Effects of chilling to 0 degrees C on the morphology of meiotic spindles in human metaphase II oocytes

Objective: To determine the effects of chilling to 0 degreesC on the meioti c spindle of human metaphase II as observed by optical sectioning microscop y. Design: Laboratory study. Setting: Academic research laboratory in a medical school. Patient(s): Seventy-two women undergoing infertility treatment donated a to tal of 108 oocytes. Intervention(s): Metaphase II oocytes were stripped of their cumulus cells, cooled directly to 0 degreesC, and for periods of 1 to 10 minutes. They we re then fixed at 37 degreesC, stained for immunofluorescence, and microscop ically. Main Outcome Measure(s): Morphology of the meiotic spindle in chilled and c ontrol oocytes. Result(s): Microscopic evaluations of 46 chilled oocytes revealed various t ime-dependent changes in microtubules compared to 9 control oocytes. After 1 minute at 0 degreesC, spindle damage was negligible, but in oocytes coole d for 2 or 3 minutes, there was obvious shortening of the spindle and loss of polarity. Cooling to 0 degreesC for 4 to 9 minutes resulted in increasin gly more drastic changes; by 10 minutes the spindles had totally disappeare d. Despite depolymerization of microtubular tubulin at 0 degreesC, the chro mosomes did not become dispersed, but remained anchored even in the absence of spindles. Conclusion(s): Even brief exposure of human oocytes to temperatures near 0 degreesC causes profound alterations of the meiotic spindle. (Fertil Steril (R) 2001;75:769-77. (C) 2001 by American Society for Reproductive Medicine .) dispersed, but remained anchored even in the absence of spindles.