The eects of gender and psychoneuroimmunological factors resulting from the social environment and status of males were investigated with regard to the concentrations of testosterone and corticosterone and the course of Trypanosoma cruzi infection in mice. Hormone concentrations varied considerably; and only testosterone concentrations showed a tendency to be higher in dominant males. Females kept singly developed lower and more similar parasitaemias than males kept singly or together with a female. This dierence was signi®cant when comparing groups of females or males. Within groups of male mice, parasitaemia was strongly correlated with the social position, being high in inferior males and low in dominant ones. The importance of these ®ndings is that they clearly prove that chronic social stress in males strongly aects the course of infection with T. cruzi.
Female BALB/c or C57Bl/6 mice, kept in small groups of three or ®ve animals with or without male odor, all had a similar progesterone and corticosterone level, mean number of estrus and duration of estrus cycle. However, if males were kept in the same room, the mean duration of the estrus cycle was longer for both strains; and C57Bl/6 females had a signi®cantly higher number of estrus than BALB/c mice and showed a tendency to synchronize the estrus cycle within a group. After infection of females of both mouse strains with vector-derived metacyclic trypomastigotes of Trypanosoma cruzi, anestrus with intense phlegm production occurred during the acute phase of infection and this was positively correlated with higher parasitemia. Within individual groups of BALB/c mice, the female with the relatively highest corticosterone and progesterone level had the lowest parasitemia. In groups kept separate from male pheromones, one or two females in each group developed high parasitemias.
Four Trypanosoma species were examined for damage following prolonged storage in liquid nitrogen (-196 degrees C). The stabilates were successfully recovered after a cryopreservation period of approximately 30 years. The structure of specimens was studied by means of light microscopy and scanning (SEM) and transmission (TEM) electron microscopy. All of the species tested--T. evansi, T. equinum, T. brucei, and T. congolense--proved to be infective to mice. However, as compared with controls, the trypomastigote bloodstream forms, which had been frozen and later recovered, showed clear differences. Formerly deep-frozen organisms usually appeared to have shrunk as a result of solution effects, which occur during freezing and thawing. Ultrastructural changes such as separation of the cytoplasm from the pellicle, the occurrence of large vacuoles in the cytoplasm and karyoplasm, a loss of cytoplasmatic ribosomes, membrane injuries, enlargement of the flagellar pocket, and denaturation of chromatin became obvious. The extent of the ultrastructural alterations appeared to be much greater after a cryopreservation period of approximately 30 years than those previously reported after a 13-year storage period. These changes, however, did not result in a complete loss of infectivity to mice.
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