Fig 1.
Experimental time course and schematic illustration of intrinsic signal imaging.
(a) In one group of mice we performed WD by bilaterally plucking all macro-vibrissae and in another group we induced AD by bilateral malleus removal. The first imaging session (day 0) for mapping V1 started immediately after the deprivation followed by a second imaging session at day 3 and a third imaging session at day 7. (b) For visual stimulation we used an upward or downward moving white light bar with 100% contrast which was presented in the right binocular visual field. We always recorded V1 responses in the left hemisphere. Thus, according to the position of the recorded hemisphere the left eye represents the ipsilateral and the right eye represents the contralateral eye.
Fig 2.
Representative V1 maps evoked by the stimulation of either the contralateral or ipsilateral eye at day 0, 3 and after 7 days.
(a) Upper row: In normal control mice contralateral eye stimulation always evoked similarly strong V1 responses. Lower row: V1 responses evoked by ipsilateral eye stimulation were equally strong over the time tested but these responses were always weaker that V1 maps obtained after visual stimulation of the contralateral eye. (b) Upper row: Like in control mice, WD did not lead to alterations of V1 responses elicited by contralateral eye input. Lower row: However, V1 responses elicited by ipsilateral eye stimulation markedly increased 3 days after WD which was followed by a decrease of V1 response strength 7 days after WD. (c) Upper row: Responsiveness of V1 to visual stimulation of contralateral eye remained stable after AD over the time tested. Lower row: 3 days after AD there was a massive increase of V1 responses evoked by ipsilateral eye stimulation which was followed by a recovery of V1 activity 7 days after AD. Thus, the deprivation in both senses (somatosensory or auditory) alters the OD within the binocular zone of V1. Scale bar: 1 mm.
Fig 3.
Both WD and AD shift OD in the binocular V1 in fully adult mice.
(a, b) V1 activity evoked by visual stimulation of the contra or ipsilateral eye in untreated control mice (n = 5) remained unchanged at 0, 3 and 7 days. (c) Thus, over the same time course the ODI did not change underlining the reliability of repeated intrinsic signal imaging. (d) During one week after WD (n = 7), V1 activity elicited by contralateral eye stimulation was unaltered. (e) However, V1 responsiveness to ipsilateral eye stimulation markedly increased 3 days after WD followed by a recovery of V1 activity 7 days after WD. (f) These alterations of V1 responsiveness led to an ODI shift towards zero at day 3 which was followed by a readjustment of the ODI 7 days after WD. (g) After AD (n = 6) V1 activity elicited by contralateral eye stimulation remained unchanged during the time tested. (h) However, V1 responses evoked by visual stimulation of the ipsilateral eye massively increased after 3 days of AD. After the 7 days V1 responses due to the ipsilateral eye input decreased back to the starting level measured at day 0. (i) Hence, the ODI displayed a dramatic shift towards zero 3 days after AD which was followed by a complete recovery after one week. Thus, the deprivation of a non-visual input altered OD in the spared V1. Open circles represent measurements of individual animals. Closed circles represent the means of each group ± s.e.m.; *p<0.05, repeated measures AVOVA.
Table 1.
The effects of WD and AD on V1 responsiveness and OD.
Data are presented as means ± s.e.m.
Fig 4.
Both WD or AD induce an ODI shift compared to normal control mice.
(a, b) V1 responses evoked by visual stimulation of either the contra or ipsilateral eye immediately after WD (n = 7) or AD (n = 6) were indistinguishable from values obtained in normal control mice (n = 5). (c) Hence, directly after WD or AD there was no alteration of the ODI. (d) After 3 days of either WD or AD V1 responses elicited by contralateral eye stimulation was not different from control values. (d) However, V1 activity evoked by stimulation of the eye ipsilateral to the recorded hemisphere was increased 3 days after WD or AD compared to control levels. (f) Thus, at this time point there was a significant shift of the ODI towards zero. (g) After 7 days of WD or AD V1 responses elicited by the stimulation of contralateral eye were unchanged compared to the values of control mice. (h) Interestingly, V1 responsiveness to ipsilateral eye stimulation was re-adjusted to control levels after one week of either WD or AD. (i) Consequently, the ODI of WD or AD mice was completely restored back to control values after 7 days. Bars represent the means ± s.e.m. and open or filled circles represent measurements of individual animals; *p<0.05, **p<0.01, one way ANOVA.
