In the present study, the short-term consequences of various perinatal asphyctic periods were studied at the peripheral and CNS levels in the rat. Perinatal asphyxia was induced in rat pups delivered by caesarean section within the last day of gestation, by placing the uterus horns including the fetuses in a water bath at 37 degrees C for various periods of time (0-23 min). Following asphyxia, the uterus horns were opened. The pups were then removed and stimulated to breathe. Subcutaneous levels of pyruvate (Pyr), lactate (Lact), glutamate (Glu), and aspartate (Asp) were monitored with microdialysis 40 min after delivery. In parallel experiments, the pups were sacrificed 80 min after delivery. The brains were removed, fixed, cut, and processed for Fos immunocytochemistry. The number of Fos-immunoreactive (IR) cells in different brain structures was counted under light microscopy. Subcutaneous levels of Pyr, Lact, Glu, and Asp increased following perinatal asphyxia, as compared to caesarean-delivered pups or to spontaneously delivered controls. A maximum increase in Pyr levels (approximately threefold) was observed with 2-3 min of asphyxia, while Lact levels increased along with the length of asphyxia. A maximum increase in Glu and Asp levels (approximately threefold) was observed with 10-11 min of asphyxia. Fos-IR nuclei were predominantly found in the piriform cortex, and in the cortical amygdaloid complex. In some cases, mainly in pups exposed to asphyxia, Fos-positive cells were also seen in other tele-diencephalic structures.