Figure 3.

Differences between principal olive (PO) and Dorsal cap of Kooy (DCK) neurons. (A) Drawing lf brain slice showing climbing fiber projection (red) of DCK neurons to the contralateral cerebellar flocculus, and afferent GABAergic input (green) to the DCK from the bilateral prepositus hypoglossi nuclei. (B–D) Effect of membrane potential on DCK and PO firing (in same slice). (B) Recordings from DCK neuron showing increased firing frequency with membrane potential. Each action potential is followed by a large, long-lasting afterhyperpolarization. (Action potentials were truncated and recorded with a high-potassium intracellular solution) (C) Patch recordings from a PO neuron showing subthreshold oscillations at the same membrane potentials as in (A) Amplitude increased, but frequency was unchanged. (D) Representative currents in DCK and PO neurons (in response to 100-ms depolarizing square pulses recorded by using a high-potassium electrode solution). Inward currents were followed by a small outward current in PO neurons while the same depolarizing square pulses activated a strong outward current in DCK neurons. (E) I–V curve for cells in panel (D). (F) DCK neurons had a single current peak near a membrane potential of −20 mV that was blocked by ω-Agatoxin-TK (a specific P/Q calcium channel blocker). (G) In the PO cells, two inward components, peaking near −20 and −10 mV were seen. The second component was reduced by application of ω-Agatoxin-TK and further reduced by application of ω-Conotoxin-GVIA (a specific N-type calcium channel blocker). Thus, the inward calcium currents of DCK neurons were mediated only by P/Q-type channels, while both P/Q-type and N-type channels are present in PO neurons. Fl, flocc; Pfl, paraflocculus; PHN, prepositus hypoglossi nuclei. (Modified from Urbano et al., 2006).