A simple method for organotypic cultures of nervous tissue

Hippocampal slices prepared from 2-23-day-old neonates were maintained in culture at the interface between air and a culture medium. They were placed on a sterile, transparent and porous membrane and kept in petri dishes in an incubator. No plasma clot or roller drum were used. This method yields thin slices which remain 1-4 cell layers thick and are characterized by a well preserved organotypic organization. Pyramidal neurons labelled by extra- and intracellular application of horse radish peroxidase resemble by the organization and complexity of their dendritic processes those observed in situ at a comparable developmental stage. Excitatory and inhibitory synaptic potentials can easily be analysed using extra- or intracellular recording techniques. After a few days in culture, long-term potentiation of synaptic responses can reproducibly be induced. Evidence for a sprouting response during the first days in culture or following sections is illustrated. This technique may represent an interesting alternative to roller tube cultures for studies of the developmental changes occurring during the first days or weeks in culture.

Regulatory phosphorylation of AMPA-type glutamate receptors by CaM-KII during long-term potentiation

Long-term potentiation (LTP), a cellular model of learning and memory, requires calcium-dependent protein kinases. Induction of LTP increased the phosphorus-32 labeling of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPA-Rs), which mediate rapid excitatory synaptic transmission. This AMPA-R phosphorylation appeared to be catalyzed by Ca2+- and calmodulin-dependent protein kinase II (CaM-KII): (i) it correlated with the activation and autophosphorylation of CaM-KII, (ii) it was blocked by the CaM-KII inhibitor KN-62, and (iii) its phosphorus-32 peptide map was the same as that of GluR1 coexpressed with activated CaM-KII in HEK-293 cells. This covalent modulation of AMPA-Rs in LTP provides a postsynaptic molecular mechanism for synaptic plasticity.

LTP promotes formation of multiple spine synapses between a single axon terminal and a dendrite

Structural remodelling of synapses and formation of new synaptic contacts has been postulated as a possible mechanism underlying the late phase of long-term potentiation (LTP), a form of plasticity which is involved in learning and memory. Here we use electron microscopy to analyse the morphology of synapses activated by high-frequency stimulation and identified by accumulated calcium in dendritic spines. LTP induction resulted in a sequence of morphological changes consisting of a transient remodelling of the postsynaptic membrane followed by a marked increase in the proportion of axon terminals contacting two or more dendritic spines. Three-dimensional reconstruction revealed that these spines arose from the same dendrite. As pharmacological blockade of LTP prevented these morphological changes, we conclude that LTP is associated with the formation of new, mature and probably functional synapses contacting the same presynaptic terminal and thereby duplicating activated synapses.

Synaptic plasticity and dynamic modulation of the postsynaptic membrane

The biochemical composition of the postsynaptic membrane and the structure of dendritic spines may be rapidly modulated by synaptic activity. Here we review these findings, discuss their implications for long-term potentiation (LTP) and long-term depression (LTD) and propose a model of sequentially occurring expression mechanisms.

PSA-NCAM is required for activity-induced synaptic plasticity

Hippocampal organotypic slice cultures maintained 10-20 days in vitro express a high level of the polysialylated embryonic form of neural cell adhesion molecule (NCAM) (PSA-NCAM). Treatment of the cultures with endoneuraminidase-N selectively removed polysialic acid (PSA) from NCAM and completely prevented induction of long-term potentiation (LTP) and long-term depression (LTD) without affecting cellular or synaptic parameters. Similarly, slices prepared from transgenic mice lacking the NCAM gene exhibited a decaying LTP. No inhibition of N-methyl-D-aspartic acid receptor-dependent synaptic responses was detected. Washout of the enzyme resulted in reexpression of PSA immunoreactivity which correlated with a complete recovery of LTP and LTD. This reexpression was blocked by TTX and low calcium and enhanced by bicuculline. Taken together, these results indicate that neuronal activity regulates the expression of PSA-NCAM at the synapse and that this expression is required for the induction of synaptic plasticity.

