Neonatal Borna disease virus infection (BDV)-induced damage to the cerebellum is associated with sensorimotor deficits in developing Lewis rats

Neonatal Borna disease virus (BDV) infection of the brain produces developmental damage to the cerebellum in Lewis rats, with minimal classical inflammatory responses. In the present study, we assessed the consequences of this damage by measuring motor coordination and postural skills in developing (postnatal days 4 to 30) Lewis rats that were neonatally infected with BDV. Neonatal BDV infection-induced motor impairments were selective and correlated with the time course of BDV damage to cerebellar development. BDV-induced motor deficits were not seen until the end of postnatal week 2. By postnatal week 3, BDV-infected rats had deficits in negative geotropism, fore- and hind limb placing and grasping. BDV-infected rats also exhibited deficits in the ability to hold on to a bar and to cross a suspended bar. Neonatal BDV infection induced impairments in the acoustic startle response. Compared to controls, neonatally BDV-infected rats exhibited attenuated habituation of the acoustic startle at postnatal day (PND) 23 and decreased startle responsiveness at PND 30. Prepulse inhibition of the acoustic startle remained unaltered in BDV-infected rats. The data demonstrate that neonatal BDV brain infection of rats can be a valuable animal model system for studying the relationship between abnormal brain development and resultant behavioral deficits. Further studies of this model may elucidate specific pathogenic mechanisms that that may have implications in the study of neurodevelopmental human disorders.     

Effects of genetic background on neonatal Borna disease virus infection-induced neurodevelopmental damage. I. Brain pathology and behavioral deficits

The pathogenic mechanisms of gene-environment interactions determining variability of human neurodevelopmental disorders remain unclear. In the two consecutive papers, we used the neonatal Borna disease virus (BDV) infection rat model of neurodevelopmental damage to evaluate brain pathology, monoamine alterations, behavioral deficits, and responses to pharmacological treatments in two inbred rat strains, Lewis and Fisher344. The first paper reports that despite comparable virus replication and distribution in the brain of both rat strains, neonatal BDV infection produced significantly greater thinning of the neocortex in BDV-infected Fisher344 rats compared to BDV-infected Lewis rats, while no strain-related differences were found in BDV-induced granule cell loss in the dentate gyrus of the hippocampus and cerebellar hypoplasia. Unlike BDV-infected Lewis rats, more severe BDV-induced brain pathology in Fisher344 rats was associated with (1) greater locomotor activity to novelty and (2) impairment of habituation and prepulse inhibition of the acoustic startle response. The present data demonstrate that the same environmental insult can produce differential neuroanatomical and behavioral abnormalities in genetically different inbred rat strains.     

Effects of neonatal rat Borna disease virus (BDV) infection on the postnatal development of the brain monoaminergic systems

Effects of neonatal Borna disease virus infection (BDV) on the postnatal development of brain monoaminergic systems in rats were studied. Tissue content of norepinephrine (NE), dopamine (DA) and its metabolite, 3,4-dihydroxyphenol acetic acid (DOPAC), and serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA) were assayed by means of HPLC-EC in frontal cortex, cerebellum, hippocampus, hypothalamus and striatum of neonatally BDV-infected and sham-inoculated male Lewis rats of 8, 14, 21, 60 and 90 days of age. Both NE and 5-HT concentrations were significantly affected by neonatal BDV infection. The cortical and cerebellar levels of NE and 5-HT were significantly greater in BDV-infected rats than control animals at postnatal days (PND) 60 and 90. Tissue content of NE in hippocampus was unaffected. In hippocampus, neonatally BDV-infected rats had lower 5-HT levels at PND 8 and significantly elevated levels at PND 21 and onwards. Neither striatal levels of 5-HT nor hypothalamic levels of 5-HT and NE were affected by neonatal BDV infection, suggesting that the monoamine systems in the prenatally maturing brain regions are less sensitive to effects of neonatal viral infection. 5-HIAA/5-HT ratio was not altered in BDV-infected rats indicating no changes in the 5-HT turnover in the brain regions damaged by the virus. Neither DA nor DOPAC/DA ratio was affected by neonatal BDV infection in any of the brain regions examined. The present data demonstrate significant and specific alterations in monoaminergic systems in neonatally BDV-infected rats. This pattern of changes is consistent with the previously reported behavioral abnormalities resulting from neonatal BDV infection.     

