Physiological activities of late-gestation rat fetuses in vitro.

A novel method for the in vitro maintenance of rat fetuses was used to study their physiological properties. Rat fetuses together with the uterus were isolated from anesthetized pregnant rats of 14.5-21.5 days gestation, placed in a chamber, perfused through a cannula inserted into the uterine artery with a physiological solution, and decerebrated. In this condition, it was possible to maintain heartbeats of rat fetuses for 24 h. The in vitro fetuses showed various spontaneous body movements including those that resembled respiration. Various body movements were also observed when mechanical or electrical stimulation was applied to the skin. These body movements were abolished by application of general anesthetics. It was shown that reflex-like electrical activities were retained in spinal cords isolated from fetuses which had been maintained in vitro for 10 h. These results show that in vitro rat fetuses retain abilities to generate various body movements that are presumably mediated by the electrical activities of the central nervous system. The presence of various neural activities, some of which are known to be particularly susceptible to poor psychological conditions, suggests that the condition of the in vitro fetuses is good and that the method may be applied to various studies on late-gestation mammalian fetuses.