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Keywords:

  • brainstem;
  • human;
  • mood disorders;
  • post-mortem brain;
  • immunoautoradiography;
  • serotonin

Abstract

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. Tissue collection
  5. Tissue preparation and radioimmunocytochemistry
  6. Quantitative image analysis
  7. Statistical analyses
  8. Results
  9. Discussion
  10. Acknowledgements
  11. References

A variety of evidence suggests that serotonin neurotransmission is altered in the brain of suicide victims and depressed patients. While numerous post-mortem studies have investigated serotonin transporters and receptors, few studies have examined the biosynthetic integrity of the rate-limiting enzyme, tryptophan hydroxylase (TPH), in post-mortem specimens of depressed suicide subjects. Therefore, the aim of the present study was to test the hypothesis that the levels of TPH immunoreactivity (IR) are altered in specific subnuclei of the dorsal raphe (DR) in depressed suicide victims. Suicide victims with a confirmed diagnosis of major depression were matched with non-psychiatric controls based on age, gender and post-mortem interval. Frozen tissue sections containing the DR were selected from two anatomical levels and processed for TPH radioimmunocytochemistry. The optical density corresponding to the regional levels of TPH-IR was quantified in specific subnuclei of the DR from the film autoradiographic images. No significant differences in the levels of TPH-IR were found in any DR subnuclei between depressed suicide victims and control subjects. The lack of change in TPH-IR levels does not necessarily imply that serotonin synthesis or neurotransmission is not altered in the brain of depressed subjects. Many factors influence and regulate serotonin synthesis, and it is conceivable that alterations exist at other levels of regulation of serotonin biosynthesis in depression. Our findings indicate that TPH biosynthesis, at least at the protein level, is not significantly altered in the DR of depressed suicide victims.

Abbreviations used
BSA

bovine serum albumin

DR

dorsal raphe

DRd

dorsal subnucleus of the dorsal raphe

DRif

interfascicular subnucleus of the dorsal raphe

DRv

ventral subnucleus of the dorsal raphe

DRvl

ventrolateral subnucleus of the dorsal raphe

5-HIAA

5-hydroxyindoleactic acid

5-HT

serotonin

IR

immunoreactivity

PBS

phosphate-buffered saline

RT

room temperature

TPH

tryptophan hydroxylase

Although the pathophysiological mechanisms underlying depression and suicide are not fully understood, considerable evidence supports an alteration in serotonin neurotransmission in the brain of depressed subjects and suicide victims. In spite of contradictions, lower levels of serotonin (5-hydroxytryptamine, 5-HT) and the metabolite 5-hydroxyindoleacetic acid (5-HIAA) have been repeatedly reported in the cerebrospinal fluid (CSF) of depressed suicide attempters (Åsberg et al. 1976; Banki et al. 1984; Virkkunnen et al. 1989). Furthermore, results of studies measuring 5-HT and 5-HIAA in post-mortem tissue have also yielded inconsistent findings, with either lower (Shaw et al. 1967; Beskow et al. 1976) or unchanged levels (Lloyd et al. 1974) of 5-HT and 5-HIAA in the brainstem of suicide victims. Recent receptor autoradiography studies found either increased (Stockmeier et al. 1998) or decreased (Arango et al. 2001) 5-HT1A autoreceptor binding sites in the dorsal raphe (DR) of depressed suicide subjects, whereas normal densities of serotonin transporter binding sites were found in the DR of suicide victims with major depression (Bligh-Glover et al. 2000; Arango et al. 2001).

Despite the post-mortem evidence of alterations in various serotonergic parameters in depression and suicide discussed above, less attention has been focused on investigating tryptophan hydroxylase (TPH), the initial and rate-limiting enzyme that catalyzes the biosynthesis of 5-HT, in post-mortem specimens of depressed subjects. To date, there have been no biochemical studies conducted that have measured TPH levels in brain tissue of suicide victims. However, two morphological studies have reported alterations in the number or density of neurons in the DR of depressed subjects. Underwood et al. (1999) reported that the average density of TPH-immunoreactive (IR) neurons was increased by 35% throughout the entire DR in the suicide group relative to controls. However, a recent study by Baumann et al. (2002) found that in Nissl-stained sections, neuron numbers and volumes in the entire DR were not significantly different between the mood disorder group and control group, but the ventrolateral subnucleus of the DR showed a 31% reduction in the number of neurons in the mood disorder group relative to controls. Although these two reports are conflicting, they do suggest that perhaps alterations in TPH protein expression may exist in the DR of depressed suicide subjects.

