Neuro-glial neurotrophic interaction in the S-100 beta retarded mutant mouse (Polydactyly Nagoya). II. Co-cultures study

A review of the neuroprotective properties of the 5-HT1A receptor agonist repinotan HCl (BAYx3702) in ischemic stroke

Repinotan HCl (repinotan, BAYx3702), a highly selective 5-HT1A receptor agonist with a good record of safety was found to have pronounced neuroprotective effects in experimental models that mimic various aspects of brain injury. Repinotan caused strong, dose-dependent infarct reductions in permanent middle cerebral artery occlusion, transient middle cerebral artery occlusion, and traumatic brain injury paradigms. The specific 5-HT1A receptor antagonist WAY 100635 blocked these effects, indicating that the neuroprotective properties of repinotan are mediated through the 5-HT1A receptor. The proposed neuroprotective mechanisms of repinotan are thought to be the result of neuronal hyperpolarization via the activation of G protein-coupled inwardly rectifying K+ channels upon binding to both pre- and post-synaptic 5-HT1A receptors. Hyperpolarization results in inhibition of neuron firing and reduction of glutamate release. These mechanisms, leading to protection of neurons against overexcitation, could explain the neuroprotective efficacy of repinotan per se, but not necessarily the efficacy by delayed administration. The therapeutic time window of repinotan appeared to be at least 5 h in in vivo animal models, but may be even longer at higher doses of the drug. Experimental studies indicate that repinotan affects various mechanisms involved in the pathogenesis of brain injury. In addition to the direct effect of repinotan on neuronal hyperpolarization and suppression of glutamate release this compound affects the death-inhibiting protein Bcl-2, serotonergic glial growth factor S-100beta and Nerve Growth Factor. It also suppresses the activity of caspase-3 through MAPK and PKCalpha; this effect may contribute to its neuroprotective efficacy. The dose- and time-dependent neuroprotective efficacy of repinotan indicates that the drug is a promising candidate for prevention of secondary brain damage in brain-injured patients suffering from acute ischemic stroke. Unfortunately, however, the first, randomized, double blind, placebo-controlled clinical trial did not demonstrate the efficacy of repinotan in acute ischemic stroke.

Formation of the Astroglia in the Mouse Neocortex after Temporary Prenatal Blockade of Serotonin Synthesis

The dynamics of the appearance of astrocytes in the mouse neocortex after prenatal blockade of serotonin synthesis was studied. Experiments were performed on F1(CBA/C57Bl) hybrid mice. Serotonin release was suppressed with parachlorophenylalanine, given as single doses to mothers during the early postimplantation stage of pregnancy. Astrocytes differentiating in the brain were visualized by an immunohistochemical method for detecting astrocyte intermediate filament protein, this being a specific glial fibrillary acidic protein (GFAP) allowing not only marking of cells, but also assessment of the presence, extent, and rate of cell differentiation. The results showed that in normal conditions, GFAP-positive cells appeared in layer I of all neocortical areas during the first week after birth, i.e., the area cingularis, the area occipitalis, the area parietalis, the area insularis, the area praepiriformis, the area piriformis, the area entorhinalis, and the area subiculum. The process of astrocyte differentiation intensified with development. Barrier structures also formed. During the first days of postnatal development, astrocytes and their processes appeared around vessels and the walls of the lateral ventricles. The neocortex of rats developing in conditions of blockade of serotonin synthesis showed smaller numbers of GFAP-positive cells, particularly in the white matter, at all stages of postnatal development studied.

