Mapping of glial fibrillary acidic protein-immunoreactivity in the rat forebrain and mesencephalon by computerized image analysis

Evolutionary Modifications Are Moderate in the Astroglial System of Actinopterygii as Revealed by GFAP Immunohistochemistry

The present paper is the first comparative study on the astroglia of several actinopterygian species at different phylogenetical positions, teleosts (16 species), and non-teleosts (3 species), based on the immunohistochemical staining of GFAP (glial fibrillary acidic protein), the characteristic cytoskeletal intermediary filament protein, and immunohistochemical marker of astroglia. The question was, how the astroglial architecture reflexes the high diversity of this largest vertebrate group. The actinopterygian telencephalon has a so-called ‘eversive’ development in contrast to the ‘evagination’ found in sarcopterygii (including tetrapods). Several brain parts either have no equivalents in tetrapod vertebrates (e.g., torus longitudinalis, lobus inferior, lobus nervi vagi), or have rather different shapes (e.g., the cerebellum). GFAP was visualized applying DAKO polyclonal anti-GFAP serum. The study was focused mainly on the telencephalon (eversion), tectum (visual orientation), and cerebellum (motor coordination) where the evolutionary changes were most expected, but the other areas were also investigated. The predominant astroglial elements were tanycytes (long, thin, fiber-like cells). In the teleost telencephala a ‘fan-shape’ re-arrangement of radial glia reflects the eversion. In bichir, starlet, and gar, in which the eversion is less pronounced, the ‘fan-shape’ re-arrangement did not form. In the tectum the radial glial processes were immunostained, but in Ostariophysi and Euteleostei it did not extend into their deep segments. In the cerebellum Bergmann-like glia was found in each group, including non-teleosts, except for Cyprinidae. The vagal lobe was uniquely enlarged and layered in Cyprininae, and had a corresponding layered astroglial system, which left almost free of GFAP the zones of sensory and motor neurons. In conclusion, despite the diversity and evolutionary alterations of Actinopterygii brains, the diversity of the astroglial architecture is moderate. In contrast to Chondrichthyes and Amniotes; in Actinopterygii true astrocytes (stellate-shaped extraependymal cells) did not appear during evolution, and the expansion of GFAP-free areas was limited.

Astrocyte regional heterogeneity revealed through machine learning-based glial neuroanatomical assays

Evaluation of reactive astrogliosis by neuroanatomical assays represents a common experimental outcome for neuroanatomists. The literature demonstrates several conflicting results as to the accuracy of such measures. We posited that the diverging results within the neuroanatomy literature were due to suboptimal analytical workflows in addition to astrocyte regional heterogeneity. We therefore generated an automated segmentation workflow to extract features of glial fibrillary acidic protein (GFAP) and aldehyde dehydrogenase family 1, member L1 (ALDH1L1) labeled astrocytes with and without neuroinflammation. We achieved this by capturing multiplexed immunofluorescent confocal images of mouse brains treated with either vehicle or lipopolysaccharide (LPS) followed by implementation of our workflows. Using classical image analysis techniques focused on pixel intensity only, we were unable to identify differences between vehicle-treated and LPS-treated animals. However, when utilizing machine learning-based algorithms, we were able to (1) accurately predict which objects were derived from GFAP or ALDH1L1-stained images indicating that GFAP and ALDH1L1 highlight distinct morphological aspects of astrocytes, (2) we could predict which neuroanatomical region the segmented GFAP or ALDH1L1 object had been derived from, indicating that morphological features of astrocytes change as a function of neuroanatomical location. (3) We discovered a statistically significant, albeit not highly accurate, prediction of which objects had come from LPS versus vehicle-treated animals, indicating that although features exist capable of distinguishing LPS-treated versus vehicle-treated GFAP and ALDH1L1-segmented objects, that significant overlap between morphologies exists. We further determined that for most classification scenarios, nonlinear models were required for improved treatment class designations. We propose that unbiased automated image analysis techniques coupled with well-validated machine learning tools represent highly useful models capable of providing insights into neuroanatomical assays.

Distribution of GFAP in Squamata: Extended Immunonegative Areas, Astrocytes, High Diversity, and Their Bearing on Evolution

Squamata is one of the richest and most diverse extant groups. The present study investigates the glial fibrillary acidic protein (GFAP)-immunopositive elements of five lizard and three snake species; each represents a different family. The study continues our former studies on bird, turtle, and caiman brains. Although several studies have been published on lizards, they usually only investigated one species. Almost no data are available on snakes. The animals were transcardially perfused. Immunoperoxidase reactions were performed with a mouse monoclonal anti-GFAP (Novocastra). The original radial ependymoglia is enmeshed by secondary, non-radial processes almost beyond recognition in several brain areas like in other reptiles. Astrocytes occur but only as complementary elements like in caiman but unlike in turtles, where astrocytes are absent. In most species, extended areas are free of GFAP—a meaningful difference from other reptiles. The predominance of astrocytes and the presence of areas free of GFAP immunopositivity are characteristic of birds and mammals; therefore, they must be apomorphic features of Squamata, which appeared independently from the evolution of avian glia. However, these features show a high diversity; in some lizards, they are even absent. There was no principal difference between the glial structures of snakes and lizards. In conclusion, the glial structure of Squamata seems to be the most apomorphic one among reptiles. The high diversity suggests that its evolution is still intense. The comparison of identical brain areas with different GFAP contents in different species may promote understanding the role of GFAP in neuronal networks. Our findings are in accordance with the supposal based on our previous studies that the GFAP-free areas expand during evolution.

Selective brain neuronal and glial losses without changes in GFAP immunoreactivity: Young versus mature adult Wistar rats

Normal ageing results in brain selective neuronal and glial losses. In the present study we analyze neuronal and glial changes in Wistar rats at two different ages, 45 days (young) and 420 days (mature adult), using Nissl staining and glial fibrillary acidic protein (GFAP) immunohistochemistry associated to the Sholl analysis. Comparing mature adults with young rats we noted the former present a decrease in neuronal density in the cerebral cortex, corpus callosum, pyriform cortex, L.D.D.M., L.D.V.L., central medial thalamic nucleus and zona incerta. A decrease in glial density was found in the dorsomedial and ventromedial hypothalamic nuclei. Additionally, the neuron/glia ratio was reduced in the central medial thalamic nucleus and increased in the habenula. No changes were found in the neuronal and glial densities or neuron/glia ratio in the other studied regions. The number of astrocytic primary processes and the number of intersections counted in the Sholl analysis presented no significant difference in any of the studied regions. Overall, neither GFAP positive astrocytic density nor GFAP immunoreactivity showed alteration.

Disappearance of cerebrovascular laminin immunoreactivity as related to the maturation of astroglia in rat brain

The present paper provides novel findings on the temporo-spatial correlation of perivascular laminin immunoreactivity with the early postnatal astrocyte development. The cerebrovascular laminin immunoreactivity gradually disappears during development. The fusion of the glial and vascular basal laminae during development makes the laminin epitopes inaccessible for antibody molecules (Krum et al., 1991, Exp Neurol 111:151). The fusion is supposed to correlate with the maturation of the glio-vascular connections. Glial development was followed by immunostaining for GFAP (glial fibrillary acidic protein), S100 protein, glutamine synthetase as glial markers and for nestin to visualize the immature glial structures. Our investigation focused on the period from postnatal day (P)2 to P16, on the dorso-parietal pallium. In the wall of the telencephalon the laminin immunoreactivity disappeared between P5 and P10; in subcortical structures it persisted to P12 or even to P16. Its disappearance overlapped the period when GFAP-immunopositive astrocytes were taking the place of radial glia. Despite the parallel time courses, however, the spatial patterns of the two processes were just the opposite: disappearance of the laminin immunoreactivity progressed from the middle zone whereas the appearance of GFAP from the pial surface and the corpus callosum. Rather, the regression of the vascular laminin immunoreactivity followed the progression of the immunoreactivities of glutamine synthetase and S100 protein. Therefore, the regression really correlates with a 'maturation' of astrocytes which, however, affects other astrocyte functions rather than cytoskeleton.

