Tryptophan hydroxylase-2 polymorphism is associated with white matter integrity in first-episode, medication-naïve major depressive disorder patients.

Considerable evidence suggests that the tryptophan hydroxylase-2 (TPH2) gene is associated with the pathophysiology of major depressive disorder (MDD). In the present study, we investigated alterations of white matter (WM) integrity and the impact of TPH2 polymorphism on WM in a sample of 118 first-episode, medication-naïve, MDD patients and 118 well-matched healthy controls. Whole brain analyses of fractional anisotropy (FA) were performed using tract-based spatial statistics (TBSS). The results showed that the MDD group had significantly reduced FA values for the genu and body of the corpus callosum (CC) and the bilateral anterior corona radiate (ACR). In the MDD patient group, the GG homozygote subgroup exhibited a widespread reduction of FA (uncorrected) and significantly reduced FA in the left retrolenticular portion of the internal capsule and left superior longitudinal fasciculus (SLF) compared with those of the T carriers (GT/TT) (FWE corrected). No significant correlation was found between the FA values in any brain region and the patients' clinical variables. Our findings demonstrate the presence of abnormal white matter integrity in untreated patients with first-episode depression. TPH2-rs4570625 polymorphisms may be involved in the pathological mechanism of WM microarchitecture in patients.

B56δ-related protein phosphatase 2A dysfunction identified in patients with intellectual disability.

Here we report inherited dysregulation of protein phosphatase activity as a cause of intellectual disability (ID). De novo missense mutations in 2 subunits of serine/threonine (Ser/Thr) protein phosphatase 2A (PP2A) were identified in 16 individuals with mild to severe ID, long-lasting hypotonia, epileptic susceptibility, frontal bossing, mild hypertelorism, and downslanting palpebral fissures. PP2A comprises catalytic (C), scaffolding (A), and regulatory (B) subunits that determine subcellular anchoring, substrate specificity, and physiological function. Ten patients had mutations within a highly conserved acidic loop of the PPP2R5D-encoded B56δ regulatory subunit, with the same E198K mutation present in 6 individuals. Five patients had mutations in the PPP2R1A-encoded scaffolding Aα subunit, with the same R182W mutation in 3 individuals. Some Aα cases presented with large ventricles, causing macrocephaly and hydrocephalus suspicion, and all cases exhibited partial or complete corpus callosum agenesis. Functional evaluation revealed that mutant A and B subunits were stable and uncoupled from phosphatase activity. Mutant B56δ was A and C binding-deficient, while mutant Aα subunits bound B56δ well but were unable to bind C or bound a catalytically impaired C, suggesting a dominant-negative effect where mutant subunits hinder dephosphorylation of B56δ-anchored substrates. Moreover, mutant subunit overexpression resulted in hyperphosphorylation of GSK3ß, a B56δ-regulated substrate. This effect was in line with clinical observations, supporting a correlation between the ID degree and biochemical disturbance.

The role of primary cilia in corpus callosum formation is mediated by production of the Gli3 repressor.

Agenesis of the corpus callosum (AgCC) is a frequent brain disorder found in over 80 human congenital syndromes including ciliopathies. Here, we report a severe AgCC in Ftm/Rpgrip1l knockout mouse, which provides a valuable model for Meckel-Grüber syndrome. Rpgrip1l encodes a protein of the ciliary transition zone, which is essential for ciliogenesis in several cell types in mouse including neuroepithelial cells in the developing forebrain. We show that AgCC in Rpgrip1l(-/-) mouse is associated with a disturbed location of guidepost cells in the dorsomedial telencephalon. This mislocalization results from early patterning defects and abnormal cortico-septal boundary (CSB) formation in the medial telencephalon. We demonstrate that all these defects primarily result from altered GLI3 processing. Indeed, AgCC, together with patterning defects and mispositioning of guidepost cells, is rescued by overexpressing in Rpgrip1l(-/-) embryos, the short repressor form of the GLI3 transcription factor (GLI3R), provided by the Gli3(Δ699) allele. Furthermore, Gli3(Δ699) also rescues AgCC in Rfx3(-/-) embryos deficient for the ciliogenic RFX3 transcription factor that regulates the expression of several ciliary genes. These data demonstrate that GLI3 processing is a major outcome of primary cilia function in dorsal telencephalon morphogenesis. Rescuing CC formation in two independent ciliary mutants by GLI3(Δ699) highlights the crucial role of primary cilia in maintaining the proper level of GLI3R required for morphogenesis of the CC.

