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Biomedical subjects

M Stasiak

Publications and source records attributed to M Stasiak.

At least 19 recordsLinked to original sources
PubMed2006

Plasticization of poly(L-lactide) with poly(propylene glycol).

A new plasticizer for poly(L-lactide) (PLA)-poly(propylene glycol) (PPG) is proposed. The advantage of using PPG is that it does not crystallize, has low glass transition temperature, and is miscible with PLA. PLA was plasticized with PPGs with nominal Mw of 425 and 1000 g/mol. Poly(ethylene glycol) (PEG), long known as a plasticizer for PLA, with nominal Mw of 600 g/mol, was also used to plasticize PLA for comparison. The thermal and tensile properties of PLA and PLA with 5-12.5 wt % of the plasticizers were studied. In blends of PLA with PPGs the glass transition temperature was lower than that of neat PLA. Both PPGs enhanced the crystallizability of PLA albeit less than PEG. All of the plasticizers increased also the ability of PLA to plastic deformation which was reflected in a decrease of yield stress and in an increase of elongation at break. The effect was enhanced by the higher PPG content and also by lower molecular weight of PPG. A phase separation occurred only in the blend containing 12.5 wt % of PPG with higher molecular weight. The evidences of crazing were found in deformed samples of PLA with low plasticizer content, whereas the samples with higher content of plasticizers crystallized due to deformation.

Calorimetry, Differential Scanning↗
PubMed2001

The effect of early specific feeding on food conditioning in cats.

Four cats were fed with beef only (beef cats) and 4 cats were fed with tuna only (tuna cats) during the first 6 months of their lives. Thus, they were deprived of a variety of food tastes. The cats then were trained in instrumental conditioning. After criterion performance was achieved, they were retrained with alternated food: In the beef cats, tuna was used, and in tuna cats, beef was used. There were six stages with alternated food. The beef cats acquired a pushing response markedly slower than the tuna cats because they often refused to eat the beef reward. Moreover, both the beef and the tuna cats preferred tuna in stages with alternated food. In contrast, there was no difference in attractiveness between beef or tuna in another 4 cats nondeprived of a variety of food tastes. Hence, early deprivation of a variety of food tastes may reveal an inborn food preference.

Aging↗
PubMed2000

Food conditioning is impaired in cats deprived of the taste of food in early life.

Cats were fed by stomach tube during the first 75 days of their life. Thus, they were deprived of the taste of food and the food reward. The cats were then trained to find food behind the gate. They acquired this simple response very slowly and during the first weeks of training they often refused to eat the food reward. Moreover, they extinguished the response poorly. We conclude that the deprived cats did not originally perceive the food reward as attractive, but they were able to learn this, and they were poorly able to form both excitatory and inhibitory food conditioned connections.

Animals↗
PubMed1999

C-terminally shortened alamethicin on templates: influence of the linkers on conductances.

In order to test the influence of chemical modifications designed to allow covalent coupling of channel-forming peptide motifs into variable sized oligomers, a series of alamethicin derivatives was prepared. The building block encompassing the N-terminal 1-17 residues of alamethicin behaved normally in the conductance assay on planar lipid bilayers, albeit at higher concentration and with a slightly reduced voltage-dependence. A linker Ac-K-OCH(2)C(6)H(4)CH(3)p attached via the epsilon amino group of lysine to the C-terminus of alamethicin(1-17) increased membrane affinity. The latter was further enhanced in a dimer and a tetramer in which alamethicin(1-17) chains were tethered to di- or tetra-lysine linkers, respectively, but macroscopic current-voltage curves displayed much reduced voltage-dependencies and reversed hysteresis. An usual behaviour with high voltage-dependence was restored with the modified dimer of alamethicin(1-17) in which alanine separated the two consecutive lysine residues in the linker. Of special interest was the development of a 'negative resistance' branch in macroscopic current-voltage curves for low concentrations of this dimer with the more flexible linker. Single channel events displayed only one single open state with fast kinetics and whose conductance matches that of the alamethicin heptamer or octamer.

Alamethicin↗
PubMed1999

Sealed environment chamber for canopy light interception and trace hydrocarbon analyses.

Two sealed chambers were constructed, each measuring approximately 4.5 m x 3 m x 2.5 m (LxWxH). Heat exchangers and air handling components were integrated within the sealed environment. Construction materials were chosen to minimize off-gassing and oxidation. Acceptable materials included stainless steel, Teflon (TM), glass and Heresite (TM) or baked enamel coated metal parts. The glass-topped chambers have externally mounted microwave powered light sources providing minimum PAR at canopy level of 1000 micrometers m-2 s-1. Major gases (CO2, O2) were monitored. Other environmental variables relevant to plant production (humidity, temperature, nutrient solution) were monitored and controlled continuously. Typical environment control capability and system specifications are presented. The facility is described as a venue ideally suited to address specific research objectives in plant canopy light interception, such as the roles of novel microwave powered overhead and inner-canopy light sources for dense plant canopies. In addition, control of recycled hydroponic nutrient solutions and analysis of trace atmospheric hydrocarbons in the context of sealed environment life support can be concurrently monitored.

