Figure 2

Feed-forward inhibitory activity driven by SP through NK1 receptor activation. a, Effects of exogenously applied neuropeptides on IPSCs recorded in rat lamina V neurons. Neuropeptides tested include galanin (0.3 μM, n = 4), somatostatin (2 μM, n = 4), NPY (1 μM, n = 4), CGRP (0.5 μM, n = 5), and substance P (1 μM, n = 6). b, Antagonism of capsaicin-induced increases in inhibitory activity in rat lamina V neurons. Capsaicin was applied in the presence of neurokinin receptor antagonists APTL (10 μM, n = 5), L-733, 060 (2 μM, n = 4), L-732,138 (100 μM, n = 5), SB222200 (2 μM, n = 8), and the Gi/o protein blockers pertussis toxin (2 μg/ml, n = 4) and NEM (100 μM, n = 5). c, Antagonism of electrical stimulation-induced increases in inhibitory activity by the SP antagonist APTL (10 μM, n = 7). Recordings were from rat lamina V neurons. d, Effects of capsaicin and SP on IPSCs in NK1R^+/+ mice (n = 8 for capsaicin, n = 10 for SP) and NK1R^-/- mice (n = 21 for cap, n = 11 for SP). Experiments were performed in the presence of 3 mM kynurenic acid (a–d) or 20 μM CNQX plus 50 μM APV (some experiments in a&b). e, Images show a cultured GIN mice EGFP neuron (arrow indicated) before (left) and after loading the Ca²⁺ indicator Fluor-3 (middle), and following application of 100 nM SP (Right). The experiment was performed in the presence of 500 nM TTX and 3 mM kynurenic acid. Similar results were obtained from 22 EGFP neurons. f, The florescence image shows a spinal cord slice obtained from a GIN mouse. An EGFP neuron in lamina V is indicated by a small box and enlarged in a bigger box. g, Non-adaptive action potential firing induced by depolarizing current (50 pA) in the EGFP neuron. h, Application of 1 μM SP produced a prolonged depolarization and action potential firings (top) in the same cell. The dotted line (bottom) shows, at expanded scale, the membrane depolarization (action potentials are omitted for clarity). Kynurenic acid (3 mM) was present throughout the experiments (n = 7).