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Background: The high-affinity N-methyl-D-aspartate (NMDA) antagonist ketamine exerts rapid antidepressant effects but has psychotomimetic properties. AZD6765 is a low-trapping NMDA channel blocker with low rates of associated psychotomimetic effects. This study investigated whether AZD6765 could produce rapid antidepressant effects in subjects with treatment-resistant major depressive disorder (MDD)., Methods: In this double-blind, randomized, crossover, placebo-controlled study, 22 subjects with DSM-IV treatment-resistant MDD received a single infusion of either AZD6765 (150 mg) or placebo on 2 test days 1 week apart. The primary outcome measure was the Montgomery-Åsberg Depression Rating Scale, which was used to rate overall depressive symptoms at baseline and 60, 80, 110, and 230 min postinfusion and on Days 1, 2, 3, and 7 postinfusion. Several secondary outcome measures were also used, including the Hamilton Depression Rating Scale., Results: Within 80 min, Montgomery-Åsberg Depression Rating Scale scores significantly improved in subjects receiving AZD6765 compared with placebo; this improvement remained significant only through 110 min (d = .40). On the Hamilton Depression Rating Scale, a drug difference was found at 80 and 110 min and at Day 2 (d = .49). Overall, 32% of subjects responded to AZD6765, and 15% responded to placebo at some point during the trial. No difference was observed between the groups with regard to psychotomimetic or dissociative adverse effects., Conclusions: In patients with treatment-resistant MDD, a single intravenous dose of the low-trapping NMDA channel blocker AZD6765 was associated with rapid but short-lived antidepressant effects; no psychotomimetic effects were observed., (Published by Elsevier Inc.)

Background: Clinical evidence that ketamine, a nonselective N-methyl-D-aspartate receptor (NMDAR) antagonist, has therapeutic effects within hours in people suffering from depression suggests that modulating glutamatergic neurotransmission is a fundamental step in alleviating the debilitating symptoms of mood disorders. Acutely, ketamine increases extracellular glutamate levels, neuronal excitability, and spontaneous γ oscillations, but it is unknown whether these effects are key to the mechanism of antidepressant action of ketamine., Methods: Twenty drug-free major depressive disorder patients received a single, open-label intravenous infusion of ketamine hydrochloride (.5 mg/kg). Magnetoencephalographic recordings were made approximately 3 days before and approximately 6.5 hours after the infusion, whereas patients passively received tactile stimulation to the right and left index fingers and also while they rested (eyes-closed). Antidepressant response was assessed by percentage change in Montgomery-Åsberg Depression Rating Scale scores., Results: Patients with robust improvements in depressive symptoms 230 min after infusion (responders) exhibited increased cortical excitability within this antidepressant response window. Specifically, we found that stimulus-evoked somatosensory cortical responses increase after infusion, relative to pretreatment responses in responders but not in treatment nonresponders. Spontaneous somatosensory cortical γ-band activity during rest did not change within the same timeframe after ketamine in either responders or nonresponders., Conclusions: These findings suggest NMDAR antagonism does not lead directly to increased cortical excitability hours later and thus might not be sufficient for therapeutic effects of ketamine to take hold. Rather, increased cortical excitability as depressive symptoms improve is consistent with the hypothesis that enhanced non-NMDAR-mediated glutamatergic neurotransmission via synaptic potentiation is central to the antidepressant effect of ketamine., (Copyright © 2012 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)

Background: Currently, no pharmacological treatments for bipolar depression exist that exert rapid (within hours) antidepressant or antisuicidal effects. We previously reported that intravenous administration of the N-methyl-D-aspartate antagonist ketamine produced rapid antidepressant effects in patients with treatment-resistant bipolar depression. The present study sought to replicate this finding in an independent sample., Methods: In this double-blind, randomized, crossover, placebo-controlled study, 15 subjects with DSM-IV bipolar I or II depression maintained on therapeutic levels of lithium or valproate received a single intravenous infusion of either ketamine hydrochloride (.5 mg/kg) or placebo on 2 test days 2 weeks apart. The primary outcome measure was the Montgomery-Asberg Depression Rating Scale, which was used to rate overall depressive symptoms at baseline; at 40, 80, 110, and 230 minutes postinfusion; and on days 1, 2, 3, 7, 10, and 14 postinfusion., Results: Within 40 minutes, depressive symptoms, as well as suicidal ideation, significantly improved in subjects receiving ketamine compared with placebo (d = .89, 95% confidence interval = .61-1.16, and .98, 95% confidence interval = .64-1.33, respectively); this improvement remained significant through day 3. Seventy-nine percent of subjects responded to ketamine and 0% responded to placebo at some point during the trial. The most common side effect was dissociative symptoms, which occurred only at the 40-minute time point., Conclusions: This study replicated our previous finding that patients with bipolar depression who received a single ketamine infusion experienced a rapid and robust antidepressant response. In addition, we found that ketamine rapidly improved suicidal ideation in these patients., (Copyright © 2012 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)