Relationship between S100β and GFAP expression in astrocytes during infarction and glial scar formation after mild transient ischemia

The expression of astrocyte marker proteins (S100beta and GFAP) during infarction and glial scar formation after transient middle cerebral artery (MCA) occlusion was examined using double immunostaining. S100beta immunoreactivity markedly decreased in the core of the injured area when observed immediately after reperfusion and did not increase again. In the periphery, however, S100beta expression increased, showing that S100beta synthesis was up-regulated. S100beta+/iNOS+ astrocytes in the periphery were observed from day 1, when small infarct areas were detectable, up to day 5, when infarct expansion had almost ended. TUNEL+ cells in the periphery were present from days 1 to 5. S100beta+/TUNEL+ cells were observed centrally and around the periphery of the injured area, predicting that cell death contributes to the increase of S100beta concentration in the injured area. Our results suggest that (1) higher concentration of S100beta in the extracellular space due to S100beta leakage from damaged astrocytes leads to up-regulation of S100beta synthesis and induction of inducible nitric oxide synthase (iNOS) synthesis in astrocytes, contributing to infarct expansion that results in DNA damage or cell death via NO and ROS production, and (2) GFAP, but not S100beta, is a main contributor to glial scar formation. On day 1 postreperfusion, the microdiascopic images of the injured areas from the unstained thick sections or the areas detected by S100beta immunoreactivity were larger than those of the infarct areas detected by hematoxylin--eosin (HE)-staining. The difference between these sizes might be useful to predict infarct expansion.

S100B in brain damage and neurodegeneration

S100B is a calcium-binding peptide produced mainly by astrocytes that exert paracrine and autocrine effects on neurons and glia. Some knowledge has been acquired from in vitro and in vivo animal experiments to understand S100B's roles in cellular energy metabolism, cytoskeleton modification, cell proliferation, and differentiation. Also, insights have been gained regarding the interaction between S100B and the cerebral immune system, and the regulation of S100B activity through serotonergic transmission. Secreted glial S100B exerts trophic or toxic effects depending on its concentration. At nanomolar concentrations, S100B stimulates neurite outgrowth and enhances survival of neurons during development. In contrast, micromolar levels of extracellular S100B in vitro stimulate the expression of proinflammatory cytokines and induce apoptosis. In animal studies, changes in the cerebral concentration of S100B cause behavioral disturbances and cognitive deficits. In humans, increased S100B has been detected with various clinical conditions. Brain trauma and ischemia is associated with increased S100B concentrations, probably due to the destruction of astrocytes. In neurodegenerative, inflammatory and psychiatric diseases, increased S100B levels may be caused by secreted S100B or release from damaged astrocytes. This review summarizes published findings on S100B regarding human brain damage and neurodegeneration. Findings from in vitro and in vivo animal experiments relevant for human neurodegenerative diseases and brain damage are reviewed together with the results of studies on traumatic, ischemic, and inflammatory brain damage as well as neurodegenerative and psychiatric disorders. Methodological problems are discussed and perspectives for future research are outlined.

Effects of ethanol and ipsapirone on the development of midline raphe glial cells and astrocytes

Previously, results of studies from our laboratory have shown that the offspring of ethanol-fed female rats have a significant decrease in serotonin (5-HT) neurons and glia that contain S100B, an essential trophic factor for the development of 5-HT neurons. The deficiency of S100B-immunopositive glia was detected during the vulnerable period in 5-HT neuron development and in brain areas proximal to these neurons. The reductions of both 5-HT neurons and S100B-positive glia were prevented by maternal treatment with a 5-HT(1A) agonist (i.e., ipsapirone or buspirone). In the current study, we investigated whether the offspring of ethanol-fed rats had a general decrease in the density of glial cells in the brain areas that contain 5-HT neurons, and we determined whether these changes were prevented by maternal treatment with ipsapirone between gestational days (GDs) 13 and 20. We estimated the density of vimentin-positive glia of the midline raphe glial structure (MRGS) at GD 20 and postnatal day (PND) 5 and of glial fibrillary acidic protein (GFAP)-positive astrocytes proximal to the dorsal and median raphe at PNDs 5 and 19. The results of this study provide evidence that in utero ethanol exposure is associated with a reduced density of GFAP-immunopositive astrocytes proximal to the dorsal and median raphe. Maternal ipsapirone treatment significantly increased astroglial density in the dorsal raphe at PNDs 5 and 19 and in the median raphe at PND 5, such that it either prevented (dorsal raphe, PNDs 5 and 19) or blunted (median raphe, PND 5) the effects of ethanol.

