Immunological investigations into synaptic plasticity

Abstract

Antibody technology was applied to the study of synaptic plasticity resulting from passive avoidance training in the chick and long-term potentiation in the rat. These studies fell into three categories: 1) the disruption of memory for a one-trial passive avoidance task by intracranial injection of an anti-postsynaptic density antiserum 2) mapping time- and locus-specific changes in the chick brain using antisera to the cytoskeletal proteins (Xtubulin and microtubule-associated protein 2 following passive avoidance training and 3) using antibodies to synaptically-enriched antigens to map time- and locus-specific changes in hippocampal subfields following long-term potentiation in the rat. In the first series of experiments an antiserum (RI4) was raised against protein from chick forebrain postsynaptic densities (PSDs). The antiserum was characterised and was found to recognise six distinct antigens as determined by Western Blots. These antigens were found to have a primarily (but not exclusively) synaptic location. Intracranial injections of IgG isolated from R14 resulted in amnesia for a one-trial passive avoidance paradigm in the chick when administered 60min pre-training (but not 30min or 15min pre-training or 1000n post-training), in chicks tested 24hrs (but not Ihr or 3hrs) post-training. In the second set of experiments monoclonal antibodies were used to examine changes in levels of the cytoskeletal proteins a-tubulin and microtubule-associated protein 2 (MAP2) in specific forebrain loci following passive avoidance training in the chick. Of the regions examined, elevations in the titre of anti-a-tubulin were found in the left Intermediate Hyperstriatum Ventrale (IMHV) l hr, 6hrs and 24hrs following passive training, in the left Lobus Parolfactorius (LPO) 1hr following training and in the right LPO 6hrs and 24hrs following training. A hemispherically-asymmetrical change was found in the titre of anti-MAP2 which was interpreted as possibly reflecting a decrease in the amount of the antigen in the left IMHV 24hrs following training. No training-related changes were detected, using either antibody, in a third forebrain region, the Paleostriatum Augmentatum (PA). During the characterisation of antiserum R14 it was found that only one antigen (with an apparent molecular weight of 230kDa) is conserved between the chick and rat brain. The antigen is enriched in synaptic fractions isolated from the rat hippocampus and was used, as well as a PSD-specific monoclonal antibody, 411B, to examine possible changes in hippocampal subfields CAl, CA3 and the dentate area taken at several time-points following tetanisation of the right perforant path. 24hrs following tetanisation (but not at earlier time-points), the titre of R14 was elevated in the dentate area ipsilateral to tetanisation and in both the ipsi- and contralateral CAL The titre of 411B was increased specifically in the target, dentate area and only at 8hrs following tetanisation, an increase which was abolished in the presence of the protein synthesis inhibitor, anisomycin. These results are discussed in the context of current models of synaptic plasticity.