) Thirty minutes to two hours after GSI-IX training, the compound synaptic current (CSC) elicited by a bar moving in each of the four cardinal directions was measured in whole cell voltage clamp recordings

of tectal neurons. The response to each direction was normalized to the average response across all four directions. A schematic of the experimental timeline is shown in Figure 2A. Cells from conditioned animals (n = 14) developed a significant preference for the bar moving in the trained direction (untrained: 91.6% ± 7.4% versus trained: 143% ± 18.74%). On the other hand, cells from the group that had not been conditioned (untrained: 100.7% ± 6.6% versus trained: 109% ± 12.9%, n = 12), or conditioned

cells with BDNF MO knockdown (untrained: Rigosertib cost 100.5% ± 8.2% versus trained: 95.9% ± 10.7%, n = 11) did not exhibit significant direction training for the entire population of neurons studied (Figures 2B and 2C). The slight increase in sensitivity to the trained direction observed in the nonconditioned group is comparable to that previously reported by Zhou et al. (2003). In that study, an approximate 25% change was observed in 12 out of 25 cells. There was no significant difference between cells from animals that had not been electroporated (n = 8) and those that had been electroporated with the scrambled MO (n = 4). These groups were therefore combined. These results suggest that the upregulation of proBDNF induced by prior visual conditioning facilitated a change in direction sensitivity in tectal neurons. As plasticity of direction sensitivity in these neurons is thought to involve the induction of LTD and LTP (Mu and Poo, Megestrol Acetate 2006), we next examined how conditioning may have impacted retinotectal synaptic plasticity. Although spike-timing-dependent LTP and LTD have been proposed as possible

mechanisms underlying the induction of direction selectivity at the retinotectal synapse (Engert et al., 2002, Mu and Poo, 2006 and Vislay-Meltzer et al., 2006), we instead used a synaptic pairing protocol (holding −35 mV, 300 pulses at 1 Hz) to induce LTD in this study. This protocol was selected because the sensitivity of the retinotectal synapse to spike-timing protocols has been shown to be greatly reduced by the stage of development used in this study (Tsui et al., 2010). In nonconditioned animals, pairing depolarization of the tectal neuron with repeated electrical stimulation at the optic chiasm induced a transient depression of retinotectal α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type glutamatergic excitatory postsynaptic current (EPSC) amplitudes that recovered (100.6% ± 5.8% of baseline before induction) around 20 min after stimulation (Figures 3A and 3B).