Cortical interlaminar astrocytes across the therian mammal radiation

Interlaminar astrocytes (ILA) in the cerebral cortex possess a soma in layer I and extend an interlaminar process that runs perpendicular to the pia into deeper cortical layers. We examined cerebral cortex from 46 species that encompassed most orders of therian mammalians, including 22 primate species. We described two distinct cell types with interlaminar processes that have been referred to as ILA, that we termed pial ILA and supial ILA. ILA subtypes differ in somatic morphology, position in layer I, and presence across species. We further described rudimentary ILA that have short GFAP⁺ processes that do not exit layer I, and "typical" ILA with longer GFAP⁺ processes that exit layer I. Pial ILA were present in all mammalian species analyzed, with typical ILA observed in Primates, Scandentia, Chiroptera, Carnivora, Artiodactyla, Hyracoidea, and Proboscidea. Subpial ILA were absent in Marsupialia, and typical subpial ILA were only found in Primate. We focused on the properties of pial ILA by investigating the molecular properties of pial ILA and confirming their astrocytic nature. We found that while the density of pial ILA somata only varied slightly, the complexity of ILA processes varied greatly across species. Primates, specifically bonobo, chimpanzee, orangutan, and human, exhibited pial ILA with the highest complexity. We showed that interlaminar processes contact neurons, pia, and capillaries, suggesting a potential role for ILA in the blood-brain barrier and facilitating communication among cortical neurons, astrocytes, capillaries, meninges, and cerebrospinal fluid.

Exposure to environmental enrichment prior to a cerebral cortex stab wound attenuates the postlesional astroglia response in rats

Modulation of astroglial components involved in reactive postlesional responses in the rat cerebral cortex was analyzed following exposure to environmental enrichment (EE) condition prior to injury. For this purpose, changes in % immunoreactive (IR) area of GFAP, vimentin, EAAT1 and ezrin were evaluated in the perilesional zone after placing a cortical stab wound in the visual cerebral cortex of adult rats. GFAP-IR postlesional reactive astrocytosis in the perilesional cortex was significantly lower in the animal group exposed to EE during postnatal development. This GFAP-IR reaction seems to be associated with existing astroglia, because neither BrdU- nor endogenous Ki-67-labeled nuclei were found in the perilesional cortex analyzed. Increased ezrin-IR area in the visual cortex of rats exposed to EE condition suggests the formation of new synapses or the enhancement of astroglial involvement in the existing ones. No effects of EE were found on either EAAT1- or vimentin-IR area. Results suggest that exposure to EE conditions prior to injury attenuates the postlesional astroglia GFAP-response in the perilesional cortex of rats. Whether this attenuated postlesional astroglia GFAP-response promotes or not protective effects on the cortical neuropil remains to be explored in futures studies.

MAP2 immunostaining in thick sections for early ischemic stroke infarct volume in non-human primate brain

The delineation of early infarction in large gyrencephalic brain cannot be accomplished with triphenyl-tetrazolium chloride (TTC) due to its limitations in the early phase, nor can it be identified with microtubule-associated protein 2 (MAP2) immunohistochemistry, due to the fragility of large thin sections. We hypothesize that MAP2 immunostaining of thick brain sections can accurately identify early ischemia in the entire monkey brain. Using ischemic brains of one rat and three monkeys, a thick-section MAP2 immunostaining protocol was developed to outline the infarct region over the entire non-human primate brain. Comparison of adjacent thick and thin sections in a rat brain indicated complete correspondence between ischemic regions (100.4mm(3)+/-1.2%, n=7, p=0.44). Thick sections in monkey brain possessed the increased structural stability necessary for the extensive MAP2 immunostaining procedure permitting quantification of the ischemic region as a percent of total monkey brain, giving infarct volumes of 11.4, 16.3, and 19.0% of total brain. Stacked 2D images of the intact thick brain tissue sections provided a 3D representation for comparison to MRI images. The infarct volume of 16.1cm(3) from the MAP2 sections registered with MRI images agreed well with the volume calculated directly from the stained sections of 16.6 cm(3). Thick brain tissue section MAP2 immunostaining provides a new method for determining infarct volume over the entire brain at early time points in a non-human primate model of ischemic stroke.

Neuropathological and genetic findings in autism: the significance of a putative minicolumnopathy

Autism is a condition manifested as abnormalities of relatedness, communication, range of interests, and repetitive behaviors. Despite alarming prevalence estimates and exhortations to research, little is known regarding its pathophysiology. Recent reports of a putative minicolumnopathy explain changes in brain size, gray/white matter ratios, and interareal connectivity. This article summarizes possible links between minicolumns and other topics-cortical modularity, age of onset, gliosis, and genetics-relevant to the pathophysiology of autism.

