CLATHRIN PROTEINS AND RECOGNITION MEMORY

Strong converging evidence indicates thar the intermediate and medial part of the hyperstriatum ventrale (IMHV) of the chick forebrain is a site of recognition memory for the learning process of imprinting. Cla thrin proteins have been implicated in synaptic plasticity. In the pre sent study we demonstrate for the first time that they are involved in vertebrate learning, Chicks were trained by exposure to a conspicuous object and their preference for it versus a novel object subsequently measured as a preference score (an index of learning). Trained chicks with low preference scores were classed as ''poor learners'' and thos e with high preference scores as ''good learners''. An additional grou p of chicks was untrained (''dark-reared''). Tissue was removed from t he left and right IMHV, hyperstriatum accessorium and posterior neostr iatum 9.5 h or 24 h after training. Clathrin heavy chain and clathrin light chains a and b were assayed using sodium dodecyl sulphate-polyac rylamide gel electrophoresis and immunoblotting. In the IMHV, and only for clathrin heavy chain, was there a significant effect of training. The effect occurred 24 h bur not 9.5 h after training, and was signif icant only in the left IMHV. In this region at 24 h, there was (i) sig nificantly more clathrin heavy chain in good learners than in dark-rea red chicks, and (ii) a significant positive correlation between the am ount of clathrin heavy chain and preference score; the amount of prote in present in the dark-reared chicks did not differ significantly from the amount predicted from the regression line for trained chicks perf orming at chance (preference score 50). These findings imply that for the left IMHV, visual experience per se, locomotor activity and other side effects of training did not affect the amount of clathrin heavy c hain. Rather, the increase observed was a function of the amounts chic k learned and, because it was delayed, is likely to be involved in lon g-term memory. The results for clathrin heavy chain taken together sug gest that enhanced presynaptic events in the IMHV, possibly associated with an increase in synaptic vesicle release/uptake, are important in the recognition memory underlying imprinting. (C) 1997 IBRO. Publishe d by Elsevier Science Ltd.