Diphenyl diselenide modulates gene expression of antioxidant enzymes in the cerebral cortex, hippocampus and striatum of female hypothyroid rats.

INTRODUCTION: Cellular antioxidant signaling can be altered either by thyroid disturbances or by selenium status. AIMS: To investigate whether or not dietary diphenyl diselenide can modify the expression of genes of antioxidant enzymes and endpoint markers of oxidative stress under hypothyroid conditions. METHODS: Female rats were rendered hypothyroid by continuous exposure to methimazole (MTZ; 20 mg/100 ml in the drinking water) for 3 months. Concomitantly, MTZ-treated rats were either fed or not with a diet containing diphenyl diselenide (5 ppm). mRNA levels of antioxidant enzymes and antioxidant/oxidant status were determined in the cerebral cortex, hippocampus and striatum. RESULTS: Hypothyroidism caused a marked upregulation in mRNA expression of catalase, superoxide dismutase (SOD-1, SOD-3), glutathione peroxidase (GPx-1, GPx-4) and thioredoxin reductase (TrxR-1) in brain structures. SOD-2 was increased in the cortex and striatum, while TrxR-2 increased in the cerebral cortex. The increase in mRNA expression of antioxidant enzymes was positively correlated with the Nrf-2 transcription in the cortex and hippocampus. Hypothyroidism caused oxidative stress, namely an increase in lipid peroxidation and reactive oxygen species levels in the hippocampus and striatum, and a decrease in nonprotein thiols in the cerebral cortex. Diphenyl diselenide was effective in reducing brain oxidative stress and normalizing most of the changes observed in gene expression of antioxidant enzymes. CONCLUSION: The present work corroborates and extends that hypothyroidism disrupts antioxidant enzyme gene expression and causes oxidative stress in the brain. Furthermore, diphenyl diselenide may be considered a promising molecule to counteract these effects in a hypothyroidism state.

Catechol-O-methyltransferase Val158Met polymorphism on the relationship between white matter hyperintensity and cognition in healthy people.

BACKGROUND: White matter lesions can be easily observed on T2-weighted MR images, and are termed white matter hyperintensities (WMH). Their presence may be correlated with cognitive impairment; however, the relationship between regional WMH volume and catechol-O-methyltransferase (COMT) Val158Met polymorphism in healthy populations remains unclear. METHODS: We recruited 315 ethnic Chinese adults with a mean age of 54.9 ± 21.8 years (range: 21-89 y) to examine the genetic effect of COMT on regional WMH and the manner in which they interact to affect cognitive function in a healthy adult population. Cognitive tests, structural MRI scans, and genotyping of COMT were conducted for each participant. RESULTS: Negative correlations between the Digit Span Forward (DSF) score and frontal WMH volumes (r = -.123, P = .032, uncorrected) were noted. For the genetic effect of COMT, no significant difference in cognitive performance was observed among 3 genotypic groups. However, differences in WMH volumes over the subcortical region (P = .016, uncorrected), whole brain (P = .047, uncorrected), and a trend over the frontal region (P = .050, uncorrected) were observed among 3 COMT genotypic groups. Met homozygotes and Met/Val heterozygotes exhibited larger WMH volumes in these brain regions than the Val homozygotes. Furthermore, a correlation between the DSF and regional WMH volume was observed only in Met homozygotes. The effect size (cohen's f) revealed a small effect. CONCLUSIONS: The results indicate that COMT might modulate WMH volumes and the effects of WMH on cognition.

