Laminins of the adult mammalian CNS; laminin-alpha 2 (merosin M-) chain immunoreactivity is associated with neuronal processes

Laminins are glycoproteins with three subunits, i.e. a longer alpha chain, a shorter beta chain and a shorter gamma chain. Well-characterized laminins are laminin-1 (EHS laminin; alpha 1-beta 1-gamma 1), laminin-2 (merosin; alpha 2-beta 1-gamma 1), laminin-3 (alpha 1-beta 2-gamma 1) and laminin-4 (alpha 2-beta 2-gamma 1). The present study shows that in the adult mammalian CNS (rat, rabbit, pig and monkey) alpha 2 chain immunoreactivity is associated most evidently with neuronal fibers and punctate, potentially synaptic, structures of limbic brain regions. Third ventricle tanycytes and ensheathing cells of the olfactory nerve also express intense alpha 2 chain immunoreactivity. Immunostaining for gamma 1 chain is present throughout the central nervous system (CNS) in essentially all neuronal cell bodies and their most proximal processes. Immunoreactivity for all chains investigated (alpha 1, alpha 2, beta 1, beta 2 and gamma 1) were present around blood vessels, especially evident in lightly fixed tissues. The finding that, other than blood vessels, neurons and other structures exhibited immunoreactivity for only one or two (and not three) chains, suggests that variant forms of laminin with yet undiscovered chains or other configurations than the heterotrimeric form are present in the CNS. The association of alpha 2-like immunoreactivity with neuronal fibers and synaptic structures is of great interest in light of the known neurite-promoting and cell attachment activities of laminin-2. (C) 1997 Elsevier Science B.V.