Husseini K. Manji

The cellular neurobiology of depression.

Major depressive disorders, long considered to be of neurochemical origin, have recently been associated with impairments in signaling pathways that regulate neuroplasticity and cell survival. Agents designed to directly target molecules in these pathways may hold promise as new therapeutics for depression.

Discovering Endophenotypes for Major Depression

The limited success of genetic studies of major depression has raised questions concerning the definition of genetically relevant phenotypes. This paper presents strategies to improve the phenotypic definition of major depression by proposing endophenotypes at two levels: First, dissecting the depressive phenotype into key components results in narrow definitions of putative psychopathological endophenotypes: mood bias toward negative emotions, impaired reward function, impaired learning and memory, neurovegetative signs, impaired diurnal variation, impaired executive cognitive function, psychomotor change, and increased stress sensitivity. A review of the recent literature on neurobiological and genetic findings associated with these components is given. Second, the most consistent heritable biological markers of major depression are proposed as biological endophenotypes for genetic studies: REM sleep abnormalities, functional and structural brain abnormalities, dysfunctions in serotonergic, catecholaminergic, hypothalamic-pituitary-adrenocortical axis, and CRH systems, and intracellular signal transduction endophenotypes. The associations among the psychopathological and biological endophenotypes are discussed with respect to specificity, temporal stability, heritability, familiality, and clinical and biological plausibility. Finally, the case is made for the development of a new classification system in order to reduce the heterogeneity of depression representing a major impediment to elucidating the genetic and neurobiological basis of this common, severe, and often life-threatening illness.

Cellular Mechanisms Underlying the Antidepressant Effects of Ketamine: Role of α-Amino-3-Hydroxy-5-Methylisoxazole-4-Propionic Acid Receptors

BACKGROUND Ketamine exerts a robust, rapid, and relatively sustained antidepressant effect in patients with major depression. Understanding the mechanisms underlying the intriguing effects of N-methyl d-aspartate (NMDA) antagonists could lead to novel treatments with a rapid onset of action. METHODS The learned helplessness, forced swim, and passive avoidance tests were used to investigate ketamines behavioral effects in mice. Additional biochemical and behavioral experiments were undertaken to determine whether the antidepressant-like properties of ketamine and other NMDA antagonists involve alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor throughput. RESULTS Subanesthetic doses of ketamine treatment caused acute and sustained antidepressant-like effects. At these doses, ketamine did not impair fear memory retention. MK-801 (dizocilpine) and Ro25-6981, an NR2B selective antagonist, also exerted antidepressant-like effects; these effects, however, were not sustained as long as those of ketamine. Pre-treatment with NBQX, an AMPA receptor antagonist, attenuated both ketamine-induced antidepressant-like behavior and regulation of hippocampal phosphorylated GluR1 AMPA receptors. CONCLUSIONS NMDA antagonists might exert rapid antidepressant-like effects by enhancing AMPA relative to NMDA throughput in critical neuronal circuits.

A Randomized Add-on Trial of an N-methyl-d-aspartate Antagonist in Treatment-Resistant Bipolar Depression

CONTEXT Existing therapies for bipolar depression have a considerable lag of onset of action. Pharmacological strategies that produce rapid antidepressant effects-for instance, within a few hours or days-would have an enormous impact on patient care and public health. OBJECTIVE To determine whether an N-methyl-D-aspartate-receptor antagonist produces rapid antidepressant effects in subjects with bipolar depression. DESIGN A randomized, placebo-controlled, double-blind, crossover, add-on study conducted from October 2006 to June 2009. SETTING Mood Disorders Research Unit at the National Institute of Mental Health, Bethesda, Maryland. Patients Eighteen subjects with DSM-IV bipolar depression (treatment-resistant). INTERVENTIONS Subjects maintained at therapeutic levels of lithium or valproate received an intravenous infusion of either ketamine hydrochloride (0.5 mg/kg) or placebo on 2 test days 2 weeks apart. The Montgomery-Asberg Depression Rating Scale was used to rate subjects at baseline and at 40, 80, 110, and 230 minutes and on days 1, 2, 3, 7, 10, and 14 postinfusion. MAIN OUTCOME MEASURES Change in Montgomery-Asberg Depression Rating Scale primary efficacy measure scores. RESULTS Within 40 minutes, depressive symptoms significantly improved in subjects receiving ketamine compared with placebo (d = 0.52, 95% confidence interval [CI], 0.28-0.76); this improvement remained significant through day 3. The drug difference effect size was largest at day 2 (d = 0.80, 95% CI, 0.55-1.04). Seventy-one percent of subjects responded to ketamine and 6% responded to placebo at some point during the trial. One subject receiving ketamine and 1 receiving placebo developed manic symptoms. Ketamine was generally well tolerated; the most common adverse effect was dissociative symptoms, only at the 40-minute point. CONCLUSION In patients with treatment-resistant bipolar depression, robust and rapid antidepressant effects resulted from a single intravenous dose of an N-methyl-D-aspartate antagonist.