Some Galeomorph Sharks Express a Mammalian Microglia-Specific Protein in Radial Ependymoglia of the Telencephalon

Ionized calcium-binding adapter molecule 1 (Iba1), also known as allograft inflammatory factor 1 (AIF-1), is a highly conserved cytoplasmic scaffold protein. Studies strongly suggest that Iba1 is associated with immune-like reactions in all Metazoa. In the mammalian brain, it is abundantly expressed in microglial cells and is used as a reliable marker for this cell type. The present study used multiple-label microscopy and Western blotting to examine Iba1 expression in the telencephalon of 2 galeomorph shark species, the swellshark (Cephaloscyllium ventriosum) and the horn shark (Heterodontus francisci), a member of an ancient extant order. In the swellshark, high Iba1 expression was found in radial ependymoglial cells, many of which also expressed glial fibrillary acidic protein. Iba1 expression was absent from most cells in the horn shark (with the possible exception of perivascular cells). The difference in Iba1 expression between the species was supported by protein analysis. These results suggest that radial ependymoglia of the elasmobranchs may be functionally related to mammalian microglia and that Iba1 expression has undergone evolutionary changes in this cartilaginous group.

Mechanical restriction of intracortical vessel dilation by brain tissue sculpts the hemodynamic response

Understanding the spatial dynamics of dilation in the cerebral vasculature is essential for deciphering the vascular basis of hemodynamic signals in the brain. We used two-photon microscopy to image neural activity and vascular dynamics in the somatosensory cortex of awake behaving mice during voluntary locomotion. Arterial dilations within the histologically-defined forelimb/hindlimb (FL/HL) representation were larger than arterial dilations in the somatosensory cortex immediately outside the FL/HL representation, demonstrating that the vascular response during natural behaviors was spatially localized. Surprisingly, we found that locomotion drove dilations in surface vessels that were nearly three times the amplitude of intracortical vessel dilations. The smaller dilations of the intracortical arterioles were not due to saturation of dilation. Anatomical imaging revealed that, unlike surface vessels, intracortical vessels were tightly enclosed by brain tissue. A mathematical model showed that mechanical restriction by the brain tissue surrounding intracortical vessels could account for the reduced amplitude of intracortical vessel dilation relative to surface vessels. Thus, under normal conditions, the mechanical properties of the brain may play an important role in sculpting the laminar differences of hemodynamic responses.

Cytoarchitecture-Dependent Decrease in Propagation Velocity of Cortical Spreading Depression in the Rat Insular Cortex Revealed by Optical Imaging

Cortical spreading depression (SD) is a self-propagating wave of depolarization accompanied by a substantial disturbance of the ionic distribution between the intra- and extracellular compartments. Glial cells, including astrocytes, play critical roles in maintenance of the extracellular environment, including ionic distribution. Therefore, SD propagation in the cerebral cortex may depend on the density of astrocytes. The present study aimed to examine the profile of SD propagation in the insular cortex (IC), which is located between the neocortex and paleocortex and is where the density of astrocytes gradually changes. The velocity of SD propagation in the neocortex, including the somatosensory, motor, and granular insular cortices (5.7 mm/min), was higher than that (2.8 mm/min) in the paleocortex (agranular insular and piriform cortices). Around thick vessels, including the middle cerebral artery, SD propagation was frequently delayed and sometimes disappeared. Immunohistological analysis of glial fibrillary acidic protein (GFAP) demonstrated the sparse distribution of astrocytes in the somatosensory cortex and the IC dorsal to the rhinal fissure, whereas the ventral IC showed a higher density of astrocytes. These results suggest that cortical cytoarchitectonic features, which possibly involve the distribution of astrocytes, are crucial for regulating the velocity of SD propagation in the cerebral cortex.

Electroacupuncture reduces injury to the blood-brain barrier following cerebral ischemia/ reperfusion injury

This study used electroacupuncture at Renzhong (DU26) and Baihui (DU20) in a rat model of cerebral ischemia/reperfusion injury. Neurological deficit scores, western blotting, and reverse transcription-PCR results demonstrated that electroacupuncture markedly reduced neurological deficits, decreased corpus striatum aquaporin-4 protein and mRNA expression, and relieved damage to the blood-brain barrier in a rat model of cerebral ischemia/reperfusion injury. These results suggest that electroacupuncture most likely protects the blood-brain barrier by regulating aquaporin-4 expression following cerebral ischemia/reperfusion injury.

Shared features of S100B immunohistochemistry and cytochrome oxidase histochemistry in the ventroposterior thalamus and lateral habenula in neonatal rats

The ventroposterior thalamus and the habenular nuclei of the epithalamus are relevant to the monoaminergic system functionally and anatomically. The glia-derived S100B protein plays a critical role in the development of the nervous system including the monoaminergic systems. In this study, we performed an immunohistochemical study of glia-related proteins including S100B, serotonin transporter, and microtubule-associated protein 2, as well as cytochrome oxidase histochemistry in neonatal rats. Results showed the same findings for S100B immunohistochemistry between the ventroposterior thalamus and the lateral habenula at postnatal day 7: intense staining in cell bodies of astrocytes, diffusely spread immunoproduct in the intercellular space, and S100B-free areas as well as a strong reaction to cytochrome oxidase histochemistry. Further common features were the scarcity of glial fibrillary acidic protein-positive astrocytes and the few apoptotic cells observed. The results of the cytochrome oxidase reaction suggested that S100B is released actively into intercellular areas in restricted brain regions showing high neuronal activity at postnatal day 7. Pathology of the ventroposterior thalamus and the habenula is suggested in mental disorders, and S100B might be a key factor for investigations in these areas.

Dynamics of dystroglycan complex proteins and laminin changes due to angiogenesis in rat cerebral hypoperfusion

Permanent bilateral carotid occlusion is a well known cerebral hypoperfusion model in rats. The aim of our study was to investigate the different stages of vascular reaction by detecting changes in the extracellular martix proteins and to examine their relationship to angiogenesis after occlusion. Experiments were performed on adult male rats. Brain samples were investigated from day 1 to day 30 post-surgery. Immunohistochemical analysis was performed on the whole hippocampus and on the adjacent cortex in order to investigate extracellular martix proteins, such as the markers of dystroglycan complex (β-dystroglycan, α-dystrobrevin and utrophin) and a marker of basal lamina (laminin). The levels of the proteins were estimated by western blot analysis. Vascular density as well as blood-brain barrier permeability were studied on brain slices from the same regions. Our results showed altered laminin and β-dystroglycan immunoreactivity beginning 2 days after the onset of occlusion followed by an increased utrophin immunoreactivity without blood-brain barrier disruption 5 days later. By day 30 of hypoperfusion, when increased vascular density was detected, all changes returned to baseline levels. Western blot analysis showed significant differences in β-dystroglycan and utrophin expression. Our results indicate that the different stages of neovascularisation resulting from cerebral hypoperfusion can be well defined by the markers laminin, β-dystroglycan, and utrophin and that these markers are more likely to correlate with glio-vascular decoupling than does altered blood-brain barrier function.

