Female house mice develop a unique ovarian lesion in colonies that are at maximum population density

Colonies of house mice reach maximum population density in 120-180 days, ir respective of cage size and initial number of colonizing animals. Reproduct ion ceases because the females become aggressive and unreceptive to mating. The aggressive behavior is correlated with elevated levels of testosterone (T) and corticosterone (B) (Chapman et al., Phys Behav 64:529-533, 1998), In two of seven strains of mice, females developed ovarian lesions. The occ urrence of the lesion in one strain was correlated with the age of the anim al and duration of the study. In the second strain, cage size was the deter mining factor. Lesioned ovaries weighed significantly more than nonlesioned ovaries. The lesion consisted of accumulations of luteal membrane and orga nelle fragments, and other cellular debris, suggestive of incomplete and pr olonged luteolysis, Electron microscopic (EM) analyses revealed the presenc e of deposits of permanganate-resistant congophilic amyloid fibrils in the intima and smooth muscle cells of luteal thecal arteries. Population females had thymus glands and uteri that weighed significantly l ess than the same organs from females housed in the breeding colony, wherea s the adrenal glands from the population females weighed significantly more . It is proposed that the female aggression is due to high levels of T. It is also proposed that the high levels of B suppress the immune cells involved in normal luteolysis and contribute to the incomplete and prolonged luteol ysis.