FOS and Anxiety: As serotonergic systems within the DR, particularly those within the mid-rostrocaudal and caudal DR, are thought to play a role in facilitation of anxiety-related behavior, and as rats exposed to the HL condition in the open-field test responded with increased anxiety-related behavior, we expected to find greater increases in c-Fos expression in serotonergic neurons in rats exposed to the HL condition, compared to the LL condition in the open-field.