A functional alternative splicing mutation in human tryptophan hydroxylase-2

The brain serotonergic system has an essential role in the physiological functions of the central nervous system and dysregulation of serotonin (5-HT) homeostasis has been implicated in many neuropsychiatric disorders. The tryptophan hydroxylase-2 (TPH2) gene is the rate-limiting enzyme in brain 5-HT synthesis, and thus is an ideal candidate gene for understanding the role of dysregulation of brain serotonergic homeostasis. Here, we characterized a common, but functional single-nucleotide polymorphism (SNP rs1386493) in the TPH2 gene, which decreases efficiency of normal RNA splicing, resulting in a truncated TPH2 protein (TPH2-TR) by alternative splicing. TPH2-TR, which lacks TPH2 enzyme activity, dominant-negatively affects full-length TPH2 function, causing reduced 5-HT production. The predicted mRNA for TPH2-TR is present in postmortem brain of rs1386493 carriers. The rs13864923 variant does not appear to be overrepresented in either global or multiplex depression cohorts. However, in combination with other gene variants linked to 5-HT homeostasis, this variant may exhibit important epistatic influences.

The reduction of R1, a novel repressor protein for monoamine oxidase A, in major depressive disorder

The novel transcriptional repressor protein, R1 (JPO2/CDCA7L/RAM2), inhibits monoamine oxidase A (MAO A) gene expression and influences cell proliferation and survival. MAO A is implicated in several neuropsychiatric illnesses and highly elevated in major depressive disorder (MDD); however, whether R1 is involved in these disorders is unknown. This study evaluates the role of R1 in depressed subjects either untreated or treated with antidepressant drugs. R1 protein levels were determined in the postmortem prefrontal cortex of 18 untreated MDD subjects and 12 medicated MDD subjects compared with 18 matched psychiatrically normal control subjects. Western blot analysis showed that R1 was significantly decreased by 37.5% (p<0.005) in untreated MDD subjects. The R1 level in medicated MDD subjects was also significantly lower (by 30%; p<0.05) compared with control subjects, but was not significantly different compared with untreated MDD subjects. Interestingly, the reduction in R1 was significantly correlated with an increase (approximately 40%; p<0.05) in MAO A protein levels within the MDD groups compared with controls. Consistent with the change in MAO A protein expression, the MAO A catalytic activity was significantly greater in both MDD groups compared with controls. These results suggest that reduced R1 may lead to elevated MAO A levels in untreated and treated MDD subjects; moreover, the reduction of R1 has been implicated in apoptotic cell death and apoptosis has also been observed in the brains of MDD subjects. Therefore, modulation of R1 levels may provide a new therapeutic target in the development of more effective strategies to treat MDD.

5-HTTLPR genotype and gender, but not chronic fluoxetine administration, are associated with cortical TREK1 protein expression in rhesus macaques

TREK1 is a widely expressed background potassium channel. Similar to mice treated with selective serotonin reuptake inhibitors (SSRIs), TREK1 knockout mice are resistant to depression-like behavior and have elevated serotonin levels leading to speculation that TREK1 inhibition may contribute to the therapeutic effects of SSRIs. This study examined how chronic fluoxetine administration and a common functional polymorphism in the serotonin-transporter-linked promoter region (5-HTTLPR) influence cortical TREK1 expression in 24 rhesus monkeys. The short rh5-HTTLPR allele as well as female gender were associated with reduced cortical TREK1 protein expression but chronic SSRI administration had no effect. These results suggest that serotonin may influence TREK1, but that chronic SSRI treatment does not result in long lasting changes in cortical TREK1 protein expression. TREK1 gender differences may be related to gender differences in serotonin and require further research.

The mTOR signaling pathway in the prefrontal cortex is compromised in major depressive disorder

