Distinct localization of two serine-threonine kinase receptors for activin and TGF-beta in the rat brain and down-regulation of type I activin receptor during peripheral nerve regeneration

Distribution of Smad mRNA and proteins in the rat brain

Smad proteins are known to transduce the action of TGF-β superfamily proteins including TGF-βs, activins, and bone morphogenetic proteins (BMPs). In this study, we examined the expression of Smad1, -2, -3, -4, -5, and -8 mRNA in the rat brain by means of RT-PCR and in situ hybridization (ISH). In addition, we examined the nuclear accumulation of Smad1, -2, -3, -5, and -8 proteins after intracerebroventricular injection of TGF-β1, activin A, or BMP6 with immunohistochemistry to investigate whether TGF-β, activin, and/or BMP activate Smads in the rat brain. RT-PCR analysis revealed that Smad1, -2, -3, -4, -5, and -8 mRNA was expressed in the brain and that the Smad3 and Smad8 mRNA differed in the expression level between brain regions. For example, there were high levels of expression of Smad3 mRNA in the cerebral cortex, caudate putamen/globus pallidus, and cerebellum, but low levels in the thalamus and midbrain. Expression of Smad8 mRNA was higher in the midbrain, cerebellum, and pons/medulla oblongata in comparison to the olfactory bulb, cerebral cortex, caudate putamen/globus pallidus, hippocampus/dentate gyrus, and thalamus. ISH signals for Smad1 mRNA were widely detected in the brain except for a small number of regions including the olfactory tubercle, posterior region of hypothalamus, and cerebellar nuclei. ISH signals for Smad2 mRNA were abundantly observed in several brain regions including the olfactory bulb, piriform cortex, basal ganglia, cingulate cortex, epithalamus, including the pineal gland and medial habenular nuclei, hypothalamus, inferior colliculi of the midbrain, and some nuclei in the pons, cerebellar cortex, and choroid plexus. ISH signals for Smad3 mRNA were also abundantly observed in several brain regions. Especially strong signals for Smad3 mRNA were observed in the olfactory tubercle, piriform cortex, basal ganglia, dentate gyrus, and cingulate cortex. ISH signals for Smad5 and Smad8 mRNA were restricted to a small number of brain regions, the signal intensity of which was weak. ISH signals for Smad4 mRNA were detected in all regions examined. Intracerebroventricular injection of activin A induced nuclear accumulation of Smad2 and Smad3 immunoreactivity in neurons. In contrast, intracerebroventricular injection of TGF-β1 or BMP6 did not induce nuclear accumulation of the immunoreactivity for any Smad in neurons. These results suggest that activin-Smad signaling plays an important role in brain homeostasis.

Temporal and regional patterns of Smad activation in the rat hippocampus following global ischemia

In this study, we examined the temporal and regional patterns of Smad activation in the rat hippocampus following global ischemia. We also examined the association between Smad activation and ischemia-induced pathology in the hippocampus. We found that 1) Smad1, -2, -3, and -5 proteins were detected in the rat hippocampus by means of western blot and immunohistochemistry; 2) after 5 min of ischemia, Smad2 and Smad3 proteins accumulated in the nuclei of pyramidal cells in the CA1 region, which is vulnerable to ischemia; 3) after 3 min of ischemia, which was non-lethal, there was no such nuclear accumulation of Smad2 and Smad3 in the CA1 region; 4) following injection of activin A, nuclear accumulation of Smad2 and Smad3 was induced not only in pyramidal cells of the CA1 region, but also in pyramidal cells of the CA3 region as well as in granule cells of the DG region; 5) activin A-induced nuclear accumulation of Smad2 and Smad3 neither caused degeneration of hippocampal neurons nor prevented degeneration induced by ischemia. These results suggest that in the hippocampus, ischemia-induced activation of Smad2 and Smad3 is associated with the response to stress but is not related to neuronal survival or death.

Kinase/phosphatase overexpression reveals pathways regulating hippocampal neuron morphology

Kinases and phosphatases that regulate neurite number versus branching versus extension are weakly correlated.

The kinase family that most strongly enhances neurite growth is a family of non-protein kinases; sugar kinases related to NADK.

