Polysynaptic neural pathways from low threshold trunk cutaneous afferents to tail motoneurons in the spinalized cat

Postsynaptic potentials (PSPs) after stimulating the cutaneous nerves of the trunk, dorsal cutaneous nerve (DC) and ventral cutaneous nerve (VC) were recorded from alpha-motoneurons innervating two tail muscles, the m. extensor caudae lateralis (ECL) and m. flexor caudae longus (FCL) in 22 spinalized (T10) cats. Stable recordings were obtained from 33 ECL and 42 FCL motoneurons. Stimulation of cutaneous nerves at 1.5-5 times threshold typically produced three types of synaptic effects in ECL and FCL motoneurons: predominant excitation (EPSP), or predominant inhibition (IPSP), or mixed effects characterized chiefly by early excitation followed by inhibition (EPSP/IPSP). The average central latencies of PSPs were distributed over a wide range (4.5-15.6 ms). Latency measurements indicated that most neural circuits from the trunk cutaneous afferents to the tail muscle motoneurons were oligosynaptic pathways via intraspinal slow-conducting fibers or polysynaptic pathways.