Normal development of serotonergic neurons in mice lacking S100B

S100B, a glia-derived calcium binding protein, exhibits strong neurite extension activity in cultured serotonergic neurons. Using S100B-knockout mice, we examined whether this protein possesses in vivo serotonergic trophic activity. The distribution of serotonergic fibers, determined by immunohistochemistry, in the brains of S100B-knockout mice was quite similar to that of wild-type mice. Furthermore, the content of serotonin and its metabolite 5-hydroxyindole-3-acetic acid in knockout mice was also indistinguishable from those of wild-type mice. Our findings argue against the hypothesis that S100B has a crucial role in neurite extension of serotonergic neurons.

A biogenic amine-synapse mechanism for mental retardation and developmental disabilities

Recent studies have demonstrated that biogenic amines have a function of facilitating formation and maintenance of synapses in diverse regions of the central nervous system in developing and adult animals. The normal number of synapses maintained by biogenic amines are crucial to acquire learning and memory. The level of biogenic amines was reported to decrease in the brain by several neurodevelopmental disorders associated with mental retardation and developmental disabilities such as Rett syndrome, autism and Down syndrome. Taken into consideration this fact together with the function of biogenic amines for synapses, the density of synapses appears to decrease considerably in the brains of patients suffered from the neurodevelopmental disorders. The synaptic overproduction during the critical period of development especially 1 year after birth has been considered as a background mechanism to provide plasticity for the developing brain. Synaptic overproduction does not appear to occur in the brains of patients suffered from the neurodevelopmental disorders, which they are observed mental retardation occurring in the first 1 year after birth. Along with the neurodevelopmental disorders, environmental factors (stress, drugs and nutrition) during pre- and post-natal critical developmental periods are known to change levels of biogenic amines in the brain. In fact, maternal stress has been shown to decrease the levels of serotonin and the density of synapses in the hippocampus of the offspring, and they showed developmental disabilities in the spatial learning and memory. A cascade appears to exist from either the child neurological disorders or the environmental factors to mental retardation and developmental disabilities by decreases in the levels of biogenic amines and synaptic density.

Astrocyte-mediated trophic support of developing serotonin neurons: effects of ethanol, buspirone, and S100B

Previously, this laboratory demonstrated that the development of serotonin (5-HT) neurons and S100B-immunopositive glia proximal to these neurons is impaired in the offspring of ethanol-fed rats. However, maternal treatment with a 5-HT(1A) agonist, e.g., buspirone or ipsapirone, between gestational days 13 and 20 prevented most of the ethanol-associated changes to developing 5-HT neurons and S100B-immunopositive glia in offspring. The present in vitro studies examined the hypothesis that the protective effects of a 5-HT(1A) agonist on ethanol-exposed, developing 5-HT neurons are mediated in part by astrocyte-produced factors such as S100B. Primary cultures of fetal 5-HT neurons were maintained in conditioned medium (CM) that was obtained from ethanol- and buspirone-treated astrocytes. In order to assess the potential contribution of S100B to the protective effects of buspirone, a mouse monoclonal antibody to S100B was added to the CM to block the biological effects of this protein. These studies demonstrated that CM, obtained from ethanol-treated astrocytes, was unable to support normal development of 5-HT neurons; there was a significant reduction in the number of 5-HT neurons/well. However, CM that was obtained from astrocytes that were co-treated with buspirone and ethanol prevented the ethanol-associated reduction, and the protective effects of buspirone required S100B. We also investigated whether exogenous S100B could protect 5-HT neurons from damage caused by direct exposure to ethanol. Direct exposure of fetal brainstem neurons to ethanol in chemically-defined medium was associated with a significant reduction in the number of 5-HT immunopositive neurons/well. However, exogenous S100B protected 5-HT neurons from the ethanol-associated reduction. Our observations suggest that the protective effects of buspirone on ethanol-exposed, developing 5-HT neurons are mediated in part by the astrocyte-produced factor S100B.

