Fig. 2: Isoeugenol affects the action potential of a central neuron only at high concentration.

a Example of an action potential (AP) recorded in the Mauthner neuron (MN) to illustrate the measurements taken. b In fish anesthetized with isoeugenol at the concentration of 10 mg L⁻¹ (n = 25; red circles indicate individual fish) no effect was seen on the AP, i.e., all values were not significantly different from those determined in control fish anesthetized with 2-PE [400 mg L⁻¹] (n = 20; blue circles). Means ± standard errors of mean are indicated. c–e Dotted vertical lines indicate moment of change to higher concentration at time = 0 min. Connected circles indicate mean values in individuals. c No significant changes after increase in isoeugenol concentration from 10 to 20 mg L⁻¹ (n = 7 fish). d, e At 40 (n = 7 fish) and 60 mg L⁻¹ (n = 5 fish), the slope of the AP decreased slightly within 10–30 min after increasing dose. At 60 mg L⁻¹, peak amplitude, I₁ and the duration of the AP were also affected. Effects also took more than 10 min to occur. Red asterisks highlight significant differences between values at baseline concentration (Pre; red circles) and values obtained 90 min after the increase in concentration (orange-filled circles). Violet hashtags indicate significant differences between values obtained 90 min after dose increase (orange-filled circles) and values determined also after dose increase but earlier (black-outlined circles). One, two, three symbols indicate P ≤ 0.05, P ≤ 0.01, or P ≤ 0.001, respectively.