Therefore, we sought to test the hypothesis that alterations in TPH protein expression may occur in the DR of depressed suicide victims. The present study was designed to quantify the regional levels of TPH immunoreactivity in tissue sections containing the DR from suicide victims with a diagnosis of major depression and matched control subjects by using radioimmunocytochemical methods.

Tissue collection

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. Tissue collection
  5. Tissue preparation and radioimmunocytochemistry
  6. Quantitative image analysis
  7. Statistical analyses
  8. Results
  9. Discussion
  10. Acknowledgements
  11. References

All procedures in our study were approved by the University of Pittsburgh's Institutional Review Board for Biomedical Research. Human brain specimens were obtained in the course of routine autopsies conducted at the Allegheny County Coroner's Office, Pittsburgh, PA, after obtaining consent from a surviving family member. Thirteen subjects who died by suicide and had a diagnosis of major depression were each matched with one control subject for gender and as closely as possible for age and post-mortem interval (Table 1). Twelve of the pairs were also matched for race. For each subject, a consensus DSM-IV diagnosis was made by an independent panel of experienced clinicians after reviewing medical records and the results of structured interviews conducted with family members of the deceased. Twelve suicide subjects had a diagnosis of major depression, and one subject had a depressive disorder not otherwise specified (NOS). Three of the depressed subjects also had an Axis II diagnosis of obsessive compulsive personality disorder and one depressed subject had an Axis II diagnosis of paranoid personality disorder. Three subjects with depression had a prior history of alcohol abuse and one depressed subject had a history of opioid abuse, but these disorders were in remission in all four subjects at time of death. The mean (± SD) age at the onset of depression was 51.2 ± 16.5 years, and the average duration of illness was 4.4 ± 6.0 years. Nine of the 13 depressed subjects had a family history of depression. Neuropathological condition of each brain specimen was evaluated by macroscopic and microscopic examination. Thioflavin-S staining revealed a few senile plaques in subjects 564, 598, 600, 685, 699 and 795, but clinical and neuropathological criteria to establish a diagnosis of Alzheimer's disease were not met. Toxicological screens were positive for doxepin and fluoxetine for one depressed subject (564), chlordiazepoxide for another depressed subject (598) and CO for two other depressed subjects (614, 628). Also, three depressed subjects (598, 689, 698) were receiving antidepressants at the time of death and two of these subjects were treated with antipsychotics at the time of death. Three depressed subjects (614, 596, 613) had been off antidepressant medication for 0.6, 1.8 and 7.1 years, respectively, and one subject (613) off antipsychotic medication for 7.6 years. The other five depressed subjects had no documented history of antidepressant medication. The depressed suicide subject group was composed of a disproportionate number of males (M : F, 12 : 1). Although men complete suicide at a rate four times that of women, our ratio of males to females (92%) is higher than the male to female ratio of previously published reports (59–80%).

Table 1.  Demographic characteristics of the subjects
Control subjectsDepressed subjects
PairCaseSex/ raceAge PMIaStorage timeb Cause of deathcCaseDSM-IV diagnosisSex/ raceAge PMIaStorage timeb Cause of deathd
  • a

    PMI indicates post-mortem interval in hours.

  • b

    b Storage time in months.

  • c

    c ASCVD indicates atherosclerotic coronary vascular disease.

  • d

    d CO poisoning indicates carbon monoxide poisoning.

  • e

    e Alcohol abuse, in remission at time of death.

  • f

    f Other substance abuse in remission at time of death; NOS indicates not otherwise specified.

