Monocular Enucleation Research Articles

VEGF, but Not BDNF, Prevents the Downregulation of KCC2 Induced by Axotomy in Extraocular Motoneurons.

The potassium-chloride cotransporter KCC2 is the main extruder of Cl- in neurons. It plays a fundamental role in the activity of the inhibitory neurotransmitters (GABA and glycine) since low levels of KCC2 promote intracellular Cl- accumulation, leading to the depolarizing activity of GABA and glycine. The downregulation of this cotransporter occurs in neurological disorders characterized by hyperexcitability, such as epilepsy, neuropathic pain, and spasticity. KCC2 is also downregulated after axotomy. If muscle reinnervation is allowed, the KCC2 levels recover in motoneurons. Therefore, we argued that target-derived neurotrophic factors might be involved in the regulation of KCC2 expression. For this purpose, we performed the axotomy of extraocular motoneurons via the monocular enucleation of adult rats, and a pellet containing either VEGF or BDNF was chronically implanted in the orbit. Double confocal immunofluorescence of choline acetyl-transferase (ChAT) and KCC2 was carried out in the brainstem sections. Axotomy led to a KCC2 decrease in the neuropil and somata of extraocular motoneurons, peaking at 15 days post-lesion, with the exception of the abducens motoneuron somata. VEGF administration prevented the axotomy-induced KCC2 downregulation. By contrast, BDNF either maintained or reduced the KCC2 levels following axotomy, suggesting that BDNF is involved in the axotomy-induced KCC2 downregulation in extraocular motoneurons. The finding that VEGF prevents KCC2 decrease opens up new possibilities for the treatment of neurological disorders coursing with neuronal hyperactivity due to KCC2 downregulation.

Effects of early monocular enucleation on cortical spreading depression in well-nourished and malnourished adult rats.

Sensory development is a complex process that can influence physiological and pathological factors. In laterally-eyed mammals, monocular enucleation (ME) during development and the subsequent lack of external sensory stimuli can result in permanent morphological and physiological changes. Malnutrition, especially in early life, also can cause permanent morphofunctional changes due to inadequate nutrient intake in both hemispheres. This study investigated the effects of early (postnatal day 7) ME and malnutrition during the suckling period on cortical excitability in adulthood (110-140 days of life). For this, we compared the speed propagation of cortical spreading depression in the occipital and parietal cortex of malnourished and well-nourished adult rats, previously suckled small-sized litters with three pups (L3/dam) medium-sized litters with six pups (L6/dam), and large-sized litters with twelve pups (L12/dam). The CSD velocity was augmented by the ME in the contralateral side of the removed eye in the parietal and occipital cortex. These findings suggest that visual sensory input deprivation is associated with permanent functional changes in the visual pathways, which can alter cortical excitability and lead to modifications in CSD propagation.

Factors associated with depressive and anxiety symptoms among anophthalmic patients wearing ocular prostheses

This study aimed to investigate the prevalence of anxiety and depression among individuals with ocular prostheses and to identify factors associated with these psychological symptoms. A sample of patients who underwent monocular enucleation and socket implantation participated in the study, responding to digital questionnaires covering demographics, psychosocial factors, and aspects related to their ocular prostheses. Depressive and anxiety symptoms were evaluated using Patient Health Questionnaire-9 (PHQ-9) and Generalized Anxiety Disorder-7 (GAD-7), respectively. Optimal scale regression analysis was employed to explore factors linked to psychological symptoms in ocular prosthesis users. Results from 100 valid participants revealed a 51% prevalence of depressive symptoms and a 45% prevalence of anxiety symptoms. The mean PHQ-9 score was 4.91 ± 1.98, and the mean GAD-7 score was 4.99 ± 2.15. Factors such as undergoing right eye enucleation, longer duration of ocular prosthesis use, comfort with prosthesis wearing, and greater satisfaction correlated with milder depressive symptoms. In terms of anxiety, those who used ocular prostheses due to trauma or tumors were affected by more severe symptoms, while individuals who were comfortable with their prosthesis or using alumina-based prostheses reported fewer anxiety symptoms. In conclusion, ocular prosthesis users wrestle with significant challenges of depressive and anxiety symptoms. Factors including age, household registration, economic status, enucleation side, cause of anophthalmos, prosthetic material, and satisfaction and duration of prosthesis use were associated with depressive or anxiety symptoms. Long-term comprehensive care targeting these vulnerable individuals is imperative to alleviate depression and anxiety.

