Synaptic organization of dorsal root projections to lumbar motoneurons in the clawed toad (Xenopus laevis).

Synaptic connexions between dorsal root primary afferents and lumbar motoneurons have been investigated in the isolated spinal cord of the clawed toad. The study of monosynaptic actions evoked in motoneurons by 9th or 10th dorsal root stimulation or by impulses in single primary afferents provided evidence for both electrical and chemical junctional transmission at the sensory-motor synapses. The anterograde filling of the 9th and 10th dorsal roots with horseradish peroxidase (HRP) shows that afferents do project to the motoneuron field of the segments IX and X.

Tracing of frog sensory-motor synapses by intracellular injection of horseradish peroxidase.

Monosynaptically connected primary afferent fibres and motoneurones of the isolated spinal cord of the frog were injected with horseradish peroxidase (HRP). Six labelled afferent fibre-motoneurone pairs were reconstructed and subjected to detailed analysis. Frog motoneurones possess eight to twelve dendritic arrays displaying some dorso-ventral asymmetry.

Relation between structural and release parameters at the frog sensory-motor synapse.

The sensory-motor synaptic connexions in the frog lumbar cord have been used to examine the relationship between the statistical characteristics of the unitary excitatory post-synaptic potential (e.p.s.

Synaptic connexions between primary afferents and thoracic motoneurones in the frog.

Synaptic actions were evoked in thoracic motoneurones of the isolated frog spinal cord by 6th or 7th dorsal root volleys or impulses in single primary afferents. In a few cases the impaled motoneurones or the whole dorsal root were filled with horseradish peroxidase. Although HRP labelling has revealed that motoneurones have extensive dendritic arborizations extending into the dorsal horn, the zone in which thoracic dorsal root afferents terminate, there is no positive evidence for a direct link between them.