Development of interlaminar astroglial processes in the cerebral cortex of control and Down's syndrome human cases

Glial cytoarchitecture in human cerebral cortex is constituted by two overlapping layouts: the (general mammalian) "glial syncytium" and the (primate-specific) "interlaminar glial palisade" (IGP) composed by astroglial cells, with long, radial processes that traverse several supragranular layers. In this study, the emergence and early organization of the IGP was analyzed using immunocytochemical procedures in postmortem infantile human control and age matched, Down's syndrome (DS) cases. In control cases, first signs of a radial array of unbranched astroglial processes were apparent at the end of the period of "physiological astrocytosis" (20-40 days of postnatal life), and its general profile (except perhaps the density of cell processes) reached the adult-like configuration by the second month of life. The initial organization of the IGP was similar in control and DS cases, although a breakdown in DS became manifest by the first year of age, or earlier, albeit with individual variations. These changes tended to evolve in a "mosaic" fashion and included partial disruption of the palisade, or persistence of the "physiological astrocytosis". These observations were compared against samples from elder DS cases with an Alzheimer's type of dementia (AtD). Collectively, results suggest that DS also involves astroglial alterations during early stages of brain development, and that those changes progress with age, until an AtD ensues during adult life.

Interlaminar astroglia of the cerebral cortex: a marker of the primate brain

Evidence for "cable-like" processes stemming from astroglial cells in the supragranular cerebral cortex has been recently presented. In addition to what could be called the "general mammalian-like" astroglial architecture (the so-called "panglial syncytium") of the cerebral cortex, composed of typical stellate astrocytes (intralaminar astrocytes), the anthropoid species, mostly catarrhines, show a manifest vertical, radial distribution of long (interlaminar) astroglial processes. It can be tentatively proposed that evolutionary pressures resulted in the progressive appearance, in primates, of a new type of glial cell. Its soma has a superficial location and unusually long cellular processes that invade, in a predominant radial fashion, the supragranular region of the cerebral cortex. Their existence has been ignored for more than a century. On the neuronal side, modular (columnar) organization of the cerebral cortex may represent an evolutionary acquisition that could optimize communication and information processing, with the least volume compromise in terms of wiring. Yet, for such columns to be functionally operative, adequate isolation from neighboring units would be required. A "mass" operation of the astroglial architecture would tend to compromise spatial definition and the degrees of freedom of such columnar modules. It is proposed that the presence of a "palisade" of interlaminar glial processes represents a relatively recent evolutionary event, instrumental for the optimization of the modular (columnar) organization of the cerebral cortex. It is interesting that the supragranular cortical region has undergone the largest growth among mammalian species during brain evolution, and has been associated with a crucial role in cortico-cortical interactions.

Disruption of astroglial interlaminar processes in Alzheimer's disease

A palisade of long, interlaminar astroglial processes in supragranular layers of the cerebral cortex is characteristic of adult individuals of anthropoid species. In the present study, this distinctive cytoarchitectonic feature was analyzed in tissue deriving from the neocortex of cases affected by Alzheimer's disease (n=14) and age-matched control cases (n=10). Samples of different cortical areas, and in particular prefrontal, temporal and striate fields, were analyzed. Astroglia was labeled by glial fibrillary acidic protein immunoreactivity, that allowed a clear distinction between the classical, stellate intralaminar astroglia and the interlaminar glial processes. The occurrence and relative density of neuritic plaques were ascertained in the same specimens with Bielchowsky staining. In most cortical regions of cases diagnosed as severe Alzheimer's disease by the donor institutions, interlaminar astroglia was found to be markedly altered or absent, and replaced by hypertrophic intralaminar astrocytes. Cases diagnosed as milder or uncertain Alzheimer's disease showed a less consistent involvement of the interlaminar glial palisade. Alterations of the interlaminar palisade in the cortex affected by Alzheimer's disease did not strictly correlate with the density of neuritic plaques in the examined specimens. The findings indicate that loss/severe disruption of the interlaminar palisade of astroglial processes is part of the array of neuropathological changes occurring in the cerebral cortex during Alzheimer's disease. In addition, our data indicate that different types of neocortical astrocytes (namely intralaminar and interlaminar astrocytes) respond differently to the pathobiology of Alzheimer's disease in the neocortex, inasmuch as interlaminar processes tend to disappear while intralaminar processes become reactive.

Vascularization in the primate visual cortex during development

We studied the relationship between vascularization and neuronal activity in the visual cortex during postnatal development in the primate. Analyses were focused on layer IVC that displays a sequential pattern of maturation for the magno- and parvocellular systems in separate sublayers, respectively IVC alpha and IVC beta. Cytochrome oxidase and endogenous alkaline phosphatase histochemistry was used to analyse, on the same sections, the laminar patterns of cortical activity and vessel density in the primary visual cortex of the marmoset (Callithrix jacchus). Experiments were carried out in five young and two adult animals. We showed that the temporal pattern of angiogenesis differs in layer IVC alpha and IVC beta. During the first postnatal month, vessel density is higher in IVC alpha than in IVC beta and runs parallel to cytochrome oxidase intensity. In 2-month-old animals, both vessel densities and cytochrome oxidase activity are similar in IVC alpha and IVC beta. In adults, the vessel densities in IVC alpha and IVC beta are the reverse of those observed during the first postnatal month. Vessel diameter does not account for this evolution in vascular patterns. In the discussion, we suggest that such a developmental time-course of angiogenesis might be linked to the synaptogenesis requirements that proceed differently for the magno- and parvocellular systems in the primate striate cortex.