Air Conditioning↗
PubMed1998

Alpha-hydroxymethylserine as a peptide building block: synthetic and structural aspects.

A synthetic methodology has been developed for peptide bond formation with alpha-hydroxmethylserine as the carboxyl or amino component and also for the preparation of homo-sequences. The key intermediate, O,O-protected alpha-hydroxymethylserine in the form of an isopropylidene derivative, is easily accessible and represents the first example of a heterocyclic C(alpha,alpha)-disubstituted amino acid containing an 1,3-dioxane ring. The use of this intermediate facilitates protection of the sterically hindered amino and carboxyl groups and is advantageous for the coupling and deprotection steps. X-ray structure determination of Z-HmS(Ipr)-Ala-OMe revealed that the two crystallographically independent molecules present in the asymmetric unit adopt an S-shaped conformation. In the one molecule the achiral HmS(Ipr) residue has the torsion angle values (phi = 61.4 degrees, psi, = 40.8 degrees) in the left-handed helical region of the Ramachandran map, while in the second molecule the negative torsion angles (phi = -60.1 degrees, psi = -44.4 degrees) are associated with the right-handed helix.

Chromatography, High Pressure Liquid↗
PubMed1998

Lack of projections from medial geniculate body to suprasylvian cortex in cat: a study with horseradish peroxidase.

Because both electrophysiological and behavioral methods have implicated the suprasylvian cortex of cat in audition, its afferents were studied using retrograde transport of horseradish peroxidase. The bulk-filling method was used to maximize the likelihood that virtually all afferents to the area would be labeled. Despite the vivid retrograde labeling of many thalamic cells with this procedure, no direct auditory projections to the suprasylvian cortex could be found in the thalamus (i.e. in medial geniculate body or in the dorsolateral part of the posterior nucleus). Furthermore, very few cells were labeled in the primary auditory cortex of the nearby ectosylvian gyrus. The source of afferents to the suprasylvian cortex originate mostly from the pulvinar-lateral posterior complex and to a lesser extent from ventral lateral and ventral anterior nuclei of the thalamus.

Animals↗
PubMed1998

[Clinical symptomatology and laboratory diagnosis of 75 cases of ethylene glycol poisonings].

Between 1991 and 1995 there were 75 cases of ethylene glycol poisoning (GE) hospitalised in the Clinic of Acute Poisoning of Institute of Occupational Medicine in Lódź, which comprised 0.9% of the total number of patients. The most common were cases of accidental antifreeze liquids consumption. On admittance to the clinic the state of 59% of the patients was diagnosed as severe and very severe. The main symptoms were: metabolic acidosis, which developed in 77% cases of poisoning, and its consequences--the central nervous damage and the cardiovascular system distributions. The average pH amounted to 7.06 while the base deficit to 22.42 mmol/l. Among complications the most commonly observed was the acute renal failure (84%) which developed during the first 24 hrs in all the 25 cases ending in deaths. Only in 16 out of 63 cases, in which the acute renal failure occurred, multiple hemodialyses proved necessary. Other complications accompanying the poisoning were as follows: anaemia, pneumonia, the irreversible central nervous system damage, the disseminated intravascular coagulation syndrome, and the hepatic damage. The comparative analysis (base on the chi2 and median test) of the deceased and cured patients has shown a significant difference (p < 0.05), among others, concerning the plasma osmolality, the frequency of the acute renal failure and the central nervous system damage occurrence.

Acute Kidney Injury↗
PubMed1998

EEG activity in cat's isolated brainstem.

Midbrain and pons were isolated together by two brainstem transections, at the junctions between midbrain and forebrain on one hand and the medulla and pons on the other hand. Low-voltage, high-frequency and high-voltage, low-frequency EEG activity were present in the isolated brainstem. This is in contrast to previous findings, showing that in the midbrain and pons separately isolated the EEG activity was greatly depressed, although accompanied by brisk single-unit spike activity. Thus, neural connections between pons and midbrain may lead to synchronization of single-unit activity.

Animals↗
PubMed1997

Habituation of ocular following reflex requires corpus callosum for interhemispheric transfer.

In cats, unanesthetized following transection of the brainstem at a level precluding painful sensation, and limiting ocular motility to a vertically oriented course (the pretrigeminal preparation), habituation of the orienting reflex, consisting of ocular fixation and smooth pursuit, readily transferred between moving visual stimuli directed first at one and then the other cerebral hemisphere. Under the same conditions, when the corpus callosum had been transected 2 weeks prior to the habituation, interhemispheric transfer was absent. Thus, despite substantial brainstem involvement and bilateral coordination of ocular motility the neocortex plays an essential role in this habituation, just as it does in the interhemispheric transfer of visual discrimination learning. This suggests that habituation is a fundamental form of learning in the mammalian forebrain.

