Passive Avoidance Learning Results in Region-Specific Changes in Concentration of and Incorporation into Colchicine-Binding Proteins in the Chick Forebrain

Abstract: Incorporation of ¹⁴T]leucine into trichloracetic acid-precipitable material and tubulin-enriched fractions, and total tubulin levels as determined by colchicine-binding activity and retention on DE81 filter discs, were measured in various regions of the chick brain following training on a one-trial passive avoidance task, suppression of pecking at a chromed bead as a consequence of the aversive taste of methylanthranilate. Radioactive pulse time was 0.5 h. The only brain region in which changes were found was the anterior forebrain roof, the same area in which biochemical changes in response to exposure of the birds to an imprinting stimulus have been observed previously. In the anterior forebrain roof the changes observed as a consequence of training were detectable at 0.5 and 24 h after the 10-s training experience but not 48 h subsequently. One-half hour after training, there were increases of the order of 20 or 30% in ¹⁴T]leucine incorporation into particulate and postmitochondrial TCA-precipitable material and a tubulin-enriched fraction purified as above. There were comparable increases in the total amount of colchicine-binding activity. By 48 h, none of these increases were detectable. Subcellular fractionation of the particulate fraction showed that most of the increase of incorporation into the tubulin-enriched fraction and in colchicine-binding activity was present in the soluble content of the synaptosomes; there were no increases in either measure in the synaptic membrane fraction. The possible role of changed levels and turnover of tubulin in the plastic responses of the brain to learning experiences is discussed.