Time-dependent mechanical behavior of partially oxidized polyvinyl alcohol hydrogels for tissue engineering.

Polyvinyl alcohol (PVA) hydrogels are synthetic polymers which can be used as scaffolds for tissue engineering due to their biocompatibility and large water content. To improve their biodegradation properties, partial oxidation of PVA is achieved by means of different oxidizing agents, such as potassium permanganate, bromine and iodine. The effect of this process on hydrogels mechanical performance has not been fully investigated in view of tissue engineering applications.

Macrolide antibiotics protect neurons in culture against the N-methyl-D-aspartate (NMDA) receptor-mediated toxicity of glutamate.

The immunosuppressive macrolide FK-506 has been shown to protect neurons in culture against glutamate excitotoxicity. This effect was attributed to the binding of immunosuppressants to calcineurin-inhibiting immunophilins. We now report that also the non-immunosuppressive macrolide antibiotics protect neurons in culture against NMDA- but not kainate-mediated excitotoxicity.

NMDA-stimulated expression of BDNF mRNA in cultured cerebellar granule neurones.

The brain-derived neurotrophic factor (BDNF) affects the developing cerebellar granule cells. Exposure of 9-11-day-old primary cultures of rat cerebellar granule neurones for 3 h to a more depolarizing medium (additional 15-30 mM KCl) stimulated the release of glutamate and increased the BDNF mRNAs levels. This BDNF and mRNA upregulation was inhibited by dizocilpine (MK-801), the noncompetitive blocker of N-methyl-D-aspartate (NMDA)-sensitive glutamate receptors, and mimicked by NMDA.

Trans-azetidine-2,4-dicarboxylic acid activates neuronal metabotropic receptors.

The expression of metabotropic glutamate receptors (mGluRs) in primary cultures of cerebellar granule neurones can be: (i) modulated by the degree of depolarization during the culture period, rendering neurones differently sensitive to agonist-stimulated inositol phosphate (IP) hydrolysis; (ii) down-regulated by specific mGluR agonists. In this culture the new rigid glutamate analogue, (+/-)-trans-azetidine-2,4-dicarboxylic acid (t-ADA) and the known mGluR agonist 1S,3R-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) stimulated IP formation in line with the depolarization-modified expression of mGluR1. However, the two compounds caused different patterns of mGluR down-regulation.

Functional evidence for a L-AP3-sensitive metabotropic receptor different from glutamate metabotropic receptor mGluR1.

The efficacy of mGluR agonists quisqualate and 1S,3R-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) in stimulating the inositol phosphate (IP) formation in primary cultures of cerebellar granule neurons correlated with mGluR1 mRNA expression and was affected by the medium KCl content. L-2-Amino-3-phosphonopropionic acid (L-AP3) mimicked the stimulatory action of mGluR agonists. Maximal stimulatory doses of mGluR agonist 1S,3R-ACPD and L-AP3 were additive, suggesting the action of L-AP3 on a receptor different from mGluR1.

Carboxyl domain of glutamate receptor directs its coupling to metabolic pathways.

Of the six metabotropic glutamate receptors (mGluRs) only mGluR1 and mGluR5, which possess a large carboxyl terminal domain, are positively linked to phosphoinositide (PI) hydrolysis. We expressed a 3' deletion of mGluR1 alpha (mGluR1T) lacking the terminal 290 codons and the full length mGluR1 alpha cDNAs in human embryonic kidney 293 cells. Agonist stimulation of both mGluR1 alpha and mGluR1T stimulated PI hydrolysis.

A subpopulation of cerebellar granule neurons in culture expresses a functional mGluR1 metabotropic glutamate receptor: effect of depolarizing growing conditions.

Homogeneous neuronal cultures of cerebellar granule neurons express different levels of metabotropic glutamate receptor mGluR1 mRNA depending on the concentration of KCl present during the culture period. We have studied the effect of KCl on mGluR1 expression at the single neuron level by measuring: i) the effect of mGluR agonist 1S,3R-aminocyclopentane-1,3-dicarboxylic acid, tACPD, on intracellular free calcium concentration, [Ca2+]i; ii) the immunocytochemical quantitation of mGluR1 alpha protein. tACPD-induced increases in cytoplasmic free Ca2+ were pertussis toxin-sensitive.

