Activity of motoneurons during fictitious scratch reflex in the cat

Abstract

(1) Intracellular recording of motoneurons of different hindlimb muscles: tibialis anterior (TA), gastrocnemius and soleus (GS), vastus crureus (Vast), posterior biceps and semitendinosus (PBSt), was carried out during the fictitious scratch reflex in decerebrate cats. (2) During the postural stage of the reflex, a depolarizaiton (3.8 mV on average) was observed in TA motoneurons accompanied by tonic discharge. No change of the membrane potential (MP) and no discharge were observed during this stage in GS, Vast and PBSt motoneurons. (3) In the rhythmical stage of the reflex, the MP of TA motoneurons changed only slightly during the 'long' (L) phase of the scratch cycle and remained at approximately the same level as during the postural stage. In this phase, motoneurons discharged at frequencies of 20-100 pps. In the 'short' (S) phase of the scratch cycle a strong repolarization occurred, the MP reached the same level as observed during resting conditons (MP0), and the discharge discontinued. (4) GS motoneurons were gradually depolarized during the second half of the L-phase. The depolarization reached its maximum (5.5 mV on average in relation to the MP0) on average in relation to the MP0) in the S-phase, and several action potentials were generated with intervals of 5-10 msec. Then, at the beginning of the L-phase, the motoneurons were repolarized and the MP reached the level of the MP0. The behavior of Vast motoneurons was essentially similar to that of GS motoneurons. (5) The PBSt motoneurons usually had two peaks of depolarization per cycle--in the S-phase and at the beginning of the L-phase. The maximal depolarization was 3.5 mV (on average). The motoneurons generated action potentials at one or both peaks of depolarization. (6) The possible organization of the central influences upon motoneurons of different muscles during scratching is discussed.