[Suppression of the dorsal root potentials of the cat spinal cord by manganese and cobalt ions].

In anesthetized spinal cats, perfusion of lumbosacral spinal cord with artificial CSF containing manganese (1.5-3.0 Mm/l) or cobalt (6.0 mM/l) ions, led to reversible suppression of negative dorsal root potentials (DRP), induced by stimulation of ipsilateral hindlimbs' afferent nerves. The depression of the DRP proceeded in connection with the depression of presynaptic inhibition of extensor monosynaptic reflexes induced with impulse volleys in the group I flexor muscle afferents. The depression of inhibition was not associated with changes in amplitudes of testing monosynaptic reflexes. The DRP is concluded to have a synaptic origin.