Heparan sulfotransferases Hs6st1 and Hs2st keep Erk in check for mouse corpus callosum development.

The corpus callosum (CC) connects the left and right cerebral hemispheres in mammals and its development requires intercellular communication at the telencephalic midline mediated by signaling proteins. Heparan sulfate (HS) is a sulfated polysaccharide that decorates cell surface and extracellular matrix proteins and regulates the biological activity of numerous signaling proteins via sugar-protein interactions. HS is subject to regulated enzymatic sulfation and desulfation and an attractive, although not proven, hypothesis is that the biological activity of HS is regulated by a sugar sulfate code. Mutant mouse embryos lacking the heparan sulfotransferases Hs2st or Hs6st1 have severe CC phenotypes and form Probst bundles of noncrossing axons flanking large tangles of midline glial processes. Here, we identify a precocious accumulation of Sox9-expressing glial cells in the indusium griseum region and a corresponding depletion at the glial wedge associated with the formation of Probst bundles along the rostrocaudal axis in both mutants. Molecularly, we found a surprising hyperactivation of Erk signaling in Hs2st(-/-) (2-fold) and Hs6st1(-/-) (6-fold) embryonic telencephalon that was most striking at the midline, where Erk signaling is lowest in wild-types, and a 2-fold increase in Fgf8 protein levels in Hs6st1(-/-) embryos that could underpin Erk hyperactivation and excessive glial movement to the indusium griseum. The tightly linked Hs6st1(-/-) CC glial and axonal phenotypes can be rescued by genetic or pharmacological suppression of Fgf8/Erk axis components. Overall, our data fit a model in which Hs2st and Hs6st1 normally generate conditions conducive to CC development by generating an HS-containing environment that keeps Erk signaling in check.

Distribution of oligodendrocyte loss and mitochondrial toxicity in the cuprizone-induced experimental demyelination model.

Cuprizone is a copper-chelating mitochondrial toxin that causes oligodendrocyte apoptosis and demyelination preferentially in the corpus callosum (CC) and the superior cerebellar peduncles, but not in the spinal cord (SC) of C57BL/6 mice. Here we aimed to determine the activities of copper-containing enzymes in correlation with the distribution of demyelination during exposure to cuprizone. The study revealed mitochondrial complex IV and superoxide dismutase activity alterations in both the pathology-affected CC and the non-affected SC. This observation raises the possibility that regionally different subcellular molecular interactions lead to the selective oligodendrocyte loss induced by the nonselective mitochondrial toxin, cuprizone.

Brain 3-Mercaptopyruvate Sulfurtransferase (3MST): Cellular Localization and Downregulation after Acute Stroke.

3-Mercaptopyruvate sulfurtransferase (3MST) is an important enzyme for the synthesis of hydrogen sulfide (H2S) in the brain. We present here data that indicate an exclusively localization of 3MST in astrocytes. Regional distribution of 3MST activities is even and unremarkable. Following permanent middle cerebral artery occlusion (pMCAO), 3MST was down-regulated in both the cortex and striatum, but not in the corpus collosum. It appears that the down-regulation of astrocytic 3MST persisted in the presence of astrocytic proliferation due to gliosis. Our observations indicate that 3MST is probably not responsible for the increased production of H2S following pMCAO. Therefore, cystathionine ß-synthase (CBS), the alternative H2S producing enzyme in the CNS, remains as a more likely potential therapeutic target than 3MST in the treatment of acute stroke through inhibition of H2S production.

Differences in phosphodiesterase 3A and 3B expression after ischemic insult.

