Diazepam suppresses the stress-induced dopaminergic release in the amygdala of methamphetamine-sensitized rat.

Although the benzodiazepine class of drugs has proven useful in treating anxiety symptoms, recent studies yield no consistent empirical support for their use in treating psychiatric disorders. However, animal studies using a fear conditioning paradigm have suggested that benzodiazepines facilitate fear memory extinction, dependent on treatment timing and subject conditions. However, we have no data on the effect of subject conditions. The purpose of this study was to investigate whether the effect of benzodiazepines depends on hypersensitivity to fear-memory processing. We examined the effect of diazepam, a benzodiazepine, on the extracellular dopamine level in the left amygdala of methamphetamine-sensitized, fear-conditioned model rats, using microdialysis and high-performance liquid chromatography. In this model, the dopamine level in the amygdala excessively increases in response to a fear-conditioned stimulus; the phenomenon has been proposed as a biological marker for hypersensitivity to fear-memory processing. Diazepam inhibited this excessive increase. The extent of the inhibitory effect was greater in the sensitized condition. Diazepam alone increased amygdalar dopamine levels under physiological conditions but not under sensitized conditions. Diazepam did not shorten freezing time in any group. These results suggest that diazepam modulates amygdala dopamine with state dependence and that amygdalar dopamine fine-tuning accounts for part of the therapeutic effect of benzodiazepines on fear memory processing. Further investigation is required to identify patients suitable for treatment with benzodiazepines. This is the first report on the pharmacodynamic effects of benzodiazepine on the amygdalar dopamine basal level and on fear memory processing.