LAMININ-ALPHA-2 CHAIN-LIKE ANTIGENS IN CNS DENDRITIC SPINES

The laminin-alpha 2 chain is a component of brain capillary basement m embranes and appears also to be present in neurons of rat, rabbit, pig and non-human primate brain as evidenced by immunohistochemistry. In the present study, we have further characterized this very distinct ne uronal laminin-alpha 2 chain-like immunoreactivity in the hippocampus of various species. Immunoelectron microscopy with poly- and monoclona l antibodies to the laminin-alpha 2 chain G-domain localized laminin-a lpha 2 chain immunoreactivity in adult rat and rabbit hippocampus to d endritic processes, primarily to dendritic spines. In the developing r at hippocampus, spine-associated laminin-alpha 2 chain-like immunoreac tivity first appeared at a time corresponding to that of active synapt ogenesis. After an entorhinal cortex lesion in adult rats, the time co urse of denervation-induced loss and reactive reappearance of spines i n the molecular layer of the dentate gyrus was correlated closely to t he loss and reappearance of laminin-alpha 2 chain immunoreactivity. Im munoblot analysis of normal adult rat, rabbit and pig brain revealed a protein similar in size to the reported 80-kDa laminin-alpha 2 chain fragment of human placenta as well as 140/160-kDa proteins. These resu lts suggest the presence of proteins with antigenic homology to the la minin-alpha 2 chain and/or laminin-alpha 2 isoforms in dendrites and d endritic spines in selected areas of the brain, predominately in the h ippocampus and other limbic structures. Given the adhesion and neurite promoting functions of laminins, it is possible that neuronal laminin -alpha 2 chain-like proteins play a role in synaptic function and plas ticity in the CNS. (C) 1997 Elsevier Science B.V.