Retinotectal plasticity induced by monocular enucleation during the critical period is dependent of A2a adenosine receptor: A possible role of astrocytes

The retinotectal topography of rats develops within the first three postnatal weeks during the critical period. Previous studies have shown that monocular enucleation results in plasticity of the intact retinotectal pathway in a time-dependent manner. Glial fibrillary acidic protein (GFAP), an astrocyte marker, is up-regulated after central nervous system injury. Adenosine is a neuromodulator involved in the development and plasticity of the visual system acting through the inhibitory A1 and excitatory A2a receptor activities. Herein, we examined whether adenosine receptors and astrocytes are crucial for monocular enucleation (ME)-induced plasticity. We also investigate whether A2a blockade alters retinotectal plasticity in an astrocyte-dependent manner. Lister Hooded rats were submitted to monocular enucleation at postnatal day 10 (PND10) or PND21 and, after different survival times, were processed for immunohistochemistry or western blotting assays. Another group underwent subpial implantation of ELVAX containing vehicle (DMSO) or SCH58261 (1 μM - an A2a receptor antagonist), simultaneously with ME at PND10. After a 72 h survival, GFAP content and the retinotectal plasticity were evaluated. Our data show that monocular enucleation leads to an upregulation in GFAP expression in the contralateral superior colliculus. At PND10, a slight increase in GFAP labeling was observed at 72 h post-enucleation, while at PND21 GFAP increase was detected in the deafferented superior colliculus after 1 to 3 weeks of survival. The content of adenosine receptors also varies in the contralateral target after ME. A transient increase in A1 receptors is observed in the early periods of plasticity, while A2a receptors are upregulated later. Interestingly, the local blockade of A2a receptors abolished the increase in GFAP and the retinotectal reorganization induced by monocular enucleation during the critical period. Taken together these results suggest a correlation between astrocytes and A2a adenosine receptors in the subcortical visual plasticity.

Cross-hierarchical plasticity of corticofugal projections to dLGN after neonatal monocular enucleation.

Perception is the result of interactions between the sensory periphery, thalamus, and cerebral cortex. Inputs from the retina project to the first‐order dorsal lateral geniculate nucleus (dLGN), which projects to the primary visual cortex (V1). In return, the cortex innervates the thalamus. While layer 6 projections innervate all thalamic nuclei, cortical layer 5 neurons selectively project to the higher order lateral posterior nucleus (LP) and not to dLGN. It has been demonstrated that a subpopulation of layer 5 (Rbp4‐Cre+) projections rewires to dLGN after monocular or binocular enucleation in young postnatal mice. However, the exact cortical regional origin of these projections was not fully determined, and it remained unclear whether these changes persisted into adulthood. In this study, we report gene expression changes observed in the dLGN after monocular enucleation at birth using microarray, qPCR at P6, and in situ hybridization at P8. We report that genes that are normally enriched in dLGN, but not LP during development are preferentially downregulated in dLGN following monocular enucleation. Comparisons with developmental gene expression patters in dLGN suggest more immature and delayed gene expression in enucleated dLGN. Combined tracing and immuno‐histochemical analysis revealed that the induced layer 5 fibers that innervate enucleated dLGN originate from putative primary visual cortex and they retain increased VGluT1+ synapse formation into adulthood. Our results indicate a new form of plasticity when layer 5 driver input takes over the innervation of an originally first‐order thalamic nucleus after early sensory deficit.

The Expression Patterns of Cytochrome Oxidase and Immediate-Early Genes Show Absence of Ocular Dominance Columns in the Striate Cortex of Squirrel Monkeys Following Monocular Inactivation.

