Systemic Administration of Porphyromonas Gingivalis Lipopolysaccharide Induces Glial Activation and Depressive-Like Behavior in Rats.

BACKGROUND: Periodontitis is one of the most common chronic inflammatory disorders in adults. Although clinical studies have suggested a causal relationship between periodontitis and major depression (MD), the biological mechanisms by which periodontitis instigates MD are unknown. We investigated whether a systemic administration of lipopolysaccharide (LPS) from Porphyromonas gingivalis (Pg), a major Gram-negative pathogen of periodontitis, causes depressive-like behavior and glial activation in the hippocampus and the prefrontal cortex (PFC), which are MD-related brain regions. MATERIALS AND METHODS: Eight-week-old male Sprague Dawley rats were randomly divided into a behavioral test group and an immunohistochemistry group. The rats in each group were further assigned to the sham injection (saline) and Porphyromonas gingivalis-lipopolysaccharide (Pg-LPS) injection protocols. The rats received an intraperitoneal injection of saline or Pg-LPS with gradually increasing doses (day 1: 0.5, day 2: 0.5, day 3: 0.75, day 4: 0.75, day 5: 1.0, day 6: 1.0, and day 7: 1.0 mg/kg of body weight) for seven consecutive days. After the systemic administration, the behavior test group underwent the forced swimming test (FST) and Y-maze test. For the immunohistochemistry group, we quantified the immunoreactivity for microglial Iba-1 (ionized calcium-binding adapter molecule 1) and astrocytic glial fibrillary acidic protein (GFAP) in the hippocampus (dentate gyrus [DG], cornu ammonis [CA1 and CA3]) and PFC (prelimbic [PrL] and the infralimbic [IL]) areas. RESULTS: The FST immobility time in the Pg-LPS group was significantly longer than that in the sham group. In the Y-maze test, a significant decline in spontaneous alternation behavior was observed in the Pg-LPS group compared to the sham group. The peripheral administration of Pg-LPS significantly increased the immunoreactivity for Iba-1 in the CA3 and PrL. Pg-LPS injection significantly increased the immunoreactivity for GFAP in the DG, CA1, and CA3. CONCLUSIONS: The major result of this study is that a repeated systemic administration of Pg-LPS caused depressive-like behavior and both microglial and astrocytic activation in rats. This finding may comprise biological evidence of a causal relationship between periodontitis and MD.

Normalizing hyperactivity of the Gunn rat with bilirubin-induced neurological disorders via ketanserin.

BACKGROUND: Severe neonatal hyperbilirubinemia has been known to cause the clinical syndrome of kernicterus and a milder one the syndrome of bilirubin-induced neurologic dysfunction (BIND). BIND clinically manifests itself after the neonatal period as developmental delay, cognitive impairment, and related behavioral and psychiatric disorders. The complete picture of BIND is not clear. METHODS: The Gunn rat is a mutant strain of the Wistar rat with the BIND phenotype, and it demonstrates abnormal behavior. We investigated serotonergic dysfunction in Gunn rats by pharmacological analyses and ex vivo neurochemical analyses. RESULTS: Ketanserin, the 5-HT2AR antagonist, normalizes hyperlocomotion of Gunn rats. Both serotonin and its metabolites in the frontal cortex of Gunn rats were higher in concentrations than in control Wistar rats. The 5-HT2AR mRNA expression was downregulated without alteration of the protein abundance in the Gunn rat frontal cortex. The TPH2 protein level in the Gunn rat raphe region was significantly higher than that in the Wistar rat. CONCLUSIONS: It would be of value to be able to postulate that a therapeutic strategy for BIND disorders would be the restoration of brain regions affected by the serotonergic dysfunction to normal operation to prevent before or to normalize after onset of BIND manifestations. IMPACT: We demonstrated serotonergic dysregulation underlying hyperlocomotion in Gunn rats. This finding suggests that a therapeutic strategy for bilirubin-induced neurologic dysfunction (BIND) would be the restoration of brain regions affected by the serotonergic dysfunction to normal operation to prevent before or to normalize after the onset of the BIND manifestations. Ketanserin normalizes hyperlocomotion of Gunn rats. To our knowledge, this is the first study to demonstrate a hyperlocomotion link to serotonergic dysregulation in Gunn rats.

