Fig. 7. Serotonin increases resting muscle tension most strongly at the coldest temperatures. (A) Bath temperature recorded as a function of time illustrating the change from 2°C to 22°C and back to 2°C before and during application of 50 nmol l^–1 5-HT (hatched bar). (B) Resting muscle tension in the same preparation recorded at temperatures indicated in A. (C) Muscle tension (mean ± s.e.m.) recorded at 2°C and 22°C in the absence and presence (hatched bar) of 5-HT (50 nmol l^–1) in the same seven preparations. Values for P (paired t-test) are indicated by horizontal brackets. The break in the x-axis indicates the distinction between the first temperature warming protocol and the second.