Ultra-Structural Alterations in In Vitro Produced Four-Cell Bovine Embryos Following Controlled Slow Freezing or Vitrification.

Cryopreservation is the process of freezing and preserving cells and tissues at low temperatures. Controlled slow freezing and vitrification have successfully been used for cryopreservation of mammalian embryos. We investigated the effect of these two cryopreservation methods on in vitro produced four-cell stage bovine embryos which were classified according to their quality and separated into three groups. The first group was maintained as untreated controls (n = 350). Embryos of the second (n = 385) and the third (n = 385) groups were cryopreserved either by controlled slow freezing or by vitrification. Embryos in groups 2 and 3 were thawed after 1 day. Hundred embryos were randomly selected from the control group, and 100 morphologically intact embryos from the second and third group were thawed after 1 day and cultured to observe the development up to the blastocyst stage. The blastocyst development rate was 22% in the control group, 1% in the slow-freezing group and 3% in the vitrification group. Remaining embryos of all three groups were examined by light microscopy, transmission electron microscopy and immunofluorescence confocal microscopy with subsequent histological staining procedures. Cryopreservation caused degenerative changes at the ultra-structural level. Compared with vitrification, slow freezing caused an increased mitochondrial degeneration, cytoplasmic vacuolization, disruption of the nuclear and plasma membrane integrity, organelle disintegration, cytoskeletal damage, a reduced thickness of the zona pellucida and a formation of fractures in the zona pellucida. Further studies are required to understand and decrease the harmful effects of cryopreservation.

The time course of attack priming effects in female golden hamsters.

In two experiments using different procedures we have found that attack latency, having been reduced by a previous priming attack, returns to baseline levels over a 24 hr period. In both experiments an unexpected, transient increase in attack latency occured 2 hr postpriming. The procedure of the second experiment precludes the possibility that this is a circadian effect. There were no cumulative effects of successive priming attacks suggesting that, under the conditions of these experiments, each attack "resets" the animals' aggressive state. The effects of a single brief agonistic encounter are substantial and persistent enough to be involved in such phenomena as the escalation and redirection of aggression observed in field studies.