This study is a very nice extension of earlier work on brain interstitial tau concentrations performed in humans following traumatic brain injury (Marklund et al., 2009). It is now important to examine tau homeostasis in normal conditions. Personally, I believe that extracellular tau in the absence of pathological processes may reflect neuroaxonal plasticity. This hypothesis is to some degree backed by studies on normal newborns who have very high levels of total and phosphorylated tau in their CSF (Mattsson et al., 2010). The first months after birth are characterized by extensive synaptic and neuronal remodeling, which may involve physiological tau phosphorylation and release of tau proteins from retracting and regrowing axons.

References:
Marklund N, Blennow K, Zetterberg H, Ronne-Engström E, Enblad P, Hillered L. Monitoring of brain interstitial total tau and beta amyloid proteins by microdialysis in patients with traumatic brain injury. J Neurosurg. 2009 Jun;110(6):1227-37. Abstract

Mattsson N, Sävman K, Osterlundh G, Blennow K, Zetterberg H. Converging molecular pathways in human neural development and degeneration. Neurosci Res. 2010 Mar;66(3):330-2. Abstract

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