Visual experience modulates spatio-temporal dynamics of circuit activation

Abstract

Persistent reduction in sensory drive in early development results in multiple plastic changes of different cortical synapses. How these experience-dependent modifications affect the spatio-temporal dynamics of signal propagation in neocortical circuits is poorly understood. Here we demonstrate that brief visual deprivation significantly affects the propagation of electrical signals in the primary visual cortex. The spatio-temporal spread of circuit activation upon direct stimulation of its input layer (Layer 4) is reduced, as is the activation of L2/3 - the main recipient of the output from L4. Our data suggest that the decrease in spatio-temporal activation of L2/3 depends on reduced L4 output, and is not intrinsically generated within L2/3. The data shown here suggest that changes in the synaptic components of the visual cortical circuit result not only in alteration of local integration of excitatory and inhibitory inputs, but also in a significant decrease in overall circuit activation. Furthermore, our data indicate a differential effect of visual deprivation on L4 and L2/3, suggesting that while feedforward activation of L2/3 is reduced, its activation by long range, within layer inputs is unaltered. Thus, brief visual deprivation induces experience-dependent circuit re-organization by modulating not only circuit excitability, but also the spatio-temporal patterns of cortical activation within and between layers.

Keywords: GABA; microcircuitry; signal propagation; synaptic plasticity; visual cortex; visual deprivation.

Figure 1

Similar input/output (I/O) curves for optical signals and LFP. (A) Sample LFP in L2/3. (B) Cumulative I/O plot of LFPs. (C) Pharmacological dissection of LFPs. Black: ACSF; Blue: ACSF + APV; Red: ACSF + APV + DNQX; Green: ACSF + APV + DNQX + Ptx; Purple: ACSF + APV + DNQX + Ptx + TTX. (D) Sample L4 circuit activation at increasing intensities of stimulation. Analysis was done on frames taken 5 ms after stimuli. White box: ROI in L4. (E) Sample time course of the optical signals in the ROI shown in (D). (F) Cumulative I/O plot of the peak optical signals in L4. (G) Pharmacological dissection of the L4 optical signal. Black: ACSF; Blue: ACSF + APV; Red: ACSF + APV + DNQX; Green: ACSF + APV + DNQX + Ptx; Purple: ACSF + APV + DNQX + Ptx + TTX. (H) Sample L2/3 circuit activation at increasing intensities of stimulation. Analysis was done on frames taken 7.5 ms after the stimulus. White box: ROI in Layer 2/3. (I) Sample time course of the optical signal recorded in the ROI in (H). (J) Cumulative I/O plot of the peak optical signal in L2/3. (K) Pharmacological dissection of the L2/3 optical signal. Black: ACSF; Blue: ACSF + APV; Red: ACSF + APV + DNQX; Green: ACSF + APV + DNQX + Ptx; Purple: ACSF + APV + DNQX + Ptx + TTX. The size of the images was cropped to better visualize the activated region (from 88 × 60 to 45 × 50 pixels of 20 μm each).

Figure 2

MD-dependent reduction in cortical activation. (A) Sample LFP at 50 μA in Control (black) and Deprived (gray) slices. The stimulation artifact was cut to better visualize the LFP signal. (B) Cumulative I/O plot of for LFP signals in Control (black) and Deprived (gray) slices. (C) Top: sample frames acquired 5 ms after a 50-μA stimulus in Control and Deprived slices. Bottom: time course of the optical signal in L4 for control (black) and deprived (gray) hemispheres. (D) Cumulative I/O plot of optical signals in control (black) and deprived (gray) hemispheres. (E) Top: sample frames acquired 7.5 ms after a 50-μA stimulus in Control and Deprived slices. Bottom: time course of the optical signal in L2/3 for Control (black) and Deprived (gray) hemispheres. (F) Cumulative I/O plot of the optical signals in control (black) and deprived (gray) hemispheres. The size of the images field was cropped to better visualize the activated region (from 88 × 60 to 45 × 50 pixels of 20 μm each).

Figure 3

Reduced inter-laminar propagation of stimuli. (A) Temporal sequence of optical signals after L4 stimulation in Control (top) and Deprived (bottom) slices. The size of the images field was cropped to better visualize the activated region (from 88 × 60 to 45 × 50 pixels of 20 μm each). Vertical dotted line across the cortical mantle: ROI quantified in (C,D). White square: ROI of the optical signal in (B). The stimulus intensity was 50 μA. (B) Top: time course of optical signals measured in L4 [bottom white squares in (A)]. Black: Control; gray: Deprived. Bottom: Time course of the percent ΔF/F measured in L2/3 [top white squares in (A)] for Control (black) and Deprived (gray) slices. (C) Time course of the percent ΔF/F measured in the ROI indicated by the dotted line in (A). Black: Control; gray: Deprived. Shaded areas: SE for both conditions. Arrows indicate the peak intensity plotted in (D). Dark gray arrowheads indicate the peak activation of L5. (D) Peak percent ΔF/F at the different time points in Control (black) and Deprived (gray). Asterisks indicate significant changes.

