Stephen K. Brannan

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.

VNS therapy in treatment-resistant depression: clinical evidence and putative neurobiological mechanisms.

Currently available therapeutic interventions for treatment-resistant depression, including switch, combination, and augmentation strategies, are less than ideal. Observations of mood elevation during vagus nerve stimulation (VNS) therapy for pharmacoresistant epilepsy suggested a role for VNS therapy in refractory major depression and prompted clinical investigation of this neurostimulation modality. The VNS Therapy System™ has been available for treatment of pharmacoresistant epilepsy since 1997 and was approved by the US Food and Drug Administration for treatment-resistant depression in July, 2005. The physiology of the vagus nerve, mechanics of the VNS Therapy System™, and efficacy and safety in pharmacoresistant epilepsy are reviewed. Promising results of VNS therapy for treatment-resistant depression have been forthcoming from both acute and long-term studies, evidenced in part by progressive improvements in depression rating scale scores during the 1st year of treatment with maintenance of response thereafter. VNS therapy is well tolerated in patients with either pharmacoresistant epilepsy or treatment-resistant depression. As in epilepsy, the mechanisms of VNS therapy of treatment-resistant depression are incompletely understood. However, evidence from neuroimaging and other studies suggests that VNS therapy acts via innervation of the nucleus tractus solitarius, with secondary projections to limbic and cortical structures that are involved in mood regulation, including brainstem regions that contain serotonergic (raphe nucleus) and noradrenergic (locus ceruleus) perikarya that project to the forebrain. Mechanisms that mediate the beneficial effects of VNS therapy for treatment-resistant depression remain obscure. Suggestions for future research directions are described.

Durability of antidepressant response to vagus nerve stimulation (VNS

This study characterized the durability of improvement in patients who responded early or late while receiving vagus nerve stimulation (VNS). In both a pilot and pivotal study, patients were identified who had at least a 50% reduction in symptom scores 3 months (early responders) or 12 months (late responders) after starting VNS. Probabilities were determined for maintenance of response at 12-month and 24-month time-points. Consistency of improvement throughout the 24-month study period was evaluated, testing for change in serial depression ratings. In the pilot study, 30.5%, 23.7% and 45.8% were early responders, later responders, and non-responders, respectively. These rates were 14.6%, 19.5%, and 65.9% in the pivotal trial. The potential confound of alterations in antidepressant treatment was examined in the pivotal trial. In the pilot study, 72.2% and 61.1% of early responders (n=18) were responders at 12 and 24 months, respectively; 78.8% of late responders (n=14) were responders at 24 months. In the pivotal trial, of early responders (n=30), 63.3% and 76.7% maintained response at 12 and 24 months, respectively; of late responders (n=40), 65.0% maintained response at 24 months. Early and late responders had fewer changes in medication than non-responders across the pivotal study period. In both studies, analyses of serial depression ratings showed stable improvement in early and late responders. These samples had exceptional levels of chronicity and treatment resistance. Yet patients who showed substantial clinical benefit maintained the improvement at remarkably high rates. This durability of benefit was not attributable to alterations in other treatments.

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.

Erratum: VNS therapy in treatment-resistant depression: Clinical evidence and putative neurobiological mechanisms (Neuropsychopharmacology (2006) 31 (1345-1355) DOI: 10.1038/sj.npp.1301082)

Correction to: Neuropsychopharmacology (2006) 31, 1345–1355. doi.10.1038/sj.npp.1301082 In the above article, it was disclosed that the report was supported by an unrestricted educational grant from Cyberonics Inc. Of the nine authors, eight are academic researchers who are also consultants for Cyberonics Inc.