Prenatal alteration and distribution of the GABAB1 and GABAB2 receptor subunit mRNAs during rat central nervous system development

Abstract

The prenatal developmental expression changes and distribution of the γ-aminobutyric acid (GABA) B1 and GABA B2 receptor subunit were investigated using in situ hybridization and RNase protection assay (RPA). We defined a different expression pattern of GABA B1 subunit mRNA to that of GABA B2 subunit. GABA B1 subunit mRNA signals were moderately expressed in the cerebral cortex neuroepithelium of discrete brain regions on gestational day (GD) 11.5 and 12.5 and were highly expressed in the brain and spinal cord on GD 13.5 and 15.5. However, GABA B2 subunit mRNAs were not detected on GD 11.5 and 12.5 and were first weakly detected on GD 13.5. On GD 15.5, 17.5, and 19.5, these subunit mRNAs were found in the retina, hippocampus, cerebral cortex, spinal cord, and cerebellum area. On GD 19.5 and 21.5, these subunits mRNA signals increased in the cerebral cortex, hippocampus, thalamus, and cerebellum, but decreased in the spinal cord, spinal ganglion, and midbrain, reaching similar levels to that of the adult brain. On GD 21.5, these subunit mRNAs were similarly expressed in almost all brain areas with a higher expression level of GABA B1 subunit mRNA than GABA B2 subunit mRNA. Our results found that GABA B1 and GABA B2 subunit mRNAs showed different expression patterns, with the GABA B1 subunit expressed earlier and higher. We suggest that GABA B1 and GABA B2 subunits might have a role in the fetal brain during the gestational period for pre- and post-synaptogenesis, proliferation, differentiation, and neuronal maturation, and GABA B1 subunit may be more important than GABA B2 subunit during rat prenatal development.