The role of innate immunity and macrophage recruitment to the inner ear after hair cell injury is a subject where little is known. In this paper, we demonstrate recruitment of monocytes and macrophages to the inner ear after kanamycin. We also examined the effect of fractalkine receptor (CX3CR1) deletion in kanamycin ototoxicity. We observed more functional and structural damage in CX3CR1 null mice compared to wild-type and heterozygous littermates. In order to determine if increased susceptibility to kanamycin resulted from CX3CR1 deletion from cochlear leukocytes, we created bone marrow chimeras by transplanting CX3CR1-null bone marrow into wild-type mice whose native bone marrow was ablated by lethal irradiation. These mice were then treated with kanamycin sulfate. Auditory brainstem responses (ABR), hair cell counts, and numbers of macrophages recruited to the cochlea were recorded in irradiated mice that received either wild-type, CX3CR1 heterozygous, or CX3CR1 knockout bone marrow. A strong correlation was present between numbers of macrophages and hair cell death in recipients transplanted with CX3CR1 null marrow. No correlation between macrophage number and hair cell loss was present in mice transplanted with wild-type or CX3CR1 heterozygous marrow. We suggest that CX3CR1 plays a role in modulating the detrimental effects of cochlear macrophages after kanamycin ototoxicity. Our data point to the possibility that CX3CR1-deficient cochlear macrophages exacerbate kanamycin ototoxicity while CX3CR1-expressing monocytes do not.

Cochlear macrophages have been shown to accumulate in the murine cochlea following acoustic trauma. This investigation was performed to determine whether cochlear macrophages could be replaced by donor transplantation of bone marrow precursors. Lethally irradiated C57BL/6 mice were transplanted with hematopoietic precursors from CX3CR1(GFP/GFP) fetal mice. CX3CR1(GFP/GFP) mice express green fluorescent protein (GFP) in monocytes and macrophages and possess no functional CX3CR1. Donor monocytes and macrophages can be easily traced in the wild-type recipient with fluorescent microscopy. We studied mice at 2-16 weeks after transplantation to assess repopulation of cochlear macrophages. A separate group of chimeras was exposed to octave band noise (8-16 kHz for 2 hours) 2 weeks after transplantation to evaluate the migration properties of donor hematopoietic precursors. We found that macrophages derived from donor hematopoietic precursors appeared in cochlea 3-4 weeks after transplantation and increased week by week. Noise exposure induced a massive accumulation of leukocytes, particularly in the spiral ligament of the basal turn. There was no difference between CX3CR1(GFP/GFP) donor/wild-type recipient chimeras and the wild-type donor/wild-type recipient chimeras in hearing thresholds, accumulation of cochlear macrophages, or tissue injury after noise exposure. These data indicate that cochlear macrophages are derived from bone marrow precursors and that they are an exchanging and migratory population. Furthermore, CX3CR1 in hematopoietic precursors is not necessary for macrophage migration into cochlea and when deleted in this cell population, the absence of CX3CR1 does not substantially effect the outcomes after noise.

Combinations of aminoglycosides and loop diuretics have been known to have a synergistic effect in ototoxic injury. Because murine hair cells are relatively resistant to ototoxicity compared to those of other mammals, investigators have turned to combination therapies to create ototoxic lesions in the mouse inner ear. In this paper, we perform a systematic comparison of hearing thresholds, hair cell damage and monocyte migration into the mouse cochlea after kanamycin versus combined kanamycin/furosemide and explore the pathophysiology of enhanced hair cell loss in aminoglycoside ototoxicity in the presence of loop diuretic. Combined kanamycin-furosemide resulted in elevation of threshold not only in the high frequencies, but across all frequencies with more extensive loss of outer hair cells when compared to kanamycin alone. The stria vascularis was severely atrophied and stellate cells in the spiral limbus were missing in kanamycin-furosemide exposed mice while these changes were not observed in mice receiving kanamycin alone. Monocytes and macrophages were recruited in large numbers to the spiral ligament and spiral ganglion in these mice. Combination therapy resulted in a greater number of macrophages in total, and many more macrophages were present further apically when compared to mice given kanamycin alone. Combined kanamycin-furosemide provides an effective method of addressing the relative resistance to ototoxicity that is observed in most mouse strains. As the mouse becomes increasingly more common in studies of hearing loss, and combination therapies gain popularity, recognition of the overall effects of combined aminoglycoside-loop diuretic therapy will be critical to interpretation of the interventions that follow.

Fourteen patients with a Pendred syndrome gene (Pds) mutation and three patients without the mutation were studied to evaluate long-term vestibular and auditory manifestations among patients with bilateral enlarged vestibular aqueducts (EVA). Charts were reviewed retrospectively for age, gender, otological history, presence or absence of vertigo, results of magnetic resonance imaging, relevant gene mutations and perchlorate discharge test. A missense mutation, His 723 Arg (H723R), was identified in the homozygous state in six patients and in the heterozygous state in seven patients. Another missense mutation, Tyr 410 Met (T410 M), was identified in the heterozygous state in one patient. Patients with vertigo tended to have hearing fluctuation, compared with the patients without vertigo. Patients homozygous for H723R tended to have more episodes of vertigo than the heterozygous individuals. Only one patient who was homozygous for H723R had goiter. The long-term outcome of hearing level in patients with the H723R mutation was significantly better compared with published results for patients with a Pds mutation, but not for those with the H723R mutation. Whether environmental factors or a subtype of the Pds mutation H723R are related to the long-term outcome for these patients must be clarified.

The amygdala plays a critical role in emotion. Its functional coupling with the hippocampus and ventromedial prefrontal cortex extending to a portion of the anterior cingulate cortex (ACC) is implicated in anxiogenesis and hypothalamic-pituitary-adrenal (HPA) system regulation. However, it remains unclear how amygdala-centred functional connectivity (FC) affects anxiety and cortisol concentrations in everyday life. Here, we investigate the relationship between daily cortisol concentrations (dCOR) and amygdala-centred FC during emotional processing in forty-one healthy humans. FC analyses revealed that higher dCOR predicted strengthened amygdala-centred FC with the hippocampus and cerebellum, but inhibited FC with the supramarginal gyrus and a perigenual part of the ACC (pgACC) when processing fearful faces (vs. neutral faces). Notably, the strength of amygdala-hippocampus FC mediated the positive relationship between cortisol and anxiety, specifically when the effect of amygdala-pgACC FC, a presumptive neural indicator of emotional control, was taken into account. Individuals with diminished connectivity between the amygdala and pgACC during fear-related processing might be more vulnerable to anxiogenesis as it pertains to greater circulating cortisol levels in everyday life. Individual functional patterns of amygdala-hippocampal-pgACC connectivity might provide a key to understand the complicate link between cortisol and anxiety-related behaviors.