One of the co-authors, Ryota Hashimoto, United Graduate School of Child Development, Osaka University, is an editor of PLOS ONE. This does not alter the authors’ adherence to PLOS ONE policies on sharing data and materials.
Conceived and designed the experiments: YW NT. Performed the experiments: YW HT AT YK MN RH HY M. Fujimoto. Analyzed the data: YW M. Fukunaga. Contributed reagents/materials/analysis tools: YW M. Fukunaga. Wrote the paper: YW.
The dopamine hypothesis suggests that excessive dopamine release results in the symptoms of schizophrenia. The purpose of this study was to elucidate the dopaminergic and noradrenergic neurons using 3-T neuromelanin magnetic resonance imaging (MRI) in patients with schizophrenia and healthy control subjects.
We prospectively examined 52 patients with schizophrenia (M: F = 27∶25, mean age, 35 years) and age- and sex-matched healthy controls. Using a 3T MRI unit, we obtained oblique T1-weighted axial images perpendicular to the brainstem. We measured the signal intensity and area for the substantia nigra (SNc), midbrain tegmentum, locus ceruleus (LC), and pons. We then calculated the contrast ratios (CR) for the SNc (CRSN) and LC (CRLC), which were compared between patients and healthy controls using unpaired
The SNc and LC were readily identified in both patients and healthy controls as areas with high signal intensities in the posterior part of the cerebral peduncle and in the upper pontine tegmentum. The CRSN values in patients were significantly higher than those in healthy controls (10.89±2.37 vs. 9.6±2.36, p<0.01). We observed no difference in the CRLC values between the patients and healthy controls (14.21±3.5 vs. 13.44±3.37, p = 0.25). Furthermore, there was no difference in area of the SNc and LC between schizophrenia patients and controls.
Neuromelanin MRI might reveal increased signal intensity in the SNc of patients with schizophrenia. Our results indicate the presence of excessive dopamine products in the SNc of these patients.
Dopamine dysfunction plays an important role in the pathogenesis of schizophrenia
Neuromelanin is a byproduct of the synthesis of monoamine neurotransmitters, such as noradrenalin and dopamine, and is mainly distributed within neurons of the substantia nigra (SNc) or locus ceruleus (LC)
The purpose of this study was to use 3T neuromelanin MRI for examining dopaminergic and noradrenergic nuclei in patients with schizophrenia and healthy controls.
From April to November 2012, we prospectively examined 63 consecutive patients with schizophrenia who met the
This study was performed in accordance with the World Medical Association’s Declaration of Helsinki and approved by the local institutional review board (2013-423, Osaka University Ethics Committee). Written informed consent was obtained by all subjects. If the subjects were under 20 years old, written informed consent was obtained from both minors and guardians. If the patients with schizophrenia were difficult condition to accept consent by theirself, these patients were not included in this study.
Using a 3T MRI unit (Signa Excite HDxt, GE healthcare, Milwaukee, Wisconsin), we obtained oblique T1-weighted oblique axial images perpendicular to the brainstem. The T1-weighted sequence was acquired with a 3D-spoiled GRASS sequence with magnetization transfer contrast: TR/TE = 38.4/2.4 ms, FA = 20 degrees, matrix size 480×320 in axial plane, FOV = 220 mm, and acquisition time = 3 min 25 s. A 40-mm slab thickness was used and images were reconstructed 40 slices with a slice thickness of 2 mm with in-slice zero-fill interpolation (ZIP2). We also obtained axial T2-weighted images of the whole brain to exclude coexisting disorders and any abnormal findings that might influence the signals for the SNc or LC. The T2-weighted image parameters are as follows: TR/TE = 4500/88 ms, FOV = 220 mm, Matrix = 512×256, 24 slices with slice thickness 5 mm, and 6 mm slice interval.
