Effect of an inhibitor of dopamine-beta-hydroxylase on the acquisition and retention of four different avoidance tasks in mice

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Abstract
The effect of [bis-(4-methyl-1-homopiperazinylthiocarbonyl)-disulfide] (FLA-63) (40 mg/kg, i.p.) on acquisition and retention in four different avoidance tasks was evaluated in mice. In all tasks animals were submitted to a training session on one day and to a retest session 24 h later. The drug or its vehicle were given either 2 h prior to training and/or retest (pretrial treatments) or immediately after the end of the training session (posttrial treatments). Two hours after injection, FLA-63 was found to lower brain norepinephrine (NE) levels by 51% without affecting those of dopamine (DA). Pretrial administration of the drug resulted in poorer performance of step-through and step-down passive avoidance as well as of step-up active avoidance in retest sessions. There was no apparent posttrial effect of the drug nor any effect on acquisition in these tasks. The drug was without influence on either acquisition or retention in an any-way passive avoidance task in which the response required from the animals was immobility. No evidence for statedependent learning was detected in any of the tasks. The data are consistent with the hypothesis of an involvement of NE either in memory processes or in events parallel and related to memory processes. The present results rule out, however, several such possible parallel events (effects on acquisition, motor disturbances, and effects on reactivity to shocks).