Developmental alterations in serotoninergic neurotransmission in Borna disease virus (BDV)-infected rats: A multidisciplinary analysis

Neonatal Borna disease virus (BDV) infection of the rat brain serves as a valuable model for studying the pathogenesis of neurodevelopmental abnormalities following early brain injury. Previous experiments have demonstrated significant alterations in regional tissue content of serotonin (5-HT) in neonatally BDV-infected Lewis rats. The present study sought to provide more insights into postnatal virus-associated alterations in 5-HT neurotransmission by evaluating the density of 5-HT1a receptors in the hippocampus and 5-HT2a receptors in the cortex, regional 5-HT tissue concentrations, behavioral responses to a 5-HT agonist, quipazine, and numbers of neurons in specific subfields of the hippocampus on days 7, 14, and 30 after neonatal BDV infection in Lewis rats. Neonatal BDV infection was found to be associated with a gradual increase in the density of 5-HT2a and 5-HT1a postsynaptic receptors followed by an elevation of 5-HT contents at both the levels of synaptic terminals (i.e., cortex and hippocampus) and cell bodies (i.e., raphe nuclei). In addition, there was an enhanced behavioral response to quipazine. Virus-associated neurochemical and behavioral changes were accompanied by a decline in the number of neurons in the dentate gyrus and in the CA1 field of the hippocampus. No change in the number of neurons in the CA3/2 field of the hippocampus was observed. The present pattern of BDV-associated alterations in 5-HT brain system along with available data from other laboratories suggest that BDV might compromise axonal transport and/or release of 5-HT, resulting in decreased 5-HT neurotransmission.     

Alterations in neurotrophin and neurotrophin receptor gene expression patterns in the rat central nervous system following perinatal Borna disease virus infection

Infection of newborn rats with Borna disease virus (BDV) leads to persistence in the absence of overt signs of inflammation. BDV persistence, however, causes cerebellar hypoplasia and hippocampal dentate gyrus neuronal cell loss, which are accompanied by diverse neurobehavioral abnormalities. Neurotrophins and their receptors play important roles in the differentiation and survival of hippocampal and cerebellar neurons. We have examined whether BDV can cause alterations in the neurotrophin network, thus promoting neuronal damage. We have used RNase protection assay to measure mRNA levels of the neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3), and their trkC and trkB receptors, as well as the growth factors insulin-like growth factor I (IGF-1) and basic fibroblast growth factor (bFGF), in the cerebellum and hippocampus of BDV-infected and control rats at different time points p.i. Reduced mRNA expression levels of NT-3, BDNF and NGF were found after day 14 p.i. in the hippocampus, but not in the cerebellum, of newborn infected rats. Three weeks after infection, trkC mRNA expression levels were reduced in both hippocampus and cerebellum of infected rats, whereas decreased trkB mRNA levels were only observed in the cerebellum. Reduced trkC mRNA expression was confined to the dentate gyrus of the hippocampus, as assessed by in situ hybridization. TUNEL assay revealed massive apoptotic cell death in the dentate gyrus of infected rats at days 27 and 33 p.i. Increased numbers of apoptotic cells were also detected in the cerebellar granular layer of infected rats after 8 days p.i. Moreover, a dramatic loss of cerebellar Purkinje cells was seen after day 27 p.i. Our results support the hypothesis, that BDV-induced alterations in neurotrophin systems might contribute to selective neuronal cell death.     

