Optimization and pharmacological validation of a set-shifting procedure for assessing executive function in rats

BACKGROUND

Set-shifting tests represent a reliable paradigm to assess executive functions in humans and animals. In the rat, set-shifting in a cross-maze is a recognized method. In this test, rats must learn an egocentric rule to locate food reinforcement. Once acquired, a second rule, based on visual-cue strategy, allows the location of the food. Ability of rats to shift from the first to the second rule is considered to reflect cognitive flexibility.

NEW METHOD

This study aimed at optimizing the most currently used set-shifting protocol in a cross-maze for standardized drug testing by modulating the parameters related to caloric restriction, reward preference, and by redefining the notion of turn bias and classification of errors sub-types, i.e. perseverative vs. regressive. The new protocol has then been used to assess rats treated by sub-chronic phencyclidine administration and investigate the potential reversal effect of tolcapone, a brain penetrant catechol-O-methyl transferase inhibitor.

RESULTS

The new procedure resulted in a decreased total duration and a re-definition of turn bias and error subtypes. Despite preferences for sweet rewards, caloric restriction had to be maintained to motivate animals. Overall, sub-chronic PCP-treated rats made mostly perseverative errors compared to controls and required more trials to shift between the two rules. Tolcapone partly reversed impairments observed in PCP-treated rats.

CONCLUSION

The new protocol has improved the reliability of key parameters and has contributed to the decrease of the test duration. PCP-treated rats submitted to this protocol have been shown to have significant deficits that could be reversed by tolcapone.

[Vascularization of the head and neck during development]

One of the earliest priorities of the embryonic vascular system is to ensure the metabolic needs of the head. This review covers some of the principles that govern the cellular assembly and localization of blood vessels in the head. In order to understand the development and organization of the cephalic vascular tree, one needs to recall the morphogenetic movements underlying vertebrate head formation and giving rise to the constituent cells of the vascular system. Some of the major signaling molecules involved in vascular development are discussed, including the angiopoietins, the endothelins, the FGFs, the Notch receptors, the PDGFs, Sonic hedgehog, the TGF family and the VEGFs, in order to underline similarities between embryonic and postnatal vascular development, even in the context of increasingly divergent form.

Axolemmal repair requires proteins that mediate synaptic vesicle fusion

A damaged cell membrane is repaired by a seal that restricts entry or exit of molecules and ions to that of the level passing through an undamaged membrane. Seal formation requires elevation of intracellular Ca(2+) and, very likely, protein-mediated fusion of membranes. Ca(2+) also regulates the interaction between synaptotagmin (Syt) and syntaxin (Syx), which is thought to mediate fusion of synaptic vesicles with the axolemma, allowing transmitter release at synapses. To determine whether synaptic proteins have a role in sealing axolemmal damage, we injected squid and crayfish giant axons with an antibody that inhibits squid Syt from binding Ca(2+), or with another antibody that inhibits the Ca(2+)-dependent interaction of squid Syx with the Ca(2+)-binding domain of Syt. Axons injected with antibody to Syt did not seal, as assessed at axonal cut ends by the exclusion of extracellular hydrophilic fluorescent dye using confocal microscopy, and by the decay of extracellular injury current compared to levels measured in uninjured axons using a vibrating probe technique. In contrast, axons injected with either denatured antibody to Syt or preimmune IgG did seal. Similarly, axons injected with antibody to Syx did not seal, but did seal when injected with either denatured antibody to Syx or preimmune IgG. These results indicate an essential involvement of Syt and Syx in the repair (sealing) of severed axons. We suggest that vesicles, which accumulate and interact at the injury site, re-establish axolemmal continuity by Ca(2+)-induced fusions mediated by proteins such as those involved in neurotransmitter release.

Biological evaluation of RGD peptidomimetics, designed for the covalent derivatization of cell culture substrata, as potential promotors of cellular adhesion

Our aim was to replace the proteins and peptides, generally used for the biocompatibilization of polymer substrata, with synthetic molecules mimicking the RGD (Arg-Gly-Asp) active sequence. Based on the (L)-tyrosine template, RGD peptidomimetics were constructed; one molecule 3 was equipped with an anchorage arm that allowed its covalent grafting on a culture substratum made from poly(ethylene terephthalate) (PET) microporous membrane. The amount of fixed molecules was readily determined by XPS, using a fluorine tag incorporated in the peptidomimetic structure. The binding of peptidomimetics 1-3 to the vitronectin (VN) and fibronectin (FN) receptors could not be revealed in a test of inhibition of MSC 80 cells adhesion, by the synthetic compounds in solution placed in competition with the adhesive proteins (VN and FN) coating polystyrene plates. However, the cell-attachment activity of peptidomimetic 3 was shown by culturing CaCo2 cells, in the absence of serum, on the PET substratum grafted with 3. The performance of this support was similar to that of PET grafted with the reference peptide RGDS (Arg-Gly-Asp-Ser), and only reduced by half comparatively to the PET grafted with FN.

Fibronectin-pluronic coadsorption on a polystyrene surface with increasing hydrophobicity: relationship to cell adhesion

Recently, patterned polystyrene surfaces containing hydrophobic (PS) and more hydrophilic (PSox) areas have been shown to be capable of directing cellular growth, which is mainly due to the competitive adsorption of adhesive and antiadhesive molecules. In this article, the competitive adsorption between a pluronic surfactant and fibronectin was studied on homogeneous PS or PSox substrates conditioned with mixtures containing increasing concentrations of one of the two molecules. Radiolabeling and X-ray photoelectron spectroscopy techniques showed that fibronectin adsorption increased on both surfaces if the fibronectin concentrations increased in the conditioning mixture. In contrast, fibronectin adsorption decreased on PSox and did not occur on PS surfaces when pluronic concentrations increased in the coating mixture. A comparison of these data with pheochromocytoma and Schwann cells cultured on patterned surfaces showed that the direction of cell growth on PSox areas depended first on the relative concentrations of the two components in the mixtures, and second, on their ratio; the best concentration ratio probably depends on the cell's ability to recondition its support.

