Remember ketamine, the old veterinary (and sometimes street) drug? Apparently it rapidly and significantly reduces anhedonia in those with treatment-resistant bipolar disorder, according to a new study.
Anhedonia, which is a lack of interest in activities that once gave a person pleasure, is a key feature of treatment-resistant bipolar disorder. According to a recent NIH-funded clinical trial, ketamine restored pleasure-seeking behavior independent of its other antidepressant properties in these patients. What’s more, it did so about 40 minutes after a single infusion, and the effect lasted as long as 14 days.
To me the most interesting part of this study is that ketamine did not act on the midbrain areas typically involved in depressive symptoms. Rather, PET scans on patients in the depressive phase of bipolar disorder showed that after ketamine infusion, there was activity in the dorsal anterior cingulate cortex (dACC). This region lies deep within the brain, resting on the medial surface of the frontal lobes. Its precise role remains somewhat elusive, though it is thought to govern conscious control of goal-directed behavior. The most recent significant study I could find on its function was a 2012 paper in Nature suggesting that the dACC is involved in optimizing behavioral adaptations to continuously evolving demands by predicting the difficulty of a task.
“Our findings help to deconstruct what has traditionally been lumped together as depression,” explained Carlos Zarate, M.D., of NIMH. “We break out a component that responds uniquely to a treatment that works through different brain systems than conventional antidepressants — and link that response to different circuitry than other depression symptoms.”
Imaging studies similar to the one just published are underway in patients with major depression, though results are not yet available. Other studies have suggested that ketamine may be exerting these effects through glutamate and dopamine pathways. Research is underway to explore easier methods of drug delivery, such as nasal spray.
Of late, ketamine has been studied for its rapid antidepressant properties, providing relief within hours rather than the weeks required for traditional medications to work. At present, ketamine is not FDA approved for treatment of depression and it is still used primarily in a veterinary setting.
Ketamine is an NMDA receptor antagonist, though it also inhibits reuptake of dopamine, serotonin, and norepinephrine. It was developed in 1962 and has been used in both humans and animals. It is categorized as a dissociative agent. It has been used for general anesthesia, sedation, and as a pain killer. Side effects include amnesia and agitation, and its street use has led to hallucinations, delirium, and death.