Fig. 4. Changes in glutamate (A) and GABA (B,C) immunoreactivity in the brainstem of the epaulette shark in response to hypoxic exposure. In A, the only statistically significant difference between the hypoxic (left) and control (right) animal occurred in the median longitudinal fasciculus (mlf), otherwise glutamate homeostasis was maintained, including the fasciculus of Steida (fSt). In B,C, a statistically significant increase in GABA immunoreactivity was observed in hypoxia (B) compared with normoxia (C) over the entire coronal section, and small GABAergic neurons were only evident in the mlf of animals exposed to hypoxia.