MONITORING CELLULAR EDEMA AT SINGLE-NEURON LEVEL BY ELECTRICAL-RESISTANCE MEASUREMENTS

Electrical resistance measurements have been used for investigating ex tracellular volume fraction (EVF) of brain tissue. Conventional techni ques using multiple metal electrodes are limited in their spatial reso lution, and thus not suitable for detecting local EVF changes at cellu lar level. We used a multibarrelled glass microelectrode to monitor ce llular swelling locally at single-neuron level. The microelectrode was placed in CA1 region of the rat hippocampus, in situ. A constant curr ent pulse was applied between one of the barrels and a reference elect rode placed in the neck. The resultant voltage drop, which was directl y proportional to the resistance of the immediate environment surround ing the lip of the microelectrode, was recorded through another barrel . A third barrel was used for iontophoretic injection of N-methyl-D-as partate (NMDA) for inducing local cellular edema. The effect of diffus e edema induced by bilateral carotid artery ligation on EVF was also i nvestigated. NMDA application increased the local tissue resistance by 2.0-, and ischemia, by 3.4-folds. We conclude that the method describ ed can detect changes in EVF of minute volumes of brain tissue, and is suitable for monitoring very local effects of drugs or changes in the metabolism on cell volume. (C) 1997 Elsevier Science B.V.