1516M/B2014.053.0Homicide by gunshot628Major depressionM/W2621.635.6Suicide by CO poisoning
2551M/W6116.048.2Cardiac tamponade613Major depression with psychotic featureseM/W5915.637.8Suicide by gunshot
3557M/W4715.946.8ASCVD614Major depression, dysthymiaM/W3919.537.7Suicide by CO poisoning
4568F/W609.545.4ASCVD564Major depression with psychotic featuresF/W5616.646.0Suicide by hanging
5620M/W6417.336.7Accidental drowning596Major depressionM/W6820.541.1Suicide by gunshot
6685M/W5614.528.5Hypoplastic coronary artery600Major depressionM/W639.940.4Suicide by hanging
7700M/W4226.126.2ASCVD668Major depression with psychotic featureseM/W3424.331.3Suicide by hanging
8510M/W6312.453.4Gastrointestinal bleeding598Major depressionfM/W695.940.6Suicide by hanging
9643M/W5024.033.8ASCVD689Major depression with psychotic featureseM/W4524.227.6Suicide by acid ingestion
10736M/W5415.521.5ASCVD698Major depression with psychotic featuresM/W607.026.6Suicide by hanging
11704M/W7020.625.7ASCVD687Depressive disorder NOSM/W8222.128.2Suicide by gunshot
12795M/W6812.09.4Rupture abdominal aortic aneurysm699Major depressionM/W655.526.6Suicide by gunshot
13841M/W7022.3025.0ASCVD874Major depressionM/W8017.120.0Suicide by gunshot
Mean  55.716.934.9 Mean  55.716.133.8 
SD  13.84.913.6 SD  17.06.87.6 

Tissue preparation and radioimmunocytochemistry

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. Tissue collection
  5. Tissue preparation and radioimmunocytochemistry
  6. Quantitative image analysis
  7. Statistical analyses
  8. Results
  9. Discussion
  10. Acknowledgements
  11. References

Upon extraction of the brain from the cranium, the cerebellum was removed and the brainstem was separated by a transverse cut at the rostral border of the superior colliculi. The brainstems were then cut into midbrain/pons and caudal medulla blocks, immediately frozen in isopentane and stored at − 80°C. The frozen midbrain/pontine blocks were sectioned transversally (20 µm), sections were thaw-mounted onto gelatin-coated microscope slides and every 10th tissue section stained for Nissl substance with cresyl violet. The slides were stored at − 80°C until processed. The human DR nucleus has been divided into five anatomically distinct subnuclei based on cytoarchitectonic characteristics: interfascicular (DRif), ventral (DRv), dorsal (DRd), ventrolateral (DRvl) and caudal (DRc) (Baker et al. 1990). Slide-mounted tissue sections were selected from two anatomical levels of the midbrain for assay. The one anatomical level of the DR identified as level II corresponded to the caudal limit of the trochlear nucleus and included the DRif, DRv, and DRd and DRvl subnuclei. The other anatomical level of the DR identified as level III was located caudal to the trochlear nucleus and included the DRif, DRv and DRd subnuclei. The radioimmunocytochemical assay was performed as previously described with some modifications (Austin et al. 2003). Five sections of the midbrain were selected at 200 µm intervals from each anatomical level for each subject. Slides were removed from the − 80°C freezer, thawed to − 20°C and placed in 4% paraformaldehyde for 14 h. Tissue sections were then rinsed twice for 15 min in phosphate-buffered saline (PBS) and 1 × 15 min in PBS containing 0.4% Triton X-100 at room temperature (RT). After rinsing, non-specific binding was blocked by pre-treating tissue in PBS with 0.4% Triton X-100, 1.5% normal goat serum and 0.5% normal human serum for 1 h.

The concentration of TPH primary antiserum [mouse anti-phenylalanine hydroxylase (PH8), Chemicon, Temecula, CA, USA] used on the tissue sections from the subject pairs was determined from a dilution curve constructed from control brainstem tissue sections that were incubated with varying concentrations of the primary antibody (1 : 1000–1 : 20 000), processed for radioimmunocytochemistry and quantified using densitometry. The 1 : 10 000 concentration of primary antibody was chosen for the experiments because this antibody concentration produced the best signal-to-noise ratio from the autoradiographic images. Tissue sections from each matched pair were incubated at 4°C for 22–23 h with the primary antibody to PH8 (1 : 10 000) diluted in PBS containing 1.5% normal goat serum, 0.05% bovine serum albumin (BSA) and 0.4% Triton X-100. The sections were then washed three times for 5 min in PBS containing 0.4% Triton X-100 and then incubated with the [125I]-labeled secondary antibody {sheep anti-mouse IgG [125I-]F(ab′)2 fragment; NEN (Boston, MA, USA), specific activity 1320 Ci/mm, initial concentration 0.5 µCi/mL} using a dilution of 1 : 200 in PBS containing 3% normal goat serum and 0.4% Triton X-100 for 120 min at RT. Following this incubation, the sections were washed for 15 min in 0.4% Triton X-100 in PBS followed by 15 min washes in PBS. Additional sections from each case were included to assess non-specific binding of the [125I]-IgG and were processed as described above except that the primary antiserum was not included in the buffer. After washing, tissue sections were rinsed in 70% ethanol and air-dried. The dried tissue sections were apposed to β-max Hyperfilm (Amersham, Arlington Heights, IL, USA) and exposed for 48 h with a set of 14C standards, which were cross-calibrated to iodinated standards (Amersham).

