Development of precise maps in visual cortex requires patterned spontaneous activity in the retina

Abstract

The visual cortex is organized into retinotopic maps that preserve an orderly representation of the visual world, achieved by topographically precise inputs from the lateral geniculate nucleus. We show here that geniculocortical mapping is imprecise when the waves of spontaneous activity in the retina during the first postnatal week are disrupted genetically. This anatomical mapping defect is present by postnatal day 8 and has functional consequences, as revealed by optical imaging and microelectrode recording in adults. Pharmacological disruption of these retinal waves during the first week phenocopies the mapping defect, confirming both the site and the timing of the disruption in neural activity responsible for the defect. Analysis shows that the geniculocortical miswiring is not a trivial or necessary consequence of the retinogeniculate defect. Our findings demonstrate that disrupting early spontaneous activity in the eye alters thalamic connections to the cortex.

Figure 1. Topographically Precise Mapping of Geniculocortical Projections in WT Mice

(A) Visual stimuli used to assess cortical retinotopy. The monitor was placed as indicated in the left panel, contralateral to the hemisphere under study. Stimuli were thin moving bars (middle and right panels). Elevation and azimuth maps were obtained by stimulating the animal with bars moving vertically and horizontally, respectively. The position on the monitor that drove each site on the cortex is color-coded, as shown next to the monitors in the middle and right panels. (B) Cortical vasculature pattern in the region being imaged and retinotopic maps of a WT mouse. The two colored dots indicate the locations where retrograde markers of corresponding colors were injected under the guidance of functional retinotopic maps. In the maps, the position of the visual field is represented by color according to the color scales in (A), and the response magnitude, by lightness. (C) A coronal section of the injection sites. (D) Retrogradely labeled neurons in the dLGN of this mouse. Four continuous coronal sections (100 μm thick) from rostral (left) to caudal (right) are shown. Dotted lines mark the border of the dLGN.

Figure 2. Point-to-Point Mapping of Geniculocortical Projection Is Imprecise in β2^−/− Mice

(A) Retrogradely labeled neurons in the dLGN of a β2^+/− mouse. Green neurons (left panel), red neurons (middle), and overlay of the two (right) are shown. (B) Retrogradely labeled geniculate neurons at a similar level of a coronal section in a β2^−/− mouse. Note the larger labeled areas and overlap of the two colors in the β2^−/− dLGN compared to those in the β2^+/−. (C) Quantification of retrogradely labeled areas in the dLGN. The percentage of labeled pixels was plotted as a function of the distance from the center of all of the labeled pixels. Each curve represents the average of one animal, with black curves from controls (both WTs and β2^+/−) and red curves from β2^−/−. Clear separation between controls and β2^−/− is evident. (D) The dispersion, the distance within which 80% of the labeled pixels are included, is plotted against the size of the injection site. The injections in the β2^−/− mice were similar in size to those in the controls, and labeled areas in the dLGN were significantly larger (p < 0.0001) in β2^−/− mice (134 ± 4μm) compared with those in the controls (90 ± 5μm).

Figure 3. Cortical Retinotopic Maps Are Defective in β2^−/− Mice

(A) Color code used to represent positions of different elevation lines on the stimulus monitor (top panel) and gray scale for response amplitude as fractional change in reflection × 10⁴ (bottom panel). (B) Elevation map of a β2^+/− mouse. Both retinotopy (top panel) and response magnitude (bottom panel) are shown. (C) Elevation map of a β2^−/− mouse. (D) The color code and gray scale for plotting azimuth maps. (E and F) Azimuth maps of the β2^+/− and the β2^−/− mouse. Note that the β2^−/− retinotopy is more scattered and the response magnitude is weaker compared to those seen in the maps of β2^+/−. (G–J) Quantification of cortical map defects in β2^−/− mice. Compared to those of WT mice (n = 6), the β2^+/− cortical maps (n = 5) are normal in terms of map quality (panels G and I: p = 0.77 for elevation; p = 0.38 for azimuth) and magnitude (panels H and J: p = 0.97 for elevation; p = 0.35 for azimuth). In contrast, the cortical maps of β2^−/− (n = 14) are of lower quality (p < 0. 05 for elevation; p < 0.001 for azimuth) and weaker (p < 0.05 for elevation; p < 0.0001 for azimuth). Error bars represent the mean ± SEM.