Figure 4

MD reduces the extent of intralaminar circuit activation. (A) Representative frames of the time course of optical signals following L4 stimulation in Control and Deprived slices. The size of the imaged field was cropped to visualize the activated region (from 88 × 60 to 45 × 50 pixels of 20 μm each). Dotted lines parallel to the pia: ROIs corresponding in L4 (lower dotted lines) and L2/3 (upper dotted lines). The stimulation intensity was 50 μA. (B) Distribution of the percent ΔF/F in L4 measured in the bottom ROI in (A). TFS: 10 ms. Black: Control; gray: Deprived. Shaded areas: SE for both conditions. (C) Average HMW plot in L4 at different TFS. Black: Control; gray: Deprived. (D) Distribution of the percent ΔF/F in L2/3 at a TFS of 10 ms [top ROI in (A)]. Black: Control; gray: Deprived. Shaded areas: SE. (E) Cumulative HMW plot in L2/3 at different TFS. Black: Control; gray: Deprived.

Figure 5

Changes in L4 and L2/3 activation are correlated. (A) Cumulative bar plot of the ratio between the peak percent ΔF/F (L2/3 versus L4) and width (WL2/3 versus WL4) of L2/3 and L4. Black: Control; gray: Deprived. (B) Distribution of the peak percent ΔF/F of L2/3 plotted against L4 for all intensities of stimulation tested and across all slices. Black: Control; gray: Deprived. (C) Distribution of the HMW in L2/3 and L4 measured at TFS of 2.5, 5 and 10 ms. The stimulation intensity was 50 μA. Black: Control; gray: Deprived. Lines in (B,C) indicate the linear fit of the data. R² are the regression coefficients for Control and Deprived conditions.

Figure 6

MD leaves direct L2/3 activation unaffected. (A) Sample frames of the temporal sequence of optical signals in response to direct stimulation of L2/3 in Control (top frames) and Deprived (bottom frames) conditions. Images show the full field of acquisition (88 × 60 pixels, 20 μm each). White squares: ROIs for optical signal shown in (B). Dotted lines across from the pia to the white matter indicate the ROI for the analysis in (C). Dotted lines parallel to the pia: ROIs for the analysis in (D,E). Stimulation intensity: 50 μA. (B) Time course of the optical signal from the white square ROIs in (A). Black: Control; gray: Deprived. (C) Average peak percent ΔF/F from the ROIs represented by the dotted line across the cortical mantle. Black: Control; gray: Deprived. (D) Distribution of percent ΔF/F from the ROI parallel to the pia. TFS: 10 ms. Black: Control; gray: Deprived. Shaded areas: SE. (E) Cumulative bar plot of the peak percent ΔF/F within L2/3 at different TFSs. Black: Control; gray: Deprived.

Figure 7

Potentiation of inhibition as a mechanism for the MD-induced decrease in circuit activation. (A) Synaptic components of the optical signal measured in ROIs of 2 × 2 pixels within L4 in control and deprived hemispheres. Top left: optical signal in ACSF; top right: NMDA components of the optical signal; bottom left: AMPA components and bottom right: GABA_A components. Black: Control; Gray: Deprived. (B) Cumulative bar plot of the AMPA, NMDA, and GABA_A components of the optical signals. Control (black) and Deprived (gray). (C) Synaptic components of the optical signal were quantified in ROIs of 2 × 2 pixels in L2/3 from control and deprived hemispheres. Top left: optical signal in ACSF; top right: NMDA components of the optical signal; bottom left: AMPA components and bottom right: GABA_A components. Black: Control; Gray: Deprived. (D) Cumulative bar plot of the AMPA, NMDA and GABA_A components of the optical signal. Control (black) and Deprived (gray). Stimulation intensity: 50 μA. Asterisk indicates significant changes.

Figure 8

MD increases the GABA_A synaptic component measured intracellularly. (A) Sample evoked IPSCs recorded in voltage clamp in response to extracellular stimulation in L4. Black: Control; gray: Deprived. (B) Cumulative bar plot of the average IPSC amplitude. Black: Control; gray: Deprived. Asterisk indicates significant changes.

Figure 9

Partial blockade of GABA_A-mediated inhibition rescues Deprived spatio-temporal patterns of activation. (A) Sample optical responses from L4 in Control and Deprived slices in the presence of increasing concentrations of Ptx. Control, Black: ACSF; Blue: 5 μm Ptx. Deprived, Gray: ACSF; Blue: 5 μm Ptx. The dotted line indicates the amplitude of the optical signal measured in ACSF in Control. (B) Cumulative bar plot of the average peak L4 optical signals in Control (black), Control in the presence of 5 μM Ptx (White/blue line), Deprived (gray) and Deprived in the presence of 5 μM Ptx (blue). (C) Sample optical responses from L2/3 in Control and Deprived slices. Control, Black: ACSF; Blue: 5 μM Ptx. Deprived, Gray: ACSF; Blue: 5 μm Ptx. Notice the full recovery of the signal in L2/3 after partial blockade of inhibition (dotted line). (D) Cumulative bar plot showing the average amplitude of L4 optical signals in Control (black), Control in the presence of 5 μM Ptx (White/blue line), Deprived (gray) and Deprived in the presence of 5 μM Ptx (blue). Asterisks indicate significant differences.