Studies of individual differences as a method for discriminating the stages of acquisition of a conditioned reflex.

Learning of a two-way active avoidance response in a shuttle box, which reflects the establishment of a complex reflex, was characterized by a high level of individual variability for learning measures. Our previous report (Savonenko and Zelin'ski, 1997) showed that rats with different rates of learning have different parameters for the freezing response, demonstrating that the animals' behavior shows a conflicting drive not to enter into the other half of the box. We analyze here the sequence of freezing, avoidance, and escape responses in groups of rats with different rates of learning. The results support the hypothesis that the need to overcome conflict is a separate stage of learning, occurring before the stage at which the avoidance response forms and stabilizes.

[The study of individual differences as a method for dividing into stages the acquisition of a complex reflex]. / Izuchenie individual'nykh razlichii kak metod vychleneniia étapov vyrabotki slozhnogo refleksa.

Two-way active avoidance learning is a complex task characterized by a high level of interindividual variability. We have demonstrated in our previous paper that rats with different rate of learning vary in expression of freezing responses, which reflects a conflict tendency not to re-enter the previous chock compartment [4]. In the present work we analyzed as main indices the proportions of avoidance, rapid escape, and freezing responses and their distribution within a session. Sequences of occurrence of these three types of responses were examined in groups of rats with different success of avoidance learning. The obtained results confirmed a hypothesis that overcoming the conflict tendency was a separate stage of learning which preceded avoidance response appearance and subsequent stabilization. Only in rats which failed to learn and develop avoidance responses within the first session, freezing responses were observed in successive session being indicative of reappearance of the conflict tendency. The intensity of the conflict tendency did not depend on the type of the first response of an animal (fleeing or freezing) to an unexpected aversive stimulus.

[The serotonin content in human platelets is unstable: data and possible mechanisms]. / Soderzhanie serotonina v trombotsitakh cheloveka nestabil'no: fakty i vozmozhnye mekhanizmy.

The study of serotonin content in platelets showed the instability of this trait and its interrelation with plasma serotonin. The oscillations of platelet serotonin are stabilized by the removing of plasma proteins, calcium and by incubation with lithium. The model of synchronization of serotonin transport via the membrane of platelets bound into a spongy net by fibrinogen molecules is discussed.