Increased efflux of a haemoglobin-like protein and an 80 kDa protease into push-pull perfusates following the induction of long-term potentiation in the dentate gyrus.

In a previous communication, we reported an increase in protein efflux into perfusates obtained from push-pull cannulation of the dentate gyrus, following induction of long-term potentiation (LTP) in the perforant path. LTP was accompanied by a delayed but general increase in protein efflux. Protein B5 (MW 14 kDa), because of its relatively high concentration in the perfusates and absence from serum, has been chosen for further characterization. Spectrophotometric analysis, in situ proteolysis, two-dimensional electrophoresis and immunoblotting, revealed that protein B5 is indistinguishable from haemoglobin. A persistent increase in an 80 kDa protease, detected by SDS-PAGE zymography, was also seen after the induction of LTP. We consider the possibility that the increased haemoglobin content of perfusates after the induction of LTP may reflect an LTP-associated increase in the release (or activation) of proteases into extracellular space, leading to proteolytic breakdown of blood clots in the vicinity of the cannula. Evidence in favour of this hypothesis is provided.