Phosphodiesterase (PDE) exists in the cardiovascular system, adipose tissue and platelets, and its inhibition increases the cellular levels of cAMP, which could activate cAMP-responsive element binding protein (pCREB). The present study was designed to map the expression of PDE3A/B in the forebrain and define the time course of PDE3 expression in the ischemic boundary zone after ischemia. The number of PDE3A-positive cells (neurons and endothelial cells) remained unchanged, while PDE3B-positive cells gradually increased after ischemia/reperfusion. In the corpus callosum, PDE3B was expressed in oligodendrocytes, oligodendrocyte progenitor cells, and astrocytes. PDE3B-expressing astrocytes showed gradual increase after ischemia/reperfusion. In the cortex, the majority of PDE3B-expressing cells before ischemia were neurons, though few were astrocytes. Ischemic insult resulted in gradual increase in PDE3B-expressing astrocytes and neurons, with larger increase in astrocytes. Expression of brain derived neurotrophic factor (BDNF) and B-cell leukemia/lymphoma 2 protein (Bcl-2) was detected in pCREB-positive cells, not in PDE3B-positive cells. Our results demonstrated that ischemic insult increased PDE3B expression, but not PDE3A, and changed the number and type of cells in a time-dependent manner. The variation of PDE3B-expression in the brain might play a crucial pathophysiological role, and regulation of PDE3B production might protect against ischemic brain damage.

Expression of peroxiredoxin 1, 2, and 6 in the rat brain during perinatal development and in response to dexamethasone.

Peroxiredoxins (Prdx), a family of antioxidant proteins, have important defensive roles in the degenerative brain diseases and neuronal cell death in adult subjects. However, little is known in the neonatal brain. Here, we studied the developmental expression of Prdxs and their response to dexamethasone in the perinatal rat brain. Prdx 1 expression increased during late gestations and peaked at postnatal-day 1, when its expression gradually decreased. Prdx 2 expression remained largely unchanged. Prdx 6 expression continually increased as growing. Using immunohistochemistry, each Prdx showed a strong expression in the cerebral cortex and hippocampus. Prdx 1 was strongly expressed in the corpus callosum. The dexamethasone injection increased the expression of Prdx 6. In conclusion, we reveal for the first time that Prdx 1, 2 and 6 are found in abundance in the perinatal rat brain and are differentially expressed during development. The expression of Prdx 6 was affected by dexamethasone treatment.

GAD65 is essential for synthesis of GABA destined for tonic inhibition regulating epileptiform activity.

GABA is synthesized from glutamate by glutamate decarboxylase (GAD), which exists in two isoforms, that is, GAD65 and GAD67. In line with GAD65 being located in the GABAergic synapse, several studies have demonstrated that this isoform is important during sustained synaptic transmission. In contrast, the functional significance of GAD65 in the maintenance of GABA destined for extrasynaptic tonic inhibition is less well studied. Using GAD65-/- and wild type GAD65+/+ mice, this was examined employing the cortical wedge preparation, a model suitable for investigating extrasynaptic GABA(A) receptor activity. An impaired tonic inhibition in GAD65-/- mice was revealed demonstrating a significant role of GAD65 in the synthesis of GABA acting extrasynaptically. The correlation between an altered tonic inhibition and metabolic events as well as the functional and metabolic role of GABA synthesized by GAD65 was further investigated in vivo. Tonic inhibition and the demand for biosynthesis of GABA were augmented by injection of kainate into GAD65-/- and GAD65+/+ mice. Moreover, [1-(13) C]glucose and [1,2-(13) C]acetate were administered to study neuronal and astrocytic metabolism concomitantly. Subsequently, cortical and hippocampal extracts were analyzed by NMR spectroscopy and mass spectrometry, respectively. Although seizure activity was induced by kainate, neuronal hypometabolism was observed in GAD65+/+ mice. In contrast, kainate evoked hypermetabolism in GAD65-/- mice exhibiting deficiencies in tonic inhibition. These findings underline the importance of GAD65 for synthesis of GABA destined for extrasynaptic tonic inhibition, regulating epileptiform activity.

Developmental expression of histone deacetylase 11 in the murine brain.