Recent studies demonstrate that rapid antidepressant response to ketamine is mediated by activation of the mammalian target of rapamycin (mTOR) signaling pathway, leading to increased synaptic proteins in the prefrontal cortex (PFC) of rats. Our postmortem studies indicate robust deficits in prominent postsynaptic proteins including N-methyl-d-aspartate (NMDA) receptor subunits (NR2A, NR2B), metabotropic glutamate receptor subtype 5 (mGluR5) and postsynaptic density protein 95kDa (PSD-95) in the PFC in major depressive disorder (MDD). We hypothesize that deficits in the mTOR-dependent translation initiation pathway contribute to the molecular pathology seen in the PFC of MDD subjects, and that a rapid reversal of these abnormalities may underlie antidepressant activity. The majority of known translational regulation occurs at the level of initiation. mTOR regulates translation initiation via its downstream components: p70-kDa ribosomal protein S6 kinase (p70S6K), and eukaryotic initiation factors 4E and 4B (eIF4E and eIF4B). In this study, we examined the expression of mTOR and its core downstream signaling targets: p70S6K, eIF4E, and eIF4B in the PFC of 12 depressed subjects and 12 psychiatrically healthy controls using Western blot. Levels of eIF4E phosphorylated at serine 209 (p-eIF4E-Ser209) and eIF4B phosphorylated at serine 504 (p-eIF4B-Ser504) were also examined. Adjacent cortical tissue samples from both cohorts of subjects were used in our previous postmortem analyses. There was a significant reduction in mTOR, p70S6K, eIF4B and p-eIF4B protein expression in MDD subjects relative to controls. No group differences were observed in eIF4E, p-eIF4E or actin levels. Our findings show deficits in mTOR-dependent translation initiation in MDD particularly via the p70S6K/eIF4B pathway, and indicate a potential association between marked deficits in synaptic proteins and dysregulation of mTOR signaling in MDD.

Vascular and extravascular immunoreactivity for intercellular adhesion molecule 1 in the orbitofrontal cortex of subjects with major depression: age-dependent changes

BACKGROUND

Vascular and immune alterations in the prefrontal cortex may contribute to major depression in elderly subjects. Intercellular adhesion molecule-1 (ICAM-1), major inflammatory mediator in vessels and astrocytes, could be altered in geriatric depression, but little is known about its age-dependent expression in subjects with depression and its relationship to astrocytes identified by the marker glial fibrillary acidic protein (GFAP), found to be reduced in depression.

METHODS

We measured the percentage of gray matter area fraction covered by ICAM-1 immunoreactivity in blood vessels and in extravascular accumulations of ICAM-1 immunoreactivity in 19 non-psychiatric comparison subjects and 18 subjects with major depression, all characterized by postmortem psychological diagnosis. Association of extravascular ICAM-1 to GFAP-positive astrocytes was investigated by double-labeling immunofluorescence.

RESULTS

Vascular and extravascular fractions of ICAM-1 immunoreactivity were lower in subjects with MDD than in non-psychiatric comparison subjects. Non-psychiatric comparison subjects older than 60 experienced dramatic increase in extravascular ICAM-1 immunoreactivity, but this increase was attenuated in elderly subjects with MDD, particularly in those dying by suicide. Most extracellular ICAM-1 immunoreactivity was coextensive with GFAP-immunoreactive astrocytes in both groups.

LIMITATIONS

Heterogeneity in type and dosage of antidepressant medication. Difficulty in determining the exact onset of depression in subjects older than 60 at the time of death. Routine cerebrovascular pathological screening may miss subtle subcellular and molecular changes.

CONCLUSIONS

There is significant attenuation of extravascular and vascular ICAM-1 immunoreactivity in elderly subjects with major depression suggesting an astrocyte-associated alteration in immune function in the aging orbitofrontal cortex of subjects with MDD.

Reduced metabotropic glutamate receptor 5 density in major depression determined by [(11)C]ABP688 PET and postmortem study

OBJECTIVE

Clinical and preclinical evidence suggests a hyperactive glutamatergic system in clinical depression. Recently, the metabotropic glutamate receptor 5 (mGluR5) has been proposed as an attractive target for novel therapeutic approaches to depression. The goal of this study was to compare mGluR5 binding (in a positron emission tomography [PET] study) and mGluR5 protein expression (in a postmortem study) between individuals with major depressive disorder and psychiatrically healthy comparison subjects.

METHOD

Images of mGluR5 receptor binding were acquired using PET with [(11)C]ABP688, which binds to an allosteric site with high specificity, in 11 unmedicated individuals with major depression and 11 matched healthy comparison subjects. The amount of mGluR5 protein was investigated using Western blot in postmortem brain samples of 15 depressed individuals and 15 matched comparison subjects.

RESULTS

The PET study revealed lower levels of regional mGluR5 binding in the prefrontal cortex, the cingulate cortex, the insula, the thalamus, and the hippocampus in the depression group relative to the comparison group. Severity of depression was negatively correlated with mGluR5 binding in the hippocampus. The postmortem study showed lower levels of mGluR5 protein expression in the prefrontal cortex (Brodmann's area 10) in the depression group relative to the comparison group, while prefrontal mGluR1 protein expression did not differ between groups.

CONCLUSIONS

The lower levels of mGluR5 binding observed in the depression group are consonant with the lower levels of protein expression in brain tissue in the postmortem depression group. Thus, both studies suggest that basal or compensatory changes in excitatory neurotransmission play roles in the pathophysiology of major depression.

