Developmental profiles of GISP and GABAB receptor subunits in rat brain. Membrane extracts were prepared from rat whole brain taken at the ages indicated in days (E, embryonic, P, post-natal, Ad, adult) and probed for GISP, GABAB1 and GABAB2 immunoreactivity. GISP was expressed at the every stage when either GABAB1 or GABAB2 is expressed. Note that the two GABAB1 isoforms show a markedly different profile. Only GISP was abundant prior to birth. The data are representative of three separate experiments. β-actin blots were performed as a loading controls (data not shown).