Effects of perinatal asphyxia on the mesostriatal/mesolimbic dopamine system of neonatal and 4-week-old male rats

The present study was undertaken in order to study the effects of perinatal asphyxia on tyrosine hydroxylase (TH) activity, dopamine levels and turnover, and dopamine metabolites (3,4-dihydroxyphenylacetic acid, DOPAC, homovanillic acid, HVA, and 3-methoxytyramine, 3-MT, analyzed by high-performance liquid chromatography, HPLC) measured in the basal ganglia of the 20- to 40-min-old newborn and 4-week-old male rat. Asphyxia was induced in pups by placing the fetuses, still in their uterus horns removed by hysterectomy from pregnant rats at full term, in a 37°C water bath for 15–16 min or 19–20 min. Following asphyxia, the uterus horns were opened, and the pups were removed and stimulated to breathe. A 100% and 50–80% pup survival was obtained following 15–16 min and 19–20 min of asphyxia, respectively. Acute changes were studied in brains from newborn pups 20–40 min after delivery, and long-term changes were studied in brains from 4-week-old rats. No changes in TH-activity could be observed in the substantia nigra/ventral tegmental area (SN/VTA), the striatum, or the accumbens nucleus/olfactory tubercle (ACC/TUB), in the newborn or the 4-week-old rat. In the newborn rat, 19–20 min of asphyxia increased (as compared to controls) dopamine levels in the SN/VTA to 136±14% and in the ACC/TUB to 160±10%, indicating an increased synthesis and/or release of dopamine. DOPAC levels were increased in the SN/VTA to 150±14% and in the ACC/TUB to 151±10%, and HVA levels were increased to 152±16% in the striatum and to 117±4% in the ACC/TUB. Following 15–16 min of asphyxia, dopamine levels were increased to 130±12% in the ACC/TUB, and DOPAC levels were increased to 135±6% and 130±12% in the SN/VTA and the ACC/TUB, respectively. This suggests that the increased dopamine levels may preferably reflect an increased release of dopamine following perinatal asphyxia. In the 4-week-old rat, dopamine levels were decreased in the SN/VTA to 71±4%, in the striatum to 52±8%, and in the ACC/TUB to 53±7%, following 19–20 min of perinatal asphyxia as compared to controls. No changes were observed in DOPAC, HVA, or 3-MT levels, indicating that the reduced dopamine levels reflect a reduced dopamine synthesis following perinatal asphyxia. A decrease in dopamine utilization was observed in the striatum to 15±8% and in the ACC/TUB to 9±13% following 19–20 min of perinatal asphyxia as compared to controls. This indicates that perinatal asphyxia produced long-lasting reductions in activity in the mesostriatal/mesolimbic dopamine systems in the 4-week-old rat.