Effect of perinatal asphyxia on tyrosine hydroxylase and D2 and D1 dopamine receptor mRNA levels expressed during early postnatal development in rat brain.

This study was designed to investigate the postnatal developmental plasticity of the mesostriatal and mesolimbic dopamine systems that occurs following perinatal asphyxia. The time course and patterning of the changes in levels of tyrosine hydroxylase (TH), and D1 and D2 dopamine receptor (R) mRNA in the cell body region, substantia nigra and ventral tegmental area (SN/VTA), and projection fields, striatum and limbic regions at the age of 6 and 24 h, and 1 week after asphyxia were studied with a quantitative reverse transcription polymerase chain reaction method with appropriate internal cRNA standard. In Caesarean-delivered control rats (Sprague-Dawley), TH, D2R and D1R mRNA levels showed regional and temporal specificity in both absolute levels and developmental kinetics during the first week of life. TH mRNA levels were >10-fold higher in SN/VTA than in striatum and limbic regions. Compared to Caesarean delivered controls, severe asphyxia (15-20 min) induced an increase of TH and D2R mRNA in SN/VTA 6 h and 1 week after birth. In addition, asphyxia induced an increase of TH mRNA in the projection fields, striatum and limbic regions, at 1 week. Perinatal asphyxia did not appear to exert any effect on D1R mRNA levels. No differences in any of the parameters were observed between spontaneous- and Caesarean-delivered animals. The present results indicate that perinatal asphyxia triggers coordinated changes in the expression of TH, and dopamine receptor mRNA in SN/VTA, striatum and limbic regions. These changes may affect differently dopamine D2R and D1R expression along development, contributing to long-term neurocircuitry imbalances.