Modern views on an ancient chemical: serotonin effects on cell proliferation, maturation, and apoptosis

Evolutionarily, serotonin existed in plants even before the appearance of animals. Indeed, serotonin may be tied to the evolution of life itself, particularly through the role of tryptophan, its precursor molecule. Tryptophan is an indole-based, essential amino acid which is unique in its light-absorbing properties. In plants, tryptophan-based compounds capture light energy for use in metabolism of glucose and the generation of oxygen and reduced cofactors. Tryptophan, oxygen, and reduced cofactors combine to form serotonin. Serotonin-like molecules direct the growth of light-capturing structures towards the source of light. This morphogenic property also occurs in animal cells, in which serotonin alters the cytoskeleton of cells and thus influences the formation of contacts. In addition, serotonin regulates cell proliferation, migration and maturation in a variety of cell types, including lung, kidney, endothelial cells, mast cells, neurons and astrocytes). In brain, serotonin has interactions with seven families of receptors, numbering at least 14 distinct proteins. Of these, two receptors are important for the purposes of this review. These are the 5-HT1A and 5-HT2A receptors, which in fact have opposing functions in a variety of cellular and behavioral processes. The 5-HT1A receptor develops early in the CNS and is associated with secretion of S-100beta from astrocytes and reduction of c-AMP levels in neurons. These actions provide intracellular stability for the cytoskeleton and result in cell differentiation and cessation of proliferation. Clinically, 5-HT1A receptor drugs decrease brain activity and act as anxiolytics. The 5-HT2A receptor develops more slowly and is associated with glycogenolysis in astrocytes and increased Ca(++) availability in neurons. These actions destabilize the internal cytoskeleton and result in cell proliferation, synaptogenesis, and apoptosis. In humans, 5-HT2A receptor drugs produce hallucinations. The dynamic interactions between the 5-HT1A and 5-HT2A receptors and the cytoskeleton may provide important insights into the etiology of brain disorders and provide novel strategies for their treatment.

Potential involvement of S100B in the protective effects of a serotonin-1a agonist on ethanol-treated astrocytes

Previously, this laboratory found that the offspring of rats that consumed ethanol on a chronic basis prior to parturition exhibited a significant reduction in serotonin (5-HT) neurons and in astrocytes proximal to these neurons. This laboratory also showed that maternal treatment with a 5-HT(1A) agonist during the latter part of gestation prevented the reduction of 5-HT neurons and most of the astrocyte abnormalities. The present in vitro studies extended our prior in vivo work by examining the potential involvement of S100B with the protective effects of a 5-HT(1A) agonist, i.e., buspirone, on astrocytes. Astrocyte cultures were either maintained in chemically defined media in the presence and absence of ethanol and buspirone or in conditioned media that was generated by ethanol- and buspirone-treated astrocytes. A mouse monoclonal antibody to S100B was used to assess the potential involvement of S100B with the protective effects of buspirone. Additional in vitro studies measured the direct effects of S100B and ethanol on astrocyte proliferation. These investigations demonstrate that in vitro ethanol exposure reduces the number of astrocytes, and that treatment with the 5-HT(1A) agonist buspirone prevents the ethanol-associated reduction in astrocyte number. The protective effects of buspirone appear to be mediated by factors that are secreted by astrocytes; such factors likely include S100B. In addition, added S100B prevents an ethanol-associated reduction in [(3)H]-thymidine incorporation into proliferating astrocytes.

Serotonergic heterotypic sprouting in the unilaterally dopamine-depleted mouse neostriatum

The effects of unilateral 6-hydroxydopamine (6-OHDA) treatment on striatal serotonin neurons in 12-day-old mice were studied using immunohistochemistry. The unilateral 6-OHDA lesions were evaluated with tyrosine hydroxylase (TH) immunohistochemistry. The majority of the TH-immunoreactive structures disappeared from the substantia nigra and neostriatum on the 6-OHDA lesioned side. However, the density of serotonin fibers was markedly increased throughout the 6-OHDA-depleted neostriatum 1 year later. These results suggest that serotonergic heterotypic sprouting may be permanent.

