The development of the cerebral mantle in the mouse embryo after brief in utero hyperthermic stress.

The width of the different layers of the cerebral mantle of 16-day mouse embryos was measured after exposure of pregnant dams to a hyperthermic stress of 43 degrees C for 10 minutes in a laboratory oven, during the period of neural tube closure. The dams were exposed on day 7 1/2 or 8 1/2 post coitum. A control group of mice was placed in the oven at ambient temperature (28 degrees C) for 10 minutes. At 43 degrees C oven temperature, the core temperature of the pregnant dams was elevated by 2-3 degrees C (P < or = 0.001). In non-pregnant mice, this degree of heat stress results in a sustained hyperthermia of about six minutes and a return to normal temperature 15 minutes after removal from the oven. There were no congenital malformations of the central nervous system. The mean litter sizes, percentage resorptions and fixed embryonic weights were similar in the experimental and control groups. The width of the cortical plate was significantly reduced in all the regions measured (P < or = 0.001). The width of the matrix layer was reduced only in the fronto-parietal region. The results suggest that this sub-teratogenic dose of hyperthermic stress reduces neuronal population in the cerebral cortex. This may be the structural substrate for the impairment of function in animals heat stressed during prenatal development.