Glutamine synthetase becomes nitrated and its activity is reduced during repetitive seizure activity in the pentylentetrazole model of epilepsy

PURPOSE

The astrocyte-specific glutamine synthetase (GS) plays a key role in glutamate recycling and Gamma-aminobutyric acid (GABA) metabolism. Changes in the expression or activity of GS have been proposed to contribute to epileptogenesis. The mechanisms or how and where GS may contribute to epilepsy is still a matter of discussion. Here we asked the question whether brain regions, which show an astrocytic stress response respond with alterations of GS.

METHODS

Biochemical and histological alterations of GS, HSP-27, and GFAP were studied after pentylenetetrazole-induced repetitive epileptic seizures (PIRS) in rats using a topographical quantification of the GS-immunoreactivity (GSIR) in relation to the focal heat shock response (HSR). Saline-treated rats served as controls and rats treated by the GS-inhibitor, L-methionine-sulfoximine (MSO) served as a positive control.

RESULTS

No changes in the amount of GSIR and GS-protein occurred during PIRS. A significant reduction of GSIR was observed by histochemistry (in situ) and in native (nonheated) protein extracts of MSO-treated rats. In rats affected by PIRS, GS-activity showed a significant, region-specific reduction in association with a nitration of the enzyme.

DISCUSSION

These results show that neither PIRS nor GS-inhibition reduced the amount of GS protein, but that MSO interferes with antibody binding to native GS. PIRS resulted in a focal increase of astrocytic stress response, whereas MSO caused a widespread, homogeneous astrocytic HSR independent from quantitative changes of GS content. In rats with PIRS the regions showing a strong glial HSR, respond with reduced GS-activity and GS-nitration, which all together are clear indicators of a nitrosative stress response.

Manganese intoxication decreases the expression of manganoproteins in the rat basal ganglia: an immunohistochemical study

Manganese (Mn) is a cofactor for some metalloprotein enzymes, including Mn-superoxide dismutase (Mn-SOD), a mitochondrial enzyme predominantly localized in neurons, and glutamine synthetase (GS), which is selectively expressed in astroglial cells. The detoxifying effects of GS and Mn-SOD in the brain, involve catabolizing glutamate and scavenging superoxide anions, respectively. Mn intoxication is characterized by impaired function of the basal ganglia. However, it is unclear whether regional central nervous system expression of manganoproteins is also affected. Here, we use immunocytochemistry in the adult rat brain, to examine whether Mn overload selectively affects the expression of GS, Mn-SOD, Cu/Zn-SOD, another component of the SOD family, and glial fibrillary acid protein (GFAP), a specific marker of astrocytes. After chronic Mn overload in drinking water for 13 weeks, we found that the number and immunostaining intensity of GS- and Mn-SOD-positive cells was significantly decreased in the striatum and globus pallidus, but not in the cerebral frontal cortex. In addition, we found that GS enzymatic activity was decreased in the strio-pallidal regions but not in the cerebral cortex of Mn-treated animals. In contrast, Cu/Zn-SOD- and GFAP-immunoreactivity was unchanged in both the cerebral cortex and basal ganglia of Mn-treated rats. Thus, we conclude that in response to chronic Mn overload, a down-regulation of some manganoproteins occurs in neurons and astrocytes of the striatum and globus pallidus, probably reflecting the vulnerability of these regions to Mn toxicity.

Glial fibrillary acidic protein immunoreactivity in the rat suprachiasmatic nucleus: circadian changes and their seasonal dependence

The pacemaker of the biological clock, the suprachiasmatic nucleus (SCN) of the hypothalamus, was studied in intact male rats to determine its immunoreactivity to glial fibrillary acidic protein (GFAP), a specific marker of astrocytes. Animals were kept under 12-h light-dark cycles in synchrony with day-night periods. Immunohistochemical reactions were carried out at midday and late at night in both winter (January) and summer (July). In winter, GFAP immunoreactivity was found to be low during the day and high at night. The findings were reversed in summer, when GFAP immunoreactivity was high during the day and low at night. Increased GFAP immunoreactivity appeared in the form of an abundance of thick immunopositive fibres rather than of cell bodies. This was interpreted as a hypertrophy of pre-existing astrocytes due to alternating photic stimulation conveyed by retinofugal fibres to the SCN. The observed seasonal reversal in the direction of GFAP oscillations raises the possibility that a circannual timer exists outside the SCN.

A field guide to the anterior olfactory nucleus (cortex)

While portions of the mammalian olfactory system have been studied extensively, the anterior olfactory nucleus (AON) has been relatively ignored. Furthermore, the existing research is dispersed and obscured by many different nomenclatures and approaches. The present review collects and assembles the relatively sparse literature regarding the portion of the brain situated between the olfactory bulb and primary olfactory (piriform) cortex. Included is an overview of the area's organization, the functional, morphological and neurochemical characteristics of its cells and a comprehensive appraisal of its efferent and afferent fiber systems. Available evidence suggests the existence of subdivisions within the AON and demonstrates that the structure influences ongoing activity in many other olfactory areas. We conclude with a discussion of the AON's mysterious but complex role in olfactory information processing.

Bilateral, vascular and perivascular glial upregulation of heat shock protein-27 after repeated epileptic seizures

Heat shock protein-27 (HSP-27) is an inducible stress response protein. It inhibits apoptotic cell death and is a reliable marker for oxidative stress. We studied the induction of HSP-27 in rat brains on days 1, 4 and 14 after repeated, pentylenetetrazole (PTZ)-induced seizures using immunohistochemisty. Saline treated control rats showed no induction of HSP-27. HSP-27 reactive astrocytes were rarely seen 1 or 4 days after PTZ injection. When present, single astrocytes were located in the cortex and/or the hippocampus. After 14 days PTZ treatment, a bilateral distribution of HSP-27 immunoreactive glia was present in piriform and entorhinal cortices and in the dentate gyrus of most brains. Rats with most intense HSP-27 upregulation showed HSP-27 in amygdala and thalamic nuclei. Astrocytes associated with blood vessels presented strongest HSP-27 staining, but did not show upregulation of gial fibrillary acidic protein and none responded with HSP-47 expression. Additionally, HSP-27 immunoreactivity increased in the endothelial cells of blood vessels in the affected brain regions, although no neuronal induction occurred. Contrastingly, a subconvulsive dose of the glutamine synthetase inhibitor L-methionine sulfoxime, which acts directly on astrocytes, resulted in a rapid, homogeneous astrocyte-specific HSP-27 upregulation within 24 h. Thus, repeated PTZ-induced seizure activity elicits a focal "heat shock" response in endothelial cells and astrocytes of selected cerebral regions indicating that expression of HSP-27 occurred in a seizure-dependent manner within the affected cerebral circuitries. Therefore, this PTZ-model of repeated seizure activity exhibited a cortical pattern of HSP-27 expression which is most comparable to that known from patients with epilepsy.

