Gilles Bronchti | Université du Québec à Trois-Rivières (original) (raw)
Papers by Gilles Bronchti
NeuroReport, 1992
We investigated the effect of neonatal eye removal on the tangential extent of the barrelfield in... more We investigated the effect of neonatal eye removal on the tangential extent of the barrelfield in mice. Areas were measured in drawings made from tangentially cut Nisslstained sections of somatosensory cortex. We compared areas of 29 barrels, corresponding to 29 mystacial vibrissae, between adult mice enucleated at birth (n = 13) and their intact littermates (n = 13). Multivariate analysis of variance showed that the barrelfield was larger in enucleated mice. This expansion was mainly due to the increase in areal extent of the barrels corresponding to the dorsalmost row of vibrissae, and of a set of barrels corresponding to rostral vibrissae near the nose and mouth. Evidently, early enucleation has a significant cross-modal effect on the somatosensory cortex.
International Journal of Developmental Neuroscience, 2008
and augmented IL-1 signalling above and beyond levels reported for HI alone. Multiplex antibody c... more and augmented IL-1 signalling above and beyond levels reported for HI alone. Multiplex antibody cytokine assay demonstrates a spectrum of pro-inflammatory cytokines elevated at 24 h post injury. Consistent with the observed increases in oxidative stress components in the HI rat pups resuscitated with 100% oxygen, there was an increase in COX-2 levels likely to account in part for the increase in oxidative stress. In 80% of preterm infants, the common view is that the benefits of oxygen therapy outweigh the risks. We have shown deficits in attention, motor, visual-motor, and executive processing skills in preterm infants otherwise considered ''healthy,'' but these are not apparent before entry into formal learning settings [Smith et al., 2008. Int. J. Dev. Neurosci. 26(1): 125-131]. Few clinical studies have attempted to target improving outcomes in this large preterm population. These deficits may be accounted for by inflammation caused by the use of 100% oxygen resuscitation. Our long-term goal is to guide clinical trials of oxygen resuscitation by exploring its consequences in the P7 rat model of HI and developing novel interventions that will enhance benefits while decreasing inflammatory consequences.
International Journal of Developmental Neuroscience, 2006
International Journal of Developmental Neuroscience, 2008
and augmented IL-1 signalling above and beyond levels reported for HI alone. Multiplex antibody c... more and augmented IL-1 signalling above and beyond levels reported for HI alone. Multiplex antibody cytokine assay demonstrates a spectrum of pro-inflammatory cytokines elevated at 24 h post injury. Consistent with the observed increases in oxidative stress components in the HI rat pups resuscitated with 100% oxygen, there was an increase in COX-2 levels likely to account in part for the increase in oxidative stress. In 80% of preterm infants, the common view is that the benefits of oxygen therapy outweigh the risks. We have shown deficits in attention, motor, visual-motor, and executive processing skills in preterm infants otherwise considered ''healthy,'' but these are not apparent before entry into formal learning settings [Smith et al., 2008. Int. J. Dev. Neurosci. 26(1): 125-131]. Few clinical studies have attempted to target improving outcomes in this large preterm population. These deficits may be accounted for by inflammation caused by the use of 100% oxygen resuscitation. Our long-term goal is to guide clinical trials of oxygen resuscitation by exploring its consequences in the P7 rat model of HI and developing novel interventions that will enhance benefits while decreasing inflammatory consequences.
International Journal of Developmental Neuroscience, 2008
These findings demonstrate dramatic regional differences in the potential of progenitor domains o... more These findings demonstrate dramatic regional differences in the potential of progenitor domains of the developing spinal cord to generate astrocytes. In relative terms, the Ngn3 domain is the most astrogenic, followed by the Olig2 domain and Math-1. Ongoing studies will document contributions from additional domains in the DV axis. And we plan to generate genetic tools to target astrocyte subpopulations and further characterize whether astrocytes generated from different domains are functionally heterogeneous.
