Thomas M. Hyde

Reduced brain-derived neurotrophic factor in prefrontal cortex of patients with schizophrenia

Anatomical and molecular abnormalities of excitatory neurons in the dorsolateral prefrontal cortex (DLPFC) are found in schizophrenia. We hypothesized that brain-derived neurotrophic factor (BDNF), a protein capable of increasing pyramidal neuron spine density and augmenting synaptic efficacy of glutamate, may be abnormally expressed in the DLPFC of patients with schizophrenia. Using an RNase protection assay and Western blotting, we detected a significant reduction in BDNF mRNA (mean=23%) and protein (mean=40%) in the DLPFC of patients with schizophrenia compared to normal individuals. At the cellular level, BDNF mRNA was expressed at varying intensities in pyramidal neurons throughout layers II, III, V, and VI of DLPFC. In patients with schizophrenia; neuronal BDNF expression was decreased in layers III, V and VI. Our study demonstrates a reduction in BDNF production and availability in the DLPFC of schizophrenics, and suggests that intrinsic cortical neurons, afferent neurons, and target neurons may receive less trophic support in this disorder.

Dopaminergic modulation of cortical function in patients with Parkinson's disease.

Patients with idiopathic Parkinsons disease suffer not only from classic motor symptoms, but from deficits in cognitive function, primarily those subserved by the prefrontal cortex as well. The aim of the current study was to investigate the modulatory effects of dopaminergic therapy on neural systems subserving working memory and motor function in patients with Parkinsons disease. Ten patients with stage I and II Parkinsons disease were studied with functional magnetic resonance imaging, during a relatively hypodopaminergic state (ie, 12 hours after a last dose of dopamimetic treatment), and again during a dopamine‐replete state. Functional magnetic resonance imaging was performed under three conditions: a working memory task, a cued sensorimotor task and rest. Consistent with prior data, the cortical motor regions activated during the motor task showed greater activation during the dopamine‐replete state; however, the cortical regions subserving working memory displayed greater activation during the hypodopaminergic state. Interestingly, the increase in cortical activation during the working memory task in the hypodopaminergic state positively correlated with errors in task performance, and the increased activation in the cortical motor regions during the dopamine‐replete state was positively correlated with improvement in motor function. These results support evidence from basic research that dopamine modulates cortical networks subserving working memory and motor function via two distinct mechanisms: nigrostriatal projections facilitate motor function indirectly via thalamic projections to motor cortices, whereas the mesocortical dopaminergic system facilitates working memory function via direct inputs to prefrontal cortex. The results are also consistent with evidence that the hypodopaminergic state is associated with decreased efficiency of prefrontal cortical information processing and that dopaminergic therapy improves the physiological efficiency of this region.

Expression analysis of neuregulin-1 in the dorsolateral prefrontal cortex in schizophrenia

Genetic linkage and association have implicated neuregulin-1 (NRG-1) as a schizophrenia susceptibility gene. We measured mRNA expression levels of the three major isoforms of NRG-1 (ie type I, type II, and type III) in the postmortem dorsolateral prefrontal cortex (DLPFC) from matched patients and controls using real-time quantitative RT-PCR. Expression levels of three internal controls—GAPDH, cyclophilin, and β-actin—were unchanged in schizophrenia, and there were no changes in the absolute levels of the NRG-1 isoforms. However, type I expression normalized by GAPDH levels was significantly increased in schizophrenia DLPFC (by 23%) and positively correlated with antipsychotic medication dosage. Type II/type I and type II/type III ratios were significantly decreased (18 and 23% respectively). There was no effect on the NRG-1 mRNA levels of genotype at two SNPs previously associated with schizophrenia, suggesting that these alleles are not functionally responsible for abnormal NRG-1 expression patterns in patients. Subtle abnormalities in the expression patterns of NRG-1 mRNA isoforms in DLPFC may be associated with schizophrenia.

Tourette Syndrome: Prediction of Phenotypic Variation in Monozygotic Twins by Caudate Nucleus D2 Receptor Binding

Tourette syndrome, a chronic tic disorder with autosomal dominant inheritance, exhibits considerable phenotypic variability even within monozygotic twin pairs. The origins of this variability remain unclear. Recent findings have implicated the caudate nucleus as a locus of pathology, and pharmacological evidence supports dopaminergic involvement. Within monozygotic twins discordant for Tourette syndrome severity, differences in D2 dopamine receptor binding in the head of the caudate nucleus predicted differences in phenotypic severity (r = 0.99); this relation was not observed in putamen. These data may link Tourette syndrome with a spectrum of neuropsychiatric disorders that involve associative striatal circuitry.