Animals↗
PubMed1997

Stereodependent inhibition of plasminogen activator inhibitor type 1 by phosphorothioate oligonucleotides: proof of sequence specificity in cell culture and in vivo rat experiments.

Hexadecadeoxyribonucleotides complementary to a fragment of human PAI-1 mRNA located upstream of the start codon and their phosphorothioate analogs were studied in cultured HUVECs as sequence-dependent inhibitors of PAI-1 expression. The activity of the random mixture of diastereomers of phosphorothioate hexadecanucleotide PS-16H has been compared with that of isosequential, stereoregular [All-Sp] and [All-Rp] isomers. The highest inhibitory effect on PAI-1 synthesis was observed with the [All-Sp] diastereomer. Stereorandom phosphorothioate oligonucleotide PS-16R complementary to the same region of rat PAI-1 mRNA, when injected into tail vein of rats, substantially decreased the level of PAI-1 in blood plasma.

Animals↗
PubMed1996

Electrical activity of the acutely isolated pons in cats.

The cat's pons was isolated by two brainstem transections, at the junction of medulla and pons and at the junction of pons and midbrain. In the deafferented pons the EEG activity was virtually absent, whereas the spatial density of active units and the rate of their spontaneous spike activity were at a high level. In the pons of control preparations with brainstem transected only at the ponto-midbrain junction the EEG activity was present, while the single-unit activity was such as in the isolated pons. The electrical activity of the isolated pons was similar to that previously described in the cat's isolated midbrain. The discrepancy between EEG and single-unit activity suggests that in the deafferented pons or midbrain many neurones are asynchronously autoactive. Also, these results show that a flat EEG record is not necessarily a sign of absence of the neural activity and neural death.

Animals↗
PubMed1996

Auditory quality cues are more effective than auditory location cues in a R--no R (go--no go) differentiation: the extension of the rule to primitive mammals (American opossum, Didelphis virginiana).

Discrimination learning of instrumental responses to auditory compound stimuli was investigated in opossums using the R-no R (go-no go) differentiation. Each compound stimulus consisted of two factors: quality and location. Each correct response performed to the conditioned positive, or "safe" stimulus, was rewarded by food and never punished. Each incorrect response performed to the conditioned negative, or "warning" stimulus, was punished by an electric shock. In subsequent testing, each opossum proved to use only the quality cues to solve the task even though later testing showed them capable of using the location cues. Thus, the rule discovered in higher mammals, that the efficacy of auditory stimuli in differentiation depends on the perceptual ability of the animal as well as the type of the behavioral response with which the animal is confronted, may be extended to neurologically primitive mammals and also to a joint conditioned approach-avoidance method.

Acoustic Stimulation↗
PubMed1996

Visual neglect in pretrigeminal cats with lateral suprasylvian lesions.

Eleven cats with brain stem transected at the pretrigeminal level were used. The cortex of the middle suprasylvian sulcus was removed on the left side. The vertical following reflex was evoked by a slit of light (1 degree x 4 degrees) or a black bar (1 degree x 1 degree x 4 degrees) moving along the vertical meridian or parallel to it out to 40 degrees in the left or right hemifield. In all cats the following reflexes to the contralesional hemifield were low or absent. A corresponding suprasylvian lesion was made subsequently on the right side. In 6 cats the reflexes to both hemifields were absent or low. In contrast, surprisingly in 5 cats the reflexes were large, much higher than those evoked previously from the contralateral hemifield after the first lesion. This might be due to a process of disinhibition occurring in the superior colliculi.

Animals↗
PubMed1994

The contralateral impairment of the orienting ocular-following reflex after lesions of the lateral suprasylvian cortex in cats.

The cortex of the middle suprasylvian sulcus was removed unilaterally in cats with brain stem transected at the pretrigeminal level. The vertical following reflex was evoked by a slit of light (1 degree x 4 degrees) moving along the vertical meridian or parallel to it up to 40 degrees in the left or right hemifield. The reflexes from the contralateral hemified were greatly reduced. This contrasts with previous reports with perimetry test where authors made smaller lesions.

Animals↗
PubMed1993

Delayed response learning to auditory stimuli is impaired in cage-reared cats.

Four normal and eight cage-reared cats were used. Four of the cage-reared cats were visually deprived in the first 6 months of life. The cats were trained on a three-choice delayed response task to auditory stimuli. All normal cats mastered a 1-min delay and two cats even a 6-min delay. In contrast, two cage-reared cats failed to cope even with a 5-s delay, four cats with a 15-s delay and the remaining two cats with a 1-min delay. No significant difference was found between the non-deprived and the deprived cage-reared cats. The deficits was analogous to that shown by cage-reared cats during delayed response, visual learning. Thus, cage-rearing strongly impairs delayed responding to at least two different sensory modalities.

Acoustic Stimulation↗