Schizophrenia is a debilitating and complex mental disorder with a prevalence of approximately 1% worldwide. The etiology remains unclear, despite massive research efforts. Hyperactive dopaminergic signal transduction in the central nervous system is suggested to be involved in the pathophysiology of schizophrenia (the dopamine hypothesis). The dopamine D2–receptor (DRD2) gene is thus a promising candidate for associations with risk of schizophrenia. We investigated DRD2 and found a novel missense nucleotide change causing an amino acid substitution of serine with cysteine at codon 311 (Ser311Cys). We performed an association study using 156 schizophrenia patients and 300 controls. Cys311 in DRD2 was significantly associated with schizophrenia. Patients with the Cys311 allele displayed shorter duration of hospitalization and less severe negative symptoms and were more frequently married compared to patients without this allele, suggesting good response to treatment. We expanded samples to 291 patients with schizophrenia (including 11 postmortem brain samples), 579 controls, and 78 patients with affective disorders in a further case-control study. Cys311 was associated with schizophrenia, particularly in patients without negative symptoms, and bipolar disorder with mood-incongruent psychotic symptoms. Three meta-analyses using over 20 published studies confirmed the association. In vitro studies showed that Cys311-type D2 receptor impairs dopamine-induced sequestration, which appears to be consistent with the dopamine hypothesis.
Dopamine plays a central role in the regulation of psychomotor functions. The effect of dopamine is largely mediated through the cAMP/PKA signaling cascade and therefore controlled by phosphodiesterases (PDEs). Multiple PDEs with different substrate specificities and subcellular localization are expressed in the striatum, and the functional roles of PDE10A, PDE4, and PDE1B are extensively studied. Biochemical and behavioral profiles of PDE inhibition by selective inhibitors and/or genetic deletion related to dopaminergic neurotransmission are compared among those PDEs. The inhibition of PDE up-regulates cAMP/PKA signaling in three neuronal subtypes, resulting in the stimulation of dopamine synthesis at dopaminergic terminals, the inhibition of dopamine D2–receptor signaling in striatopallidal neurons, and the stimulation of dopamine D1–receptor signaling in striatonigral neurons. Predominant roles of PDE families or isoforms are implicated in each neuronal subtype: PDE4 at dopaminergic terminals, PDE10A and PDE4 in striatopallidal neurons, and PDE1B in striatonigral neurons. PDE10A and PDE4 inhibition may exhibit D2 antagonist–like, antipsychotic effects, whereas PDE1B inhibition may exhibit D1 agonist–like effects in the striatum. Development of PDE isoform–specific inhibitors is essential for better understanding of the function of each PDE isoform and treatment of neuropsychiatric disorders.
5R-L-Erythro-5,6,7,8-tetrahydrobiopterin (BH4) is an essential cofactor for tyrosine hydroxylase (TH). Recently, a type of dopa-responsive dystonia (DRD) (DYT5, Segawa’s disease) was revealed to be caused by dominant mutations of the gene encoding GTP cyclohydrolase I (GCHI), which is the rate-limiting enzyme of BH4 biosynthesis. In order to probe the role of BH4 in vivo, we established BH4-depleted mice by disrupting the 6-pyruvoyltetrahydropterin synthase (PTS) gene (Pts−/−) and rescued them by introducing human PTS cDNA under the control of the human dopamine β-hydroxylase (DBH) promoter (Pts−/−-DPS). The Pts−/−-DPS mice developed hyperphenylalaninemia. Interestingly, tyrosine hydroxylase protein was dramatically reduced in the dopaminergic nerve terminals of these mice, and they developed abnormal posture and motor disturbance. We propose that the biochemical and pathologic changes of Pts−/−-DPS mice are caused by mechanisms common to human DRD, and understanding these mechanisms could give us insight into other movement disorders.
