NA+, K+-ATPASE ACTIVITY IN YOUNG CHICKS AFTER TASTE STIMULATION

The activity of specific ouabain-sensitive Na+,K+-ATPase was studied in crude membrane fraction of the brain of 1- to 3-day-old chicks after the administration of a chemical aversant methylanthranilate (MeA), shown in previous behavioral studies to induce avoidance of pecking of an otherwise attractive stimulus. Enzyme activity was dramatically decreased (by 40-50%) in the time interval between 10 min-2 h after MeA administration onto the tongue of awake chicks. It was possible to localize these changes in Na+,K+-ATPase activity into forebrain structures contained within the dorsal ventricular ridge comprising the hyperstriatum accessorium (HA), hyperstriatum ventrale (HV), hyperstriatum dorsale (HD), and parts of neostriatum (N). In contrast, Na+,K+-ATPase activity in the ectostriatum (E), the medial neostriatum (NM), and the paleostriatal complex were unaffected. Results from experiments involving preincubation of membrane fractions and with partial purification using detergents, suggest that some substances with inhibitory effects were produced under the effect of MeA and bound to membrane fractions in their respective areas. A similar decrease of Na+,K+-ATPase activity as after MeA administration in vivo was observed when inhibitory mediators (GABA, glycine) were added to membrane fractions in vitro. These findings may have implications for memory processing in chicks following aversive learning using MeA as the aversant.