Recent studies indicate that neural cell development in the central nervous system (CNS) correlates with a reduction in acetylation of histone core proteins. Moreover, histone hypoacetylation is thought to be important to oligodendrocyte lineage development. The mechanisms mediating the reduction in acetylation during postnatal neural development remain to be defined. To begin to understand these mechanisms, we investigated the expression of histone deacetylase 11 (HDAC11), a newly identified HDAC, in mouse brain during postnatal development. We show that HDAC11 was widely expressed in the brain and that this expression gradually increased in a region-specific pattern between birth and 4 weeks of age. At the cellular level HDAC11 protein was predominately localized in the nuclei of mature oligodendrocytes but only minimally in astrocytes. Although dentate gyrus granule neurons abundantly expressed HDAC11, granule neuron precursors in the subgranule layer exhibited little HDAC11 immunoreactivity. Double-immunostaining of the corpus callosum and dentate gyrus demonstrated that HDAC11 and Ki67, a cell-proliferating marker, are rarely colocalized in same cells. Our data show that HDAC11 was expressed in the developing brain in a temporal and spatial pattern that correlates with the maturation of neural cells, including cells of the oligodendrocyte lineage. These findings support a role for HDAC11 in CNS histone deacetylation and the development of oligodendrocytes and neurons during postnatal development.

The representation of the visual field in three extrastriate areas of the ferret (Mustela putorius) and the relationship of retinotopy and field boundaries to callosal connectivity.

We describe representations of the visual field in areas 18, 19 and 21 of the ferret using standard microelectrode mapping techniques. In all areas the azimuths are represented as islands of peripheral visual field surrounded by central visual field representation. The zero meridian was found at the 17/18 and 19/21 borders; at the 18/19 and anterior border of 21 the relative periphery of the visual field was found. In areas 18 and 19, elevations are represented in a smooth medio-lateral progression from lower to upper visual field. In several cases the elevations in area 21 evidenced a similar medio-lateral progression; however, in others the elevations exhibited a split representation of the horizontal meridian. Anatomically determined callosal connections coincided with the representation of azimuths near the zero meridian. Medio-lateral bands of callosal connectivity that straddle the 17/18 and 19/21 borders are connected by bridges of callosally projecting cells. Acallosal cortical islands corresponded to the peripheral visual field and were found straddling the 18/19 border and the anterior border of area 21. The results are discussed in relation to callosal connectivity and retinotopy in extrastriate visual cortex and to proposed homologies of carnivore and primate visual cortex.

Chronic cerebral hypoperfusion induces MMP-2 but not MMP-9 expression in the microglia and vascular endothelium of white matter.

White matter lesions are closely associated with cognitive impairment and motor dysfunction in the aged. To explore the pathophysiology of these lesions, the authors examined the expression of matrix metalloproteinase-2 (MMP-2) and MMP-9 in the white matter in a rat model of chronic cerebral hypoperfusion. After bilateral clipping of the common carotid arteries, myelin staining revealed demyelinating changes in the optic tract and the corpus callosum on day 7. Zymographic analyses indicated an increase in the level of MMP-2, but not MMP-9, after the hypoperfusion. Immunohistochemical analyses revealed the presence (most abundantly on day 3) of MMP-2-expressing activated microglia in the optic tract and corpus callosum. In contrast, the capillary endothelial cells expressed MMP-2 later. IgM-immunoreactive glial cells were absent in the sham-operated animals, but were present in the hypoperfused animals by day 3, reflecting the disrupted blood-brain barrier. These findings suggest that the main sources of the elevated MMP-2 were the microglia and the endothelium, and that these cells may contribute to the remodeling of the white matter myelin and microvascular beds in chronic cerebral hypoperfusion.

Inhibition of cyclin E-cyclin-dependent kinase 2 complex formation and activity is associated with cell cycle arrest and withdrawal in oligodendrocyte progenitor cells.