Compensatory responses in the aging hippocampal serotonergic system following neurodegenerative injury with 5,7-dihydroxytryptamine

This study utilized a multidisciplinary approach to examine injury-induced compensatory responses in the aging hippocampal serotonin transporter (5-HTT), a membrane protein implicated in a variety of neurodegenerative disorders. Age-dependent cellular, anatomical, and physiological changes of the 5-HTT were evaluated in female Fischer 344 rats (2 and 17 months) following denervation of the serotonergic afferents (fimbria-fornix and cingulum bundle) to the dorsal hippocampus using the neurotoxicant 5,7-dihydroxytryptamine (5,7-DHT). Seven days following 5,7-DHT administration, a uniform loss of the hippocampal 5-HTT immunoreactivity was observed in both age groups. However, at 21 days 5-HTT immunoreactivity in young 5,7-DHT-treated animals was similar to control levels, indicative of recovery, while older animals exposed to 5,7-DHT did not show recovery of hippocampal 5-HTT expression. 5-HTT binding site density, as determined by quantitative autoradiography ([3H]citalopram), supported the immunohistochemical results by demonstrating a recovery of 5-HTT binding sites in young, but not old animals, at 21 days following the lesion (P < 0.001). Furthermore, cellular electrophysiological function of hippocampal CA1 pyramidal neurons in 3- and 18-month-old F344 rats at 21 days following 5,7-DHT or vehicle treatment were assessed using in vivo microiontophoretic application of serotonin (5-HT). Independent of changes in sensitivity to the inhibitory effects of 5-HT application, the time to recovery of cell firing following application of 5-HT was significantly increased in the 18-month 5,7-DHT group compared to the 18-month vehicle and 3-month 5,7-DHT groups (60 and 59% increases, respectively; P < 0.05). Overall, these series of studies comprise a model which can be used to identify cellular events underlying both the formation of injury-induced compensatory processes in younger animals and the lack thereof with advancing age.

Stimulation of 5-HT(1A) receptors reduces apoptosis after transient forebrain ischemia in the rat

It has recently been shown that 5-HT(1A) receptor stimulation reduced the infarct volume after occlusion of the middle cerebral artery in rats. Since there is increasing evidence that apoptosis is involved in neurodegenerative diseases and stroke, we investigated whether the 5-HT(1A) agonist Bay x 3702 could protect neurons against apoptotic damage in a rat model of transient forebrain cerebral ischemia. Bay x 3702 (4 microg/kg i.v.) caused a 10% reduction of neuronal damage in the hippocampal CA1 subfield. Higher doses of Bay x 3702 (40 and 12 microg/kg i.v.) did not cause any neuroprotective effect, most likely because of the strong reduction of mean arterial blood pressure during the period of Bay x 3702 infusion. Bay x 3702 (4 microg/kg i.v.) diminished DNA laddering in the hippocampus and striatum 4 days after 10 min forebrain ischemia. These results were confirmed by TUNEL-staining. The anti-apoptotic effect was abolished by additional treatment with the 5-HT(1A) receptor antagonist WAY 100635 (1 mg/kg). Taken together, the results suggest that Bay x 3702 can rescue hippocampal as well as striatal neurons from apoptotic cell death in vivo via stimulation of 5-HT(1A) receptors.

Effects of in utero ethanol exposure and maternal treatment with a 5-HT(1A) agonist on S100B-containing glial cells

This laboratory previously showed that in utero ethanol exposure severely impairs the development of the cell bodies and projections of serotonin (5-HT) neurons, and that maternal treatment with a 5-HT(1A) agonist prevents many of these abnormalities. Others demonstrated that stimulation of fetal astroglial 5-HT(1A) receptors increases production and release of S100B, a glial trophic factor that is essential for the development of 5-HT neurons. The present study investigated a potential mechanism by which ethanol hinders development of 5-HT neurons, and by which maternal 5-HT(1A) agonist treatment prevents this damage. This study tested the hypothesis that in utero ethanol exposure reduces the number of S100B immunopositive glia and that maternal 5-HT(1A) agonist treatment prevents ethanol-associated changes in S100B. To test our hypothesis, we determined the effects of in utero ethanol exposure and maternal treatments with the 5-HT(1A) agonists ipsapirone and buspirone on S100B immunopositive glial cells. On gestation day 20 (G20), S100B immunopositive cells were quantified in the midline raphe glial structure (MRGS), a large transient structure that contains substantial numbers of S100B-positive glial cells and that spans the dorsal raphe, median raphe, and B9 complex of 5-HT neurons. S100B immunopositive glial cells were also determined in an area proximal to the dorsal raphe in postnatal day 2 (PN2) rats. In utero ethanol exposure significantly reduced S100B immunopositive glial cells in the MRGS at G20 and in the dorsal raphe at PN2. In addition, treatment of pregnant rats with a 5-HT(1A) agonist between G13 and G20 prevented the ethanol-associated reduction in S100B immunopositive glial cells. These studies demonstrated that part of ethanol's damaging effects on developing 5-HT neurons is mediated by a reduction of S100B and that some of the protective effects of maternal 5-HT(1A) agonist treatment are related to the actions of these drugs on glial cells.

