Fig. 1. Effect of kynurenic acid on sustained excitation of the retzius cell following cell tr1 stimulation. Control: In normal physiological saline, brief depolarization of cell Tr1 results in a sustained excitation of the Retzius cell and an increase in dorsal posterior (DP) nerve activity. Kynurenic acid: Exposure of the nerve cord to saline containing 100 mM kynurenic acid results in elimination of the cell Tr1-induced response in the Retzius cell. The dashed line indicates the resting membrane potential in this and other figures. The tops of Retzius cell action potentials were clipped to enhance the membrane potential changes in response to cell Tr1 stimulation. In this and subsequent figures, the number in parentheses denotes the mid-body ganglion in which the soma or nerve root is located; R refers to the (rostral) neuromere in the subesophageal ganglion. CALIBRATION: 12 mV (Retzius cell) and 20 mV (cell Tr1), 500 ms.