Brain Research, 2014
Somatosensory Auditory Cross-modal plasticity Thalamus a b s t r a c t Anophthalmia is a conditio... more Somatosensory Auditory Cross-modal plasticity Thalamus a b s t r a c t Anophthalmia is a condition in which the eye does not develop from the early embryonic period. Early blindness induces cross-modal plastic modifications in the brain such as auditory and haptic activations of the visual cortex and also leads to a greater solicitation of the somatosensory and auditory cortices. The visual cortex is activated by auditory stimuli in anophthalmic mice and activity is known to alter the growth pattern of the cerebral cortex. The size of the primary visual, auditory and somatosensory cortices and of the corresponding specific sensory thalamic nuclei were measured in intact and enucleated C57Bl/6J mice and in ZRDCT anophthalmic mice (ZRDCT/An) to evaluate the contribution of cross-modal activity on the growth of the cerebral cortex. In addition, the size of these structures were compared in intact, enucleated and anophthalmic fourth generation backcrossed hybrid C57Bl/6J Â ZRDCT/An mice to parse out the effects of mouse strains and of the different visual deprivations. The visual cortex was smaller in the anophthalmic ZRDCT/An than in the intact and enucleated C57Bl/6J mice. Also the auditory cortex was larger and the somatosensory cortex smaller in the ZRDCT/An than in the intact and enucleated C57Bl/6J mice. The size differences of sensory cortices between the enucleated and anophthalmic mice were no longer present in the hybrid mice, showing specific genetic differences between C57Bl/6J and ZRDCT mice. The post natal size increase of the visual cortex was less in the enucleated than in the anophthalmic and intact hybrid mice. This suggests differences in the activity of the visual cortex between enucleated and anophthalmic mice and that early in-utero spontaneous neural activity in the visual system contributes to the shaping of functional properties of cortical networks. b r a i n r e s e a r c h ] ( ] ] ] ] ) ] ] ] -] ] ] Please cite this article as: Massé, I., et al., Strain differences of the effect of enucleation and anophthalmia on the size and growth of sensory cortices in mice. Brain Research (2014), http://dx.b r a i n r e s e a r c h ] ( ] ] ] ] ) ] ] ] -] ] ] b r a i n r e s e a r c h ] ( ] ] ] ] ) ] ] ] -] ] ] b r a i n r e s e a r c h ] ( ] ] ] ] ) ] ] ] -] ] ]
Neuroreport, 1991
Previously we have shown that the dorsal lateral geniculate body (LGB), which is strictly visual ... more Previously we have shown that the dorsal lateral geniculate body (LGB), which is strictly visual in sighted mammals, receives a strong auditory input in the naturally blind mole rat (Spalax ehrenbergi). Here we show with the 2-deoxyglucose technique and with single-unit recordings that in this species the initially non-degenerated visual cortex, as defined by its connection with LGB, is also activated by the auditory modality. These findings suggest that cross-modal compensation may occur as a natural consequence of the degeneration of a sense organ.
Neuroscience Letters, 2008
Anatomical and imaging studies show ample evidence for auditory activation of the visual cortex f... more Anatomical and imaging studies show ample evidence for auditory activation of the visual cortex following early onset of blindness in both humans and animal models. Anatomical studies in animal models of early blindness clearly show intermodal pathways through which auditory information can reach the primary visual cortex. There is clear evidence for intermodal corticocortical pathways linking auditory and visual cortex and also novel connections between the inferior colliculus and the visual thalamus. A recent publication [L.K. Laemle, N.L. Strominger, D.O. Carpenter, Cross-modal innervation of primary visual cortex by auditory fibers in congenitally anophthalmic mice, Neurosci. Lett. 396 (2006) 108-112] suggested the presence of a direct reciprocal connection between the inferior colliculus and the primary visual cortex (V1) in congenitally anophthalmic ZRDCT/An mice. This implies that this mutant mouse would be the only known vertebrate having a direct tectal connection with a primary sensory cortex. The presence of this peculiar pathway was reinvestigated in the ZRDCT/An mouse with highly sensitive neuronal tracers. We found the connections normally described in the ZRDCT/An mouse between: (i) the inferior colliculus and the dorsal lateral geniculate nucleus, (ii) V1 and the superior colliculus, (iii) the lateral posterior nucleus and V1 and between (iv) the inferior colliculus and the medial geniculate nucleus. We also show unambiguously that the auditory subcortical structures do not connect the primary visual cortex in the anophthalmic mouse. In particular, we find no evidence of a direct projection from the auditory mesencephalon to the cortex in this animal model of blindness.
Neuroscience, 2007
A number of studies on humans and animals have demonstrated better auditory abilities in blind wi... more A number of studies on humans and animals have demonstrated better auditory abilities in blind with respect to sighted subjects and have tried to define the mechanisms through which this compensation occurs. The aim of the present study, therefore, was to examine the participation of primary visual cortex (V1) to auditory processing in early enucleated rats. Here we show, using gaussian noise bursts, that about a third of the cells in V1 responded to auditory stimulation in blind rats and most of these (78%) had ON-type responses and low spontaneous activity. Moreover, they were distributed throughout visual cortex without any apparent tonotopic organization. Optimal frequencies determined using pure tones were rather high but comparable to those found in auditory cortex of blind and sighted rats. On the other hand, sensory thresholds determined at these frequencies were higher and bandwidths were wider in V1 of the blind animals. Blind and sighted rats were also stimulated for 60 min with gaussian noise, their brains removed and processed for c-Fos immunohistochemistry. Results revealed that c-Fos positive cells were not only present in auditory cortex of both groups of rats but there was a 10-fold increase in labeled cells in V1 and a fivefold increase in secondary visual cortex (V2) of early enucleated rats in comparisons to sighted ones. Also, the pattern of distribution of these labeled cells across layers suggests that the recruitment of V1 could originate at least in part through inputs arising from the thalamus. The ensemble of results appears to indicate that cross-modal compensation leading to improved performance in the blind depends on cell recruitment in V1 but probably also plastic changes in lower-and higher-order visual structures and possibly in the auditory system.