Pathological phosphorylation causes neuronal death: effect of okadaic acid in primary culture of cerebellar granule cells.

We have investigated the role of protracted phosphatase inhibition and the consecutive protracted protein phosphorylation on neuronal viability. We found that in primary cultures of cerebellar granule neurons, the protracted (24-h) inhibition of the serine/threonine protein phosphatases 1 and 2A (EC 3.1.

Photochemical stroke and brain-derived neurotrophic factor (BDNF) mRNA expression.

In situ hybridization and Northern blotting were used to study the expression of brain-derived neurotrophic factor (BDNF) mRNA in the rat brain following photochemical stroke. A focal thrombotic lesion of the sensorimotor cortex was produced by intravenously injecting the light-sensitive dye rose bengal and exposing the skull to a controlled beam of light. Four hours after the light exposure the level of BDNF mRNA was increased in the hippocampus and cortex ipsilateral and perifocal to the lesion.

Depolarization- and agonist-regulated expression of neuronal metabotropic glutamate receptor 1 (mGluR1).

In established 8-12-day-old primary cultures of differentiated rat cerebellar granule neurons the level of metabotropic glutamate receptor 1 (mGluR1) mRNA and the sensitivity of cultures to the agonist-stimulated inositol phosphate (IP) formation was reversibly modified by changing the depolarizing properties of the medium, i.e. the medium KCl concentration.

Glutamate neurotoxicity is independent of calpain I inhibition in primary cultures of cerebellar granule cells.

Glutamate-induced neurotoxicity and calpain activity were studied in primary cultures of rat cerebellar granule neurons and glial cells. Calpain activation, as monitored by quantitative immunoblotting of spectrin, required micromolar concentrations of Ca2+ in neuronal homogenates (calpain I) and millimolar Ca2+ concentrations in glial homogenates (calpain II). Glutamate-induced toxicity and calpain activation were observed in neuronal, but not in glial, cultures.

Down-regulation of protein kinase C protects cerebellar granule neurons in primary culture from glutamate-induced neuronal death.

Exposing primary cultures of cerebellar granule neurons to 100 nM phorbol 12-myristate 13-acetate (PMA) for 24 hr decreases the Ca2+/phosphatidylserine/diolein-dependent protein kinase C (PKC; ATP:protein phosphotransferase, EC 2.7.1.

Ganglioside-mediated protection from glutamate-induced neuronal death.

Glutamate, an excitatory amino acid (EAA), plays an important role in neuron to neuron signaling by binding to specific receptors. When, during neuronal firing, quanta of glutamate are released from the nerve terminal, they interact with the receptors for a few milliseconds and, thereafter, glutamate is promptly cleared by appropriate mechanisms. The neurotoxic action of glutamate arises from its capacity to trigger a pathophysiological chain of events when it acts continuously and abusively on its receptors (e.

Glutamate-induced neuronal death in primary cultures of cerebellar granule cells: protection by synthetic derivatives of endogenous sphingolipids.

The delayed neuronal death induced by a brief (15 min) application of glutamate to primary cultures of cerebellar granule cells can be prevented by pretreating the cultures with the natural ganglioside monosialoglycosylceramide (GM1), the semisynthetic GM1 with N-acetyl sphingosine (LIGA4), GM1 with N-dichloroacetyl sphingosine (LIGA20) and d-eritro 1,3-dihydroxy-2-dichloroacetylamide-4-trans-octadecene (PKS3). The semisynthetic lipids LIGA4, LIGA20 and PKS3 are more potent than the parent natural compounds. The rank order of potency for the protection against glutamate-induced neuronal death is: LIGA20 greater than or equal to LIGA4 greater than PKS3 greater than GM1; the corresponding EC50 values are 4.

Delayed increase of Ca2+ influx elicited by glutamate: role in neuronal death.

The mechanism of delayed neurotoxicity, triggered by glutamate, was studied in 7-8-day-old primary cultures of rat cerebellar granule cells. Treatment of cultures for 15 min with 50 microM glutamate in Mg2+ -free medium, followed by removal of the excitoxin, resulted in neuronal death, which started to appear 2-3 hr after the termination of glutamate treatment. The number of dead neurons increased gradually in the next few hours and 80-85% of neurons were found dead 24 hr later.