Among the various dopamine receptors, D2-like receptors (D2R, D3R, and D4R) are characterized by a large third cytoplasmic loop, a short carboxyl-terminal tail, and the ability to activate inhibitory G proteins. The diverse activities of D2-like receptors are partly mediated by proteins that interact with the third cytoplasmic loop, which regulate receptor signaling, receptor trafficking, and stability. Furthermore, in the case of D2R and D3R genes, mRNA splicing generates isoforms in the region of the third cytoplasmic loop. The gene encoding D2R gives rise to two isoforms, termed the dopamine D2 receptor long isoform (D2LR) and the dopamine D2 receptor short isoform (D2SR), which lacks 29 amino acids of the D2LR within the third cytoplasmic loop. The D3R gene also produces at least seven distinct alternative splicing variants including D3nf, in which 98 base pairs in the carboxyl-terminal region of the third intracellular loop are deleted. In this review, we focus on proteins interacting with the dopamine D2/D3 receptors in the third cytoplasmic loop. We also define a novel binding protein, heart-type fatty acid–binding protein (H-FABP), which specifically interacts with the 29 D2LR amino acids deleted in D2SR and document its function in D2LR signaling.
Postprandial hyperglycemia (PPH) and intermittent hypoxia related to the sleep apnea syndrome are important predictors of cardiovascular disease. We investigated the effects of intermittent hypoxia on pathological changes in the left ventricular (LV) myocardium caused by PPH in lean mice and evaluated the influence of acarbose, an α-glucosidase inhibitor. Male C57BL/6J mice aged 8 weeks were exposed to intermittent hypoxia (8 h/day during the daytime) or kept under normoxia. PPH was induced by restriction of feeding to 1-h periods twice a day, with the restricted diet (RD) mice receiving either standard chow or chow containing 0.02% acarbose. Another group of mice were fed standard chow ad libitum (AL). Plasma glucose levels after food intake were significantly elevated in RD but not in AL mice, and glucose levels were suppressed by acarbose. Intermittent hypoxia exacerbated cardiomyocyte hypertrophy and interstitial fibrosis in the LV myocardium of RD mice. Superoxide production and expression of 4-hydroxy-2-nonenal in the LV myocardium with intermittent hypoxia were increased in RD mice, but not AL mice. In addition, expression of tumor necrosis factor α (TNF-α) mRNA was increased in hypoxic RD mice. Treatment with acarbose inhibited oxidative stress and TNF-α mRNA expression and preserved the histological architecture of the LV myocardium.
The aim of the present study was to establish a novel embolic model of cerebral infarction and to evaluate the effect of Stachybotrys microspora triprenyl phenol-7 (SMTP-7), a novel fungal triprenyl phenol metabolite. Thrombotic occlusion was induced by transfer of acetic acid–induced embolus into the brain. The regional cerebral blood flow was measured by a laser Doppler flowmeter to check the ischemic condition. Infarction area was assessed by 2% 2,3,5-triphenyltetrazolium chloride (TTC) staining. Neurological scores were determined by a modified version of the method described by Longa et al. Emboli were accumulated at the temporal or parietal region of the middle cerebral artery. Additionally, we found that this model showed decreased cerebral blood flow and increased infarction area and neurological scores. Treatment with tissue plasminogen activator (t-PA) reduced infarction area and the neurological scores in a dose-dependent manner; moreover, the decreased cerebral blood flow recovered. SMTP-7 also reduced these values. The therapeutic time window of SMTP-7 was longer than that of t-PA. These results indicate that this model may be useful for understanding the pathophysiological mechanisms of cerebral infarction and evaluating the effects of therapeutic agents. Additionally, SMTP-7 is a promising approach to extend the therapeutic time window. Therefore, this novel compound may represent a novel approach for the treatment of cerebral infarction.