Apparent scarcity of glial fibrillary acidic protein expression in the brain of the pygmy shrew Sorex minutus as revealed by immunocytochemistry

We examined astroglial cells in the brain of the pygmy shrew Sorex minutus (Insectivora). For that purpose we labeled glial fibrillary acidic protein (GFAP) immunohistochemically in brain sections with a polyclonal antibody. Antigen retrieval experiments were performed to counteract formaldehyde fixation masking of GFAP epitopes. Our results showed remarkable paucity of GFAP-immunoreactive cells and fibers in the cerebral cortex and nuclei, as well as in the majority of the diencephalic and mesencephalic structures. In the forebrain, significant numbers of GFAP-containing astrocytes were found only in the ependyma and subventricular zones, superficial part of layer I of the cerebral cortex, and the majority of white matter structures. In the diencephalon, habenular nuclei were rich in GFAP-immunopositive astrocytes and labeled radial fibers were extended between median eminence and the third ventricle. A considerably higher density of labeled astrocytes was detected in the caudal brainstem and cerebellum. In contrast, in the mouse brain, immunoreactive astrocytes were present in large quantities in various structures. Staining of sections of the shrew brain against glutamine synthetase revealed abundance of immunofluorescent astrocytes in many areas, especially in the shrew cerebral cortex. It seems probable that in the shrew brain only a limited fraction of astroglia expresses GFAP, while other astroglial cells can be detected with different markers. It is possible that the rodent type of astroglial GFAP expression might not be common to insectivores and probably to some other mammalian orders.

Glial fibrillary acidic protein and vimentin immunoreactivity of astroglial cells in the central nervous system of the African lungfish,Protopterus annectens (Dipnoi: Lepidosirenidae)

The distribution of glial intermediate filament molecular markers, glial fibrillary acidic protein (GFAP), and vimentin, in the brain and spinal cord of the African lungfish, Protopterus annectens, was examined by light microscopy immunoperoxidase cytochemistry. Glial fibrillary acidic protein immunoreactivity is clear and is evident in a radial glial system. It consists of fibers of different lengths and thicknesses that are arranged in a regular radial pattern throughout the central nervous system (CNS). They emerge from generally immunopositive radial ependymoglia (tanycytes), lining the ventricular surface, and are directed from the ventricular wall to the meningeal surface. These fibers give rise to endfeet that are apposed to the subpial surface and to blood vessel walls forming the glia limitans externa and the perivascular glial layer, respectively. GFAP-immunopositive star-shaped astrocytes were not found in P. annectens CNS. In the gray matter of the spinal cord, cell bodies of immunopositive radial glia are displaced from the ependymal layer. Vimentin-immunopositive structures are represented by thin fibers mostly localized in the peripheral zones of the brain and the spinal cord. While a few stained fibers appear in the gray matter, the ependymal layer shows no antivimentin immunostaining. In P. annectens the immunocytochemical response of the astroglial intermediate filaments is typical of a mature astroglia cell lineage, since they primarily express GFAP immunoreactivity. This immunocytochemical study shows that the glial pattern of the African lungfish resembles that found in tetrapods such as urodeles and reptiles. The glial pattern of lungfishes is comparable to that of urodeles and reptiles but is not as complex as that of teleosts, birds, and mammals.

Differential activation of astrocytes and microglia during post-natal development of dopaminergic neuronal death in the weaver mouse

In order to understand the relationship between astrocytes, microglia and injured neurons, we studied the weaver mutant mouse. One of the main characteristics of this mutant is the progressive degeneration of the dopaminergic (DA) nigrostriatal pathway that starts around postnatal day 15 (P15), in the substantia nigra pars compacta (SNpc) and progresses until adult age (P60). In the present paper, we analysed the relationship between astroglial and microglial cells within DA neurons in the nigrostriatal system of homozygous weaver mice, at different postnatal ages corresponding to specific stages of the DA neuronal loss. The activation of astrocytes was found to be an early event in weaver DA denervation, appearing massively at the onset of DA neuronal loss in the SNpc at P15. Astrocytes remained activated in the adult brain even after the slowing down of the neuronal death process. Interestingly, in the ventral tegmental area, where no DA neuronal death could be detected, a profound, permanent astrogliosis was also observed in adult animals. In contrast, an activation of microglial cells was transiently observed in the SNpc but only at the postnatal age when maximal neuronal death was observed (P30). Lastly, in the striatum, where there was a massive loss of DA nerve terminals, neither astrogliosis nor microglial activation was detected. Hence, the reaction of astrocytes and microglial cells to progressive and spontaneous DA neuronal death showed different temporal kinetics, suggesting a different role for these two cell types in the DA neurodegenerative process in the weaver mouse.

Macroglia distribution in the developing and adult inferior colliculus

Macroglia distribution in the developing and adult gerbil inferior colliculus (IC) was investigated using two oligodendrocytic [myelin-associated-glycoprotein (MAG) and oligodendrocyte-specific molecule (Rip)] and two astrocytic [glial fibrillary acidic protein (GFAP) and S100] markers and immunohistochemistry. There was a spatio-temporal pattern of myelin marker expression starting in the ventral area of the IC and continuing to the dorsal part of the nucleus. Myelination, as revealed by MAG and Rip markers, starts in the IC during the second postnatal week. The intensity of myelination increased between stages P15 and P21 and extended to the whole IC. The appearance of myelin proteins in the IC may suggest a possible axonal outgrowth inhibition by oligodendrocytes in this structure. A differential pattern of staining was obtained with S100 and GFAP antibodies. Astrocytes identified as S100 immunoreactive cells were observed in the IC by birth and the staining was localized to their cell body and processes. S100 positive cells were homogeneously distributed within the IC nucleus. S100 pattern of staining remained the same in stages P7, P15 and P21. In adult IC, S100 positive cell processes were in contact with neuronal cell bodies, other S100 positive cells and blood vessels. Quantitative analysis showed an increase in the density of positive cells during the first postnatal week and a decrease then after through to adulthood. Unlike S100, GFAP immunoreactivity showed a different pattern of staining. At birth GFAP positive astrocytes were observed along the collicular brain midline and around the IC nucleus delimiting its boundaries. The GFAP pattern of labelling remained the same during development and in the adult. This data suggests the presence of two astrocytes subtypes with different locations in the IC nucleus. The GFAP positive astrocytes were located along the edge of the nucleus, while the S100 positive ones displayed a homogeneous distribution across the nucleus.

Layer-specific reductions in GFAP-reactive astroglia in the dorsolateral prefrontal cortex in schizophrenia

Neuroimaging studies have implicated the prefronto-striatal loop as a substrate for the cognitive deficits in schizophrenia (SCHZ). Postmortem morphometric studies reveal that layers III and V of the dorsolateral prefrontal cortex (dlPFC), which gave rise to glutamatergic projections to neostriatum, demonstrate the most structural pathology in this region of the SCHZ. These neuronal alterations in SCHZ are not accompanied by marked glial changes as revealed by Nissl staining. We examined the glial-type specific pathology in SCHZ by analyzing the glial fibrillary acidic protein- (GFAP) immunoreactive astroglia in contrast to the Nissl-stained general pool of glial cells in dlPFC (area 9) from 9 subjects with SCHZ and 15 psychiatrically normal control subjects. In layer V of the dlPFC in SCHZ, there was a significant 32% reduction in the GFAP-area fraction, 81% increase in the density of the GFAP-positive cell bodies and a 14% decrease in the width of the cortical layer V, as compared to the control subjects. None of these parameters were affected in layers III and IV in the SCHZ. Therefore, only subtle, type- and layer-specific glial pathology is present in the dlPFC in SCHZ. Astroglial pathology in dlPFC may reflect disturbances of the neuron-glia interactions in layer V and may be related to the dysfunctional prefronto-striatal circuits, dopaminergic alterations and cognitive pathology in SCHZ.