Hippocampal long-term potentiation and neural cell adhesion molecules L1 and NCAM

Synaptic membranes express cell adhesion molecules. Here we investigate the role of the neural cell adhesion molecules L1 and NCAM in hippocampal long-term potentiation (LTP), a sustained-use-dependent increase in synaptic efficacy that has been implicated in learning and memory. L1 and NCAM mediate cell interactions during neural development and are strongly expressed in the hippocampus. They cooperate to strengthen L1-dependent cell adhesion and are coupled to second messenger pathways. We show that LTP in CA1 neurons of rat hippocampal slices was reduced by application of various L1 and NCAM antibodies, recombinant L1 fragments, and upon dissociation of the L1/NCAM complex through oligomannosidic carbohydrates and NCAM peptides. Neither the activation of NMDA (N-methyl-D-aspartate) receptors nor the maintenance of LTP was affected. These results suggest that L1 and NCAM modulate the development or the stabilization of LTP.

Contributions of quisqualate and NMDA receptors to the induction and expression of LTP

The contributions of two subclasses of excitatory amino acid transmitter receptors to the induction and expression of long-term potentiation (LTP) were analyzed in hippocampal slices. The quisqualate/kainate receptor antagonist DNQX (6,7-dinitro-quinoxaline-2,3-dione) blocked 85% of the evoked field potential, leaving a small response that was sensitive to D-AP5 (D-2-amino-5-phosphonopentanoate), an N-methyl-D-aspartate (NMDA) receptor blocker. This residual D-AP5-sensitive response was of comparable size in control and previously potentiated inputs. High-frequency stimulation in the presence of DNQX did not result in the development of robust LTP. Washout of the drug, however, revealed the potentiation effect. Thus NMDA-mediated responses can induce, but are not greatly affected by, LTP; non-NMDA receptors, conversely, mediate responses that are not needed to elicit LTP but that are required for its expression.

Successful ex vivo gene therapy directed to liver in a patient with familial hypercholesterolaemia

An ex vivo approach to gene therapy for familial hypercholesterolaemia (FH) has been developed in which the recipient is transplanted with autologous hepatocytes that are genetically corrected with recombinant retroviruses carrying the LDL receptor. We describe the treatment of a 29 year old woman with homozygous FH by ex vivo gene therapy directed to liver. She tolerated the procedures well and in situ hybridization of liver tissue four months after therapy revealed evidence for engraftment of transgene expressing cells. The patient's LDL/HDL ratio declined from 10-13 before gene therapy to 5-8 following gene therapy, improvements which have remained stable for the duration of the treatment (18 months). This represents the first report of human gene therapy in which stable correction of a therapeutic endpoint has been achieved.

The collagenase gene family in humans consists of at least four members

Stromelysin is a collagenase-related connective-tissue-degrading metalloproteinase. We have detected RNAs capable of hybridizing to a rat stromelysin cDNA in 11 of 69 human tumours tested. Molecular cloning of cDNAs to these RNAs has identified them as a mixture of stromelysin RNA and a transcript of a hitherto-undescribed related human gene, the stromelysin-2 gene. We have also isolated cDNAs corresponding to a more distantly related new human gene, the pump-1 gene. A comparison of the cDNA-derived amino acid sequences of stromelysin-2 and pump-1 with the known sequences of stromelysin and collagenase reveals significant similarities, with conservation of sequence motifs believed to have functional importance in metalloproteinase action. We conclude that the collagenase gene family in humans consists of at least four members, and speculate that expression of these genes plays a role in cancer.

Enhanced hippocampal long-term potentiation and learning by increased neuronal expression of tissue-type plasminogen activator in transgenic mice

Adult cortical neurons can produce tissue-type plasminogen activator (tPA), an extracellular protease that plays a critical role in fibrinolysis and tissue remodelling processes. There is growing evidence that extracellular proteolysis may be involved in synaptic plasticity, axonal remodelling and neurotoxicity in the adult central nervous system. Here we show that transgenic mice overexpressing tPA in post-natal neurons have increased and prolonged hippocampal long-term potentiation (LTP), and improved performance in spatial orientation learning tasks. Extracellular proteolysis catalysed by tPA may facilitate synaptic micro-remodelling, and thereby play a role in activity-dependent neuronal plasticity and learning.

