Regional analysis of neurofilament protein immunoreactivity in the hamster's cortex

Architecture of the inferior parietal cortex in capuchin monkey

We studied the organization of the inferior parietal cortex (IPC) in five capuchin monkey (6 hemispheres) using cytoarchitectonic (Nissl), myeloarchitectonic (Gallyas), and immune-architectonic (SMI-32 monoclonal antibody) techniques. We partitioned the IPC into five distinct areas: PFG, PG, Opt, PFop, and PGop. Since we used parasagittal sections, we were not able to study area PF due to its far lateral position, which yielded slices that were tangential to the pial surface. Areas PFG, PG, and Opt were in the convexity close to the lateral sulcus, while PFop and PGop were positioned more posteriorly, in the opercular region of IPC. Of all the five regions, area Opt was the one most similar to its analogue in the macaque, especially as revealed with SMI-32 staining. Namely, in both primate species area Opt showed a low density of large pyramidal neurons. Additionally, the apical dendrites of these neurons were sparse and vertically orientated, resembling columns. We also found area PG to be similar: both species exhibited cell body layers with a radial arrangement. On the other hand, Nissl staining revealed area PFG to be architectonically different between New and Old-World monkeys: PFG in the capuchin showed a comparatively higher cell density than in macaques, especially in layers II and IV. These results suggest that evolution may have enabled the functional specialization of these brain regions based on behavioral demands of upper limb use. The small differences in the IPC of the two primates may be linked to interspecies variability.

Specific neuronal subpopulations in the amygdala of macaque monkeys express high levels of nonphosphorylated neurofilaments

Pyramidal neurons in the neocortex that express nonphosphorylated neurofilaments (NPNFs) are especially vulnerable to degeneration in Alzheimer's disease. Since the basolateral nuclear complex of the amygdala (BNC) and cortical nuclear complex of the amygdala (CNC) are cortex-like structures, containing both pyramidal (PNs) and nonpyramidal neurons (NPNs), it is of interest to determine which cell types in the primate BNC and CNC are NPNF+. We also studied NPNF expression in the non-cortex-like nuclei of the amygdala (central and medial nuclei). Digitized images of sections through fetal, newborn, infant, and adult macaque brains stained for NPNFs, obtained from the Macaque Brain Resource (MacBrainResource, MBR), were analyzed. The pattern of NPNF immunoreactivity (NPNF-ir) in the BNC, CNC, and medial nucleus was essentially identical in all four age groups, but there were some age-dependent differences in the central nucleus. All BNC and CNC nuclei contained a moderate density of NPNF+ NPNs. Both the somata and the entire dendritic arborizations of these NPNs were stained. PNs with robust NPNF-ir in their somata and proximal dendrites were only seen in the basal magnocellular nucleus, where it appeared that virtually every PN was NPNF+. This pattern of NPNF expression is distinct from that seen in the mammalian neocortex, where NPNF+ neurons are almost entirely PNs, but is very similar to that seen in a recent study of the rat BNC. These findings, in conjunction with the cortical data, suggest the possibility that NPNF+ neuronal subpopulations in the BNC and CNC might be especially vulnerable in Alzheimer's disease.

Specific neuronal subpopulations in the rat basolateral amygdala express high levels of nonphosphorylated neurofilaments

Cortical pyramidal neurons (PNs) containing nonphosphorylated neurofilaments (NNFs) localized with the SMI-32 monoclonal antibody have been shown to be especially vulnerable to degeneration in Alzheimer's disease (AD). The present investigation is the first to study the expression of SMI-32+ NNFs in neurons of the basolateral nuclear complex of the amygdala (BNC), which contains cortex-like PNs and nonpyramidal neurons (NPNs). We observed that PNs in the rat basolateral nucleus (BL), but not in the lateral (LAT) or basomedial (BM) nuclei, have significant levels of SMI-32-ir in their somata with antibody diluents that did not contain Triton X-100, but staining in these cells was greatly attenuated when the antibody diluent contained 0.3% Triton. Using Triton-containing diluents, we found that all SMI-32+ neurons in all three of the BNC nuclei were NPNs. Using a dual-labeling immunoperoxidase technique, we demonstrated that most of these SMI-32+ NPNs were parvalbumin-positive (PV+) or somatostatin-positive NPNs but not vasoactive intestinal peptide-positive or neuropeptide Y-positive NPNs. Using a technique that combines retrograde tracing with SMI-32 immunohistochemistry using intermediate levels of Triton in the diluent, we found that all BNC neurons projecting to the mediodorsal thalamic nucleus (MD) were large NPNs, and most were SMI-32+. In contrast, BNC neurons projecting to the ventral striatum or cerebral cortex were PNs that expressed low levels of SMI-32 immunoreactivity (SMI-32-ir) in the BL, and no SMI-32-ir in the LAT or BM. These data suggest that the main neuronal subpopulations in the BNC that degenerate in AD may be PV+ and MD-projecting NPNs.

