Aberrant development and plasticity of excitatory visual cortical networks in the absence of cpg15

Abstract

During development, experience plays a crucial role in sculpting neuronal connections. Patterned neural activity guides formation of functional neural circuits through the selective stabilization of some synapses and the pruning of others. Activity-regulated factors are fundamental to this process, but their roles in synapse stabilization and maturation is still poorly understood. CPG15, encoded by the activity-regulated gene candidate plasticity gene 15, is a small, glycosylphosphatidylinositol (GPI)-linked, extracellular protein that promotes synapse stabilization. Here we show that global knock-out of cpg15 results in abnormal postnatal development of the excitatory network in visual cortex and an associated disruption in development of visual receptive field properties. In addition, whereas repeated stimulation induced potentiation and depression in wild-type mice, the depression was slower in cpg15 knock-out mice, suggesting impairment in short-term depression-like mechanisms. These findings establish the requirement for cpg15 in activity-dependent development of the visual system and demonstrate the importance of timely excitatory network development for normal visual function.

Keywords: depression; plasticity; potentiation; visual cortex.

Figure 1.

Abnormal growth of L2/3 pyramidal neuron basal dendrites in cpg15 KO mice. A, Example of a diolistically labeled neuron in slice (left) and after tracing (right) from a P14 mouse. B, Average number of primary dendrites per neuron. C, Total length of basal dendrites in KO and WT littermates. D–F, Scholl analysis of basal dendrites at P10 (D), P14 (E), and P28 (F). P10, n = 24 WT and KO cells; P14, n = 23 WT cells and n = 21 KO cells; P28, n = 22 WT cells and n = 25 KO cells. **p < 0.01; ***p < 0.001, Kruskal–Wallis with Dunn's post-test.

Figure 2.

Reduced mEPSC amplitudes and frequencies in cpg15 KO mice associated with reduced mushroom spine density. A, Examples of whole-cell patch-clamp mEPSC recordings from neurons of KO and WT littermates. B, Cumulative distribution of mEPSC amplitudes. C, Average mEPSC amplitudes. D, Cumulative distribution of mEPSC interevent intervals. E, Average mEPSC frequencies (P10, n = 14 WT cells and n = 15 KO cells; P14, n = 17 WT and KO cells; P28, n = 13 WT cells and n = 14 KO cells; Mann–Whitney U test, *p < 0.05 and **p < 0.01). F, Representative images of spines on basal dendrites from L2/3 pyramidal neurons. G, Quantification of total spine density [n = 10 cells (1124 spines) in WT and n = 9 cells (726 spines) in KO] and classification as thin, stubby, or mushroom at P28 (t test, *p < 0.05).

Figure 3.

Visual responses and development of receptive field properties in cpg15 KO mice. A, Representative WT and KO cumulative histograms of spikes in response to 12 orientated gratings or a uniform gray stimulus at P28–P32. B–E, Averages of spontaneous activity (B), maximal evoked response (C), signal-to-noise ratio (D), and coefficient of variation (E) (WT, n = 24 and 36 cells; KO, n = 43 and 37 cells at P28–P32 and adult, respectively). F, Cumulative percentage of cells and average OSI. G, Cumulative percentage of cells and average DSI among cells tuned for the orientation. *p < 0.05; **p < 0.01; ***p < 0.001, Kruskal–Wallis with Dunn's post-test.

Figure 4.

In vivo rapid adaptation to repeated stimulation is disrupted in cpg15 KO mice. A, Experimental design and representative WT spike trains at P28–P32. B, Percentage of cells (D, cell with depression; P, cell with potentiation; =, no modification). C, Time-course responses of cells from WT and KO mice displaying an increase to repeated stimulation (*p < 0.05; **p < 0.01; ***p < 0.001, Friedman test and Dunn's post-test). D, Time-course responses of cells displaying a decrease to repeated stimulation (Friedman test and Dunn's post-test; WT, *p < 0.05, **p < 0.01, ***p < 0.001; KO, ^ϕp < 0.05, ^ϕϕp < 0.01). E, F, Average of the slope calculated over 100 stimulations (E) and the 40 first stimulations (F) (*p < 0.05; **p < 0.01, Kruskal-Wallis with Dunn's post-test). Cells with potentiation: n = 10 in WT and 9 in KO at P28–P32; n = 4 in adult KO. Cells with depression: n = 7 in WT and KO at P28–P32; n = 13 in WT and 6 in KO at adulthood.