Influence of the in vivo deregulation of the expression of ntrk3 (trkc) on cortical development of a murine model of panic/anxiety disorder

Alteracions durant el desenvolupament cerebral produirien canvis en la connectivitat neuronal i la bioquímica cel•lular que podrien resultar en una disfunció cognitiva i/o emocional, desembocant a trastorns psiquiàtrics. Les neurotrofines intervenen en els processos del neurodesenvolupament i en la funcionalitat del cervell adult i, conseqüentment, serien bons candidats com a factors de predisposició en diverses malalties mentals. S’ha suggerit la implicació del receptor de la neurotrofina 3, TrkC, en el trastorn de pànic. Nosaltres proposem que la sobreexpressió del gen NTRK3 (TrkC) és un mediador comú dels desencadenants genètics i ambientals d’aquest trastorn. Concretament, la seva desregulació podria produir canvis estructurals i funcionals a l’escorça cerebral dels pacients pel seu paper durant l’establiment dels circuïts corticals i la neuroplasticitat a l’adult, probablement esdevenint elements de predisposició a patir atacs de pànic. Els objectius principals d’aquest treball han estat: 1/determinar la contribució específica del gen NTRK3 a les alteracions de l’escorça cerebral observades en pacients, utilitzant un model murí modificat genèticament (TgNTRK3), i 2/analitzar l’impacte específic de la sobreexpressió de NTRK3 sobre la corticogènesi durant estadis embrionaris o postnatals estudiant la neurogènesi i la neuritogènesi. Els resultats indiquen que la sobreexpressió de NTRK3 als ratolins produeix una reducció del gruix de l’escorça frontal, recapitulant la hipofrontalitat dels pacients, que comportaria una menor inhibició dels nuclis subcorticals del sistema límbic com l’amígdala, i alteracions citoarquitectòniques a l’escorça prefrontal medial que recolzen la hipòtesi del seu mal funcionament. Tanmateix, els ratolins TgNTRK3 presenten canvis estructurals a l’escorça somatosensorial, suggerint que el processament de la informació sensorial podria estar alterat, el que encara no s’ha explorat en pacients. La sobreexpressió de NTRK3 també afecta la neuritogènesi en cultius primaris corticals i modifica la resposta de les neurones a l’estimulació amb neurotrofines. Per tant, el fenotip cortical adult dels TgNTRK3 podria dependre d’alteracions durant la corticogènesi.

Effect of mannitol and hypertonic saline on cerebral oxygenation in patients with severe traumatic brain injury and refractory intracranial hypertension.

BACKGROUND: The impact of osmotic therapies on brain oxygen has not been extensively studied in humans. We examined the effects on brain tissue oxygen tension (PbtO(2)) of mannitol and hypertonic saline (HTS) in patients with severe traumatic brain injury (TBI) and refractory intracranial hypertension. METHODS: 12 consecutive patients with severe TBI who underwent intracranial pressure (ICP) and PbtO(2) monitoring were studied. Patients were treated with mannitol (25%, 0.75 g/kg) for episodes of elevated ICP (>20 mm Hg) or HTS (7.5%, 250 ml) if ICP was not controlled with mannitol. PbtO(2), ICP, mean arterial pressure, cerebral perfusion pressure (CPP), central venous pressure and cardiac output were monitored continuously. RESULTS: 42 episodes of intracranial hypertension, treated with mannitol (n = 28 boluses) or HTS (n = 14 boluses), were analysed. HTS treatment was associated with an increase in PbtO(2) (from baseline 28.3 (13.8) mm Hg to 34.9 (18.2) mm Hg at 30 min, 37.0 (17.6) mm Hg at 60 min and 41.4 (17.7) mm Hg at 120 min; all p<0.01) while mannitol did not affect PbtO(2) (baseline 30.4 (11.4) vs 28.7 (13.5) vs 28.4 (10.6) vs 27.5 (9.9) mm Hg; all p>0.1). Compared with mannitol, HTS was associated with lower ICP and higher CPP and cardiac output. CONCLUSIONS: In patients with severe TBI and elevated ICP refractory to previous mannitol treatment, 7.5% hypertonic saline administered as second tier therapy is associated with a significant increase in brain oxygenation, and improved cerebral and systemic haemodynamics.

