Synaptic Influences on Motoneurones of the Spinal Cord in Vertebrates
The mode of synaptic transmission between coupled spinal motoneurones and between primary somatic afferent fibres and motoneurones was studied in various vertebrate species. In frogs and carp the majority of interacting motoneurones were found to be coupled electrically. In lampreys, only electrotonic motoneuronal interactions were observed. In rats the interactions between motoneurones were found to be mostly mixed electrical and chemical ones. Direct monosynaptic control of motoneurones by the somatic primary afferents has been shown to occur in two aquatic species (lamprey, carp). Consequently, their mechanism does not depend on the presence of muscle spindles, which are absent in both species.
In the lamprey, carp and frog the transmission in these synapses is a bimodal electrical and chemical one.
Comparison between transmission modes in homologous rows of synapses reveals an evolutionary trend towards a decrease in the number of synapses exhibiting the electric mode of transmission.
KeywordsSpinal Cord Ringer Solution Primary Afferents Synaptic Interaction Rana Ridibunda
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