Depression in Youth Is Tough to Treat and Requires Persistence and Creativity
At a symposium on ketamine for the treatment of depression in children at the 2013 meeting of the American Academy of Child and Adolescent Psychiatry, David Brent, a professor at the University of Pittsburg, gave the opening talk on the fact that as many as 20% of adolescents who are depressed fail to improve, develop chronic illness, and are thus in need of alternatives to traditional treatment. Predictors of non-improvement include substance use, low-level manic symptoms, poor adherence to a medication regimen, low blood levels of antidepressants, family conflict, high levels of inflammation in the body, and importantly, maternal depression. In adolescents insomnia was associated with poor response, but in younger children insomnia was associated with a better response.
Brent suggested using melatonin and sleep-focused cognitive behavioral therapy for insomnia in youth, but not using trazodone (which is commonly prescribed). Trazodone is converted to a compound called Meta-chlorophenylpiperazine or MCPP, which induces anxiety and dysphoria. MCPP is metabolized by hepatic enzymes 2D6, and fluoxetine and paroxetine inhibit 2D6, so if trazodone is combined with these antidepressants, the patient may get too much MCPP.
Surprisingly and contrary to some data in adults about the positive effects of therapy in those with abuse histories, in the study TORDIA (Treatment of SSRI-Resistant Depression in Adolescents), if youth with depression had experienced abuse in childhood, they did less well on the combination of cognitive behavioral therapy and selective serotonin reuptake inhibitors (SSRIs) compared to SSRIs alone.
Drugs that Antagonize the Glutamate NMDA Receptor are a New Approach to Antidepressant Treatment
Several antidepressant drugs work by blocking activity at the NMDA receptor for the excitatory neurotransmitter glutamate. These drugs include intravenous ketamine, a potent NMDA receptor blocker that can produce antidepressant effects within 2 hours of administration, and memantine (Namenda), which is less potent, acts more slowly, and can potentiate the antidepressant effects of lamotrigine and help stabilize mood in patients with treatment-resistant bipolar disorder. Now a drug with a related mechanism, D-cycloserine, has been shown to have antidepressant effects. High doses of the drug act as an antagonist at the glycine site of the NMDA receptor, blocking glycine’s ability to facilitate glutamate transmission through the receptor.
Glutamate is the major excitatory neurotransmitter in the brain and is important for the development of long-term memory. However, glutamate overactivity may contribute to depression. Decreasing this overactivity with the drugs noted above appears to produce antidepressant effects.
Uriel Heresco-Levy et al. reported in a 2013 article in the Journal of Neuropsychopharmacology that high doses of D-cycloserine (1000mg/day) had substantially greater antidepressant effects than placebo in a study of 26 patients with treatment-resistant depression. The drug was well tolerated.
Interestingly, low doses of the same drug have a different effect, acting as a partial agonist at the same site, facilitating glutamate transmission and enhancing the new learning that is necessary in cognitive behavioral therapy for anxiety disorders.
Editor’s Note: D-cycloserine requires further study in larger controlled trials, but this small study suggests promise. While ketamine’s effects are rapid in onset, they are also difficult to sustain. This study suggests a possible route to a slower onset with longer-lasting antidepressant effects.
Psychiatric Revolution: Changes in Behavior Are Associated with Dendritic Spine Shape and Number
Neuron cell
New research shows that cocaine, defeat stress, the rapid-acting antidepressant ketamine, and learning and memory can change the size, shape, or number of spines on the dendrites of neurons. Dendrites conduct electrical impulses into the cell body from neighboring neurons.
Cocaine
Several researchers, including Peter Kalivas at the Medical University of South Carolina, have reported that cocaine increases the size of the spines on the dendrites of a certain kind of neurons (GABAergic medium spiny neurons) in the nucleus accumbens (the reward center in the brain). This occurs through a dopamine D1 selective mechanism. N-acetylcysteine, a drug that can be found in health food stores, decreases cocaine intake in animals and humans, and also normalizes the size of dendritic spines.
Depression
Depression in animals and humans is associated with decreases in Rac1, a protein in the dendritic spines on GABA neurons in the nucleus accumbens. Rac1 regulates actin and other molecules that alter the shape of the spines.