Fig 5.
Exclusion of saturation of V1 responses evoked by contralateral eye stimulation.
(a) Representative V1 amplitude maps evoked by visual stimulation of the ipsi and contralateral eye and elicited by binocular stimulation of normal untreated mice (n = 4). (b) V1 responsiveness to ipsilateral eye stimulation was always weaker compared to V1 responsiveness to contralateral eye stimulation. However, V1 activity elicited by visual stimulation of the contralateral eye was significantly weaker than V1 activity evoked by binocular stimulation. Hence, V1 responses, measured with intrinsic signal imaging, are not saturated by the input through the contralateral eye. (c) V1 responses evoked by contralateral eye stimulation with a visual stimulus of 10% contrast at 0 and 3 days after WD (n = 4) remained unchanged. (d) However, there was a potentiation of V1 responses to the input through the ipsilateral eye between 0 and 3 days after WD. (e) Thus, the ODI significantly shifted towards zero. Hence, visual stimulation with a weaker visual stimulus reveals the same effect of WD on V1 activity like visual stimulation with a strong visual stimulus. Open circles represent measurements of individual animals. Closed circles represent the means of each group ± s.e.m.; *p<0.05, **p<0.01; Scale bar: 1 mm.
Fig 6.
Cross-modally induced ODI shift requires patterned vision through the ipsilateral eye.
(a) Combining WD with a MD of the contralateral eye (n = 4) did not lead to changes of V1 responses evoked by the contralateral eye between 0 and 3 days after WD. (b) However, there was a significant increase of V1 activity elicited by visual stimulation of the ipsilateral eye, like found after WD only. (c) Thus, the ODI markedly shifted towards zero. (d, e) In contrast, if we combined WD with a MD of the ipsilateral eye (n = 5), V1 activity evoked by both contra and ipsilateral eye stimulation remained statistically unchanged after 3 days. (f) Moreover, there was no ODI shift after this treatment suggesting that patterned vision through the ipsilateral eye is required for cross-modally induced OD shifts. Open circles represent measurements of individual animals. Closed circles represent the means of each group ± s.e.m.; *p<0.05, **p<0.01.
Fig 7.
WD cross-modally increases mEPSC amplitudes in V1 layer 4.
(a) Representative traces of mEPSCs recorded in control mice (n = 4) and 3 d after WD (n = 3) (b) Cumulative distribution of all mEPSC amplitudes was right shifted in WD mice compared to control animals. Hence, the mean amplitude of mEPSCs was significantly increased in WD mice. These results suggest that WD induces synaptic plasticity in V1 layer 4. (c) Mean frequency of mEPSCs was unaltered after WD. (d) Plot of rank ordered mEPSC amplitudes from control and WD mice. The red line represents a linear regression of the data points. (e) Cumulative histograms of mEPSC amplitudes. Individual mEPSC amplitudes of WD mice were transformed with the equation y = 1.818x. The distribution of the transformed values is significantly different with the distribution of control values (Kolmogorov-Smirnov test). Bars represent means together with s.e.m., Open and filled circles represent measurements of individual animals; **p<0.01.
Fig 8.
Concentration changes of neurotransmitters in V1 after WD revealed by post-mortem HPLC analyzes.
(a) Compared to the V1 glutamate level of control mice (n = 5), there was a significant increase of V1 glutamate content 3 days after WD (n = 5). (b) There was slight but not significant reduction of the V1 GABA concentration at 3 days after WD (n = 6) compared to controls. (c) The glutamate/GABA ratio was markedly increased at 3 after WD. Bars represent means together with s.e.m., Open and filled circles represent measurements of individual animals; *p<0.05.
