Structural plasticity underlies experience-dependent functional plasticity of cortical circuits

Abstract

The stabilization of new spines in the barrel cortex is enhanced after whisker trimming, but its relationship to experience-dependent plasticity is unclear. Here we show that in wild-type mice, whisker potentiation and spine stabilization are most pronounced for layer 5 neurons at the border between spared and deprived barrel columns. In homozygote alphaCaMKII-T286A mice, which lack experience-dependent potentiation of responses to spared whiskers, there is no increase in new spine stabilization at the border between barrel columns after whisker trimming. Our data provide a causal link between new spine synapses and plasticity of adult cortical circuits and suggest that alphaCaMKII autophosphorylation plays a role in the stabilization but not formation of new spines.

Figure 1.

Chessboard whisker deprivation and response potentiation. a, Protocol used to induce and record response potentiation in L5 of the barrel cortex. b, Representation of chessboard deprivation with alternating spared and deprived whiskers. c, Average number of spikes measured in response to stimulation of a spared or principal whisker in deprived, border, and spared regions of the barrel field L5. Red columns indicate data from deprived mice. *A significant difference in average spike response to the spared whisker was found for cells in the border between barrels within 50 μm of the septal center (t₍₇₂₎ = −2.71, p < 0.01). The response to principal whisker stimulation in the spared barrel was not affected by deprivation (histogram bars on right).

Figure 2.

In vivo imaging protocol and analysis of new spine formation and stabilization. a, Timeline for imaging and definitions of spine categories. Spines observed during every imaging session were AP (yellow circles and arrows); spines that were first observed on imaging day 8 or thereafter, and were present for the last 8 d of imaging were NP (orange); TN spines (green) include all spines that were first observed between day 8 and 20. b, c, Examples of spine categories in a: b, Images from a WT mouse. c, Images from an αCaMKII-T286A +/+ mouse. Scale bars, 5 μm.

Figure 3.

The growth of new persistent spines is enhanced near the border between spared and deprived barrel columns. a, An overview of L1 apical arbors of L5B neurons imaged in vivo. b, CO-stained tangential section through the L4 barrel field. The arrow points to a GFP-positive apical dendrite of a L5B neuron, corresponding to the left dendritic arbor in a (between barrel D3 and D2). c, The reconstructed L5B neuron placed in a schematic of the barrel field. The apical dendrite travels in the septal column at the border of the two barrels (gray), between spared (white) and deprived (black) barrel columns. d, Coronal view of c. e, The number of total new spines per length of dendrite (TN mm⁻¹) for neurons in different locations within the barrel field. f, The probability that new spines persist after whisker trimming (NP/TN). Each symbol represents a cell. Blue, Untrimmed control; red, trimmed experimental. “Deprived” indicates neurons with apical dendrites that passed through a deprived barrel column in L4 (filled black as in c); “Border,” septal column neurons located within 50 μm of the septal center (filled gray as in c); “Spared,” spared barrel column neurons. Triangles, GFP-M transgenic background only; circles, WT mice from the CaMKII-T286A × GFP-M cross; *p < 0.01.

Figure 4.

Lack of experience-dependent spine stabilization in αCaMKII-T286A mutant mice. All data are from septal column neurons in barrel border regions. a, The number of total new spines per length of dendrite (TN mm⁻¹). b, The probability that new spines persist after whisker trimming (NP/TN). *p < 0.01; ns, nonsignificant.