Polysynaptic neuronal pathways from tail cutaneous afferents to hindlimb motoneurons in the spinalized cat.

Postsynaptic potentials (PSPs) were recorded in motoneurons innervating the m. posterior biceps and semitendinosus (PBSt-MN) and m. triceps surae (GS-MN) in 19 spinalized adult cats, after electrical stimulation of the dorsal and ventral tail cutaneous nerves (TDC and TVC). With stimulation at 1,5-5 time threshold, inhibitory PSPs (IPSPs), excitatory PSPs (EPSPs), and mixed PSPs (IPSP/EPSPs, EPSP/IPSPs) were recorded in approximately 90% of PBSt-MN and 70% of GS-MN. IPSPs (IPSPs, IPSP/EPSPs) after stimulation of the contralateral TVC and TDC were observed in 54% and 52% of PBSt motoneurons, respectively. EPSPs (EPSP, EPSP/IPSPs) were recorded after stimulation of ipsilateral TVC in 56% of PBSt motoneurons. IPSPs produced after stimulation of ipsilateral TDC and TVC were observed in 65% and 63%, respectively, of GS-MN showing PSPs after stimulation of tail cutaneous nerves. Measurement of segmental latencies of the earliest PSPs (PBSt-MN, IPSPs: 2.1-7.4 ms, EPSPs: 3.1-18.9 ms, GS-MN, IPSPs: 2.5-17.1 ms, EPSPs: 4.2-19.4 ms) suggested that most of the neural pathways from tail cutaneous afferents to hindlimb motoneurons are at least trisynaptic in the L7 spinal segments. Hemisection of spinal cord at S1-S2 indicated that neural pathways from both the ipsilateral and contralateral low threshold cutaneous afferents pass through the ipsilateral spinal cord at S1-S2. The neural pathways from tail cutaneous afferents to hindlimb motoneurons to maintain the balance of the pelvic girdle were discussed.