Fig 9.
Both increasing inhibition and blocking NMDA receptor activation block cross-modally induced V1 plasticity.
(a) In WD mice treated with saline (n = 4) or diazepam (n = 4) or CPP (n = 4) V1 responses evoked by visual stimulation of the contralateral eye remained unchanged. (b) There was a significant increase of V1 responses elicited by ipsilateral eye stimulation in WD+Saline mice. However, these changes were completely abolished by diazepam or CPP injections. (c) We found a significant reduction of ODI in saline treated WD mice, whereas ODI did not change after diazepam of CPP administration. Taken together, our data suggest that cross-modally induced alterations of V1 OD depend on increased glutamateric excitation and NMDA receptor activation. Open circles represent measurements of individual animals. Closed circles represent the means of each group ± s.e.m.; **p<0.01.
Table 2.
The effects of diazepam and CPP administration on cross-modally induced V1 activity changes after WD.
Data are presented as means ± s.e.m.
Fig 10.
Both WD and AD cross-modally provoke a potentiation of the visual OKR.
(a) In control mice (n = 4), spatial frequency thresholds did not change over the whole time period tested. However, after WD (n = 4) there was a marked improvement of the spatial frequency sensitivity which reached a peak on day 3. Subsequently, spatial frequency thresholds levels slightly decreased and remained at a stable level above control values until 10 days after WD. (b) Contrast sensitivity of the OKR in control mice remained unchanged over 10 days. After WD, contrast thresholds massively improved until day 3. After a slight decrease at 4 days after WD, values then remained at a stable level above control values until 10 days after WD. (c) We used values of the same control mice like in Fig 4a. AD (n = 4) led to a marked increase of spatial frequency thresholds peaking at 3 days. Subsequently, spatial frequency sensitivity slightly decreased until day 5 after AD and remained at a stable level above control values until 10 days after AD. (d) Contrast thresholds markedly increased until day 3 after AD which was followed by a slight decrease to a stable level above contrast values of control mice. (e, f) WD or AD led to similar improvements of the OKR. Open and filled circles represent mean values together with the s.e.m. However, vertical lines of s.e.m. are often occluded by data symbols. ***p<0.001.
Fig 11.
Aspiration of V1 reveals V1 contribution to cross-modally induced enhancements of the OKR.
(a) V1 was located using intrinsic signal imaging. (b) Representative V1 amplitude maps elicited by visual stimulation before and after V1 aspiration. It is clearly visible that after V1 aspiration visually evoked cortical responses were absent demonstrating the efficiency of the aspiration surgery. (c) Nissl stained brain slice obtained 10 days after V1 aspiration. (d) Spatial frequency thresholds remained unchanged in mice after V1 aspiration only (n = 3). After combined WD and V1 aspiration (n = 3) spatial frequency sensitivity slightly increased until day 3 and remained at this level for the remaining 7 days. Interestingly, the strong peak of spatial frequency thresholds obtained 3 days after WD only (n = 4) was absent in mice after WD and V1 aspiration whereas the long-lasting improvement was almost identical in mice of both groups. (e) In WD only, V1aspi only and WD+V1aspi mice, the course of contrast sensitivity thresholds closely followed the course of spatial frequency thresholds in mice of the same groups. Taken together our data suggest that WD leads to V1 dependent and V1 independent improvements of the OKR. Open and filled squares represent mean values together with the s.e.m. However, vertical lines of s.e.m. are often occluded by data symbols.
Fig 12.
Cross-modally induced OKR potentiation requires NMDAR activation.
(a,b) In both control mice (n = 4) and WD mice which received daily injections of CPP (n = 4) spatial frequency and contrast thresholds remained completely unchanged for 10 days. Hence, blocking NMDARs abolished both V1 dependent and V1 independent potentiation of OKR thresholds found after WD only.