High Serum Cortisol Levels as a Potential Indicator for Changes in Well-Regulated Daily Life among Junior High School Students.

Problematic smartphone use among adolescents has become a social concern and is associated with poor sleep quality. The relationship between life habits, such as smartphone use and sleep duration, and levels of immunological and neuroendocrine biomarkers, including the stress hormone cortisol, in adolescents seems to be important to objectively comprehend their health and well-being in school life. However, such a relationship has not been well documented. We therefore studied rural junior high school students in Japan to elucidate the relationship between serum cortisol (SC) levels and their life habits. A total of 155 students in the seventh grade in 2016 were recruited as subjects. Of them, 140 students with eligible responses and blood samples (12-13 years; 80 boys, 60 girls) were finally included in the study (response rate 90.3%). A questionnaire survey concerning wake-up time, sleep duration, and the length of time using a smartphone per day was conducted. Blood samples were collected from peripheral veins of participants under fasting conditions between 8:30 and 11:00 a.m. The Spearman rank correlation coefficients were as follows: between SC and wake-up time, 0.199 (p = 0.018); between SC and sleep duration, 0.185 (p = 0.029); and between SC and time spent on smartphones, 0.172 (p = 0.042). The multiple regression analysis showed that high SC levels were significantly associated with late wake-up time and with short sleep duration. We therefore propose that measuring SC levels is useful for early detection of the change in the well-regulated daily life among junior high school students.

The Possible Causal Link of Periodontitis to Neuropsychiatric Disorders: More Than Psychosocial Mechanisms.

Increasing evidence implies a possible causal link between periodontitis and neuropsychiatric disorders, such as Alzheimer's disease (AD) and major depression (MD). A possible mechanism underlying such a link can be explained by neuroinflammation induced by chronic systemic inflammation. This review article focuses on an overview of the biological and epidemiological evidence for a feasible causal link of periodontitis to neuropsychiatric disorders, including AD, MD, Parkinson's disease, and schizophrenia, as well as the neurological event, ischemic stroke. If there is such a link, a broad spectrum of neuropsychiatric disorders associated with neuroinflammation could be preventable and modifiable by simple daily dealings for oral hygiene. However, the notion that periodontitis is a risk factor for neuropsychiatric disorders remains to be effectively substantiated.

Electroconvulsive shock attenuated microgliosis and astrogliosis in the hippocampus and ameliorated schizophrenia-like behavior of Gunn rat.

BACKGROUND: Although electroconvulsive therapy (ECT) is regarded as one of the efficient treatments for intractable psychiatric disorders, the mechanism of therapeutic action remains unclear. Recently, many studies indicate that ECT affects the immune-related cells, such as microglia, astrocytes, and lymphocytes. Moreover, microglial activation and astrocytic activation have been implicated in the postmortem brains of schizophrenia patients. We previously demonstrated that Gunn rats showed schizophrenia-like behavior and microglial activation in their brains. The present study examined the effects of electroconvulsive shock (ECS), an animal counterpart of ECT, on schizophrenia-like behavior, microgliosis, and astrogliosis in the brain of Gunn rats. METHODS: The rats were divided into four groups, i.e., Wistar sham, Wistar ECS, Gunn sham, and Gunn ECS. ECS groups received ECS once daily for six consecutive days. Subsequently, prepulse inhibition (PPI) test was performed, and immunohistochemistry analysis was carried out to determine the activation degree of microglia and astrocytes in the hippocampus by using anti-CD11b and anti-glial fibrillary acidic protein (GFAP) antibody, respectively. RESULTS: We found PPI deficit in Gunn rats compared to Wistar rats, and it was significantly improved by ECS. Immunohistochemistry analysis revealed that immunoreactivity of CD11b and GFAP was significantly increased in Gunn rats compared to Wistar rats. ECS significantly attenuated the immunoreactivity of both CD11b and GFAP in Gunn rats. CONCLUSIONS: ECS ameliorated schizophrenia-like behavior of Gunn rats and attenuated microgliosis and astrogliosis in the hippocampus of Gunn rats. Accordingly, therapeutic effects of ECT may be exerted, at least in part, by inhibition of glial activation. These results may provide crucial information to elucidate the role of activated glia in the pathogenesis of schizophrenia and to determine whether future therapeutic interventions should attempt to up-regulate or down-regulate glial functions.

