In this issue we reprise a Feature called _Circumspectives_. The general format of a _Circumspectives_ article is similar to a debate, with separate sections in which two thought leaders

articulate their individual positions on a topic of great importance to our community of researchers. The distinguishing element, however, is that the piece ends with a ‘reconciliation’ that

is co-authored by both and includes ideas or experiments that will move the field forward. The current _Circumspectives_ (Sanacora and Schatzberg, 2015) is entitled ‘Ketamine: Promising

Path or False Prophecy in the Development of Novel Therapeutics for Mood Disorders?’. It is co-authored by Gerard Sanacora and Alan F Schatzberg, who are leaders in this field. The article

effects in patients with severe (treatment-resistant) depression has changed our thinking. Perhaps the most important legacy of this discovery is that there is now a greater appreciation

for the fact that it is possible to design a therapeutic regimen that produces rapid antidepressant effects. At the time of the seminal ketamine report (Zarate et al, 2006), the prevailing

dogma was that all antidepressant therapies required a time lag of several weeks to become effective. The finding that standard antidepressants stimulate adult hippocampal neurogenesis, a

process that requires weeks for new cells to be born and differentiate into neurons, provided a compelling explanation for both the therapeutic effects of the drugs as well as their time lag

(Dranovsky and Hen, 2006). The neurogenesis hypothesis has justifiably had a tremendous influence on research and drug development strategies. However, the discovery that ketamine has rapid

antidepressant effects in humans—detectable within hours of administration—demonstrated that neurogenesis is not required for an antidepressant response, thereby providing a prominent

exception to an influential hypothesis and offering hope that fast-acting but safe antidepressants are possible. Despite growing enthusiasm for ketamine and its promise, Dr Schatzberg

describes some sobering details and gaps in knowledge. Ketamine is a drug of abuse and, despite some exceptionally elegant studies on the mechanism (eg, Li et al, 2010; Autry et al, 2011),

there is no consensus on how it produces therapeutic effects. As one example, Dr Schatzberg points out similarities in some of the molecular actions of ketamine and scopolamine, another

familiar and long-standing member of our phamacopea shown to produce rapid antidepressant effects (Furey and Drevets, 2006). It is interesting that the broad classes of agents to which

ketamine and scopolamine belong (NMDA antagonists and muscarinic acetylcholine antagonists, respectively) have long been used by behavioral phamacologists to disrupt learning and memory

processes in laboratory animals, making it conceivable that, despite common actions on discrete molecules, their key similarity is on more general circuit function, and that a tendency to

disrupt memory is what provides relief to patients with treatment-resistant depression. Perhaps the most provocative aspect of Dr Schatzberg’s piece, however, lies in his rhetorical

question: is it important to understand ketamine’s mechanism of action? This question will be welcomed by some and viewed as heresy by others—which, incidentally, is exactly the intention of

_Circumspectives_. The question should provoke thought when considering the history of research on antidepressants and the current state of neuroscience research and development in the

pharmaceutical industry. Decades of research and billions of dollars have been invested toward understanding the mechanisms by which drugs such as fluoxetine produce their therapeutic

effects. Despite these efforts, there is still no consensus on which of their myriad actions are most crucial, there are currently no major breakthroughs that can trace their heritage to

this massive investment, and leading pharmaceutical companies have elected to divest of this type of research. These facts give weight to our rhetorical answer that it may be easier and more

fruitful to focus on how the brain works than on how the drugs work. The individuals who played key roles in the conceptualization, development, and implementation of this article include

Amit Etkin, Tony George, and Gerard Sanacora. The Editors welcome suggestions for future _Circumspectives_ topics and authors, which can be submitted to [email protected]. Please note that

unsolicited articles of this type will not be considered. We envision publishing 1–2 of these Features each year; the next one is already underway. FUNDING AND DISCLOSURE The authors declare

no conflict of interest. REFERENCES * Autry AE, Adachi M, Nosyreva E, Na ES, Los MF, Cheng PF _et al_ (2011). NMDA receptor blockade at rest triggers rapid behavioural antidepressant

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1136–1143. Article  CAS  Google Scholar  * Furey ML, Drevets WC (2006). Antidepressant efficacy of the antimuscarinic drug scopolamine: a randomized, placebo-controlled clinical trial. _Arch

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development of novel therapeutics for mood disorders? _Neuropsychopharmacology_ (this issue). * Zarate CA Jr, Singh JB, Carlson PJ, Brutsche NE, Ameli R, Luckenbaugh DA _et al_ (2006). A

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INFORMATION AUTHORS AND AFFILIATIONS * Department of Psychiatry, Harvard Medical School, McLean Hospital, Belmont, MA, USA William A Carlezon * Department of Psychiatry, University of

Toronto, Toronto, Ontario, Canada Tony P George Authors * William A Carlezon View author publications You can also search for this author inPubMed Google Scholar * Tony P George View author

publications You can also search for this author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to William A Carlezon. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS

ARTICLE CITE THIS ARTICLE Carlezon, W., George, T. Circumspectives: The Promise of Ketamine. _Neuropsychopharmacol_ 40, 257–258 (2015). https://doi.org/10.1038/npp.2014.270 Download

citation * Published: 11 December 2014 * Issue Date: January 2015 * DOI: https://doi.org/10.1038/npp.2014.270 SHARE THIS ARTICLE Anyone you share the following link with will be able to read

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