There is evidence that reactive oxygen species (ROS) are formed in the cochlea during acoustic injury. However, very little is known about the involvement of ROS signals in the spiral ligament (SL) during such injury. The purpose of this study was to determine the effect of the multifunctional antioxidant tempol and the nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) on acoustic injury and the c-Jun N-terminal kinase (JNK) pathway in the SL. Exposure of adult mice to noise (8-kHz octave band, 110-dB SPL for 1 h) produced permanent hearing loss. Noise exposure increased not only the formation of a protein modified by 4-hydroxynonenal and formation of nitrotyrosine, but also the level of phospho-JNK in the SL. Pretreatment with tempol or L-NAME was effective in protecting the noise-exposed animals from hearing loss, as well as in abolishing the noise-induced activation of the JNK signaling pathway. Interestingly, noise exposure caused a dramatic decrease in connexin26 level in the SL. This decrease was prevented by tempol or L-NAME. Taken together, our data suggest that noise-induced hearing loss is due at least in part to ROS / nitric oxide–mediated activation of the JNK pathway and down-regulation of connexin26 in the SL of mice.
2-Aminophenoxazine-3-one (Phx-3) induced cellular apoptosis in mouse melanoma B16 cells as detected by DNA laddering and upregulated Fas expression in the cells in vitro. Next, the anti-metastatic effects of Phx-3 were investigated in C56BL/6 mice. When B16 melanoma cells were injected into the tail veins of mice, significant metastasis of the cells was indicated in the lungs, 14 days after treatment. In contrast, when 0.5 mg/kg Phx-3 was administered to mice through the tail veins, once simultaneously with or every three days after the administration of B16 melanoma cells, the number of metastasized pulmonary cells was extremely reduced. Moderate reduction of the number of metastasized pulmonary cells was indicated in the mice with a single dose of Phx-3 on day 3 after injection of the cells. However, when Phx-3 was administered in a single dose, 6 or 9 days after the injection of the cells, the number of metastasized pulmonary cells remained the same. The present results indicate that the metastasis of mouse B16 melanoma cells to the lung was significantly inhibited in mice administered Phx-3, which activated the intrinsic and extrinsic apoptotic pathways. The present study suggests that Phx-3 might be a potential anti-metastatic agent as well as an anticancer agent.
Plant-derived compounds with potent anti-inflammatory activity have attracted a great deal of attention as a source for novel anti-arthritic agents with minimal side effects. We attempted to determine the anti-arthritic effects of orally administered honokiol isolated from Magnolia species. The oral administration of honokiol inhibited the progression and severity of type II collagen (CII)-induced arthritis (CIA) by reducing clinical arthritis scores and paw swelling. The histological analysis demonstrated preserved joint space; and the immunohistochemical data showed that the levels of interleukin (IL)-17, matrix metalloproteinase (MMP)-3, MMP-9, MMP-13, and receptor activator for nuclear factor-κB ligand, as well as nitrotyrosine formation, were substantially suppressed in the honokiol-treated CIA mice. The elevated serum levels of tumor necrosis factor-α and IL-1β in the CIA mice were also restored to control levels via honokiol treatment. In the CIA mice, honokiol inhibited CII- or lipopolysaccharide-stimulated cytokine secretion in spleen cells, as well as CII-stimulated spleen cell proliferation. Furthermore, honokiol treatment reduced CIA-induced oxidative damage in the liver and kidney tissues of CIA mice. Collectively, the oral administration of honokiol inhibited CIA development by reducing the production of pro-inflammatory cytokines, MMP expressions, and oxidative stress. Thus, honokiol is an attractive candidate for an anti-arthritic agent.
Nerve growth factor (NGF) and its high-affinity receptor, TrkA, are one of the targets in the production of new drugs for the treatment of neuropathic pain. NGF contributes to both the initiation and maintenance of sensory abnormalities after peripheral nerve injury. This study examined the effects of IPTRK3, a new synthetic cell-penetrating peptide that antagonizes TrkA function, on neuropathic pain in mice. Partial sciatic nerve ligation (PSNL) was used to generate neuropathic pain, and we injected IPTRK3 (2 or 10 mg/kg) intraperitoneally on day 7 after PSNL. Effects of the peptide on hyperalgesia, allodynia, and expression of Fos in the spinal cord were examined. Single administration of the peptide on day 7 significantly suppressed both thermal hyperalgesia and mechanical allodynia. Gentle touch stimuli–evoked Fos expression in the lumbar spinal cord was also significantly reduced. Intraperitoneal injection of a cell-penetrating peptide antagonizing TrkA function appears effective for treatment of neuropathic pain in a mouse pain model.