Synaptic strength as a function of post- versus presynaptic expression of the neural cell adhesion molecule NCAM

To evaluate the contributions of the pre- versus postsynaptic expression of NCAM in regulation of synaptic efficacy, we cultured dissociated hippocampal cells from NCAM-deficient and wild-type mice in homo- and heterogenotypic combinations. Double recordings from synaptically coupled neurons maintained in heterogenotypic cocultures showed that synaptic strength of excitatory but not inhibitory synapses depended on expression of NCAM post- but not presynaptically. This correlated with higher levels of potentiation and synaptic coverage of NCAM-expressing neurons compared to NCAM-deficient neurons in heterogenotypic cocultures. Synaptic density was the same in homogenotypic cultures of NCAM-deficient and wild-type neurons as well as in heterogenotypic cocultures in which glutamate receptors were blocked. These observations indicate that the relative levels of postsynaptic NCAM expression control synaptic strength in an activity-dependent manner by regulating the number of synapses.

The trophic factors S-100beta and basic fibroblast growth factor are increased in the forebrain reactive astrocytes of adult callosotomized rat

S-100 is a calcium-binding protein that is predominantly found in astrocytes of the central nervous system. In the present study, we investigated the temporal and spatial changes of S-100beta immunoreactivity after a stereotaxic mechanical lesion of the adult rat corpus callosum performed with an adjustable wire knife. Rats were killed 7, 14 and 28 days after surgery. S-100beta immunoreactivity was found within the cytoplasm and processes of quiescent putative astrocytes that were observed throughout the gray and white matters of the forebrain of sham-operated rats. Following callosotomy, the S-100beta immunoreactive profiles showed increased size and thick processes, as well as increased amount of S-100beta immunoreactivity. Unbiased stereologic analysis revealed a sustained and widespread increase of the Areal Fraction of S-100beta immunoreactive profiles in the medial and lateral regions of the white matter of callosotomized rats at the studied time-intervals. In the cerebral cortex of callosotomized rats, the estimated total number of S-100beta immunoreactive profiles was also increased 7 and 14 days after the lesion. Since the cellular and temporal changes in S-100beta immunoreactivity were closely similar to those described for basic fibroblast growth factor (bFGF) following brain lesions, we co-localized the S-100beta and bFGF immunoreactivities after callosotomy. bFGF immunoreactivity was found in the nuclei of S-100beta immunoreactive glial profiles throughout the forebrain regions of the sham-operated rats. bFGF immunoreactivity was increased in the nuclei of reactive S-100beta immunoreactive putative astrocytes in the forebrain white matter and in the cerebral cortex of callosotomized rats. These results indicate that after transection of the corpus callosum of adult rats, the reactive astrocytes may exert paracrine trophic actions through S-100beta and bFGF. Interactions between S-100beta and bFGF may be relevant to the events related to neuronal maintenance and repair following brain injury.