Because at least some squirrel monkeys lack ocular dominance columns (ODCs) in the striate cortex (V1) that are detectable by cytochrome oxidase (CO) histochemistry, the functional importance of ODCs on stereoscopic 3-D vision has been questioned. However, conventional CO histochemistry or trans-synaptic tracer study has limited capacity to reveal cortical functional architecture, whereas the expression of immediate-early genes (IEGs), c-FOS and ZIF268, is more directly responsive to neuronal activity of cortical neurons to demonstrate ocular dominance (OD)-related domains in V1 following monocular inactivation. Thus, we wondered whether IEG expression would reveal ODCs in the squirrel monkey V1. In this study, we first examined CO histochemistry in V1 of five squirrel monkeys that were subjected to monocular enucleation or tetrodotoxin (TTX) treatment to address whether there is substantial cross-individual variation as reported previously. Then, we examined the IEG expression of the same V1 tissue to address whether OD-related domains are revealed. As a result, staining patterns of CO histochemistry were relatively homogeneous throughout layer 4 of V1. IEG expression was also moderate and homogeneous throughout layer 4 of V1 in all cases. On the other hand, the IEG expression was patchy in accordance with CO blobs outside layer 4, particularly in infragranular layers, although they may not directly represent OD clusters. Squirrel monkeys remain an exceptional species among anthropoid primates with regard to OD organization, and thus are potentially good subjects to study the development and function of ODCs.

In vivo MRI evaluation of early postnatal development in normal and impaired rat eyes

This study employed in vivo 7-T magnetic resonance imaging (MRI) to evaluate the postnatal ocular growth patterns under normal development or neonatal impairments in Sprague–Dawley rats. Using T2-weighted imaging on healthy rats from postnatal day (P) 1 (newborn) to P60 (adult), the volumes of the anterior chamber and posterior chamber (ACPC), lens, and vitreous humor increased logistically with ACPC expanding by 33-fold and the others by fivefold. Intravitreal potassium dichromate injection at P1, P7, and P14 led to T1-weighted signal enhancement in the developing retina by 188–289%. Upon unilateral hypoxic-ischemic encephalopathy at P7, monocular deprivation at P15, and monocular enucleation at P1, T2-weighted imaging of the adult rats showed decreased ocular volumes to different extents. In summary, in vivo high-field MRI allows for non-invasive evaluation of early postnatal development in the normal and impaired rat eyes. Chromium-enhanced MRI appeared effective in examining the developing retina before natural eyelid opening at P14 with relevance to lipid metabolism. The reduced ocular volumes upon neonatal visual impairments provided evidence to the emerging problems of why some impaired visual outcomes cannot be solely predicted by neurological assessments and suggested the need to look into both the eye and the brain under such conditions.

Ocular dominance columns in V1 are more susceptible than associated callosal patches to imbalance of eye input during precritical and critical periods.

In Long Evans rats, ocular dominance columns (ODCs) in V1 overlap with patches of callosal connections. Using anatomical tracers, we found that ODCs and callosal patches are present at postnatal day 10 (P10), several days before eye opening, and about 10 days before the activation of the critical period for ocular dominance plasticity (~P20). In rats monocularly enucleated at P10 and perfused ~P20, ODCs ipsilateral to the remaining eye desegregated, indicating that rat ODCs are highly susceptible to monocular enucleation during a precritical period. Monocular enucleation during the critical period exerted significant, although smaller, effects. Monocular eye lid suture during the critical period led to a significant expansion of the ipsilateral projection from the nondeprived eye, whereas the contralateral projection invaded into, and intermixed with, ipsilateral ODCs innervated by the deprived eye. We propose that this intermixing allows callosal connections to contribute to the effects of monocular deprivation assessed in the hemisphere ipsilateral to the nondeprived eye. The ipsilateral and contralateral projections from the deprived eye did not undergo significant shrinkage. In contrast, we found that callosal patches are less susceptible to imbalance of eye input. In rats monocularly enucleated during either the precritical or critical periods, callosal patches were maintained in the hemisphere ipsilateral to the remaining eye, but desegregated in the hemisphere ipsilateral to the enucleated orbit. Callosal patches were maintained in rats binocularly enucleated at P10 or later. Similarly, monocular deprivation during the critical period had no significant effect on callosal patches in either hemisphere.

