Biomedical subjects

G Sagvolden

Publications and source records attributed to G Sagvolden.

4 recordsLinked to original sources

PubMed1999

Cell adhesion force microscopy.

The adhesion forces of cervical carcinoma cells in tissue culture were measured by using the manipulation force microscope, a novel atomic force microscope. The forces were studied as a function of time and temperature for cells cultured on hydrophilic and hydrophobic polystyrene substrates with preadsorbed proteins. The cells attached faster and stronger at 37 degreesC than at 23 degreesC and better on hydrophilic than on hydrophobic substrates, even though proteins adsorb much better to the hydrophobic substrates. Because cell adhesion serves to control several stages in the cell cycle, we anticipate that the manipulation force microscope can help clarify some cell-adhesion related issues.

Adsorption↗

PubMed1999

Protein adhesion force dynamics and single adhesion events.

Using the manipulation force microscope, a novel atomic force microscope, the adhesion forces of bovine serum albumin, myoglobin, ferritin, and lysozyme proteins to glass and polystyrene substrates were characterized by following the force necessary to displace an adsorbed protein-covered microsphere over several orders of magnitude in time. This force was consistent with a power law with exponent a = 0.37 +/- 0.03 on polystyrene, indicating that there is no typical time scale for adhesion on this substrate. On glass, the rate of adhesion depended strongly on protein charge. Forces corresponding to single protein adhesion events were identified. The typical rupture force of a single lysozyme, ferritin, bovine serum albumin, and myoglobin protein adhering to glass was estimated to be 90 +/- 10 pN, 115 +/- 13 pN, 277 +/- 44 pN, and 277 +/- 44 pN, respectively, using a model of the experimental system. These forces, as well as the force amplitudes on hydrophobic polystyrene, correlate with protein stiffness.

Animals↗

PubMed1993

Frequent reward eliminates differences in activity between hyperkinetic rats and controls.

The spontaneously hypertensive rat (SHR) is a strain that is a potential animal model of attention-deficit hyperactivity disorder (ADHD)/childhood hyperkinesis/disturbance of activity and attention, as SHR exhibit both hyperactivity and attention problems. Altered reinforcement (reward) processes have been suggested as the mechanism for the development of hyperactivity in SHR and ADHD. The purpose of the present study was to analyze basic reinforcement and response processes in the hyperactive SHR and in the progenitor Wistar-Kyoto (WKY) control strain. The results show that differences between the strains emerge in response rates maintained by infrequent reinforcers rather than in asymptotic rates of responding maintained by higher rates of reinforcement. The SHR strain required fewer reinforcers per minute to maintain high rates of responding, but when reinforcer rates were high enough to maintain asymptotic response rates in both strains, the rates were similar. Thus, the increased response rates for hyperactive rats at low reinforcement rates may reflect not only barpresses for water, but possibly also barpresses for other stimuli the animal produces by pressing the lever switch. Extrapolating to hyperactive children (ADHD), the results suggest that ADHD behavior might be made more similar to non-ADHD if reinforcers were scheduled more frequently.

Animals↗

PubMed1992

The spontaneously hypertensive rat (SHR) as an animal model of childhood hyperactivity (ADHD): changed reactivity to reinforcers and to psychomotor stimulants.

Childhood hyperactivity (attention-deficit hyperactivity disorder, ADHD) is a behavior disorder affecting 2-6% of grade-school children. The main symptoms are attention problems and hyperkinesis. The disorder is commonly treated with psychomotor stimulants, usually methylphenidate hydrochloride (ritalin) or d-amphetamine. Neither the cause of the disorder nor the basis of the effectiveness of the drug treatment is well understood. Differences in reinforcement processes have been implicated as part of the underlying problem. The main purpose of the present research was to investigate reinforcement processes and motor characteristics with and without stimulant medication in SHR, as an animal model of ADHD, and WKY controls, its normoactive progenitor strain. SHR behavior turned out to be more sensitive to immediate reinforcement and proportionately less sensitive to delayed reinforcement when compared to the behavior of WKY, as demonstrated by systematic changes in rates of responding throughout fixed-interval schedules of reinforcement of bar-presses by water. The psychomotor stimulants weakened the control by immediate reinforcers and strengthened the control by delayed reinforcers, with the effect of the drugs being more pronounced in WKY than in SHR. The results are consistent with clinical observations that ADHD children are less willing than others to accept "delayed gratification" and that methylphenidate increases the control of delayed reward over their behavior.

Analysis of Variance↗