Effects of whole-body heat on male germ cell development and sperm motility in the laboratory mouse.

Plain-language summary

This experiment followed what whole-body heat does to sperm as they are made, in laboratory mice. Adult males were held at 37 to 38 degrees Celsius (98.6 to 100.4 degrees Fahrenheit) for eight hours a day for three days running, with controls at room temperature, and a second group heated once for eight hours. Heated mice had lighter testes 16 hours and 14 days afterwards, and more of their developing sperm cells were dying, at specific stages rather than across the board. They also carried far more caspase-3 (an enzyme a cell switches on when dismantling itself, so more means more cells dying). After the single exposure, sperm were moving less and more had damaged membranes. By 21 days the heated mice did not show a significant difference from controls, and 21 days in a mouse is roughly two to two and a half turns of the sperm-production cycle, long enough for many damaged batches to clear and for some recovery, but not a full run start to finish. It comes from the same laboratory and the same heating protocol as the study of sperm membrane damage in mice submitted alongside it, which the second experiment continued.

Key findings

• Heated mice had lighter testes 16 hours and 14 days after exposure.
• More developing sperm cells were dying, concentrated at particular stages of the production cycle rather than spread evenly through it.
• Caspase-3, the marker of a cell dismantling itself, was far higher 16 hours after heating.
• Sperm were moving less and showed more membrane damage eight hours after a single heat exposure.
• By 21 days the heated mice did not show a significant difference from controls.