Janet L. Tekell

Cingulate function in depression: A potential predictor of treatment response

THE relationship between pretreatment regional cerebral glucose metabolism and eventual antidepressant drug response was measured using positron emission tomography (PET) in hospitalized patients with unipolar depression. Rostral anterior cingulate metabolism uniquely differentiated eventual treatment responders from non-responders. Hypometabolism characterized non-responders when compared with controls, in contrast to responders who were hypermetabolic. Metabolism in no other region discriminated the two groups, nor did associated demographic, clinical or behavioral measures, including motor speed, cognitive performance, depression severity or illness chronicity. Cingulate hypermetabolism may represent an important adaptive response to depression and failure of this response may underlie poor outcome. A critical role for rostral cingulate area 24a/b in the limbic-cortical network involved in abnormal mood states is proposed.

Regional metabolic effects of fluoxetine in major depression: serial changes and relationship to clinical response

BACKGROUND Treatment of major depression with antidepressants is generally associated with a delay in onset of clinical response. Functional brain correlates of this phenomenon have not been previously characterized. METHODS Time course of changes in brain glucose metabolism were measured using positron emission tomography in hospitalized unipolar depressed patients treated with fluoxetine. Time-specific and response-specific effects were examined at 1 and 6 weeks of treatment. RESULTS Changes were seen over time, and characterized by three distinct patterns: 1) common changes at 1 and 6 weeks, 2) reversal of the 1-week pattern at 6 weeks, and 3) unique changes seen only after chronic treatment. Fluoxetine responders and nonresponders, similar at 1 week, were differentiated by their 6-week pattern. Clinical improvement was uniquely associated with limbic and striatal decreases (subgenual cingulate, hippocampus, insula, and pallidum) and brain stem and dorsal cortical increases (prefrontal, parietal, anterior, and posterior cingulate). Failed response was associated with a persistent 1-week pattern and absence of either subgenual cingulate or prefrontal changes. CONCLUSIONS Chronic treatment and clinical response to fluoxetine was associated with a reciprocal pattern of subcortical and limbic decreases and cortical increases. Reversal in the week-1 pattern at 6 weeks suggests a process of adaptation in specific brain regions over time in response to sustained serotonin reuptake inhibition. The inverse patterns in responders and nonresponders also suggests that failure to induce these adaptive changes may underlie treatment nonresponse.

Reduction of platelet serotonin content in depressed patients treated with either paroxetine or desipramine

Drugs thought to be selective inhibitors of either the uptake of serotonin (5-HT) or norepinephrine (NE) are known to be effective antidepressants. In general, a relative selectivity for NE vs. 5-HT uptake inhibition greater than 50-fold in vitro is thought to be sufficient to maintain such selectivity in vivo. To explore this issue, we carried out a study in which depressed patients were treated with either the selective serotonin reuptake inhibitor (SSRI) paroxetine or the selective norepinephrine reuptake inhibitor (SNRI) desipramine. Patients were treated with either drug or placebo for 6 wk. Drug levels in plasma and platelet 5-HT content were measured 12 times during the treatment period using HPLC procedures. Both drug treatments caused a significant reduction of platelet 5-HT content. Paroxetine reduced platelet 5-HT content to approx. 1% of pretreatment levels (n = 3). The inhibition of 5-HT uptake by paroxetine appeared to be immediate and complete. Desipramine reduced platelet 5-HT content to 38.7+/-6.2 % of pretreatment levels (n = 5) at a mean plasma level of 195 ng/ml. The percent reduction of platelet 5-HT content after 6 wk of drug treatment was proportional to the steady state plasma level of desipramine. The IC50 value of desipramine to reduce platelet 5-HT was 135 ng/ml. These results demonstrate that therapeutic concentrations of the SNRI desipramine as well as the SSRI paroxetine inhibited serotonin uptake in platelets of depressed patients. If such effects occur in the brain, desipramine might have some component of its therapeutic effects due to actions on the uptake of 5-HT.