Synaptic Vesicle Proteins and Acetylcholine Levels in Chick Forebrain Nuclei Are Altered by Passive Avoidance Training

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Abstract
In a search for biochemical markers of modified synaptic function following training of day‐old chicks on a passive avoidance task, we have assayed two monoclonal antibodies to synaptic vesicle proteins (anti‐p65 and anti‐SV2) and one raised to postsynaptic densities (411B). We have also measured total acetylcholine (ACh) content. Measurements were made on three forebrain regions known to show metabolic and morphological change consequent on training—the lobus parolfactorius (LPO), paleostriatuni augmentatum (PA), and medial hyperstriatum ventrale (MHV)—in the right and left hemispheres 2 and 24 h after training chicks on a passive avoidance task, in which they learn to avoid pecking a bead coated with methylanthranilate [methylanthranilate‐trained (M‐trained)]. Control chicks were trained on a water‐coated bead [water‐trained (W‐trained)]. Twenty‐four hours after training, 411B levels showed no differences between W‐trained and M‐trained chicks in any region. M‐training reduced the litre of antip65 by 16% in the left PA and 15% in the left MHV and that of anti‐SV2 by 19% in the left PA. M‐trained chicks showed reduced total ACh content in the LPO by up to 40% and in the PA by up to 48% but had no change in ACh level in the MHV. The decreases in antibody titre were not seen in forebrains analysed 2 h after training, but tendencies toward increases in levels in the right PA and MHV were observed with all three antibodies. Significant differences between right and left hemispheric regions, independent of training, were observed for all the antibodies and for ACh content. In the LPO, antibody litres were some 10% lower in the left compared with the right hemisphere and 34% lower for ACh content, but in the PA, the left hemisphere titre was higher by 14–86%. We discuss these results in the context of morphometric and electrophysiological data oblained from W‐trained and M‐trained chicks.