Distribution of GFAP immunoreactive structures in the rhombencephalon of the sterlet (Acipenser ruthenus) and its evolutionary implication

Previous studies have revealed that although the brains of cypriniform teleosts (iberian barb, Barbus comiza; carp, Cyprinus carpio; goldfish, Carassius auratus) are rich in glial fibrillary acidic protein (GFAP), they have, however, areas devoid of GFAP immunoreactivity. The largest ones of these are in the rhombencephalon, e.g., the zones of the sensory and motor neurons in the vagal lobe. Our studies in amniotes suggested that the GFAP immunonegative areas could be characteristic of the more advanced brains (avian and mammalian), whereas no similar areas were found in reptiles. A similar tendency was found in the Chondrichthyes, i.e., GFAP immunonegative areas appeared as brain complexity progressed. The question arose whether the GFAP immunonegative brain areas in the Teleostei were also the result of such a tendency. Within the radiation of ray-finned fishes (Actinopterygii), Chondrostei represent a less advanced level as compared to the Teleostei. Therefore, the distribution of GFAP immunoreactivity was investigated in the rhombencephalon of the sterlet (Acipenser ruthenus) as a representative of Chondrostei, and in the carp. Serial vibratome sections were processed according to the avidin-biotinylated horseradish peroxidase method.Several comparable GFAP immunoreactive structures were found in the two species: the dense periventricular ependymoglial plexus, the midsagittal glial septum, the small glial septa separating the nerve fiber bundles, and the wide glial endfeet lining the meningeal surface. In the vagal lobe in the zones adjacent to the meningeal and ventricular surfaces, the glial structures also proved to be similar. In contrast to the carp, however, no areas were found devoid of GFAP immunoreactivity in the sterlet.The results suggest that this trend of glial evolution, i.e., GFAP immunonegative areas appearing as brain complexity progressed, is a common feature shared by Actinopterygii, Amniota, and Chondrichthyes, despite their separate evolutionary histories. J. Exp. Zool. 293:395-406, 2002.

GFAP expression withdraws--a trend of glial evolution?

This study is a summary of investigations in the last decade with several collaborators on representatives of different vertebrate stocks. The results suggest that in the main vertebrate stocks (Agnathi, Chondrichthyes, Actinopterygii, Sarcopterygii-Amniotes), which had their parallel brain evolutions from the laminar brains to the elaborated ones, the astroglia also developed in parallel, and had a common trend of evolution. With growing brain complexity, free astrocytes arose and tended to predominate, and the spontaneous glial fibrillary acidic protein (GFAP)-expression regressed, in several areas. In the mammalian, avian, teleost, and batoid brains, therefore, large areas display a paucity, almost a lack of GFAP-immunoreactivity. The GFAP-expression in the GFAP-free areas seems to be inducible only in the presence of free astrocytes.

Sexual dimorphism of glial fibrillary acidic protein (GFAP) immunoreactivity in the rat interpeduncular nucleus

The intensity of immunostaining for the glial fibrillary acidic protein (GFAP) is outstandingly high in the interpeduncular nucleus. This nucleus was compared in males and females for its GFAP immunoreaction. Immunohistochemistry was carried out on free floating vibratome slices and evaluated by surface densitometry. While in males the reactions were similar, females showed individual variations. Since the interpeduncular nucleus is a hormonally inactive brain area where gonadal hormones do not induce plastic synaptic changes, it is concluded that concerning this astroglial marker a sexual dimorphism exists also outside the "endocrine brain".

A comparison of intermediate filament markers for presumptive astroglia in the developing rat neocortex: immunostaining against nestin reveals more detail, than GFAP or vimentin

The present study compares the immunopositive elements in the developing rat cortex between the day of birth (P0) and the 18th postnatal day (P18), after immunostaining against nestin, vimentin and glial fibrillary acidic protein (GFAP). Nestin immunostaining revealed more structural details than either vimentin or GFAP, or they together. While vimentin immunostaining preferred radial glia and GFAP preferred astrocytes, nestin immunostaining detected both. Stellate-shaped astrocyte-like cells were already seen at P0 and cells of typical astrocytic morphology were numerous at P3, and were predominating elements from P7, whereas GFAP-immunopositive astrocytes were very scarce even at P7, and became numerous only by P11, when nestin immunopositivity started to disappear. Nestin immunostaining revealed such structures which were not seen in GFAP- or vimentin immunostained sections: cell body-like structures 'hanging' at the end the radial fibers, seeming to divide with their fibers, or having astrocyte-like processes. Nestin immunostaining is therefore highly recommended for studies of the glial architecture in the early post-natal brain development.

Glial fibrillary acidic protein immunoreactivity in the prefrontal cortex distinguishes younger from older adults in major depressive disorder

BACKGROUND

Recent postmortem studies in major depressive disorder (MDD) provide evidence for a reduction in the packing density and number of glial cells in different regions of the prefrontal cortex; however, the specific types of glia involved in those morphologic changes are unknown.

METHODS

The territory occupied by the astroglial marker glial fibrillary acidic protein (GFAP) was measured as an areal fraction in cortical layers III, IV, and V in sections from the dorsolateral prefrontal cortex (dlPFC) of MDD and control subjects. In addition, the packing density of GFAP-immunoreactive somata was measured by a direct three-dimensional cell counting method.

RESULTS

The mean areal fraction and packing density of GFAP-immunoreactive astrocytes in the dlPFC of MDD subjects were not significantly different from those in control subjects; however, in MDD there was a significant strong positive correlation between age and GFAP immunoreactivity. When the MDD group was divided into younger (30-45 years old) and older (46-86) adults, in the five younger MDD adults, areal fraction and packing density were smaller than the smallest values of the control subjects. In contrast, among older MDD subjects these parameters tended to be greater than in the older control subjects.

CONCLUSIONS

The present results suggest that the GFAP-immunoreactive astroglia is differentially involved in the pathology of MDD in younger compared with older adults.

Lesions do not provoke GFAP-expression in the GFAP-immunonegative areas of the teleost brain

In the mammalian and avian brains the predominant astroglial elements are astrocytes, and the distribution of GFAP-immunopositivity is rather uneven, some large brain areas being almost devoid of GFAP-immunopositivity. In these areas however, an intense GFAP-immunopositivity appears following injury. In the teleost brain most of the areas are GFAP-immunopositive and ependymoglia predominates. However, a large area, the layer of the sensory neurons in the vagal lobe, is devoid of GFAP. The question arises, whether the lack of GFAP-immunopositivity in the teleost brain is also due to the repression of the GFAP-production, as in birds and mammals, or due to the lack of cells capable of expressing GFAP. To answer this question, stab wounds were made in the vagal lobe of goldfish, as well as in the tectum, in which moderately dense but highly organized GFAP-immunopositive glia has been detected in intact animals. In the layer of the sensory neurons in the vagal lobe no GFAP-immunopositivity appeared even after lesions had been introduced. In the tectum, a rather slight increase of the intensity of the immunostaining was observed in the glial fibers near the lesions but no typical reactive glia similar to that found in mammals or birds, was observed. The results suggest that a lesion does not provoke GFAP-expression in GFAP-immunonegative brain areas in teleosts, in contrast to what is observed in mammals and birds.

Ovarian cycle-related changes of glial fibrillary acidic protein (GFAP) immunoreactivity in the rat interpeduncular nucleus

The interpeduncular nucleus (IPN) of female rats was studied across the estrous cycle to observe whether the expression of the astroglial marker, glial fibrillary acidic protein (GFAP) reacts to hormonal changes in an area not belonging to the 'endocrine brain'. A marked reduction of immunoreactive GFAP was observed in estrus as compared to the immunoreactivities in met- and proestrus. This finding is consistent with earlier observations in the endocrine hypothalamus, but also proves that gonadal steroids influence astroglia in brain regions not involved in neuroendocrine regulation. Since cyclic fluctuations of synaptic numbers in the female have been described only for the endocrine hypothalamus, decrease of immunoreactive GFAP in the IPN during estrus may reflect a down-regulation of GFAP synthesis.

