Figure 1.

Ascending axon synapses to Purkinje cells are resistant to long-term depression. a, The positioning of stimulating and recording electrodes in the granule cell and molecular layers for selective activation of ascending axon and parallel fiber synapses to Purkinje cells is shown. The effects of conjunctive activation of the CF input with parallel fiber (b) and ascending axon (c) pathway stimulation are shown. d and e illustrate the effects of 1 Hz raised intensity stimulation (1 Hz RIS) applied to the parallel fiber (n = 10) and ascending axon pathways (n = 8), respectively. The means and SEs are shown. Shown superimposed above are the means of six consecutive sweeps sampled before (darker traces) and 20 min after (lighter traces) the period of 1 Hz RIS for each pathway. Responses to parallel fiber activation are shown on the lefthand side and ascending axon responses are shown to the right. f shows the relative changes in CV⁻² values plotted against relative changes in mean EPSC amplitudes for each pathway with SEs before and 20 min after climbing fiber-independent LTD. Square symbols represent time-matched control data in which both pathways were activated alternately at 0.2 Hz throughout. g, The means and SEs of parallel fiber (gray) and ascending axon pathway EPSC amplitudes (black) sampled 30 min after control stimulation are shown, along with those after pairing each pathway with the climbing fiber input or after presentation of the climbing fiber-independent LTD protocol. The asterisks indicate significant differences between pathways (Wilcoxon matched pairs test; p < 0.05). Each data set represents a minimum of six separate experiments. In all panels, gray and black hues represent parallel fiber and ascending axon responses, respectively. Closed circles indicate when the conjunctive stimulation was applied to the parallel fiber pathway, and closed triangles represent the ascending axon pathway. bl, Baseline; aa, ascending axon; cf, climbing fiber; pf, parallel fiber.