Learning and novelty induced increase of central benzodiazepine receptors from chick forebrain, in a food discrimination task.

Young chicks were trained to discriminate food grains from inedible pebbles. On Day 1 and Day 2 of the task, latency to peck, and number of pecks were scored and the forebrain [3H]flunitrazepam receptor binding was also determined at 0 and 30 min after an 8-min training session. Compared with quiet controls, the receptor density increased 46%, 30 min after the training session on Day 1. Compared with chicks that had learned the discrimination and were merely repeating already learned behavior on Day 2, the receptor increased more than 46%. Since chicks that had learned the discrimination had a higher behavioral activity, we interpret that the learning of a new task is itself responsible in addition to stress for the receptor density increase. Stressful factors accompanying the learning task as handling and novelty increased 17% the receptor density, 30 min after a training session without food, compared with quiet controls. However, receptor density did not increase in chicks repeating the same housing conditions, suggesting that chicks were habituated to handling and novelty on Day 2. Differences in receptor density were not observed between quiet controls and experimental groups, at 0 min after the training session, indicating that changes were time dependent. In all cases the affinity remained unchanged. Our results suggest that, the GABA(A) receptor (i) is involved in early stages of memory formation and in stress adaptive responses, and (ii) is modulated by new non-repetitive environmental conditions.