The third wave: Intermediate filaments in the maturing nervous system

Intermediate filaments are critical for the extreme structural specialisations of neurons, providing integrity in dynamic environments and efficient communication along axons a metre or more in length. As neurons mature, an initial expression of nestin and vimentin gives way to the neurofilament triplet proteins and α-internexin, substituted by peripherin in axons outside the CNS, which physically consolidate axons as they elongate and find their targets. Once connection is established, these proteins are transported, assembled, stabilised and modified, structurally transforming axons and dendrites as they acquire their full function. The interaction between these neurons and myelinating glial cells optimises the structure of axons for peak functional efficiency, a property retained across their lifespan. This finely calibrated structural regulation allows the nervous system to maintain timing precision and efficient control across large distances throughout somatic growth and, in maturity, as a plasticity mechanism allowing functional adaptation.

Neurofilament heavy chain expression and neuroplasticity in rat auditory cortex after unilateral and bilateral deafness

Deafness induces many plastic changes in the auditory neural system. For instance, dendritic changes cause synaptic changes in neural cells. SMI-32, a monoclonal antibody reveals auditory areas and recognizes non-phosphorylated epitopes on medium- and high-molecular-weight subunits of neurofilament proteins in cortical pyramidal neuron dendrites. We investigated SMI-32-immunoreactive (-ir) protein levels in the auditory cortices of rats with induced unilateral and bilateral deafness. Adult male Sprague-Dawley rats were divided into unilateral deafness (UD), bilateral deafness (BD), and control groups. Deafness was induced by cochlear ablation. All rats were sacrificed, and the auditory cortices were harvested for real-time quantitative polymerase chain reaction (RT-qPCR) and western blot analyses at 2, 4, 6, and 12 weeks after deafness was induced. Immunohistochemical staining was performed to evaluate the location of SMI-32-ir neurons. Neurofilament heavy chain (NEFH) mRNA expression and SMI-32-ir protein levels were increased in the BD group. In particular, SMI-32-ir protein levels increased significantly 6 and 12 weeks after deafness was induced. In contrast, no significant changes in protein level were detected in the right or left auditory cortices at any time point in the UD group. NEFH mRNA level decreased at 4 weeks after deafness was induced in the UD group, but recovered thereafter. Taken together, BD induced plastic changes in the auditory cortex, whereas UD did not affect the auditory neural system sufficiently to show plastic changes, as measured by neurofilament protein level.

Neuron Types in the Presumptive Primary Somatosensory Cortex of the Florida Manatee (Trichechus manatus latirostris)

Within afrotherians, sirenians are unusual due to their aquatic lifestyle, large body size and relatively large lissencephalic brain. However, little is known about the neuron type distributions of the cerebral cortex in sirenians within the context of other afrotherians and aquatic mammals. The present study investigated two cortical regions, dorsolateral cortex area 1 (DL1) and cluster cortex area 2 (CL2), in the presumptive primary somatosensory cortex (S1) in Florida manatees (Trichechus manatus latirostris) to characterize cyto- and chemoarchitecture. The mean neuron density for both cortical regions was 35,617 neurons/mm(3) and fell within the 95% prediction intervals relative to brain mass based on a reference group of afrotherians and xenarthrans. Densities of inhibitory interneuron subtypes labeled against calcium-binding proteins and neuropeptide Y were relatively low compared to afrotherians and xenarthrans and also formed a small percentage of the overall population of inhibitory interneurons as revealed by GAD67 immunoreactivity. Nonphosphorylated neurofilament protein-immunoreactive (NPNFP-ir) neurons comprised a mean of 60% of neurons in layer V across DL1 and CL2. DL1 contained a higher percentage of NPNFP-ir neurons than CL2, although CL2 had a higher variety of morphological types. The mean percentage of NPNFP-ir neurons in the two regions of the presumptive S1 were low compared to other afrotherians and xenarthrans but were within the 95% prediction intervals relative to brain mass, and their morphologies were comparable to those found in other afrotherians and xenarthrans. Although this specific pattern of neuron types and densities sets the manatee apart from other afrotherians and xenarthrans, the manatee isocortex does not appear to be explicitly adapted for an aquatic habitat. Many of the features that are shared between manatees and cetaceans are also shared with a diverse array of terrestrial mammals and likely represent highly conserved neural features. A comparative study across manatees and dugongs is necessary to determine whether these traits are specific to one or more of the manatee species, or can be generalized to all sirenians.