Glucocorticoids up-regulate the expression of glial fibrillary acidic protein in the rat suprachiasmatic nucleus

Immunoreactivity against glial fibrillary acidic protein (GFAP) was used as a dynamic index in adrenalectomized rats subjected or not to corticosterone replacement to investigate whether glucocorticoids may interact with astrocytes in the suprachiasmatic nucleus (SCN), the master component of the central circadian clock. GFAP staining in the SCN was significantly higher in rats having received implants that restored physiological plasma levels of corticosterone within diurnal or nocturnal limits than in non-normalized rats. The effects of corticosterone were similar in the parvocellular portion of the paraventricular nucleus but were opposite in the hippocampus, another major site of negative feed-back regulation of the hypothalamic-pituitary-adrenal axis, where a decreased GFAP staining was observed in discrete regions of the dentate gyrus. This indicates that glucocorticoids may positively or negatively regulate GFAP, depending on the target brain structure. In the SCN, that contains only few if any glucocorticoid receptors, indirect mechanisms that may involve serotoninergic neurons are probably responsible for the effects of corticosterone level. It is proposed that the corticosterone-induced increase in GFAP staining in that nucleus accounts for dynamic changes in neurone-astrocyte interactions that might occur in relation with natural fluctuations of glucocorticoids over the 24 h period.

Three-dimensional measurement of cerebral microvascular plasma perfusion, glial fibrillary acidic protein and microtubule associated protein-2 immunoreactivity after embolic stroke in rats: a double fluorescent labeled laser-scanning confocal microscopic study

Early astroglial response to post-ischemic microvascular hypoperfusion may contribute to progressive cerebral microcirculatory impairment and ischemic neuronal injury. Using laser-scanning confocal microscopy and three fluorescent probes, we measured in three-dimensions cerebral microvascular plasma perfusion, astrocytic reactivity, and neuronal injury assessed by fluorescein isothiocyanate (FITC)-dextran, GFAP immunoreactivity, and microtubule associated protein-2 (MAP2) immunoreactivity, respectively, in rats subjected to 2 h of middle cerebral artery occlusion. Three-dimensional quantitative analysis revealed that 2 h of embolic ischemia resulted in a significant (P<0.05) reduction of cerebral microvascular plasma perfusion in the ipsilateral cortex and subcortex. Tissue within the ipsilateral cortex and subcortex with low plasma perfusion exhibited a significant (P<0.05) increase in GFAP immunoreactivity compared with the homologous contralateral tissue. Three-dimensional re-constructed images showed that prominent GFAP immunoreactive astrocytes surrounded large vessels with decreased plasma perfusion in downstream capillaries in the ipsilateral MCA territory when compared to the vessels in the contralateral homologous tissue. Triple fluorescence probe-stained sections showed that tissue with decreased plasma perfusion and with increased GFAP immunoreactivity was accompanied by a reduction of MAP2 immunoreactivity. The present study demonstrates that an impairment of microvascular perfusion induces an early increase in GFAP immunoreactivity, and reactive astrocytes may contribute to a further reduction of cerebral microvascular plasma perfusion. The three-dimensional quantitative imaging analysis used in the present study provides a means to investigate parenchymal cellular responses to changes of cerebral microvascular plasma perfusion after MCA occlusion.

Morphological alterations of hypothalamic nuclei due to intrahypothalamic hyperinsulinism in newborn rats

In former studies, a temporary, intrahypothalamically localized hyperinsulinism during brain development was shown to result in overweight and metabolic disturbances during later life in rats. Therefore, we tested the hypothesis whether intrahypothalamic insulin treatment during early postnatal life may lead to hypothalamic morphological alterations, i.e., of numerical density of neurons and area of neuronal nuclei or area of neuronal cytoplasm, in this animal model. For this purpose, on the 8th day of age in Wistar rats a long-acting insulin was bilaterally applicated stereotactically into the hypothalamus (12 mIU on each side), while in controls the insulin-free agar-vehicle was given only. By computer-assisted morphometric analysis on the 15th day of life a decrease of the mean area of neuronal nuclei and the mean nucleus-cytoplasm-ratio within the VMN of the insulin-treated animals was observed, as compared to control rats (P < 0.05), while no significant alterations were found in the lateral hypothalamic area (LHA). Analysis of topographically distinct parts of the VMN revealed significant reductions of the mean area of neuronal nuclei (P < 0.001) and nucleus-cytoplasm-ratio (P < 0.05) in the anterior part of the VMN (VMNpa). Furthermore, in the ventrolateral part (VMNpv) a decreased mean neuronal density was observed in the insulin group (P < 0.01). In contrast, the dorsomedial part of the VMN (VMNpd) displayed an increased mean neuronal density in the insulin-treated animals (P < 0.05). In the dorsomedial hypothalamic nucleus (DMN) a significant increase of the mean area of neuronal nuclei (P < 0.01) and the area of neuronal cytoplasm were observed (P < 0.001). These alterations were accompanied by a significantly elevated mean numerical density of astrocytes (positive for glial fibriallary acidic protein; GFAP+) within the periventricular hypothalamic area (PER) of the insulin-treated rats (P < 0.05). These observations speak for a varying vulnerability of LHA, DMN and distinct parts of the VMN to hyperinsulinism during early development, possibly leading to a disturbed organization and, consecutively, permanent dysfunction of these morphologically connected and functionally interacting hypothalamic nuclei.

Serotonin depletion in the adult rat produces differential changes in highly polysialylated form of neural cell adhesion molecule and tenascin-C immunoreactivity

Levels of immunoreactivity for highly polysialylated neural cell adhesion molecule (PSA-NCAM), NCAM, and tenascin-C (TN-C), were examined in the basal ganglia regions and hypothalamic nuclei of adult rats after serotonergic (5-HT) lesions induced by 5,7-dihydroxytryptamine injections in the dorsal and medial raphe nuclei. Decreases in the density of serotonin fibers were associated with no changes in NCAM and general decreases in PSA-NCAM staining, the time-course of changes being selective for each region. Taken that the confocal analysis indicated that serotonin neurons do not express PSA-NCAM and that similar decreases in PSA-NCAM staining were observed after inhibition of 5-HT synthesis induced by parachlorophenylalanine administration, these results suggest that 5-HT may reduce adhesion by acting on PSA-NCAM expression in its environment, and thus facilitate plasticity in adult brain. Two months after the neurotoxin lesions, a normalization of PSA-NCAM staining was associated with a partial restoration in 5-HT fiber density in the nucleus accumbens and the supraoptic nucleus, suggesting that PSA-NCAM may facilitate sprouting of 5-HT fibers. Since a similar normalization was also detected in the suprachiasmatic nucleus, which remained deprived of serotonin fibers, negative factors are likely to be involved in regeneration processes. Indeed, increases in glial fibrillary acidic protein (GFAP) followed by increases in TN-C were observed in these areas, suggesting that the secretion of TN-C by astrocytes may have negative consequences on the sprouting of 5-HT fibers. Finally, the lack of changes in striatal PSA-NCAM or TN-C staining observed after selective lesions of the dopaminergic pathway induced by intranigral injections of 6-hydroxydopamine indicates that 5-HT has a selective and critical role in adult brain plasticity.

Pre- or postembedding immunocytochemistry: which to choose for the localization of glial fibrillary acidic protein (GFAP)?