Identification of early metabolic markers of various degrees of ischemia in the mouse brain by localized H-1 magnetic resonance spectroscopy

Objectives: Magnetic resonance (MR) imaging and spectroscopy (MRS) allow the establishment of the anatomical evolution and neurochemical profiles of ischemic lesions. The aim of the present study was to identify markers of reversible and irreversible damage by comparing the effects of 10-mins middle cerebral artery occlusion (MCAO), mimicking a transient ischemic attack, with the effects of 30-mins MCAO, inducing a striatal lesion. Methods: ICR-CD1 mice were subjected to 10-mins (n = 11) or 30-mins (n = 9) endoluminal MCAO by filament technique at 0 h. The regional cerebral blood flow (CBF) was monitored in all animals by laser- Doppler flowmetry with a flexible probe fixed on the skull with < 20% of baseline CBF during ischemia and > 70% during reperfusion. All MR studies were carried out in a horizontal 14.1T magnet. Fast spin echo images with T2-weighted parameters were acquired to localize the volume of interest and evaluate the lesion size. Immediately after adjustment of field inhomogeneities, localized 1H MRS was applied to obtain the neurochemical profile from the striatum (6 to 8 microliters). Six animals (sham group) underwent nearly identical procedures without MCAO. Results: The 10-mins MCAO induced no MR- or histologically detectable lesion in most of the mice and a small lesion in some of them. We thus had two groups with the same duration of ischemia but a different outcome, which could be compared to sham-operated mice and more severe ischemic mice (30-mins MCAO). Lactate increase, a hallmark of ischemic insult, was only detected significantly after 30-mins MCAO, whereas at 3 h post ischemia, glutamine was increased in all ischemic mice independently of duration and outcome. In contrast, glutamate, and even more so, N-acetyl-aspartate, decreased only in those mice exhibiting visible lesions on T2-weighted images at 24 h. Conclusions: These results suggest that an increased glutamine/glutamate ratio is a sensitive marker indicating the presence of an excitotoxic insult. Glutamate and NAA, on the other hand, appear to predict permanent neuronal damage. In conclusion, as early as 3 h post ischemia, it is possible to identify early metabolic markers manifesting the presence of a mild ischemic insult as well as the lesion outcome at 24 h.

The naturally occurring food mycotoxin fumonisin B1 impairs myelin formation in aggregating brain cell culture.

The effects of subchronical applications of the mycotoxin Fumonisin B1 (FB1) were analyzed in vitro, using aggregating cell cultures of fetal rat telencephalon as a model. As cells in the aggregates developed from an immature state to a highly differentiated state, with synapse and compact myelin formation, it was possible to study the effects of FB1 at different developmental stages. The results showed that FB1 did not cause cell loss and it had no effects on neurons. However it decreased strongly the total content of myelin basic protein, the main constituent of the myelin sheath, during the myelination period (DIV 18-28). The loss of myelin was not accompanied by a loss of oligodendrocytes, the myelinating cells. However FB1 had effects on the maturation of oligodendrocytes, as revealed by a decrease in the expression of galactocerebroside, and on the compaction of myelin, as shown by a reduction of the expression of the mnyelin/oligodendrocyte glycoprotein MOG. The content of the cytoskeletal component glial fibrillary acidic protein (GFAP) was decreased in differentiated astrocytes, exclusively, while neurons were not affected by 40 microM of FB1 applied continuously for 10 days. In summary, FB1 selectively affected glial cells. In particular, FB1 delayed oligodendrocyte development and impaired myelin formation and deposition.

Evaluation of the early changes occurring in the draining lymph node upon subcutaneous stimulation

