Excitatory postsynaptic currents in response to different synaptic inputs of frog spinal motoneurons.
Excitatory postsynaptic currents (EPSCs) evoked by the primary afferents (dorsal root; DR) and the descending lateral column (LC) fibers were studied in frog spinal motoneurons under voltage clamp with two separate electrodes. The average rise time and half-width of the EPSCs were shorter for LC-EPSCs than for DR-EPSCs, though the values of the parameters for LC- and DR-EPSCs were distributed within a similar range. The relation between the amplitudes of the EPSP and EPSC was almost linear. The amount of current required to generate a 1 mV increment in the EPSP was 5.0 +/- 2.3 nA for the DR-EPSC and 3.8 +/- 1.2 nA for the LC-EPSC. The decay time was shortened by hyperpolarization and prolonged by depolarization in DR- and LC-EPSCs and spontaneous EPSCs. The reversal potential ranged from -30 to -5 mV and was almost identical for DR- and LC-EPSCs and spontaneous EPSCs in individual motoneurons. The current-voltage relation was linear from -100 to +50 mV for these EPSCs. Spontaneous EPSCs became more prominent and frequent during a large hyperpolarization or a large depolarization. These results suggest that the ionic mechanisms underlying EPSC are similar for the functionally different excitatory synapses located on motoneurons.
Kuno
M
M
Department of Physiology, Osaka City University Medical School, Japan.
Yasunami
T
T
Matsuura
S
S
D000200:Action Potentials; D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009046:Motor Neurons / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D011892:Rana catesbeiana; D013116:Spinal Cord / Q000502:physiology*