Pathway analysis revealed that genes in several cancer pathways were highly active in enhancing neurite growth.

In neural development, neuronal precursors differentiate, migrate, extend long axons and dendrites, and finally establish connections with their targets. Clinical conditions such as spinal cord injury, traumatic brain injury, stroke, multiple sclerosis, Parkinson's disease, Huntington's disease, and Alzheimer's disease are often associated with a loss of axon and/or dendrite connectivity and treatment strategies would be enhanced by new therapies targeting cell intrinsic mechanisms of axon elongation and regeneration.

Phosphorylation controls most cellular processes, including the cell cycle, proliferation, metabolism, and apoptosis. Neuronal differentiation, including axon formation and elongation, is also regulated by a wide range of kinases and phosphatases. For example, the non-receptor tyrosine kinase Src is required for cell adhesion molecule-dependent neurite outgrowth. In addition to individual kinases and phosphatases, signaling pathways like the MAPK, growth factor signaling, PIP3, cytoskeletal, and calcium-dependent pathways have been shown to impinge on or control neuronal process development. Recent results have implicated GSK3 and PTEN as therapeutically relevant targets in axonal regeneration after injury. However, these and other experiments have studied only a small fraction of the total kinases and phosphatases in the genome. Because of recent advances in genomic knowledge, large-scale cDNA production, and high-throughput phenotypic analysis, it is now possible to take a more comprehensive approach to understanding the functions of kinases and phosphatases in neurons.

We performed a large, unbiased set of experiments to answer the question ‘what effect does the overexpression of genes encoding kinases, phosphatases, and related proteins have on neuronal morphology?' We used ‘high-content analysis' to obtain detailed results about the specific phenotypes of neurons. We studied embryonic rat hippocampal neurons because of their stereotypical development in vitro (Dotti et al, 1988) and their widespread use in studies of neuronal differentiation and signaling. We transfected over 700 clones encoding kinases and phosphatases into hippocampal neurons and analyzed the resulting changes in neuronal morphology.

Many known genes, including PP1a, ERK1, ErbB2, atypical PKC, Calcineurin, CaMK2, IGF1R, FGFR, GSK3, and PIK3 were observed to have significant effects on neurite outgrowth in our system, consistent with earlier findings in the literature.

We obtained quantitative data for many cellular and neuronal morphological parameters from each neuron imaged. These included nuclear morphology (nuclear area and Hoechst dye intensity), soma morphology (tubulin intensity, area, and shape), and numerous parameters of neurite morphology (e.g. tubulin intensity along the neurites, number of primary neurites, neurite length, number of branches, distance from the cell body to the branches, number of crossing points, width and area of the neurites, and longest neurite; Supplementary Figure 1). Other parameters were reported on a ‘per well' basis, including the percentage of transfected neurons in a condition, as well as the percentage of neurons initiating neurite growth. Data for each treatment were normalized to a control (pSport CAT) within the same experiment, then aggregated across replicate experiments.

Correlations among the 19 normalized parameters were analyzed for neurons transfected with all kinase and phosphatase clones (Figure 2). On the basis of this analysis, the primary variables that define the neurite morphology are primary neurite count, neurite average length, and average branches. Interestingly, primary neurite count was not well correlated with neurite length or branching. The Pearson correlation coefficient (r²) between the number of primary neurites and the average length of the neurites was 0.3, and between the number of primary neurites and average branching was 0.2. In contrast, the correlation coefficient of average branching with neurite average length was 0.7. The most likely explanation is that signaling mechanisms underlying the neurite number determination are different than those controlling length/branching of the neurites.

Related proteins are often involved in similar neuronal functions. For example, families of receptor protein tyrosine phosphatases are involved in motor axon extension and guidance in both Drosophila and in vertebrates, and a large family of Eph receptor tyrosine kinases regulates guidance of retinotectal projections, motor axons, and axons in the corpus callosum. We therefore asked whether families of related genes produced similar phenotypes when overexpressed in hippocampal neurons. Our set of genes covered 40% of the known protein kinases, and many of the non-protein kinases and phosphatases.

