Short-term effects of perinatal asphyxia studied with fos-immunocytochemistry and in vivo microdialysis in the rat

Abstract

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°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. Suncutaneous 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 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 (≈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 (≈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. The number of Fos-IR cells in the piriform cortex increased following short asphyctic periods, with a maximum increment in animals exposed to 2–3 min asphyxia (≈twofold). In contrast, asphyctic periods longer than 10 min were associated with a decrease in the number of Fos-IR cells (>50%). A strong decrease in Fos-IR was also observed in the cortical amygdaloid complex following longer than 19 min asphyxia. The changes in amino acids and metabolism products and Fos-IR observed during recirculation in rats surviving various asphyctic periods are suggestive of diffuse stimulatory and inhibitory responses to the progressive failure in energy reserves that follows prolonged asphyxia. It is speculated that these changes may be involved in the processes leading to the behavioral alterations observed in experimental animals as well as in humans surviving perinatal asphyxia.