Study of paired-pulse inhibition of transcallosal response in the pyramidal tract neuron in vivo

The effects of a specific GABA(B) receptor antagonist, p-(3-aminopropyl)-p-diethoxymethyl-phosphonic acid (CGP 35348), on pyramidal tract neuron responses to transcallosal stimulation were investigated in the cat motor cortex in vivo. The paired-pulse method was used to obtain more insight into the role of GABA(B) receptors. At a 200-ms inter-stimulus interval the spike response was inhibited in 75% of the neurons. There was an approximately 40% depression of the mean spike value in the control. CGP 35348 reduced paired-pulse inhibition, while (-)-baclofen increased it. Stronger drug effects on the second stimulation-induced response possibly indicate their presynaptic action on GABA(B) receptors.