Relationship between the release and uptake of noradrenaline by rat brain synaptosomes in the formation of defensive conditioned reflex.

The defensive conditioned reflex with two-way avoidance was developed in rats in a shuttle-box. Immediately and 30 min after learning the animals were decapitated and synaptosomes were isolated from the whole brain and brain cortex. Using [14C] and [3H]-noradrenaline (NA), the processes of uptake, spontaneous and potassium depolarization-induced (60 mM KCl) release of NA by brain synaptosomes of trained and control animals were studied in vitro. Immediately after learning the inhibition of NA uptake was observed, but 30 min following learning the ability of synaptosomes to take up NA was recovered to the initial level. Thirty minutes after learning the potassium depolarization-induced release of NA previously taken up by synaptosomes increased as compared to the control. NA spontaneous release did not change under these conditions. With the increase of Ca2+ concentration in the incubation medium from 1.2 mM to 2.4 mM, the induced NA release from brain synaptosomes of trained and control animals regularly increased. Changes in NA release and uptake are specific for the development of conditioned reflex