Effects of genetic background on neonatal Borna disease virus infection-induced neurodevelopmental damage. II. Neurochemical alterations and responses to pharmacological treatments

The gene-environment interplay is thought to determine variability in clinical conditions and responses to therapy in human neurodevelopmental disorders. Studying abnormal brain and behavior development in inbred strains of rodents can help in the identification of the complex pathogenic mechanisms of the host-environment interaction. This paper is the second one in a series of the two reports of the use of the Borna disease virus (BDV) infection model of neurodevelopmental damage to characterize effects of genetic background on virus-induced neurodevelopmental damage in inbred rat strains, Lewis and Fisher344. The present data demonstrate that neonatal BDV infection produced regional and strain-related alterations in levels of serotonin, norepinephrine and in levels of serotonin turnover at postnatal day 120. Neonatal BDV infection also induced upregulation of hippocampal 5-HT(1a) and cortical 5-HT(2a) receptors in Lewis rats and downregulation of cortical 5-HT(2a) receptors in Fisher344 rats. BDV-associated regional downregulation of D(2) receptors and dopamine transporter sites were noted in Fisher344 rats. In addition to the neurochemical disturbances, neonatal BDV infection induced differential responses to serotonin compounds. While 8-OH-DPAT suppressed virus-enhanced ambulation in BDV-infected Fisher344, fluoxetine inhibited virus-induced hyperactivity in BDV-infected Lewis rats only. The present data provide new insights into the pathogenic events that lead to differential responses to pharmacological treatments in genetically different animals following exposure to the same environmental challenge.     

Abnormal social behaviors in young and adult rats neonatally infected with Borna disease virus

Autism spectrum disorders (ASD) have been the focus of a great deal of research and clinical speculation. This intense interest relates to both the perplexing pathogenesis and devastating consequences of these disorders. One of the obstacles to understanding the pathogenesis of autism and to developing efficient treatment has been the paucity of animal models that could be used for hypotheses-driven mechanistic studies of abnormal brain and behavior development and for the pre-clinical testing novel pharmacological treatments. In this report, we briefly review our animal model of ASD based on neonatal Borna disease virus (BDV) infection and present new data about abnormal social interaction in adult BDV-infected rats. We found that neonatal BDV infection profoundly affected social behaviors in adult rats. Compared to the control rats, both 90- and 180-day-old infected rats spent less time in active social interaction and more time in following their partners. In the intruder-resident test, the BDV-infected resident rats exhibited less aggression towards the intruders and showed more the following-the-intruder behavior. The following-the-partner behavior may be an example of "stereotypic" activity due to BDV-induced abnormal social communication between rats. The previously published results and present findings indicate that neonatal BDV infection significantly altered the normal pattern of social interaction in rats. Co-localization of activated microglia and dying Purkinje cells in BDV-infected rats suggests that the BDV model could be used to study a pathogenic link of Purkinje cell dropout and neuroinflammation to abnormal social behaviors.     

Developmental brain injury associated with abnormal play behavior in neonatally Borna disease virus-infected Lewis rats: a model of autism

Play behavior, nonsocial exploratory activity, and nonplay social interaction were observed in male juvenile Lewis rats with brain developmental injury following neonatal infection with Borna disease virus (BDV). These behaviors were tested using the ‘intruder-resident' paradigm, with social isolation of residents for six days prior to testing. Four experimental pairings of infected (BDV) and uninfected (NL) rats were studied as follows: NL–NL; NL–BDV; BDV–NL; and BDV–BDV (the first member is the resident, the second member is the intruder). Observation of social activities was carried out for 10 min on two consecutive days. Nonsocial exploratory activity (e.g. ambulation and rearing) was similar in BDV and NL residents. Duration of nonplay social investigation (e.g. sniffing, approach, and follow) was higher in BDV residents as compared to NL residents when tested on the first test day. On the second day, all rats showed similar level of nonplay social interaction. When confronted with NL intruders, NL residents exhibited significantly more play behavior compared to the NL–BDV, BDV–NL and BDV–BDV pairs, when play behavior was measured by the number of ‘pins'. Moreover, irrespective of a type of intruder, NL residents demonstrated higher play soliciting behavior than BDV residents, indicating attenuated readiness to play in BDV-infected rats. The number of pins and play solicitations in BDV–NL pairs significantly increased over the two days of testing, while play activity in NL–BDV pairs declined on the second test day. This pattern suggests that the degree of social reinforcement on the first day of testing affected the level of play on the second day. These data demonstrate deficits in play behavior and other social interactions following BDV-associated developmental brain injury, thus supporting the value of the neonatally BDV-infected rat as an animal model of autism.     

