Utilization of the rat as a model of mammalian aging: impact of pathology on behavior

Because pathology is concomitant to aging in rat strains, extraneous variance can be added to studies of aging at all levels of analysis. Thus, several gerontologists have made recent requests for characterization of pathology in aging studies including not only investigators' reports of diseases commonly observed (e.g., Sendai virus) and the occurrence of prevalent age-related lesions (e.g., nephropathy, leukemia, radiculoneuropathy) in rodent colonies, but also how specific disease processes might impact on the variable of interest in their investigation. Reported here are simple techniques (e.g., physical examination, necropsy to identify lesions, hematocrit, Wright stain) used routinely by our laboratory to screen for the presence of age-related disease in studies using Fischer 344 and Wistar rats. Routine health screening by physical examination and blood testing in our studies has allowed us either to eliminate moribund rats or to assess whether deficient performance was related to health status when these animals had been included in behavioral investigations. Additional health screens (e.g., antibodies for specific tumors) need to be developed. Investigators should be encouraged to utilize existing techniques, such as those reported here, and new technologies either to screen moribund animals from studies or to demonstrate that the pathology observed does or does not impact on the variable under investigation.