Glial and glutamatergic markers in depression, alcoholism, and their comorbidity

BACKGROUND

Alteration of glutamatergic neurotransmission in the prefrontal cortex (PFC) may contribute to the pathophysiology of alcoholism and major depressive disorder (MDD). Among glial cells, astrocytes are mostly responsible for recycling synaptic glutamate by uptake through excitatory amino acid transporters 1 and 2 (EAAT1 and EAAT2), and conversion to glutamine with glutamine synthetase (GS). Low density of astrocytes in the PFC of "uncomplicated' alcoholics and MDD subjects may parallel altered glutamate transporters and GS in the PFC.

METHODS

Immunohistochemistry and Western blotting for glutamate transporters, GS and glial fibrillary acidic protein (GFAP) were applied to postmortem tissue of the left orbitofrontal cortex from 13 subjects with MDD, 13 with alcoholism, 10 with comorbid alcoholism plus MDD (MDA), and 13 non-psychiatric controls. Area fraction of immunoreactivity was measured in sections, and protein levels in Western blots.

RESULTS

EAAT2 immunoreactivity was significantly lower in MDD and MDA subjects than in controls. EAAT1 levels were lower in MDA and MDD subjects as compared to controls, while GS levels in MDA were significantly lower than in alcoholics and controls, and lower in MDD subjects than in alcoholics. Area fraction of GFAP was lower in MDD, but not in MDA subjects as compared to controls or alcoholics.

LIMITATIONS

High variability of protein levels in some groups and effects of antidepressant treatment, although appearing to be limited, cannot be fully evaluated.

CONCLUSIONS

There are differential changes in the expression of glial glutamatergic markers in depression and alcoholism, suggesting a depletion of certain aspects of glutamatergic processing in depression.

A negative regulator of MAP kinase causes depressive behavior

The lifetime prevalence (∼16%) and the economic burden ($100 billion annually) associated with major depressive disorder (MDD) make it one of the most common and debilitating neurobiological illnesses. To date, the exact cellular and molecular mechanisms underlying the pathophysiology of MDD have not been identified. Here we use whole-genome expression profiling of postmortem tissue and show significantly increased expression of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1, encoded by DUSP1, but hereafter called MKP-1) in the hippocampal subfields of subjects with MDD compared to matched controls. MKP-1, also known as dual-specificity phosphatase-1 (DUSP1), is a member of a family of proteins that dephosphorylate both threonine and tyrosine residues and thereby serves as a key negative regulator of the MAPK cascade, a major signaling pathway involved in neuronal plasticity, function and survival. We tested the role of altered MKP-1 expression in rat and mouse models of depression and found that increased hippocampal MKP-1 expression, as a result of stress or viral-mediated gene transfer, causes depressive behaviors. Conversely, chronic antidepressant treatment normalizes stress-induced MKP-1 expression and behavior, and mice lacking MKP-1 are resilient to stress. These postmortem and preclinical studies identify MKP-1 as a key factor in MDD pathophysiology and as a new target for therapeutic interventions.

Decreased expression of Freud-1/CC2D1A, a transcriptional repressor of the 5-HT1A receptor, in the prefrontal cortex of subjects with major depression

Serotonin1A (5-HT(1A)) receptors are reported altered in the brain of subjects with major depressive disorder (MDD). Recent studies have identified transcriptional regulators of the 5-HT(1A) receptor and have documented gender-specific alterations in 5-HT(1A) transcription factor and 5-HT(1A) receptors in female MDD subjects. The 5' repressor element under dual repression binding protein-1 (Freud-1) is a calcium-regulated repressor that negatively regulates the 5-HT(1A) receptor gene. This study documented the cellular expression of Freud-1 in the human prefrontal cortex (PFC) and quantified Freud-1 protein in the PFC of MDD and control subjects as well as in the PFC of rhesus monkeys chronically treated with fluoxetine. Freud-1 immunoreactivity was present in neurons and glia and was co-localized with 5-HT(1A) receptors. Freud-1 protein level was significantly decreased in the PFC of male MDD subjects (37%, p=0.02) relative to gender-matched control subjects. Freud-1 protein was also reduced in the PFC of female MDD subjects (36%, p=0.18) but was not statistically significant. When the data was combined across genders and analysed by age, the decrease in Freud-1 protein level was greater in the younger MDD subjects (48%, p=0.01) relative to age-matched controls as opposed to older depressed subjects. Similarly, 5-HT(1A) receptor protein was significantly reduced in the PFC of the younger MDD subjects (48%, p=0.01) relative to age-matched controls. Adult male rhesus monkeys administered fluoxetine daily for 39 wk revealed no significant change in cortical Freud-1 or 5-HT(1A) receptor proteins compared to vehicle-treated control monkeys. Reduced protein expression of Freud-1 in MDD subjects may reflect dysregulation of this transcription factor, which may contribute to the altered regulation of 5-HT(1A) receptors observed in subjects with MDD. These data may also suggest that reductions in Freud-1 protein expression in the PFC may be associated with early onset of MDD.