Immunostaining for glial fibrillary acidic protein was performed in the hippocampus and cerebellum of adult rats in order to compare the distributions of immunolabelling after pre- and postembedding procedures. The reactions of protoplasmic astrocytes and pericapillary astrocyte processes were investigated at the electron microscopic level. After the pre-embedding reaction, visualized with 3,3'-diaminobenzidine tetrahydrochloride, a granular precipitate was observed to decorate the rough endoplasmic reticulum of the astrocyte cell bodies and a precipitate filled the cytoplasm in the astrocyte processes. In studies with the postembedding procedure, immunogold particles were observed to be attached exclusively to the intermediate filaments of the astrocytic cytoskeleton both in the cell body and in the processes. It is concluded that the diaminobenzidine precipitate diffuses in the cytosol, pre-embedding immunocytochemistry is therefore, suitable for the overall labelling of astrocytes, whereas the postembedding procedure reveals the exact intracytoplasmic localization of glial fibrillary acidic protein. This explains the similar pre-embedding immunostaining patterns of astrocytes with markedly different amounts of glial filaments (e.g. protoplasmic, fibrous and reactive) and stresses the importance of the use of the postembedding method when an exact intracellular localization is required. The results also suggest that, in spite of claims of soluble cytoplasmic pools of this protein, the glial filaments are the exclusive domains of immunoreactive glial fibrillary acidic protein.

Synaptic degeneration and remodelling after fast kindling of the olfactory bulb

Kindling of the olfactory bulb using a novel fast protocol (within 24 h) was studied in rats. In target brain regions, the effects of kindling were measured on the concentration of glial fibrillary acidic protein (GFAP) by dot-blot and on the concentrations of neural cell adhesion molecule (NCAM) and the 25 kDa synaptosomal associated protein of the D3 immunoprecipitate (D3(SNAP-25)) by crossed immunoelectrophoresis. Bilateral increases in the levels of GFAP, indicating activation of astrocytes, were detected in primary olfactory cortical projection areas, including the piriform cortex, and also in the basolateral amygdala and dentate gyrus, suggesting that these regions may be functionally altered during the kindling process. In the piriform cortex and dentate gyrus increased NCAM/D3(SNAP-25) ratios found ipsilaterally at seven days after kindling probably reflect an elevated rate of synaptic remodelling. At this time, however, an overall pattern of ipsilateral decreases in the synaptic marker proteins NCAM and D3(SNAP-25) indicated that this remodelling occurred on a background of synaptic degeneration. These results confirm previous studies showing that kindling is associated with synaptic remodelling and neuronal degeneration in the hippocampal formation and extends the area of plasticity to include the piriform cortex which is believed to be central to the kindling process.

Rapid laminar-dependent changes in GFAP immunoreactive astrocytes in the visual cortex of rats reared in a complex environment

Neuronal changes in the visual cortex have previously been found to occur within days of housing weanling rats in a complex environment (EC) compared to rats housed in standard laboratory cages (IC). In contrast, layer IV astrocytes immunostained for glial fibrillary acidic protein (GFAP) have been found to be slow to change. Recent quantitative analysis has shown the surface density of GFAP immunoreactive (GFAP-IR) astrocytes in young rats to be significantly lower in layer IV in comparison to layer II/III. In the present study, the analysis of experience effects on GFAP-IR astrocytes was extended to include layer II/III as well as layer IV of EC and IC rats. The surface density of GFAP-IR processes was found to be significantly increased within layer II/III after 4-10 days of EC rearing in comparison to IC rats. Consistent with previous findings, housing condition did not significantly affect GFAP-IR within layer IV during these early time points. It is possible that GFAP immunocytochemistry is not a sensitive means of detecting experience-induced early changes in astrocytes within layer IV of weanling rats. The rapid astrocytic changes detected in layer II/III are suggestive of a close relationship between astrocytic plasticity and experience-induced synaptic plasticity.

Age and sex do not affect the volume, cell numbers, or cell size of the suprachiasmatic nucleus of the rat: an unbiased stereological study

The circadian rhythms displayed by numerous biological functions are known to be sex specific and affected by aging. It has not been settled yet whether the sex- and age-related characteristics of circadian rhythms derive from changes in the anatomy of the suprachiasmatic nucleus. To shed light on these issues, we applied unbiased stereological techniques to estimate the volume of the suprachiasmatic nucleus as well as the total number of its cells and the mean volume of their somata and nuclei in progressively older groups of male and female Wistar rats (aged 1, 6, 12, 18, 24, and 30 months). The volume of the nucleus was estimated with the Cavalieri principle on serial sections. The total numbers of neurons and astrocytes were estimated by applying the optical fractionator, and the mean somatic and nuclear volumes of cells were estimated by using isotropic, uniform random sections and the nucleator method. On average, the volume of the suprachiasmatic nucleus was 0.044 mm3, and the total number of neurons and astrocytes was 17,400. Cells of the dorsomedial and ventrolateral components of the nucleus, which are morphologically different, have identical mean perikaryal and nuclear volumes, which we estimated to be 750 microns3 and 400 microns3, respectively. We further demonstrated that, at all ages analysed, the volume of the suprachiasmatic nucleus, the total cell number, and the mean somatic and nuclear volumes of its cells are affected neither by the age nor by the sex of the animal, regardless of the presence of sex- and age-related variations in circadian rhythms. However, the possibility that females may display changes in the volume of the suprachiasmatic nucleus at older ages cannot be ruled out. No effect of aging was observed in the total number of neurons or in the total number of astrocytes.

Altered pattern of immunohistochemical staining for glial fibrillary acidic protein (GFAP) in the forebrain and cerebellum of the mutant spastic rat

The spastic rat is a neurological mutant of the Han-Wistar strain with prominent spasticity, tremor, and ataxia. Neurodegeneration is found in the CA3 sector of the hippocampus and in Purkinje cells of the cerebellum. We examined the forebrain and cerebellum of spastic rats for glial reactions by using immunolabelling for the astrocytic marker, glial fibrillary acidic protein (GFAP). First, a map of the GFAP-distribution was made representing a systematic series of frontal sections in controls. Reactive astrocytes with increased GFAP should occur in the areas with established neuronal degeneration, but they could also demarcate further regions with pathology in this rat strain. Since the baseline levels of GFAP-immunoreactivity differ between brain regions, control rats and clinically normal littermates served as controls to judge relative increases in major structures. In the CA3 sector and hilus of the dorsal hippocampus, a massive gliosis was detected. In the cerebellum, a patchy increase of GFAP labelling in Bergmann glia was found. Further increases of GFAP-labelling in reactive astrocytes occurred in fiber tracts, the ventral thalamic nuclei, medial geniculate nuclei, pontine region and optic layer of the superior colliculus. Inconsistent changes were noted in cortex and pallidum. No defects of glial labelling or malformations in glial architectonics were found. The reactive changes of astroglial cells in hippocampus and cerebellum are in proportion to the neuronal degeneration. The glial reactions in the other brain regions possibly reflect a reaction to fiber degeneration and incipient neuronal degeneration or functional alterations of glial cells in response to neuronal dysfunction.

Expression of a human insulin transgene in cholinergic neurons of the mouse medial habenula

We explored the possibility that an insulin gene deleted in its 5'-flanking region is expressed in adult mouse brain. We used three independent lines of mice carrying a human insulin transgene which included the insulin gene transcription unit flanked by 168 base pairs upstream and 5.5 kb downstream. Using a reverse transcription-polymerase chain reaction assay, human insulin mRNAs were detected in whole brain extracts. In all three lines, human insulin mRNAs were localized by in situ hybridization in a single cerebral site, the medial habenula. With a monoclonal antibody specific for human C-peptide and human proinsulin, labelling was restricted to a subset of habenular cholinergic neurons, with rare immunostained fibers. No labelling was observed in the projection fibers of the retroflexus fasciculus or in their axon terminals in the interpeduncular nucleus. Electron microscope studies suggested that the transgene expressing cells. These findings demonstrate that the human insulin transgene tested here includes a habenula specific promoter which could be useful for physiological and molecular studies on the habenula.

