[A synthetic review on the cerebral extracellular space evaluated by biochemical procedures (author's transl)].

The Authors present a synthetic review on the problem of the cerebral extracellular space evaluated by biochemical procedures. The studies in vitro are numerous, focused on various aspects, such as the choice of the marker, the influence of temperature, and that of the chemical composition of incubation media, the regional heterogeneity of the brain, and so on; it has been observed that inulin, which is the most commonly employed marker, gives an extracellular space of about 40-66%, whereas other markers give values higher than 45%; the variability of values depends on various experimental factors. The studies in vivo present some methodological difficulties due to the existence of the brain barrier; the most reliable procedure appears that of the continuous perfusion of the marker into the cerebrospinal fluid associated with a simultaneous intravenous perfusion; this procedure gives quantitative estimates of extracellular space of about 14-30%. Taking into account that other experimental methods (such as the morphological and the electrophysiological) give lower values, respectively of 5-20% and 18-25%, the Authors found that it should be possible to agree about an average value of cerebral extracellular space of 15-20%. This appears to be of some relevance especially in studying the pathological problems of the brain, and particularly cerebral edema.