Signaling pathways modulated by monocular enucleation in the superior colliculus of juvenile rats

Monocular eye enucleation (ME) is a classical paradigm to induce neural plasticity in retinal ganglion cells (RGCs) axons from the intact eye, especially when performed within the critical period of visual system development. However, the precise mechanisms underlying the axonal sprouting and synaptogenesis seen in this model remain poorly understood. In the present work, we investigated the temporal alterations in phosphorylation of three kinases related to axonal growth and synaptogenesis-GSK3β (an important repressor of axonal outgrowth), AKT, and ERK-in superior colliculus of rats submitted to ME during early postnatal development. Western blotting analysis showed an increase in pGSK3β, the inactive form of this enzyme, 24 and 48hr after ME. Accordingly, an increase in pERK levels was detected 24hr after ME, indicating that phosphorylation of these enzymes might be related to axonal reorganization induced by ME. Interestingly, AKT phosphorylation was increased just 1week after ME, suggesting it may be involved in the stabilization of newly formed synapses, rising from the axonal reorganization of remaining eye. A better understanding of how signaling pathways are modulated in a model of intense axonal sprouting can highlight possible therapeutic targets in RGCs injuries in adult individuals, where axonal regrowth is nearly absent.

Blockade of retinal or cortical activity does not prevent the development of callosal patches normally associated with ocular dominance columns in primary visual cortex.

Callosal patches in primary visual cortex of Long Evans rats, normally associated with ocular dominance columns, emerge by postnatal day 10 (P10), but they do not form in rats monocularly enucleated a few days before P10. We investigated whether we could replicate the results of monocular enucleation by using tetrodotoxin (TTX) to block neural activity in one eye, or in primary visual cortex. Animals received daily intravitreal (P6-P9) or intracortical (P7-P9) injections of TTX, and our physiological evaluation of the efficacy of these injections indicated that the blockade induced by a single injection lasted at least 24h. Four weeks later, the patterns of callosal connections in one hemisphere were revealed after multiple injections of horseradish peroxidase in the other hemisphere. We found that in rats receiving either intravitreal or cortical injections of TTX, the patterns of callosal patches analyzed in tangential sections from the flattened cortex were not significantly different from the pattern in normal rats. Our findings, therefore, suggest that the effects of monocular enucleation on the distribution of callosal connections are not due to the resulting imbalance of afferent ganglion cell activity, and that factors other than neural activity are likely involved.

Wilbrand's Knee: To Be or Not to Be a Knee?

Wilbrand's knee of the optic chiasm refers to crossing fibers from one optic nerve that stray for a short distance into the opposite optic nerve before joining the optic tract. This loop of aberrant axons, although small, has generated much controversy. In a previous study, labeling of the optic pathway in normal monkeys with a radioactive tracer revealed no Wilbrand's knee. Monocular enucleation induced a typical knee to form. These findings suggested that Wilbrand's knee is absent normally, but appears after atrophy of one optic nerve. This conclusion has been challenged by images showing Wilbrand's knee in the normal human chiasm using anisotropic light scattering. It has also been resisted by some clinicians who believe that Wilbrand's knee is necessary to explain the anterior chiasmal syndrome. Early in his distinguished career, William F. Hoyt examined the fiber organization of the monkey optic nerve and chiasm. He found no evidence for Wilbrand's knee and rejected its importance for the topical diagnosis of chiasmal lesions. His conclusion is supported by new data showing that anisotropic light scattering is not a reliable method for tracing axons. Hence, that method has given a misleading impression that Wilbrand's knee exists in normal subjects. Although Wilbrand's knee has fascinated neuro-ophthalmologists for more than a century, it is an inconsequential structure that develops only after a longstanding monocular optic neuropathy.

Astrocytes shape the plastic response of adult cortical neurons to vision loss.