Induction of long-term potentiation is associated with major ultrastructural changes of activated synapses

Long-term potentiation (LTP), an increase in synaptic efficacy believed to underlie learning and memory mechanisms, has been proposed to involve structural modifications of synapses. Precise identification of the morphological changes associated with LTP has however been hindered by the difficulty in distinguishing potentiated or activated from nonstimulated synapses. Here we used a cytochemical method that allowed detection in CA1 hippocampus at the electron microscopy level of a stimulation-specific, D-AP5-sensitive accumulation of calcium in postsynaptic spines and presynaptic terminals following application of high-frequency trains. Morphometric analyses carried out 30-40 min after LTP induction revealed dramatic ultrastructural differences between labeled and nonlabeled synapses. The majority of labeled synapses (60%) exhibited perforated postsynaptic densities, whereas this proportion was only 20% in nonlabeled synaptic contacts. Labeled synaptic profiles were also characterized by a larger apposition zone between pre- and postsynaptic structures, longer postsynaptic densities, and enlarged spine profiles. These results add strong support to the idea that ultrastructural modifications and specifically an increase in perforated synapses are associated with LTP induction in field CA1 of hippocampus and they suggest that a majority of activated contacts may exhibit such changes.

Increased phosphorylation of Ca2+/calmodulin-dependent protein kinase II and its endogenous substrates in the induction of long-term potentiation

Induction of long-term potentiation in the CA1 region of hippocampal slices is associated with increased activity of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) (Fukunaga, K., Stoppini, L., Miyamoto, E., and Muller, D. (1993) J. Biol. Chem. 268, 7863-7867). Here we report that application of high but not low frequency stimulation to two groups of afferents in the CA1 region of 32P-labeled slices resulted in the phosphorylation of two major substrates of this enzyme, synapsin I and microtubule-associated protein 2, as well as in the autophosphorylation of CaM kinase II. Furthermore, immunoblotting analysis revealed that long term potentiation induction was associated with an increase in the amount of CaM kinase II in the same region. All these changes were prevented when high frequency stimulation was applied in the presence of the N-methyl-D-aspartate receptor antagonist, D-2-amino-5-phosphonopentanoate. These results indicate that activation of CaM kinase II is involved in the induction of synaptic potentiation in both the postsynaptic and presynaptic regions.

Brain-derived neurotrophic factor restores long-term potentiation in polysialic acid-neural cell adhesion molecule-deficient hippocampus

The neural cell adhesion molecule (NCAM) and its polysialylated form (PSA-NCAM) contribute to long-term potentiation (LTP) in the CA1 hippocampus. Here we report that the deficient LTP found in slices prepared from NCAM knockout mice and in organotypic slice cultures treated with Endo-N, an enzyme that cleaves the PSA moiety of NCAM, can be rescued by brain-derived neurotrophic factor (BDNF). This effect is not reproduced by nerve growth factor, but can be obtained with high concentrations of NT4/5. The effect of BDNF cannot be accounted for by modifications of N-methyl-D-aspartate receptor-dependent responses or of high-frequency bursts. PSA-NCAM, however, could directly interact with BDNF. Exogenous application of PSA residues or recombinant PSA-NCAM also prevents LTP. Furthermore trkB phosphorylation, and thus BDNF signaling, is reduced in both NCAM knockout mice and Endo-N-treated slice cultures. These results suggest that one action of PSA-NCAM could be to sensitize pyramidal neurons to BDNF, thereby modulating activity-dependent synaptic plasticity.

Time course of synaptic development in hippocampal organotypic cultures

Using electrophysiological recordings of field potentials, we investigated the time course of synapse formation and maturation in organotypic cultures prepared from neonate animals of different ages. Following explanation, the size of the maximal synaptic responses elicited in area CA1 by stimulation of a small group of CA3 neurons increased progressively during the first three weeks in culture in a way that corresponded to the changes observed in synaptic contact density. Growth of synaptic responses was found to occur much more rapidly in cultures prepared from 8-day-old as compared with 2-day-old rats. Development of synaptic connections between CA3 and CA1 neurones was also faster than between granule cells and CA3 neurones. Acquisition of mature synaptic properties occurred in vitro as indicated by changes in degree of paired-pulse facilitation and the onset of long-term potentiation (LTP) after a few days in culture. The onset of LTP was much faster in cultures prepared from 8-day-old as compared with 2-day-old neonates and corresponded approximately to the 12-14th postnatal day. It is concluded that development proceeds in the cultures with a time course that resembles the in situ situation.