Neuroprotective effect of 5-HT1A receptor agonist, Bay X 3702, demonstrated in vitro and in vivo

It has been shown recently that Bay X 3702 ((-)-(R)-2-[4-[[(3,4-dihydro-2H-1-benzopyran-2-yl)methyl]amino]butyl]-1, 2,-benzisothiazol-3(2H)-one 1,1-dioxide monohydrochloride), a highly potent and selective 5-HT1A receptor agonist, has a neuroprotective potency associated with its ability to inhibit ischemia-induced excessive release of glutamate. 5-HT1A receptors are highly expressed in brain areas, such as the hippocampus and the cerebral cortex, sensitive to neuronal damage induced by ischemic stroke or brain trauma. Therefore, we investigated whether Bay X 3702 can rescue cultured hippocampal neurons subjected to excitotoxic damage. The hippocampal neurons exposed to 0.5 mM L-glutamate for 1 h had pronounced damage characteristic of neuronal necrosis as evaluated 18 h later by trypan blue staining and morphological criteria. However, treatment with Bay X 3702 (0.001 to 1 microM) reduced the number of damaged neurons, and preserved cell morphology and integrity of the neuronal network. Bay X 3702 was added immediately after the end of exposure to glutamate and was present until the evaluation of neuronal damage. Furthermore, the neuroprotective activity of Bay X 3702 (0.1 microM) was abolished by WAY 100635 (N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl cyclo-hexanecarboxamide) (1 microM), a selective 5-HT1A receptor antagonist, indicating that the neurorescuing activity of Bay X 3702 was mediated via stimulation of 5-HT1A receptors. Additionally, we attempted to find whether the drug could protect rat brain tissue from ischemic insult due to permanent occlusion of the middle cerebral artery in rats. Bay X 3702 (12 and 40 microg/kg), infused within a period of 4 h, immediately after induction of ischemia greatly reduced cortical infarct volume (57 and 55% of controls, respectively) suggesting that this drug might be useful for the treatment of acute cerebral infarction.

Neuro-glial neurotrophic interaction in the S-100 beta retarded mutant mouse (Polydactyly Nagoya). III. Transplantation study

The hippocampus and caudo-dorsal cortex of the homozygote of polydactyly mutant mouse (Polydactyly Nagoya, Pdn/Pdn) were markedly reduced in S-100 beta positive astrocytes and serotonergic fibers as compared to the heterozygote (Pdn/+) and wild type (+/+) [39]. The Pdn/Pdn mice die within 2 days after birth, so it is impossible to examine postnatal changes. To demonstrate the developmental change of Pdn/Pdn hippocampal tissue, we transplanted hippocampal pieces of neonatal Pdn/Pdn and +/+ mice into the right and left hippocampus of the same adult +/+ mice, respectively, and immunocytochemically examined them. Two weeks after transplantation, +/+ hippocampal tissue contained a large number of glial fibrillary acidic protein (GFAP) and S-100 beta positive astrocytes and a number of serotonergic fibers. While Pdn/Pdn hippocampal tissue contained numerous GFAP positive astrocytes, S-100 beta positive astrocytes and serotonergic fibers were not observed. Two months after transplantation, GFAP and S-100 beta were expressed in the Pdn/Pdn hippocampal tissue similar to the +/+ tissue. Serotonergic fibers were distributed in the +/+ tissue, while no serotonergic fibers were observed in the Pdn/Pdn transplant tissue. In contrast, no difference was observed in the tyrosine hydroxylase positive fibers between Pdn/Pdn and +/+ grafts. The expression of 5-HT1A receptor-like immunoreactivity was higher in the +/+ tissue than that of Pdn/Pdn tissue. The present results suggest that the expression of S-100 beta in the astrocytes of early stage of transplantation is a critical for fiber ingrowth of serotonergic neurons and expressions of 5-HT1A receptor.

