c-Fos expression in seawater control (0 ppb, white bars), low (75 ppb, light gray), and high (150 ppb, dark gray) saxitoxin (STX) exposed killifish brains (N = 6, data are means ± S.E.). Ant. Telen., anterior telencephalon; Post. Telen., posterior telencephalon; Ant. Optic, anterior optic lobe; Post. Optic, posterior optic lobe; Midbrain, midbrain tegmentum; and Brainstem, rhombencephalon. The y-axis is percentage of c-Fos expression per area (mm2). Dose dependant significant decreases in c-Fos expression occurred in the Ant. Optic and Post. Optic regions (**p = 0.01 and ***p = 0.001, respectively).