Regional cerebral blood flow in late-onset schizophrenia: a SPECT study using 99mTc-ECD.

Progressive disability in schizophrenia has been considered to be associated with onset-age. The objective of this study was to evaluate age onset-related degeneration in rCBF in patients with schizophrenia. We evaluated characteristic changes in brain perfusion by age, gender, medication and clinical symptoms in medicated patients with early-onset (EOS: developed at younger than 40 years old: n = 44) and late-onset (LOS: developed at older than 40 years old: n = 19) schizophrenia and control subjects matched for age and gender (n = 37) using statistical parametric mapping (SPM8) applied to 99mTc-ECD SPECT. We performed SPECT with 99mTc-ECD on the brains of subjects. A voxel-by-voxel group analysis was performed using SPM 8 and ANOVA. rCBF in EOS was found to be reduced in the precentral and inferior frontal gyri; on the other hand, rCBF was reduced in the bilateral postcentral gyrus in LOS. This study revealed a significant difference in brain perfusion between EOS and LOS. The present study might suggest that the characteristic changes in rCBF are related to onset-age in schizophrenia.

Analysis of oxidative stress expressed by urinary level of biopyrrins and 8-hydroxydeoxyguanosine in patients with chronic schizophrenia.

AIMS: Previous studies have supported the claim that psychological stress induces the production of reactive oxygen species. Several authors have suggested that patients with psychiatric disorders show high levels of oxidative stress markers. We examined different oxidative stress markers in patients with chronic schizophrenia. METHODS: This study included 29 patients with chronic schizophrenia and 30 healthy volunteers. The concentration of urinary biopyrrins and 8-hydroxydeoxyguanosine (8-OHdG), as measured by enzyme-linked immunosorbent assay, were normalized to the urinary concentration of creatinine. Psychiatric symptoms were assessed by the administration of the Brief Psychiatric Rating Scale (BPRS). RESULTS: The concentration of biopyrrins in patients with chronic schizophrenia was significantly higher when compared with healthy volunteers. The correlation between biopyrrin level and the duration of illness was highly significant. There were no significant differences in the levels of urinary 8-OHdG between the two groups. In schizophrenic patients, the level of urinary biopyrrins showed correlations with BPRS scores, while the level of urinary 8-OHdG did not show correlations with BPRS. CONCLUSIONS: Urinary biopyrrins are increased in patients with chronic schizophrenia while urinary 8-OHdG is not increased. These findings suggest that patients with chronic schizophrenia are under the condition of certain oxidative stresses.

Purinergic responses of calcium-dependent signaling pathways in cultured adult human astrocytes.

