Chloramphenicol-Induced Amnesia for Passive Avoidance Training in the Day-Old Chick

The antibiotic chloramphenicol, an inhibitor of mitochondrial protein synthesis, was used to investigate the time-related changes in protein synthesis following passive avoidance training in the day-old chick (white leghorn–black Australorp). Retention of memory for this simple learning task is known to be prevented by an inhibitor of cytosolic protein synthesis, anisomycin, in a biphasic manner, with the first phase of sensitivity occurring up to 90 min post-training and the second phase between 4 and 5 h post-training (Freeman, Rose, & Scholey, 1995). Birds received bilateral intracranial injections of chloramphenicol (10 μl/hemisphere of a 7.4 mM solution) at various times relative to training and were tested 24 h later. This report shows that at the second phase of anisomycin susceptibility there was a chloramphenicol-sensitive period (5 h post-training) which had an onset time less than 1 h after injection. The effect of chloramphenicol appears not to be due to the mitochondria being energetically compromised since intracranial injections of an uncoupler of mitochondrial oxidative phosphorylation, 2,4-dinitrophenol (0.1 mM), did not disrupt memory formation when injected 5 h after training, even though it did cause amnesia when injected at the earlier time point of 20 min post-training. These results are discussed in the context of what is already known about memory formation in the day-old chick.