Ocular dominance plasticity in mouse visual cortex is age-dependent.

<p>Representative experiments of animals in all four age groups studied (PD25, PD95, PD130 and PD215) are displayed. Optical imaging maps of responses to the ipsi- and contralateral eye in the binocular region of mouse visual cortex in both control animals (left column: a, c, e, g) and monocularly deprived animals (right column: b, d, f, h) are shown. Both colour-coded polar maps of retinotopy (top) and grey-scale coded response magnitude maps (below) are illustrated. For each experiment, the histogram of ocular dominance scores, the average ocular dominance index (ODI) and the corresponding 2-D ocular dominance maps (ODI values colour-coded according to the scheme shown in the lower right corner of the figure: blue represents negative, red positive values) is included. Note that in control animals of all ages, activity patches evoked by the stimulation of the contralateral eye were consistently darker than those after stimulation of the ipsilateral eye (a, c, e, g) and that 2-D ocular dominance maps are red and yellow indicating contralateral dominance. In contrast, monocular deprivation for 4 days in PD25 animals (b) or for 7 days in PD95 animals (d) induced a significant ocular dominance shift so that the response magnitude maps of both ipsi- (open) and contralateral (deprived) eye are now equally dark, the histograms of ocular dominance scores shift to the left (compare a to b and c to d) and colder colours prevail in the 2-D ocular dominance maps. In the two older animal groups, PD130 and PD215 mice, monocular deprivation for 7 days (f) or 14 days (h) fail to induce ocular dominance shifts and both histograms of ocular dominance scores and 2-D ocular dominance maps are similar to control animals (compare e to f and g to h). The scale bar is 1 mm and applies to all panels showing maps. Abbreviations: MD = monocular deprivation, OD = ocular dominance, contra = contralateral eye, ipsi = ipsilateral eye.</p

Enhancement of vision after monocular deprivation declines with age.

<p>Visual acuity of the animals was analyzed using a virtual optomotor system (Prusky et al., 2004). During 7 days of monocular deprivation and daily testing, spatial frequency selectivity of the optokinetic response of the nondeprived (open) eye increased from 0.39 cyc/deg to approximately 0.52 cyc/deg. While interocular plasticity was present in all analyzed age groups, it was significantly stronger in PD95 compared to PD130 and PD215 animals (p<0.01 and p<0.001), and in PD25 animals compared to PD215 animals (p<0.01, Bonferroni post hoc).</p

Decline of ocular dominance plasticity after monocular deprivation in animals older than 110 days of age.

<p>ODIs of control and monocularly deprived animals of all age groups. A positive ODI indicates dominance of the contralateral eye, a negative ODI ipsilateral dominance. Symbols represent ODI values of individual animals; means are marked by the thick horizontal lines. Circles represent values obtained from control animals, triangles, squares and diamonds values of animals after 4 days (4d), 7 days (7d) and 14 days (14d) monocular deprivation, respectively. Note that four days of monocular deprivation in PD25 and 7 days of monocular deprivation in PD95 animals induced a significant ocular dominance shift towards the open eye (p<0.001 and p<0.01, respectively, Bonferroni-corrected t-test). In both PD130 and PD215 animals, monocular deprivation has no such effect. In addition, the ODI of PD95 animals after 7 days of monocular deprivation was significantly different from the ODIs of PD130 and PD215 animals after the same deprivation period (p<0.05 and p<0.01, respectively, Bonferroni-corrected t-test).</p

Quantitative analyses of the effect of muscimol- and control PBS-injection on V1-activation.

<p>Data of the the injected (left) and non-injected (right) V1 are shown. (A, B) Muscimol reliably blocked both ipsilateral (A) and contralateral eye evoked activity in the left V1 (B), reduced ipsilateral but not contralateral eye evoked V1-activity in the right V1 (C, D), while PBS-injection in a control group of animals had no significant effect (E–H). Evoked responses shown as line plots from single animals (top; each line represents data from one animal before/after the muscimol- or PBS-injection, p of paired t-tests are given), bar plots with group averages (middle plots) and mediolateral profiles (bottom plots, X-axis in 150 pixels equaling 3600 µm) before (black) and after injection (red).</p

AFI-recordings yield higher magnitude activity maps after craniotomy in V1 of mice compared to OIS.

<p>Data displayed as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085225#pone-0085225-g001" target="_blank">Figure 1</a>. Schematic diagram of the visual stimulation condition showing the mouse and the stimulus monitor (A,B). As observed in the visual wulst of zebra finches, activity maps (open arrows in E,F) recorded with AFI had higher amplitude and retinotopic maps had lower map scatter compared to OIS. In addition, blood vessel artifacts (labelled by the arrowheads) were reduced in AFI-recordings (compare Figs. 3C and D). Scale bar <b> = </b>1 mm.</p

Transferring enriched environment-mice to standard cages (SCs) immediately abolished ocular dominance-plasticity.

<p>Intrinsic signal imaging of V1-activation in EE→SC-mice after MD, and its quantification. MD was induced after 1 day (1d) or one week (1w) in SC. Layout and data display as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186999#pone.0186999.g001" target="_blank">Fig 1</a>.</p

AFI- and OIS-recordings from the visual cortex of mice with intact skull.

<p>Data displayed as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085225#pone-0085225-g001" target="_blank">Figure 1</a>. Schematic diagram of the visual stimulation condition showing the mouse and the stimulus monitor (A,B). Activity and retinotopic maps recorded with either AFI or OIS appeared very similar (C–R). Similarly, quantitative analyses of the maps did not reveal any significant differences between the two imaging techniques (S–V): both V1-activation and retinotopic map quality were rather similar. Scale bar <b> = </b>1 mm.</p

Demonstration of the lack of foveal overrepresentation.

<p>X-axis represents the various 10° wide segments of the visual field. Y axis shows the number of pixels (1 pixel = 8.89 μm) contained in the activated area. Open circles denote individual values, horizontal red lines the means of the various segments. The open blue arrow points to the segment including the foveal representation (denoted by ‘F’). There was no significant difference between the pixel numbers in the different segments. Data from five birds are illustrated.</p

Ocular dominance-shifts happen already after 2 days of monocular deprivation in adult enriched environment mice.

<p>Chronic imaging of V1-activation in enriched environment (EE)-mice before and after monocular deprivation (MD), and its quantification. <b>A</b>: V1-activity maps of a P143 EE-mouse after visual stimulation of the contra- (contra) and ipsilateral (ipsi) eye, before (noMD, first row) and after 2/4 days of MD (second/third row). Layout and data display as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186999#pone.0186999.g001" target="_blank">Fig 1</a>. <b>B-E</b>: Ocular dominance indices (B), average V1-activation (C) and individual V1-activation after deprived and open eye stimulation before and after MD of the three chronically imaged EE-mice.</p

Quantification of optically recorded V1-activation in enriched environment-mice of three different age groups before and after varying monocular deprivation durations.

<p><b>A.</b> Optically imaged ODIs of critical period, young and old enriched environment (EE) mice. Symbols represent individual ODI-values, means are marked by horizontal lines; values after monocular deprivation (MD) are indicated by half-black squares. <b>B.</b> V1-activation elicited by stimulation of the contralateral (C) or ipsilateral (I) eye without and with MD (black filled circle indicates MD eye).</p