BACKGROUND: The properties of Ca2+ signaling mediated by purinergic receptors are intrinsically linked with functional activity of astrocytes. At present little is known concerning Ca2+-dependent purinergic responses in adult human astrocytes. This work has examined effects of purinergic stimulation to alter levels of intracellular Ca2+ in adult human astrocytes. Ca2+-sensitive spectrofluorometry was carried out to determine mobilization of intracellular Ca2+ following adenosine triphosphate (ATP) or 3'-O-(4-benzoyl)benzoyl-ATP (Bz-ATP) stimulation of adult human astrocytes. In some experiments pharmacological modulation of Ca2+ pathways was applied to help elucidate mechanisms of Ca2+ signaling. RT-PCR was also performed to confirm human astrocyte expression of specific purinoceptors which were indicated from imaging studies. RESULTS: The endogenous P2 receptor agonist ATP (at 100 µM or 1 mM) applied in physiological saline solution (PSS) evoked a rapid increase of [Ca2+]i to a peak amplitude with the decay phase of response exhibiting two components. The two phases of decay consisted of an initial rapid component which was followed by a secondary slower component. In the presence of Ca2+-free solution, the secondary phase of decay was absent indicating this prolonged component was due to influx of Ca2+. This prolonged phase of decay was also attenuated with the store-operated channel (SOC) inhibitor gadolinium (at 2 µM) added to standard PSS, suggesting this component was mediated by SOC activation. These results are consistent with ATP activation of P2Y receptor (P2YR) in adult human astrocytes leading to respective rapid [Ca2+]i mobilization from intracellular stores followed by Ca2+ entry through SOC. An agonist for P2X7 receptor (P2X7R), BzATP induced a very different response compared with ATP whereby BzATP (at 300 µM) elicited a slowly rising increase in [Ca2+]i to a plateau level which was sustained in duration. The BzATP-induced increase in [Ca2+]i was not enhanced with lipopolysaccharide pre-treatment of cells as previously found for P2X7R mediated response in human microglia. RT-PCR analysis showed that adult human astrocytes in vitro constitutively express mRNA for P2Y1R, P2Y2R and P2X7R. CONCLUSION: These results suggest that activation of metabotropic P2YR (P2Y1R and/or P2Y2R) and ionotropic P2X7R could mediate purinergic responses in adult human astrocytes.

The effects of combine treatment of memantine and donepezil on Alzheimer's disease patients and its relationship with cerebral blood flow in the prefrontal area.

BACKGROUND: In this study, we evaluated the effect on cognitive function of memantine, behavioral and psychological symptoms of dementia, and the care burden, in patients with moderate-to-severe Alzheimer's disease (AD). Furthermore, with near-infrared spectroscopy (NIRS), we examined the association between effect of memantine and brain blood flow. METHODS: We evaluated the effect of memantine administration from baseline on Clinical Global Impression-Improvement scale, mini mental state examination (MMSE), Clock Drawing Test (CDT), Neuropsychiatric Inventory (NPI), Japanese version of the Zarit Burden Interview (J-ZBI) and NIRS in two groups, donepezil administration memantine combination group (combination group, n = 19) donepezil administration memantine non-administration group (control group, n = 18) were assessed at weeks 0, 4, 12, and 24. RESULTS: Significant difference was found between the combination group and the control group in the score variation of Clinical Global Impression-Improvement scale, MMSE, CDT, NPI, and J-ZBI. In the NIRS measurements, trend oxyhemoglobin reduced suppression was observed in some channels centered on the superior frontal gyrus. A significant correlation was observed in the scores of MMSE, CDT, NPI, and J-ZBI. In addition, a significant positive correlation was also observed between the number of words in NIRS and scores of MMSE and CDT. CONCLUSIONS: In this study, by administering memantine in AD patients that inhibit the reduction of cerebral blood flow in the prefrontal area and improve clinical symptoms overall cognitive function, behavioral and psychological symptoms of dementia, thereby reducing the care burden of caregivers was suggested.

Glia as a New Target for Therapeutic Actions of Electroconvulsive Therapy.