Gene families commonly exhibit redundant function. Redundant gene function has often been identified when two or more knockouts are required to produce a phenotype. Our technique allowed us to measure whether different members of gene families had similar (potentially redundant) or distinct effects on neuronal phenotype.

To determine whether groups of related genes affect neuronal morphology in similar ways, we used sequence alignment information to construct gene clusters (Figure 6). Genes were clustered at nine different thresholds of similarity (called ‘tiers'). The functional effect for a particular parameter was then averaged within each cluster of a given tier, and statistics were performed to determine the significance of the effect. We analyzed the results for three key neurite parameters (average neurite length, primary neurite count, and average branching). Genes that perturbed each of these phenotypes are grouped in Figure 6. Eight families, most with only a few genes, produced significant changes for one or two parameters. A diverse family of non-protein kinases had a positive effect on neurite outgrowth in three of the four parameters analyzed. This family of kinases consisted of a variety of enzymes, mostly sugar and lipid kinases. A similar analysis was performed using pathway cluster analysis with pathways from the KEGG database, rather than sequence homology. Interestingly, pathways involved in cancer cell proliferation potentiated neurite extension and branching.

Our studies have identified a large number of kinases and phosphatases, as well as structurally and functionally defined families of these proteins, that affect neuronal process formation in specific ways. We have provided an analytical methodology and new tools to analyze functional data, and have implicated genes with novel functions in neuronal development. Our studies are an important step towards the goal of a molecular description of the intrinsic control of axodendritic growth.

Development and regeneration of the nervous system requires the precise formation of axons and dendrites. Kinases and phosphatases are pervasive regulators of cellular function and have been implicated in controlling axodendritic development and regeneration. We undertook a gain-of-function analysis to determine the functions of kinases and phosphatases in the regulation of neuron morphology. Over 300 kinases and 124 esterases and phosphatases were studied by high-content analysis of rat hippocampal neurons. Proteins previously implicated in neurite growth, such as ERK1, GSK3, EphA8, FGFR, PI3K, PKC, p38, and PP1a, were confirmed to have effects in our functional assays. We also identified novel positive and negative neurite growth regulators. These include neuronal-developmentally regulated kinases such as the activin receptor, interferon regulatory factor 6 (IRF6) and neural leucine-rich repeat 1 (LRRN1). The protein kinase N2 (PKN2) and choline kinase α (CHKA) kinases, and the phosphatases PPEF2 and SMPD1, have little or no established functions in neuronal function, but were sufficient to promote neurite growth. In addition, pathway analysis revealed that members of signaling pathways involved in cancer progression and axis formation enhanced neurite outgrowth, whereas cytokine-related pathways significantly inhibited neurite formation.

Increased expression of TGFβ type I receptor in brain tissues of patients with temporal lobe epilepsy

TβRs (transforming growth factor β receptors) have recently been identified in animal experiments as being involved in the pathogenesis of epilepsy. The aim of the present study was to understand further the potential effects of TβRs in human epilepsy. Tissue samples of temporal neocortices from 30 patients with temporal lobe epilepsy were prepared for detecting TβR-I (type 1 TβR) protein expression using immunohistochemistry, immunofluorescence and Western blotting. We compared these tissues with histologically normal temporal lobes from controls. TβR-I immunoreactivity was increased in the patient group compared with controls using immunohistochemistry, and this finding was consistently observed with Western blot analysis. Immunofluorescence showed that TβR-I fluorescence stain mainly accumulated in the cytoplasm of astrocytes. In conclusion, our findings demonstrate that an up-regulation of TβR-I is present in patients with temporal lobe epilepsy.