Expression of collagenase-related metalloproteinase genes in human lung or head and neck tumours

We address the question as to whether increased metalloproteinase production might be related to the high regional recurrence rate of some carcinomas, and particularly head and neck squamous-cell carcinomas (SCC). Northern blot of total RNA prepared from 26 lung carcinomas, 107 head and neck carcinoma samples and corresponding normal tissue samples demonstrates the frequent and sometimes concomitant over-expression of the 2 stromelysin genes, the type-I collagenase gene and the pump-I gene in the head and neck tumour tissue samples. In these SCC, over-expression of the 2 stromelysin genes and the type-I collagenase gene (but not the pump-I gene) is associated with a high degree of tumour differentiation. Moreover, a tumour with high levels of the stromelysin mRNAs is more likely to show high local invasiveness, suggesting that the stromelysins may be implicated in the clinical course of head and neck tumours. Evaluation of the corresponding mRNA levels may prove a useful indicator for predicting the clinical aggressiveness of these tumours.

PSA-NCAM modulates BDNF-dependent survival and differentiation of cortical neurons

We show that the loss or inactivation of the polysialic acid (PSA) tail of neural cell adhesion molecule (NCAM) on rat cortical neurons in culture leads to reduced differentiation and survival. The mechanism by which this negative effect is mediated appears to involve the neuronal response to brain-derived neurotrophic factor (BDNF): (i) in the absence of PSA or in the presence of excess free PSA added to the culture medium, BDNF-induced cell signalling is reduced; (ii) the addition of exogenous BDNF to the medium reverses the effect of PSA loss or inactivation. These data suggest that PSA-NCAM, previously shown to modulate cell migration and plasticity, is needed for an adequate sensitivity of neurons to BDNF.

Glyceraldehyde-3-phosphate dehydrogenase, the putative target of the antiapoptotic compounds CGP 3466 and R-(-)-deprenyl

R-(-)-Deprenyl (Selegiline) represents one of the drugs currently used for the treatment of Parkinson's disease. This compound was shown to protect neurons or glias from programmed cell death in a variety of models. The mechanism of action of neuroprotection as well as inhibition of apoptosis remains elusive. CGP 3466 is a structurally related analog of R-(-)-deprenyl that exhibits virtually no monoamine oxidase type B inhibiting activity but is neuroprotective in the picomolar concentration range. We showed specific binding of CGP 3466 to glyceraldehyde-3-phosphate dehydrogenase by affinity binding, by affinity labeling, and by means of BIAcore(R) technology. Apoptosis assays based on the human neuroblastoma cell line PAJU established the importance of this interaction for mediating drug-induced inhibition of programmed cell death.

Long-term potentiation differentially affects two components of synaptic responses in hippocampus

We have used low magnesium concentrations and the specific antagonist D-2-amino-5-phosphonopentanoate (D-AP5) to estimate the effects of long-term potentiation (LTP) on the N-methyl-D-aspartate (NMDA) and non-NMDA receptor-mediated components of postsynaptic responses. LTP induction resulted in a considerably larger potentiation of non-NMDA as opposed to NMDA receptor-related currents. Increasing the size of postsynaptic potentials with greater stimulation currents or with paired-pulse facilitation produced opposite effects; i.e., those aspects of the response dependent on NMDA receptors increased to a greater degree than did those components mediated by non-NMDA receptors. These results pose new constraints on hypotheses about the locus and nature of LTP and strongly suggest that postsynaptic modifications are part of the effect.

LCMV-specific, class II-restricted cytotoxic T cells in beta 2-microglobulin-deficient mice

Intracranial infection of normal mice with lymphocytic choriomeningitis virus (LCMV) causes meningitis and death mediated by CD8+ major histocompatibility complex (MHC) class I-restricted cytotoxic T lymphocytes (CTLs). beta 2-Microglobulin-deficient mice (beta 2M-/-) do not express functional MHC class I proteins and do not produce significant numbers of CD8+ T cells. When beta 2M-/- mice were infected with LCMV, many died from LCMV disease and produced a specific response to LCMV mediated by CD4+ CTLs that were class II-restricted. In these mice, CD4+ CTLs may compensate for the lack of CD8+ CTLs.

Plasma selenium level before diagnosis and the risk of prostate cancer development

PURPOSE

Epidemiological studies and a randomized intervention trial suggest that the risk of prostate cancer may be reduced by selenium intake. We investigated whether plasma selenium level before diagnosis correlated with the risk of later developing prostate cancer.