The Journal of Comparative Neurology, 1989
The blind mole rat Spalax ehrenbergi is a subterranean rodent that shows striking behavioral, str... more The blind mole rat Spalax ehrenbergi is a subterranean rodent that shows striking behavioral, structural, and physiological adaptations to fossorial life including highly degenerated eyes and optic nerves and a behavioral audiogram that indicates high specialization for low-frequency hearing. A 2-deoxyglucose functional mapping of acoustically activated structures, in conjunction with Nissl/Klüver-Barrera-stained material, revealed a typical mammalian auditory pathway with some indications for specialized low-frequency hearing such as a poorly differentiated lateral nucleus and a well-developed medial nucleus in the superior olive complex. The most striking finding was a marked 2-deoxyglucose labeling of the dorsal lateral geniculate body and of cortical regions that correspond to visual areas in sighted rodents. The results render the blind mole rat a good model system for studying natural neural plasticity and intermodal compensation. In this report, we confine ourselves to the subcortical levels. The cortical level will be dealt comprehensively in a following paper.
Hearing Research, 2003
The current study evaluated changes in [14C]-2-deoxyglucose (2-DG) uptake along the auditory path... more The current study evaluated changes in [14C]-2-deoxyglucose (2-DG) uptake along the auditory pathways of hamsters that were exposed unilaterally to intense sound. The measurement of the acoustically evoked auditory brainstem responses indicated that intense sound exposure caused asymmetrical hearing loss. The 2-DG results revealed some changes in metabolic activity in exposed animals, as compared to unexposed animals. Significant decreases in 2-DG uptake were found in the ipsilateral anteroventral and posteroventral cochlear nucleus, with respect to the exposed left ears. Exposed animals also showed significant increases in the ipsilateral nucleus of the lateral lemniscus, central nucleus of inferior colliculus and medial geniculate body. No significant changes in uptake were observed in the ipsilateral dorsal cochlear nucleus, superior olivary complex, auditory cortex and any contralateral structures. The mechanisms for the observed changes in 2-DG uptake are discussed.
European Journal of Neuroscience, 1999
We studied sensory organ reinnervation after nerve transection in the mouse whisker-to-barrel pat... more We studied sensory organ reinnervation after nerve transection in the mouse whisker-to-barrel pathway. In one set of adult mice, we determined at light microscopy level the number of ®bres reaching the caudal whisker follicles 5, 15, 20, 60, 100 days and 1 year after transection of the sensory nerve of row C. Regenerated ®bres were ®rst detected 15 days post lesionem (p.l.) and myelin ®rst observed at 20 days. Between 60 and 100 days, the number of ®bres stayed at » 80% of the values obtained in control animals. At that time, myelinated ®bres reached only 58% of their number in controls. At the electron microscopy level, these ®bres differ from control ones by a smaller ®bre diameter. The innervation of follicles of adjacent rows was not modi®ed, indicating that follicular reinnervation is row speci®c. We checked this feature by injecting in another set of mice the denervated follicles and the adjacent ones with distinct retrograde tracers 45 days and 1 year after nerve transection. The percentage of double-labelled neurons in the Gasserian ganglion did not increase in experimental animals. This con®rms the absence of colonization of intact follicles by regenerating ®bres and indicates that reinnervation of the whisker follicles takes place by regeneration of the degenerated axons without collateral reinnervation. The companion paper describes the pattern of activation of the barrel cortex relative to the present ®ndings.
European Journal of Neuroscience, 2011
Visual cortical areas are activated by auditory stimuli in blind mice. Direct heteromodal cortica... more Visual cortical areas are activated by auditory stimuli in blind mice. Direct heteromodal cortical connections have been shown between the primary auditory cortex (A1) and primary visual cortex (V1), and between A1 and secondary visual cortex (V2). Auditory afferents to V2 terminate in close proximity to neurons that project to V1, and potentially constitute an effective indirect pathway between A1 and V1. In this study, we injected a retrograde adenoviral vector that expresses enhanced green fluorescent protein under a synapsin promotor in V1 and biotinylated dextran amine as an anterograde tracer in A1 to determine: (i) whether A1 axon terminals establish synaptic contacts onto the lateral part of V2 (V2L) neurons that project to V1; and (ii) if this indirect cortical pathway is altered by a neonatal enucleation in mice. Complete dendritic arbors of layer V pyramidal neurons were reconstructed in 3D, and putative contacts between pre-synaptic auditory inputs and postsynaptic visual neurons were analysed using a laserscanning confocal microscope. Putative synaptic contacts were classified as high-confidence and low-confidence contacts, and charted onto dendritic trees. As all reconstructed layer V pyramidal neurons received auditory inputs by these criteria, we conclude that V2L acts as an important relay between A1 and V1. Auditory inputs are preferentially located onto lower branch order dendrites in enucleated mice. Also, V2L neurons are subject to morphological reorganizations in both apical and basal dendrites after the loss of vision. The A1-V2L-V1 pathway could be involved in multisensory processing and contribute to the auditory activation of the occipital cortex in the blind rodent.
