Light-Induced Responses of Slow Oscillatory Neurons of the Rat Olivary Pretectal Nucleus

Background: The olivary pretectal nucleus (OPN) is a small midbrain structure responsible for pupil constriction in response to eye illumination. Previous electrophysiological studies have shown that OPN neurons code light intensity levels and therefore are called luminance detectors. Recently, we described an additional population of OPN neurons, characterized by a slow rhythmic pattern of action potentials in light-on conditions. Rhythmic patterns generated by these cells last for a period of approximately 2 minutes. Methodology: To answer whether oscillatory OPN cells are light responsive and whether oscillatory activity depends on retinal afferents, we performed in vivo electrophysiology experiments on urethane anaesthetized Wistar rats. Extracellular recordings were combined with changes in light conditions (light-dark-light transitions), brief light stimulations of the contralateral eye (diverse illuminances) or intraocular injections of tetrodotoxin (TTX). Conclusions: We found that oscillatory neurons were able to fire rhythmically in darkness and were responsive to eye illumination in a manner resembling that of luminance detectors. Their firing rate increased together with the strength of the light stimulation. In addition, during the train of light pulses, we observed two profiles of responses: oscillationpreserving and oscillation-disrupting, which occurred during low- and high-illuminance stimuli presentation respectively. Moreover, we have shown that contralateral retina inactivation eliminated oscillation and significantly reduced the firin

Functional copolymers of maleic anhydride : synthesis and application

This thesis deals with the synthesis, characterization and properties of copolymers containing maleic anhydride and fluorinated building blocks prepared by means of free radical copolymerization. Free radical polymerization in binary or ternary systems usually leads to a blend of polymer chains with different composition as a consequence of different monomer reactivity, hence the most reactive monomers are consumed first, and consequently the polymer is enriched in monomers of lower reactivity. This effect is even stronger, when monomers which cannot undergo homopolymerization are used. The preferred route to overcome this problem is to feed continuously the reaction mixture with monomers at the same rate at which they are consumed. In Chapter 3 copolymerization of maleic anhydride, butyl-methacrylate and 1H,1H,2H,2H-perfluorodecylmethacrylate is described. The kinetics of the copolymerization of F8H2MA/MSA, BMA/MSA, and F8H2MA/BMA have been extensively studied under well-defined reaction conditions: the determined copolymerization parameters were rF8H2MA = 4.9, rMSA = 0, rBMA = 8.2, rMSA = 0, and rF8H2MA = 1.02, rBMA = 0.94. The reaction rates at chosen conditions were between Rp=0.47 wt%/min for a monomer mixture BMA/F8H2MA/MSA = 1.75:0.75:7.5 and Rp=0.73 wt%/min for BMA/F8H2MA/MSA = 1:1:1. The determined reaction rates and the composition of the terpolymers were used to perform successfully continuous addition experiments in order to produce a bigger quantity of homogenous terpolymers. The versatility of the method has been proven by using a different set of monomers namely dodecyl methacrylate (DMA), 1H,1H,2H,2H-per¬fluo¬ro¬de¬cyl¬ meth¬acry¬late (F8H2MA) and maleic anhydride (MSA). The copolymers were characterized in term of molecular weight and thermal properties. Fluorinated terpolymers P[RFMA-co-RHMA-co-MSA] (RH = C4H9-, C12H25-, RF- = C10H4F19-) obtained in continuous addition experiments and containing ca. 20 mol% fluorinated side chains can be dissolved in semi polar solvents like tetrahydrofuran, chloroform or ethyl acetate as well as in fluorinated solvents like HFX and Freon 113 (Chapter 4). On incorporation of dodecyl-side chains (RH = C12H25-) the polymers become also soluble in alkane solvents. Up to 15-20 mol% MSA content is not sufficient to induce water solubility, even in case of carboxylate formation by hydrolysis of the anhydride units. Emulsification of solutions in organic solvents of the terpolymers showed to be unstable; they demix within days. The P[RFMA-co-RHMA-co-MSA] terpolymers were coated on glass from 1 wt% solution in chloroform. The contact angles of water and hexadecane as wetting liquids were measured at 20°C prior and immediately after an annealing step (12h, 120°C) and were found to be equal: 110 ° against water and above 70 ° for hexadecane. This means that during the film formation process the mobility of fluorinated chains is sufficient to ensure proper orientation of the fluorinated side chains already at room temperature. Such behavior is possible because of relatively low Tg of these copolymers. The surface properties of the coatings obtained on aluminum substrates are comparable with coatings on glass both for water and hexadecane. The properties of the coating obtained on paper are different and the measured values for both wetting liquids are lower than for the other two substrates. This phenomenon can be explained by the fact that the terpolymer solution penetrates the paper and consequently does not form a closed film. In summary RH, RF, MSA-terpolymers of moderate fluorine content are versatile, flexible to handle materials that offer wide screen of application for surface modification. To further increase the adhesion properties of these copolymers - especially to metallic surfaces - phosphoric acid groups were incorporated using ethylene glycol methacrylate phosphate (EGMP) as comonomers (Chapter 5). An obstacle in performing continuous addition polymerization experiments was the fact that due to overlapping signals in the 1H NMR spectra the composition of these copolymers could not be unequivocally determined. However, these materials showed good solubility in aqueous ammonia solution and appropriate surface properties due to the presence of fluorinated building blocks. The surface properties of different polymer composition were investigated after coating from water based formulations on glass substrates and annealing above the glass transition temperature. Coatings with hydrophobicity up to 120 ° were obtained. The relatively low thermal stability of phosphorus containing copolymers implies limitations in an application. The aim to create a synthetic, amphiphilic structure with strong antimicrobial properties comparable with natural toxins, led to copolymers of maleic anhydride with vinyl monomers (Chapter 6). Vinyl monomers and maleic anhydride yield alternating copolymers. This ensures a constant 1:1 ratio of the hydrophobic and cationic part similar to those in leucine/lysine (1:1) peptides (LK-peptides). The choice of 4-methyl-1-pentene as hydrophobic comonomer is based on the similarity of the structure with leucine, while the choice of maleic anhydride leaves ample of space for further design of the cationic/hydrophilic part by means of chemical modification. An alternating copolymer of maleic anhydride and 4-methyl-1-pentene was synthesized by means of free radical copolymerization in the presence of benzoyl peroxide (BPO) as initiator. Modification of the P[MP-alt-MSA] copolymer with diamine to poly[(4-methyl-1-pentene)-alt-(1-(3-N,N-dimethylaminopropyl)maleimide)] was performed as a one pot synthesis in relatively mild conditions (DMF at 120 °C). Poly[(4-methyl-1-pentene)-alt-(1-(3-N,N-dimethylaminopropyl)maleimide)] was converted into a polycationic polymer by means of alkyl iodide. The modification with methyl iodide yields a yellow colored powder easily soluble in water and polar solvents like DMF and DMSO but insoluble in lower alcohols and less polar solvents. Sequential quaternization with methyl iodide and dodecyl iodide ensures solubility in a wide variety of polar solvents including alcohols and ketons. Modification with dodecyl iodide only leads to polymers soluble in non-polar solvents. Copolymers with quaternary ammonium groups and long alkyl chains were tested for their antimicrobial properties