TGF-beta in neural stem cells and in tumors of the central nervous system

Mechanisms that regulate neural stem cell activity in the adult brain are tightly coordinated. They provide new neurons and glia in regions associated with high cellular and functional plasticity, after injury, or during neurodegeneration. Because of the proliferative and plastic potential of neural stem cells, they are currently thought to escape their physiological control mechanisms and transform to cancer stem cells. Signals provided by proteins of the transforming growth factor (TGF)-beta family might represent a system by which neural stem cells are controlled under physiological conditions but released from this control after transformation to cancer stem cells. TGF-beta is a multifunctional cytokine involved in various physiological and patho-physiological processes of the brain. It is induced in the adult brain after injury or hypoxia and during neurodegeneration when it modulates and dampens inflammatory responses. After injury, although TGF-beta is neuroprotective, it may limit the self-repair of the brain by inhibiting neural stem cell proliferation. Similar to its effect on neural stem cells, TGF-beta reveals anti-proliferative control on most cell types; however, paradoxically, many brain tumors escape from TGF-beta control. Moreover, brain tumors develop mechanisms that change the anti-proliferative influence of TGF-beta into oncogenic cues, mainly by orchestrating a multitude of TGF-beta-mediated effects upon matrix, migration and invasion, angiogenesis, and, most importantly, immune escape mechanisms. Thus, TGF-beta is involved in tumor progression. This review focuses on TGF-beta and its role in the regulation and control of neural and of brain-cancer stem cells.

Altered expression of Smad family members in injured motor neurons of rat

We examined changes in the expression of Smad family members, which transduce signals from TGF-beta superfamily ligands, following hypoglossal nerve injury. RT-PCR and in situ hybridization revealed that Smad1, 2, 3 and 4 mRNAs were significantly up-regulated in injured side, whereas Smad8 mRNA was down-regulated. Immunohistochemistry and Western blotting analysis confirmed the alterations of Smad1, 2 and 4 in injured neurons. These results suggest that the Smad signaling may be important for nerve regeneration.

Transforming growth factor-beta1 is a negative modulator of adult neurogenesis

Transforming growth factor (TGF)-beta1 has multiple functions in the adult central nervous system (CNS). It modulates inflammatory responses in the CNS and controls proliferation of microglia and astrocytes. In the diseased brain, TGF-beta1 expression is upregulated and, depending on the cellular context, its activity can be beneficial or detrimental regarding regeneration. We focus on the role of TGF-beta1 in adult neural stem cell biology and neurogenesis. In adult neural stem and progenitor cell cultures and after intracerebroventricular infusion, TGF-beta1 induced a long-lasting inhibition of neural stem and progenitor cell proliferation and a reduction in neurogenesis. In vitro, although TGF-beta1 specifically arrested neural stem and progenitor cells in the G0/1 phase of the cell cycle, it did not affect the self-renewal capacity and the differentiation fate of these cells. Also, in vivo, TGF-beta1 did not influence the differentiation fate of newly generated cells as shown by bromo-deoxyuridine incorporation experiments. Based on these data, we suggest that TGF-beta1 is an important signaling molecule involved in the control of neural stem and progenitor cell proliferation in the CNS. This might have potential implications for neurogenesis in a variety of TGF-beta1-associated CNS diseases and pathologic conditions.

Regulation of activin mRNA and Smad2 phosphorylation by antidepressant treatment in the rat brain: effects in behavioral models

Activin is a member of the transforming growth factor-beta family that is involved in cell differentiation, hormone secretion, and regulation of neuron survival. The cellular responses to activin are mediated by phosphorylation of a downstream target, Smad2. The current study examines the influence of chronic electroconvulsive seizures (ECSs), as well as chemical antidepressants, on the expression of activin betaA and the phosphorylation of Smad2 in the rat hippocampus and frontal cortex. Chronic ECSs (10 d) resulted in a significant increase in activin betaA mRNA expression and Smad2 phosphorylation in both the hippocampus and frontal cortex. Chronic fluoxetine did not influence activin betaA expression, but fluoxetine as well as desipramine did increase Smad2 phosphorylation in the frontal cortex. The functional significance of increased activin was further tested by examining the effects of activin infusions into the hippocampus on a behavioral model of depression, the forced swim test (FST). A single bilateral infusion of activin A or activin B into the dentate gyrus of the hippocampus produced an antidepressant-like effect in the FST that was comparable in magnitude with fluoxetine. In contrast, infusion of the activin antagonist inhibin A did not influence behavior but blocked the effect of activin A. The results suggest that regulation of activin and Smad signaling may contribute to the actions of antidepressant treatment and may represent novel targets for antidepressant drug development.

