Age-related changes in cochlear vascular conductance in mice

Vascular changes contribute to age-related hearing loss but the mechanisms involved in microvascular reactivity, particularly in the aged ear, are still incompletely understood. In this study, possible age-related changes in cochlear blood flow (CBF) and vascular reactivity were studied in presbycusic mice (C57BL/6) and young, age-matched, and old controls (CBA/J) without presbycusis. Reactivity was monitored by laser Doppler flowmetry and assessed by change in cochlear vascular conductance (VC) (defined as the ratio of CBF to blood pressure) in response to round window-applied sodium nitroprusside, a vasodilating agent. Mean VC response of C57BL/6 mice differed from controls both in maximum response and in post-drug recovery time. In C57BL/6 mice, mean VC increased about 28%, in contrast to an increase of over 40% in young and age-matched CBA/J controls. A less elevated VC response, similar to that of the presbycusic mice, was shown by aged (20-21 month) controls. Also, VC response in C57BL/6 mice was sustained throughout the 60 min observation period, while response of most CBA/J controls recovered in 50 min or less. These changes suggest age-dependent, pathologically-related altered responsiveness in cochlear vascular reactivity.