Stimulatory and inhibitory signals regulate cell proliferation through the activity of specific enzymes that operate in distinct phases of the cell cycle. We have studied cell cycle progression, arrest, and withdrawal in the oligodendrocyte progenitor (OP) cell model system, focusing on the G(1) phase and G(1)-S transition. Not only were proliferating OPs found to display higher protein levels of cyclin E and D and cyclin-dependent kinases (cdk) 2, 4, and 6 than cells that had permanently withdrawn from the cycle, but the kinase activities of both cyclin D-cdk4/6 and cyclin E-cdk2 were also higher in dividing OPs. This was associated with a decrease in the formation of the cyclin E-cdk2 and cyclin D-cdk4/cyclin D-cdk6 complexes in differentiated oligodendrocytes that had permanently withdrawn from the cell cycle. Reversible cell cycle arrest in G(1) induced by glutamatergic and beta-adrenergic receptor activation or cell depolarization, however, did not modify cyclin E and cdk2 protein expression compared with proliferating OPs. Instead, these agents caused a selective decrease in cdk2 activity and an impairment of cyclin E-cdk2 complex formation. Although cyclin D protein levels were higher than in proliferating cells, cyclin D-associated kinase activity was not modified in G(1)-arrested OPs. Analysis in corpus callosum in vivo showed that cyclin E-cdk2 activity increased between postnatal days 3 and 15 and decreased between postnatal days 15 and 30. Our results indicate that the cyclin E-cdk2 complex is a major regulator of OP cell cycle progression and that the cdks involved in reversible cell cycle arrest are distinct from those implicated in permanent cell cycle withdrawal.

Expression of induced nitric oxide synthase in amoeboid microglia in postnatal rats following an exposure to hypoxia.

The present study showed the expression of induced nitric oxide synthase (iNOS) immunoreactivity in amoeboid microglia following an exposure to transient hypoxia in postnatal rats. iNOS immunoreactivity was expressed mainly in the amoeboid microglia in corpus callosum and subependymal regions of the ventricles within 3 h after hypoxia. The expression declined after 5 h, and became undetectable after 15 h and in longer surviving rats. The immunoreactivity of these cells with OX-42, which is a marker for microglia cells and detects complement type three receptors (CR3), was comparable in the rats exposed to hypoxia and the control rats. Immunoglobulin G (IgG) immunoreactivity was observed in the amoeboid microglia up to 3 h after hypoxia but it was undetectable in longer surviving rats and in the control rats. The iNOS expression in the amoeboid mircoglial cells may be related to the host defense and maintenance of structural integrity of the highly vulnerable periventricular white matter after hypoxia. The immunostaining of amoeboid microglial cells with IgG following hypoxia indicates leakage of plasma immunoglobulin from the blood vessels and its removal by the amoeboid microglial cells.

Plasma kallikrein localisation in human blood vessels.

Immunoreactive plasma kallikrein/prekallikrein was detected in the endothelial cells and the smooth muscle cells of the arteries examined. The most intense overall immunolabelling of plasma kallikrein/prekallikrein was visualized in the medium to small size arteries. The endothelial cells of the pulmonary artery and the smooth muscle cells of the supracallosal artery showed the highest intensity of plasma kallikrein/prekallikrein labelling. The least defined labelling occurred in the tunica adventitia. The renal vein was the only blood vessel that showed no trace of immunoreactive plasma kallikrein/prekallikrein. The question arises as to the mechanisms that could be involved in the in vivo conversion of plasma kallikrein/prekallikrein into the active enzymatic molecule. The experiments indicate that a bacterial elastase cleaves the Arg371-Ile372 scissile bond within a disulphide bridge of the prekallikrein molecule. This is the bond that is cleaved also during activation of prekallikrein by trypsin-like proteinases. Functionally, the endogenous activation of plasma prekallikrein is of considerable importance, both in the regulation of blood flow and blood pressure and in the causation of septic shock. The incidental finding at histology, of patchy atheromatous disease in the coronary, vertebral and supracallosal arteries, assisted in elucidating the role of plasma kallikrein/prekallikrein in the commonest disease affecting human blood vessels. Intense labelling for plasma kallikrein was observed in the endothelial cells, foamy macrophages, inflammatory cells and fibroblasts within the thickened intima of the plaque as well as in smooth muscle cells of the underlying tunica media. The intense immunolabelling of plasma kallikrein/prekallikrein in these regions suggest that these may be induced by atheromatous disease.

