DEVELOPMENT OF SPONTANEOUS SYNAPTIC ACTIVITY IN CULTURE OF THE CHICK SPINAL-CORD NEURONS

Spontaneous postsynaptic currents in chick spinal cord neurons cultured for up to three weeks were recorded by using standard whole-cell patch-clamp techniques. Beginning with approximately the 7th to 14th day in vitro, giant postsynaptic currents, mediated presumably by glycine, were single synaptic events (inhibitory postsynaptic currents). After the 14th day in vitro excitatory postsynaptic currents appeared. Both types of currents were predominantly arranged in bursts. This pattern of synaptic activity did not change appreciably during further cultivation. Characteristics of inhibitory postsynaptic currents were studied. Decay of the majority of giant inhibitory postsynaptic currents was two-exponential. Time-constants of the decay (fast and slow) increased with depolarization and decreased with increasing temperature. Decay of miniature inhibitory postsynaptic currents was single exponential and did not depend on the membrane potential. Strychnine at concentrations of 1-2 muM was found not only to reduce the amplitude of giant inhibitory postsynaptic currents but also to prolong their decay. The time-constant of the slow component of the decay was mostly affected during the inhibitor action. Repeated binding of glycine to postsynaptic receptors due to a large presynaptic release is proposed as an explanation for the properties of giant inhibitory postsynaptic currents decay. Correlations between the development of synaptic networks under in vivo and in vitro conditions are discussed.