Developmental regulation and adult maintenance of potassium channel proteins (Kv1.1 and Kv1.2) in the cochlear nucleus of the rat

The development and maintenance of the adult expression and distribution of Kv1.1 and Kv1.2, two voltage-dependent potassium channel subunits, were investigated in the anteroventral cochlear nucleus (AVCN) of the rat. Both Kv1.1 and Kv1.2 were found in AVCN neuronal cell bodies at birth, as detected by in situ hybridization and immunocytochemistry. However, Kv1.1 and Kv1.2 were not seen in axons until the end of the third postnatal week. From postnatal day 21 through adulthood, labeling for both potassium channels was in axonal processes, whereas the number of cell bodies labeled for Kv1.1 decreased and there were no cell bodies labeled for Kv1.2. Therefore, these two potassium channel proteins are targeted to their final subcellular destinations in axons well after hearing onset. Once the adult distribution pattern of Kv1.1 and Kv1.2 is attained, its maintenance does not depend on signals from auditory nerve synapses. Eliminating auditory nerve input to the cochlear nucleus by means of bilateral cochleotomy did not change Kv1.1 or Kv1.2 expression or distribution, as seen by in situ hybridization, immunocytochemistry and Western blot. Thus, normal excitatory synaptic input in adult animals is not a requirement to regulate the expression and cellular and subcellular distribution of these potassium channel proteins.