In an animal model of depression called defeat stress, rodents are stressed by repeatedly being placed in a larger animal’s territory. Their subsequent behavior mimics clinical depression. This kind of social defeat stress decreases Rac1 and causes spines to become thin and lose some function. Replacing Rac1 returns the spines to a more mature mushroom shape and reverses the depressive behavior of these socially defeated animals. Researcher Scott Russo has also found Rac1 deficits in the nucleus accumbens of depressed patients who committed suicide. Russo suggests that decreases in Rac1 are responsible for the manifestation of social avoidance and other depressive behaviors in the defeat stress animal model, and that finding ways to increase Rac1 in humans would be an important new target for antidepressant drug development.
Another animal model of depression called chronic intermittent stress (in which the animals are exposed to a series of unexpected stressors like sounds or mild shocks) also induces depression-like behavior and makes the dendritic spines thin and stubby. The drug ketamine, which can bring about antidepressant effects in humans in as short a time as 2 hours, rapidly reverses the depressive behavior in animals and converts the spines back to the larger, more mature mushroom-shape they typically have.
Learning and Extinction of Fear
Researcher Wenbiao Gan has reported that fear conditioning can change the number of dendritic spines. When animals hear a tone paired with an electrical shock, they begin to exhibit a fear response to the tone. In layer 5 of the prefrontal cortex, spines are eliminated when conditioned fear develops, and are reformed (near where the eliminated spines were) during extinction training, when animals hear the tones without receiving the shock and learn not to fear the tone. However, in the primary auditory cortex the changes are opposite: new spines are formed with learning, and spines are eliminated with extinction.
Editor’s Note: It appears that we have arrived at a new milestone in psychiatry. In the field of neurology, changes seen in the brains of patients with strokes or Alzheimer’s dementia have been considered “real” because cells were obviously lost or dead. Psychiatry, in comparison, has been considered a soft science because neuronal changes have been more difficult to see and illnesses were and still are called “mental.” Now that new technologies have made a deeper level of precision, observation, and analysis possible, we know that the brain’s 12 billion neurons and 4 times as many glial cells are exquisitely plastic–capable of biochemical and structural changes that can be reversed using appropriate therapeutic maneuvers.
The changes associated with abnormal behaviors, addictions, and even normal processes of learning and memory now have clearly been shown to correspond with the size, shape, and biochemistry of dendritic spines. These subtle, reproducible changes in the brain and body are amenable to therapeutic intervention, and are now even more demanding of sophisticated medical attention.
New Drug Produces Rapid-Onset Antidepressant Effects
We have previously summarized studies on ketamine, which when given intravenously can bring about rapid-onset antidepressant effects. Ketamine is a full antagonist (or a blocker) of the glutamate NMDA receptors. Another drug currently in development may work in a related way.
At a recent scientific meeting, researcher Sheldon Preskorn showed that the compound GLYX-13, a partial agonist at the glycine binding site of the NMDA receptor (meaning it allows partial function of the glycine receptors that aid NMDA receptor function), exerts rapid antidepressant effects like the full antagonist ketamine when administered intravenously compared to placebo. GLYX-13 allows about 25% of the receptor activity of the full agonists glycine or D-serine, and thus might result in a 75% inhibition of NMDA receptor function.
GLYX-13 did not induce any psychotomimetic effects (like delusion or delirium), which are possible with the full NMDA antagonist ketamine. The effects of GLYX-13 appeared within 24 hours, lasted at least 6 days, but were gone by day 14.
Editor’s Note: Long-term effectiveness of ketamine for treatment of depression is unclear, but in addition to its potential psychotomimetic effects, it can also be abused. Whether GLYX-13 may be easier to use, longer-lasting, or safer for longer-term clinical effectiveness remains a key question.
Developing Rapid Onset Antidepressant Drugs That Act at the NMDA Receptor
For several years, researchers have been exploring potential rapid-acting treatments for unipolar and bipolar depression. Intravenous ketamine has the best-replicated results so far. A slow infusion of ketamine (0.5mg/kg over 40 minutes) produces a rapid onset of antidepressant effects in only a few hours, but the improved mood lasts only 3-5 days.
Ketamine blocks the receptors of the main excitatory neurotransmitter in the central nervous system, glutamate. Glutamate is released from nerve endings and travels across the synapse to receptors on the next cell’s dendrites. There are multiple types of glutamate receptors at the dendrites, and ketamine blocks one called the NMDA receptor, which allows calcium ions to enter the cell.
Some downsides to ketamine are the brief duration of its effectiveness and its dissociative side effects. The search is on for other drugs that are free from these side effects and that could extend the duration of rapid-onset antidepressant effects.
