Figure 3.

The depolarizing actions of CCK on layer 6b neurons are mediated through CCK_B receptors. A: In a representative neuron, CCK8S depolarizes the membrane in a reversible manner (Ai). Subsequent application of CCK8S at a 30 minute interval results in a smaller depolarization (Aii). The reduction in the amplitude of the second response was consistent across neurons. The average ratio of the second to the first amplitude was 51 ± 8% (n=9; Aiii). B: The depolarizing actions of CCK8S were not blocked in the presence of CCK_A antagonist (L364718, 1 μM). Following the first CCK8S application, L364718 was then bath applied. Following 30 minute interval, and in the presence of L364718, CCK8S was then reapplied and the response to second application was 53 ± 5% (n=5) of the initial response. C: In a different neuron, the depolarizing actions of CCK8S were completely attenuated in the presence of CCK_B antagonist L365260 (1 μM). The ratio between first and second response was significantly attenuated. The average ratio of the second to the first amplitude was 22 ± 5% (n=6). D: The regression lines of the second response amplitude relative to the first response amplitude show the antagonist effects clearly. The slopes of control, CCK_A antagonist, and CCK_B antagonist were 0.62, 0.55, and −0.03. The slope of CCK_B antagonist was significantly smaller than those of control and CCK_A antagonist. The dashed line indicates the slope of 1. All experiments were done in TTX.