Difference in sensory dependence of occ1/Follistatin-related protein expression between macaques and mice

Comparative analysis of structural modifications induced by monocular retinal inactivation and monocular deprivation in the developing cat lateral geniculate nucleus

During a critical period of postnatal life, monocular deprivation (MD) by eyelid closure reduces the size of neurons in layers of the dorsal lateral geniculate nucleus (dLGN) connected to the deprived eye and shifts cortical ocular dominance in favor of the non-deprived eye. Temporary inactivation of the non-deprived eye can promote superior recovery from the effects of long-term MD compared to conventional occlusion therapy. In the current study, we assessed the modification of neuron size in the dLGN as a means of measuring the impact of a brief period of monocular inactivation (MI) imposed at different postnatal ages. The biggest impact of MI was observed when it occurred at the peak of the critical period. Unlike the effect of MD, structural plasticity following MI was observed in both the binocular and monocular segments of the dLGN. With increasing age, the capacity for inactivation to alter postsynaptic cell size diminished but was still significant beyond the critical period. In comparison to MD, inactivation produced effects that were about double in magnitude and exhibited efficacy at older ages. Notwithstanding the large neural alterations precipitated by MI, its effects were remediated with a short period of binocular experience, and vision through the previously inactivated eye fully recovered. These results demonstrate that MI is a potent means of modifying the visual pathway and does so at ages when occlusion is ineffective. The efficacy and longevity of inactivation to elicit plasticity highlight its potential to ameliorate disorders of the visual system such as amblyopia.

Neuronal and microglial localization of secreted phosphoprotein 1 (osteopontin) in intact and damaged motor cortex of macaques

We previously reported that mRNA encoding secreted phosphoprotein 1 (SPP1), also known as osteopontin, is preferentially expressed in large neurons in layer V of the macaque motor cortex, most of which are presumed to be corticospinal tract neurons. As a first step to elucidating the cellular function of SPP1 in macaque neurons, we examined the localization of SPP1 in the primary motor cortex (M1) of the macaque by using immunohistochemistry. SPP1 immunoreactivity was found to be localized in the cell bodies of neurons, but not outside the cells, indicating that SPP1 was not secreted from these neurons. The results of electron microscope analysis and double-labeling analysis with marker proteins suggested that SPP1 was localized in the mitochondria of neurons. The distributions of SPP1 in the neurons corresponded to those of integrin αV, a putative receptor for SPP1. The distribution of SPP1 was also investigated in macaques whose M1 had been lesioned. We found that SPP1 was secreted by proliferated microglia in the lesioned area. Double-labeling analysis indicated that SPP1 immunoreactivity in the microglia was colocalized with CD44, another putative receptor for SPP1. Success rates in the small-object-retrieval task were positively correlated with SPP1 immunoreactivity in the neurons in the perilesional area. SPP1 has multiple roles in the macaque motor cortex, and it may be a key protein during recovery of hand movement after brain damage.

Application of viral vectors to the study of neural connectivities and neural circuits in the marmoset brain

It is important to study the neural connectivities and functions in primates. For this purpose, it is critical to be able to transfer genes to certain neurons in the primate brain so that we can image the neuronal signals and analyze the function of the transferred gene. Toward this end, our team has been developing gene transfer systems using viral vectors. In this review, we summarize our current achievements as follows. 1) We compared the features of gene transfer using five different AAV serotypes in combination with three different promoters, namely, CMV, mouse CaMKII (CaMKII), and human synapsin 1 (hSyn1), in the marmoset cortex with those in the mouse and macaque cortices. 2) We used target‐specific double‐infection techniques in combination with TET‐ON and TET‐OFF using lentiviral retrograde vectors for enhanced visualization of neural connections. 3) We used an AAV‐mediated gene transfer method to study the transcriptional control for amplifying fluorescent signals using the TET/TRE system in the primate neocortex. We also established systems for shRNA mediated gene targeting in a neocortical region where a gene is significantly expressed and for expressing the gene using the CMV promoter for an unexpressed neocortical area in the primate cortex using AAV vectors to understand the regulation of downstream genes. Our findings have demonstrated the feasibility of using viral vector mediated gene transfer systems for the study of primate cortical circuits using the marmoset as an animal model. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 354–372, 2017

c-FOS expression in the visual system of tree shrews after monocular inactivation