Figure 4. Precise Receptive Field Organization of Cortical Neurons Is Disrupted in β2^−/− Mice

(A–C) An example of cortical spiking responses to a moving bar. (A) Each trial lasted 4.5 s. For the first 3 s, the bar swept across the stimulus monitor at a speed of 25 deg/sec. (B) Raster plots of recorded spikes for 20 repeated trials of the stimulus with the bar moving from left to right. These trials were randomly interleaved by stimuli moving in other directions: right-to-left, down-to-up, and up-to-down. (C) The PSTH of the response constructed from the 20 repeats, from which the response timing in relation to the stimulus, thus the RF location, was computed. (D and E) Deviations of RF location of all recording sites from the mean RF location of individual penetrations are plotted as the function of recording depth for stimulus with vertically and horizontally moving bars. The β2^−/− mice display a much larger scatter of RF position for both elevation and azimuth. (F and G) Cumulative probability plots of RF deviations for elevation and azimuth. In both, the β2^−/− data are significantly different from those for the β2^+/− controls.

Figure 5. Cortical Retinotopic Maps Are More Defective than Subcortical Maps in β2^−/− Mice

(A and B) Azimuth maps of subcortical visual areas of a WT (A) and a β2^−/− mouse (B). The areas of SC and LGN are circled and labeled. Note that the dLGN map of the β2^−/− mouse is no worse in quality than that of WT. Inset shows color scale for plotting maps. (C) Scatter of cortical azimuth maps plotted against that of SC maps for individual animals. Note that the cortical maps of β2^−/− mice are very much more scattered than their SC maps, in contrast to WT mice in which maps of the two areas were comparable.

Figure 6. Pharmacologically Blocking Retinal Waves Disrupts the Precise Mapping of Geniculocortical Projections

(A) Retinal waves recorded with a multielectrode array. Spike trains of four representative neurons in a P4 WT retina are shown. A diagram of the array is shown to the left with colored circles representing the position of the four electrodes from which the spikes were recorded. One episode of the wave is shown in a finer time scale to display the details of the bursts. (B) Spike trains of the same four neurons are shown after perfusion with 10 nM epibatidine. The patterns of retinal activity were clearly altered. (C) Disruption of correlated spontaneous activity by epibatidine. Correlation index between retinal neurons as a function of distance between the recording electrodes. The distance-dependent correlation evident in the saline is absent in epibatidine. Error bars represent the mean ± SEM. (D) Retrogradely labeled neurons in a dLGN section of a WT mouse that has been binocularly injected with epibatidine at P1, P3, P5, and P7. Dotted lines mark the border of the dLGN. (E) dLGN section of a control mouse injected with saline at the same ages. (F) The distance within which 80% of the labeled pixels were included is plotted against the injection size. Labeled areas in the dLGN were significantly larger (p < 0.001) in epibatidine-treated mice (107 ± 4μm) than in the saline-treated controls (81 ± 4μm).

Figure 7. Geniculocortical Mapping Defect in β2^−/− Mice Is Present by P8

(A and B) Retrogradely labeled neurons in the dLGN of P8 WT (A) and P8 β2^−/− (B). Dotted lines mark the border of dLGN. (C) Quantification of retrogradely labeled areas in the dLGN. The label dispersion was plotted against the injection size. The labeled areas were significantly larger in the β2^−/− mice (p < 0.01). (D) Quantification of labeled dLGN areas in normal and enucleated β2^+/± (WT and heterozygous) and β2^−/− mice. BE-P8 (P1), binocularly enucleated at P8 (P1).

Figure 8. Retinotopic Mapping Diagrams from Retina to Cortex

(A) Topographically precise mapping of retinogeniculate and geniculocortical projections in WT mice. Color represents the range of visual field positions from nasal to temporal driving cells in retina, dLGN, and visual cortex (Vctx). Shown to the left is an episode of traveling retinal waves. (B) Three hypothetical scenarios of geniculocortical mapping when the normal activity patterns in the developing retina are disrupted, altering retinogeniculate connections. 1. normal map: geniculocortical connections do not depend on retinal activity; 2. corrected map: geniculocortical connections rearrange to compensate for retinogeniculate miswiring; 3. miswired map: geniculocortical connections are independently defective. Results demonstrate that the scenario shown in B3 is true (see Discussion).