Adjuvants have been shown since many years to have an important role in enhancing the immune responses against the co-administered antigens used as vaccines. The continuous study of the mechanism of action of adjuvants is necessary to develop further safe and efficacious vaccines. Complete Freund's adjuvant (CFA) is currently in use as adjuvant to induce some autoimmune diseases in murine models, therefore the study of the mechanisms involved in the generation of the related immune responses could be instrumental for the understanding of the induction of inflammatory Thl7 responses. In the present work, we showed in C57B1/6 mice that CFA peripheral administration induces very early, at 6 h, a potent influx of CDllb+ cells, mainly neutrophils (CD11b+Ly6GhighLy6Cint) and monocytes (CD11b+Ly6GlowLy6Chigh), in the draining lymph node. By investigating the route by which neutrophils reach the lymph node we observed that, around 20% of them arrive from the afferent lymph and the majority stains positive for Mycobacterium tuberculosis. We also observed a correlation between the influx of neutrophils and an increase in IL-23 and IL-Ιβ, together with several inflammatory chemokines, in the draining lymph node. Concomitantly, we detected the expression of the IL-23 receptor on CDllc+ DCs. Moreover, we confirmed the ability of murine neutrophils to express IL-23 both, in vitro by stimulating bone-marrow extracted PMNs with Mycobacterium tuberculosis, and on total cells from draining lymph node by immunohistochemistry. We also observed by in vivo priming a reduction in the percentage of IFN-γ and CXCR3 expressing Τ cells upon depletion of neutrophils. Altogether, we show that upon stimulation from the periphery, the draining lymph node undergo changes in cytokine/chemokine production leading to the recruitment of different leukocytes subpopulations. Here we show that CFA induces a rapid influx of neutrophils which are responsible for the production of IL-23 that in turn influences the generation of Τ helper cells.

cAMP prevents the glucose-mediated stimulation of GLUT2 gene transcription in hepatocytes.

Glucose homoeostasis necessitates the presence in the liver of the high Km glucose transporter GLUT2. In hepatocytes, we and others have demonstrated that glucose stimulates GLUT2 gene expression in vivo and in vitro. This effect is transcriptionally regulated and requires glucose metabolism within the hepatocytes. In this report, we further characterized the cis-elements of the murine GLUT2 promoter, which confers glucose responsiveness on a reporter gene coding the chloramphenicol acetyl transferase (CAT) gene. 5'-Deletions of the murine GLUT2 promoter linked to the CAT reporter gene were transfected into a GLUT2 expressing hepatoma cell line (mhAT3F) and into primary cultured rat hepatocytes, and subsequently incubated at low and high glucose concentrations. Glucose stimulates gene transcription in a manner similar to that observed for the endogenous GLUT2 mRNA in both cell types; the -1308 to -212 bp region of the promoter contains the glucose-responsive elements. Furthermore, the -1308 to -338 bp region of the promoter contains repressor elements when tested in an heterologous thymidine kinase promoter. The glucose-induced GLUT2 mRNA accumulation was decreased by dibutyryl-cAMP both in mhAT3F cells and in primary hepatocytes. A putative cAMP-responsive element (CRE) is localized at the -1074/-1068 bp region of the promoter. The inhibitory effect of cAMP on GLUT2 gene expression was observed in hepatocytes transfected with constructs containing this CRE (-1308/+49 bp fragment), as well as with constructs not containing the consensus CRE (-312/+49 bp fragment). This suggests that the inhibitory effect of cAMP is not mediated by the putative binding site located in the repressor fragment of the GLUT2 promoter. Taken together, these data demonstrate that the elements conferring glucose and cAMP responsiveness on the GLUT2 gene are located within the -312/+49 region of the promoter.

Expression and developmental regulation of Ehk-1, a neuronal Elk-like receptor tyrosine kinase in brain.

Protein tyrosine kinases are pivotal in central nervous tissue development and maintenance. Here we focus on the expression of Ehk-1, a novel Elk-related receptor tyrosine kinase. Ehk-1 gene expression is observed in the developing and adult central nervous system and is highly regulated throughout development at both the messenger RNA and protein levels. Three messenger RNA transcripts of 8.5, 5.9 and 5.1 kb are detectable in the rat brain and a variety of splice possibilities have been identified. However, a major protein species of around M(r) 120,000 predominates throughout development. Ehk-1 messenger RNA and protein levels are highest in the first postnatal week. By in situ messenger RNA hybridization the gene is expressed by all neurons of the adult brain, but mostly in the hippocampus, cerebral cortex and large neurons of the deep cerebellar nuclei, as well as the Purkinje and granular cells of the cerebellum. At earlier stages of development, transcripts are most prominent in the periventricular germinal layers of the brain. Immunohistochemistry reveals a pronounced membrane associated protein expression in immature neurons. In the adult animal, peak reactivity was found in the neuropil with sparing of most perikarya. The spatial and temporal pattern of ehk-1 gene expression suggests a role in both the development and maintenance of differentiated neurons of the central nervous system.