Tree shrews possess an unusual segregation of ocular inputs to sublayers rather than columns in the primary visual cortex (V1). In this study, the lateral geniculate nucleus (LGN), superior colliculus (SC), pulvinar, and V1 were examined for changes in c-FOS, an immediate-early gene, expression after 1 or 24 hours of monocular inactivation with tetrodotoxin (TTX) in tree shrews. Monocular inactivation greatly reduced gene expression in LGN layers related to the blocked eye, whereas normally high to moderate levels were maintained in the layers that receive inputs from the intact eye. The SC and caudal pulvinar contralateral to the blocked eye had greatly (SC) or moderately (pulvinar) reduced gene expressions reflective of dependence on the contralateral eye. c-FOS expression in V1 was greatly reduced contralateral to the blocked eye, with most of the expression that remained in upper layer 4a and lower 4b and lower layer 6 regions. In contrast, much of V1 contralateral to the active eye showed normal levels of c-FOS expression, including the inner parts of sublayers 4a and 4b and layers 2, 3, and 6. In some cases, upper layer 4a and lower 4b showed a reduction of gene expression. Layers 5 and sublayer 3c had normally low levels of gene expression. The results reveal the functional dominance of the contralateral eye in activating the SC, pulvinar, and V1, and the results from V1 suggest that the sublaminar organization of layer 4 is more complex than previously realized. J. Comp. Neurol. 525:151-165, 2017. © 2016 Wiley Periodicals, Inc.

Retinal lesions induce fast intrinsic cortical plasticity in adult mouse visual system

Neuronal activity plays an important role in the development and structural-functional maintenance of the brain as well as in its life-long plastic response to changes in sensory stimulation. We characterized the impact of unilateral 15° laser lesions in the temporal lower visual field of the retina, on visually driven neuronal activity in the afferent visual pathway of adult mice using in situ hybridization for the activity reporter gene zif268. In the first days post-lesion, we detected a discrete zone of reduced zif268 expression in the contralateral hemisphere, spanning the border between the monocular segment of the primary visual cortex (V1) with extrastriate visual area V2M. We could not detect a clear lesion projection zone (LPZ) in areas lateral to V1 whereas medial to V2M, agranular and granular retrosplenial cortex showed decreased zif268 levels over their full extent. All affected areas displayed a return to normal zif268 levels, and this was faster in higher order visual areas than in V1. The lesion did, however, induce a permanent LPZ in the retinorecipient layers of the superior colliculus. We identified a retinotopy-based intrinsic capacity of adult mouse visual cortex to recover from restricted vision loss, with recovery speed reflecting the areal cortical magnification factor. Our observations predict incomplete visual field representations for areas lateral to V1 vs. lack of retinotopic organization for areas medial to V2M. The validation of this mouse model paves the way for future interrogations of cortical region- and cell-type-specific contributions to functional recovery, up to microcircuit level.

Monocular inhibition reveals temporal and spatial changes in gene expression in the primary visual cortex of marmoset

We investigated the time course of the expression of several activity-dependent genes evoked by visual inputs in the primary visual cortex (V1) in adult marmosets. In order to examine the rapid time course of activity-dependent gene expression, marmosets were first monocularly inactivated by tetrodotoxin (TTX), kept in darkness for two days, and then exposed to various length of light stimulation. Activity-dependent genes including HTR1B, HTR2A, whose activity-dependency were previously reported by us, and well-known immediate early genes (IEGs), c-FOS, ZIF268, and ARC, were examined by in situ hybridization. Using this system, first, we demonstrated the ocular dominance type of gene expression pattern in V1 under this condition. IEGs were expressed in columnar patterns throughout layers II–VI of all the tested monocular marmosets. Second, we showed the regulation of HTR1B and HTR2A expressions by retinal spontaneous activity, because HTR1B and HTR2A mRNA expressions sustained a certain level regardless of visual stimulation and were inhibited by a blockade of the retinal activity with TTX. Third, IEGs dynamically changed its laminar distribution from half an hour to several hours upon a stimulus onset with the unique time course for each gene. The expression patterns of these genes were different in neurons of each layer as well. These results suggest that the regulation of each neuron in the primary visual cortex of marmosets is subjected to different regulation upon the change of activities from retina. It should be related to a highly differentiated laminar structure of marmoset visual systems, reflecting the functions of the activity-dependent gene expression in marmoset V1.