Solubility, Emulsification and Surface Properties of Maleic Anhydride, Perfluorooctyl and Alkyl Meth-Acrylate Terpolymers

The solubility of terpolymers containing alkyl, and perfluoroalkyl side chains as well as succinic acid moieties in the main chain, P[RFMA0.2-co-RHMA0.65-co-MAH0.15] (RH = C4H9- or C12H25-, RF- = C10H4F19-) with ca. 20 mol % fluorinated side chains and 10–22 mol % of succinic anhydride rings was tested in a number of solvents varying from water to non polar mineral oils. The polymers are well soluble in fluorinated solvents like Freon-113® and 1,3-bis(trifluoromethyl) benzene, in semi-polar solvents like chloroform, THF or lower esters and also in hydrocarbons with polymers containing dodecyl methacrylate. In self-emulsification experiments, a stable water emulsion of P[F8H2MA0.2-co-BMA0.65-co-MAH0.15] was obtained. The dispersability and emulsification of these polymers in mixtures of organic solvents and water yielded stable emulsions in the presence of additional surfactant. Thin films coated from organic solutions as well as from emulsions on glass resulted in water and oil-repelling surfaces with contact angles up to 140° against water and 71° against hexadecane. An enhancing effect of annealing was not observed

Synthesis, Characterization, and Antimicrobial Properties of Peptides Mimicking Copolymers of Maleic Anhydride and 4-Methyl-1-pentene

