TIME-DEPENDENT INCREASE IN RELEASE OF ARACHIDONIC-ACID FOLLOWING PASSIVE-AVOIDANCE TRAINING IN THE DAY-OLD CHICK

We have investigated the role of arachidonic acid, a putative retrogra de messenger, in a one-trial aversive learning task in the day-old chi ck. The left and right intermediate medial hyperstriatum ventrale (IMH V) in the chick forebrain have previously been implicated in the forma tion of memory for this task. Using an ex vivo technique we have deter mined the concentrations of various fatty acids liberated from prisms prepared from these brain regions at different time points up to 24 h following passive avoidance training. At 30, 60, and 75 min posttraini ng the concentration of arachidonic acid, but not of other fatty acids , in prisms prepared from the left IMHV, but not the right IMHV, was e nhanced compared with that in chicks trained on a nonaversive water-co ated bead. To test whether arachidonic acid liberation from the left I MHV was receptor-stimulated we showed that (a) liberation of endogenou s arachidonic acid from homogenate prepared from the left and right IM HV of untrained chicks was stimulated by depolarization with KCI (50 m M) and that (b) glutamate agonists of the NMDA and metabotropic subtyp es of glutamate receptor stimulated release of preloaded [C-14]arachid onic acid from prisms prepared from the left IMHV but not the right IM HV. These results indicate that arachidonic acid is liberated from the left IMHV following passive avoidance training in the day-old chick a nd may play a role as a retrograde messenger in this memory task.