Upregulation of COX-2 and CGRP expression in resident cells of the Borna disease virus-infected brain is dependent upon inflammation

Infection of immunocompetent adult rats with Borna disease virus (BDV) causes severe encephalitis and neural dysfunction. The expression of COX-2 and CGRP, genes previously shown to be implicated in CNS disease and peripheral inflammation, was dramatically upregulated in the cortical neurons of acutely BDV-infected rats. Neuronal COX-2 and CGRP upregulation was predominantly seen in brain areas where ED1-positive macrophages/microglia accumulated. In addition, COX-2 expression was strongly induced in brain endothelial cells and the number of COX-2 immunoreactive microglial cells was increased. In contrast, despite increased expression of viral antigens, neither COX-2 nor CGRP expression was altered in the CNS of BDV-infected rats treated with dexamethasone, or tolerant to BDV. Thus, increased CGRP and COX-2 expression in the BDV-infected brain is the result of the inflammatory response and likely to be involved in the pathogenesis of virus-induced encephalitis.     

Perinatal glucocorticoids alter dentate gyrus electrophysiology

Perinatal glucocorticoid administration produces permanent spatial discrimination learning deficits in rats, presumably referable to changes in the development of neural systems subserving such functions. Because the hippocampal dentate gyrus and its afferent/efferent circuitry appear selectively vulnerable to neonatal steroid treatments, we have examined adult rats treated with neonatally administered glucocorticoids using electrophysiological methods. The techniques were chosen to reveal the topographic and neurophysiologic responsiveness of the major afferent supply to the dentate gyrus. Rats of both sexes received either a high dose (100 mg/kg) or low dose (1 mg/kg) of the synthetic glucocorticoid dexamethasone on postnatal day four, with control subjects receiving an injection of saline. These dosages have been shown to disrupt hippocampal dependent learning [6,38]. Laminar depth profile analyses of entorhinal cortex-dentate gyrus afferents revealed a significant shift in the spatial distribution of evoked extracellular population synaptic potentials (EPSPs) in glucocorticoid treated subjects. Stimulus-response functions also differed between glucocorticoid treated and control subjects. While response amplitudes at threshold stimulus intensities did not differ between groups, at higher stimulus intensities population spike potentials and associated EPSPs differed in glucocorticoid versus control subjects.     

Dentate gyrus destruction and spatial learning impairment after corticosteroid removal in young and middle-aged rats

We investigated the functional and behavioral implications of chronic corticosteroid removal in young and middle-aged rats. Prepubertal and 13-month-old rats were adrenalectomized (ADX) or sham operated (SHAM). The young ADX rats were divided further into three groups: ADX with no hormone replacement, ADX given corticosterone chronically, (chCORT), and ADX given corticosterone acutely at the time of Morris water maze testing (acCORT). All rats were run on the Morris water maze 12 weeks after surgery. They were then sacrificed and the brains were removed for histological analysis. The results showed that prolonged corticosteroid absence caused major damage to the dentate gyrus and learning impairment on the Morris water maze. The chCORT rats had little dentate gyrus cell loss and were as efficient as the controls in Morris water maze performance, whereas the acCORT rats had dentate gyrus cell loss and were impaired in the spatial acquisition task. Furthermore, exogenously administered corticosterone had an interactive effect on ADX rats. Water maze performance was improved in dentate gyrus damaged rats (acCORT) compared to ADX rats not given corticosterone, whereas ADX rats with very little dentate gyrus damage (chCORT) did not exhibit better water maze performance relative to controls. Middle-aged ADX rats lost cells only in the dorsal blade of the dentate gyrus but they did not show a learning impairment in the Morris water maze relative to the middle-aged controls. These results indicate that corticosteroids are trophic for the dentate gyrus, that mature granule cells are less affected by adrenalectomy, that corticosteroid absence is responsible for some water maze impairment in ADX rats, but that in addition to corticosteroid absence, a substantial amount of dentate gyrus damage is necessary to impair spatial learning. © 1995 Wiley-Liss, Inc.     

