Visual information conveyed through the extrageniculate visual pathway, which runs from the retina via the superior colliculus (SC) and the lateral posterior nucleus (LPN) of the thalamus to the ...higher visual cortex, plays a critical role in the visual capabilities of many mammalian species. However, its functional role in the higher visual cortex remains unclear. Here, we observed visual cortical area activity in anesthetized mice to evaluate the role of the extrageniculate pathway on their specialized visual properties.
The preferred stimulus velocities of neurons in the higher visual areas (lateromedial LM, anterolateral AL, anteromedial AM, and rostrolateral RL areas) were measured using flavoprotein fluorescence imaging and two-photon calcium imaging and were higher than those in the primary visual cortex (V1). Further, the velocity-tuning properties of the higher visual areas were different from each other. The response activities in these areas decreased after V1 ablation; however, the visual properties’ differences were preserved. After SC destruction, these preferences for high velocities disappeared, and their tuning profiles became similar to that of the V1, whereas the tuning profile of the V1 remained relatively normal. Neural tracer experiments revealed that each of these higher visual areas connected with specific subregions of the LPN.
The preservation of visual property differences among the higher visual areas following V1 lesions and their loss following SC lesions indicate that pathways from the SC through the thalamus to higher cortical areas are sufficient to support these differences.
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•The velocity-tuning properties of mouse visual cortical areas are variable•The differences in the visual properties were preserved after V1 ablation•SC destruction disturbed the properties of the higher visual areas•Each of these higher visual areas is connected with specific LPN subdivisions
Tohmi et al. observe visual properties of mouse higher visual areas after lesioning the V1 or superior colliculus (SC) and show that unique properties of the higher visual areas depend on inputs from the SC via distinct subregions of the lateral posterior nucleus of the thalamus.
Feedback regulation from the higher association areas is thought to control the primary sensory cortex, contribute to the cortical processing of sensory information, and work for higher cognitive ...functions such as multimodal integration and attentional control. However, little is known about the underlying neural mechanisms. Here, we show that the posterior parietal cortex (PPC) persistently inhibits the activity of the primary visual cortex (V1) in mice. Activation of the PPC causes the suppression of visual responses in V1 and induces the short‐term depression, which is specific to visual stimuli. In contrast, pharmacological inactivation of the PPC or disconnection of cortical pathways from the PPC to V1 results in an effect of transient enhancement of visual responses in V1. Two‐photon calcium imaging demonstrated that the cortical disconnection caused V1 excitatory neurons an enhancement of visual responses and a reduction of orientation selectivity index (OSI). These results show that the PPC regulates the response properties of V1 excitatory neurons. Our findings reveal one of the functions of the PPC, which may contribute to higher brain functions in mice.
We show that the posterior parietal cortex (PPC) constantly inhibits the activity of the primary visual cortex (V1) in mice. Activation/inactivation of the PPC causes the suppression/enhancement of visual responses in V1. The PPC activation induces the short‐term depression of V1, which is specific to visual stimuli. We also found that the inhibitory projection from the PPC to V1 regulates the neural properties of V1.
We reviewed the methods of nonheme-iron histochemistry with special focus on the underlying chemical principles. The term nonheme-iron includes heterogeneous species of iron complexes where iron is ...more loosely bound to low-molecular weight organic bases and proteins than that of heme (iron-protoporphyrin complex). Nonheme-iron is liberated in dilute acid solutions and available for conventional histochemistry by the Perls and Turnbull and other methods using iron chelators, which depend on the production of insoluble iron compounds. Treatment with strong oxidative agents is required for the liberation of heme-iron, which therefore is not stained by conventional histochemistry. The Perls method most commonly used in laboratory investigations largely stains ferric iron, but stains some ferrous iron as well, while the Turnbull method is specific for the latter. Although the Turnbull method performed on sections fails in staining ferrous iron or stains only such parts of the tissue where iron is heavily accumulated, an in vivo perfusion-Turnbull method demonstrated the ubiquitous distribution of ferrous iron, particularly in lysosomes. The Perls or Turnbull reaction is enhanced by DAB/silver/gold methods for electron microscopy. The iron sulfide method and the staining of redox-active iron with H2O2 and DAB are also applicable for electron microscopy. Although the above histochemical methods have advantages for visualizing iron by conventional light and electron microscopy, the quantitative estimation of iron is not easy. Recent methods depending on the quenching of fluorescent divalent metal indicators by Fe2+ and dequenching by divalent metal chelators have enabled the quantitative estimation of chelatable Fe2+ in isolated viable cells.