Quantitative image analysis

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. Tissue collection
  5. Tissue preparation and radioimmunocytochemistry
  6. Quantitative image analysis
  7. Statistical analyses
  8. Results
  9. Discussion
  10. Acknowledgements
  11. References

The quantification of the autoradiographic images was accomplished using a personal computer-based image analysis system (Microcomputer Imaging Device, MCID; M5) from Imaging Research Inc. (St Catherines, Ontario, Canada). Optical density values quantified from the 14C standards (Amersham) were entered with their corresponding radioactivity values (nCi/mg protein) into a calibration table, and the relationship between tissue radioactivity and optical density determined using the MCID software. To determine the sampling boundaries of the DR on the film autoradiograms, the corresponding Nissl-stained image was digitized and the cytoarchitectonic boundaries of each raphe subnucleus outlined. This template was then superposed on the autoradiographic image and the radioactivity values measured within the individual DR subnuclei. TPH-IR values (nCi/mg) for each DR subnucleus were derived by interpolation from the standard curve. Non-specific binding of the secondary antibody to the tissue sections was measured for each case, and this average background value was subtracted from each data point. The TPH-IR value per sampled raphe nucleus was then adjusted for the sampling area by dividing the protein value by the scan area (pixel units) of the outlined region.

Statistical analyses

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. Tissue collection
  5. Tissue preparation and radioimmunocytochemistry
  6. Quantitative image analysis
  7. Statistical analyses
  8. Results
  9. Discussion
  10. Acknowledgements
  11. References

The data were analyzed using a repeated measure analysis of variance. The within factors were the subject pairing (control and depressed subjects) and the individual DR subnuclei (DRif, DRv, DRd and DRvl). Each of the variables of interest was analyzed separately. Following an omnibus test, a Scheffe's post-hoc procedure was performed to examine pairwise differences. In addition, multiple regression models were used to investigate the independent and concomitant effects of age, post-mortem interval, on the dependent variable of TPH-IR levels for each raphe subnucleus. A Mann–Whitney U-test (M-WU) was used to examine the mean differences in TPH-IR levels in the individual DR subnuclei between depressed subjects receiving antidepressants and those depressed subjects with no known history of antidepressant medication. All statistical assumptions were met, and the statistical significance was defined as p = 0.05.

Results

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. Tissue collection
  5. Tissue preparation and radioimmunocytochemistry
  6. Quantitative image analysis
  7. Statistical analyses
  8. Results
  9. Discussion
  10. Acknowledgements
  11. References

The quantitative autoradiographic measurements of TPH-IR from control subjects revealed regional differences in TPH-IR concentration among the DR subnuclei. At the rostral anatomical level, the mean TPH-IR concentration was greater in the DRif compared with the DRd (p < 0.05, Fig. 1a), whereas TPH-IR concentrations at caudal levels were higher in the DRif and DRv compared with the DRd (p < 0.001, Fig. 1b). Post-hoc pairwise comparison showed no significant differences in the mean level of TPH-IR in any rostral DR subnuclei between depressed suicide victims and matched control subjects (Fig. 1a, DRif: F1,22 = 0.04, p = 0.84; DRv: F1,22 = 0.28, p = 0.60; DRvl: F1,22 = 0.01, p = 0.92; DRd: F1,22 = 0.95 p = 0.34). Nor were there significant differences in the mean TPH-IR level in any caudal DR subnuclei between the depressed suicide victims and control subjects (Fig. 1b, DRif: F1,24 = 0.22, p = 0.64; DRv: F1,24 = 0.03, p = 0.86; DRd: F1,24 = 0.70, p = 0.41).

image

Figure 1. Histograms of the mean (± SEM) concentrations of TPH-IR in the rostral (a) and caudal (b) subnuclei of the dorsal raphe of depressed suicide subjects and control subjects. No significant differences between depressed and control subjects were found for TPH-IR in any DR subnuclei.