Long-term effects of neonatal seizures: a behavioral, electrophysiological, and histological study

Previous studies have demonstrated that recurrent seizures during the neonatal period lead to permanent changes in seizure threshold and learning and memory. The pathophysiological mechanisms for these changes are not clear. To determine if neonatal seizures cause changes in hippocampal excitability or inhibition, we subjected rats to 50 flurothyl-induced seizures during the first 10 days of life (five seizures per day). When the rats were adults, we examined seizure threshold using flurothyl inhalation, and learning and memory in the water maze. In separate groups of animals, we evaluated in vivo paired-pulse facilitation and inhibition in either CA1 with stimulation of the Schaffer collaterals or dentate gyrus with stimulation of the perforant path. Following these studies, the animals were sacrificed and the brains evaluated for mossy fiber sprouting with the Timm stain. Compared to control animals, rats with 50 flurothyl seizures had a reduced seizure threshold, impaired learning and memory in the water maze, and sprouting of mossy fibers in the CA3 pyramidal cell layer and molecular layer of the dentate gyrus. No significant differences in impaired paired-pulse inhibition was noted between the flurothyl-treated and control rats. This study demonstrates that recurrent neonatal seizures result in changes of neuronal connectivity and alterations in seizure susceptibility, learning and memory. However, the degree of impairment following 50 seizures was modest, demonstrating that the immature brain is remarkably resilient to seizure-induced damage.     

宫内缺氧及当归注射液干预对幼年大鼠海马齿状回神经元与学习记忆能力的影响

BACKGROUND： The present study analyzed the effect of 3 days （2 h/d） intrauterine hypoxia on learning and memory in juvenile rats, as well as the therapeutic effects of Angelica sinensis on dentate gyrus neurons, as well as learning and memory. OBJECTIVE： To explore the effects of intrauterine hypoxia on hippocampal dentate gyrus neurons, as well as learning and memory, in juvenile rats; to explore N-methyI-D-aspartate receptor-1 （NMDAR1） expression in the dentate gyrus of neonatal rats following intrauterine hypoxia, as well as prolonged hypoxia; to investigate the regulatory mechanisms of Angelica sinensis. DESIGN, TIME AND SETTING： A randomized and controlled experiment based on developmental neurobiology was performed at the Department of Histology and Embryology in Luzhou Medical College from October 2007 to October 2008. MATERIALS： Angelica sinensis solution （250 g/L） was obtained from Central South Hospital of Wuhan University, China. Neuron-specific enolase and NMDAR1 mRNA in situ hybridization reagents were provided by Wuhan Boster Biological Technology, China. Image-Pro Plus 6.0 analysis system was purchased from Media Cybernetics, USA. METHODS： Healthy pregnant Sprague Dawley rats （n = 30） were randomly divided into control （n = 10）, hypoxia （n = 10）, and Angelica （n = 10） groups. The Angelica and hypoxia pregnant rats were placed in a three-gas incubator （oxygen concentration： 13%） starting with day 14 of pregnancy for 2 hours/day for 5 consecutive days to establish a fetal rat intrauterine hypoxia model. One hour prior to modeling, the pregnant rats from the Angelica and hypoxia groups received Angelica sinensis and normal saline （8 mL/kg） injections, respectively, through the caudal vein. The control group procedures were identical to the hypoxia group, but lacked the hypoxic conditions. MAIN OUTCOME MEASURES： Brain tissues of neonatal rats were used to detect expression of NMDAR1 mRNA, and brain tissues of juvenile rats aged 30 days were used to determine neuron-specific enolase mRNA expression by in situ hybridization. Microscopic images （400x） of the hippocampal dentate gyrus were collected. The integral optical density （IOD） value of positive NMDAR1 mRNA cells in the dentate gyrus of neonatal rats, as well as the quantity and the IOD value of positive neuron-specific enolase mRNA cells in the dentate gyrus of juvenile rats, were analyzed with Image-Pro IPP6.0 software. At 30 days after birth, learning and memory parameters were measured in the juvenile rats using Morris water maze. RESULTS： The quantity and the IOD value of positive neuron-specific enolase mRNA cells in the dentate gyrus of the hypoxia group juvenile rats were significantly less than the control group （P 〈 0.05）, and also less than the Angelica group （P 〈 0.05）. The IOD value of positive NMDAR1 mRNA cells in the dentate gyrus of the hypoxia group neonatal rats was significantly greater than the control group, and also greater than the Angelica group （P 〈 0.05）. In the Morris water maze, the searching time during the probe trial and reversal probe trial was shorter in the hypoxia group juvenile rats compared with the control group, and the Angelica group was prolonged compared with the hypoxia group （P 〈 0.05）. CONCLUSION： Intrauterine hypoxia increased expression of NMDAR1 mRNA in the dentate gyrus of neonatal rats, reduced the number of dentate gyrus neurons, and negatively affected learning and memory in juvenile rats. In contrast, Angelica sinensis injection improved the intrauterine hypoxic condition, increased the number of dentate gyrus neurons, and improved the learning and memory deficits of the juvenile rats.     