Enhancement of hippocampal neurogenesis by lithium.

Abstract: Increasing evidence suggests that mood disorders are associated with a reduction in regional CNS volume and neuronal and glial cell atrophy or loss. Lithium, a mainstay in the treatment of mood disorders, has recently been demonstrated to robustly increase the levels of the cytoprotective B‐cell lymphoma protein‐2 (bcl‐2) in areas of rodent brain and in cultured cells. In view of bcl‐2s antiapoptotic and neurotrophic effects, the present study was undertaken to determine if lithium affects neurogenesis in the adult rodent hippocampus. Mice were chronically treated with lithium, and 5‐bromo‐2‐deoxyuridine (BrdU) labeling of dividing cells was conducted over 12 days. Immunohistochemical analysis was undertaken 1 day after the last injection, and three‐dimensional stereological cell counting revealed that lithium produced a significant 25% increase in the BrdU‐labeled cells in the dentate gyrus. Double‐labeling immunofluorescence studies were undertaken to co‐localize BrdU‐positive cells with neuron‐specific nuclear protein and showed that ∼65% of the cells were double‐labeled. These results add to the growing body of evidence suggesting that mood stabilizers and antidepressants exert neurotrophic effects and may therefore be of use in the long‐term treatment of other neuropsychiatric disorders.

The mood-stabilizing agents lithium and valproate robustly increase the levels of the neuroprotective protein bcl-2 in the CNS

Abstract : Differential display of mRNA was used to identify concordant changes in gene expression induced by two mood‐stabilizing agents, lithium and valproate (VPA). Both treatments, on chronic administration, increased mRNA levels of the transcription factor polyomavirus enhancer‐binding protein (PEBP) 2β in frontal cortex (FCx). Both treatments also increased the DNA binding activity of PEBP2αβ and robustly increased the levels of bcl‐2 (known to be transcriptionally regulated by PEBP2) in FCx. Immunohistochemical studies revealed a marked increase in the number of bcl‐2‐immunoreactive cells in layers 2 and 3 of FCx. These novel findings represent the first report of medication‐induced increases in CNS bcl‐2 levels and may have implications not only for mood disorders, but also for long‐term treatment of various neurodegenerative disorders.

The Mood‐Stabilizing Agent Valproate Inhibits the Activity of Glycogen Synthase Kinase‐3

Abstract : Valproic acid (VPA) is a potent broad‐spectrum anti‐epileptic with demonstrated efficacy in the treatment of bipolar affective disorder. It has previously been demonstrated that both VPA and lithium increase activator protein‐1 (AP‐1) DNA binding activity, but the mechanisms underlying these effects have not been elucidated. However, it is known that phosphorylation of c‐jun by glycogen synthase kinase (GSK)‐3β inhibits AP‐1 DNA binding activity, and lithium has recently been demonstrated to inhibit GSK‐3β. These results suggest that lithium may increase AP‐1 DNA binding activity by inhibiting GSK‐3β. In the present study, we sought to determine if VPA, like lithium, regulates GSK‐3. We have found that VPA concentration‐dependently inhibits both GSK‐3α and ‐3β, with significant effects observed at concentrations of VPA similar to those attained clinically. Incubation of intact human neuroblastoma SH‐SY5Y cells with VPA results in an increase in the subsequent in vitro recombinant GSK‐3β‐mediated 32P incorporation into two putative GSK‐3 substrates (~85 and 200 kDa), compatible with inhibition of endogenous GSK‐3β by VPA. Consistent with GSK‐3β inhibition, incubation of SH‐SY5Y cells with VPA results in a significant time‐dependent increase in both cytosolic and nuclear β‐catenin levels. GSK‐3β plays a critical role in the CNS by regulating various cytoskeletal processes as well as long‐term nuclear events and is a common target for both lithium and VPA ; inhibition of GSK‐3β in the CNS may thus underlie some of the long‐term therapeutic effects of mood‐stabilizing agents.