Astrocytes are vital for preserving correct brain functioning by continuously sustaining neuronal activity and survival. They are in contact with multiple synapses at once allowing the expansion of local synaptic events into activity changes in neuronal networks. Furthermore, cortical astrocytes integrate local sensory inputs and behavioral state. From an anatomical, molecular, and functional perspective, astrocytes are thus ideal candidates to influence complex large-scale brain mechanisms such as plasticity. We collected evidence for the astrocytic potential for plasticity modulation, using the monocular enucleation (ME) mouse model of visual cortex plasticity. The impact of one-eyed vision involves the functional recruitment of the deprived visual cortex by the spared senses within a 7-week time frame, reflecting a substantial change in sensory information processing. In visually deprived cortex, a swift upregulation in Aldh1l1-positive astrocyte density lasts until maximal functional recovery is reached. Transient metabolic silencing of visual cortex astrocytes at the time of ME induction, through intracranial fluorocitrate injections, reveals that astrocytes are required on site to achieve adequate long-term neuronal reactivation. In addition, chronic stimulation by Gi but not Gq G-protein coupled receptor activation of local astrocytes boosts the cortical plasticity phenomenon. Hence, functional manipulation of protoplasmic astrocytes has long-lasting effects on the functional recovery of cortical neurons upon sensory loss, possibly by influencing the neuronal threshold to reactivate. Together, our results highlight an integral role for astrocytes in mediating adult cortical plasticity and unmask astrocyte specific Gi signaling as an interesting therapeutic pathway for brain plasticity regulation.

Altered white matter structure in auditory tracts following early monocular enucleation.

Purpose: Similar to early blindness, monocular enucleation (the removal of one eye) early in life results in crossmodal behavioral and morphological adaptations. Previously it has been shown that partial visual deprivation from early monocular enucleation results in structural white matter changes throughout the visual system (Wong et al., 2018). The current study investigated structural white matter of the auditory system in adults who have undergone early monocular enucleation compared to binocular control participants. Methods: We reconstructed four auditory and audiovisual tracts of interest using probabilistic tractography and compared microstructural properties of these tracts to binocularly intact controls using standard diffusion indices. Results: Although both groups demonstrated asymmetries in indices in intrahemispheric tracts, monocular enucleation participants showed asymmetries opposite to control participants in the auditory and A1-V1 tracts. Monocular enucleation participants also demonstrated significantly lower fractional anisotropy in the audiovisual projections contralateral to the enucleated eye relative to control participants. Conclusions: Partial vision loss from early monocular enucleation results in altered structural connectivity that extends into the auditory system, beyond tracts primarily dedicated to vision.

A crucial role for endocannabinoid signalling in age-dependent cross-modal brain plasticity upon vision loss

