A continuum of response properties across the population of Unipolar Brush Cells in the Dorsal Cochlear Nucleus.

Unipolar brush cells (UBCs) in the cerebellum and dorsal cochlear nucleus (DCN) perform temporal transformations by converting brief mossy-fiber bursts into long-lasting responses. In the cerebellar UBC population, mixing inhibition with graded mGluR 1 -dependent excitation leads to a continuum of temporal responses. In the DCN, it has been thought that mGluR 1 contributes little to mossy-fiber responses, and that there are distinct excitatory and inhibitory UBC subtypes. Here, we investigate UBC response properties using non-invasive cell-attached recordings in the DCN of mice of either sex. We find a continuum of responses to mossy-fiber bursts ranging from: 100 ms excitation, to initial inhibition followed by several seconds of excitation, to inhibition lasting for hundreds of milliseconds. Pharmacological interrogation reveals excitatory responses are primarily mediated by mGluR 1 Thus, UBCs in both the DCN and cerebellum rely on mGluR 1 and have a continuum of response durations. The continuum of responses in the DCN may allow more flexible and efficient temporal processing than can be achieved with distinct excitatory and inhibitory populations. Significance statement: Unipolar brush cells (UBCs) are specialized excitatory interneurons in cerebellar-like structures that greatly prolong the temporal responses of mossy-fiber inputs. They are thought to help cancel out self-generated signals. In the DCN, the prevailing view was that there are two distinct ON and OFF subtypes of UBCs. Here, we show that instead the UBC population has a continuum of response properties. Many cells show suppression and excitation consecutively, and the response durations vary considerably. mGluR1s are crucial in generating a continuum of responses. To understand how UBCs contribute to temporal processing, it is essential to consider the continuous variations of UBC responses, which have advantages over just having opposing ON/OFF subtypes of UBCs.