Brain vascular volume, electrolytes and blood-brain interface in the cuttlefish Sepia officinalis (Cephalopoda)

Cephalopod molluscs have complex brains and behaviour, yet little is known about the permeability of their blood-brain interface. This paper presents studies on the brain fluid and electrolyte compartments of the cuttlefish Sepia, as a preliminary to characterization of the permeability of the blood-brain interface in this group. Sepia is shown to be a satisfactory experimental animal, and techniques are described for anaesthesia, cannulation, and tissue and fluid analysis. Our ionic analyses of body fluids are in general agreement with those of earlier workers. Analysis of brain tissue suggests that the extracellular space is 17-20 ml 100 g tissue-1 (i.e. 17-20%). Two large molecular weight tracers, 125I-human serum albumin (HSA) and Blue dextran, give consistent values for the brain vascular volume of 3.5-5.5%, slightly higher than in vertebrates. The HSA results further confirm that the Sepia blood-brain interface is relatively tight to proteins. Finally, we have shown that the fluid surrounding the brain, pericerebral fluid (PCF), is in relatively free communication with plasma.