Genetic variation in CACNA1C affects brain circuitries related to mental illness.

CONTEXT The CACNA1C gene (alpha-1C subunit of the L-type voltage-gated calcium channel) has been identified as a risk gene for bipolar disorder and schizophrenia, but the mechanism of association has not been explored. OBJECTIVE To identify the neural system mechanism that explains the genetic association between the CACNA1C gene and psychiatric illness using neuroimaging and human brain expression. DESIGN We used blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to measure brain activation in circuitries related to bipolar disorder and schizophrenia by comparing CACNA1C genotype groups among healthy subjects. We tested the effect of genotype on messenger RNA (mRNA) levels of CACNA1C in postmortem human brain. A case-control analysis was used to determine the association of CACNA1C genotype with schizophrenia. SETTING National Institutes of Health Clinical Center. PATIENTS Healthy men and women of white race/ethnicity participated in the fMRI study. Postmortem samples from normal human brains were used for the brain expression study. Patients with schizophrenia and healthy subjects were used in the case-control analysis. MAIN OUTCOME MEASURES BOLD fMRI, mRNA levels in postmortem brain samples, and genetic association with schizophrenia. RESULTS The risk-associated single-nucleotide polymorphism (SNP rs1006737) in CACNA1C predicted increased hippocampal activity during emotional processing (P = .001 uncorrected, P((false recovery rate [FDR])) = .05, z = 3.20) and increased prefrontal activity during executive cognition (P = 2.8e-05 uncorrected, P(FDR) = .01, z = 4.03). The risk-associated SNP also predicted increased expression of CACNA1C mRNA in human brain (P = .002). CACNA1C was associated with schizophrenia in our case-control sample (odds ratio, 1.77; P = .03). CONCLUSIONS The risk-associated SNP in CACNA1C maps to circuitries implicated in genetic risk for bipolar disorder and schizophrenia. Its effects in human brain expression implicate a molecular and neural system mechanism for the clinical genetic association.

A primate-specific, brain isoform of KCNH2 affects cortical physiology, cognition, neuronal repolarization and risk of schizophrenia

Organized neuronal firing is crucial for cortical processing and is disrupted in schizophrenia. Using rapid amplification of 5′ complementary DNA ends in human brain, we identified a primate-specific isoform (3.1) of the ether-a-go-go–related K+ channel KCNH2 that modulates neuronal firing. KCNH2-3.1 messenger RNA levels are comparable to full-length KCNH2 (1A) levels in brain but three orders of magnitude lower in heart. In hippocampus from individuals with schizophrenia, KCNH2-3.1 expression is 2.5-fold greater than KCNH2-1A expression. A meta-analysis of five clinical data sets (367 families, 1,158 unrelated cases and 1,704 controls) shows association of single nucleotide polymorphisms in KCNH2 with schizophrenia. Risk-associated alleles predict lower intelligence quotient scores and speed of cognitive processing, altered memory-linked functional magnetic resonance imaging signals and increased KCNH2-3.1 mRNA levels in postmortem hippocampus. KCNH2-3.1 lacks a domain that is crucial for slow channel deactivation. Overexpression of KCNH2-3.1 in primary cortical neurons induces a rapidly deactivating K+ current and a high-frequency, nonadapting firing pattern. These results identify a previously undescribed KCNH2 channel isoform involved in cortical physiology, cognition and psychosis, providing a potential new therapeutic drug target.

Relationship of birth weight to the phenotypic expression of Gilles de la Tourette's syndrome in monozygotic twins.

We studied 16 pairs of monozygotic twins (mean age, 12.8 ± 1.4 years; age range, 8 to 26 years; sex, 12 male pairs, four female pairs) in whom at least one twin had Gilles de la Tourettes syndrome (TS) to determine the concordance rates for TS and tic disorders and to examine environmental factors accounting for intrapair differences in tic severity. In this cohort, the concordance rate for TS was 56%, and the concordance rate for tic disorders was 94%, supporting a primary genetic basis for TS and tic disorders with a high rate of penetrance for the gene. Thirteen of the pairs had differing birth weights and the lower birth-weight twin had a higher tic score in 12 of these pairs. The magnitude of the intrapair birth-weight difference (BWD) strongly predicted the magnitude of the intrapair tic score difference. The difference in tic severity could not be explained by any postnatal medical events. These findings suggest that crucial events affecting the phenotypic expression of TS occur in utero and that the factors causing the BWD also are related to tic severity.