We measured the signal intensity of the SNc, midbrain tegmentum, LC, and pons. The region of interest (ROI) for the SNc was traced manually around the high signal area on two consecutive axial slices and ellipse ROI was set at midbrain tegmentum in the same slice (
A, C: 30-year-old male with schizophrenia, CRSN = 12.9, CRLC = 10.7; B, D: 26-year-old female healthy control, CRSN = 6.2, CRLC = 7.6 Demonstrating a region of interest drawn around the substantia nigra and midbrain tegmentum side on Figure 1B and locus ceruleus on Figure 1D.
To reduce the effects of age-related changes in the CRSN and CRLC, we selected a subset of subjects who were under 30 years of age (n = 24 for schizophrenia, n = 29 for healthy controls) and compared their ROI values.
Statistical analyses were performed using unpaired
We calculated the correlation between age and CRSN or CRLC for patients with schizophrenia and healthy controls. To elucidate the medication effects for the contrast ratio, the correlation between the chlorpromazine (CPZ) equivalents and CRSN or CRLC was analyzed.
Schizophrenia | Control | Schizophrenia | Control | |||
all n = 52 | all n = 52 | p value | <30 year n = 24 | <30 year n = 29 | p value | |
Age | 35.1 (13.3) | 34.6 (13.7) | 0.89 | 23.8 (4.1) | 23.0 (2.3) | 0.34 |
Sex (male:female) | 27∶25 | 27∶25 | 11∶13 | 16∶13 | ||
Year of education | 13.4 (2.5) | 15.4 (2.1) | <.001 | 13.0 (2.7) | 15.6 (1.6) | <.001 |
Smoking (%) | 16 (31%) | 4 (7.7%) | <.001 | 6 (25%) | 1 (3.4%) | <.001 |
Estimated premorbid IQ. | 102.0 (10.9) | 109.7 (7.3) | <.001 | 102.0 (11.2) | 111.3 (5.0) | <.001 |
Full scale IQ | 87.0 (20.9) | 113.8 (14.1) | <.001 | 87.8 (20.4) | 118.4 (11.4) | <.001 |
Age of onset | 22.9 (10.1) | 18.2 (3.3) | ||||
Duration (years) | 10.4 (10.9) | 4.9 (4.6) | ||||
CPZeq (mg/day) | 596.2 (556.2) | 495.8 (541.6) | ||||
PANSS positive | 21.0 (6.3) | 18.3 (6.3) | ||||
PANSS negative | 23.1 (7.5) | 20.1 (6.4) | ||||
PANSS general | 50.0 (13.9) | 45.8 (13.6) | ||||
PANSS total | 94.1 (26.2) | 84.1 (25.5) |
Data are shown mean (standard deviation). CPZeq: chlorpromazine equivalent of total antipsychotics.
IQ: Intelligence Quotient, PANSS: Positive and Negative Symptom Scale.
The SNc and LC were readily identified by high signal intensity areas in the posterior part of the cerebral peduncle and at the upper pontine tegmentum in both patients and healthy controls (
The left graph plots data for all subjects. The right graph plots data for selected patients under 30 years of age. The dots and bar show mean ± standard deviation. The patients showed a significantly higher CRSN, but the variation in each group was large. The dispersion of data is small to select the young patients. There was no significant difference about CRLC between the patients and healthy controls.
Schizophrenia | controls | Schizophrenia | controls | Schizophrenia | controls | |
all age n = 52 | all age n = 52 | <30 years n = 24 | <30 years n = 29 | ≧30 year n = 28 | ≧30 year n = 23 | |
CRSN (%) | 10.89±2.37 |
9.60±2.36 | 10.51±2.11 |
8.85±1.95 | 11.22±2.80 | 10.55±2.51 |
CRLC (%) | 14.21±3.5 | 13.44±3.37 | 13.73±3.37 | 13.15±3.88 | 14.63±3.56 | 13.79±2.69 |
Area-SNc (mm2) | 160.1±24.1 | 162.2±21.6 | 155.4±16.9 | 164.8±24.7 | 164.2±28.1 | 158.9±17.1 |
Area-LC (mm2) | 10.84±2.46 | 11.42±2.27 | 10.79±1.93 | 11.67±2.57 | 10.89±2.82 | 11.09±1.86 |
MaxSR SNc | 1.32±0.04 |
1.30±0.04 | 1.30±0.03 |
1.28±0.03 | 1.33±0.04 | 1.32±0.04 |
MaxSR LC | 1.28±0.05 | 1.27±0.05 | 1.27±0.05 | 1.28±0.06 | 1.29±0.05 | 1.27±0.04 |
SR, signal ratio; SNc, substantia nigra; LC, locus coeruleus; CRSN, contrast ratio of SNc; CRLC, contrast ratio of LC;
MaxSR, maximum signal intensity.