At the 2012 meeting of the International Congress of Neuropsychopharmacology (CINP), Mike Quirk of the pharmaceutical company AstraZeneca reviewed data on the intricacies of the glutamate NMDA receptor blockade and discussed the potential of AZD6765, an NMDA receptor blocker he and his colleagues have been researching.
The more the NMDA receptor is blocked, the more psychomimetic it becomes, meaning it produces hallucinations and delusions. For example, phencyclidine (PCP or angel dust) is a potent NMDA receptor blocker and psychosis inducer. For antidepressant purposes, a less complete or less persistent NMDA receptor blockade is desired. Read more
High Sustained Success Rate With Adjunctive Memantine (Namenda) in Treatment-Resistant Bipolar Disorder
Koukopoulos et al. published a study of the anti-Alzheimer’s drug memantine in the Journal of Affective Disorders in 2012. The study of memantine (10-30mg/day) as an add-on to patients’ regular treatment for highly treatment-resistant bipolar disorder was open (i.e. not blind, randomized or placebo-controlled), but it deserves careful attention for its noteworthy results. Of the 40 patients in the study, who had been severely ill for long periods of time, 72.5% showed a rating of much or very much improved on the Clinical Global Impressions Scale for Bipolar Disorders (CGI-BP) after both 6 months and 12 months. Among rapid cyclers, 68.4% stabilized and remitted on memantine.
Editor’s Note: Memantine is an antagonist of glutamate NMDA receptors and is approved by the Federal Drug Administration (FDA) for the treatment of Alzheimer’s dementia, but not for other indications. Nonetheless, few (if any) drugs have this high a response rate in such a difficult-to-treat population, and the researchers suggest that even based on these preliminary data (which replicate their previous observations), careful clinical trials of memantine in individual patients would be worthy of consideration.
The data are so promising that fast-track development of this drug for FDA approval would be warranted. More formal randomized controlled clinical trials are needed.
We have written before about a few treatments that have rapid-onset antidepressant effects, including intravenous (IV) ketamine (at a dose of 0.5mg over 40 minutes). Ketamine works by blocking glutamate NMDA receptors, but the rapid antidepressant effects it produces (within 2 hours of treatment) last only 3 to 4 days. Given the similar mechanisms of action of ketamine and memantine and memantine’s high success rate in this study by Koukopoulos, it is plausible that treatment with memantine could extend the rapid onset effects of IV ketamine. However, this speculation has not yet been tested. At the very least, the similarity between the mechanisms of memantine and ketamine in blocking the glutamate NMDA receptor lends additional support to the clinical rationale for treating bipolar disorder with adjunctive memantine.
Procedures with Rapid-Onset Antidepressant Effects
At a recent scientific meeting, Carlos Zarate of the National Institute of Mental Health (NIMH) discussed a variety of rapid-onset antidepressant manipulations. The talk focused on intravenous (IV) administration of the NMDA receptor antagonist ketamine and the anticholinergic drug scopolamine.
IV Ketamine
Intravenous ketamine has been administered to approximately 1000 patients at research centers at Mount Sinai Hospital in New York, Yale University, and at the NIMH in Bethesda. The results have been consistent; more than half of the patients experienced a rapid onset of antidepressant effect, usually within the first 2 hours. However, the effects of intravenous ketamine tend to disappear after 3 to 5 days.
In both unipolar and bipolar depressed patients whose illness has been highly resistant to multiple treatments, ketamine also brings about a rapid-onset decrease in suicidal ideation and intent. In some cases these positive effects have lasted a week or more. Thus intravenous ketamine could potentially be used at hospitals to treat suicidal emergencies.
Scopolamine
New data indicate that intravenous scopolamine, a selective blocker of muscarinic cholinergic receptors that is used to help ward off seasickness, brings about onset of antidepressant effects in up to one day and sometimes in a matter of hours. As with ketamine, these effects occur in both unipolar and bipolar depressed patients.
Mechanisms of Action of Ketamine
Editor’s Note: New data from animal studies may be able to explain some of the mechanisms behind the rapid onset of antidepressant effects that occurs with ketamine. Ketamine causes increases in brain-derived neurotrophic factor (BDNF), which is important for the development and health of neurons. In rodents, new synaptic proteins are created following intravenous administration of ketamine.