Smad-dependent alterations of PPT cholinergic neurons as a pathophysiological mechanism of age-related sleep-dependent memory impairments

In humans, memory impairments are highly prevalent in the aged population, but their functional and structural origins are still unknown. We hypothesized that circadian rhythm alterations may predict spatial memory impairment in aged rats. We demonstrate an association between sleep/wake circadian rhythm disturbances (non-REM sleep fragmentation) and spatial memory impairments in aged rats. We show by light and electron microscopy that these age-related disruptions in circadian rhythm and spatial memory are also associated with degeneration of cholinergic neurons of the pedunculopontine nucleus (PPT), a structure known to be involved in sleep and cognitive functions and which is altered during aging. Finally, we demonstrate that a trophic deregulation of the PPT occur in aged impaired rats, involving an over activation of the TGFbeta-Smad cascade, a signalling pathway involved in neurodegeneration. In conclusion these results provide a new pathophysiological mechanism for age-related sleep-dependent memory impairments opening the ground for the development of new therapeutic approaches of these pathologies.

Activin mRNA induced during amygdala kindling shows a spatiotemporal progression that tracks the spread of seizures

The progressive development of seizures in rats by amygdala kindling, which models temporal lobe epilepsy, allows the study of molecular regulators of enduring synaptic changes. Neurotrophins play important roles in synaptic plasticity and neuroprotection. Activin, a member of the transforming growth factor-beta superfamily of growth and differentiation factors, has recently been added to the list of candidate synaptic regulators. We mapped the induction of activin betaA mRNA in amygdala and cortex at several stages of seizure development. Strong induction, measured 2 hours after the first stage 2 (partial) seizure, appeared in neurons of the ipsilateral amygdala (confined to the lateral, basal, and posterior cortical nuclei) and insular, piriform, orbital, and infralimbic cortices. Activin betaA mRNA induction, after the first stage 5 (generalized) seizure, had spread to the contralateral amygdala (same nuclear distribution) and cortex, and the induced labeling covered much of the convexity of neocortex as well as piriform, perirhinal, and entorhinal cortices in a nearly bilaterally symmetrical pattern. This pattern had filled in by the sixth stage 5 seizure. Induced labeling in cortical neurons was confined mainly to layer II. A similar temporal and spatial pattern of increased mRNA expression of brain-derived neurotrophic factor (BDNF) was found in the amygdala and cortex. Activin betaA and BDNF expression patterns were similar at 1, 2, and 6 hours after the last seizure, subsiding at 24 hours; in contrast, c-fos mRNA induction appeared only at 1 hour throughout cortex and then subsided. In double-label studies, activin betaA mRNA-positive neurons were also BDNF mRNA positive, and they did not colocalize with GAD67 mRNA (a marker of gamma-aminobutyric acidergic neurons). The data suggest that activin and BDNF transcriptional activities accurately mark excitatory neurons participating in seizure-induced synaptic alterations and may contribute to the enduring changes that underlie the kindled state.

Expression of TGF-beta type II receptors in the olfactory epithelium and their regulation in TGF-alpha transgenic mice

Numerous in vitro studies of neurogenesis of olfactory receptor neurons (ORNs) suggest that transforming growth factor (TGF)-beta promotes the maturation/differentiation of olfactory progenitors. We demonstrate that in vivo both mature and immature ORNs, and possibly a basal neuronal progenitor cell, express the TGF-beta type II receptor (TGF-betaRII), suggesting that these cells are targets for TGF-beta signaling. In a previous study of neurogenesis in the OE of TGF-alpha overexpressing transgenic (T) mice, we observed an apparent reduction in the expression of olfactory marker protein (OMP), a marker of terminal differentiation in ORNs in T mice compared to nontransgenic (NT) littermate controls; this was confirmed by Western blotting and immunohistochemistry. In contrast, there was no apparent difference between T and NT mice in the intensity of immunoreactivity for a neuronal marker, protein gene product 9.5. Because TGF-alpha overexpression has been reported to affect TGF-beta signaling in other epithelia, we compared the expression of the TGF-beta type II receptor (TGF-betaRII) in T and NT mice. The intensity of TGF-betaRII immunoreactivity on ORNs was substantially reduced in T compared to NT mice. Similar reductions in TGF-betaRII expression in vomeronasal receptor neurons and in other epithelia in the nasal cavity of T mice were also observed. Taken together, these results indicate that TGF-beta signaling regulates terminal differentiation of ORNs in vivo and suggest ways in which interactions between TGF-alpha and TGF-beta signaling pathways may interact in the OE.