Apples to oranges?: a direct comparison between suicide attempters and suicide completers

BACKGROUND

Suicide attempters and completers may represent different but overlapping groups of distressed individuals. Although depression is related to an increased risk of suicide, the presence of depression may not discriminate suicide attempters from completers. The present study compared suicide attempters and suicide completers on symptoms of depression, the presence of suicide-related variables and stressful life events.

AIMS

The present study sought to identify the key differences between 50 suicide attempters and 50 completers, all diagnosed with a Major Depressive Disorder at the time of their suicidal act.

METHODS

Suicide attempters and family member informants of suicide completers participated in a thorough psychosocial evaluation. To maximize comparisons with completers, suicide attempters were subclassified based on the lethality of their attempt.

RESULTS

Suicide attempters and completers were similar on most measures of depressive symptoms. However, suicide completers were significantly more likely to use alcohol or drugs prior to their suicidal act and they were more likely to leave a suicide note. Suicide completers were significantly more likely to have encountered significant job stress and financial problems.

CONCLUSIONS

The present findings have documented several similarities and differences between suicide attempters and suicide completers. Future research may help to clarify the key warning signs that reflect the risk of completed suicide in adults who have been diagnosed with a Major Depressive Disorder.

A novel role for glyceraldehyde-3-phosphate dehydrogenase and monoamine oxidase B cascade in ethanol-induced cellular damage

BACKGROUND

Alcoholism is a major psychiatric condition at least partly associated with ethanol (EtOH)-induced cell damage. Although brain cell loss has been reported in subjects with alcoholism, the molecular mechanism is unclear. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and monoamine oxidase B (MAO B) reportedly play a role in cellular dysfunction under stressful conditions and might contribute to EtOH-induced cell damage.

METHODS

Expression of GAPDH and MAO B protein was studied in human glioblastoma and neuroblastoma cell lines exposed to physiological concentrations of EtOH. Expression of these proteins was also examined in the prefrontal cortex from human subjects with alcohol dependence and in rats fed with an EtOH diet. Coimmunoprecipitation, subcellular fractionation, and luciferase assay were used to address nuclear GAPDH-mediated MAO B activation. To test the effects of inactivation, RNA interference and pharmacological intervention were used, and cell damage was assessed by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP Nick End Labeling (TUNEL) and hydrogen peroxide measurements.

RESULTS

Ethanol significantly increases levels of GAPDH, especially nuclear GAPDH, and MAO B in neuronal cells as well as in human and rat brains. Nuclear GAPDH interacts with the transcriptional activator, transforming growth factor-beta-inducible early gene 2 (TIEG2), and augments TIEG2-mediated MAO B transactivation, which results in cell damage in neuronal cells exposed to EtOH. Knockdown expression of GAPDH or treatment with MAO B inhibitors selegiline (deprenyl) and rasagiline (Azilect) can block this cascade.

CONCLUSIONS

Ethanol-elicited nuclear GAPDH augments TIEG2-mediated MAO B, which might play a role in brain damage in subjects with alcoholism. Compounds that block this cascade are potential candidates for therapeutic strategies.

Elevated level of metabotropic glutamate receptor 2/3 in the prefrontal cortex in major depression

Clinical, postmortem and preclinical research strongly implicates dysregulation of glutamatergic neurotransmission in major depressive disorder (MDD). Recently, metabotropic glutamate receptors (mGluRs) have been proposed as attractive targets for the discovery of novel therapeutic approaches against depression. The aim of this study was to examine mGluR2/3 protein levels in the prefrontal cortex (PFC) from depressed subjects. In addition, to test whether antidepressants influence mGluR2/3 expression we also studied levels of mGluR2/3 in fluoxetine-treated monkeys. Postmortem human prefrontal samples containing Brodmann's area 10 (BA10) were obtained from 11 depressed and 11 psychiatrically healthy controls. Male rhesus monkeys were treated chronically with fluoxetine (dose escalated to 3mg/kg, p.o.; n=7) or placebo (n=6) for 39 weeks. The mGluR2/3 immunoreactivity was investigated using Western blot method. There was a robust (+67%) increase in the expression of the mGlu2/3 protein in the PFC of depressed subjects relative to healthy controls. The expression of mGlu2/3 was unchanged in the PFC of monkeys treated with fluoxetine. Our findings provide the first evidence that mGluR2/3 is elevated in the PFC in MDD. This observation is consistent with reports showing that mGluR2/3 antagonists exhibit antidepressant-like activity in animal models and demonstrates that these receptors are promising targets for the discovery of novel antidepressants.

