DIFFERENTIAL-EFFECTS OF GLYCOSAMINOGLYCANS ON NEURITE OUTGROWTH FROM HIPPOCAMPAL AND THALAMIC NEURONS

Chondroitin sulphate proteoglycans are expressed in a temporally restr icted pattern from embryonic day 17 to postnatal day 0 in both the tha lamus and the cortical subplate, to which thalamic neurones transientl y project. To study whether chondroitin sulphate proteoglycans could b e specifically involved in the modulation of thalamic axon outgrowth, we compared neurite outgrowth from cultured rat embryonic hippocampal and thalamic neurones, in the presence of chondroitin sulphate type C (isolated from shark cartilage) and chondroitin sulphate type B (derma tan sulphate; isolated from bovine mucosa). When added to the culture medium, both types of glycosaminoglycan lowered the adhesion to lamini n and polylysine of both hippocampal and thalamic neurones. However, o nly chondroitin sulphate specifically modified the pattern of thalamic but not hippocampal neurone outgrowth, promoting axon growth. The mor phological changes induced by chondroitin sulphate were concentration dependent and correlated with the selective binding of chondroitin sul phate to the neuronal plasma membrane and its subsequent internalisati on. Chondroitin sulphate loosely bound to the surface of hippocampal n eurones, but was not internalised. These results indicate that proteog lycans, and in particular the glycosaminoglycan component of these mol ecules, can differentially modulate neurite outgrowth, depending on th eir biochemical composition and on the type of neurones they bind to; this would be a possible mechanism of controlling axon guidance in viv o.