Age-related hearing loss (AHL) is the most prevalent sensory disorder in our population, reducing quality of life for millions of sufferers. The mechanisms underlying its development are not understood. There is some evidence that AHL may be preceded by a loss of function in the feedback loop which regulates auditory sensitivity via the medial olivocochlear system (MOC) (Zhu et al., 2007). These cells send a cholinergic projection to the outer hair cells of the cochlea, which regulate the gain and sensitivity of this sensory organ. In mice, the MOC neurons reside predominantly in the ventral nucleus of the trapezoid body (VNTB). This project compares VNTB neurons in two strains of mice: the C57BL/6 which demonstrates AHL from a young age and the CBA/Ca which maintains good auditory thresholds into old age. The VNTB expresses the slow delayed rectifier Kv2.2. It was postulated that differences in the expression of Kv2.2 over time may contribute to the differential progression of AHL between the strains. Mice (P8-190) were killed by decapitation in accordance with the UK Animals (Scientific Procedures) Act 1986. Immunohistochemistry (males, CBA n=3, C57 n=3) showed no difference in the expression of Kv2.2 between these strains by the age of 6 months. Whole cell voltage clamp from VNTB neurons (recorded from in vitro brainstem slices at 37°C) indicate that before hearing onset (P8 to P10) there was no significant difference (independent samples t-test) between C57 and CBA strains in the magnitude of peak outward currents (mean current ± S.E.M.). Peak currents (+60mV): CBA: 20.87± 5.84nA (n=7), C57: 18.72 ± 5.58nA (n=7). However, after hearing onset (P14 to P17) C57 VNTB neurons had greater low voltage-activated (LVA) currents than those of the CBA. Peak amplitude of outward currents in response to depolarising steps from -90mV to -30mV were: 14.73 ±12.48nA (CBA n=4) and 25.66 ± 8.25nA (C57 n=5). These preliminary data indicate differences in VNTB neuronal excitability may develop rapidly following hearing onset, which may influence later development of hearing loss.