Expression of integrins by murine MSC80 Schwann cell line: relationship to cell adhesion and migration

Schwann cells (Sc) are one of the most important factors promoting regeneration of both the peripheral and the central nervous system. They provide a permissive environment for neurite outgrowth and the making of this environment requires interactions between Sc and extracellular matrix proteins that are mediated via integrin receptors. This study characterized, by immunoprecipitation, the integrins expressed by the mouse MSC80 Sc line. Our results showed that MSC80 Sc expressed alpha1beta1, alpha5beta1 and alpha6beta1 integrins as well as the alpha v-subunit associated with an unidentified 80-90 kDa beta-subunit. Adhesion and migration assays revealed a hierarchy of protein influences that are dependent upon the type of cellular behaviour. Integrin expression correlated with MSC80 Sc line adhesion and migration on extracellular matrix proteins. The MSC80 Sc line expressed a pattern of integrins which allowed adherence on vitronectin and collagen IV, and faster migration on merosin and laminin. As the integrin pattern and the behaviour of MSC80 on ECM were similar to primary Sc, MSC80 are a potential abundant source of Sc for further in vitro and in vivo experiments.

Orientation of cell adhesion and growth on patterned heterogeneous polystyrene surface

Studies of neurite outgrowth or cell migration, two important processes in neuronal networks formation, are facilitated by cell culture models capable of orientating cellular growth and of designing a well-defined cellular pattern. Heterogeneous polystyrene surfaces composed of oxygen plasma-treated stripes (PSox) with a low hydrophobicity separated by non-treated areas (PS) have these properties. In this study, to guide cell growth, we developed a cell culture model using these supports and we identified the molecular factors involved in cellular orientation. When the heterogeneous supports were not coated, proteins from a serum culture medium were required for cells to line up on PSox. On the other hand, cell orientation on coated surfaces was clearly influenced by competitive adsorption of adhesive proteins such as fibronectin or collagen and anti-adhesive molecules as pluronic F68 or albumin. Attachment factors were adsorbed on PSox stripes while adsorption of anti-adhesive molecules on the most hydrophobic PS areas prevented cell adhesion or growth. Thus, we describe the preparation of a cell culture substrate that succeeded in orientating cell growth and that led to a line of cells on adhesive PSox stripes ranging from 2 to 100 microns width.

Adhesion of mammalian cells to polymer surfaces: from physical chemistry of surfaces to selective adhesion on defined patterns

The study of the adsorption of type I collagen from a solution containing Pluronic F68 has shown that the latter prevents collagen adsorption on polystyrene and does not prevent it on surface-oxidized polystyrene. This explains the control of mammalian cell adhesion by substrate surface hydrophobicity and composition of pre-conditioning solution. On that basis, selective adhesion of different types of mammalian cells (PC12 pheochromocytoma, MSC80 schwannoma, Hep G2 hepatoblastoma, rat hepatocytes) on patterned surfaces was achieved. Therefore tracks (width in the range of a few tens of microm) of reduced hydrophobicity were produced on polystyrene by photolithography and oxygen plasma treatment. After conditioning by a solution containing both Pluronic F68 and extracellular matrix protein (collagen, fibronectin), the latter adsorbed selectively on these paths thus allowing selective adhesion of the cells.

Fibronectin adsorption, conformation, and orientation on polystyrene substrates studied by radiolabeling, XPS, and ToF SIMS

Protein adsorption is widely studied by a variety of techniques, but there still is little known about protein orientation and conformation after adsorption. This probably is due to the large number of parameters involved, such as the characteristics of the surface and the structure of the protein. In this study, the adsorption of fibronectin was investigated with three different techniques: radiolabeling, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF SIMS) on polystyrene and oxidized polystyrene. The first two techniques have been widely used to study protein adsorption, allowing us to determine the amount of protein adsorbed on each surface. The ToF SIMS, however, is a technique just emerging for the study of protein adsorption. This study confirms its utility since ToF SIMS is found to be sensitive to the protein orientation and/or conformation at the surface. Indeed, the ToF SIMS peaks characteristic of the protein show differences in their reduced intensity between the two substrates. These differences, which are not detected by XPS, are attributed to different orientations and/or conformations of the protein.

A new plasma-based method to promote cell adhesion on micrometric tracks on polystyrene substrates

A new procedure has been developed in order to obtain heterogeneous polymer surfaces for the promotion of cell adhesion. For this purpose, a microelectronic photosensitive resin was spin coated on polystyrene (PS) substrates. The resin was then submitted to UV light irradiation through a mask and partially developed. The sample was further submitted to a plasma oxygen discharge prior to dissolution of the remaining resin. The characterization by time of flight secondary ion mass spectrometry (ToF SIMS), X-ray photoelectron spectroscopy (XPS), and dynamic contact angle (DCA) allowed us to conclude that hydrophilic paths were created on the more hydrophobic PS substrate together with the complete removal of the resin. In order to optimize cell adhesion contrast, the modified surfaces were then conditioned with a solution containing both a surfactant (pluronic F68) and a protein. Two different proteins were tested (collagen I and fibronectin). PC12 cell cultures on those conditioned surfaces showed that cell adhesion occurs only on the hydrophilic tracks. ToF SIMS spectra and images recorded on those substrates revealed the presence of the proteins only in the hydrophilic tracks. In the same time, the surfactant is suspected to adsorb mainly on the hydrophobic areas of the samples.