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We examined the potential confounding effects of current or past antidepressant medication on TPH-IR levels in the DR subnuclei in the depressed subject groups. Three of the depressed subjects (598, 689, 698) were receiving antidepressants at the time of death and one other depressed subject (564) had a positive toxicology screen for antidepressants. The remaining nine depressed subjects had no documented history that they were currently receiving antidepressants at the time of death. No statistically significant difference was found in the mean TPH-IR levels for any DR subnuclei in the depressed subjects with a history of antidepressant treatment compared with depressed subjects with no treatment history (DRvl: M-WU = 9.0, p = 0.28; DRd: M-WU = 8.0, p = 0.21; DRif: M-WU = 14.0, p = 0.81; DRv: M-WU = 10.0, 0.37) or caudal (DRv: M-WU = 14.0, p = 0.60; DRd: M-WU = 17.0, p = 0.94; DRif: M-WU = 15.0, p = 0.71). The age or PMI of the subjects did not reveal any significant correlation with the regional levels of TPH-IR in the subnuclei of the DR.

Representative immunoautoradiographic images of TPH-IR concentrations in the specific subnuclei of the DR of a control and depressed suicide subject pair are shown in Figs 2a and b, respectively.

image

Figure 2. Representative color-enhanced immunoautoradiographic image of TPH-IR concentrations in specific subnuclei of the dorsal raphe of a matched control (a) and depressed suicide subject (b) pair. The red outlined regions correspond to the specific subnuclei of the DR.

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Discussion

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. Tissue collection
  5. Tissue preparation and radioimmunocytochemistry
  6. Quantitative image analysis
  7. Statistical analyses
  8. Results
  9. Discussion
  10. Acknowledgements
  11. References

The results of the present study reveal that the concentration of TPH-IR is not altered in the subnuclei of the DR of depressed subjects committing suicide. While many investigations have examined different serotonergic parameters in the brainstem of depressed suicide victims (for a review, see Arango et al. 1997), very few studies have investigated the biosynthetic integrity of TPH in the brain of depressed suicide subjects. To date, there has been only one published report examining the expression of TPH in serotonergic neurons in the DR nucleus of suicide victims. This morphological study found that the number and density of TPH-IR neurons was significantly increased in the entire DR nucleus of suicide victims compared with controls (Underwood et al. 1999). However, the total volume of the DR as well as the density of TPH-IR neurons in individual subnuclei of the DR did not differ between the subject groups. The unaltered neuronal density in individual subnuclei was attributed to a lack of statistical power for subnuclear group measurements. Although the small number of subjects (n = 7) used in this study may be a limitation, these findings suggest that perhaps TPH biosynthesis is increased in the DR of suicide victims. The increase in number of TPH-IR neurons may reflect a compensatory mechanism where more 5-HT neurons are synthesizing TPH in an attempt to restore a deficit in the synthesis and release of 5-HT in the brain of suicide victims. However, our data do not support such a hypothesis. Furthermore, this finding is in contrast to a recent study showing that neuron numbers and volumes in the entire DR were unchanged in depressed subjects, but when examined on a subnucleus level, revealed a 31% reduction in the number of neurons in the ventrolateral subnucleus of the DR in the mood disorder group relative to controls (Baumann et al. 2002). In addition, a preliminary report using positron emission tomography with the tracer α[11C]methyl-l-tryptophan (α[11C]MTrp), a synthetic analog of the 5-HT precursor l-tryptophan, found that α[11C]MTrp trapping in the 5-HT synthesis precursor pool was not altered in the brainstem/raphe region but was lower in the terminal fields of the ventromedial prefrontal cortex in suicide attempters compared with matched healthy controls (New et al. 2002). These reports, together with our findings, suggest that the biosynthesis of TPH may remain intact in the cell body region of the DR in the brain of depressed suicide subjects.