Oligodendrocytes as providers of growth factors

Glial cells recently are being appreciated as supporters of brain neurons. This review addresses their role as growth factor providers. While the function of astrocytes in this capacity is known, new data indicate that oligodendrocytes, the myelinating cells of the brain, exhibit similar abilities. Oligodendrocytes provide trophic signals to nearby neurons and synthesize defined growth factors. Expression of growth factors is influenced by neural signals. The review summarizes these roles and their implications in brain function.

Effects of intracranial injection of transforming growth factor-beta relevant to central fatigue on the waking electroencephalogram of rats: comparison with effects of exercise

To investigate the detailed actions of transforming growth factor-beta (TGF-beta) in the brain, which increase accompanied with continuity of exercise, the authors performed electroencephalogram (EEG) spectral analysis for 2 h after intracranial injection of TGF-beta in rats and compared with the effects of swimming exercise. Relative power values (power percent) of the theta frequency band (4-7 Hz) increased and power percent of the alpha frequency band (7-13 Hz) decreased after intracranial injection of TGF-beta. The directions of these changes of EEG after intracranial injection of TGF-beta were consistent with those after exercise. The EEG pattern produced by leucine-enkephalin (Leu-enk), a typical brain peptide related to exercise, was completely different from that after exercise. The results suggested that the increase in TGF-beta concentration in the brain is, at least partly, relevant to the change of neuronal activity after exercise.

Evidence that TGF beta may directly modulate POMC mRNA expression in the female rat arcuate nucleus

The purpose of the present study was to determine whether TGF beta, a cytokine secreted by hypothalamic astrocytes, was able to regulate POMC neurons in the arcuate nucleus. In a first set of experiments, mediobasal hypothalamic fragments were exposed to TGF beta(1), and the relative POMC mRNA expression was assessed by in situ hybridization using a radiolabeled POMC riboprobe. The results showed that 4 x 10(-10) M TGF beta(1) was efficient in decreasing significantly the amounts of POMC mRNA (P < 0.01). Interestingly, the decrease of relative POMC mRNA levels was higher in the rostral than in the caudal parts of the arcuate nucleus. In a second set of experiments, we examined the occurrence of TGF beta receptors expression in arcuate POMC neurons. Dual labeling in situ hybridization and in situ hybridization, coupled to immunohistochemical labeling, were performed to examine mRNA expression of the type I serine-threonine kinase receptor for TGF beta and the presence of type II receptor for TGF beta, respectively, in POMC neurons. The results indicated that TGF beta receptor I mRNA and TGF beta receptor II protein were expressed in numerous POMC neurons. Regional analysis revealed that the highest proportion of POMC neurons expressing TGF beta receptors was located in the rostral part of the arcuate nucleus. Using dual labeling immunohistochemistry, we also found that Smad2/3 immunoreactivity, a TGF beta(1) downstream signaling molecule, was present in the cytoplasm and nucleus of some POMC (beta-endorphin) neurons. We next examined whether the number of POMC neurons expressing TGF beta-RI mRNA was affected by sex steroids. Quantification of the number of POMC neurons expressing TGF beta receptor I mRNA in ovariectomized, ovariectomized E2-treated, and ovariectomized E2 plus progesterone-treated animals revealed that estrogen treatment decreased the expression of TGF beta receptor I mRNA in POMC neurons located in the rostral half of the arcuate nucleus, an effect reversed by progesterone in a subset of the most rostral cells. Taken together, these data reveal that TGF beta(1) may directly modulate the activity of POMC neurons through the activation of TGF beta receptors. Therefore, the present study provides additional evidence for the involvement of TGF beta(1) in the regulation of neuroendocrine functions and supports the existence of a glial-to-neurons communication within the arcuate nucleus.

