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A novel role for vasopressin in the brain modulation of a radial, activity dependent water flux


, : A novel role for vasopressin in the brain modulation of a radial, activity dependent water flux. Society for Neuroscience Abstracts 26(1-2): Abstract No -537 18

The brain contains an intrinsic vasopressin fiber system and astrocytes express high levels of a water channel, aquaporin-4 (AQP4). Since vasopressin is known to regulate AQP2 expression and translocation in kidney collecting ducts we hypothesize that vasopressin might have a similar function in the brain. Electrical stimulation of layer VI of the neocortex elicits a water flux towards superficial layers that is thought to accompany the spatial buffering of excess K+. Water redistribution was assessed by recording the intrinsic optical signal (IOS) which reflects changes in the extracellular volume. A distinct dark IOS (indicative of an extracellular volume increase) was recorded in the superficial layers and the tangential extent of this signal was enhanced by application of vasopressin or vasopressin V1a agonists. V1a antagonists abolished this effect and reduced the IOS size also in control conditions. V2 agonists and antagonists showed no effect. The vasopressin effect on water redistribution was abolished by thapsigargin and bisindolylmaleimide. The extracellular volume changes occurred within seconds after electrical stimulation suggesting that specialized water channels are involved. The distribution of AQP4 was analysed. AQP4 was concentrated in the subpial plasma membranes and in perivascular endfeet throughout the cortex. The subcellar distribution of this channel was not changed by vasopressin.

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