Inhibitory miniature synaptic potentials in rat motoneurons

Abstract

In the newborn rat spinal cord, spontaneous potentials were recorded, with KCl electrodes, from motoneurons in the presence of tetrodotoxin (10$^{-6}$ g ml$^{-1}$) to abolish nerve impulses. These potentials occurred at low frequencies (< 2 Hz), and their mean amplitude was a fraction of 1 m V An increase of osmolarity with sucrose or an increase of extracellular K$^{+}$, increased the frequency of miniature synaptic potentials. The amplitude of the spontaneous potentials was increased by intracellular injection of Cl$^{-}$. Strychnine (2-25 $\mu $M) completely abolished the spontaneous potentials. It is suggested that these potentials are produced by the spontaneous release of packages of inhibitory transmitter at synapses on motoneurons.