Figure 6. Lowering of extracellular pH or application of somatostatin reduces the locomotor rhythm.

(a) Illustration of arrangement for ventral root recordings with suction electrodes in the intact, isolated spinal cord preparation (VR-L, VR-R, left and right side ventral root, respectively). (b) Bilateral ventral root recording during NMDA (100 μM)-induced fictive locomotion in the isolated lamprey spinal cord, during control conditions (pH 7.4; black traces) and during lowered pH of 6.9 (red traces) and 6.5 (orange traces). (c) Decreases in extracellular pH prolonged the cycle period. The mean period was determined during 20 cycles for each of the conditions and normalized to the value during control conditions (% of control; n=7). (d) Bilateral ventral root recording during control conditions (pH 7.4; black traces), during pH 6.9 (red traces) and in the presence of the ASIC3 blocker APETx2 (1 μM; blue traces). (e) Application of APETx2 blocked the effect of lowered extracellular pH (6.9) on the cycle period, which recovered upon washout (mean values calculated for 20 cycles during each condition; n=2 preparations). (f) Effect of somatostatin (10 nM, 100 nM and 1μΜ) on the cycle period of the locomotor activity. Somatostatin significantly increased the period at all tested concentrations (n=19). (g) Bilateral ventral root recording in the isolated spinal cord, during control conditions (pH 7.4; black traces), during pH 6.5 (orange traces) and following application of the somatostatin receptor sst₂ antagonist CYN-154806 (2 μM; green traces). (h) Application of CYN-154806 lead to a shortening of the period length at control pH 7.4 (dark green; n=4). In the presence of the antagonist, a decrease of pH (here to 6.5; light green) had no effect on the cycle period. The data are represented as means±s.e.m. (c,f,h) and ±s.d. (e); Student's t-test: ***P<0.001; **P<0.01, significant difference compared with control; NS: non-significant, ^NSP>0.5.