Anxiogenic modulation of spontaneous and evoked neuronal activity in the basolateral amygdala.

The amygdala has a well-established role in stress, anxiety, and aversive learning, and anxiolytic and anxiogenic agents are thought to exert their behavioral actions via the amygdala. However, despite extensive behavioral data, the effects of noradrenergic anxiogenic drugs on neuronal activity within the amygdala have not been examined. The present experiments examined how administration of the anxiogenic drug yohimbine affects spontaneous and evoked neuronal activity in the basolateral amygdala (BLA) of rats. Yohimbine produced both excitatory and inhibitory effects on neurons of the BLA, with an increase in spontaneous activity being the predominant response in the lateral and basomedial nuclei of the BLA. Furthermore, yohimbine tended to facilitate neuronal responses evoked by electrical stimulation of the entorhinal cortex, with this facilitation seen more often in lateral and basomedial nuclei of the BLA. These data are the first to examine the effects of the anxiogenic agent yohimbine on BLA neuronal activity, and suggest that neurons in specific subnuclei of the amygdala exhibit unique responses to administration of such pharmacological agents.