E. Manjarrez et al., Modulation of synaptic transmission from segmental afferents by spontaneous activity of dorsal horn spinal neurones in the cat, J PHYSL LON, 529(2), 2000, pp. 445-460
1. We examined, in the anaesthetised cat, the influence of the neuronal ens
embles producing spontaneous negative cord dorsum potentials (nCDPs) on seg
mental pathways mediating primary afferent depolarisation (PAD) of cutaneou
s 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 ge
neration of these potentials were located in the dorsal horn of lumbar segm
ents, in the same region of termination of low-threshold cutaneous afferent
s.
3. During the occurrence of spontaneous nCDPs, transmission from low-thresh
old 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. PD of Ia afferents was instead inhibited.
4. Monosynaptic reflexes of flexors and extensors were facilitated during t
he 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 an
d 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 concluded that the spontaneous nCDPs were produced by the activati
on of a population of dorsal horn neurones that shared the same functional
pathways and involved the same set of neurones as those responding monosyna
ptically to stimulation of large cutaneous afferents. The spontaneous activ
ity of these neurones was probably the main cause of the fluctuations of th
e monosynaptic reflexes observed under anaesthesia and could provide a dyna
mic linkage between segmental sensory and motor pathway.