Figure 1.

Impact of locomotor-related synaptic signaling on τ_in. (A) Intracellular tight-seal voltage recording (upper trace) from a rhythmically active interneuron in the isolated neonatal rat spinal cord during 5-HT- and NMDA-induced locomotor-related activity. No holding current was applied. The motoneuron activity was recorded from the ventral roots (lower trace). (A1) With the neuron hyperpolarized just below spike threshold, the charging time constant (τ_in), measured from the average of the voltage response to 25 hyperpolarizing current steps (−20 pA), was 65 ms. SEM is added as a dotted line. (B) Seven minutes after bath application of TTX, the synaptic currents and the root activity disappeared. (B1) The average τ_in of the voltage response was now 80 ms (same size current injection). (C) With the cell hyperpolarized to −65 mV the voltage responses to depolarizing and hyperpolarizing current steps (±20 pA) showed τ_in of 56 and 58 ms before (thin lines) and 76 and 73 ms after (thick lines) TTX application. (D) τ_in of the voltage responses in A1, B1, and C can be better evaluated as the negative slope on a semilogarithmic plot. Thin lines before and thick lines after TTX application.