Differential expression patterns of striate cortex-enriched genes among Old World, New World, and prosimian primates

A group of 5 genes, OCC1, testican-1, testican-2, 5-HT1B, and 5-HT2A, are selectively expressed in layer 4 (4C of Brodmann) of striate cortex (visual area V1) of both Old World macaques and New World marmoset monkeys. The expression of these genes is activity dependent, as expression is reduced after blocking retinal activity. Surprisingly, the pronounced expression pattern has not been found in rodents or carnivores. Thus, these genes may be highly expressed in V1 of some but perhaps not all primates. Here, we compared the gene expression in members of 3 major branches of primate evolution: prosimians, New World monkeys, and Old World monkeys. Although the expression pattern of 5-HT1B was well conserved, those of the other genes varied from the least distinct in prosimian galagos to successively more in New World owl monkeys, marmosets, squirrel monkeys, and Old World macaque monkeys. In owl monkeys, the expression of 5-HT2A was significantly reduced by monocular tetrodotoxin injection, while those of OCC1 and 5-HT1B were not. Thus, we propose that early primates had low levels of expression and higher levels emerged with anthropoid primates and became further enhanced in the Old World catarrhine monkeys that are more closely related to humans.

Selective gene expression in regions of primate neocortex: implications for cortical specialization

The neocortex, which is characteristic of mammals, has evolved to play important roles in cognitive and perceptual functions. The localization of different functions in different regions of the neocortex was well established within the last century. Studies on the formation of the neocortex have advanced at the molecular level, thus clarifying the mechanisms that control neural or glial cell differentiation and sensory projections. However, mechanisms that underlie cortical area specialization remain unsolved. To address this problem, our approach has been to isolate and characterize the genes that are selectively expressed in particular subsets of neocortical areas in primates; these areas are most distinctive among mammals. By differential display and restriction landmark cDNA scanning (RLCS) methods, we have identified two major classes of genes that are specifically expressed in the adult macaque monkey neocortical areas: one is expressed in the primary sensory areas, particularly, in the primary visual cortex (V1) and the other is expressed in the association areas. The genes that show these specific expression patterns are limited to only several gene families among our large-scale screening. In this review, I first describe the isolation and characterization of these genes, along with another class of genes specifically expressed in motor areas. Then, I discuss their functional significance in the primate neocortex. Finally, I discuss the implication of these gene expression patterns in neocortical specialization in primates and possible future research directions.

Evidence for cross-modal plasticity in adult mouse visual cortex following monocular enucleation

The goal of this study was to assess cortical reorganization in the visual system of adult mice in detail. A combination of deprivation of one eye and stimulation of the remaining eye previously led to the identification of input-specific subdivisions in mouse visual cortex. Using this information as a reference map, we established to what extent each of these functional subdivisions take part in cortical reactivation and reorganization upon unilateral enucleation. A recovery experiment revealed a differential laminar and temporal reactivation profile. Initiation of infragranular recovery of molecular activity near the border with nonvisual cortex and simultaneous hyperactivation of this adjacent cortex implied a partial nonvisual contribution to this plasticity. The strong effect of somatosensory deprivation as well as stimulation on infragranular visual cortex activation in long-term enucleated animals support this view. Furthermore, targeted tracer injections in visual cortex of control and enucleated animals revealed preexisting connections between the visual and somatosensory cortices of adult mice as possible mediators. In conclusion, this study supports an important cross-modal component in reorganization of adult mouse visual cortex upon monocular enucleation.

The expression pattern of Follistatin-like 1 in mouse central nervous system development

Follistatin-like 1 (Fstl1), also named TSC-36 (TGF-beta-stimulated clone 36), was first cloned from the mouse osteoblastic MC3T3-E1 cell line and can be up-regulated by TGF-beta. To better study the function of Fstl1 during the development of the mouse central nervous system (CNS), we examined Fstl1 expression in the developing mouse CNS, in detail, by in situ hybridization. Our results show that Fstl1 is strongly expressed in the telencephalon, diencephalon, brainstem, limbic system and spinal cord. In the telencephalon, Fstl1 positive cells are mainly located in the ventricular zone (VZ) and the subventricular zone (SVZ); a relatively weak signal was observed in layers II and III of the neocortex at postnatal stages. Fstl1 expression is robust in the developing hippocampus and persists to P20. In the developing diencephalon and hindbrain, abundant Fstl1 signals were also detected in nuclei including the medial habenular nucleus, the medial dorsal nucleus, the cochlear nuclei and so on. In addition, a strong expression of Fstl1 was detected in the thalamencephalic signal center, as well as in the olfactory cortex from E14.5 to P0. Meanwhile, Fstl1 was expressed in the septal area and the cingulate gyrus of the limbic system after birth. A high level of expression was also observed in the ventral horn of the spinal cord. These results indicate that Fstl1 may play an important role during CNS development in the mouse.

