[Electrotonic and chemical EPSPs in lamprey motor neurons following stimulation of the descending tract and posterior root afferents].

In experiments carried out on the isolated spinal cord of the lamprey (Lampetra fluviatilis) post-synaptic responses produced in spinal motoneurons by stimulation of the descending tract and dorsal roots were investigated by means of the intracellular recording technique. It is found that, in addition to giant reticulospinal (Müller's) axons, many other descending fibres as well as dorsal root afferents establish synaptic linkage with both chemical and electrical mode of transmission as revealed by their sensitivity to calcium-deficient and magnesium-rich perfusing solutions. Complex electrotonic EPSPs could have a very fast time course characteristic for the elementary responses but could also produce slow depolarization of the post-synaptic membrane, thus suggesting an integrative function of electrical synapses.