Architectonic mapping of somatosensory areas involved in skilled forelimb movements and tool use

Cebus monkeys stand out from other New World monkeys by their ability to perform fine hand movements, and by their spontaneous use of tools in the wild. Those behaviors rely on the integration of somatosensory information, which occurs in different areas of the parietal cortex. Although a few studies have examined and parceled the somatosensory areas of the cebus monkey, mainly using electrophysiological criteria, very little is known about its anatomical organization. In this study we used SMI-32 immunohistochemistry, myelin, and Nissl stains to characterize the architecture of the parietal cortical areas of cebus monkeys. Seven cortical areas were identified between the precentral gyrus and the anterior bank of the intraparietal sulcus. Except for areas 3a and 3b, distinction between different somatosensory areas was more evident in myelin-stained sections and SMI-32 immunohistochemistry than in Nissl stain, especially for area 2 and subdivisions of area 5. Our results show that cebus monkeys have a relatively complex somatosensory cortex, similar to that of macaques and humans. This suggests that, during primate evolution, the emergence of new somatosensory areas underpinned complex manual behaviors in most Old World simians and in the New World cebus monkey. J. Comp. Neurol. 524:1399-1423, 2016. © 2015 Wiley Periodicals, Inc.

Specific distribution of non-phosphorylated neurofilaments characterizing each subfield in the mouse auditory cortex

Recent imaging studies revealed the presence of functional subfields in the mouse auditory cortex. However, little is known regarding the morphological basis underlying the functional differentiation. Distribution of particular molecules is the key information that may be applicable for identifying auditory subfields in the post-mortem brain. Immunoreactive patterns using SMI-32 monoclonal antibody against non-phosphorylated neurofilament (NNF) have already been used to identify or parcellate various brain regions in various animals. In the present study, we investigated whether distribution of NNF is a reliable marker for identifying functional subfields in the mouse auditory cortex, and found that each auditory subfield has region-specific cellular and laminar patterns of immunoreactivity for NNF.

Delineation of a frequency-organized region isolated from the mouse primary auditory cortex

The primary auditory cortex (AI) is the representative recipient of information from the ears in the mammalian cortex. However, the delineation of the AI is still controversial in a mouse. Recently, it was reported, using optical imaging, that two distinct areas of the AI, located ventrally and dorsally, are activated by high-frequency tones, whereas only one area is activated by low-frequency tones. Here, we show that the dorsal high-frequency area is an independent region that is separated from the rest of the AI. We could visualize the two distinct high-frequency areas using flavoprotein fluorescence imaging, as reported previously. SMI-32 immunolabeling revealed that the dorsal region had a different cytoarchitectural pattern from the rest of the AI. Specifically, the ratio of SMI-32-positive pyramidal neurons to nonpyramidal neurons was larger in the dorsal high-frequency area than the rest of the AI. We named this new region the dorsomedial field (DM). Retrograde tracing showed that neurons projecting to the DM were localized in the rostral part of the ventral division of the medial geniculate body with a distinct frequency organization, where few neurons projected to the AI. Furthermore, the responses of the DM to ultrasonic courtship songs presented by males were significantly greater in females than in males; in contrast, there was no sex difference in response to artificial pure tones. Our findings offer a basic outline on the processing of ultrasonic vocal information on the basis of the precisely subdivided, multiple frequency-organized auditory cortex map in mice.

Topography and architecture of visual and somatosensory areas of the agouti

We analyzed the organization of the somatosensory and visual cortices of the agouti, a diurnal rodent with a relatively big brain, using a combination of multiunit microelectrode recordings and histological techniques including myelin and cytochrome oxidase staining. We found multiple representations of the sensory periphery in the parietal, temporal, and occipital lobes. While the agouti's primary (V1) and secondary visual areas seemed to lack any obvious modular arrangement, such as blobs or stripes, which are found in some primates and carnivores, the primary somatosensory area (S1) was internally subdivided in discrete regions, isomorphically associated with peripheral structures. Our results confirm and extend previous reports on this species, and provide additional data to understand how variations in lifestyle can influence brain organization in rodents.

Laminar and neurochemical organization of the dorsal cochlear nucleus of the human, monkey, cat, and rodents

The dorsal cochlear nucleus (DCN) is a brainstem structure that receives input from the auditory nerve. Many studies in a diversity of species have shown that the DCN has a laminar organization and identifiable neuron types with predictable synaptic relations to each other. In contrast, studies on the human DCN have found a less distinct laminar organization and fewer cell types, although there has been disagreement among studies in how to characterize laminar organization and which of the cell types identified in other animals are also present in humans. We have reexamined DCN organization in the human using immunohistochemistry to analyze the expression of several proteins that have been useful in delineating the neurochemical organization of other brainstem structures in humans: nonphosphorylated neurofilament protein (NPNFP), nitric oxide synthase (nNOS), and three calcium-binding proteins. The results for humans suggest a laminar organization with only two layers, and the presence of large projection neurons that are enriched in NPNFP. We did not observe evidence in humans of the inhibitory interneurons that have been described in the cat and rodent DCN. To compare humans and other animals directly we used immunohistochemistry to examine the DCN in the macaque monkey, the cat, and three rodents. We found similarities between macaque monkey and human in the expression of NPNFP and nNOS, and unexpected differences among species in the patterns of expression of the calcium-binding proteins.

