Chondroitin sulphate proteoglycan and embryonic brain inlargement in the chick

Abstract

Abstraer. Prcvious studies of thc car l y dcvclopment of the ncural tube ha ve shown thc ex istence of an intraneural nuid, which causes a positivc pressure inside this pri­ m ordium, and seems to play a key role in the early dcvcl­ opmcn l of the central nervous syslc m. I n the present sludy wc invest igated the composition and synthesis of lhis int ra neural fluid. By usi n g a scqucntial method, wh ich includes fixation with gl utaraldch yde plus cclylpyridinium chl oride, opening thc ncural cavity after critica! point drying and scan ning clcctron microscopy analysis, we found a water-soluble extracellular matrix that filled up thc brain vesicles of chick embryos al the ea rliest stages of thc ncural tu be. An ultrastructura l study of the neural cpit hcliu m during these stages revea led the cxistcnce of a secretion proccss in the neural cells toward thc apical side, the future neural cavity. An immunocyto­ chemical study to asscs thc nature of the secreted materi­ al has shown that the intraneu ral matrix conta ins chon­ droitin sulphate proteoglycan, which appeared homoge­ n ously distributed throughout lhc neura l cavity. Our findings demonstra te that thc int raneural liquid is a nuid of com plcx composilion and includes chondroiti n su l­ phate protcoglycan as a n osmotically active molccule. Th is suggests a morphogenetic role for the proteoglycan during ea rl y brain enlargcmcnt. Thc neural ectoderm is a polarized epi thelium from carly developmental stages and secretes the in t rancural malrix.