Although electroconvulsive therapy (ECT) has immediate and profound effects on severe psychiatric disorders compared to pharmacotherapy, the mechanisms underlying its therapeutic effects remain elusive. Increasing evidence indicates that glial activation is a common pathogenetic factor in both major depression and schizophrenia, raising the question of whether ECT can inhibit glial activation. This article summarizes the findings from both clinical and experimental studies addressing this key question. Based on the findings, it is proposed that the suppression of glial activation associated with neuroinflammation is the mechanism by which ECT restores brain homeostasis and exerts its therapeutic effects.

Yokukansan promotes hippocampal neurogenesis associated with the suppression of activated microglia in Gunn rat.

BACKGROUND: The pathophysiology of schizophrenia (SCZ) remains unclear, and its treatment is far from ideal. We have previously reported that yokukansan (YKS), which is a traditional Japanese medicine, is effective as an adjunctive therapy for SCZ. However, the mechanisms underlying the action of YKS have not yet been completely elucidated. A recent meta-analysis study has shown that adjuvant anti-inflammatory drugs are effective for SCZ treatment, and it has been proposed that some of the cognitive deficits associated with inflammation may in part be related to inflammation-induced reductions in adult hippocampal neurogenesis. Although certain ingredients of YKS have potent anti-inflammatory activity, no study has determined if YKS has anti-inflammatory properties. METHODS: Using the Gunn rat, which has been reported as a possible animal model of SCZ, we investigated whether YKS affects cognitive dysfunction in an object-location test and the suppression of microglial activation and neurogenesis in the hippocampus. RESULTS: We found that YKS ameliorated spatial working memory in the Gunn rats. Furthermore, YKS inhibited microglial activation and promoted neurogenesis in the hippocampal dentate gyrus of these rats. These results suggest that the ameliorative effects of YKS on cognitive deficits may be mediated in part by the suppression of the inflammatory activation of microglia. CONCLUSIONS: These findings shed light on the possible mechanism underlying the efficacy of YKS in treating SCZ.

Video polysomnographic analysis of elevated EMG activity and rapid eye movements before abnormal behaviors in REM sleep behavior disorder.

The pathogenesis of rapid eye movement (REM) sleep behavior disorder (RBD) is unclear. According to the cortical hypothesis, severe RBD episode (RBDE) occurs when spinal motoneurons are less inhibited and cortical and limbic systems are more active. We made this study to prove the hypothesis for the development of RBDE using video-polysomnography (VPSG). VPSG records of 35 patients with RBD were analyzed. According to severity, RBDEs were classified into three motor events (MEs): ME 1; small movements or jerks, ME 2; proximal movements including violent behavior, and ME 3; axial movements including bed falls. For each ME, we measured the number of MEs preceded or not preceded by both REM sleep without atonia (RWA) and REMs during the 10-s-period immediately before ME onset. In severe RBDE (ME 3), the number of MEs preceded by both RWA and REMs was significantly higher than that of MEs not preceded by both (0.8 vs. 0.2, P = 0.033). This was not the case for mild RBDE (ME 1) and moderate RBDE (ME 2). Our results suggest that both RWA and REMs are associated with the development of severe RBDE.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid attenuates human astrocyte neurotoxicity induced by interferon-γ.

BACKGROUNDS: Increasing evidence shows that the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) possesses potent anti-inflammatory and immunomodulatory properties. It is tempting to evaluate the potential of SAHA as a therapeutic agent in various neuroinflammatory and neurodegenerative disorders. METHODS: We examined the effects of SAHA on interferon (IFN)-γ-induced neurotoxicity of human astrocytes and on IFN-γ-induced phosphorylation of signal transducer and activator of transcription (STAT) 3 in human astrocytes. We also studied the effects of SAHA on the astrocytic production of two representative IFN-γ-inducible inflammatory molecules, namely IFN-γ-inducible T cell α chemoattractant (I-TAC) and intercellular adhesion molecule-1 (ICAM-1). RESULTS: SAHA significantly attenuated the toxicity of astrocytes activated by IFN-γ towards SH-SY5Y human neuronal cells. In the IFN-γ-activated astrocytes, SAHA reduced the STAT3 phosphorylation. SAHA also inhibited the IFN-γ-induced astrocytic production of I-TAC, but not ICAM-1. These results indicate that SAHA suppresses IFN-γ-induced neurotoxicity of human astrocytes through inhibition of the STAT3 signaling pathway. CONCLUSION: Due to its anti-neurotoxic and anti-inflammatory properties, SAHA appears to have the therapeutic or preventive potential for a wide range of neuroinflammatory disorders associated with activated astrocytes.