Event Abstract Back to Event A crucial role for endocannabinoid signalling in age-dependent cross-modal brain plasticity upon vision loss Lucas Durieux1*, Maroussia Hennes1, Michele Giugliano2 and Lutgarde Arckens1 1 KU Leuven, Biology, Belgium 2 University of Antwerp, Belgium When sensory inputs become reduced or lost, the brain can undergo neuroplasticity events in order to reorganize the deprived cortex to support new function. Monocular enucleation (ME) is a validated model to study visual cortex reorganization in relation to one-eyed vision. The partially deprived binocular visual cortex will become reactivated by open-eye potentiation though inputs coming from the remaining eye. The deprived monocular visual cortex will however become responsive to non-visual inputs, the cortical neurons will start to respond to whisker stimulation, a typical example of cross-modal brain plasticity. Interestingly, cortical reactivation induced by this cross-modal plasticity phase appears to be age-dependent. Previous research revealed that adolescent mice (P45) do not show this plasticity phenomenon while adult mice (P120) do, and that an altered state of the GABAergic system plays a key role in this age dependency. CB1R is the main endocannabinoid (ECB) receptor of the central nervous system and as a neuronal and astroglial receptor is capable of regulating GABAergic synaptic transmission. Moreover, this receptor shows a similar age-dependent cortical expression pattern and is already known to be an important mediator of synaptic plasticity. With this project, we aim to decipher the involvement of the CB1R in ME-induced cross-modal plasticity as well as its contribution to age-related differences in neuroplasticity in general. Therefore, we will characterize CB1R expression in the ME model and attempt to identify causality between ECB signalling and cross-modal brain plasticity by using a pharmacological approach. In addition, we will interrogate the link between cell-specific adaptations to the GABAergic system, ECBs and cross-modal plasticity by ex vivo slice electrophysiology and decipher the specific contribution of the astroglial CB1R to cross-modal plasticity via a cell type specific gene manipulation strategy. References L. Van Brussel, A. Gerits, L. Arckens, Cerebral Cortex 21 (2011) J. Nys, K. Smolders, M.-E. Laramee, I. Hofman, T.-T. Hu, L. Arckens, Journal of Neuroscience 35 (2015) D. Piomelli, Nature Reviews Neuroscience 4 (2003) T. Yoneda, K. Kameyama, K. Esumi, Y. Daimyo, M. Watanabe, Y. Hata, PLoS ONE 8 (2013) Keywords: CB1 cannabinoid receptor (CB1), Monocular enucleation, neuroplasticity, Visual Cortex, Neuron-astrocyte communication Conference: 13th National Congress of the Belgian Society for Neuroscience , Brussels, Belgium, 24 May - 24 May, 2019. Presentation Type: Poster presentation Topic: Cellular/Molecular Neuroscience Citation: Durieux L, Hennes M, Giugliano M and Arckens L (2019). A crucial role for endocannabinoid signalling in age-dependent cross-modal brain plasticity upon vision loss. Front. Neurosci. Conference Abstract: 13th National Congress of the Belgian Society for Neuroscience . doi: 10.3389/conf.fnins.2019.96.00035 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 24 Apr 2019; Published Online: 27 Sep 2019. * Correspondence: Mr. Lucas Durieux, KU Leuven, Biology, Leuven, 3000, Belgium, lucas.durieux@kuleuven.be Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Lucas Durieux Maroussia Hennes Michele Giugliano Lutgarde Arckens Google Lucas Durieux Maroussia Hennes Michele Giugliano Lutgarde Arckens Google Scholar Lucas Durieux Maroussia Hennes Michele Giugliano Lutgarde Arckens PubMed Lucas Durieux Maroussia Hennes Michele Giugliano Lutgarde Arckens Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

5-HTR2A and 5-HTR3A but not 5-HTR1A antagonism impairs the cross-modal reactivation of deprived visual cortex in adulthood

Visual cortical areas show enhanced tactile responses in blind individuals, resulting in improved behavioral performance. Induction of unilateral vision loss in adult mice, by monocular enucleation (ME), is a validated model for such cross-modal brain plasticity. A delayed whisker-driven take-over of the medial monocular zone of the visual cortex is preceded by so-called unimodal plasticity, involving the potentiation of the spared-eye inputs in the binocular cortical territory. Full reactivation of the sensory-deprived contralateral visual cortex is accomplished by 7 weeks post-injury. Serotonin (5-HT) is known to modulate sensory information processing and integration, but its impact on cortical reorganization after sensory loss, remains largely unexplored. To address this issue, we assessed the involvement of 5-HT in ME-induced cross-modal plasticity and the 5-HT receptor (5-HTR) subtype used. We first focused on establishing the impact of ME on the total 5-HT concentration measured in the visual cortex and in the somatosensory barrel field. Next, the changes in expression as a function of post-ME recovery time of the monoamine transporter 2 (vMAT2), which loads 5-HT into presynaptic vesicles, and of the 5-HTR1A and 5-HTR3A were assessed, in order to link these temporal expression profiles to the different types of cortical plasticity induced by ME. In order to accurately pinpoint which 5-HTR exactly mediates ME-induced cross-modal plasticity, we pharmacologically antagonized the 5-HTR1A, 5-HTR2A and 5-HTR3A subtypes. This study reveals brain region-specific alterations in total 5-HT concentration, time-dependent modulations in vMAT2, 5-HTR1A and 5-HTR3A protein expression and 5-HTR antagonist-specific effects on the post-ME plasticity phenomena. Together, our results confirm a role for 5-HTR1A in the early phase of binocular visual cortex plasticity and suggest an involvement of 5-HTR2A and 5-HTR3A but not 5-HTR1A during the late cross-modal recruitment of the medial monocular visual cortex. These insights contribute to the general understanding of 5-HT function in cortical plasticity and may encourage the search for improved rehabilitation strategies to compensate for sensory loss.