Choroid plexus: target for polypeptides and site of their synthesis

Choroid plexus (CP) is an important target organ for polypeptides. The fenestrated phenotype of choroidal endothelium facilitates the penetration of blood-borne polypeptides across the capillary walls. Thus, both circulating and cerebrospinal fluid (CSF)-borne polypeptides can reach their receptors on choroidal epithelium. Several polypeptides have been demonstrated to regulate CSF formation by controlling blood flow to choroid plexus and/or the activity of ion transport in choroidal epithelium. However, many ligand-receptor interactions occurring in the CP are not involved in the regulation of fluid secretion. Increasing evidence suggests that the choroidal epithelium plays an important role in hormonal signaling via a receptor-mediated transport into the brain (e.g., leptin) and helps to clear certain CSF-borne polypeptides (e.g., soluble amyloid beta-protein). Thus, impaired choroidal transport or insufficient clearance of polypeptides may contribute to pathogenesis of systemic or central nervous system (CNS) disorders, such as obesity or Alzheimer's disease. CP epithelium is not only a target but is also a source of neuropeptides, growth factors, and cytokines in the CNS. These polypeptides following their release into the CSF may exert distal, endocrine-like effects on target cells in the brain due to bulk flow of this fluid. Distinct temporal patterns of choroidal expression of several polypeptides are observed during brain development and in various CNS disorders, including traumatic brain injury and ischemia. Therefore, it is proposed that the CP plays an integral role not only in normal brain functioning, but also in the recovery from the injury. This review attempts to critically analyze the available data to support the above hypothesis.

Evidence that members of the TGFbeta superfamily play a role in regulation of the GnRH neuroendocrine axis: expression of a type I serine-threonine kinase receptor for TGRbeta and activin in GnRH neurones and hypothalamic areas of the female rat

The present study was designed to determine whether transforming growth factor (TGF)beta and/or activin participate in the regulation of the gonadotropin releasing hormone (GnRH) neuroendocrine axis in vivo. Single-label in situ hybridization histochemistry was used to determine the anatomical distribution of a TGFbeta and activin type I receptor (B1) mRNA, in the adult female rat hypothalamic areas that are known to be important sites for the regulation of reproduction. Dual-label in situ hybridization histochemistry was performed to determine whether B1 mRNA was expressed in GnRH neurones. The results of these studies revealed an extensive distribution of B1 mRNA in the hypothalamic regions, including diagonal bands of Broca, preoptic area, arcuate nucleus and median eminence. In the median eminence, B1 mRNA was detected in tanycytes and in the endothelial cells of the pituitary portal blood capillaries. Dual-label in situ hybridization histochemistry showed that 31+/-5% of GnRH neurones expressed B1 mRNA, thus providing evidence that TGFbeta and/or activin can act directly on GnRH neurones to modulate their activity. Taken together, these data provide morphological arguments in favour of a participation of TGFbeta and/or activin in the regulation of reproduction at the hypothalamic level.

Transforming growth factor-beta activated during exercise in brain depresses spontaneous motor activity of animals. Relevance To central fatigue

Intracerebroventricular administration into sedentary mice of the high molecular mass fraction of cerebrospinal fluid (CSF) from exercise-exhausted rats produced a decrease in spontaneous motor activity [K. Inoue, H. Yamazaki, Y. Manabe, C. Fukuda, T. Fushiki, Release of a substance that suppresses spontaneous motor activity in the brain by physical exercise, Physiol. Behav. 64 (1998) 185-190]. CSF from sedentary rats had no such effect. This suggests the presence of a substance regulating the urge for motion as a response to fatigue. A bioassay system using hydra, a freshwater coelenterate, showed an activity indistinguishable from transforming growth factor-beta (TGF-beta) in the CSF from exercise-fatigued rats, while not in that from sedentary rats. The increase in the concentration of active TGF-beta in the CSF from exercise-fatigued rat was also ascertained by another bioassay system using mink lung epithelial cells (Mv1Lu). Injection of TGF-beta into the brains of sedentary mice elicited a similar decrease in spontaneous motor activity in a dose-dependent manner. Increasing the exercise load on rats raised both the levels of active TGF-beta and the activity of depression on spontaneous motor activity of mice in the CSF of rats. Taken together, these results suggest that exercise increases active TGF-beta in the brain and it creates the feeling of fatigue and thus suppresses spontaneous motor activity.