Cytoarchitecture, areas, and neuron numbers of the Etruscan shrew cortex

The Etruscan shrew, Suncus etruscus, is one of the smallest mammals. Etruscan shrews can recognize prey shape with amazing speed and accuracy, based on whisker-mediated tactile cues. Because of its small size, quantitative analysis of the Etruscan shrew cortex is more tractable than in other animals. To quantitatively assess the anatomy of the Etruscan shrew's brain, we sectioned brains and applied Nissl staining and NeuN (neuronal nuclei) antibody staining. On the basis of these stains, we estimated the number of neurons of 10 cortical hemispheres by using Stereoinvestigator and Neurolucida (MBF Bioscience) software. On average, the neuron number per hemisphere was found to be ~1 million. We also measured cortical surface area and found an average of 11.1 mm² (n = 7) and an average volume of 5.3 mm³ (n = 10) per hemisphere. We identified 13 cortical regions by cytoarchitectonic boundaries in coronal, sagittal, and tangential sections processed for Nissl substance, myelin, cytochrome oxidase, ionic zinc, neurofilaments, and vesicular glutamate transporter 2 (VGluT2). The Etruscan shrew is a highly tactile animal with a large somatosensory cortex, which contains a barrel field, but the barrels are much less clearly defined than in rodents. The anatomically derived cortical partitioning scheme roughly corresponds to physiologically derived maps of neocortical sensory areas.

Distribution of SMI-32-immunoreactive neurons in the central auditory system of the rat

SMI-32 antibody recognizes a non-phosphorylated epitope of neurofilament proteins, which are thought to be necessary for the maintenance of large neurons with highly myelinated processes. We investigated the distribution and quantity of SMI-32-immunoreactive(-ir) neurons in individual parts of the rat auditory system. SMI-32-ir neurons were present in all auditory structures; however, in most regions they constituted only a minority of all neurons (10-30%). In the cochlear nuclei, a higher occurrence of SMI-32-ir neurons was found in the ventral cochlear nucleus. Within the superior olivary complex, SMI-32-ir cells were particularly abundant in the medial nucleus of the trapezoid body (MNTB), the only auditory region where SMI-32-ir neurons constituted an absolute majority of all neurons. In the inferior colliculus, a region with the highest total number of neurons among the rat auditory subcortical structures, the percentage of SMI-32-ir cells was, in contrast to the MNTB, very low. In the medial geniculate body, SMI-32-ir neurons were prevalent in the ventral division. At the cortical level, SMI-32-ir neurons were found mainly in layers III, V and VI. Within the auditory cortex, it was possible to distinguish the Te1, Te2 and Te3 areas on the basis of the variable numerical density and volumes of SMI-32-ir neurons, especially when the pyramidal cells of layer V were taken into account. SMI-32-ir neurons apparently form a representative subpopulation of neurons in all parts of the rat central auditory system and may belong to both the inhibitory and excitatory systems, depending on the particular brain region.

Neurodevelopmental disruption of cortico-striatal function caused by degeneration of habenula neurons

Background

The habenula plays an important role on cognitive and affective functions by regulating monoamines transmission such as the dopamine and serotonin, such that its dysfunction is thought to underlie a number of psychiatric conditions. Given that the monoamine systems are highly vulnerable to neurodevelopmental insults, damages in the habenula during early neurodevelopment may cause devastating effects on the wide-spread brain areas targeted by monoamine innervations.

Methodology/Principal Findings

Using a battery of behavioral, anatomical, and biochemical assays, we examined the impacts of neonatal damage in the habenula on neurodevelopmental sequelae of the prefrontal cortex (PFC) and nucleus accumbens (NAcc) and associated behavioral deficits in rodents. Neonatal lesion of the medial and lateral habenula by ibotenic acid produced an assortment of behavioral manifestations consisting of hyper-locomotion, impulsivity, and attention deficit, with hyper-locomotion and impulsivity being observed only in the juvenile period, whereas attention deficit was sustained up until adulthood. Moreover, these behavioral alterations were also improved by amphetamine. Our study further revealed that impulsivity and attention deficit were associated with disruption of PFC volume and dopamine (DA) receptor expression, respectively. In contrast, hyper-locomotion was associated with decreased DA transporter expression in the NAcc. We also found that neonatal administration of nicotine into the habenula of neonatal brains produced selective lesion of the medial habenula. Behavioral deficits with neonatal nicotine administration were similar to those caused by ibotenic acid lesion of both medial and lateral habenula during the juvenile period, whereas they were different in adulthood.

