GABAB-receptor-mediated actions of baclofen in rat isolated neocortical slice preparations: antagonism by phosphono-analogues of GABA.

Baclofen, 3-amino-propylphosphonic acid (3-APPA), and beta-phenyl-GABA (BPG), each reduced the frequency of spontaneous paroxysmal discharges in rat neocortical slices maintained in Mg2+-free medium, reversibly antagonised by phaclofen and 4-amino-butylphosphonic acid (4-ABPA). At lower concentrations, not influencing the discharges, both 3-APPA and BPG also reversibly antagonised this action of baclofen. However, des-chloro-phaclofen was inactive. Thus, phaclofen and 4-ABPA are GABAB-receptor antagonists in neocortex, whereas both 3-APPA and BPG have partial agonist/antagonist activity at cortical GABAB-receptors.