EXPRESSION OF GABAA RECEPTOR α3-, θ-, AND ε-SUBUNIT mRNAs DURING RAT CNS DEVELOPMENT AND IMMUNOLOCALIZATION OF THE ε SUBUNIT IN DEVELOPING POSTNATAL SPINAL CORD

Ionotropic GABA(A) receptors are heteromeric structures composed of a combination of five from at least 16 different subunits. Subunit genes are expressed in distinct cell types at specific times during development. The most abundant native GABAA receptors consist of alpha 1-, beta 2-, and gamma 2-subunits that are co-expressed in numerous brain areas. alpha 3-, theta-, And epsilon-subunits are clustered on the X chromosome and show striking overlapping expression patterns throughout the adult rat brain. To establish whether these subunits are temporally and spatially co-expressed, we used in situ hybridization to analyze their expression throughout rat development from embryonic stage E14 to postnatal stage P12. Each transcript exhibited a unique or a shared regional and temporal developmental expression profile. The thalamic expression pattern evolved from a restricted expression of epsilon and theta transcripts before birth, to a theta and alpha 3 expression at birth, and finally to a grouped epsilon, theta and alpha 3 expression postpartum. However, strong similarities occurred, such as a grouped expression of the three subunits within the hypothalamus, tegmentum and Pontine nuclei throughout the developmental process. At early stages of development (E17), epsilon and theta appeared to have a greater spatial distribution before the dominance of the alpha 3 subunit transcript around birth. We also revealed expression of alpha 3, theta, and epsilon in the developing spinal cord and identified neurons that express epsilon in the postnatal dorsal horn, intermediolateral column and motoneurons. Our findings suggest that various combinations of alpha 3-, theta- and epsilon-subunits may be assembled at a regional and developmental level in the brain. (C) 2009 IBRO. Published by Elsevier Ltd. All rights reserved.