In conclusion the use of permanent light as a negative reinforcer can help to evaluate the importance of enriching items for group-housed mice according to the consumer demand theory.
Further research should be carried out in order to determine if the high light intensities lead to a retinal degeneration in the BALB/c mice.
In addition to that, this research should be carried out with different strains of mice, mice of an older age as well as different enrichment items.
6 Summary
Consumer Demand Experiments in group-housed mice with light as a negative reinforcer for environmental enrichment
Anke Schraepler
Due to legislation and ethics environmental enrichment has become an important issue in laboratory animal science. Many studies using preference tests prove that animals prefer enriched cages to non-enriched and that a more complex environment affects the mice’ development and behaviour beneficially. As preference tests only lead to a hierarchy of preferred items and the animals’ long-term welfare is not necessarily assured they always bare the possibility of misinterpretation. In addition to that, several studies showed that environmental enrichment influences the results of animal experiments. Therefore it is essential to standardize housing conditions using enrichment items because only in that case the enhancement of the animal’s well-being as well as the accuracy of experimental results will be assured.
The consumer demand theory -a means to measure the strength of a preference- is considered to be an appropriate method for the objective evaluation of enrichment objects. So far, these test have not been carried out with group-housed mice and the purpose of this study was to evaluate light as a negative reinforcer for group-housed mice and to test enrichment objects using this method.
At the age of three weeks male and female BALB/c mice, originated from Harlan Winkelmann, were marked and randomly allocated into Makrolon® Type III cages (single cage period = SC) in groups of four of the same sex. After two weeks they were transferred into the ‘double cage’, an apparatus consisting of two Makrolon® Type III cages connected by a Perspex tube. Both cages were equipped with food, tab water and wood shavings. The animals again had two weeks to adapt to the new environment (double cage period = DC). Afterwards the contents of the cages as well as the light regime changed (aversion period = AV). One cage (C1) was exposed to a 12:12 dark/light cycle while the light intensity in the other cage (C2) was increased
C1 was equipped with food and water and C2 contained wood shavings. In experiment 4 both cages were supplied with food, tap water and wood shavings and C2 additionally contained one mouse house. All mice had to accept the increasing light intensities in order to get access to the resource placed in C2. After 18 days of AV the mice were euthanized and morphological parameters were compared with respect to the four different housing situations in the AV.
Experiment 5 and 6 investigated on the possibility that the additional cage itself can be considered as enrichment by mice. The SC was the same as in experiments 1 to 4. The double cage consisted of one Makrolon® Type III cage (C3) equipped with food, water and wood shavings and either another Makrolon® Type III cage or a Makrolon® Type II long cage left empty (C4). After two weeks in this double cage the animals were transferred back into a single Makrolon® Type III cage where they stayed for three days (single cage period 2 = SC2) before they were euthanized.
In all experiments at the end of each period blood samples were taken in order to determine the plasma corticosterone levels.
The results of this study show that light is a possible negative reinforcer to evaluate enrichment items for mice. According to other studies the male as well as the female mice accepted the negative reinforcer light in order to get access to the water, the wood shavings and the mouse house, respectively, whereas other behavioural patterns were performed less frequently. The mice showed an inelastic demand for water, wood shavings as well as for the mouse house.
Regarding the corticosterone concentrations, male mice seem either to have different strategies to cope with aversive situations than females because during the AV the corticosterone titers of male mice decreased whereas in female mice the concentrations increased compared to the values of the DC.
The different housing conditions of the experiments led to significant changes in morphological parameters such as the heart weight, the spleen weight and the adrenal weight.
Aufgrund von Gesetzgebungen und ethischen Bedenken sind Umweltanreicherungen für Labortiere ein wichtiger Bestandteil in der Versuchstierkunde geworden. Studien zur Ermittlung der Präferenz zeigten, dass Tiere angereicherte Umgebungen nicht angereicherten vorziehen, und dass komplexere Umgebungen die Entwicklung von Mäusen und auch ihres Verhaltens positiv beeinflussen. Jedoch können Ergebnisse von Präferenztest leicht fehlinterpretiert werden, da sie lediglich eine Rangordnung der Anreicherungen zeigen und das gewünschte Langzeitwohlbefinden nicht zwangsläufig erreicht wird.
