Fig. 1. Helisoma buccal neuron B5 is inhibited by glutamate and low concentrations of kainite (KA). (A) Diagram of the buccal ganglia showing the bilateral location of left and right (shaded in grey) B5 neuron cell bodies (adapted from Quinlan et al., 1995). (B) A right B5 neuron was injected with Lucifer Yellow. Its main axon extends out through the ipsilateral esophageal trunk. Fine processes extending from the cell body are occluded by the brightness of the cell body staining. Fluorescence image is layered on a DIC image of the same field (see Materials and methods). Scale bar, 100 µm. (C) Glutamate (Glu) dose-dependently reduced action potential (AP) frequency in a B5 neuron. Membrane potential was measured using standard intracellular recording techniques. Glutamate was perfused during the times indicated by the horizontal bars. Arrowhead indicates 0 mV. (D) Dose-dependent reduction by glutamate of mean (±s.e.m.) AP frequency (^*P<0.05, N=5). (E) KA (10 µmol l^–1) appeared to reduce the AP frequency in a B5 neuron. The effect was blocked by 50 µmol l^–1 CNQX. Drugs were perfused during the times indicated by the horizontal bars. Arrowhead indicates 0 mV. (F) Mean (±s.e.m.) AP frequency of B5 neurons (N=9) during perfusion of KA (10 and 30 µmol l^–1) and/or 50 µmol l^–1 CNQX. ANOVA indicated a significant effect of 10 µmol l^–1 KA, 50 µmol l^–1 CNQX and the combined KA/CNQX. The increase in AP frequency with 30 µmol l^–1 KA was not significant, whereas the decrease in frequency with 10 µmol l^–1 KA was significantly different from control (^*P<0.05, t-test, N=9). ET, esophageal trunk; LBN, lateral buccal nerve; VBN, ventral buccal nerve; CBC, cerebrobuccal connective.