Expression of the Kv3.1 potassium channel in the avian auditory brainstem

The Shaw-like potassium channel Kv3.1, a delayed rectifier with a high thre shold of activation, is expressed in the time coding nuclei of the bird aud itory brainstem. In both barn owls and chickens, Kv3.1 mRNA was expressed i n the cochlear nucleus magnocellularis (NM) and the nucleus laminaris (NL). Western blot analysis showed that an antibody raised against the synthetic peptide sequence of rat Kv3.1 (rKv3.1) specifically recognized the same 92 kDa protein bands in both rat and chicken synaptosomal preparations. Immun ohistochemical analyses using this anti-rKv3.1 antibody revealed a prominen t gradient in Kv3.1 immunoreactivity along the tonotopic axis of the barn o wl NM and NL and a less prominent gradient in the chicken. The precise loca lization of the Kv3.1 immunoproduct was resolved by electron microscopy. In both the owl and the chicken, Kv3.1 was targeted postsynaptically in NM an d NL. The major difference in localization of Kv3.1 protein between the two birds was the expression of Kv3.1 in the NM axons and terminals in the reg ion of the barn owl NL. This location of Kv3.1 channels supports its postul ated function in reducing the width of action potentials as they invade the presynaptic terminal. The presynaptic localization may be a specialization for enabling neurons in owl NM to transmit high-frequency temporal informa tion with little jitter.