Reduced density of calbindin immunoreactive GABAergic neurons in the occipital cortex in major depression: relevance to neuroimaging studies

BACKGROUND

Several lines of evidence suggest dysfunction of the gamma-aminobutyric acid (GABA)ergic system in major depressive disorder. Neuroimaging studies report reduced levels of GABA in the dorsolateral prefrontal and occipital cortex of depressed patients. Our previous postmortem study revealed a reduction in the density and size of calbindin-immunoreactive (CB-IR) GABAergic neurons in the prefrontal cortex in major depressive disorder. The goal of this study was to test whether the changes in CB-IR neurons can also be detected in the occipital cortex, where neuroimaging studies report a prominent GABA decrease.

METHODS

A three-dimensional cell counting probe was used to assess the cell-packing density and size of CB-IR neurons in layer II of the occipital cortex in 10 major depressive disorder subjects and 10 psychiatrically healthy control subjects.

RESULTS

The density of CB-IR neurons was significantly decreased by 28% in major depressive disorder subjects compared with the control group. The size of CB-IR neurons was unchanged in major depressive disorder subjects when compared with control subjects.

CONCLUSIONS

The reduction in the density of CB-IR GABAergic neurons in the occipital cortex in depression is similar to that observed previously in the prefrontal cortex. Deficit in cortical GABAergic interneurons may contribute to the low GABA levels detected in neuroimaging studies in major depressive disorder patients.

Transcriptional expression of serotonergic regulators in laser-captured microdissected dorsal raphe neurons of subjects with major depressive disorder: sex-specific differences

The relationship between serotonin (5-HT) and major depressive disorder (MDD) has been extensively studied but certain aspects are still ambiguous. Given the evidence that 5-HT neurotransmission is reduced in depressed subjects, it is possible that one or more of the 5-HT regulators may be altered in the dorsal raphe nucleus (DR) of depressed subjects. Candidates that regulate 5-HT synthesis and neuronal activity of 5-HT neurons include intrinsic regulators such as tryptophan hydroxylase 2, 5-HT autoreceptors, 5-HT transporter and transcription factors, as well as afferent regulators such as estrogen and brain-derived neurotrophic factor. The present study was designed to quantify mRNA concentrations of the above 5-HT regulators in an isolated population of 5-HT-containing DR neurons of MDD subjects and gender-matched psychiatrically normal control subjects. We found that mRNA concentrations of the 5-HT1D receptor and the transcription factors, NUDR and REST, were significantly increased in DR-captured neurons of female MDD subjects compared to female control subjects. No significant differences were found for the transcripts in male MDD subjects compared to male controls. This study reveals sex-specific alterations in gene expression of the pre-synaptic 5-HT1D autoreceptors and 5-HT-related transcription factors, NUDR and REST, in DR neurons of women with MDD.

Human Freud-2/CC2D1B: a novel repressor of postsynaptic serotonin-1A receptor expression

BACKGROUND

Altered expression of serotonin-1A (5-HT1A) receptors, both presynaptic in the raphe nuclei and post-synaptic in limbic and cortical target areas, has been implicated in mood disorders such as major depression and anxiety. Within the 5-HT1A receptor gene, a powerful dual repressor element (DRE) is regulated by two protein complexes: Freud-1/CC2D1A and a second, unknown repressor. Here we identify human Freud-2/CC2D1B, a Freud-1 homologue, as the second repressor.

METHODS

Freud-2 distribution was examined with Northern and Western blot, reverse transcriptase polymerase chain reaction, and immunohistochemistry/immunofluorescence; Freud-2 function was examined by electrophoretic mobility shift, reporter assay, and Western blot.

RESULTS

Freud-2 RNA was widely distributed in brain and peripheral tissues. Freud-2 protein was enriched in the nuclear fraction of human prefrontal cortex and hippocampus but was weakly expressed in the dorsal raphe nucleus. Freud-2 immunostaining was co-localized with 5-HT1A receptors, neuronal and glial markers. In prefrontal cortex, Freud-2 was expressed at similar levels in control and depressed male subjects. Recombinant hFreud-2 protein bound specifically to 5' or 3' human DRE adjacent to the Freud-1 site. Human Freud-2 showed strong repressor activity at the human 5-HT1A or heterologous promoter in human HEK-293 5-HT1A-negative cells and neuronal SK-N-SH cells, a model of postsynaptic 5-HT1A receptor-positive cells. Furthermore, small interfering RNA knockdown of endogenous hFreud-2 expression de-repressed 5-HT1A promoter activity and increased levels of 5-HT1A receptor protein in SK-N-SH cells.