Chronic neonatal MK-801 treatment results in an impairment of spatial learning in the adult rat

Chronic neonatal treatment with the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 from postnatal day 8 through 19 has been shown to affect hippocampal NMDA receptor function of adult rats. Since many studies have shown that NMDA receptors play a crucial role in learning and memory, and since one of the hippocampal functions is spatial learning, we have examined whether this changed response of hippocampal neurons is associated with changes in its normal function. We therefore tested spatial learning and memory using a water maze in adult rats neonatally treated with MK-801. MK-801-treated rats were able to learn the spatial task as well as control rats but at a significantly slower rate. Performance in a visual cue task was not affected by the neonatal treatment, suggesting that the slower spatial learning is not caused by locomotor or sensory deficits. These results suggest that chronic NMDA receptor blockade during the neonatal period leads to long-lasting disturbances of hippocampal function.     

激光调控内源性神经干细胞的增殖分化及脑功能重建**☆

背景: 大量研究表明增强脑内源性神经细胞的增殖能力和自我修复将成为治愈缺血缺氧性脑损伤有价值的方法之一。 目的：观察氦氖激光对新生大鼠缺血缺氧性脑损伤内源性神经干细胞增殖分化及脑功能重建的影响。 方法：7 d龄健康Wistar新生大鼠,建立缺血缺氧性脑损伤模型后第2天开始,激光穴位照射组给予氦氖激光照射。穴位选取顶骨正中的“百会”穴,以及第7颈椎与第1胸椎间、背部正中的“大椎”穴。假手术组和模型组不给予激光照射。于第2疗程结束后,用Y-型迷宫检测各组大鼠的学习记忆能力。随后制备脑海马切片,分别进行巢蛋白和微管关联蛋白2免疫组织化学染色。 结果与结论：①激光穴位照射组大鼠的学习和记忆能力明显高于模型组(P < 0.05),但与假手术组相比,无明显差异(P > 0.05)。②大鼠内源性神经干细胞的表达：与假手术组比较,模型组、激光治疗组齿状回内巢蛋白免疫阳性细胞均明显增多(P < 0.05),且激光治疗组增多幅度大于模型组(P < 0.05)。③神经元特有结构蛋白的表达：激光治疗组大脑皮质微管关联蛋白2表达相当广泛,强阳性染成棕褐色的树突呈条索样、流星样放射状分布,海马各区锥体神经元和齿状回颗粒细胞层神经元排列比较整齐,树突连续阳性染色呈树枝状交叉分布于分子层。假手术组与激光治疗组染色所见无明显差别。模型组微管关联蛋白2表达明显减弱。结果提示激光治疗能够促进缺血缺氧性脑损伤新生大鼠脑内源性神经干细胞增殖,诱导其向神经元方向分化,并达到学习记忆功能的重建。     

