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The standard view of the mechanisms underlying learning is that they involve strengthening or weakening synaptic connections. Learned response timing is thought to combine such plasticity with temporally patterned inputs to the neuron. We show here that a cerebellar Purkinje cell in a ferret can learn to respond to a specific input with a temporal pattern of activity consisting of temporally specific increases and decreases in firing over hundreds of milliseconds without a temporally patterned input. Training Purkinje cells with direct stimulation of immediate afferents, the parallel fibers, and pharmacological blocking of interneurons shows that the timing mechanism is intrinsic to the cell itself. Purkinje cells can learn to respond not only with increased or decreased firing but also with an adaptively timed activity pattern.cerebellum | eyeblink conditioning | temporal control | glutamate transmission

In addition to proton-pumping complex I, plant mitochondria contain several type II NAD(P)H dehydrogenases in the electron transport chain. The extra enzymes allow the nonenergy-conserving electron transfer from cytoplasmic and matrix NAD(P)H to ubiquinone. We have investigated the type II NAD(P)H dehydrogenase gene families in Arabidopsis. This model plant contains two and four genes closely related to potato (Solanum tuberosum) genes nda1 and ndb1, respectively. A novel homolog, termed ndc1, with a lower but significant similarity to potato nda1 and ndb1, is also present. All genes are expressed in several organs of the plant. Among the nda genes, expression of nda1, but not nda2, is dependent on light and circadian regulation, suggesting separate roles in photosynthesis-associated and other respiratory NADH oxidation. Genes from all three gene families encode proteins exclusively targeted to mitochondria, as revealed by expression of green fluorescent fusion proteins and by western blotting of fractionated cells. Phylogenetic analysis indicates that ndc1 affiliates with cyanobacterial type II NADH dehydrogenase genes, suggesting that this gene entered the eukaryotic cell via the chloroplast progenitor. The ndc1 should then have been transferred to the nucleus and acquired a signal for mitochondrial targeting of the protein product. Although they are of different origin, the nda, ndb, and ndc genes carry an identical intron position.Plant and fungal mitochondria have highly branched electron transport chains. The protonpumping respiratory complexes I, III, and IV work to a varying extent in parallel with non-protonpumping enzymes, i.e. type II NAD(P)H dehydrogenases and alternative oxidase. Thus, the coupling of electron transport to ATP formation varies depending on the electron path (Siedow and Umbach, 1995;Joseph-Horne et al., 2001).Complex I, the proton-pumping (type I) NAD(P)H dehydrogenase, is a multisubunit enzyme that is inhibited by rotenone in most organisms. It is present in ␣-proteobacteria and mitochondria of all eukaryotes except fermenting yeasts e.g. Saccharomyces cerevisiae. A homologous complex with unclear enzymatic properties is also present in chloroplasts (Yagi, 1991;Friedrich et al., 1995;Rasmusson et al., 1998).Type II, or rotenone-insensitive, NAD(P)H dehydrogenases have been found in several bacterial species and in plant and fungal mitochondria. The most studied enzymes, Escherichia coli NDH and S. cerevisiae NDI1, are FAD-containing single-polypeptide enzymes of 45 to 50 kD de Vries and Grivell, 1988). The S. cerevisiae NDI1 is located on the inner surface of the inner mitochondrial membrane, where it catalyzes the oxidation of matrix NADH (de Vries et al., 1992). Two homologous S. cerevisiae proteins, NDE1 and NDE2, are located on the external side of the inner membrane, where they oxidize cytoplasmic NADH (Luttik et al., 1998;Small and McAlister-Henn, 1998). An NADPHspecific type II dehydrogenase, NDE1, is present on the external surface of the inner membrane of Neurospora crassa ...