We examined the in vivo antiviral activities of 2-amino-4,4α-dihydro-4α-7-dimethyl-3H-phenoxazine-3-one (Phx-1), 3-amino-1,4α-dihydro-4α-8-dimethyl-2H-phenoxazine-2-one (Phx-2), and 2-aminophenoxazine-3-one (Phx-3) against herpes viruses. The virus yield three days after administration, changes in the 6-degree’s lesion scores, and the morbidity were assessed after herpes simplex virus type-1 (HSV-1) [acyclovir (ACV)-sensitive KOS strain or ACV-resistant A4-3 strain] or HSV-2 (ACV-sensitive UW 268 strain) was inoculated intravaginally to mice with administration of Phx-1, Phx-2, Phx-3, or ACV (0.2 mg per administration, 3 times daily) for 8 days starting from 1 day before virus inoculation to 7 days after infection. Phx-1, Phx-2, and Phx-3 extensively suppressed the virus yield of HSV-1. Only Phx-2 exerted moderate inhibitory effects against HSV-2 in mice. The lesion scores, as clinical signs manifested by infection of the KOS strain of HSV-1, were extensively suppressed by intravaginal application of Phx-1, Phx-2, or Phx-3. The lesion scores in HSV-2–infected mice indicated moderate suppression, when Phx-1, Phx-2, or Phx-3 was applied. Without treatment by one of the compounds, none of the HSV-1–infected mice died, but all the HSV-2–infected ones did. However, by the administration of Phx-1, Phx-2, or Phx-3 fairly improved the survival rates of the HSV-2–infected mice. Phx-2 showed dose-dependent anti-HSV-2 efficacy when administered at doses of 0.2 and 1 mg per administration. The present in vivo data suggest that the Phx-1, Phx-2, and Phx-3 are attractive candidates for agents to prevent both replication of HSV and aggravation of lesions caused by these viruses.
The purpose of this study is to identify the membrane transport machinery and cell signaling involved in the neurokinin A–inducible release of adenosine triphosphate (ATP) as an autocrine/paracrine signal from cultured guinea-pig taenia coli (T. coli) smooth muscle cells (SMCs). ATP release evoked by neurokinin A was inhibited by L-659877, a NK2-receptor antagonist; by modulators for Ins(1,4,5)P3-sensitive Ca2+-signaling, U-73122, thapsigargin, and 2-APB; and by W-7, a calmodulin inhibitor, and staurosporine, a protein kinase C (PKC) inhibitor, but not by wortmannin, a phosphoinositide 3-kinase inhibitor. The evoked release was suppressed by a multidrug resistance protein (MRP)-transporter inhibitors, MK-571, indomethacin, and benzbromarone, but not by CFTR-inh 172, a CFTR-Cl− channel blocker, and α-glycyrrhetinic acid, a gap junction hemichannel blocker. Neurokinin A caused a marked accumulation of Ins(1,4,5)P3 and an increase in [Ca2+]i in the cultured cells. These findings suggest that stimulation of Gq/11 protein–coupled NK2 receptor with neurokinin A caused a substantial release of ATP from cultured T. coli SMCs and that the evoked release may be mediated by Ins(1,4,5)P3-sensitive Ca2+-signaling, further by PKC and Ca2+/calmodulin signals, and finally by an activation of MRP transporters as the membrane device.
