Formation of neural plasticity differentially regulates the integration of new neurons into the activated circuit.

<p>(<b>A</b>) LTP induction at the no-spine stage of new neurons (12 dpi) specifically increases their spine size and spine expression rate within the LTP-induced layer by 3 (19 dpi) and 4 weeks of neuronal age (28 dpi), respectively. (<b>B</b>) LTP induction at the time of initial spinogenesis of new neurons (16 dpi) locally inhibits the later expression of spines in an LTP-induced layer-specific manner. (<b>C</b>) LTP induction after the drastic spinogenesis stage of new neurons, at 21 dpi, induced their later spine enlargement in the LTP-induced layer at 28 dpi. The spine enlargement is return to basal level, and the later spinogenesis is inhibited by 35 dpi. All LTP-mediated changes are tightly correlated with actual formation of the activity-dependent neural plasticity. <b>Left,</b> Schematic representation of morphology of each new neurons at 12, 16, or 21 days after birth ( = 12, 16, or 21 dpi, respectively). High frequency stimulation [HFS(500)] for LTP induction is specifically delivered at MML of ipsilateral hemisphere in all experiments of present study. <b>Middle,</b> The mean values of spine density at indicated timing under control and LTP-induced conditions are plotted by white (represented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045270#pone-0045270-g001" target="_blank">Figure 1F</a>) and black circles, respectively. <b>Right,</b> Graph shows the mean values of ipsilateral (Ipsi)/contralateral (Contra) ratio of spine cross-sectional area in MML and OML. Abbreviations: GCL, granule cell layer; IML, MML, and OML, inner, middle, and outer molecular layer, respectively.