Hinzu kommt, dass es in einigen Studien zu einer Beeinflussung der Ergebnisse durch die Umweltanreicherungen kam. Aus diesem Grund ist es nötig, Tiere mit standardisierten Umweltanreicherungen zu halten, denn nur dann wird das Wohlbefinden der Tiere bei gleichzeitiger Exaktheit der Ergebnisse gefördert.
Die Konsumententheorie, mit deren Hilfe die Stärke einer Präferenz gemessen werden kann, wird als die Methode angesehen, mit der eine objektive Beurteilung von Umweltanreicherungen möglich ist. In der Regel wurden diese Versuche mit Einzeltieren durchgeführt. Daher war es Ziel dieser Arbeit, Licht als negativen Verstärker für in Gruppen gehaltene Mäuse zu etablieren und nachfolgend verschiedene Umweltanreicherungen mit dieser Methode zu testen.
Drei Wochen alte männliche und weibliche BALB/c Mäuse (Züchter Harlan Winkelmann) wurden zufällig auf gleich-geschlechtliche Vierergruppen verteilt, markiert und in Makrolon® Typ III Käfige gehalten (Einzelkäfigphase = SC). Nach zwei Wochen wurden die Tiere in den ‚Doppelkäfig’ verbracht, der aus zwei durch eine Plexiglasröhre verbundenen Makrolon® Typ III Käfige bestand. Beide Käfige enthielten Futter, Wasser und Einstreu. Die Tiere konnten sich zwei Wochen an den
Versuchsapparat adaptieren (Doppelkäfigphase = DC). Hiernach wurden die Ausstattung der Käfige sowie das Lichtregime verändert. Einer der Käfige (C1) war einem 12:12 Stunden Hell-Dunkel-Rhythmus ausgesetzt während der andere (C2) im Dauerlicht stand und die Lichtintensität alle drei Tage logarithmisch von 100 lux bis 3200 lux erhöht wurde (Aversionsphase = AV). Die Käfige waren durch eine lichtundurchlässige Wand voneinander getrennt. In Versuch 1 enthielten beide Käfige Futter, Wasser und Einstreu. In Versuch 2 enthielt C1 Futter und Einstreu während C2 Wasser enthielt. C1 des dritten Versuchs enthielt Futter und Wasser und C2 Einstreu. Im vierten Versuch enthielten beide Käfige Futter, Wasser und Einstreu sowie ein Mouse House in C2. Um zu der jeweiligen Ressource zu gelangen, mussten alle Mäuse die steigenden Lichtintensitäten in Kauf nehmen. Nach 18 Tagen AV wurden die Tiere getötet und die Organe der einzelnen Versuche miteinander verglichen.
Die Versuche 5 und 6 untersuchten, ob Mäuse den Zusatzkäfig selber als Umweltanreicherung ansehen. Die SC entsprach der Versuche 1 bis 4. Der Doppelkäfig bestand in diesen Versuchen aus zwei Makrolon® Typ III Käfig (C2) oder aus einem Makrolon® Typ III Käfig, der mit einem Makrolon® Typ II lang Käfig (C4) verbunden war. Beide Zusatzkäfige blieben leer. Nach zwei Wochen DC wurden die Mäuse wieder in einen Einzelkäfig verbracht (2. Einzelkäfigphase = SC2). Dort blieben sie drei Tage bevor sie getötet wurden.
Bei allen Versuchen wurde nach jeder Phase eine Blutprobe genommen, in der der Corticosteronspiegel bestimmt wurde.
Die Ergebnisse dieser Studie zeigen, dass Licht zur Beurteilung von Umweltanreicherungen für Mäuse genutzt werden kann. Übereinstimmend mit anderen Untersuchungen akzeptierten alle Mäuse den negativen Verstärker, um an Wasser, Einstreu und das Mouse House zu gelangen während andere Verhaltensweisen vermindert gezeigt wurden. Wasser, Einstreu und das Mouse House sind inelastische Ressourcen für Mäuse.
Nebennierengewichts.
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