European Journal of Neuroscience, 2005
To study the degree and time course of the functional recovery in the somatosensory cortex (SI) a... more To study the degree and time course of the functional recovery in the somatosensory cortex (SI) after an excitotoxic lesion in the adult mouse thalamus, metabolic activity was determined in SI at various times points post-lesion. Immediately after the lesion, metabolic activity in the thalamically deafferented part of SI was at its lowest value but increased progressively at subsequent time points. This was seen in all cortical layers; however, layers I and Vb recovered more rapidly than layers II, III, IV, Va and VI. Removal of the mystacial whiskers corresponding to the deafferented area, 5 weeks after cortical recovery, produced a subsequent 32% drop in metabolic activity, demonstrating peripheral sensory activation of this part of the cortex. Tracing experiments revealed that the deafferented cortex did not receive a novel thalamic input but that cortico-cortical and contralateral barrel cortex projections to this area were reinforced. We conclude that the cortical functional recovery after a thalamic lesion is, at least partially, due to modified cortico-cortical and callosal projections to the deafferented cortical area.
European Journal of Neuroscience, 2004
Enrichment of the environment is an effective means of enhancing neuronal development and plastic... more Enrichment of the environment is an effective means of enhancing neuronal development and plasticity but its effect on the cross-modal compensation resulting from sensory deprivation has never been investigated. The present study used c-Fos immunohistochemistry and dextran-biotin neuronal tracing to examine the reorganization of sensory modalities in the brain of anophthalmic mutant mice (ZRDCT/An) raised in either enriched or standard environments. Auditory stimulation was found to elicit strong neuronal activation in thalamic and cortical structures that are normally visual. An important finding was that the latter auditory-evoked cortical activity was considerably enhanced in blind mice raised in the enriched environment. The axonal tracing study demonstrated auditory inputs from the inferior colliculus to the visual thalamus. This animal model will be useful for understanding neuronal mechanisms underlying some cross-modal sensory phenomena observed in blind or deaf humans.
European Journal of Neuroscience, 2002
The mole rat (Spalax ehrenbergi) is a subterranean rodent whose adaptations to its fossorial life... more The mole rat (Spalax ehrenbergi) is a subterranean rodent whose adaptations to its fossorial life include an extremely reduced peripheral visual system and an auditory system suited for the perception of vibratory stimuli. We have previously shown that in this blind rodent the dorsal lateral geniculate nucleus, the primary visual thalamic nucleus of sighted mammals, is activated by auditory stimuli. In this report we focus on the manifestation of this cross-modal compensation at the cortical level. Cyto-and myeloarchitectural analyses of the occipital area showed that despite the almost total blindness of the mole rat this area has retained the organization of a typical mammalian primary visual cortex. Application of the metabolic marker 2-deoxyglucose and electrophysiological recording of evoked ®eld potentials and single-unit activity disclosed that a considerable part of this area is activated by auditory stimuli. Previous neuronal tracing studies had revealed the origin of the bulk of this auditory input to be the dorsal lateral geniculate nucleus which itself receives auditory input from the inferior colliculus.
European Journal of Neuroscience, 2007
The occipital cortex, normally visual, can be activated by auditory or somatosensory tasks in the... more The occipital cortex, normally visual, can be activated by auditory or somatosensory tasks in the blind. This cross-modal compensation appears after early or late onset of blindness with differences in activation between early and late blind. This could support the hypothesis of a reorganization of sensory pathways in the early blind that does not occur in later onset blindness. Using immunohistochemistry of the c-Fos protein following a white noise stimulus and injections of the anterograde tracer dextran-biotin in the inferior colliculus, we studied how the occurrence of blindness influences cross-modal compensation in the mutant anophthalmic mouse strain and in C57BL/6 mice enucleated at birth. We observed, in mutant mice, immunolabeled nuclei in the visual thalamus - the dorsal lateral geniculate nucleus - in the primary visual area (V1) and a few labeled nuclei in the secondary visual area (V2). In enucleated mice, we observed auditory activity mainly in V2 but also sparsely in V1. No labeled cells could be found in the visual thalamus. Tracing studies confirmed the difference between anophthalmic and birth-enucleated mice: whereas the first group showed inferior colliculus projections entering both the dorsal lateral geniculate and the latero-posterior nuclei, in the second, auditory fibers were found only within the latero-posterior thalamic nucleus. None was found in controls with intact eyes. We suggest that the prenatal period of spontaneous retinal activity shapes the differences of the sensory reorganization in mice.