Urinary biopyrrins and free immunoglobin light chains are biomarker candidates for screening at-risk mental state in adolescents.

BACKGROUND: Early diagnosis of individuals' at-risk mental state (ARMS) is important for preventing their pathogenesis or, at least, delaying onset of overt psychosis. Traditional diagnosis of ARMS subjects is mainly based on structured interviews, but future diagnosis would be carried out together with biomarkers. AIM: In this study, we report urinary biopyrrins and free immunoglobin light chains κ and λ (κFLC and λFLC) as novel diagnostic biomarker candidates for screening ARMS subjects. METHODS: Nineteen ARMS subjects and 21 age- and sex-matched healthy controls were enrolled in this study. Inclusion criteria of the ARMS subjects were based on a comprehensive assessment of Structured Interview for Prodromal Syndromes. We compared oxidative stress and immunological markers in the urine of ARMS subjects with those of healthy controls by ELISA protocol. RESULTS: Augmentation of biopyrrins and reduction of κFLC and λFLC were found in the ARMS samples, and their diagnostic performance was evaluated by receiver operating characteristic analysis, of which area under the curve was as large as 0.915 in combination. CONCLUSION: Our findings suggest that the ARMS subjects were under higher oxidative stress but lower in B cell activation, and that the combined assay of urinary biopyrrins and free immunoglobulin light chains would be useful for the early detection and screening of ARMS subjects among adolescents.

Improvement in both severe obsessive-compulsive disorder and refractory tardive dystonia following electroconvulsive therapy: A case report.

Background: Obsessive-compulsive disorder (OCD) is often resistant to treatment and may be complicated by tardive dystonia (TDt) with the use of neuroleptics. Furthermore, patients with TDt often have an inadequate response to pharmacotherapy. Although electroconvulsive therapy (ECT) is considered a common treatment option for both TDt and OCD, its efficacy has not been well established for either condition. Case Presentation: Our case was a 37-year-old Japanese woman who showed improvement in both refractory TDt and severe OCD following ECT. A total of 12 ECT sessions resulted in an improvement in both diseases. To the best of our knowledge, this is the first report of a case in which ECT was effective for both TDt and OCD. Conclusion: Our report highlights the following two points: when TDt is associated with severe OCD, and the effect of pharmacotherapy is inadequate, ECT may be considered as a treatment option; given the common mechanism of frontal cortex-basal dysfunction reported in both dystonia and OCD, ECT may have an effect on this pathway.

Proton pump inhibitors reduce interferon-γ-induced neurotoxicity and STAT3 phosphorylation of human astrocytes.

Proton pump inhibitors (PPIs) are known to possess anti-inflammatory properties. Inflammatory processes, including astrocytic activation, are implicated in the pathogenesis of different neurodegenerative diseases. Our recent study has indicated that interferon (IFN)-γ-induced astrocytic neurotoxicity is mediated, at least in part, by phosphorylation of signal transducer and activator of transcription (STAT) 3. We therefore studied the effects of PPIs on IFN-γ-induced neurotoxicity and STAT3 activation of human astrocytes. Both lansoprazole (LPZ) and omeprazole (OPZ) significantly attenuated IFN-γ-induced neurotoxicity of human astrocytes and astrocytoma cells. These drugs inhibited IFN-γ-induced phosphorylation of STAT 3, but not STAT1. We found that LPZ significantly reduced secretion of IFN-γ-inducible T cell α chemoattractant from IFN-γ-activated astrocytes. Neither LPZ nor OPZ suppressed expression of intercellular adhesion molecule-1 by IFN-γ-activated astrocytes. These results suggest that PPIs attenuate IFN-γ-induced neurotoxicity of human astrocytes through inhibition of the STAT3 signaling pathway. PPIs that possess antineurotoxic properties may be a useful treatment option for Alzheimer's disease and other neuroinflammatory disorders associated with activated astrocytes.