Conclusions/Significance

Because of similarity between behavioral and brain alterations caused by neonatal insults in the habenula and the symptoms and suggested neuropathology in attention deficit/hyperactivity disorder (ADHD), these results suggest that neurodevelopmental deficits in the habenula and the consequent cortico-striatal dysfunctions may be involved in the pathogenesis and pathophysiology of ADHD.

Cyto-, myelo- and chemoarchitecture of the prefrontal cortex of the Cebus monkey

Background

According to several lines of evidence, the great expansion observed in the primate prefrontal cortex (PfC) was accompanied by the emergence of new cortical areas during phylogenetic development. As a consequence, the structural heterogeneity noted in this region of the primate frontal lobe has been associated with diverse behavioral and cognitive functions described in human and non-human primates. A substantial part of this evidence was obtained using Old World monkeys as experimental model; while the PfC of New World monkeys has been poorly studied.

In this study, the architecture of the PfC in five capuchin monkeys (Cebus apella) was analyzed based on four different architectonic tools, Nissl and myelin staining, histochemistry using the lectin Wisteria floribunda agglutinin and immunohistochemistry using SMI-32 antibody.

Results

Twenty-two architectonic areas in the Cebus PfC were distinguished: areas 8v, 8d, 9d, 12l, 45, 46v, 46d, 46vr and 46dr in the lateral PfC; areas 11l, 11m, 12o, 13l, 13m, 13i, 14r and 14c in the orbitofrontal cortex, with areas 14r and 14c occupying the ventromedial corner; areas 32r, 32c, 25 and 9m in the medial PfC, and area 10 in the frontal pole. This number is significantly higher than the four cytoarchitectonic areas previously recognized in the same species. However, the number and distribution of these areas in Cebus were to a large extent similar to those described in Old World monkeys PfC in more recent studies.

Conclusions

The present parcellation of the Cebus PfC considerably modifies the scheme initially proposed for this species but is in line with previous studies on Old World monkeys. Thus, it was observed that the remarkable anatomical similarity between the brains of genera Macaca and Cebus may extend to architectonic aspects. Since monkeys of both genera evolved independently over a long period of time facing different environmental pressures, the similarities in the architectonic maps of PfC in both genera are issues of interest. However, additional data about the connectivity and function of the Cebus PfC are necessary to evaluate the possibility of potential homologies or parallelisms.

Altered expression of parvalbumin and calbindin in interneurons within the primary visual cortex of neonatal enucleated hamsters

In the present study, we tested the hypothesis that the expression of calcium binding proteins (CaBPs), parvalbumin (PV), calretinin (CR) and calbindin (CB), is dependent upon sensory experience as emphasized in visual deprivation and deafferentation studies. The expression of CaBPs was studied in interneurons within the primary and extrastriate visual cortices (V1, V2M, V2L) and auditory cortex (AC) of adult hamsters enucleated at birth. The effects of enucleation were mainly confined to area V1 where there was a significant volume reduction (26%) and changes in the laminar distribution of PV and CB immunoreactive (IR) cells. The density of PV-IR cell bodies was significantly increased in layer IV and reduced in layer V. Moreover, the density of CB-IR neurons was inferior in layer V of V1 in enucleated hamsters (EH) compared to controls. These results suggest that some features of the laminar distribution of specific CaBPs, in primary sensory cortices, are dependent upon or modulated by sensory input.

Areas of cat auditory cortex as defined by neurofilament proteins expressing SMI-32

The monoclonal antibody SMI-32 was used to characterize and distinguish individual areas of cat auditory cortex. SMI-32 labels non-phosphorylated epitopes on the high- and medium-molecular weight subunits of neurofilament proteins in cortical pyramidal cells and dendritic trees with the most robust immunoreactivity in layers III and V. Auditory areas with unique patterns of immunoreactivity included: primary auditory cortex (AI), second auditory cortex (AII), dorsal zone (DZ), posterior auditory field (PAF), ventral posterior auditory field (VPAF), ventral auditory field (VAF), temporal cortex (T), insular cortex (IN), anterior auditory field (AAF), and the auditory field of the anterior ectosylvian sulcus (fAES). Unique patterns of labeling intensity, soma shape, soma size, layers of immunoreactivity, laminar distribution of dendritic arbors, and labeled cell density were identified. Features that were consistent in all areas included: layers I and IV neurons are immunonegative; nearly all immunoreactive cells are pyramidal; and immunoreactive neurons are always present in layer V. To quantify the results, the numbers of labeled cells and dendrites, as well as cell diameter, were collected and used as tools for identifying and differentiating areas. Quantification of the labeling patterns also established profiles for ten auditory areas/layers and their degree of immunoreactivity. Areal borders delineated by SMI-32 were highly correlated with tonotopically-defined areal boundaries. Overall, SMI-32 immunoreactivity can delineate ten areas of cat auditory cortex and demarcate topographic borders. The ability to distinguish auditory areas with SMI-32 is valuable for the identification of auditory cerebral areas in electrophysiological, anatomical, and/or behavioral investigations.

