Participation of the GABA B receptors in presynaptic inhibition of the spinal cord descending projections fibers in the frog Rana ridibunda

(-)-Baclophen was found to depress in a dose-dependent and reversible way the excitatory post-synaptic potentials (EPSPS) of motor neurons and the ventral root potentials evoked by stimulation of fibres of the ipsi- and contralateral ventral columns. The (-)-baclophen depressing effect could be eliminated with saclophen. Picrotoxin eliminated the depressing effect of the GABA on the descending EPSPS. Depressing effects of (-)-baclophen and GABA upon the ventral root potentials were also shown. The data obtained in pharmacological analysis corroborate to a certain extent existence of the GABAB receptor presynaptic inhibition in descending fibres monosynaptically corrected with the spinal cord motor neurons in the frog Rana ridibunda.