The Role of Glycoproteins in Neural Plasticity in Domestic Chick

Zamani, Mohammad Reza (1992). The Role of Glycoproteins in Neural Plasticity in Domestic Chick. PhD thesis The Open University.



In this project various neurochemical and immunological approaches were used to identify and analyse the role of glycoproteins in neural plasticity. Where appropriate, the one-trial passive avoidance paradigm was used (Gibbs & Ng 1977).

Initially, the role of a glycosylation inhibitor, 2-deoxy-D-galactose (2DGal), was examined both in vivo and in vitro. The results of these studies agreed with previous reports that 2DGal inhibits incorporation of fucose and galactose into glycoproteins. However, 2DGal inhibited fucosylation and galactosylation of only a sub-set of these macromolecules. The localization of these glycoproteins in synaptic plasma membranes (SPMs) and postsynaptic densities (PSDs) suggested differential glycoprotein synthesis and distribution across the synaptic cleft.

Subsequent studies attempted to identify the fucosylglycoproteins involved in learning and memory formation and to characterize their structure, sub-cellular distribution and the timecourse of their expression. An in vitro increase in the rate of fucosylation was found in the right forebrain base after training. Further, the rate of fucosylation of a protein component of Mr 110-120kD increased significantly within the first four posttraining hours. A number of glycoproteins showing significant increase in fucosylation either 6hr or 24hr after training, or at both posttraining time-points were identified in vivo. Most were concentrated in SPMs and PSDs of LPO as summarised in figure A.1.

Polyclonal antibody R15 was raised and it recognized a 60-62kD antigen in SPM and PSD fractions. It rendered chicks amnesic when injected bilaterally 30min before training. Immunocytochemical studies showed medium density labelling of axonal membranes and SPMs and PSDs.

Finally, the sugar contents of SPM and PSD membrane-bound glycoproteins were analysed using specific lectins. Chick brain glycoproteins were separated by two-dimensional gel electrophoresis and identified using the lectin Ulex Europaeus type I (UEA.I). Some 55 fucosylated polypeptides were found in SPMs and PSDs. Specific antibodies whose antigens have been implicated in learning and memory formation were used to examine whether their immunoreactivity changed as a result of passive avoidance training. Both anti-N-CAM antibodies and anti-ependymin antibodies cross-reacted with chick antigens from SPM and PSD fractions, but immunoblotting did not show training-induced changes.

The results reported in this thesis are discussed in the light of current understanding of neural mechanisms of learning and memory. Several hypotheses are considered which collectively recognize glycoproteins as major contributors to neural network formation/re-formation during learning and formation and consolidation of memory.

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