INVOLVEMENT OF GLUTAMATE RECEPTORS, PROTEIN-KINASES, AND PROTEIN-SYNTHESIS IN MEMORY FOR VISUAL-DISCRIMINATION IN THE YOUNG CHICK

Two-day-old chicks were trained to discriminate between edible chick c rumbs and arrays of colored beads glued to the floor of their cage. No rmal chicks learned this task within a few minutes and retained it for at least 24 h. The role of several biochemical systems known to be re quired for other forms of early learning in the chick was explored in this task. Antagonists and inhibitors of these systems were used in th e doses known to produce amnesia in a related passive avoidance learni ng model. Drugs were injected intracerebrally just before training, an d retention was tested at various times subsequently. The protein synt hesis inhibitor anisomycin (240 nmol/chick) was without effect on rete ntion at 30 min posttraining, but chicks were amnestic at 3 and 24 h. The protein kinases inhibitors melittin (1.2 nmol/chick) and 1-(5-isoq uinolinylsulfonyl)-2-methylpiperazine hydrochloride (100 nmol/chick) w ere without effect on retention at 30 min posttraining but were amnest ic by 3 h. While these effects are similar to those found for one-tria l passive avoidance training, neither the N-methyl-D-aspartate recepto r antagonists 0,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine malea te (up to 15 nmol/chick) or DL-2-amino-5-phosphonovalerate (1.3 nmol/c hick), both of which are amnestic for passive avoidance, nor the non-N MDA-glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3,-dion e (4 nmol/chick) were amnestic for the visual discrimination task. By contrast, the metabotropic glutamate receptor blocker (RS)-alpha-methy l-4-carboxyphenylglycine (300 nmol/chick) injected 5 min pretraining r esulted in amnesia at 3 h posttraining. The implications of these find ings for the putative ''memory consolidation cascade'' are discussed. (C) 1996 Academic Press, Inc.