European Journal of Neuroscience, 2012
NeuroReport, 1992
We investigated the effect of neonatal eye removal on the tangential extent of the barrelfield in... more We investigated the effect of neonatal eye removal on the tangential extent of the barrelfield in mice. Areas were measured in drawings made from tangentially cut Nisslstained sections of somatosensory cortex. We compared areas of 29 barrels, corresponding to 29 mystacial vibrissae, between adult mice enucleated at birth (n = 13) and their intact littermates (n = 13). Multivariate analysis of variance showed that the barrelfield was larger in enucleated mice. This expansion was mainly due to the increase in areal extent of the barrels corresponding to the dorsalmost row of vibrissae, and of a set of barrels corresponding to rostral vibrissae near the nose and mouth. Evidently, early enucleation has a significant cross-modal effect on the somatosensory cortex.
International Journal of Developmental Neuroscience, 2008
and augmented IL-1 signalling above and beyond levels reported for HI alone. Multiplex antibody c... more and augmented IL-1 signalling above and beyond levels reported for HI alone. Multiplex antibody cytokine assay demonstrates a spectrum of pro-inflammatory cytokines elevated at 24 h post injury. Consistent with the observed increases in oxidative stress components in the HI rat pups resuscitated with 100% oxygen, there was an increase in COX-2 levels likely to account in part for the increase in oxidative stress. In 80% of preterm infants, the common view is that the benefits of oxygen therapy outweigh the risks. We have shown deficits in attention, motor, visual-motor, and executive processing skills in preterm infants otherwise considered ''healthy,'' but these are not apparent before entry into formal learning settings [Smith et al., 2008. Int. J. Dev. Neurosci. 26(1): 125-131]. Few clinical studies have attempted to target improving outcomes in this large preterm population. These deficits may be accounted for by inflammation caused by the use of 100% oxygen resuscitation. Our long-term goal is to guide clinical trials of oxygen resuscitation by exploring its consequences in the P7 rat model of HI and developing novel interventions that will enhance benefits while decreasing inflammatory consequences.
International Journal of Developmental Neuroscience, 2006
International Journal of Developmental Neuroscience, 2008
and augmented IL-1 signalling above and beyond levels reported for HI alone. Multiplex antibody c... more and augmented IL-1 signalling above and beyond levels reported for HI alone. Multiplex antibody cytokine assay demonstrates a spectrum of pro-inflammatory cytokines elevated at 24 h post injury. Consistent with the observed increases in oxidative stress components in the HI rat pups resuscitated with 100% oxygen, there was an increase in COX-2 levels likely to account in part for the increase in oxidative stress. In 80% of preterm infants, the common view is that the benefits of oxygen therapy outweigh the risks. We have shown deficits in attention, motor, visual-motor, and executive processing skills in preterm infants otherwise considered ''healthy,'' but these are not apparent before entry into formal learning settings [Smith et al., 2008. Int. J. Dev. Neurosci. 26(1): 125-131]. Few clinical studies have attempted to target improving outcomes in this large preterm population. These deficits may be accounted for by inflammation caused by the use of 100% oxygen resuscitation. Our long-term goal is to guide clinical trials of oxygen resuscitation by exploring its consequences in the P7 rat model of HI and developing novel interventions that will enhance benefits while decreasing inflammatory consequences.
International Journal of Developmental Neuroscience, 2008
These findings demonstrate dramatic regional differences in the potential of progenitor domains o... more These findings demonstrate dramatic regional differences in the potential of progenitor domains of the developing spinal cord to generate astrocytes. In relative terms, the Ngn3 domain is the most astrogenic, followed by the Olig2 domain and Math-1. Ongoing studies will document contributions from additional domains in the DV axis. And we plan to generate genetic tools to target astrocyte subpopulations and further characterize whether astrocytes generated from different domains are functionally heterogeneous.