CONCLUSIONS

Human Freud-2 binds to the 5-HT1A DRE and represses the human 5-HT1A receptor gene to regulate its expression in non-serotonergic cells and neurons.

Reductions in neuronal density in elderly depressed are region specific

OBJECTIVE

Frontal regions, including the orbitofrontal cortex (ORB) and dorsolateral prefrontal cortex (dlPFC) have been implicated in the neuropathology of geriatric depression. Prominent reductions in pyramidal neuron density have been recently reported in the ORB of older depressed subjects. However, the cellular pathology of the dlPFC has not yet been examined in these subjects.

METHODS

Postmortem tissue from the dlPFC (Brodmann's area 9, BA9) was collected from 10 older (>60 years old) subjects diagnosed with major depression and 10 age-matched non-psychiatric controls (CTRL). The majority of the subjects were the same as those used for our previous study on neuronal reductions in the ORB in older depressed. Overall (all six layers combined), and laminar density of pyramidal (presumably glutamatergic), and non-pyramidal (GABAergic) neurons as well as cortical and laminar width were measured using linear optical disector of Stereoinvestigator software.

RESULTS

Neither the overall nor laminar density of pyramidal or non-pyramidal neurons was significantly different between groups. The cortical and laminar widths were also not affected.

CONCLUSIONS

These results suggest that neuronal prefrontal pathology in elderly depressed is region specific. No significant changes were detected in the density of any type of neurons in the dlPFC of elderly depressed subjects (present study) whereas, prominent reductions in the density of pyramidal glutamatergic neurons were observed previously in the ORB.

Reduced levels of NR2A and NR2B subunits of NMDA receptor and PSD-95 in the prefrontal cortex in major depression

Recent neuroimaging and postmortem studies have demonstrated abnormalities in glutamatergic transmission in major depression. Glutamate NMDA (N-methyl-d-aspartate) receptors are one of the major mediators of excitatory neurotransmission in the central nervous system. At synaptic sites, NMDA receptors are linked with postsynaptic density protein-95 (PSD-95) that plays a key role in mediating trafficking, clustering, and downstream signaling events, following receptor activation. In this study, we examined the expression of NMDA receptor subunits NR1, NR2A, and NR2B as well as PSD-95 in the anterior prefrontal cortex (PFC) using Western blot method. Cortical samples were obtained from age, gender and postmortem interval matched depressed and psychiatrically healthy controls. The results revealed that there was a reduced expression of the NMDA receptor subunits NR2A (-54%) and NR2B (-48%), and PSD-95 protein level (-40%) in the PFC of depressed subjects relative to controls, with no change in the NR1 subunit. The alterations in NMDA receptor subunits, especially the NR2A and NR2B, as well as PSD-95 suggest an abnormality in the NMDA receptor signaling in the PFC in major depression. Our findings in conjunction with recent clinical, cellular, and neuroimaging studies further implicate the involvement of glutamate neurotransmission in the pathophysiology of depression. This study provides additional evidence that NMDA receptor complex is a target for discovery of novel antidepressants.

Glutamate signaling proteins and tyrosine hydroxylase in the locus coeruleus of alcoholics

It has been postulated that alcoholism is associated with abnormalities in glutamatergic neurotransmission. This study examined the density of glutamate NMDA receptor subunits and its associated proteins in the noradrenergic locus coeruleus (LC) in deceased alcoholic subjects. Our previous research indicated that the NMDA receptor in the human LC is composed of obligatory NR1 and regulatory NR2C subunits. At synapses, NMDA receptors are stabilized through interactions with postsynaptic density protein (PSD-95). PSD-95 provides structural and functional coupling of the NMDA receptor with neuronal nitric oxide synthase (nNOS), an intracellular mediator of NMDA receptor activation. LC tissue was obtained from 10 alcohol-dependent subjects and eight psychiatrically healthy controls. Concentrations of NR1 and NR2C subunits, as well as PSD-95 and nNOS, were measured using Western blotting. In addition, we have examined tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of norepinephrine. The amount of NR1 was lower in the rostral (-30%) and middle (-41%) portions of the LC of alcoholics as compared to control subjects. No differences in the amounts of NR2C, PSD-95, nNOS and TH were detected comparing alcoholic to control subjects. Lower levels of NR1 subunit of the NMDA receptor in the LC implicates altered glutamate-norepinephrine interactions in alcoholism.

