Intraneuronal laminin-like molecule in the central nervous system: demonstration of its unique differential distribution.

Laminin, an extracellular matrix glycoprotein rich in basement membrane, is a multifunctional molecule of approximately 1000 kDa and is known to possess a potent neurotrophic activity. Laminin-like immunoreactivity (LLI) was for the first time demonstrated in mouse and rat CNS neurons by a sensitive immunohistochemical technique. Transblotting of SDS-PAGE of the supernatant of the mouse and rat brain homogenate identified distinct 180 kDa and weak 380 kDa bands immunoreactive to anti-laminin and these molecules differed from authentic laminin subunits. The intraneuronal distribution of LLI disclosed two distinct patterns; LLI-1 (diffuse perikaryal stain) and LLI-2 (coarse granular stain). By immunoelectron microscopy, LLI was localized to the ERs in LLI-1 neurons, whereas it appeared to be confined to lysosomes in LLI-2 neurons. LLI-1 neurons were found predominantly in hippocampal pyramidal, granule and neocortical layers 1-3, 6 neurons, in most of the striatal and thalamic neurons, and Purkinje cells. The majority of neurons in neocortical layers 4-5, medial septal and Meynert neurons, somatic motor neurons, and neurons of the deep cerebellar nuclei were classified as LLI-2 cells. No LLI was found in hypothalamic mammillary, habenular and vagal dorsal motor neurons (LLI-3). These observations may indicate intraneuronal production of laminin-related molecules in central neurons. We speculate that the laminin-related molecules (neurolaminin) play important roles in trophic or servo mechanisms in the CNS.