Brain Research, 2014
Somatosensory Auditory Cross-modal plasticity Thalamus a b s t r a c t Anophthalmia is a conditio... more Somatosensory Auditory Cross-modal plasticity Thalamus a b s t r a c t Anophthalmia is a condition in which the eye does not develop from the early embryonic period. Early blindness induces cross-modal plastic modifications in the brain such as auditory and haptic activations of the visual cortex and also leads to a greater solicitation of the somatosensory and auditory cortices. The visual cortex is activated by auditory stimuli in anophthalmic mice and activity is known to alter the growth pattern of the cerebral cortex. The size of the primary visual, auditory and somatosensory cortices and of the corresponding specific sensory thalamic nuclei were measured in intact and enucleated C57Bl/6J mice and in ZRDCT anophthalmic mice (ZRDCT/An) to evaluate the contribution of cross-modal activity on the growth of the cerebral cortex. In addition, the size of these structures were compared in intact, enucleated and anophthalmic fourth generation backcrossed hybrid C57Bl/6J Â ZRDCT/An mice to parse out the effects of mouse strains and of the different visual deprivations. The visual cortex was smaller in the anophthalmic ZRDCT/An than in the intact and enucleated C57Bl/6J mice. Also the auditory cortex was larger and the somatosensory cortex smaller in the ZRDCT/An than in the intact and enucleated C57Bl/6J mice. The size differences of sensory cortices between the enucleated and anophthalmic mice were no longer present in the hybrid mice, showing specific genetic differences between C57Bl/6J and ZRDCT mice. The post natal size increase of the visual cortex was less in the enucleated than in the anophthalmic and intact hybrid mice. This suggests differences in the activity of the visual cortex between enucleated and anophthalmic mice and that early in-utero spontaneous neural activity in the visual system contributes to the shaping of functional properties of cortical networks. b r a i n r e s e a r c h ] ( ] ] ] ] ) ] ] ] -] ] ] Please cite this article as: Massé, I., et al., Strain differences of the effect of enucleation and anophthalmia on the size and growth of sensory cortices in mice. Brain Research (2014), http://dx.b r a i n r e s e a r c h ] ( ] ] ] ] ) ] ] ] -] ] ] b r a i n r e s e a r c h ] ( ] ] ] ] ) ] ] ] -] ] ] b r a i n r e s e a r c h ] ( ] ] ] ] ) ] ] ] -] ] ]
Neuroreport, 1991
Previously we have shown that the dorsal lateral geniculate body (LGB), which is strictly visual ... more Previously we have shown that the dorsal lateral geniculate body (LGB), which is strictly visual in sighted mammals, receives a strong auditory input in the naturally blind mole rat (Spalax ehrenbergi). Here we show with the 2-deoxyglucose technique and with single-unit recordings that in this species the initially non-degenerated visual cortex, as defined by its connection with LGB, is also activated by the auditory modality. These findings suggest that cross-modal compensation may occur as a natural consequence of the degeneration of a sense organ.
Neuroscience Letters, 2008
Anatomical and imaging studies show ample evidence for auditory activation of the visual cortex f... more Anatomical and imaging studies show ample evidence for auditory activation of the visual cortex following early onset of blindness in both humans and animal models. Anatomical studies in animal models of early blindness clearly show intermodal pathways through which auditory information can reach the primary visual cortex. There is clear evidence for intermodal corticocortical pathways linking auditory and visual cortex and also novel connections between the inferior colliculus and the visual thalamus. A recent publication [L.K. Laemle, N.L. Strominger, D.O. Carpenter, Cross-modal innervation of primary visual cortex by auditory fibers in congenitally anophthalmic mice, Neurosci. Lett. 396 (2006) 108-112] suggested the presence of a direct reciprocal connection between the inferior colliculus and the primary visual cortex (V1) in congenitally anophthalmic ZRDCT/An mice. This implies that this mutant mouse would be the only known vertebrate having a direct tectal connection with a primary sensory cortex. The presence of this peculiar pathway was reinvestigated in the ZRDCT/An mouse with highly sensitive neuronal tracers. We found the connections normally described in the ZRDCT/An mouse between: (i) the inferior colliculus and the dorsal lateral geniculate nucleus, (ii) V1 and the superior colliculus, (iii) the lateral posterior nucleus and V1 and between (iv) the inferior colliculus and the medial geniculate nucleus. We also show unambiguously that the auditory subcortical structures do not connect the primary visual cortex in the anophthalmic mouse. In particular, we find no evidence of a direct projection from the auditory mesencephalon to the cortex in this animal model of blindness.
Neuroscience, 2007
A number of studies on humans and animals have demonstrated better auditory abilities in blind wi... more A number of studies on humans and animals have demonstrated better auditory abilities in blind with respect to sighted subjects and have tried to define the mechanisms through which this compensation occurs. The aim of the present study, therefore, was to examine the participation of primary visual cortex (V1) to auditory processing in early enucleated rats. Here we show, using gaussian noise bursts, that about a third of the cells in V1 responded to auditory stimulation in blind rats and most of these (78%) had ON-type responses and low spontaneous activity. Moreover, they were distributed throughout visual cortex without any apparent tonotopic organization. Optimal frequencies determined using pure tones were rather high but comparable to those found in auditory cortex of blind and sighted rats. On the other hand, sensory thresholds determined at these frequencies were higher and bandwidths were wider in V1 of the blind animals. Blind and sighted rats were also stimulated for 60 min with gaussian noise, their brains removed and processed for c-Fos immunohistochemistry. Results revealed that c-Fos positive cells were not only present in auditory cortex of both groups of rats but there was a 10-fold increase in labeled cells in V1 and a fivefold increase in secondary visual cortex (V2) of early enucleated rats in comparisons to sighted ones. Also, the pattern of distribution of these labeled cells across layers suggests that the recruitment of V1 could originate at least in part through inputs arising from the thalamus. The ensemble of results appears to indicate that cross-modal compensation leading to improved performance in the blind depends on cell recruitment in V1 but probably also plastic changes in lower-and higher-order visual structures and possibly in the auditory system.
