OPENING OF THE MOUSE ZONA-PELLUCIDA BY LASER WITHOUT A MICROMANIPULATOR

A contact-free laser system is described for ablation of the embryonic mouse zona pellucida using a pulsed excimer 308 nm laser. Effects on further embryonic development were evaluated. Zonae of 8- to 16-cell m ouse embryos were either lased (n = 189), zona-drilled with acidified Tyrode's solution (n = 183) or left zona-intact (n = 188). Blastocyst formation (99-100%) was similar in the three groups. Hatching occurred earlier in lased embryos compared to those of the control group. Thes e blastocysts hatched through the laser ablated area. Significantly mo re embryos were hatching on day 4 in the conventionally drilled group when compared to the laser treated group (50% versus 24% respectively) . On day 7 of development, significantly (P < 0.05) more embryos conve ntionally zona-drilled (37%) were intact than those which were previou sly laser treated (10%). Abnormal development was also noted in a smal l group of embryos which were lased just on the outside of the zona in comparison to 1/3 of an embryonic width away from the zona. The curre nt results suggest that apparently precise zona laser ablation with an excimer laser at 308 nm may have potential adverse effects which may only be manifested after a prolonged period of culture past the cavita tion stage. However, implantation rates of morphologically normal lase r abalated embryos were not impaired when compared to control embryos.