Figure 4.

Ghrelin decreases the firing rate of TH-EGFP neurons as well as ST-stimulated APs. A, Representative trace from a current-clamp experiment showing the firing rate of a TH-EGFP neuron. Bath application of ghrelin (100 nm) significantly reduced the basal firing rate of five of six TH-EGFP neurons. Ghrelin also hyperpolarized three of six neurons (average effect, 6.8 ± 1.3 mV), including the example shown here. The effect was partially reversed after a wash (n = 5). Action potentials were truncated at +10 mV. The arrow denotes where evoked APs were tested. B, Representative traces in current clamp after a train of five stimulations given to the ST at 0.2 Hz, each stimulation is indicated by a gray circle. Under control conditions, the majority of trains resulted in an AP [I–O ratio, 0.87 ± 0.13 (n = 11)]. In the presence of ghrelin, stimulation of the ST failed to evoke an AP most of the time (I–O ratio was reduced in 7 of 11 neurons to 0.38 ± 0.14). This effect was partially reversed after wash (I–O ratio, 0.66 ± 0.12). C, Average I–O ratio or success rate of the ST stimulation resulting in an AP under control conditions (ACSF), 100 nm ghrelin, and after a 10 min wash (n = 7). *p < 0.01 versus control (ACSF); ^#p < 0.01 versus control and ghrelin. D, Average firing rate of TH-EGFP neurons in control (ACSF), 20 μm NBQX and NBQX plus 100 nm ghrelin. *p < 0.01 versus control (ACSF) (n = 7). Ghrelin did not hyperpolarize any neurons in the presence of NBQX. Error bars indicate SEM.