiments also will examine whether the regenerative capacity in isolated utricles is affected by the lack of CSF-1 and/or resident macrophages in the osteopetrotic (op/op) mutant mouse. Additional work in support of subprojects 1 and 3 will evaluate the potential role of macrophages in regulating the regeneration of gustatory and olfactory receptors again using the op/op mutant mouse model.