Phospholipids can influence the interconversion of flat epithelial-like and stellate process-bearing astroglial cells in culture: relationships between molecular structure and biological activity.

Secondary cultures of neonatal rat astroglial cells, maintained in a serum-free, chemically defined medium were treated with several agents known to elevate intracellular cyclic AMP levels in these cells. Earlier studies had shown such drugs to induce a process-bearing (stellate) morphology in the astroglial cells, a response that is antagonized or reversed by the presence of exogenously added gangliosides. As a next step in understanding the basis for such an influence on cell morphologics, we have examined in more detail the molecular specificity of this response.

Gangliosides prevent glutamate and kainate neurotoxicity in primary neuronal cultures of neonatal rat cerebellum and cortex.

Using a sensitive histofluorescence staining method that allows for a quantitation of neuronal death, we compared the protective effects of gangliosides (a group of naturally occurring glycosphingolipids), phencyclidine (PCP), and MK-801 (dibenzocyclohepteneimine) on glutamate- and kainate-induced neuronal death in primary cultures of cortical and cerebellar neurons prepared from neonatal rats. PCP and MK-801 block neurotoxicity induced by glutamate doses 50 times higher than the LD50 (LD50 in Mg2+-free medium, 10 microM) but only partially block the kainate neurotoxicity (LD50 in presence of Mg2+, 100 microM). In contrast, pretreatment with gangliosides (GT1b greater than GD1b greater than GM1) results in complete and insurmountable protection against the neurotoxicity elicited by glutamate or kainate.

Inhibition of DNA synthesis in C6 glioma cells following cellular incorporation of GM1 ganglioside and choleragenoid exposure.

The B subunit of cholera toxin, which is multivalent and binds specifically to GM1 ganglioside on the cell surface, has previously been used as a ganglioside-specific probe to regulate DNA synthesis in thymocytes and fibroblasts. To explore in more detail this growth-regulatory action of gangliosides, C6 glioma cells (which are GM1 ganglioside deficient) were used as a model system. When cultures of C6 cells were first treated with GM1, followed by exposure to the B subunit, proliferation was inhibited, as measured by 3H-labeled thymidine incorporation into DNA.

Development and survival of neurons in dissociated fetal mesencephalic serum-free cell cultures: I. Effects of cell density and of an adult mammalian striatal-derived neuronotrophic factor (SDNF).

The use of CNS cultures for detection and quantification of neuronotrophic activity in the CNS has been analyzed. In particular the development, i.e.

A role for gangliosides in astroglial cell differentiation in vitro.

Rat cerebral astroglial cells in culture display specific morphological and biochemical behaviors in response to exogenously added gangliosides. To examine a potential function for endogenous gangliosides in the processes of astroglial cell differentiation, we have used the B subunit of cholera toxin as a ganglioside-specific probe. The B subunit, which is multivalent and binds specifically to GM1 ganglioside on the cell surface, induced a classical star-shaped (stellate) morphology in the astroglial cells and inhibited DNA synthesis in a dose-dependent manner.

Pathways for Ca2+ efflux in heart and liver mitochondria.

1. Two processes of Ruthenium Red-insensitive Ca2+ efflux exist in liver and in heart mitochondria: one Na+-independent, and another Na+-dependent. The processes attain maximal rates of 1.

Intrinsic uncoupling of mitochondrial proton pumps. 1. Non-ohmic conductance cannot account for the nonlinear dependence of static head respiration on delta microH.

The passive membrane conductance LH1 of rat liver mitochondria has been measured and compared with the quantity nJesh/delta microHsh (n = H+/e stoichiometry; Jesh = rate of electron transfer in static head) over a delta microH range. The two curves approach each other only in the lower part of the range, while they sharply diverge at large values of delta microH. Thus nJesh/delta microHsh cannot be considered to be a measure of LH1 in the upper delta microH region.

Tissue-specific modulation of the mitochondrial calcium uniporter by magnesium ions.

This paper analyzes the kinetics of the Ca2+ uniporter of mitochondria from rat heart, kidney and liver operating in a range of Ca2+ concentrations near the steady-state value (1-4 microM). Heart mitochondria exhibit the lowest activity, and physiological Mg2+ concentrations inhibit the mitochondrial Ca2+ uniporter by approx. 50% in heart and kidney, and by 20% in liver.