Towards the utilization of EEG as a brain imaging tool.

Recent advances in signal analysis have engendered EEG with the status of a true brain mapping and brain imaging method capable of providing spatio-temporal information regarding brain (dys)function. Because of the increasing interest in the temporal dynamics of brain networks, and because of the straightforward compatibility of the EEG with other brain imaging techniques, EEG is increasingly used in the neuroimaging community. However, the full capability of EEG is highly underestimated. Many combined EEG-fMRI studies use the EEG only as a spike-counter or an oscilloscope. Many cognitive and clinical EEG studies use the EEG still in its traditional way and analyze grapho-elements at certain electrodes and latencies. We here show that this way of using the EEG is not only dangerous because it leads to misinterpretations, but it is also largely ignoring the spatial aspects of the signals. In fact, EEG primarily measures the electric potential field at the scalp surface in the same way as MEG measures the magnetic field. By properly sampling and correctly analyzing this electric field, EEG can provide reliable information about the neuronal activity in the brain and the temporal dynamics of this activity in the millisecond range. This review explains some of these analysis methods and illustrates their potential in clinical and experimental applications.

The more you drink, the greater your risk of brain haemorrhage

The poster highlights that alcohol increases your risk of brain haemorrhage.

BOLD responses to trigeminal nerve stimulation.

The current study investigates a new model of barrel cortex activation using stimulation of the infraorbital branch of the trigeminal nerve. A robust and reproducible activation of the rat barrel cortex was obtained following trigeminal nerve stimulation. Blood oxygen level-dependent (BOLD) effects were obtained in the primary somatosensory barrel cortex (S1BF), the secondary somatosensory cortex (S2) and the motor cortex. These cortical areas were reached from afferent pathways from the trigeminal ganglion, the trigeminal nuclei and thalamic nuclei from which neurons project their axons upon whisker stimulation. The maximum BOLD responses were obtained for a stimulus frequency of 1 Hz, a stimulus pulse width of 100 μs and for current intensities between 1.5 and 3 mA. The BOLD response was nonlinear as a function of frequency and current intensity. Additionally, modeling BOLD responses in the rat barrel cortex from separate cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO(2)) measurements showed good agreement with the shape and amplitude of measured BOLD responses as a function of stimulus frequency and will potentially allow to identify the sources of BOLD nonlinearities. Activation of the rat barrel cortex using trigeminal nerve stimulation will contribute to the interpretation of the BOLD signals from functional magnetic resonance imaging studies.

Impact of reduced cerebral perfusion pressure on outcome after severe traumatic brain injury is dependent on brain tissue oxygen pressure

INTRODUCTION. Reduced cerebral perfusion pressure (CPP) may worsen secondary damage and outcome after severe traumatic brain injury (TBI), however the optimal management of CPP is still debated. STUDY HYPOTHESIS: We hypothesized that the impact of CPP on outcome is related to brain tissue oxygen tension (PbtO2) level and that reduced CPP may worsen TBI prognosis when it is associated with brain hypoxia. DESIGN. Retrospective analysis of prospective database. METHODS. We analyzed 103 patients with severe TBI who underwent continuous PbtO2 and CPP monitoring for an average of 5 days. For each patient, duration of reduced CPP (\60 mm Hg) and brain hypoxia (PbtO2\15 mm Hg for[30 min [1]) was calculated with linear interpolation method and the relationship between CPP and PbtO2 was analyzed with Pearson's linear correlation coefficient. Outcome at 30 days was assessed with the Glasgow Outcome Score (GOS), dichotomized as good (GOS 4-5) versus poor (GOS 1-3). Multivariable associations with outcome were analyzed with stepwise forward logistic regression. RESULTS. Reduced CPP (n=790 episodes; mean duration 10.2 ± 12.3 h) was observed in 75 (74%) patients and was frequently associated with brain hypoxia (46/75; 61%). Episodes where reduced CPP were associated with normal brain oxygen did not differ significantly between patients with poor versus those with good outcome (8.2 ± 8.3 vs. 6.5 ± 9.7 h; P=0.35). In contrast, time where reduced CPP occurred simultaneously with brain hypoxia was longer in patients with poor than in those with good outcome (3.3±7.4 vs. 0.8±2.3 h; P=0.02). Outcome was significantly worse in patients who had both reduced CPP and brain hypoxia (61% had GOS 1-3 vs. 17% in those with reduced CPP but no brain hypoxia; P\0.01). Patients in whom a positive CPP-PbtO2 correlation (r[0.3) was found also were more likely to have poor outcome (69 vs. 31% in patients with no CPP-PbtO2 correlation; P\0.01). Brain hypoxia was an independent risk factor of poor prognosis (odds ratio for favorable outcome of 0.89 [95% CI 0.79-1.00] per hour spent with a PbtO2\15 mm Hg; P=0.05, adjusted for CPP, age, GCS, Marshall CT and APACHE II). CONCLUSIONS. Low CPP may significantly worsen outcome after severe TBI when it is associated with brain tissue hypoxia. PbtO2-targeted management of CPP may optimize TBI therapy and improve outcome of head-injured patients.