Critical factors in gene expression in postmortem human brain: Focus on studies in schizophrenia.

BACKGROUND Studies of postmortem human brain are important for investigating underlying pathogenic molecular mechanisms of neuropsychiatric disorders. They are, however, confounded by pre- and postmortem factors. The purpose of this study was to identify sources of variation that will enable a better design of gene expression studies and higher reliability of gene expression data. METHODS We assessed the contribution of multiple variables to messenger RNA (mRNA) expression of reference (housekeeping) genes measured by reverse transcriptase-polymerase chain reaction (RT-PCR) by multiple regression analysis in a large number (N = 143) of autopsy samples from the hippocampus and white and grey matter of the dorsolateral prefrontal cortex (DLPFC) of patients with schizophrenia and normal control subjects. RESULTS The strongest predictor of gene expression was total RNA quality. Other significant factors included pH, postmortem interval, age and the duration of the agonal state, but the importance of these factors depended on transcript measured, brain region analyzed, and diagnosis. The quality of RNA obtained from the DLPFC white matter was also adversely affected by smoking. CONCLUSIONS Our results show that normalization of expression data of target genes with a geometric mean of multiple housekeeping genes should be used to control for differences in RNA quality between samples. The results also suggest that accurate assessment of other confounding factors and their inclusion as regressors in the analysis is critical for obtaining reliable and accurate quantification of mRNA expression.

Cerebral morphometric abnormalities in Tourette's syndrome: A quantitative MRI study of monozygotic twins

Article abstract—Although the pathologic substrate of Tourettes syndrome (TS) is unknown, studies have implicated subtle changes in the basal ganglia. To further investigate structural basal ganglia pathology in TS, we performed morphometric analyses of MRIs of 10 monozygotic twin pairs discordant for severity of TS but concordant for the presence of tic disorders (mean age, 16.3 years; range, 9 to 31 years). Right caudate volume was slightly but significantly reduced in the relatively more severely affected twins as a group compared with the less affected twins (mean difference = 6%, p < 0.01). Most of this difference was attributable to volume reduction in the anterior right caudate (p < 0.02), which was smaller in the more severely affected twin in nine of 10 twin sets. The mean volume of the left lateral ventricle was 16% smaller in the more severely affected twins than in the less severely affected twins (p < 0.01). The normal asymmetry of the lateral ventricles (left greater than right) was not present in the more severely affected twins, who had a trend toward a larger right lateral ventricle. Moreover, the difference within a pair in the degree of loss of the normal ventricular asymmetry correlated with the difference within a pair in the severity of the tic disorder (r = 0.75, p < 0.02). There were no other basal ganglia, ventricular volumetric, or asymmetry abnormalities. These findings partially replicate other MRI studies and suggest that subtle structural abnormalities in the CNS, particularly in the caudate, may play a role in the pathophysiology of TS. Because monozygotic twins are genetically identical, these structural abnormalities must reflect adverse environmental events.

Reduction of synapsin in the hippocampus of patients with bipolar disorder and schizophrenia

Several studies suggest that decreased expression of presynaptic proteins may be characteristic of schizophrenia. We examined one such protein, synapsin, in schizophrenia and bipolar disorder. Samples of hippocampal tissue from controls (n = 13), patients with schizophrenia (n = 16), or bipolar disorder (n = 6), and suicide victims (n = 7) were used. The membrane and cytosolic fractions were analyzed by Western immunoblotting for synapsin using an antibody that detects synapsin Ia, IIa, and IIIa proteins. Synaptophysin was also measured for comparison. Total synapsin was decreased significantly in patients with schizophrenia (P = 0.034) and in bipolar disorder (P = 0.00008) as compared to controls. The synapsin/synaptophysin ratios were decreased in schizophrenia and bipolar disorder, and additionally in suicide victims (P = 0.014). Age, postmortem interval, percentage of protein extracted, and pH of brain were not different between groups. No changes in total synapsin or synaptophysin in the hippocampus were produced by injecting rats with either lithium or haloperidol for 30 days. Reductions in synapsin in both patients with schizophrenia (synapsin IIa and IIIa) and bipolar disorder (synapsin Ia, IIa and IIIa) imply that altered or reduced synaptic function in the hippocampus may be involved in these disorders.