The Journal of Comparative Neurology, 1989
The blind mole rat Spalax ehrenbergi is a subterranean rodent that shows striking behavioral, str... more The blind mole rat Spalax ehrenbergi is a subterranean rodent that shows striking behavioral, structural, and physiological adaptations to fossorial life including highly degenerated eyes and optic nerves and a behavioral audiogram that indicates high specialization for low-frequency hearing. A 2-deoxyglucose functional mapping of acoustically activated structures, in conjunction with Nissl/Klüver-Barrera-stained material, revealed a typical mammalian auditory pathway with some indications for specialized low-frequency hearing such as a poorly differentiated lateral nucleus and a well-developed medial nucleus in the superior olive complex. The most striking finding was a marked 2-deoxyglucose labeling of the dorsal lateral geniculate body and of cortical regions that correspond to visual areas in sighted rodents. The results render the blind mole rat a good model system for studying natural neural plasticity and intermodal compensation. In this report, we confine ourselves to the subcortical levels. The cortical level will be dealt comprehensively in a following paper.
Hearing Research, 2003
The current study evaluated changes in [14C]-2-deoxyglucose (2-DG) uptake along the auditory path... more The current study evaluated changes in [14C]-2-deoxyglucose (2-DG) uptake along the auditory pathways of hamsters that were exposed unilaterally to intense sound. The measurement of the acoustically evoked auditory brainstem responses indicated that intense sound exposure caused asymmetrical hearing loss. The 2-DG results revealed some changes in metabolic activity in exposed animals, as compared to unexposed animals. Significant decreases in 2-DG uptake were found in the ipsilateral anteroventral and posteroventral cochlear nucleus, with respect to the exposed left ears. Exposed animals also showed significant increases in the ipsilateral nucleus of the lateral lemniscus, central nucleus of inferior colliculus and medial geniculate body. No significant changes in uptake were observed in the ipsilateral dorsal cochlear nucleus, superior olivary complex, auditory cortex and any contralateral structures. The mechanisms for the observed changes in 2-DG uptake are discussed.
European Journal of Neuroscience, 1999
We studied sensory organ reinnervation after nerve transection in the mouse whisker-to-barrel pat... more We studied sensory organ reinnervation after nerve transection in the mouse whisker-to-barrel pathway. In one set of adult mice, we determined at light microscopy level the number of ®bres reaching the caudal whisker follicles 5, 15, 20, 60, 100 days and 1 year after transection of the sensory nerve of row C. Regenerated ®bres were ®rst detected 15 days post lesionem (p.l.) and myelin ®rst observed at 20 days. Between 60 and 100 days, the number of ®bres stayed at » 80% of the values obtained in control animals. At that time, myelinated ®bres reached only 58% of their number in controls. At the electron microscopy level, these ®bres differ from control ones by a smaller ®bre diameter. The innervation of follicles of adjacent rows was not modi®ed, indicating that follicular reinnervation is row speci®c. We checked this feature by injecting in another set of mice the denervated follicles and the adjacent ones with distinct retrograde tracers 45 days and 1 year after nerve transection. The percentage of double-labelled neurons in the Gasserian ganglion did not increase in experimental animals. This con®rms the absence of colonization of intact follicles by regenerating ®bres and indicates that reinnervation of the whisker follicles takes place by regeneration of the degenerated axons without collateral reinnervation. The companion paper describes the pattern of activation of the barrel cortex relative to the present ®ndings.
European Journal of Neuroscience, 2011
Visual cortical areas are activated by auditory stimuli in blind mice. Direct heteromodal cortica... more Visual cortical areas are activated by auditory stimuli in blind mice. Direct heteromodal cortical connections have been shown between the primary auditory cortex (A1) and primary visual cortex (V1), and between A1 and secondary visual cortex (V2). Auditory afferents to V2 terminate in close proximity to neurons that project to V1, and potentially constitute an effective indirect pathway between A1 and V1. In this study, we injected a retrograde adenoviral vector that expresses enhanced green fluorescent protein under a synapsin promotor in V1 and biotinylated dextran amine as an anterograde tracer in A1 to determine: (i) whether A1 axon terminals establish synaptic contacts onto the lateral part of V2 (V2L) neurons that project to V1; and (ii) if this indirect cortical pathway is altered by a neonatal enucleation in mice. Complete dendritic arbors of layer V pyramidal neurons were reconstructed in 3D, and putative contacts between pre-synaptic auditory inputs and postsynaptic visual neurons were analysed using a laserscanning confocal microscope. Putative synaptic contacts were classified as high-confidence and low-confidence contacts, and charted onto dendritic trees. As all reconstructed layer V pyramidal neurons received auditory inputs by these criteria, we conclude that V2L acts as an important relay between A1 and V1. Auditory inputs are preferentially located onto lower branch order dendrites in enucleated mice. Also, V2L neurons are subject to morphological reorganizations in both apical and basal dendrites after the loss of vision. The A1-V2L-V1 pathway could be involved in multisensory processing and contribute to the auditory activation of the occipital cortex in the blind rodent.