Data are presented as mean ± standard deviation.
*p<0.05 compared to controls,
p<0.005 compared to controls.
In the subset of subjects that were under the age of 30, CRSN values were significantly higher in patients with schizophrenia than in healthy controls (10.51±2.11 vs. 8.85±1.95; p<0.005;
There is weak correlation between age and CRSN (R = 0.325, p = 0.019) for healthy controls and (R = 0.263, p = 0.053) for schizophrenia. There is no correlation between age and CRLC (R = −0.008, p = 0.95) for healthy controls and (R = 0.196, p = 0.164) for schizophrenia. The CPZ equivalent and CRSN showed weak correlation (R = 0.353, p = 0.010) and there is no correlation between CPZ equivalent and CRLC (R = 0.023, p = 0.870) for patients with schizophrenia.
Our results demonstrate the excessive levels of dopamine products in the SNc of living patients with schizophrenia and this supports the dopamine hypothesis for schizophrenia. Recently, Howers et al
It has been suggested that dopamine dysfunction plays an important role in the pathogenesis of schizophrenia. This hypothesis is supported by evidence provided by numerous observations and studies. For example, the stimulants amphetamine and cocaine, which increase dopamine levels in the brain, can cause symptoms resembling those for psychosis
It has been reported that T1-weighted MRI with 3T can indicate T1-shortening tissues containing neuromelanin at SNc and LC
Sasaki et al
These two previous reports indicate the CRSN in patients with schizophrenia is higher than that in controls, but this was not statistically significant due to a small sample size and large variations. We performed a similar comparison in our study using a lager patient group (52 patients) and observed a significant difference. The mean CRSN was significantly higher in patients with schizophrenia than in healthy controls, but the CRSN values showed large variations with overlap between patients and healthy controls (
The absolute value of CRSN observed in our study differed from those in two previous reports, which likely resulted from differences of the reference ROIs and MR sequence. We used a reference ROI located in the midbrain tegmentum, whereas previous reports used the decussation of the superior cerebellar peduncle. We use 3D-SPGR sequence to obtain T1-weighted image and previous reports performed a 2D-fast spin echo sequence. 3D acquisition is superior to obtain high signal to noise ratio image in less time. We showed significant difference using short time neuromelanin imaging and this was of great advantage to exam the schizophrenic patients who were sometimes difficult to hold steady head position for long examination time in MR unit.
There are several limitations to our study. First, we included all patients examined with neuromelanin MRI from April to November 2012. Many of these patients were under treatment with antipsychotic drugs. Our results showed that there is a weak correlation between CPZ equivalent and CRSN, therefor these drugs have the potential to influence neuromelanin levels. The number of participants in this study was not enough to perform subgroup analysis and further study is needed to select first episode medication-naive patients to exclude the drug effect. Second, we could not evaluate the ventral tegmental area (VTA), which is the origin of the dopaminergic cell bodies of the mesolimbic-cortical dopaminergic system, because of the difficulty in detection the border of the VTA by neuromelanin-MRI. Third, the years of education and IQ were significantly higher in healthy controls than in patients with schizophrenia. Schizophrenia is characterized by general intellectual deficits
In conclusion, neuromelanin MRI revealed increased signal intensity in the SNc of patients with schizophrenia. This finding indicates the presence of an excessive level of dopamine products in the SNc of these patients. Therefore, neuromelanin imaging has the potential to be useful for accurate diagnosis of schizophrenia and to serve as a surrogate marker for medication.