Administration of recombinant human Activin-A has powerful neurotrophic effects on select striatal phenotypes in the quinolinic acid lesion model of Huntington's disease

Huntington disease is characterized by the selective loss of striatal neurons, particularly of medium-sized spiny glutamate decarboxylase67 staining/GABAergic projection neurons which co-contain the calcium binding protein calbindin. Lesioning of the adult rat striatum by intrastriatal injection of the N-methyl-D-aspartate receptor agonist quinolinic acid (100 nmol) results in a pattern of striatal neuropathology seven days later that resembles that seen in the Huntington brain. Using this animal model of human Huntington's disease we investigated the effect of daily intrastriatal infusion of the nerve cell survival molecule ActivinA (single bolus dose of 0.73 microg daily for seven days) on the quinolinic acid-induced degeneration of various striatal neuronal phenotypes. By seven days, unilateral intrastriatal infusion of quinolinic acid produced a partial but significant loss (P < 0.01) in the number of striatal neurons immunoreactive for glutamate decarboxylase (to 51.0+/-5.8% of unlesioned levels), calbindin (to 58.7+/-5.1%), choline acetyltransferase (to 68.6+/-6.1%), NADPH-diaphorase (to 47.4+/-5.4%), parvalbumin (to 58.8+/-4.1%) and calretinin (to 60.6+/-8.6%) in adult rats that were administered intrastriatal phosphate-buffered saline for seven days following quinolinic acid. In contrast, in rats that received intrastriatal recombinant human ActivinA once daily for seven days following quinolinic acid, phenotypic degeneration was significantly attenuated in several populations of striatal neurons. Treatment with ActivinA had the most potent protective effect on the striatal cholinergic interneuron population almost completely preventing the lesion induced decline in choline acetyltransferase expression (to 95.1+/-5.8% of unlesioned levels, P < 0.01). ActivinA also conferred a significant protective effect on parvalbumin (to 87.5+/-7.7%, P < 0.01) and NADPH-diaphorase (to 77.5+/-7.5%, P < 0.01) interneuron populations but failed to prevent the phenotypic degeneration of calretinin neurons (to 56.6+/-5.5%). Glutamate decarboxylase67 and calbindin-staining nerve cells represent largely overlapping populations and both identify striatal GABAergic projection neurons. We found that ActivinA significantly attenuated the loss in the numbers of neurons staining for calbindin (to 79.7+/-6.6%, P < 0.05) but not glutamate decarboxylase67 (to 61.1+/-5.9%) at seven days following quinolinic acid lesioning. Taken together these results suggest that exogenous administration of ActivinA can rescue both striatal interneurons (labelled with choline acetyltransferase, parvalbumin, NADPH-diaphorase) and striatal projection neurons (labelled by calbindin) from excitotoxic lesioning with quinolinic acid. Longer-term studies will be required to determine whether these surviving calbindin-expressing projection neurons recover their ability to express the glutamate decarboxylase67/GABAergic phenotype. These results therefore suggest that treatment with ActivinA may help to prevent the degeneration of vulnerable striatal neuronal populations in Huntington's disease.

Cloning and studies of the mouse cDNA encoding Smad3

Following stimulation by the transforming growth factor-beta (TGF-beta) family in the cytoplasm, the Smad family is phosphorylated and translocated to the nucleus and activates several gene transcriptions. In this study, the mouse Smad3 cDNA including the open reading frame (ORF) was cloned from the mouse brain using a RACE (rapid amplification of cDNA ends) technique, and its expression pattern was analyzed in mouse tissue using northern blot. The predicted amino acid (aa) sequences of mouse Smad3 showed a high homology with human Smad3 (99.3%) and mouse Smad2 (85.4%). It revealed that this protein may be highly conserved in different species of mammals. Northern blot analyses revealed that Smad3 was highly expressed in the brain and ovary, and that the size of major transcript was about 5.7 kb. In situ hybridization analyses revealed the high expression of Smad3 was detected in the pyramidal cells of the hippocampus, the granule cells of the dentate gyrus, the granular cells of the cerebral cortex and the granulosa cells of the ovary. Smad3 may be essential transducer of signals from TGF-beta and activin in these cells.