If animals are subjected to chronic unpredictable stress, dendritic spines (on which synapses are formed) appear to shrink. However, when ketamine is administered intravenously to these animals, not only is their behavior rapidly ameliorated, but the thin dendritic spines shift back to their more mature, mushroomed-shaped form within a few hours. (A slightly slower, less dramatic change in spines occurs with scopolamine.) A loss of dendritic volume has also been demonstrated in depressed people.
The data in animals are not only valuable for their potential application in clinical treatment and emergency situations involving suicidal ideation, but they also demonstrate a mechanism by which a single administration of intravenous ketamine or scopolamine is capable not only of reversing depressive behaviors in animals, but changing dendritic spine morphology. Given this development, it may be possible to identify other treatments that induce rapid-onset antidepressant effects using other parts of the same neurological pathways.
Other Rapid-Onset Approaches: TRH and Sleep Deprivation
Intravenous thyrotropin releasing hormone (TRH) also has rapid-onset antidepressant effects within 24 hours in depressed patients, but tolerance develops after repeated use.
Surprisingly, one night of complete sleep deprivation can also bring about dramatic onset of antidepressant effects the following day in approximately 50% of severely depressed patients.
In animal studies by Ron Duman and colleagues at Yale University, administration of brain-derived neurotrophic factor (BDNF) either into a rodent’s blood or its brain has induced rapid-onset antidepressant-like effects.
Taken together, these data indicate that there are ways to bring about rapid improvement in depression, even if conventional antidepressants usually require 2 to 4 weeks to exert their maximum antidepressant effects. Read more
IV Scopolamine Brings About Rapid Onset Of Antidepressant Effects
Frankel and colleagues from the National Institute of Mental Health presented a randomized, placebo-controlled clinical trial of intravenous (IV) scopolamine for bipolar depression at the 9th International Conference on Bipolar Disorder (ICBD) in 2011. The same group of investigators previously showed that IV scopolamine was able to induce fast-acting antidepressant responses in those with unipolar major depression. This represents a new and independent study exclusively among patients with bipolar depression.
In the first phase of the study, three sessions of either IV scopolamine at 4 mcg/kg or a sham treatment were scheduled three to five days apart. In the second phase of the study, the patients were switched to the other treatment for three sessions. The results showed a rapid improvement in depression following the first session with scopolamine, more than occurred with the sham treatment. Hamilton Anxiety Rating scale (HAMA) scores also improved more on scopolamine than with the sham treatment, while Young Mania Rating Scores (YMRS) did not differ.
Editor’s note: As previously discussed in the BNN, scopolamine, an antagonist of acetylcholine muscarinic receptors, appears to exert rapid onset antidepressant effects in both unipolar and bipolar depression. When administered intravenously it takes its place with other rapidly acting antidepressant treatments, including IV ketamine, IV thyrotropin releasing hormone (TRH), and one night of sleep deprivation. The new data indicate that both unipolar and bipolar depression can respond rapidly (i.e. within a matter of hours) to certain treatments, even though most conventionally acting antidepressant modalities can take weeks to achieve maximum antidepressant effects. Read more
Episodic vs. Continuous Social Stress Result in Different Rates of Cocaine Use
In a study of rodents exposed to stress (by being forced to enter another rodent’s territory) and given the opportunity to self-administer cocaine, those exposed to a few brief episodes of stress increased their cocaine use and engaged in binge-like episodes, while those exposed to stress chronically showed suppressed cocaine use.
At the American College of Neuropsychopharmacology meeting in December 2009, Klaus Miczek and colleagues from Tufts University in Boston presented a fascinating study indicating that the temporal aspects of the experience of social stress may have dramatic impact not only on defeat stress behaviors and the associated biochemistry, but also on the likelihood that an animal adopts cocaine self-administration. These investigators compared episodic versus chronic defeat stress in rodents.
Episodic social defeat stress consisted of four brief confrontations between an intruding animal and an aggressive resident rat over the course of a period of ten days. In contrast, chronic subordination stress involved the continuous exposure of the intruder rat to an aggressive resident over five weeks, during which time the intruder lived in a protective cage within the resident’s home cage.
The episodically defeated intruder rats showed increases in intravenous cocaine self-administration and prolonged binge-like episodes, along with increases in brain-derived neurotropic factor (BDNF), which is necessary for long-term learning and memory, in the midbrain ventral-tegmental area (VTA) and increased dopamine release in the nucleus accumbens, the reward area of the brain. In contrast, the continuously subordinate rats showed the opposite pattern of suppressed cocaine intake, suppression of dopamine release in the n. accumbens, and reduced BDNF in the VTA.
