Topographic sensitivity of cat spinal motoneurones to iontophoretically applied l-glutamate and glycine.

1. The effects of micro-iontophoretically applied L-glutamate (GLU) and glycine (GLY) were studied by recording intracellularly from cat motoneurones in the 6th and 7th lumbar segments. 2. Applications of GLU and GLY were performed at varying distances (80-350 micrometers: "somatic" or "dendritic" applications) from the probable intrasomatic location of the recording tip. 3. "Somatic" applications of GLU caused a depolarization and a progressive increase in the membrane conductance. Applications of GLY caused a hyperpolarization and a marked increase in conductance associated with a decrease of postsynaptic transients. 4. "Dendritic" applications of GLU led to a depolarization after a significantly shorter delay than applications to more "somatic" sites. On the contrary, the onset latency of GLY induced hyperpolarisations was longer for "dendritic" than for "somatic" applications. 5. These results give evidence in favour of different preferential localizations of GLU and GLY receptive sites on spinal motoneurones.