To explore the role of the serotonergic system in modulating absence seizures, we examined the effects of 5-HT1A and 5-HT2 agonists on the incidence of spike-and-wave discharges (SWD) in Groogy (GRY) rats, a novel rat model of absence-like epilepsy. GRY rats exhibited spontaneous absence-like seizures characterized by the incidence of sudden immobile posture and synchronously-associated SWD. The total duration of SWD in GRY rats was about 300 – 400 s/15-min observation period under the control conditions. However, the incidence of SWD was markedly reduced either by the 5-HT1A agonist (±)-8-hydroxy-2-(di-n-propylamino)-tetralin [(±)8-OH-DPAT] or the 5-HT2 agonist (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane [(±)DOI]. The 5-HT reuptake inhibitors, fluoxetine and clomipramine, also inhibited the SWD generation. In addition, the inhibitory effects of (±)8-OH-DPAT and (±)DOI were reversed by WAY-100135 (5-HT1A antagonist) and ritanserin (5-HT2 antagonist), respectively. The present results suggest that the serotonergic system negatively regulates the incidence of absence seizures by stimulation of 5-HT1A and 5-HT2 receptors.
Although the opioid system is known to modulate depression-like behaviors, its role in the effects of antidepressants is not yet clear. We investigated the role of μ-opioid receptors (MOPs) in the effects of venlafaxine, a serotonin and norepinephrine reuptake inhibitor, in the forced swim test using MOP–knockout (KO) mice. Venlafaxine reduced immobility time in wild-type mice (C57BL/6J), but not in MOP-KO mice, although no significant effects were observed on locomotor activity. These results suggest that MOPs play an important role in the antidepressant-like effects of venlafaxine.
We examined the effect of azimilide, a class III antiarrhythmic drug, on Na+/Ca2+ exchange current (INCX) in guinea-pig cardiac single ventricular cells. External application of azimilide suppressed bi-directional INCX in a concentration-dependent manner. IC50 values for outward and inward INCX were 45 and 40 μM, respectively, with Hill coefficients of 1. Azimilide attenuated INCX in the presence of trypsin in the patch pipette, indicating that azimilide is a trypsin-insensitive NCX inhibitor. Delayed afterdepolarization induced by electrical stimulation with ouabain disappeared in the presence of 30 μM azimilide. We conclude that azimilide inhibits NCX at supratherapeutic concentrations.
Hyperuricemia is currently recognized as a risk factor for cardiovascular diseases. It has been reported that the angiotensin II–receptor blocker (ARB) losartan decreases serum uric acid level. In this study, the effects of another ARB, irbesartan, on [14C]uric acid–transport activity of renal uric acid reabsorptive transporters URAT1 and URATv1 were examined with Xenopus oocytes expressing each transporter. The results showed that irbesartan (100 – 500 μM) inhibited the uptake of uric acid via both transporters. The inhibitory effects of irbesartan exceeded those of losartan and other ARBs, and the results suggest that irbesartan can reduce serum uric acid level.
To assess the pharmacological profile of AS1892802, a novel and selective Rho kinase (ROCK) inhibitor, we examined the effects of repeated dosing with AS1892802 on models of monoiodoacetate-induced arthritis and streptozotocin-induced neuropathy. Although single dosing of AS1892802 exerted a short-acting, moderate analgesic effect, repeated dosing exhibited a long-lasting and more potent analgesic effect in both models. Furthermore, the analgesic effect was sustained for seven days after the last administration. These results suggest that peripheral ROCK plays a crucial role in chronic pain maintenance and that AS1892802 may be useful in treating chronic pain.
We investigated the roles of β- and α2-adrenoceptors within the central nucleus of the amygdala (CeA) in the negative affective and sensory components of visceral pain in rats. We observed a dose-dependent reduction of intraperitoneal acetic acid-induced conditioned place aversion by bilateral injections of timolol, a β-adrenoceptor antagonist, or clonidine, an α2-adrenoceptor agonist, without reducing writhing behaviors. These data suggest a pivotal role of intra-CeA adrenoceptors in the negative affective, but not sensory, component of visceral pain.