The S-100: a protein family in search of a function

The S-100 is a group of low molecular weight (10-12 kD) calcium-binding proteins highly conserved among vertebrates. It is present in different tissues as dimers of homologous or different subunits (alpha, beta). In the nervous system, the S-100 exists as a mixture composed of beta beta and alpha beta dimers with the monomer beta represented more often. Its intracellular localisation is mainly restricted to the glial cytoplasmic compartment with a small fraction bound to membranes. In this compartment the S-100 acts as a potent inhibitor of phosphorylation on several substrates including the synaptosomal C-Kinase and Tau, a microtubule-associated protein. The S-100 in particular conditions, after binding with specific membrane sites (Kd = 0.2 microM; Bmax = 4.5 nM), is able to modify the activity of adenylate cyclase, probably via G-proteins. In addition, the Ca2+ homeostasis is also modulated by S-100 via an increase of specific membrane conductance and/or Ca2+ release from intracellular stores. "In vitro" and "in vivo" experiments showed that lower (nM) concentrations of extracellular S-100 beta act on glial and neuronal cells as a growth-differentiating factor. On the other hand, higher concentrations of the protein induce apoptosis of some cells such as the sympathetic-like PC12 line. Finally, data obtained from physiological (development, ageing) or pathological (dementia associated with Down's syndrome, Alzheimer's disease) conditions showed that a relationship could be established between the S-100 levels and some aspects of the statii.

Rapid serotonergic fiber sprouting in response to ibotenic acid lesion in the striatum and hippocampus

Serotonergic (5-HT) sprouting occurs after damage of neighboring 5-HT or non-5-HT fibers. The sprouting signals appear to originate from the target tissue where neural trophic factors are secreted. In order to determine the cellular source of the trophic signal we currently report that removal of local neurons with a neurotoxin, ibotenic acid (IB), triggered a vigorous sprouting of 5-HT fibers in the striatum as early as 3 days after the lesion, which lasted throughout the entire length (21 days) of our study. The 5-HT fiber density in the injection site increased 10-fold in the striatum compared to the contralateral side, and the density of 5-HT varicosities increased 4-fold of normal. The 5-HT level in the striatum correspondingly increased on the lesion side. Three clear morphological concentric zones were formed by the lesion: acellular, aneuronal and outer zones. These zones represent the characteristic reorganization of astrocytes and neurons following an injection of IB. Devoid of any cells, the small acellular zone in the center of the injection site contained few 5-HT fibers. Devoid of neurons, the aneuronal zone contained reactive astrocytes and an abnormally high density of 5-HT fibers with increased staining of S-100. Containing neurons and astrocytes, the outer zone had a normal 5-HT fiber density. The induced 5-HT sprouting in the aneuronal zone strongly suggests that local neurons could provide a trophic factor, but that astrocytes would be the most plausible candidate. This is not an isolated case, IB injections in the hippocampus also induce a similar phenomenon.

Neuro-glial neurotrophic interaction in the S-100 beta retarded mutant mouse (Polydactyly Nagoya). I. Immunocytochemical and neurochemical studies

The homozygote of a mouse strain with genetic polydactyly (Polydactyly Nagoya; Pdn) shows several brain abnormalities, and significant decrease of S-100 beta in the brain. In order to clarify the effects of the retarded production of S-100 beta on the development of monoaminergic neuronal systems and supporting glial cells, immunocytochemical studies of tyrosine hydroxylase (TH), serotonin (5-HT), S-100 beta and glial fibrillary acidic protein (GFAP). In addition, high-performance liquid-chromatography (HPLC) measurements of serotonin and 5-hydroxyindoleacetic acid (5-HIAA) of homozygote (Pdn/Pdn) mouse were examined, and the results were compared with those of other genotypes; heterozygote (Pdn/+) and wild type (+/+) mice. In all types of mice, S-100 beta positive cells and serotonergic fibers were widely distributed throughout the brains and serotonergic cell bodies were located in the brainstem. However, the hippocampus and caudo-dorsal cortex of Pdn/Pdn mouse were markedly reduced in S-100 beta positive cells and in serotonergic fibers. Furthermore, abnormal distribution of GFAP positive cells and fibers were observed in the neocortex and hippocampus of Pdn/Pdn brain. No differences were seen in the distribution of TH neurons or fibers distribution. In the HPLC study, the content of 5-HT and 5-HIAA of the hippocampus and cortex of Pdn/Pdn mouse was lower than those of Pdn/+ and +/+ mice. The present results suggest that the developmental defect of serotonergic fibers in the Pdn mutant mouse is correlate to the deficiency of S-100 beta in the astrocyte of this mutant.