Search PubMed⌕ Search

Biomedical subjects

W R Schmidek

Publications and source records attributed to W R Schmidek.

10 recordsLinked to original sources
PubMed2004

Social condition affects hormone secretion and exploratory behavior in rats.

Studies of behavior, endocrinology and physiology have described experiments in which animals housed in groups or in isolation were normally tested individually. The isolation of the animal from its group for testing is perhaps the most common situation used today in experimental procedures, i.e., there is no consideration of the acute stress which occurs when the animal is submitted to a situation different from that it is normally accustomed to, i.e., group living. In the present study, we used 90 male 120-day-old rats (Rattus norvegicus) divided into 5 groups of 18 animals, which were housed 3 per cage, in a total of 6 cages. The animals were tested individually or with their groups for exploratory behavior. Hormones were determined by radioimmunoassay using specific kits. The results showed statistically significant differences between testing conditions in terms of behavior and of adrenocorticotrophic hormone (ACTH: from 116.8 +/- 15.27 to 88.77 +/- 18.74 when in group and to 159.6 +/- 11.53 pg/ml when isolated), corticosterone (from 561.01 +/- 77.04 to 1036.47 +/- 79.81 when in group and to 784.71 +/- 55.88 ng/ml when isolated), luteinizing hormone (from 0.84 +/- 0.09 to 0.58 +/- 0.05 when in group and to 0.52 +/- 0.06 ng/ml when isolated) and prolactin (from 5.18 +/- 0.33 to 9.37 +/- 0.96 when in group and to 10.18 +/- 1.23 ng/ml when isolated) secretion, but not in terms of follicle-stimulating hormone or testosterone secretion. The most important feature observed was that in each cage there was one animal with higher ACTH levels than the other two; furthermore, the exploratory behavior of this animal was different, indicating the occurrence of almost constant higher vigilance in this animal (latency to leave the den in group: 99.17 +/- 34.95 and isolated: 675.3 +/- 145.3 s). The data indicate that in each group there is an animal in a peculiar situation and its behavior can be detected by ACTH determination in addition to behavioral performance.

Adrenocorticotropic Hormone↗
PubMed1997

Handling and isolation in three strains of rats affect open field, exploration, hoarding and predation.

Male albino (Al), brown hooded (Br) and black hooded (Bl) rats were raised in social isolation or in pairs, with or without systematic handling. At 90 and 180 days of age, the animals were individually tested for activity in an open field (Of), exploratory behavior in a complex environment, food hoarding (Hd) and insect predation (Pd). Multivariate analysis of the results showed significant influences of all three factors (strain, handling and social isolation) and interactions among them. Strain affected Of, Hd and Pd, with contrastingly high performances of Br in Of, Al in Hd and Bl in Pd. Handling increased Of and exploration scores in both test series. Isolation induced higher performances in all the four behaviors in the second test series. Accentuated and stable individual differences occurred in the performances off all the behaviors. The results emphasize the subtleness and complexity of the interplay of genetic and environmental influences and stress the independence of the regulatory processes of different behaviors.

Animals↗
PubMed1988

Differences in individual rat preference for light levels.

Behavioral observations assessing the position of individual animals in relation to a light gradient have shown that rats have strong preference for environmental locations with reduced luminosity. Albino rats have a significantly greater darkness preference than a strain of hooded rats although no intersexual differences were detected. Individual animals show marked and stable differences in their darkness preference. These tendencies are already present in weanling rats and are maintained throughout development.

Animals↗
PubMed1986

Effect of xylocaine and carbachol applied to the caudate nucleus of rats on barbiturate sleeping time.

Since lesion of subcortical structures may affect the barbiturate sleeping time (bST), we decided with the present study to elucidate the role of the caudate nucleus in the determination of central sensitivity to barbiturates. Rats implanted with a cannula in the caudate nucleus of one or both sides, as well as with a jugular cannula, were utilized. Intravenous injections of sodium pentobarbital (40 mg/kg), intracerebral injections of Xylocaine (0.04 microgram), carbachol (0.2 micrograms) or artificial cerebrospinal fluid (ACF) into the caudate nucleus were performed. Both Xylocaine and carbachol, but not ACF, increased the bST regardless of the preparation used, the only exception being Xylocaine which did not alter the bST, if injected into the left caudate nucleus. The results suggest that the caudate nucleus may act as a modulator of the central sensitivity to barbiturates.

Animals↗
PubMed1984

Influence of ambient temperature on the sleep-wakefulness cycle in the golden hamster.

The sleep-wakefulness cycle (SWC) of euthermic golden hamsters (Mesocricetus auratus) after 5 weeks of warm (30 degrees C) and of cold (5 degrees C) acclimation, was recorded at ambient temperatures between 5 degrees and 35 degrees C. Significant influences both of acclimation and of recording temperature were detected. Amount of paradoxical sleep (P%) after warm acclimation was maximal at 30 degrees C decreasing markedly at lower and higher temperatures. Variations in P% were mainly consequent to alterations in the frequency of occurrence of paradoxical sleep (PS) episodes. After cold acclimation (CA) P% was maximal at 20 degrees C but no strong decreases occurred at lower temperatures. Influences of CA upon SWC were already detectable after 3 days of cold exposure. Significant individual differences as well as strong fluctuations in P% during CA occurred. Acute oscillations in abdominal temperature along the SWC were recorded. Reductions in abdominal temperature during PS episodes, in relation to ambient temperature and to the length of the episode tended to occur.

Acclimatization↗
PubMed1983

Total calorimetric measurements in the rat: influences of the sleep-wakefulness cycle and of the environmental temperature.

Rates of production as well as dry and evaporative heat loss during the sleep-wakefulness cycle were studied in 11 male, adult albino rats with chronically implanted electrodes and thermocouple re-entrant tubes. Two groups of animals chronically acclimated to 6 or 23 degrees C were acutely studied at 15, 20, 25, 30 and 35 degrees C. Statistical analysis of the data shows that rates of heat production and dry heat loss differ with respect to acclimation and acute environmental temperatures, and show significant differences depending on the states of the sleep-wakefulness cycle. Rate of heat production was highest during wakefulness, intermediate during synchronized sleep and lowest during paradoxical sleep. Rate of dry heat loss of 15 degrees C was maximal during paradoxical sleep. Rate of evaporative heat loss apparently did not change with the states of the sleep-wakefulness cycle. Heat storage estimated from difference in rates of heat production and heat loss was positive during wakefulness, slightly negative during synchronized sleep and markedly negative during paradoxical sleep. The data presented suggest a clear although partial suppression of thermoregulatory mechanisms during paradoxical sleep in the white rat.

Acclimatization↗
PubMed1983

An inexpensive event recorder for continuous behavioral recording.

An event recorder for use in ethological studies which is of simple and inexpensive construction is described. The apparatus consists essentially of a constant speed paper transport device and an ethogram sheet holder. Up to 20 different behavioral items may be recorded continuously in an accurate time sequence. The items are coded as hand-drawn pencil lines of different length perpendicular to the direction of the paper movement. Since the ethogram code sheets are exchangeable, an unlimited number of different ethograms may be used.

Animals↗