SPATIAL RE-ARRANGEMENT OF THE VESICLE APPARATUS IN FOREBRAIN SYNAPSESOF CHICKS 30 MIN AFTER PASSIVE-AVOIDANCE TRAINING

A quantitative ultrastructural study of synapses was carried out in th e forebrain IMHV (intermediate and medial hyperstriatum ventrale) of 1 -day-old chicks 30 min after training to avoid pecking at a bead coate d with methyl anthranilate. In 10 birds (5 control and 5 trained), the length, curvature and the number of the synaptic active zone profiles were measured, and the active zone profile length was observed to inc rease in trained chicks. The spatial arrangement of synaptic vesicles with respect to the active zone was examined using a statistical stere ological approach. This showed that vesicles are not located uniformly but accumulate in two spatial pools which appear to rearrange followi ng training, with a greater number of vesicles near the active zone. T hese data may reflect subtle changes in the functional efficacy of syn apses in the IMHV in the initial phases of memory formation.