MATERIALS AND METHODS

A case control study was performed on men from the Baltimore Longitudinal Study of Aging registry, including 52 with known prostate cancer and 96 age matched controls with no detectable prostatic disease. Plasma selenium was measured at an average time plus or minus standard deviation of 3.83 +/- 1.85 years before the diagnosis of prostate cancer by graphite furnace atomic absorption spectrophotometry. Adjusted odds ratio and 95% confidence interval were computed with logistic regression.

RESULTS

After correcting for years before diagnosis, body mass index, and smoking and alcohol use history, higher selenium was associated with a lower risk of prostate cancer. Compared with the lowest quartile of selenium (range 8.2 to 10.7 microg./dl.), the odds ratios of the second (10.8 to 11.8), third (11.9 to 13.2) and fourth (13.3 to 18.2) quartiles were 0.15 (95% confidence interval 0.05 to 0.50), 0.21 (0.07 to 0.68) and 0.24 (0.08 to 0.77, respectively, p =0.01). Furthermore, plasma selenium decreased significantly with patient age (p <0.001).

CONCLUSIONS

Low plasma selenium is associated with a 4 to 5-fold increased risk of prostate cancer. These results support the hypothesis that supplemental selenium may reduce the risk of prostate cancer. Because plasma selenium decreases with patient age, supplementation may be particularly beneficial to older men.

Synaptic transmission at nicotinic acetylcholine receptors in rat hippocampal organotypic cultures and slices

1. Whole-cell clamp recordings of the compound synaptic current elicited by afferent stimulation of Schaffer collaterals showed that blockade of the NMDA, AMPA and GABAA receptor-mediated components by 6-nitro-7-sulphamoyl- benzo(f)quinoxaline-2,3-dione (NBQX), 3-((R)-2-carboxypiperazine-4-yl)propyl-1-phosphonate (R-CPP) and picrotoxin, respectively, left a small residual current in 39 out of 41 CA1 pyramidal neurones in organotypic cultures and 9 out of 16 CA1 cells in acutely prepared slices. 2. This current represented 2. 9 +/- 0.4 % of the compound evoked synaptic response in organoypic cultures and 1.4 +/- 0.5 % in slices. It was characterized by a slightly rectifying I-V curve and a reversal potential of 3.4 +/- 5. 1 mV. 3. This residual current was insensitive to blockers of GABAB, purinergic, muscarinic and 5-HT3 receptors, but it was essentially blocked by the nicotinic receptor antagonist d-tubocurarine (91 +/- 4 % blockade; 20 microM), and partly blocked by alpha-bungarotoxin (200 nM) and methyllycaconitine (10 nM), two antagonists with a higher selectivity for alpha7 subunit-containing nicotinic receptors (48 +/- 3 % and 55 +/- 11 % blockade, respectively). 4. The residual current was of synaptic origin, since it occurred after a small delay; its amplitude depended upon the stimulation intensity and it was calcium dependent and blocked by the sodium channel antagonist tetrodotoxin. 5. We conclude that afferent stimulation applied in the stratum radiatum evokes in some hippocampal neurones a small synaptic current mediated by activation of neuronal nicotinic receptors.

Structural modifications associated with synaptic development in area CA1 of rat hippocampal organotypic cultures

Using morphological techniques, we characterized the developmental reorganization that takes place during the first weeks after explanation in area CA1 of organotypic hippocampal cultures maintained at the interface between medium and a CO2-enriched atmosphere. Pyramidal neurones redistributed from a vertical into an horizontal cell layer in the middle of a three-dimensional culture, with apical dendrites running above the pyramidal layer. Glial cells redistributed into a thin layer at the bottom of the culture, forming an interface between tissue and culture medium. Astrocytes were identified as the most numerous non neuronal cells. No sign of glial proliferation could be observed, except for a transient increase during the first days after explanation. The density of synaptic contacts in the stratum radiatum decreased immediately after explanation and then increased by about 20-fold to reach values in the proximal part of the apical layer after 4 weeks in culture which were only slightly smaller than those measured in 1-month-old rats. The synaptic density in the most distal part of the dendritic layer which receives connections extrinsic to the hippocampus remained significantly lower than in vivo. The ratio of spine to shaft contacts was comparable to that found in vivo. These results indicate that interface type of organotypic cultures can be used as an interesting model for studies of synaptic development in vitro.