Spinal interneurones involved in presynaptic controls of supraspinal origin†

Abstract

SUMMARY1. Interneurones presenting heterotopic and heterosensory convergence have been identified in laminae VI-VII of the lumbar dorsal horn in the cat. Stimulation of the hind limbs sometimes induced a bimodal response, but we considered only the late convergent discharge.2. The fact that response latencies are longer to hind limb than to forelimb stimulation at this level suggests the intervention of a supraspinal loop in the activation of spinal convergent units. This hypothesis is supported by the relationship between the excitability of supraspinal structures and the discharge intensity of convergent cells as well as by the absence of long latency responses in the spinal preparation.3. Electrophysiological and pharmacological evidence discloses a strong relationship between convergent unit discharges and the occurrence of dorsal root potentials to cortical, heterosegmental and heterosensory stimulation.4. It is suggested that convergent units receive information of supraspinal origin and exert control over sensory input to the cord via primary afferent depolarization.

Central nuclei and spinal pathways in feedback inhibitory spinal cord potentials in ketamine-anaesthetized rats

“…This finding supports data from our previous studies that the latencies of HSP are variable in intact rats even during ketamine anaesthesia [2] and divided into two groups in conscious human subjects [5]. Previous studies in cats [26][27][28][29][30][31] demonstrated that primary afferent depolarization (PAD) could be evoked by stimulation of several CNS structures. These findings support the fourth mechanism proposed above that the principal nuclei involved in HSP production might be situated in the medulla but be influenced by other higher CNS structures.…”

Evoked Spinal Cord Potentials

“…The differences in the central latencies of the descending N and P waves from those of the segmental N1 and P2 waves are reminiscent of the animal studies (Besson and Rivot, 1973;Hongo et al, 1966;Menétrey et al, 1980;Skinner and Willis, 1970). Experiments with cats have shown that interneuronal populations are activated monosynaptically from different descending pathways.…”

“…Thus, the interneurons producing the descending N wave may differ for the most part from those producing the segmental N1 wave, but some interneurons show convergence of the descending and segmental volleys (Besson and Rivot, 1973;Kostyuk and Vasilenko, 1979;Tobita et al, 2003). The degree of convergence of the descending and segmental volleys on the primary afferent terminals might be increased, since the descending P and segmental P2 waves interact more than the descending N and segmental N1 waves (Fig.…”