Neuron-specific enolase as an effective immunohistochemical marker for injured axons after fatal brain injury.

Recently, it has been reported that a diagnosis of diffuse axonal injury in cases with a short survival period can be made with the use of immunolabelling for beta-amyloid precursor protein (APP). We examined whether immunostaining for neuron-specific enolase (NSE) can also be a useful marker for the detection of axonal injury in its early stages. Sections of the corpus callosum from 19 cases of head injury and from 9 cases of no head injury were immunostained for NSE and stained by the standard Holmes' silver method. For comparison, serial sections from several cases were immunostained for APP. Immunostaining for NSE as well as for APP, labelled injured axons in head injury cases with as early as 1.5 h survival where Holmes' staining failed to detect any changes of axons. Since NSE and APP labelled only injured axons but not normal axons, the results were readily interpretable. These findings indicate that NSE should be an effective marker for the detection of axonal injury in its early stages.

In vivo expression of inducible nitric oxide synthase in supraventricular amoeboid microglial cells in neonatal BALB/c and athymic mice.

The present study investigated whether the supraventricular amoeboid microglial cells (SAMC) in neonatal BALB/c and athymic nude mice were able to express inducible nitric oxide synthase (iNOS) after intraperitoneal injections of lipopolysaccharide (LPS) or interferon-gamma (IFN-gamma). The results showed that iNOS, undetectable in these cells in vehicle injected mice, could clearly be demonstrated immunohistochemically in a large number of them in LPS treated normal and mutant mice. Only a few iNOS-positive SAMC were observed in IFN-gamma injected mice. Immunoelectron microscopy confirmed the microglial nature of the labelled cells and that the immunoprecipitate of iNOS was cytosolic, being diffusely present throughout the cytoplasm of the cells. It is suggested that iNOS in the SAMC of neonatal BALB/c and athymic mice may be involved in the synthesis of nitric oxide which is necessitated more for host defence mechanism against bacterial endotoxin than against immunological stimuli.

A novel cytochrome P450 expressed primarily in brain.

hct-1 (hippocampal transcript) was detected in a differential screen of a rat hippocampal cDNA library. Expression of hct-1 was enriched in the formation but was also detected in rat liver and kidney, though at much lower levels; expression was barely detectable in testis, ovary, and adrenal. In liver, unlike brain, expression was sexually dimorphic; hepatic expression was greatly reduced in female rats. In mouse, brain expression was widespread, with the highest levels being detected in corpus callosum; only low levels were detected in liver. Sequence analysis of rat and mouse hct-1 cDNAs revealed extensive homologies with cytochrome P450s (CYPs), a diverse family of heme-binding monooxygenases that metabolize a range of substrates including steroids, fatty acids, and xenobiotics. Among the CYPs, hct-1 is most similar (39% at the amino acid sequence) to cholesterol 7 alpha-hydroxylase (CYP7) and contains a postulated steroidogenic domain present in other steroid-metabolizing CYPs but clearly represents a type of CYP not previously reported. Genomic Southern analysis suggests that a single gene corresponding to hct-1 is present in mouse, rat, and human. hct-1 is unusual in that, unlike all other CYPs described, the primary site of expression is in the brain. Similarity to CYP7 and other steroid-metabolizing CYPs may argue that hct-1 (CYP7B) plays a role in steroid metabolism in brain, notable because of the documented ability of brain-derived steroids (neurosteroids) to modulate cognitive function in vivo.