Structural changes of in vitro matured buffalo and bovine oocytes following cryopreservation.

The aim of this work was to evaluate chromatin and spindle organization of buffalo and bovine in vitro matured oocytes after vitrification/warming by Cryotop and after their exposure to cryoprotectants (CP). In vitro matured oocytes were vitrified/warmed and exposed to the vitrification/warming solutions containing ethylene glycol (EG), dimethyl sulfoxide (DMSO) and sucrose as CP. Two hours after warming, oocytes were fixed and immunostained for microtubules and nuclei and examined by fluorescence microscopy. Data were analyzed by Chi Square test. A higher percentage of Telophase II stage oocytes was found in the toxicity (26 and 34% in bovine and buffalo) and the vitrification groups (13 and 7% in bovine and buffalo) compared to the control, indicating occurrence of activation. An increased percentage of oocytes with abnormal spindle and chromosome organization was found in oocytes exposed to CP (24 and 13% in bovine; 32 and 30% in buffalo respectively) and in those vitrified (26 and 31% in bovine; 26 and 29% in buffalo respectively) compared to the control (0 in bovine and 2.5% in buffalo).