Fluid content and compartments in isolated cerebral tissues.

TLDR: The methods developed have been applied to determine fluid changes during electrical excitation of the tissue, and during the action of basic proteins: both these agents were found by THOMSON and MCTLWAIN (1961) to alter tissue weight, presumably by fluid changes.

Abstract: ION MOVEMENTS are fundamental to neural activity, and their study in cerebral tissues (CUMMINS and MCILWAIN, 1961) has prompted the following re-examination of tissue fluids. This is because, although potassium loss and assimilation can be investigated with minimal knowledge of concomitant changes in fluids, the fluid movements must be known in order to appraise changes in sodium and chloride ions. In addition, some theories of ion movement (MILLER, 1960) propose that the primary point at which metabolically derived energy is applied in performing osmotic work, is on fluid rather than on ions. The present study involved appraising: (1) Changes occurring during the initial contact of the cut tissue with fluids to be used in incubation. Changes of this category have received relatively little attention, but their study is made more feasible by the recently developed technique of slicing without contact with fluid, using a narrow blade mounted in a bow-cutter (RODNIGHT and MCILWAIN, 1954; MCILWAIN, 1961). (2) Change during subsequent incubation has been examined by measuring total fluid, and also the inulin content of the tissue after its incubation in inulin-containing media. The use of inulin to obtain a measure ofintraand extra-cellular spaces in cerebral tissue was based on the studies of KOREY and MITCHELL (1951), ALLEN (1955), PAPPIUS and ELLIOTT (1956) and MCLENNAN (1957) and is appraised further below. (3) The methods developed have been applied to determine fluid changes during electrical excitation of the tissue, and during the action of basic proteins: both these agents were found by THOMSON and MCTLWAIN (1961) to alter tissue weight, presumably by fluid changes. E X P E R I M E N T A L Media and tissue Glycylglycine saline contained 124 m-NaCI , 5 m-KCI, 1.24 mM-KH,PO,, 1.3 mM-MgSO,, 2.8 mM-CaCI,, 10 m-glucose, and 30 m-glycylgtycine taken to pH 7.4 with M-NaOH and was saturated with 0,. Bicarbonate saline, unless otherwise specified, differed only in containing 26 m-NaHCO, in place of glycylglycine and was equilibrated with 95 % 0,: 5 % CO,. In media which contained inulin (see below) its concentration was 1 % unless stated otherwise. Adult guinea pigs of either sex, weighing 25o-u)o g were stunned with a blow on the neck and exsanguinated by cutting the neck; the brain was removed as described by MCILWAIN and RODNIGHT (1962) within 1.5 min of stunning. A hemisphere was taken, subcortical structures removed, and it was placed on a cutting table (MCILWAIN, 1961) with the cortex uppermost. From this, three successive slices 0.35 mm thick were cut at room temperature (17-20\") in one of two ways. (1) With a bow cutter and glass guide (MCILWAIN, 1961), avoiding all contact with fluid. The slices were picked up with a bent wire rider of a torsion balance and weighed to the nearest mg; this is the method used in most experiments. (2) With a blade and the same glass guide. lubricated with one of the incubating media described above; after cutting, these slices were floated from the blade or guide into a shallow dish of