Dopamine receptor gene expression in human amygdaloid nuclei: elevated D4 receptor mRNA in major depression

Previous findings from this laboratory demonstrating changes in dopamine (DA) transporter and D2 receptors in the amygdaloid complex of subjects with major depression indicate that disruption of dopamine neurotransmission to the amygdala may contribute to behavioral symptoms associated with depression. Quantitative real-time RT-PCR was used to investigate the regional distribution of gene expression of DA receptors in the human amygdala. In addition, relative levels of mRNA of DA receptors in the basal amygdaloid nucleus were measured postmortem in subjects with major depression and normal control subjects. All five subtypes of DA receptor mRNA were detected in all amygdaloid subnuclei, although D1, D2, and D4 receptor mRNAs were more abundant than D3 and D5 mRNAs by an order of magnitude. The highest level of D1 mRNA was found in the central nucleus, whereas D2 mRNA was the most abundant in the basal nucleus. Levels of D4 mRNA were highest in the basal and central nuclei. In the basal nucleus, amounts of D4, but not D1 or D2, mRNAs were significantly higher in subjects with major depression as compared to control subjects. These findings demonstrate that the D1, D2 and D4 receptors are the major subtypes of DA receptors in the human amygdala. Elevated DA receptor gene expression in depressive subjects further implicates altered dopaminergic transmission in the amygdala in depression.

GABAergic neurons immunoreactive for calcium binding proteins are reduced in the prefrontal cortex in major depression

Post-mortem morphometric studies report reductions in the average density and size of cortical neurons in the dorsolateral prefrontal cortex (dlPFC) and orbitofrontal cortex (ORB) in major depressive disorder (MDD). The contribution of specific neuronal phenotypes to this general pathology in depression is still unclear. Post-mortem sections from the dlPFC and ORB regions of 14 subjects with MDD and 11 controls were immunostained to visualize calbindin-immunoreactive (CB-IR) and parvalbumin-immunoreactive (PV-IR) presumptive GABAergic neurons. A three-dimensional cell counting probe was used to assess the cell packing density and size of CB-IR neurons in layers II+IIIa and PV-IR neurons in layers III-VI. The density of CB-IR neurons was significantly reduced by 50% in depression in the dlPFC and there was a trend toward reduction in the ORB. The size of CB-IR somata was significantly decreased (18%) in depression in the dlPFC with a trend toward reduction in the ORB. In contrast, there was no difference in the density of PV-IR neurons between the depressed and control groups in the dlPFC. The size of PV-IR neuronal soma was unchanged in depressed compared to control subjects in either dlPFC or ORB. In depression, subpopulations of GABAergic neurons may be affected differently in dlPFC and ORB. A significant reduction in the density and size of GABAergic interneurons immunoreactive for calcium binding proteins was found predominantly in the dlPFC region. These cellular changes are consistent with recent neuroimaging studies revealing a reduction in the cortical levels of GABA in depression.

Reduced glial and neuronal packing density in the orbitofrontal cortex in alcohol dependence and its relationship with suicide and duration of alcohol dependence

BACKGROUND

Reduced metabolism, blood flow, and tissue volume have been detected in the dorsolateral prefrontal cortex (dlPFC) of neurologically intact alcoholic subjects and these deficits are accompanied by lower density of neurons and glial cells. Another prefrontal region, the orbitofrontal cortex (ORB), functionally and structurally differentiated from the dlPFC, and heavily involved in decision-making processes, also shows functional alterations in alcoholic subjects. However, it is unknown whether changes in the packing density of neurons or glial cells also occur in the ORB and whether that density may be related to the increased suicide probability of alcoholic subjects or to the duration of alcohol dependence.

METHODS

The present study used a 3-dimensional cell-counting method in postmortem brain tissue to determine the packing density of neurons and glial cells in the ORB (area 47) of 15 subjects with alcohol dependence (8 suicides, 7 nonsuicides) and 8 normal controls and to determine whether cell density is correlated with suicide and duration of alcohol dependence.

RESULTS

There was a significantly lower density of both neurons (by 27%) and glial cells (by 25%) in the ORB of alcoholic subjects compared with controls. Packing density of either neurons or glial cells was not significantly different in alcoholic suicides compared with alcoholic nonsuicides. Age was not correlated with neuronal or glial density in either group. However, the duration of alcohol dependence and the ratio of that duration to the length of life span were significantly and negatively correlated to the overall density of neurons.

