The property of peripheral input of projection neurons in the spinal cord dorsal horn

Antidromic and orthodromic responses of the projection neurons in the dorsal horn of the spinal cord have been recorded by a glass microelectrode in anesthetized and paralyzed cats. Furthermore, the effect of cervical segment antidromic stimulation to orthodromic response of the projection neurons has been observed by way of conditioning-test stimulation. Among all the spinocervical tract neurons (SCT), the dorsal column postsynaptic neurons (DCPS) and the spinocervical tract-dorsal column postsynaptic neurons (SCT-DCPS), which were identified by cervical segment antidromic stimulation, 46% are low-threshold mechanoreceptive (LTM) and 54% are wide-dynamic-range (WDR) neurons. Most LTM neurons can evoke the same response to both 10 times (10 T) and 50 times (50 T) the threshold stimulation on the peroneal nerve. Most WDR neurons to 50 T intensity stimulation are stronger than the 10 T stimulation. Under the antidromic-cervical segment conditioning stimulation, the amount of orthodromic-discharging in most WDR and few LTM neurons reduced significantly. The result shows that both LTM and WDR projection neurons in the spinal cord can respond to all peripheral A beta fibers and part of the A delta fibers; there are some inhibitional descending fibers which affect the projection neurons in the cervical segment dorsal column and dorsolateral funiculi.