Mood Stabilizer Valproate Promotes ERK Pathway-Dependent Cortical Neuronal Growth and Neurogenesis

Manic-depressive illness has been conceptualized as a neurochemical illness. However, brain imaging and postmortem studies reveal gray-matter reductions, as well as neuronal and glial atrophy and loss in discrete brain regions of manic-depressive patients. The roles of such cerebral morphological deficits in the neuropathophysiology and therapeutic mechanisms of manic-depressive illness are unknown. Valproate (2-propylpentanoate) is a commonly used mood stabilizer. The ERK (extracellular signal-regulated kinase) pathway is used by neurotrophic factors to regulate neurogenesis, neurite outgrowth, and neuronal survival. We found that chronic treatment of rats with valproate increased levels of activated phospho-ERK44/42 in neurons of the anterior cingulate, a region in which we found valproate-induced increases in expression of an ERK pathway-regulated gene, bcl-2. Valproate time and concentration dependently increased activated phospho-ERK44/42 and phospho-RSK1 (ribosomal S6 kinase 1) levels in cultured cortical cells. These increases were attenuated by Raf and MEK (mitogen-activated protein kinase/ERK kinase) inhibitors. Although valproate affects the functions of GSK-3 (glycogen synthase kinase-3) and histone deacetylase (HDAC), its effects on the ERK pathway were not fully mimicked by selective inhibitors of GSK-3 or HDAC. Similar to neurotrophic factors, valproate enhanced ERK pathway-dependent cortical neuronal growth. Valproate also promoted neural stem cell proliferation-maturation (neurogenesis), demonstrated by bromodeoxyuridine (BrdU) incorporation and double staining of BrdU with nestin, Tuj1, or the neuronal nuclei marker NeuN (neuronal-specific nuclear protein). Chronic treatment with valproate enhanced neurogenesis in the dentate gyrus of the hippocampus. Together, these data demonstrate that valproate activates the ERK pathway and induces ERK pathway-mediated neurotrophic actions. This cascade of events provides a potential mechanism whereby mood stabilizers alleviate cerebral morphometric deficits associated with manic-depressive illness.

Variation in the Gene Encoding the Serotonin 2A Receptor Is Associated with Outcome of Antidepressant Treatment

Depressive disorders account for a large and increasing global burden of disease. Although the condition of many patients improves with medication, only a minority experience full remission, and patients whose condition responds to one medication may not have a response to others. Individual variation in antidepressant treatment outcome is, at present, unpredictable but may have a partial genetic basis. We searched for genetic predictors of treatment outcome in 1,953 patients with major depressive disorder who were treated with the antidepressant citalopram in the Sequenced Treatment Alternatives for Depression (STAR*D) study and were prospectively assessed. In a split-sample design, a selection of 68 candidate genes was genotyped, with 768 single-nucleotide-polymorphism markers chosen to detect common genetic variation. We detected significant and reproducible association between treatment outcome and a marker in HTR2A (P range 1 x 10(-6) to 3.7 x 10(-5) in the total sample). Other markers in HTR2A also showed evidence of association with treatment outcome in the total sample. HTR2A encodes the serotonin 2A receptor, which is downregulated by citalopram. Participants who were homozygous for the A allele had an 18% reduction in absolute risk of having no response to treatment, compared with those homozygous for the other allele. The A allele was over six times more frequent in white than in black participants, and treatment was less effective among black participants. The A allele may contribute to racial differences in outcomes of antidepressant treatment. Taken together with prior neurobiological findings, these new genetic data make a compelling case for a key role of HTR2A in the mechanism of antidepressant action.

Lithium increases N-acetyl-aspartate in the human brain: in vivo evidence in support of bcl-2’s neurotrophic effects?

BACKGROUND Recent preclinical studies have shown that lithium (Li) robustly increases the levels of the major neuroprotective protein, bcl-2, in rat brain and in cells of human neuronal origin. These effects are accompanied by striking neuroprotective effects in vitro and in the rodent central nervous system in vivo. We have undertaken the present study to determine if lithium exerts neurotrophic/ neuroprotective effects in the human brain in vivo. METHODS Using quantitative proton magnetic resonance spectroscopy, N-acetyl-aspartate (NAA) levels (a putative marker of neuronal viability and function) were investigated longitudinally in 21 adult subjects (12 medication-free bipolar affective disorder patients and 9 healthy volunteers). Regional brain NAA levels were measured at baseline and following 4 weeks of lithium (administered in a blinded manner). RESULTS A significant increase in total brain NAA concentration was documented (p < .0217). NAA concentration increased in all brain regions investigated, including the frontal, temporal, parietal, and occipital lobes. CONCLUSIONS This study demonstrates for the first time that Li administration at therapeutic doses increases brain NAA concentration. These findings provide intriguing indirect support for the contention that chronic lithium increases neuronal viability/function in the human brain, and suggests that some of Lis long-term beneficial effects may be mediated by neurotrophic/neuroprotective events.