Increases of glial fibrillary acidic protein in the aging female mouse brain

Age-related increases of the astrocyte marker, glial fibrillary acidic protein (GFAP), were further resolved by in situ hybridization and immunocytochemistry in female C57BL/6J mice. The age groups represented the major stages of reproductive aging: young (5 months), middle-age (18 months), and old (23 and 26 months). GFAP mRNA and protein showed generalized increases in old mice. Major white fiber tracts, such as the corpus callosum, fimbria, stria terminalis, and optic tract, showed increased GFAP immunostaining and mRNA. Gray matter showed robust > or = twofold increases in GFAP mRNA with age, especially in the thalamus and hypothalamus, areas that expressed little GFAP in the young. These generalized age-related increases of GFAP in many brain regions imply the existence of a widespread stimulus for increased activity of astrocytes during aging.

Postnatal development of glial fibrillary acidic protein, vimentin and S100 protein in monkey visual cortex: evidence for a transient reduction of GFAP immunoreactivity

In the cerebral cortex of some species, the gradual appearance of glial fibrillary acidic protein (GFAP) is often interpreted as reflecting the parallel maturation of neuronal connectivity. We studied the postnatal maturation of astrocytes in the primary visual cortex of Callithrix jacchus using antibodies against GFAP, vimentin and S100 protein as immunohistochemical markers. In the cortical grey matter of this species, the overall GFAP-immunoreactivity (IR) as measured by image analysis is high at birth (130% of the adult value), decreases until about 3 months (80%) and increases again towards adult values (100%). Vimentin-IR was high at birth, and declined towards 3 months and later. In contrast, S100-IR augmented postnatally in neuropil, and showed a laminar shift of maximum IR from layer IV to supragranular layers during ontogenesis. The decrease of GFAP-IR is predominantly due to changes in density of GFAP-positive (+) astrocytes within cortical tissue (newborn: 18,600 GFAP+astrocytes/mm3; 1 month: 11,600/mm3; 3 months: 5,700/mm3; adult: 10,200/mm3), while the overall number of astrocytes remained relatively constant as shown by the number of S100-positive astrocytic cell bodies. At times of low GFAP-IR a reduced area density of intermediate filaments was found in astrocytes by electron microscopy. The period of reduced GFAP-expression coincides with the time of prominent synapse remodeling in the visual cortex of marmosets. These data suggest that GFAP-expression may depend on functional conditions rather than time-dependent maturation.

Structural and molecular heterogeneity of astrocytes and oligodendrocytes in the gerbil lateral superior olive

The goal of this study was to determine the distribution and diversity of astrocytes and oligodendrocytes within the lateral superior olive of the gerbil. We used morphometric analyses and several immunocytochemical markers to assess differences in glial cell composition between the lateral (low-frequency projection) and the medial (high-frequency projection) limb of the lateral superior olive. Cell counts from Toluidine-stained semithin sections revealed a similar density of total astrocytes in both the lateral and the medial limbs. However, based on cytologic features, there was a prevalence of fibrous-like astrocytes in the lateral limb and protoplasmic-like astrocytes in the medial limb. In a similar manner, glial fibrillary acidic protein staining of astrocytes was intense in the lateral limb, but was largely restricted to the nucleus borders in the medial limb of the lateral superior olive. While glial fibrillary acidic protein was largely restricted to astrocytic processes, glutamine synthetase and S100 protein staining occurred, for the most part, in glial cell bodies. The density of glutamine synthetase positive cell bodies was homogeneous between the two limbs, while the density of S100-positive somata was significantly greater in the lateral limb. Cell counts obtained from semithin sections demonstrated a greater density of oligodendrocytes in the lateral limb than in the medial limb of the lateral superior olive. In a similar manner, there was a 40% greater density of carbonic anhydrase-positive somata in the lateral limb compared to the medial limb. Transferrin immunostaining was restricted to oligodendrocytes, but the density of labeled somata was identical in the lateral and medial limbs. 2',3'-Cyclic nucleotide 3'-phosphodiesterase and myelin-associated glycoprotein were also localized to the somata of oligodendrocytes, labeling both perisomatic and interfascicular cells. At the ultrastructural level, specialized contacts were found between pairs or clusters of oligodendrocytes. These results suggest that more than one type of astrocyte and oligodendrocyte is present within the gerbil lateral superior olive. Furthermore, glial cells were unevenly distributed, such that a greater density of oligodendrocytes and fibrous-like astrocytes were found in the low-frequency projection region. This heterogeneity is well correlated with known differences in the neuronal morphology within the lateral superior olive.

Distribution of glial fibrillary acidic protein-immunopositive structures in the brain of the red-eared freshwater turtle (Pseudemys scripta elegans)

The distribution of glial fibrillary acidic protein (GFAP)-immunoreactivity is described in serial Vibratome sections of the turtle brain. The results are discussed in relation to our previous studies of rat and chicken brains. In the turtle brain, the distribution of GFAP-positive elements is rather evenly abundant as compared to that observed in the chicken and rat. The GFAP-positive structures are fibers of different length and orientation, but the stellate cells are not GFAP-positive. The basic systems is the radial ependymoglia, directed from the ventricles toward the outer surface of the brain. This system also contains some transverse and randomly oriented fibers. The cell bodies are not usually GFAP-positive. The large brain tracts could be recognized by their weak immunostaining, but gray matter nuclei could not be identified on the basis of immunostaining against GFAP. The layers of the optic tectum could be distinguished, as well as the gray and white matter of brain stem and spinal cord and the molecular and granular layers of the cerebellum. In the cerebellum, a fiber system resembling the Bergmann-fibers, a strong midline raphe and coarse transverse fibers could be observed. These latter fibers have no equivalent in other cerebella. Their perikarya proved also to be GFAP-positive, and seemed to be dividing in the adult turtle brain. We conclude that the appearance of GFAP-positive stellate cells had a great importance in the evolution of avian and mammalian brains strengthening the thicker brain walls and assisting in the formation of local differences of GFAP-immunoreactivity in different brain areas.

Gonadal steroids regulate the expression of glial fibrillary acidic protein in the adult male rat hippocampus

This study demonstrates that gonadal steroids (estradiol, testosterone, dihydrotestosterone) can regulate the expression of glial fibrillary acidic protein in the adult male rat brain. Previously, we showed that castration of adult male rats increased glial fibrillary acidic protein messenger RNA in the hippocampus and that this increase was additive with the increase induced by deafferenting entorhinal cortex lesions [Day et al. (1990) Molec. Endocr. 4, 1995-2002 . We extended these effects of castration and entorhinal cortex lesion to glial fibrillary acidic protein, using immunoassays. Furthermore, we found regional differences in responses to castration and inhibited by sex steroids. In contrast, hypothalamic glial fibrillary acidic protein expression was inhibited by castration. Similar regional differences were also shown for astrocyte glial fibrillary acidic protein distribution by immunocytochemistry. The regional specificity of glial fibrillary acidic protein expression after castration and sex steroid replacement is pertinent to the role of astrocytes in synaptic plasticity in unlesioned adults as well as in responses to lesions where the steroid milieu has been shown to influence sprouting.