title: Cryopreservation of mouse oocytes using a medium with low sodium content: effect of plunge temperature.
abstract: The effect of various combinations of plunge temperature and thawing protocol on the survival and viability of mouse oocytes was examined. The oocytes were frozen either in a standard freezing medium (ETFM, embryo transfer freezing medium) or in a low-sodium, choline-based freezing medium (CJ2), with 1.5 M 1,2-propanediol and 0.1 M sucrose, and using a conventional slow cooling method. The criteria used to assess survival were morphological state after thawing (intact or lysed), ability to become fertilized, and ability to develop to the two-cell, morula, and blastocyst stage in vitro. Oocytes frozen in CJ2 and plunged into liquid nitrogen (LN(2)) from -10, -20, or -33 degrees C remained intact and developed to the blastocyst stage at significantly higher rates than oocytes frozen in ETFM. For oocytes plunged into LN(2) from -33 degrees C, very rapid thawing (10 s in 30 degrees C water) was more detrimental than rapid or slow thawing (holding in air at room temperature for 10 or 30 s, respectively, prior to submersion in water at 30 degrees C for 10 s). By contrast, oocytes plunged into LN(2) from -10 or -20 degrees C survived better when thawing was very rapid or rapid than when thawing was slow. With the current protocol CJ2 was very effective over a wide range of plunge temperatures (-20 to -33 degrees C), although the optimal thawing protocol depended on the particular plunge temperature. Over 90% of oocytes surviving after slow cooling in CJ2 to -33 degrees C could be plunged to -196 degrees C with little or no further damage.
authors.affiliation: Institute of Reproductive Medicine and Science of Saint Barnabas Medical Center, 101 Old Short Hills Road, Suite 501, West Orange, New Jersey, 07052, USA. james.stachecki@embryos.net
authors.forename: J J
authors.initials: JJ
authors.lastname: Stachecki
authors.forename: S M
authors.initials: SM
authors.lastname: Willadsen
mesh_terms: D000818:Animals; D015925:Cryopreservation; D005260:Female; D051379:Mice; D009865:Oocytes; D019188:Organ Preservation Solutions; D012964:Sodium; D013696:Temperature
chemical_list: D019188:Organ Preservation Solutions; D012964:Sodium