The effects of passive avoidance learning on the release of amino acids and other putative transmitters in the forebrain of the day-old chick

Abstract

The time course of release of amino add transmitters was examined in slices of IMHV and LPO from day-old chicks that had completed a one-trial passive avoidance learning task. Amino adds released into an incubation medium were measured using FITC-derivatisation followed by an adaptation of a published method for HPLC analysis. One hour after training chicks to avoid a bead covered with the a versant methylanthranilate (MeA), there was an increase in the Ca2+-dependent release of glutamate, aspartate and GABA from slices of left IMHV compared to chicks trained to peck a similar bead covered in water. Thirty minutes after training glutamate only was increased in MeA-chicks, but from both IMHVs. Glutamate was also increased at 3 and 6.5 hours in the right IMHV as was GABA (6.5 hours) and aspartate (3 hours). Both left and right LPOs of MeA-trained chicks showed increased GABA and glutamate release ac 3, 6.5 and 24 hours. The left only showed enhanced release of both at 30 minutes. The release of the neuromodulator adenosine was found to be increased in the IMHV of MeA-trained chicks simultaneous to the increases in glutamate. The adenosine agonist CHA inhibited glutamate release: its actions blocked by the antagonist CPT. An agonist for the excitatory adenosine receptor increased glutamate, but decreased GABA, release according to concentration applied. Pre-training injections of adenosine agonists produced amnesia 30 minutes after training: these effects were lateralised such that injections into the left hemisphere only produced amnesia, those into the right did not. These results demonstrate for the first time increases in amino acid transmitters associated with passive avoidance training, and suggest a role for adenosine modulation of these transmitters.