A long-lasting change in the excitability of fetal brain neurons following activation of dam's hypothalamus in rats

The influence of the dam's brain on the electrical activity of brain neurons was examined in the rat fetus while the fetus was still connected to the dam by the umbilical cord. Under urethan anesthesia, the spontaneous or glutamate-induced discharge of single brain stem neurons in fetuses was decreased by electrical stimulation of the dam's hypothalamus (Hyp). The changes occurred 21-122 s after start of the stimulation and persisted throughout the recording until the cells were lost after 2.4-9.5 min. The effects of electrical stimulation of dam's midbrain reticular formation (MRF) were much weaker and of shorter duration compared with Hyp stimulation. The dam's blood pressure was increased immediately after the beginning of MRF or Hyp stimulation. The change was always greater with MRF than with Hyp stimulation. Activation of the dam's MRF and Hyp had no marked influence on the blood flow in the fetal brain. These results indicate the presence of a functional interaction between the brain of the dam and that of its fetus mediated through the placenta.