Rapid plasticity of intact axons following a lesion to the visual pathways during early brain development is triggered by microglial activation

Lesions in the central nervous system (CNS) can often induce structural reorganization within intact circuits of the brain. Several studies show advances in the understanding of mechanisms of brain plasticity and the role of the immune system activation. Microglia, a myeloid derived cell population colonizes the CNS during early phases of embryonic development. In the present study, we evaluated the role of microglial activation in the sprouting of intact axons following lesions of the visual pathways. We evaluated the temporal course of microglial activation in the superior colliculus following a contralateral monocular enucleation (ME) and the possible involvement of microglial cells in the plastic reorganization of the intact, uncrossed, retinotectal pathway from the remaining eye. Lister Hooded rats were enucleated at PND 10 and submitted to systemic treatment with inhibitors of microglial activation: cyclosporine A and minocycline. The use of neuroanatomical tracers allowed us to evaluate the time course of structural axonal plasticity. Immunofluorescence and western blot techniques were used to observe the expression of microglial marker, Iba-1 and the morphology of microglial cells. Following a ME, Iba-1 immunoreactivity showed a progressive increase of microglial activation in the contralateral SC at 24 h, peaking at 72 h after the lesion. Treatment with inhibitors of microglial activation blocked both the structural plasticity of intact uncrossed retinotectal axons and microglial activation as seen by the decrease of Iba-1 immunoreactivity. The local blockade of TNF-α with a neutralizing antibody was also able to block axonal plasticity of the intact eye following a ME. The data support the hypothesis that microglial activation is a necessary step for the regulation of neuroplasticity induced by lesions during early brain development.

Early monocular enucleation selectively disrupts neural development of face perception in the occipital face area

Retinoblastoma generally occurs before 5 years of age and often requires enucleation (surgical removal of one eye) of the cancerous eye. We have previously shown using behavioural methods that this disruption in binocular vision during the critical period of visual development results in impaired face perception. In this case series study, we sought to determine the underlying neural correlates of this face perception deficit by examining brain activity in regions of cortex that preferentially respond to visual images of faces and places in 6 adults who had one eye enucleated early in life due to retinoblastoma. A group of 10 binocularly-intact adult controls were recruited for comparison. Functional magnetic resonance imaging (fMRI) was conducted over two separate runs for each participant in one scanning session. Each run consisted of 6 blocks each of face, place, and object images. Region-of-interest analyses were conducted to locate face-preferential [fusiform face area (FFA), occipital face area (OFA)] and place-preferential [parahippocampal place area (PPA), transverse occipital sulcus (TOS)] regions-of-interest. Descriptive statistics are reported. Results. Enucleated adults exhibited reduced functional activation in face-preferential regions (left FFA, right OFA, left OFA), but similar activation within the face-preferential right FFA and the place-preferential regions (bilateral PPA and TOS). Conclusions. These results indicate that early monocular enucleation prevents robust development of late-maturing face processing capabilities and that this disruption is specific to face networks and not to networks supporting other visual image categories.

Vascular Endothelial Growth Factor (VEGF) Prevents the Downregulation of the Cholinergic Phenotype in Axotomized Motoneurons of the Adult Rat.