Dual chemoarchitectonic lamination of the visual sector of the thalamic reticular nucleus

The chemoanatomical organization of the visual sector of the cat's thalamic reticular nucleus (TRN)-that is at the dorsal lateral geniculate nucleus (dLGN) and at the pulvinar nucleus (Pul)-was investigated with two novel cytoarchitectonic markers. The Wisteria floribunda agglutinin (WFA) binding reaction visualized the extracellular perineuronal net (PN) and the SMI 32 immunoreaction stained intracellular neurofilaments. Two distinct layers of the TRN could be detected, particularly by WFA- but also by SMI 32-staining. The outer tier outlined a canopy of labeling placed a bit detached from the diencephalon dorsolaterally, while the inner TRN tier is very tightly attached to the thalamic lamina limitans externa. The labeled neurons showed typically fusiform morphology with dendrites orienting in the plane of TRN. Additionally, these chemoarchitectural reactions identified a chain of structures in the ventral diencephalon connected to the TRN tiers. One stained string is formed by the subthalamic nucleus bound laterally to the peripeduncular nucleus extending further dorsolateral into the outer TRN tier. The other chain laced up the field of Forel, the zona incerta, the ventral LGN, the perigeniculate nucleus (PGN) and the previously-overlooked peripulvinar nucleus (PPulN) and so formed the inner TRN tier. In the third most distanced TRN tier, in the perireticular nucleus, a very few WFA-binding presenting neuron were found. In addition to the PN possessing TRN neurons, WFA-reactive presumable interneurons were also labeled within the visual thalamus. Following tracer injections into the feline Pul, two stripes of cells were retrogradely labeled in the neighboring visual TRN sector. The location of these reticular neurons coincided precisely with the chemoanatomically identified inner and outer TRN tiers. On the analogy of the PGN-TRN duality at the dLGN, the chemoanatomical and tract tracing findings strongly suggest a similar dual organization in the pulvinoprojecting TRN portion.

Neocortical neuron types in Xenarthra and Afrotheria: implications for brain evolution in mammals

Interpreting the evolution of neuronal types in the cerebral cortex of mammals requires information from a diversity of species. However, there is currently a paucity of data from the Xenarthra and Afrotheria, two major phylogenetic groups that diverged close to the base of the eutherian mammal adaptive radiation. In this study, we used immunohistochemistry to examine the distribution and morphology of neocortical neurons stained for nonphosphorylated neurofilament protein, calbindin, calretinin, parvalbumin, and neuropeptide Y in three xenarthran species-the giant anteater (Myrmecophaga tridactyla), the lesser anteater (Tamandua tetradactyla), and the two-toed sloth (Choloepus didactylus)-and two afrotherian species-the rock hyrax (Procavia capensis) and the black and rufous giant elephant shrew (Rhynchocyon petersi). We also studied the distribution and morphology of astrocytes using glial fibrillary acidic protein as a marker. In all of these species, nonphosphorylated neurofilament protein-immunoreactive neurons predominated in layer V. These neurons exhibited diverse morphologies with regional variation. Specifically, high proportions of atypical neurofilament-enriched neuron classes were observed, including extraverted neurons, inverted pyramidal neurons, fusiform neurons, and other multipolar types. In addition, many projection neurons in layers II-III were found to contain calbindin. Among interneurons, parvalbumin- and calbindin-expressing cells were generally denser compared to calretinin-immunoreactive cells. We traced the evolution of certain cortical architectural traits using phylogenetic analysis. Based on our reconstruction of character evolution, we found that the living xenarthrans and afrotherians show many similarities to the stem eutherian mammal, whereas other eutherian lineages display a greater number of derived traits.

Architectonic subdivisions of neocortex in the gray squirrel (Sciurus carolinensis)

Squirrels are highly visual mammals with an expanded cortical visual system and a number of well-differentiated architectonic fields. To describe and delimit cortical fields, subdivisions of cortex were reconstructed from serial brain sections cut in the coronal, sagittal, or horizontal planes. Architectonic characteristics of cortical areas were visualized after brain sections were processed with immunohistochemical and histochemical procedures for revealing parvalbumin, calbindin, neurofilament protein, vesicle glutamate transporter 2, limbic-associated membrane protein, synaptic zinc, cytochrome oxidase, myelin or Nissl substance. In general, these different procedures revealed similar boundaries between areas, suggesting that functionally relevant borders were being detected. The results allowed a more precise demarcation of previously identified areas as well as the identification of areas that had not been previously described. Primary sensory cortical areas were characterized by sparse zinc staining of layer 4, as thalamocortical terminations lack zinc, as well as by layer 4 terminations rich in parvalbumin and vesicle glutamate transporter 2. Primary areas also expressed higher levels of cytochrome oxidase and myelin. Primary motor cortex was associated with large SMI-32 labeled pyramidal cells in layers 3 and 5. Our proposed organization of cortex in gray squirrels includes both similarities and differences to the proposed of cortex in other rodents such as mice and rats. The presence of a number of well-differentiated cortical areas in squirrels may serve as a guide to the identification of homologous fields in other rodents, as well as a useful guide in further studies of cortical organization and function.

