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Biomedical subjects

M Holmgren

Publications and source records attributed to M Holmgren.

8 recordsLinked to original sources
PubMed1991

Food anticipatory yawning rhythm in the rat.

The effect of feeding schedules on the daily rhythm in spontaneous yawning activity was studied in high yawning (HY) Sprague-Dawley rats. If the animals are fed ad libitum and changed from a standard 12-12 light-dark (LD) illumination regime to constant light (LL), the normal predark circadian peak in yawning disappears, to be replaced, after 3 weeks, by two or more ultradian smaller peaks in yawning frequency. Restriction of food availability to 2-2:30 regular hours of the day, in rats under LL conditions, leads to the appearance of a significant preprandial (food anticipatory) peak in yawning. A similar eating-fasting daily cycle of 2-22 h in rats under LD conditions determines the disappearance of the pre-dark peak in yawning activity, and a significant shift in higher yawning frequency towards the couple of hours preceding food availability. This result suggests that restricted feeding is more potent than the LD transition in the entrainment of the daily rhythm in yawning activity.

Animals↗
PubMed1990

Serial dependency in the discharge pattern of dorsal spinocerebellar tract neurons: a computer simulation analysis.

We have developed a model in order to analyze the factors eventually responsible for the strong negative serial dependency between successive interspike intervals in the discharge of the Dorsal Spinocerebellar Tract (DSCT) neurons. This dependency is reflected, phenomenologically, by short intervals followed by long ones and, quantitatively, by the first order correlation coefficient (R1-2); which can be lower than -.6 (Jansen, Nicolaysen & Rudjord, 1966; Kröller and Grüsser, 1982). We have found that the lowest values of R1-2 are always related with model parameter values which were very similar to those obtained experimentally. It was observed that EPSP amplitude distribution plays an important role in the discharge patterns of the DSCT neurons. There is one fiber that elicits EPSPs greater than 6 mV, which is responsible for the genesis of the short intervals in the discharge. Long intervals are determined basically by a suprathreshold depolarization and the afterhyperpolarization processes.

Action Potentials↗
PubMed1989

Simulation of ionic transport mediated by membrane proteins for educational purposes.

An interactive Pascal program for use in the IBM-PC and compatible computers is presented. It simulates the activation of integral membrane proteins involved in ionic transport. The program allows variation of the number of transport proteins, ionic concentrations, permeability ratios, voltage dependence of permeabilities and temperature. A separate procedure for simulation of Na+-K+ pumps has been included considering their relevance in physiology. The main purpose of the present program is to serve as a teaching aid to understand the basic principles and concepts related with the electrogenesis and the stoichiometry of membrane transport processes.

Biological Transport↗
PubMed1986

Characterization of the antinociceptive effects of some adenosine analogues in the rat.

The antinociceptive effects of the stable adenosine analogues N6-phenylisopropyladenosine (L-PIA), N6-cyclohexyladenosine (CHA) and 5'-N-ethylcarboxamidoadenosine (NECA) were investigated in conscious rats using cutaneous thermal tests (hot plate and tail flick). Subcutaneous administration of the adenosine analogues induced a dose-dependent antinociceptive response for all agents. However, NECA was approximately 15 times more potent than PIA and CHA. Approximately the same potency order and response was seen when the adenosine analogues were administered intrathecally at the lumbar level. By this route of administration, the adenosine analogues were approximately 10-20 times more potent than after S.C. administration. Intracerebroventricular administration (lateral ventricles), however, induced a variable response, in most cases a slight hyperalgesia. The nonspecific adenosine antagonist theophylline (S.C.) rapidly reduced the antinociceptive effect induced by PIA (S.C.) but enprofylline, a bronchodilating xanthine with low ability to antagonize adenosine did not influence PIA-induced antinociception. It is concluded that stable adenosine analogues and presumably adenosine itself have potent antinociceptive effects via specific adenosine receptors in the rat. The effects seem to be mediated mainly by a spinal mechanism of action.

Adenosine↗
PubMedDate not supplied

Computer simulation of diffusion processes as a teaching aid.

A computer program for the simulation of diffusion processes has been developed. It displays the trajectories of single molecules under Brownian motion. Diffusion of 40 to 100 molecules in a box with or without barriers can be simulated, and concentration-time and concentration-distance functions can be plotted. This program may be useful, when complemented with experimental work and theoretical study, for teaching diffusion and membrane permeability processes.

Chemistry↗