Vascular endothelial growth factor (VEGF) was initially characterized by its activity on the vascular system. However, there is growing evidence indicating that VEGF also acts as a neuroprotective factor, and that its administration to neurons suffering from trauma or disease is able to rescue them from cell death. We questioned whether VEGF could also maintain damaged neurons in a neurotransmissive mode by evaluating the synthesis of their neurotransmitter, and whether its action would be direct or through its well-known angiogenic activity. Adult rat extraocular motoneurons were chosen as the experimental model. Lesion was performed by monocular enucleation and immediately a gelatine sponge soaked in VEGF was implanted intraorbitally. After 7 days, abducens, trochlear, and oculomotor nuclei were examined by immunohistochemistry against choline acetyltransferase (ChAT), the biosynthetic enzyme of the motoneuronal neurotransmitter acetylcholine. Lesioned motoneurons exhibited a noticeable ChAT downregulation which was prevented by VEGF administration. To explore whether this action was mediated via an increase in blood vessels or in their permeability, we performed immunohistochemistry against laminin, glucose transporter-1 and the plasmatic protein albumin. The quantification of the immunolabeling intensity against these three proteins showed no significant differences between VEGF-treated, axotomized and control animals. Therefore, the present data indicate that VEGF is able to sustain the cholinergic phenotype in damaged motoneurons, which is a first step for adequate neuromuscular neurotransmission, and that this action seems to be mediated directly on neurons since no sign of angiogenic activity was evident. These data reinforces the therapeutical potential of VEGF in motoneuronal diseases.

Monocular enucleation alters retinal waves in the surviving eye

BackgroundActivity in neurons drives afferent competition that is critical for the refinement of nascent neural circuits. In ferrets, when an eye is lost in early development, surviving retinogeniculate afferents from the spared eye spread across the thalamus in a manner that is dependent on spontaneous retinal activity. However, how this spontaneous activity, also known as retinal waves, might dynamically regulate afferent terminal targeting remains unknown.MethodsWe recorded retinal waves from retinae ex vivo using multi-electrode arrays. Retinae came from ferrets who were binocular or who had one eye surgically removed at birth. Linear mixed effects models were used to investigate the effects of early monocular enucleation on retinal wave activity.ResultsWhen an eye is removed at birth, spontaneous bursts of action potentials by retinal ganglion cells (RGCs) in the surviving eye are shorter in duration. The shortening of RGC burst duration results in decreased pairwise RGC correlations across the retina and is associated with the retinal wave-dependent spread of retinogeniculate afferents previously reported in enucleates.ConclusionOur findings show that removal of the competing eye modulates retinal waves and could underlie the dynamic regulation of competition-based refinement during retinogeniculate development.

Enucleation Induces Parvalbumin and Glial Fibrillary Acidic Protein, but Not Calbindin D28k Protein Expression in Superior Colliculus of Wistar Rats

Background: It is known that eye enucleation causes various morphological and functional alterations in the central nervous system (CNS). The purpose of this study was to examine the sub-chronic effects of monocular enucleation on the distribution of the calcium binding proteins calbindin D28k (CB) and parvalbumin (PV) as well as the glial fibrillary acidic protein (GFAP) immunoreactivity in the superior colliculus (SC) of Wistar rats.Materials and Methods: Thirty young adult (8 weeks) male Wistar rats from SLC (Shizuoka, Japan), weighing 200-250 grams, were housed in separate cages under controlled conditions with a constant temperature kept in 12:12 light/dark cycle and ad libitum water and food. In this study the rats were divided into two groups, a control and an enucleated groups. The experimental group received unilateral eye enucleation and was allowed 1, 4 or 12 weeks recovery before sacrificed.Results: Unilateral enucleation over a period of 1 week or more caused a decrease in the number CB-immunoreactive (CBIR) neurons. This loss was associated with an increase in GFAP-IR astrocytes in the superficial gray layer and the optic layer of the SC with contralateral side predominance. In addition, the CB-IR neurons illustrated a smaller soma and poor dendritic arborization. Conversely, the GFAP-IR astrocytes were hypertrophied with longer foot processes on the contralateral side of enucleation. Interestingly, the number of PV-IR neurons was elevated for up to 4 weeks in enucleated rats versus shamoperated rats.Conclusion: This study demonstrates the importance of calcium-binding protein homeostasis and reversible glial response for maintaining variability of neuronal function in sub-cortical visual centers following optic nerve deafferentation.Keywords: enucleation, superior colliculus, calbindin D28k, parvalbumin, glial fibrillary acidic protein