Identification of new regional marker proteins to map mouse brain by 2-D difference gel electrophoresis screening

To screen for new region-specific protein markers we compared the proteome maps of the primary visual and somatosensory areas V1 and S1 in mouse brain using 2-D difference gel electrophoresis (2-D DIGE). Twenty-three protein spots showed a statistically significant difference in expression level between V1 and S1, with 52% appearing more abundantly in V1. Twenty-six proteins were mass spectrometrically identified in 22 spots. To assess the validity of this list of potential areal markers generated by 2-D DIGE, the effective area-specific distribution profile of creatine kinase brain subtype (CKB), a protein with a clearly higher expression level in S1, was monitored with in situ hybridization. The mRNA expression profile of CKB displayed a clear area-specific distribution, which allowed demarcation of S1 and its topographical borders with neighboring neocortical areas. This proteomic study demonstrates the innovative application of 2-D DIGE and MS to select new regional markers for neuroscience research.

Neurofilament protein and neuronal activity markers define regional architectonic parcellation in the mouse visual cortex

This study was designed to assess the chemoarchitectural organization and extent of the mouse visual cortex. We used nonphosphorylated neurofilament protein, a neuronal marker that exhibits region-specific cellular and laminar patterns, to delineate cortical subdivisions. A comprehensive analysis demonstrated that pyramidal and nonpyramidal neurons expressing neurofilament proteins display striking laminar and regional patterns in the mouse visual cortex permitting the delineation of the primary visual cortex (V1) and its monocular and binocular zones, 2 lateral, and 5 medial extrastriate cortical areas with clear anatomical boundaries and providing evidence that the mouse medial extrastriate cortex is not homogeneous. We also investigated the expression profiles of 2 neuronal activity markers, the immediate early genes c-fos and zif-268, following deprivation paradigms to ascertain the visual nature of all subdivisions caudal, medial, and lateral to V1. The present data indicate that neurochemically identifiable subdivisions of the mouse visual cortex exist laterally and medially to V1 and reveal specific anatomical and functional characteristics at the cellular and regional levels.

Enriched expression and developmental regulation of the middle-weight neurofilament (NF-M) gene in song control nuclei of the zebra finch

Songbirds evolved a complex set of dimorphic telencephalic nuclei that are essential for the learning and production of song. These nuclei, which together make up the oscine song control system, present several neurochemical properties that distinguish them from the rest of the telencephalon. Here we show that the expression of the gene encoding the middle-weight neurofilament (NF-M), an important component of the neuronal cytoskeleton and a useful tool for studying the cytarchitectonic organization of mammalian cortical areas, is highly enriched in large neurons within pallial song control nuclei (nucleus HVC, robustus nucleus of the arcopallium, and lateral magnocellular nucleus of the nidopallium) of male zebra finches (Taeniopygia guttata). We also show that this transcript is highly expressed in large neurons in the medulla, pons, midbrain, and thalamus. Moreover, we demonstrate that NF-M expression in song control nuclei changes during postembryonic development, peaking during an early phase of the song-learning period that coincides with the maturation of the song system. We did not observe changes in NF-M expression in auditory areas or in song control nuclei in the contexts of hearing song or singing, although these contexts result in marked induction of the transcription factor ZENK. This observation suggests that NF-M might not be under the regulatory control of ZENK in auditory areas or in song control nuclei. Overall, our data indicate that NF-M is a neurochemical marker for pallial song control nuclei and provide suggestive evidence of an involvement of NF-M in the development and/or maturation of the oscine song control system.

Structure of the cerebral cortex of the humpback whale,Megaptera novaeangliae (Cetacea, Mysticeti, Balaenopteridae)

