Hyperpolarization-activated (I) currents in auditory brainstem neurons of normal and congenitally deaf mice

We have investigated the membrane properties of brainstem auditory neurons in a mouse model of congenital deafness (dn/dn). Whole-cell recordings were made from visualized neurons in slices of the medial nucleus of the trapezoid body (MNTB) and anteroventral cochlear nucleus (AVCN). We have recently demonstrated that MNTB neurons in deaf mice are more excitable than in normal mice, due in part to a reduced expression of low-threshold potassium currents. In this study, we have examined the contribution of hyperpolarization-activated (Ih) channels to the membrane properties of MNTB and AVCN neurons. Our results show that Ih is larger in MNTB neurons from deaf mice than in normal mice. In contrast, no significant differences were found in Ih or excitability between AVCN bushy cells from dn/dn and normal mice. Experimental evidence and neuronal modelling suggests that, in the MNTB of normal mice, a small contribution of Ih helps to reduce temporal summation of synaptic potentials. A larger Ih in neurons from deaf mice has a much greater effect in reducing temporal summation of synaptic potentials, counteracting to some extent the greater excitability of these cells. Our results provide further insight into the role of activity during development in regulating the membrane and firing properties of central neurons.