Regional effects of pertussis toxin in vivo and in vitro on GABA B receptor binding in rat brain

Abstract

Agonist binding to GABA B receptors modulates the activity of the guanine nucleotide binding proteins, Go and Gi. These G proteins are ADP-ribosylated by pertussis toxin and this prevents them from coupling to the GABA B receptor resulting in a reduction in high-affinity GABA B binding. GTP, which binds to a different site on the G protein α subunit, also reduces the affinity of the receptor for the G protein, and this can be used as a “marker” for G protein-GABA B receptor linkage. We have examined GABA B binding site distribution in rat brain after unilateral intrahippocampal pertussis toxin injection in vivo, and after incubating brain slices in pertussis toxin in vitro, using the technique of receptor autoradiography. The effect of pertussis toxin was compared with that of GTPγS on GABA B binding. Intrahippocampal pertussis toxin administration reduced GABA B but not GABA A receptor binding and the effects appeared to be limited by pertussis toxin diffusion. More widespread reductions in GABA B binding were seen after incubation of brain slices in vitro but the extent varied in different brain regions. No reduction was detected in the corpus striatum. GABA B binding was also reduced in membranes prepared from cerebral cortex, hippocampus and cerebellum but there was no sigificant reduction in the corpus striatum after pertussis toxin treatment. GTPγS reduced GABA B binding to a similar extent in all areas studied irrespective of their sensitivity to pertussis toxin suggesting that while GABA B binding sites are linked to G proteins throughout the rat brain, those in the corpus striatum may be predominantly pertussis toxin insensitive.