European Journal of Neuroscience, 2005
To study the degree and time course of the functional recovery in the somatosensory cortex (SI) a... more To study the degree and time course of the functional recovery in the somatosensory cortex (SI) after an excitotoxic lesion in the adult mouse thalamus, metabolic activity was determined in SI at various times points post-lesion. Immediately after the lesion, metabolic activity in the thalamically deafferented part of SI was at its lowest value but increased progressively at subsequent time points. This was seen in all cortical layers; however, layers I and Vb recovered more rapidly than layers II, III, IV, Va and VI. Removal of the mystacial whiskers corresponding to the deafferented area, 5 weeks after cortical recovery, produced a subsequent 32% drop in metabolic activity, demonstrating peripheral sensory activation of this part of the cortex. Tracing experiments revealed that the deafferented cortex did not receive a novel thalamic input but that cortico-cortical and contralateral barrel cortex projections to this area were reinforced. We conclude that the cortical functional recovery after a thalamic lesion is, at least partially, due to modified cortico-cortical and callosal projections to the deafferented cortical area.
European Journal of Neuroscience, 2004
Enrichment of the environment is an effective means of enhancing neuronal development and plastic... more Enrichment of the environment is an effective means of enhancing neuronal development and plasticity but its effect on the cross-modal compensation resulting from sensory deprivation has never been investigated. The present study used c-Fos immunohistochemistry and dextran-biotin neuronal tracing to examine the reorganization of sensory modalities in the brain of anophthalmic mutant mice (ZRDCT/An) raised in either enriched or standard environments. Auditory stimulation was found to elicit strong neuronal activation in thalamic and cortical structures that are normally visual. An important finding was that the latter auditory-evoked cortical activity was considerably enhanced in blind mice raised in the enriched environment. The axonal tracing study demonstrated auditory inputs from the inferior colliculus to the visual thalamus. This animal model will be useful for understanding neuronal mechanisms underlying some cross-modal sensory phenomena observed in blind or deaf humans.
European Journal of Neuroscience, 2002
The mole rat (Spalax ehrenbergi) is a subterranean rodent whose adaptations to its fossorial life... more The mole rat (Spalax ehrenbergi) is a subterranean rodent whose adaptations to its fossorial life include an extremely reduced peripheral visual system and an auditory system suited for the perception of vibratory stimuli. We have previously shown that in this blind rodent the dorsal lateral geniculate nucleus, the primary visual thalamic nucleus of sighted mammals, is activated by auditory stimuli. In this report we focus on the manifestation of this cross-modal compensation at the cortical level. Cyto-and myeloarchitectural analyses of the occipital area showed that despite the almost total blindness of the mole rat this area has retained the organization of a typical mammalian primary visual cortex. Application of the metabolic marker 2-deoxyglucose and electrophysiological recording of evoked ®eld potentials and single-unit activity disclosed that a considerable part of this area is activated by auditory stimuli. Previous neuronal tracing studies had revealed the origin of the bulk of this auditory input to be the dorsal lateral geniculate nucleus which itself receives auditory input from the inferior colliculus.
European Journal of Neuroscience, 2007
The occipital cortex, normally visual, can be activated by auditory or somatosensory tasks in the... more The occipital cortex, normally visual, can be activated by auditory or somatosensory tasks in the blind. This cross-modal compensation appears after early or late onset of blindness with differences in activation between early and late blind. This could support the hypothesis of a reorganization of sensory pathways in the early blind that does not occur in later onset blindness. Using immunohistochemistry of the c-Fos protein following a white noise stimulus and injections of the anterograde tracer dextran-biotin in the inferior colliculus, we studied how the occurrence of blindness influences cross-modal compensation in the mutant anophthalmic mouse strain and in C57BL/6 mice enucleated at birth. We observed, in mutant mice, immunolabeled nuclei in the visual thalamus - the dorsal lateral geniculate nucleus - in the primary visual area (V1) and a few labeled nuclei in the secondary visual area (V2). In enucleated mice, we observed auditory activity mainly in V2 but also sparsely in V1. No labeled cells could be found in the visual thalamus. Tracing studies confirmed the difference between anophthalmic and birth-enucleated mice: whereas the first group showed inferior colliculus projections entering both the dorsal lateral geniculate and the latero-posterior nuclei, in the second, auditory fibers were found only within the latero-posterior thalamic nucleus. None was found in controls with intact eyes. We suggest that the prenatal period of spontaneous retinal activity shapes the differences of the sensory reorganization in mice.
European Journal of Neuroscience, 2012