Iron in the brain is utilized for cellular respiration, neurotransmitter synthesis/degradation, and myelin formation. Iron, especially its ferrous form, also has the potential for catalyzing the ...Fenton reaction to generate highly cytotoxic hydroxyl radicals. The amount of iron in the brain must therefore be strictly controlled. In this study, we focused on the cellular and subcellular localizations of nonheme ferric (Fe(III)) and ferrous (Fe(II)) iron in the adult female rat brain using light and electron microscopic histochemistry. Although Fe(II) deposition was much less dominant than Fe(III), the brain contained iron in both forms. Among the cellular elements of the brain, oligodendrocytes were numerically the most prominent and heavily iron-storing cells. Pericapillary astrocytes and sporadic microglial cells also showed dense iron accumulation. Large neurons involved in the motor system were relatively strongly iron-positive. Subcellularly, Fe(III) and Fe(II) were mainly localized in lysosomes, and occasionally in the cytosol and mitochondria. Furthermore, capillary endothelial cells had Fe(III)-positive reactions in lysosomes and the cytosol, with Fe(II)-positive reactions on the luminal membrane. With advancing age, both Fe(III) and Fe(II) became more extensively distributed and accumulated more numerously in oligodendrocytes and astrocytes. These findings suggest that age-related increases in Fe(II) accumulation may raise the risk of tissue damage in the normal brain.
The granular retrosplenial cortex (GRS) in the rat has a distinct microcolumn-type structure. The apical tufts of dendritic bundles at layer I, which are formed by layer II neurons, co-localize with ...patches of thalamic terminations from anteroventral (AV) thalamic nucleus. To further understand this microcolumn-type structure in the GRS, one of remaining questions is whether this structure extends into other layers, such as layers III/IV. Other than layer I, previous tracer injection study showed that AV thalamic nucleus also projects to layer III/IV in the GRS. In this study, we examined the morphology of branches in the GRS from the AV thalamus in single axon branch resolution in order to determine whether AV axon branches in layer III/IV are branches of axons with extensive branch in layer I, and, if so, whether the extent of these arborizations in layer III/IV vertically matches with that in layer I. For this purpose, we used a small volume injection of biotinylated dextran-amine into the AV thalamus and reconstructing labeled single axon branches in the GRS. We found that the AV axons consisted of heterogeneous branching types. Type 1 had extensive arborization occurring only in layer Ia. Type 2 had additional branches in III/IV. Types 1 and 2 had extensive ramifications in layer Ia, with lateral extensions within the previously reported extensions of tufts from single dendritic bundles (i.e., 30-200 μm; mean 78 μm). In type 2 branches, axon arborizations in layer III/IV were just below to layer Ia ramifications, but much wider (148-533 μm: mean, 341 μm) than that in layer Ia axon branches and dendritic bundles, suggesting that layer-specific information transmission spacing existed even from the same single axons from the AV to the GRS. Thus, microcolumn-type structure in the upper layer of the GRS was not strictly continuous from layer I to layer IV. How each layer and its components interact each other in different spatial scale should be solved future.
The transforming growth factor-betas (TGF-βs) regulate the induction of dopaminergic neurons and are elevated in the CSF of Parkinson's patients. We report here that mice with TGF-β2 ...haploinsufficiency (TGF-β2
+/−) have subclinical defects in the dopaminergic neurons of their substantia nigra pars compacta. At 6 weeks of age, the TGF-β2
+/− mice had 12% fewer dopaminergic neurons than wild-type littermates. No additional loss of neurons occurred during the next 5 months, although striatal dopamine declined to 70% of normal. The level of 3,4-dihydroxphenylacetic acid was normal in the TGF-β2
+/− mice, indicating that a compensatory mechanism maintains dopamine stimulation of their striatum. The TGF-β2
+/− mice had normal sensitivity to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tretrahydropyridine, despite having reduced levels of monoamine oxidase-B. These results raise the possibility that people with naturally low levels of TGF-β2 may have less functional reserve in their nigrostriatal pathway, causing them to be at increased risk of developing Parkinson disease.
Perfusion-Perls and -Turnbull methods supplemented by the intensification with 3,3'-diaminobenzidine (+ DAB) enabled stronger and more extensive staining of nonheme iron than the Perls + and Turnbull ...+ DAB methods carried out on tissue sections fixed with 10% formalin in 0.9% saline or PBS. The section- and perfusion-Perls + DAB methods are not specific for the demonstration of nonheme ferric iron but also stain nonheme ferrous iron. However, owing to its high sensitivity, the perfusion-Perls + DAB method would provide useful information about nonheme iron deposition regardless of oxidation states in normal and pathological conditions. The perfusion-Turnbull + DAB method is specifically demonstrable of nonheme ferrous iron and the results from this method showed significant stores of nonheme ferrous iron in the hepatocytes, Kupffer cells, splenic macrophages, and gastric parietal cells of the rat. Since nonheme ferrous iron is considered to be critically involved in free radical generation, the perfusion-Turnbull + DAB method would visualize such populations of cells that are at risk from free radical damage.
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