Cetaceans diverged from terrestrial mammals between 50 and 60 million years ago and acquired, during their adaptation to a fully aquatic milieu, many derived features, including echolocation (in odontocetes), remarkable auditory and communicative abilities, as well as a complex social organization. Whereas brain structure has been documented in detail in some odontocetes, few reports exist on its organization in mysticetes. We studied the cerebral cortex of the humpback whale (Megaptera novaeangliae) in comparison to another balaenopterid, the fin whale, and representative odontocetes. We observed several differences between Megaptera and odontocetes, such as a highly clustered organization of layer II over the occipital and inferotemporal neocortex, whereas such pattern is restricted to the ventral insula in odontocetes. A striking observation in Megaptera was the presence in layer V of the anterior cingulate, anterior insular, and frontopolar cortices of large spindle cells, similar in morphology and distribution to those described in hominids, suggesting a case of parallel evolution. They were also observed in the fin whale and the largest odontocetes, but not in species with smaller brains or body size. The hippocampal formation, unremarkable in odontocetes, is further diminutive in Megaptera, contrasting with terrestrial mammals. As in odontocetes, clear cytoarchitectural patterns exist in the neocortex of Megaptera, making it possible to define many cortical domains. These observations demonstrate that Megaptera differs from Odontoceti in certain aspects of cortical cytoarchitecture and may provide a neuromorphologic basis for functional and behavioral differences between the suborders as well as a reflection of their divergent evolution.

Variations in the structure of the prelunate gyrus in Old World monkeys

Anatomical and electrophysiological studies have revealed a complex organization in the macaque prelunate gyrus. We investigated the morphology and architecture of the prelunate gyrus in Old World monkeys. In Macaca nemestrina, we observed a sulcus crossing the prelunate gyrus within 2 mm of the vertical meridian representation. In other macaque species and other cercopithecines, we observed substantial variations in sulcal morphology across the prelunate gyrus. We did not find a sulcus in all species, and the location and depth of that indentation on the gyrus varied among species. A deep sulcus was observed in all species that emerged earlier in evolution than macaques, such as guenons, baboons, and colobines. We analyzed the regional and parcellation features of the prelunate gyrus in three macaque species, M. maura, M. mulatta, and M. radiata, and in Erythrocebus patas, with emphasis on the relation of structure to the distribution of prelunate visual areas. Nonphosphorylated neurofilament protein immunoreactivity permitted the delineation of a novel area in the prelunate gyrus of Old World monkeys, located around the prelunate sulcus. Species-specific patterns were also observed in the prelunate gyrus of the patas monkey compared to macaques. These observations, as well as a cladistic analysis of the data, suggest an expanded and diversified organization of the prelunate gyrus in some cercopithecoids that may reflect adaptation to specific ecological environments. It was, however, progressively lost in most macaques, being retained only in species that diverged early in the evolution of the genus Macaca, such as M. nemestrina and M. maura.

Morphomolecular neuronal phenotypes in the neocortex reflect phylogenetic relationships among certain mammalian orders

The cytoarchitecture of the cerebral cortex in mammals has been traditionally investigated using Nissl, Golgi, or myelin stains and there are few comparative studies on the relationships between neuronal morphology and neurochemical specialization. Most available studies on neuronal subtypes identified by their molecular and morphologic characteristics have been performed in species commonly used in laboratory research such as the rat, mouse, cat, and macaque monkey, as well as in autopsic human brain specimens. A number of cellular markers, such as neurotransmitters, structural proteins, and calcium-buffering proteins, display a highly specific distribution in distinct classes of neocortical neurons in a large number of mammalian species. In this article, we present an overview of the morphologic characteristics and distribution of three calcium-binding proteins, parvalbumin, calbindin, and calretinin, and of a component of the neuronal cytoskeleton, nonphosphorylated neurofilament protein in the neocortex of various species, representative of the major subdivisions of mammals. The distribution of these neurochemical markers defined several species- and order-specific patterns that permit assessment of the degree to which neuronal morphomolecular specialization, as well as the regional and laminar distribution of distinct cell types in the neocortex, represents derived or ancestral features. In spite of the remarkable diversity in morphologic and cellular organization that occurred during mammalian neocortical evolution, such patterns identified several associations among taxa that closely match their phylogenetic relationships.

Hierarchical Development of the Primate Visual Cortex, as Revealed by Neurofilament Immunoreactivity: Early Maturation of the Middle Temporal Area (MT)

It has been suggested that the development of the cerebral cortex reflects its hierarchical organization, with the primary sensory areas being the first to reach structural and functional maturity, and higher-order association areas being the last. In the present study, we labelled the cortex of New World marmoset monkeys of late fetal and early postnatal ages with an antibody to non-phosphorylated neurofilament, a marker of structural maturation of a subset of pyramidal cells. Supporting the concept of hierarchical maturation, we found that at birth labelled cells were found in the primary visual, auditory and somatosensory areas, but not in most other cortical fields. The exception was visual area MT, which revealed an infragranular pattern of labelling comparable to the one observed in the primary areas, as well as some supragranular staining. In MT, an adult-like pattern of labelled cells, including both supragranular and infragranular layer neurons, emerged within the first postnatal month. In comparison, the development of other extrastriate areas was delayed, with the first signs of neurofilament staining not present until the third week. The present results support the concept of MT as another primary visual area, an idea previously advanced on the basis of functional and anatomical evidence.