Long-lasting plasticity of hippocampal adult-born neurons

Adult neurogenesis occurs in the dentate gyrus of the hippocampus, which is a key structure in learning and memory. It is believed that adult-born neurons exert their unique role in information processing due to their high plasticity during immature stage that renders them malleable in response to environmental demands. Here, we demonstrate that, in rats, there is no critical time window for experience-induced dendritic plasticity of adult-born neurons as spatial learning in the water maze sculpts the dendritic arbor of adult-born neurons even when they are several months of age. By ablating neurogenesis within a specific period of time, we found that learning was disrupted when the delay between ablation and learning was extended to several months. Together, these results show that mature adult-born neurons are still plastic when they are functionally integrated into dentate network. Our results suggest a new perspective with regard to the role of neo-neurons by highlighting that even mature ones can provide an additional source of plasticity to the brain to process memory information.     

Borna disease virus-induced accumulation of macrophage migration inhibitory factor in rat brain astrocytes is associated with inhibition of macrophage infiltration

To test the hypothesis that macrophage migration inhibitory factor (MIF) plays a role in macrophage invasion during virus-induced encephalitis, we analyzed the expression and cellular localization of MIF in the Borna disease virus (BDV)-infected rat brain, monitored monocyte/macrophage infiltration, and evaluated the influence of anti-inflammatory treatment with dexamethasone. MIF mRNA expression was restricted to neurons and remained unchanged after BDV infection or after dexamethasone treatment of either BDV-infected or uninfected control rats. In contrast, MIF protein immunoreactivity (ir) was not only seen in neurons but also in glia. After BDV-induced encephalitis and treatment of uninfected rats with dexamethasone, MIF ir was only slightly altered in neurons but moderately enhanced in tanycytes, ependyma, and choroid plexus epithelium and markedly increased or induced in astrocyte end-feet at the blood-brain barrier (BBB). The increase in MIF ir in astrocytes after BDV infection was blocked by dexamethasone. The induction or enhancement of MIF ir at the BBB significantly correlated with reduced numbers of infiltrating ED1-positive monocytes/macrophages after BDV infection. Increased macrophage invasion was observed in regions where no astrocytic MIF was detected. The BDV- or dexamethasone-induced accumulation of MIF protein in astrocytes in vivo in absence of detectable astrocytic MIF mRNA expression is most likely due to MIF translocation from neurons rather than to a constitutive or induced MIF mRNA expression in astrocytes. In conclusion, we provide evidence that translocation of MIF from neurons or other extracellular sources into astrocytes is likely to modulate the inflammatory process during the course of virus-induced encephalitis by limiting monocyte/macrophage migration through the BBB.     

Amygdala stimulation ameliorates memory impairments and promotes c-Fos activity in fimbria-fornix-lesioned rats

Recently we provided data showing that amygdala stimulation can ameliorate spatial memory impairments in rats with lesion in the fimbria-fornix (FF). The mechanisms for this improvement involve early gene expression and synthesis of BDNF, MAP-2, and GAP43 in the hippocampus and prefrontal cortex. Now we have studied which brain structures are activated by the amygdala using c-Fos as a marker of neural activation. First, we studied neuronal activation after tetanic stimulation to the amygdala in intact rats. We then carried out a second study in FF-lesioned rats in which the amygdala was stimulated 15 min after daily spatial memory training in the water maze. Our results showed that amygdala stimulation produces widespread brain activation, that includes cortical, thalamic, and brain stem structures. Activation was particularly intense in the dentate gyrus and the prefrontal cortex. Training in the water maze increased c-Fos positive nuclei in the dentate gyrus of the hippocampus and in medial prefrontal cortex. Amygdala stimulation to trained FF-lesioned rats induced an increase of neural activity in the dentate gyrus and medial prefrontal cortex relative to the FF-lesioned, but not stimulated group, like the c-Fos activity seen in trained control rats. Based on these and previous results we explain the mechanisms of amygdala reinforcement of neural plasticity and the partial recovery of spatial memory deficits.