The enzymatic activity of TPH is an important mechanism regulating the biosynthesis of 5-HT in the brain. The key regulators of TPH activity are the concentration of its substrate, tryptophan, and the phosphorylation process catalyzed by protein kinases. The rate of 5-HT synthesis in the brain depends on both the concentration of tryptophan in the tissue and the intrinsic activity of TPH (Neckers et al. 1977; Hamon et al. 1981; Fernstrom 1983). For example, the depletion of tryptophan by dietary means results in decreased plasma tryptophan levels (Moja et al. 1989) and reduced brain 5-HT synthesis and release (Gartside et al. 1992). Furthermore, clinical studies by Delgado and co-workers have reported that tryptophan depletion reverses the therapeutic efficacy of selective serotonin antidepressant drugs in remitted patients with a history of depression (Delgado et al. 1990). Alternatively, TPH can be regulated by protein kinases including cyclic AMP-dependent protein kinase A (Johansen et al. 1995, 1996; Stenfors and Ross 2002). In fact, several studies have reported that various cyclic AMP-mediated signalling components are altered in the prefrontal cortex of depressed suicide victims (Cowburn et al. 1994; García-Sevilla et al. 1999; Odagaki et al. 2001; Dwivedi et al. 2002). Our finding of normal TPH-IR levels in the DR of depressed suicide victims does not exclude the possibility that alterations may exist at other levels of regulation of TPH in depressed suicide subjects. For example, alterations in the phosphorylation and subsequent enzymatic activity of TPH may occur in the brain of depressed suicide subjects and thus affect the biosynthesis of serotonin.

A variety of studies has provided evidence that TPH exhibits distinct ‘tissue-specific’ biochemical properties between the pineal gland and midbrain raphe (Darmon et al. 1988; Kim et al. 1991). Furthermore, the turnover rate of TPH appears to differ among the subnuclei of the rat DR (Weissmann et al. 1990) suggesting that TPH gene expression may be differentially expressed in subpopulations of DR neurons. We have previously reported that TPH mRNA is heterogeneously distributed in the human DR, with the greatest number of TPH mRNA-positive neurons located in the ventrolateral and interfascicular subnuclei (Austin and O'Donnell 1999). Multiple TPH mRNA species have been identified in the human pineal gland and brain (Boularand et al. 1995; Wang et al. 1998). In addition, it has been reported that human TPH is alternatively spliced giving rise to two isoforms of TPH mRNA with different C-termini and different patterns of expression in the brainstem and midbrain (Wang et al. 1998). In a recent rodent study, the effects of repeated immobilization stress on two isoforms of TPH mRNA (TPHα and TPHβ) that differ in the length of their 5′ untranslated regions was examined (Chamas and Sabban 2002). Repeated immobilization stress was found to preferentially increase mRNA levels of the TPHβ isoform but not TPHα in the rat DR. Therefore, based on this evidence, it is possible that one of the human TPH isoforms may be preferentially altered in raphe neurons of depressed patients or suicide victims.

Previous studies have shown that certain antidepressants regulate TPH activity and biosynthesis. For example, the antidepressants imipramine and milnacipran have both been reported to attenuate TPH activity (Moret and Briley 1992). Kim et al. (2002) reported that chronic administration of the selective serotonin re-uptake inhibitor (SSRI), sertraline, increased TPH mRNA and protein levels in the DR nucleus. Since three of our depressed subjects were exposed to antidepressant drugs at the time of their death and one other depressed subject had a positive toxicology screen for antidepressants, we examined whether current antidepressant use may have influenced the concentration of TPH-IR in our depressed suicide subjects. We found no difference in the mean TPH levels in the DR subnuclei between the depressed subjects receiving antidepressants at the time of death and the depressed subjects with no known history of antidepressant treatment.

In conclusion, we found that the concentration of TPH-IR in individual subnuclei of DR was not significantly different between depressed suicide subjects and control subjects. Our findings suggest that TPH biosynthesis is not altered, at least at the translational level, in the DR nucleus of suicide victims with major depression. However, it is possible that alterations in TPH may exist at other levels of regulation such as gene expression, enzymatic activity and post-translational phosphorylation in the brain of depressed suicide victims. Further studies are needed to understand the biochemical mechanisms underlying the deficiency in 5-HT neurotransmission in depression and suicide.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. Tissue collection
  5. Tissue preparation and radioimmunocytochemistry
  6. Quantitative image analysis
  7. Statistical analyses
  8. Results
  9. Discussion
  10. Acknowledgements
  11. References

The authors thank Drs Gretchen Haas, Carol Sue Johnston, Cameron Carter and Matcheri Keshavan for their participation in the diagnostic conferences, and Heather Murphy for assistance with tissue preparation. This work was supported by USPHS grants MH57011 and MH45156.

References

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. Tissue collection
  5. Tissue preparation and radioimmunocytochemistry
  6. Quantitative image analysis
  7. Statistical analyses
  8. Results
  9. Discussion
  10. Acknowledgements
  11. References
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