Ecstasy can cause brain damage

This poster informs about the dangers of Ecstasy stating: 'Medical research proves that Ecstasy can cause brain damage. Deny it all you like, but you know it won't wash'.

Reverse the 'real brain drain' for our children, urges Director of Public Health

The second annual report of the Director of Public Health (DPH) for Northern Ireland was published today. This significant report highlights the many public health challenges that affect people in Northern Ireland. Dr Carolyn Harper, Director of Public Health, leads the public health team that tackles this complex agenda, working with many statutory, community and voluntary partner organisations across health, local government, education, housing and other sectors.

Sensing of glucose in the brain.

The brain, and in particular the hypothalamus and brainstem, have been recognized for decades as important centers for the homeostatic control of feeding, energy expenditure, and glucose homeostasis. These structures contain neurons and neuronal circuits that may be directly or indirectly activated or inhibited by glucose, lipids, or amino acids. The detection by neurons of these nutrient cues may become deregulated, and possibly cause metabolic diseases such as obesity and diabetes. Thus, there is a major interest in identifying these neurons, how they respond to nutrients, the neuronal circuits they form, and the physiological function they control. Here I will review some aspects of glucose sensing by the brain. The brain is responsive to both hyperglycemia and hypoglycemia, and the glucose sensing cells involved are distributed in several anatomical sites that are connected to each other. These eventually control the activity of the sympathetic or parasympathetic nervous system, which regulates the function of peripheral organs such as liver, white and brown fat, muscle, and pancreatic islets alpha and beta cells. There is now evidence for an extreme diversity in the sensing mechanisms used, and these will be reviewed.

How local excitation-inhibition ratio impacts the whole brain dynamics.

The spontaneous activity of the brain shows different features at different scales. On one hand, neuroimaging studies show that long-range correlations are highly structured in spatiotemporal patterns, known as resting-state networks, on the other hand, neurophysiological reports show that short-range correlations between neighboring neurons are low, despite a large amount of shared presynaptic inputs. Different dynamical mechanisms of local decorrelation have been proposed, among which is feedback inhibition. Here, we investigated the effect of locally regulating the feedback inhibition on the global dynamics of a large-scale brain model, in which the long-range connections are given by diffusion imaging data of human subjects. We used simulations and analytical methods to show that locally constraining the feedback inhibition to compensate for the excess of long-range excitatory connectivity, to preserve the asynchronous state, crucially changes the characteristics of the emergent resting and evoked activity. First, it significantly improves the model's prediction of the empirical human functional connectivity. Second, relaxing this constraint leads to an unrealistic network evoked activity, with systematic coactivation of cortical areas which are components of the default-mode network, whereas regulation of feedback inhibition prevents this. Finally, information theoretic analysis shows that regulation of the local feedback inhibition increases both the entropy and the Fisher information of the network evoked responses. Hence, it enhances the information capacity and the discrimination accuracy of the global network. In conclusion, the local excitation-inhibition ratio impacts the structure of the spontaneous activity and the information transmission at the large-scale brain level.