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In immobilized intercollicularly decerebrated cats tonic underthreshold activation of the spinal scratching generator (after application of tubocurarine or bicuculline on C1-C2 segments) is accompanied by an increase in primary different terminal depolarization, decrease in N1-component of cord dorsum potential evoked by stimulation of cutaneous afferents, decrease in the amplitude of DRP and early polysynaptic responses of motoneurons evoked by stimulation of cutaneous and muscle afferents; a respective rise and reduction in activity of intermediate nucleus interneurons which are mono- and di (oligo)-synaptically connected with afferent terminals. Spinalization of animal led to reverse changes. Injection of DOPA into spinal animals allowed comparing changes in the state of lumbar segmental apparatus during tonic underthreshold activation of spinal scratching and locomotor generators.

It is shown that the state of the segmental apparatus of the lumbal spinal cord of immobilized intercollicularly decerebrated cats during formation of a scratching generator is essentially different from that of a spinal animal. The excitability of "aiming" and "scratching" motoneurons increases, recurrent and reciprocal Ia inhibition of motoneurons becomes stronger and influence of Ib afferents weaker. The flexor reflex afferents exert inhibitory influences on "aiming" motoneurons. After spinalization these influences become excitatory, and the inhibitory influences on "scratching" motoneurons become weaker. The functional role of described changes is discussed.