Synthetic amphiphilic copolymers with strong antimicrobial properties mimicking natural antimicrobial peptides were obtained via synthesis of an alternating copolymer of maleic anhydride and 4-methyl-1-pentene. The obtained copolymer was modified by grafting with 3-(dimethylamino)-1-propylamine (DMAPA) and imidized in a one-pot synthesis. The obtained copolymer was modified further to yield polycationic copolymers by means of quaternization with methyl iodide and dodecyl iodide, as well as by being sequentially quaternized with both of them. The antimicrobial properties of obtained copolymers were tested against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Staphylococcus aureus. Both tested quaternized copolymers were more active against the Gram-negative E. coli than against the Gram-positive S. aureus. The copolymer modified with both iodides was best when tested against E. coli and, comparing all three copolymers, also exhibited the best effect against S. aureus. Moreover, it shows (limited) selectivity to differentiate between mammalian cells and bacterial cell walls. Comparing the minimum inhibitory concentration (MIC) of Nisin against the Gram-positive bacteria on the molar basis instead on the weight basis, the difference between the effect of Nisin and the copolymer is significantly lower

Synthesis of Terpolymers with Homogeneous Composition by Free Radical Copolymerization of Maleic Anhydride, Perfluorooctyl and Butyl or Dodecyl Methacrylates: Application of the Continuous Flow Monomer Addition Technique

Terpolymers of homogeneous composition were prepared by free radical copolymerization of butyl or dodecyl methacrylate, 1H,1H,2H,2H-perfluorodecyl methacrylate and maleic anhydride using the continuous monomer addition technique. The copolymerization reactions were performed at 65 °C in the presence of azobisisobutyronitrile as an initiator in a mixture of methyl ethyl ketone and 1,3-bis (trifluoromethyl)benzene. The monomers and initiator are added to the reaction mixture with the same rate they are consumed in 5- and 10-fold excess compared to the initial monomer stock. The obtained terpolymers with molecular weights Mn = 50,000–70,000 are of uniform composition, close to the composition determined in low conversion experiments, proving the principle of the chosen concept. The kinetic data necessary for the design of the continuous addition experiment were obtained from binary copolymerization experiments at low monomer conversion (to avoid compositional drift). In addition, the so-called terpolymerization parameter was determined from ternary copolymerization experiments

Solubility, Emulsification and Surface Properties of Maleic Anhydride, Perfluorooctyl and Alkyl Meth-Acrylate Terpolymers

The solubility of terpolymers containing alkyl, and perfluoroalkyl side chains as well as succinic acid moieties in the main chain, P[RFMA0.2-co-RHMA0.65-co-MAH0.15] (RH = C4H9- or C12H25-, RF- = C10H4F19-) with ca. 20 mol % fluorinated side chains and 10–22 mol % of succinic anhydride rings was tested in a number of solvents varying from water to non polar mineral oils. The polymers are well soluble in fluorinated solvents like Freon-113® and 1,3-bis(trifluoromethyl) benzene, in semi-polar solvents like chloroform, THF or lower esters and also in hydrocarbons with polymers containing dodecyl methacrylate. In self-emulsification experiments, a stable water emulsion of P[F8H2MA0.2-co-BMA0.65-co-MAH0.15] was obtained. The dispersability and emulsification of these polymers in mixtures of organic solvents and water yielded stable emulsions in the presence of additional surfactant. Thin films coated from organic solutions as well as from emulsions on glass resulted in water and oil-repelling surfaces with contact angles up to 140° against water and 71° against hexadecane. An enhancing effect of annealing was not observed

Solubility, Emulsification and Surface Properties of Maleic Anhydride, Perfluorooctyl and Alkyl Meth-Acrylate Terpolymers

The solubility of terpolymers containing alkyl, and perfluoroalkyl side chains as well as succinic acid moieties in the main chain, P[RFMA0.2-co-RHMA0.65-co-MAH0.15] (RH = C4H9- or C12H25-, RF- = C10H4F19-) with ca. 20 mol % fluorinated side chains and 10–22 mol % of succinic anhydride rings was tested in a number of solvents varying from water to non polar mineral oils. The polymers are well soluble in fluorinated solvents like Freon-113® and 1,3-bis(trifluoromethyl) benzene, in semi-polar solvents like chloroform, THF or lower esters and also in hydrocarbons with polymers containing dodecyl methacrylate. In self-emulsification experiments, a stable water emulsion of P[F8H2MA0.2-co-BMA0.65-co-MAH0.15] was obtained. The dispersability and emulsification of these polymers in mixtures of organic solvents and water yielded stable emulsions in the presence of additional surfactant. Thin films coated from organic solutions as well as from emulsions on glass resulted in water and oil-repelling surfaces with contact angles up to 140° against water and 71° against hexadecane. An enhancing effect of annealing was not observed