The central nucleus of the amygdala (CeA) is a major output region of the amygdala involved in organizing the expression of fear. There is also evidence that the lateral septum (LS) provides inhibitory control of neurons in CeA and is involved in the relief of fear. This study examined single unit activity in the lateral septum (LS) and the central nucleus of the amygdala (CeA) in the open and closed arms of the elevated plus-maze, a highly validated animal model of fear and anxiety. The general presumption is that animals normally avoid the open arms because the open arms are relatively more anxiety provoking than the closed arms which represent relative safety. It was expected that neurons in CeA would increase their activity in the open arms relative to the closed arms indicative of increased anxiety and that LS neurons would decrease their activity on the open arms. Contrary to expectations it was found that the preponderance of units in CeA decreased their firing rates on the open arms compared to the closed arms. An increase in firing rates in LS was seen in the open arms compared to the closed arms. The data suggest that when animals are placed on the open arms a compensatory process takes place to suppress fear so that the animal can engage in adaptive behavior. We liken this process to that which takes place in exposure therapy for phobias in humans which involves the inhibition of fear resulting from Pavlovian extinction.
Keywords: Amygdala; Anxiety; Central nucleus; Elevated plus-maze; Lateral septum; Single-unit.
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