This study will investigate how the brain process emotions in healthy people and in patients who have major depression in order to better understand the causes of depression. It will examine what happens in the brain when a person responds to words related to different emotions while the brain's ability to manufacture a chemical called serotonin is reduced. Serotonin regulates functions such as emotion, anxiety and sleep, and stress hormones such as cortisol. In this study, participants' serotonin levels are reduced by depleting tryptophan, an amino acid that is the main building block for serotonin.

Healthy volunteers and patients with major depression that has been in remission for at least 3 months may be eligible for this study. Candidates must be between 18 and 50 years of age and right-handed. They are interviewed about their medical and psychiatric history, current emotional state and sleep pattern, and family history of psychiatric disorders. Screening also includes psychiatric interviews and rating scales, neuropsychological tests, physical examination, electrocardiogram (EKG), and blood, urine, and saliva tests. Women have their menstrual phase determined by a blood test and home urine ovulation test kit.

The study involves two clinic visits in which participants undergo tryptophan depletion and magnetic resonance imaging (MRI). Subjects arrive at the NIH Clinical Center in the morning after fasting overnight. They fill out questionnaires have a blood sample drawn, and then take 74 capsules that contain a mixture of amino acids found in the diet. At one visit they are given capsules that contain a balanced mixture of amino acids one would normally eat in a day; at the other visit, some of the capsules contain lactose instead of tryptophan, causing tryptophan depletion. At 2 p.m. participants fill out the same questionnaires they completed at the beginning of the day and have another blood sample drawn. Then they do a computerized test in the MRI scanner. MRI uses a magnet and radio waves to obtain pictures of the brain. For the test, subjects lie on a narrow bed that slides into the cylindrical MRI scanner. They are asked to press a button in response to words associated with different emotions that appear on a screen. Arterial spin labeling - a test that uses magnetism to measure blood flow in different areas of the brain-is also done during the procedure. After the scan, subjects eat a meal and then return home.

DNA from the participants' blood samples is also examined to try to better understand the genetic causes of depression. Some of the white cells from the samples may also be grown in the laboratory so that additional studies can be done later.

Major depressive disorder (MDD) has been associated with abnormally reduced function of central serotonergic systems by various types of evidence. One instructive paradigm for investigating the relationship between serotonergic function, cognition and depression has involved the mood response to tryptophan depletion (TD), achieved by oral loading with all essential amino acids excepting the 5-HT precursor, tryptophan. Subjects who are depressed show altered behavioral and neural response to affectively valenced stimuli, similar to those seen under TD. In the Affective Go/No-go test, in which subjects are required either to respond or inhibit a response to a series of emotionally valenced words, increased response latencies to happy words have been noted in both depressed patients and healthy controls following TD.

The current study employs fMRI imaging of BOLD response and arterial spin labeling to investigate response to TD in two groups, remitted MDD (rMDD) patients and healthy controls with no family history of depression. Previous studies of TD-induced in remitted MDD subjects showed that glucose metabolism decreased in the orbital, ventrolateral, and pregenual anterior cingulate areas of the prefrontal cortex (PFC) in MDD subjects who had symptom exacerbation during TD, but not in subjects who did not. Based upon a variety of evidence, it is hypothesized that the orbital and medial PFC activate during depressive episodes to attenuate or compensate for a pathological activation of the amygdala. Serotonin depletion may "release" depressive symptoms by impairing the compensatory function of the orbital cortex, since 5-HT appears to play a critical role in optimal function of PFC neurons.

The primary hypothesis is that TD will cause temporary recurrence of depressive symptoms in some rMDD subjects, accompanied by behavioral and neural changes seen in the depressed state. Behavioral change is hypothesized to include increased response latency to happy words. It is also hypothesized that resting state changes will occur specifically in the anterior cingulate, orbitofrontal and dorsolateral prefrontal cortex in patients who show temporary recurrence of depressive symptoms. While carrying out the Affective Go/No-go test it is hypothesized that patients who show temporary recurrence of depressive symptoms following TD will show increased neural response to sad distractor words in orbital cortex and increased neural response to sad target words in pregenual cingulate.

A secondary hypothesis is that mood lowering, behavioral and neural change in response to TD is mediated by polymorphism at the serotonin transporter gene.