CONCLUSION

The present results indicate that alcohol dependence is associated with a decrease in the packing density of neurons and glia in the ORB and that the reduction in neuronal but not glial density progresses with the duration of alcohol dependence.

Normal [3H]flunitrazepam binding to GABAA receptors in the locus coeruleus in major depression and suicide

Major depression and suicide are associated with altered concentrations of specific noradrenergic proteins in the human locus coeruleus (LC). Based on experimental studies that can reproduce these LC abnormalities in laboratory animals, we hypothesized that noradrenergic pathobiology in depression is a result of overactivity of the LC. LC activity is under the control of both excitatory and inhibitory inputs. A major inhibitory input to the LC is GABAergic, arising from the nucleus prepositus hypoglossi. Numerous studies demonstrating low levels of GABA in the CSF and plasma of subjects with major depressive disorder (MDD) raise the possibility that LC overactivity in depression may be secondary to reduced GABAergic input to the LC. Here, GABAergic input to the LC in depression was evaluated by studying the binding of [(3)H]flunitrazepam to GABA(A) receptors at three anatomically defined levels of the human postmortem LC. LC tissues were collected from subjects with MDD, subjects with depressive disorders including MDD that died as a result of suicide, and psychiatrically normal control subjects. A modest rostral-caudal gradient of GABA(A) receptor binding density was observed among all subjects. No significant differences in the amount of binding to GABA(A) receptors were observed between control subjects (n=21) and MDD subjects (n=9) or depressed suicide victims (n=17). These results demonstrate that GABA(A) receptor binding in the LC measured with [(3)H]flunitrazepam is not altered in subjects with depressive illnesses.

Prominent reduction in pyramidal neurons density in the orbitofrontal cortex of elderly depressed patients

BACKGROUND

Elderly depressed patients have more vascular hyperintensities in frontal white matter and basal ganglia than elderly control subjects. Cell pathology that might be related to increased vascular hyperintensities has not been examined.

METHODS

Postmortem samples from the orbitofrontal cortex (ORB) were collected in 15 elderly subjects with major depressive disorder (MDD) and 11 age-matched control subjects. Cell packing density of neurons and glia, density of pyramidal and nonpyramidal neurons, and cortical and laminar width were measured.

RESULTS

The overall (layers I-VI) packing density of ORB neurons with pyramidal morphology was markedly decreased in MDD (by 30%) as compared with control subjects. Further laminar analysis of pyramidal neurons density revealed significant reductions in layers IIIc and V in MDD. In contrast, in MDD the density of nonpyramidal neurons and glia and cortical and laminar width were comparable to control values.

CONCLUSIONS

In elderly subjects with depression, the density of pyramidal neurons in the ORB was particularly low in cortical layers V and III, the origin of prefronto-striatal and prefronto-cortical and prefronto-amygdalar projections. Degeneration of neurons furnishing these projections might be related to the white matter hyperintensities previously observed. Neuronal pathology seems to be more severe in elderly than in younger subjects with MDD.

Elevated levels of the NR2C subunit of the NMDA receptor in the locus coeruleus in depression

Low levels of the intracellular mediator of glutamate receptor activation, neuronal nitric oxide synthase (nNOS) were previously observed in locus coeruleus (LC) from subjects diagnosed with major depression. This finding implicates abnormalities in glutamate signaling in depression. Receptors responding to glutamate in the LC include ionotropic N-methyl-D-aspartate receptors (NMDARs). The functional NMDAR is a hetero-oligomeric structure composed of NR1 and NR2 (A-D) subunits. Tissue containing the LC and a nonlimbic LC projection area (cerebellum) was obtained from 13 and 9 matched pairs, respectively, of depressed subjects and control subjects lacking major psychiatric diagnoses. NMDAR subunit composition in the LC was evaluated in a psychiatrically normal subject. NR1 and NR2C subunit immunoreactivities in LC homogenates showed prominent bands at 120 and 135 kDa, respectively. In contrast to NRI and NR2C, very weak immunoreactivity of NR2A and NR2B subunits was observed in the LC. Possible changes in concentrations of NR1 and NR2C that might occur in depression were assessed in the LC and cerebellum. The overall amount of NR1 immunoreactivity was normal in the LC and cerebellum in depressed subjects. Amounts of NR2C protein were significantly higher (+ 61%, p = 0.003) in the LC and modestly, but not significantly, elevated in the cerebellum (+ 35%) of depressives as compared to matched controls. Higher levels of NR2C subunit implicate altered glutamatergic input to the LC in depressive disorders.