2% ± 21%

n = 6) despite baseline levels (101.2% ± 6.3%) similar to the untreated animals. These results demonstrate that 20 min of visual conditioning is sufficient to increase transcription under control of the BDNF exon IV promoter in an NMDAr-dependent manner in tectal neurons in the intact animal ( Figures 1B and 1C). Next, we tested whether this enhanced BDNF exon IV promoter activity led to a change in BDNF protein levels in the tectum. At 5 hr after visual conditioning, midbrains including the optic tectum, were surgically isolated and homogenized for western blotting. Blots were probed with an antibody that recognizes both the immature and mature forms of BDNF. Visual conditioning led to an increase in the ratio of proBDNF to mBDNF (control: 0.04 ± 0.01, conditioned: 0.26 ± 0.04; Figures selleck 1D and 1E, n = 3 repeats, 5 animals per condition for each experiment). Because the antibody gave several bands, we confirmed the identity

of the BDNF bands by introducing a BDNF antisense Morpholino (BDNF MO) oligonucleotide, 3 MA fluorescently tagged with lissamine rhodamine. At 5 hr postconditioning, brains that had been previously electroporated with the BDNF MO showed reduced expression of proBDNF compared with brains electroporated with a scrambled MO or conditioned animals without MO treatment (Figure 1F, n = 2 experiments, 4-5 animals per experiment). As a retrograde spread of plasticity from the tectum to the eye has been reported (Du et al., 2009), we also assayed proBDNF levels in the eyes of conditioned animals. However, conditioning did not induce a detectable change

in proBDNF levels in the eye (Figure S1 available online). Thus, the activation of the BDNF exon IV promoter by visual conditioning resulted in increased proBDNF protein levels in the tectum. The activity-dependent regulation of BDNF levels is significant, as BDNF has been reported to modulate the susceptibility of synapses to undergo plasticity. In the hippocampus, proBDNF has been shown to facilitate LTD and in Xenopus mBDNF is thought to be required for retinotectal LTP ( Du et al., 2009, Mu and Poo, 2006 and Woo et al., 2005). To determine if the proBDNF synthesized in response to visual conditioning affected old retinotectal plasticity, we first examined the effects of visual conditioning in a plasticity protocol designed to enhance stimulus direction sensitivity of tectal neurons, believed to engage both LTP and LTD at tectal cell synapses ( Engert et al., 2002, Mu and Poo, 2006 and Zhou et al., 2003). To increase proBDNF levels, animals were visually conditioned and then returned to their normal visual environments. At 4–6 hr postconditioning, animals received three bouts of training with a moving bar projected onto the retina. The training bouts were delivered at 4 min intervals. This spaced training protocol is designed to induce direction selectivity in tectal neurons as previously described (Engert et al., 2002 and Zhou et al., 2003). (n.b.