• INCLUSION CRITERIA

rMDD Sample: eighty subjects (ages 18-50) with rMDD will be selected, 20 s allele carriers and 20 l/l homozygotes. Remission is defined as a period of at least three months during which the subject has not taken an antidepressant agent (Frank et al. 1991), with Hamilton Depression Rating Scales (HDRS; 21-item) (Hamilton 1960) scores in the non-depressed range (less than 8), and with no more than one clinically significant depressive symptom. Subjects will be assessed for past psychiatric disorders using the Structured Interview for DSM IV (SCID) (Spitzer et al. 1992).

Healthy Control Sample: eighty healthy subjects (ages 18-50) without a known personal or family history of psychiatric disorders in first-degree relatives will be selected, 20 s allele carriers and 20 l/l homozygotes.

Since the s and l alleles occur with differing frequencies in different populations, it is important to control for the potential confound of population stratification. For example, the l allele occurs with 80% frequency in populations of African ancestry, while the s allele occurs with 70% frequency in populations of East Asian origin. Therefore if ethnicity is not controlled for, any association of mood response to TD with a particular allele could potentially be due to other differences between ethnicities.

In order to counteract this issue in the present study, we intend for the first 20 rMDD subjects and first 20 controls to be Caucasian. At this stage, behavioral and neural differences between the genetic sub-groups in response to TD will be analyzed. If any statistically significant differences are apparent between the genetic sub-groups, a further 20 rMDD subjects and 20 controls will be recruited who are not Caucasian, 10 l/l homozygotes and 10 s allele carriers in each group. These ethnically mixed genetic sub-groups will then be compared to the equivalent Caucasian genetic sub-groups in a final analysis to determine whether the effect of the 5-HTTLPR polymorphism on response to TD occurs independent of ethnic origin.

EXCLUSION CRITERIA

Subjects must not have taken antidepressant drugs for at least 3 months (4 months for fluoxetine) prior to the fMRI studies or other medications likely to alter monoamine neurochemistry or cerebrovascular and cardiovascular function for at least 3 weeks prior to imaging. However, effective medications will not be discontinued for the purposes of this study. Subjects will also be excluded if they have:

1. Psychosis
2. Medical or neurological illnesses likely to affect physiology or anatomy, i.e. hypertension, cardiovascular disorders
3. A history of drug (including benzodiazepines (BZD)) or alcohol abuse within 1 year or a lifetime history of alcohol or drug dependence (DSM IV criteria)
4. Current pregnancy (as documented by pregnancy testing at screening or at days of the challenge studies)
5. Current breast feeding
6. Are smokers
7. Serious suicidal ideation or behavior. In this study, there is a small risk of transient depressive symptoms occurring after ingesting the amino acid mixture. Therefore, if volunteers manifest evidence of serious suicidal ideation or behavior, they will be excluded from participating. Criteria for meeting suicidal ideation include but are not limited to: 1) thoughts of suicide within the past 3 months which are accompanied by intent to harm oneself, serious consideration of means or plan to attempt suicide, evidence of arranging for a suicide attempt (e.g. giving away prized possessions or updating a will), or clear desire to commit suicide, 2) severity of past suicide events, if applicable or 3) a current plan for harming themselves. All assessments will be conducted by an experienced, NIMH credentialed health professional, such as a psychiatrist or psychiatric nurse who will use their expert knowledge and experiences in determining the authenticity of a participant's information and handle the situation accordingly.

GENERAL MRI EXCLUSION CRITERIA:

Subjects must exhibit no or only moderate alcohol use. Subjects with current or previous regular use (greater than 4 weeks) of BZDs and excessive use of alcohol (greater than 8 ounces/day for men and greater than 6 ounces/day for women) in the past or present are ineligible for participation, as such drug use may confound the results (Primus and Gallager 1992; Ulrichsen et al. 1996). Smokers (regular use within the last 3 months) are ineligible because of the evidence for interactions between nicotine and depression (Ong and Walsh 2001), and the possibility of withdrawal symptoms that may affect behavioral and neural responses to TD.

Subjects beyond age 50 are excluded to address the biological heterogeneity encompassed by the MDD criteria, since depressives whose age-at-onset is later than 50 have a far greater likelihood of having MRI correlates of cerebrovascular disease than age-matched healthy controls or age-matched early-onset depressives (Krishnan et al. 1993). Subjects whose first major depressive episodes arose temporally after other medical or psychiatric conditions will also be excluded, since their functional imaging results generally differ from those reported in primary MDD (Drevets 2000).