STAT3 inhibitors attenuate interferon-γ-induced neurotoxicity and inflammatory molecule production by human astrocytes.

Activation of signal transducer and activator of transcription (STAT) 3 is observable in reactive astrocytes under certain neuropathological conditions. Interferon (IFN)-γ is shown to activate STAT3 in cultured rodent astrocytes. Here we investigated the effects of inhibiting STAT3 signaling on IFNγ-activated human astrocytes since we have recently demonstrated that human astrocytes become neurotoxic when stimulated by IFNγ. We found that 5'-deoxy-5'-(methylthio)adenosine (MTA) (300 µM), S3I-201 (10 µM), STAT3 inhibitor VII (3 µM) and JAK-inhibitor I (0.3 µM) had anti-neurotoxic effects on IFN-γ (50 U/ml)-activated astrocytes and U373-MG astrocytoma cells. Another inhibitor, AG490 (30 µM) had no significant effect. The active inhibitors also attenuated IFN-γ-induced phosphorylation of Tyr(705)-STAT3 and astrocytic expression of intercellular adhesion molecule-1 (ICAM-1). They also decreased astrocytic production of IFN-γ-inducible T cell α chemoattractant (I-TAC). AG490, which did not affect the Tyr(705)-STAT3 phosphorylation or ICAM-1 expression, nevertheless reduced the I-TAC secretion. Because these results indicate that pharmacological inhibition of STAT3 signaling correlates with reduced astrocytic neurotoxicity and ICAM-1 expression, but not that of I-TAC secretion, we consider that STAT3 activation mediates, at least in part, the IFN-γ-induced neurotoxicity and ICAM-1 expression by human astrocytes.

Brain-derived neurotrophic factor induces sustained elevation of intracellular Ca2+ in rodent microglia.

Microglia are intrinsic immune cells that release factors, including proinflammatory cytokines, NO, and neurotrophins, following activation after disturbance in the brain. Elevation of intracellular Ca(2+) concentration ([Ca(2+)]i) is important for microglial functions, such as the release of cytokines and NO from activated microglia. There is increasing evidence suggesting that pathophysiology of neuropsychiatric disorders is related to the inflammatory responses mediated by microglia. Brain-derived neurotrophic factor (BDNF) is a neurotrophin well known for its roles in the activation of microglia as well as in pathophysiology and/or treatment of neuropsychiatric disorders. In this study, we observed that BDNF induced a sustained increase in [Ca(2+)]i through binding with the truncated tropomyosin-related kinase B receptor, resulting in activation of the PLC pathway and store-operated calcium entry in rodent microglial cells. RT-PCR and immunocytochemical techniques revealed that truncated tropomyosin-related kinase B-T1 receptors were highly expressed in rodent microglial cells. Sustained activation of store-operated calcium entry occurred after brief BDNF application and contributed to the maintenance of sustained [Ca(2+)]i elevation. Pretreatment with BDNF significantly suppressed the release of NO from activated microglia. Additionally, pretreatment of BDNF suppressed the IFN-gamma-induced increase in [Ca(2+)]i, along with a rise in basal levels of [Ca(2+)]i in rodent microglial cells. We show direct evidence that rodent microglial cells are able to respond to BDNF, which may be important for the regulation of inflammatory responses, and may also be involved in the pathophysiology and/or the treatment of neuropsychiatric disorders.