Expression of immediate-early genes reveals functional compartments within ocular dominance columns after brief monocular inactivation

Visual inputs from the 2 eyes in most primates activate alternating bands of cortex in layer 4C of primary visual cortex, thereby forming the well-studied ocular dominance columns (ODCs). In addition, the enzymatic reactivity of cytochrome oxidase (CO) reveals "blob" structures within the supragranular layers of ODCs. Here, we present evidence for compartments within ODCs that have not been clearly defined previously. These compartments are revealed by the activity-dependent mRNA expression of immediate-early genes (IEGs), zif268 and c-fos, after brief periods of monocular inactivation (MI). After a 1-3-h period of MI produced by an injection of tetrodotoxin, IEGs were expressed in a patchy pattern that included infragranular layers, as well as supragranular layers, where they corresponded to the CO blobs. In addition, the expressions of IEGs in layer 4C were especially high in narrow zones along boundaries of ODCs, referred to here as the "border strips" of the ODCs. After longer periods of MI (>5 h), the border strips were no longer apparent. When either eyelid was sutured, changes in IEG expression were not evident in layer 4C; however, the patchy pattern of the expression in the infragranular and supragranular layers remained. These changes of IEG expression after MI indicate that cortical circuits involving the CO blobs of the supragranular layers include aligned groups of neurons in the infragranular layers and that the border strip neurons of layer 4C are highly active for a 3-h period after MI.

Identification and localization of functional subdivisions in the visual cortex of the adult mouse

We investigated the anatomical characteristics of the mouse visual system through in situ hybridization for the neuronal activity marker zif268. Our main goal was to delineate the full extent of the cortical region processing visual information and additionally to identify the monocularly and binocularly driven subregions therein. We therefore analyzed the neocortex of monocularly and binocularly enucleated mice versus visually stimulated control mice. These visual manipulations revealed eye-specific parcellations at the neocortical level. In binocularly enucleated mice we detected an unambiguous lateral border between visually driven and nonvisual cortex based on the clear deprivation-induced reduction in zif268 expression in the first. However, medially a transition zone of intermediate intensity was found between primarily visual, that is V1 and multimodal retrosplenial cortex. Also in monocularly enucleated mice, the visual cortex contralateral to the deprived eye clearly displayed distinct regions of lower signal than the ipsilateral cortex. Yet interspersed between these regions of basal activity we could clearly identify a zone of high activity spanning the V1-V2L border. A second zone of higher activity was noticeable near the medial border of visual cortex. Comparison with binocularly enucleated mice indicates the presence of both binocular input as well as nonvisual input in this medial cortical region and thus confirms the transitional nature of the recently described rostromedial areas.

Differential expression patterns of occ1-related genes in adult monkey visual cortex

We have previously revealed that occ1 is preferentially expressed in the primary visual area (V1) of the monkey neocortex. In our attempt to identify more area-selective genes in the macaque neocortex, we found that testican-1, an occ1-related gene, and its family members also exhibit characteristic expression patterns along the visual pathway. The expression levels of testican-1 and testican-2 mRNAs as well as that of occ1 mRNA start of high in V1, progressively decrease along the ventral visual pathway, and end of low in the temporal areas. Complementary to them, the neuronal expression of SPARC mRNA is abundant in the association areas and scarce in V1. Whereas occ1, testican-1, and testican-2 mRNAs are preferentially distributed in thalamorecipient layers including “blobs,” SPARC mRNA expression avoids these layers. Neither SC1 nor testican-3 mRNA expression is selective to particular areas, but SC1 mRNA is abundantly observed in blobs. The expressions of occ1, testican-1, testican-2, and SC1 mRNA were downregulated after monocular tetrodotoxin injection. These results resonate with previous works on chemical and functional gradients along the primate occipitotemporal visual pathway and raise the possibility that these gradients and functional architecture may be related to the visual activity–dependent expression of these extracellular matrix glycoproteins.