No abstract

Rudomin et al. (1987Rudomin et al. ( , 1990 used spike triggered averaging of dorsal root and ventral root potentials to disclose possible connections of intermediate nucleus interneurones with afferent fibres andÏor spinal motoneurones. They found one set of interneurones (class I) whose spontaneous activity was associated with short-latency glycinergic inhibitory potentials in motoneurones as well as in the ventral roots (iVRPs), which were produced without concurrent dorsal root potentials (DRPs). These inhibitory neurones had collaterals to Clarke's column and appeared to be the same as those mediating non-reciprocal postsynaptic inhibition of Ib origin (Harrison & Jankowska, 1985). The activity of the second set of interneurones (class II) was instead associated with the generation of short-latency DRPs and iVRPs. It was suggested that these were GABAergic interneurones directly connected with the intraspinal terminals of group I muscle afferents and spinal motoneurones, where they produced PAD and postsynaptic inhibition, respectively (Rudomin et al. 1987(Rudomin et al. , 1990. The spontaneous activity of class I and class II interneurones usually appeared in synchrony with a negative cord dorsum potential lasting 40-60 ms that was initiated 20-30 ms before the interneuronal action potentials. It was assumed that this cord dorsum potential was generated by the spontaneous activity of a population of neurones located in the most superficial regions of the spinal cord. It was not clear, however, if these were 'command' interneurones modulating transmission along the pathways Journal of Physiology (2000) 1. We examined, in the anaesthetised cat, the influence of the neuronal ensembles producing spontaneous negative cord dorsum potentials (nCDPs) on segmental pathways mediating primary afferent depolarisation (PAD) of cutaneous and group I muscle afferents and on Ia monosynaptic activation of spinal motoneurones. 2. The intraspinal distribution of the field potentials associated with the spontaneous nCDPs indicated that the neuronal ensembles involved in the generation of these potentials were located in the dorsal horn of lumbar segments, in the same region of termination of lowthreshold cutaneous afferents. 3. During the occurrence of spontaneous nCDPs, transmission from low-threshold cutaneous afferents to second order neurones in laminae III-VI, as well as transmission along pathways mediating PAD of cutaneous and Ib afferents, was facilitated. PAD of Ia afferents was instead inhibited. 4. Monosynaptic reflexes of flexors and extensors were facilitated during the spontaneous nCDPs. The magnitude of the facilitation was proportional to the amplitude of the 'conditioning' spontaneous nCDPs. This led to a high positive correlation between amplitude fluctuations of spontaneous nCDPs and fluctuations of monosynaptic reflexes. 5. Stimulation of low-threshold cutaneous afferents transiently reduced the probability of occurrence of spontaneous nCDPs as well as the fluctuations of monosynaptic reflexes. 6. It is c...

No abstract