Mitotic cell death and delay of mitotic activity in guinea-pig embryos following brief maternal hyperthermia

Pregnant guinea-pigs were exposed to an environmental temperature of 42·0–42·5 °C for 1 h on day 21 of gestation. Their embryos were removed at periods from 45 min of heating to 48 h following exposure. Histological preparations of embryos showed clumping of nuclear chromatin and subsequent death of cells which were at about the stage of mitosis. Affected cells were particularly numerous in the central nervous system. Further mitotic activity was inhibited for 6–8 h. Squash preparations of the telencephalon at 1 h after heating showed an increase from 3 to 86 % in the number of mitotic cells showing damage in the form of nuclear clumping; this number fell progressively to 30% by 24 h after heating. The proportion of cells in various stages of mitosis changed considerably at 1–8 h after heating, but had returned to pre-heating values by 24 h. The proportion of cells in prophase fell markedly, while the proportion of metaphase cells was doubled at 4 h after heating, indicating blocks to the cell generation cycle before prophase and in metaphase.