Enriched cages for groups of laboratory male rats and their effects on behaviour, weight gain and adrenal glands.

We investigated if there were any negative effects on the behaviour and physiology of rats housed in groups of five in two types of enriched cages and compared them with paired-housed rats housed in traditional cages. Eighty-four male Wistar and Sprague-Dawley rats were housed in an enriched rat cage (ERC), a rebuilt rabbit cage (RRC) or a Makrolon III cage (MC) system from 5-16 weeks of age with access to different enrichments. Recordings of behaviour and cage use (3 × 24 h video recording), weekly weighing, measuring food consumption four days/week and water consumption two days/week, were carried out. The rats' muscle strength was assessed using the 'inclined plane' at the end of the study, and after euthanasia the adrenal glands were removed and weighed. Being in the shelter was the most common behaviour in the ERC and RRC groups. In the MC group, which lacked a shelter, rats performed the highest percentage of lying, grooming, rearing, play fighting and manipulating paper shreds. Rats in the RRC had the highest percentage of standing and manipulating gnawing sticks. Water consumption was higher in MC than in ERC and RRC rats. Rats from the RRC managed to remain at a steeper angle on the 'inclined plane' than rats from the MC. There were no significant effects of cage type on weight gain, food consumption or relative weights of adrenal glands. In conclusion, male rats kept in groups of five in larger enriched cages benefited from the enrichments, and no negative effects were found in the larger groups.

Moldy environments and toxic pneumonitis.

Exposure to organic dusts might cause an acute reaction with influenza like symptoms (toxic pneumonitis). Although it is well known that endotoxin, which is often present in organic dusts, may cause this reaction, there is no information about fungal cell wall agents as causative agents. The capacity of different fungal cell wall agents to induce an acute inflammation was evaluated in animal inhalation experiments. Guinea pigs were exposed to an aerosol of endotoxin, molds, and different fungal cell wall agents (FCWA) in a continuous flow exposure chamber, and the number of free lung cells was determined 24 h thereafter. Endotoxin caused a dose-dependent increase in the number of neutrophils and macrophages. None of the other agents tested caused a neutrophil response. The results suggest that toxic pneumonitis in environments with organic dusts is caused by the presence of inhaled endotoxin. Although no effect from FCWA was found, it is well known that this inhalation under chronic conditions will cause lung disease, particularly granulomatous pneumonitis.

Microbial cell wall product contamination of bedding may induce pulmonary inflammation in rats.

To test the hypothesis that airborne microbial cell wall components could induce an inflammatory response in the lungs, measurements were made of the amounts of bacterial endotoxin and (1-->3)-beta-D-glucan in laboratory animal bedding materials. Groups of rats were exposed by inhalation to airborne endotoxin, (1-->3)-beta-D-glucan or a combination of the two for 5 weeks. The results demonstrated that measurable amounts of endotoxin and (1-->3)-beta-D-glucan could be detected in the different bedding materials. In contrast to animals at delivery, those kept on bedding for 5 weeks showed moderate inflammatory reactions in the lung. These were most pronounced among animals exposed to endotoxin and (1-->3)-beta-D-glucan. The results suggest that further studies need to be undertaken to elucidate the role of microbial cell wall products in the development of inflammatory lung responses among research animals.