Disconnection between the default mode network and medial temporal lobes in post-traumatic amnesia

Post-traumatic amnesia is very common immediately after traumatic brain injury. It is characterised by a confused, agitated state and a pronounced inability to encode new memories and sustain attention. Clinically, post-traumatic amnesia is an important predictor of functional outcome. However, despite its prevalence and functional importance, the pathophysiology of post-traumatic amnesia is not understood. Memory processing relies on limbic structures such as the hippocampus, parahippocampus and parts of the cingulate cortex. These structures are connected within an intrinsic connectivity network, the Default Mode Network. Interactions within the Default Mode Network can be assessed using resting state functional magnetic resonance imaging, which can be acquired in confused patients unable to perform tasks in the scanner. Here we used this approach to test the hypothesis that the mnemonic symptoms of post-traumatic amnesia are caused by functional disconnection within the Default Mode Network. We assessed whether the hippocampus and parahippocampus showed evidence of transient disconnection from cortical brain regions involved in memory processing. 19 traumatic brain injury patients were classified into post-traumatic amnesia and traumatic brain injury control groups, based on their performance on a paired associates learning task. Cognitive function was also assessed with a detailed neuropsychological test battery. Functional interactions between brain regions were investigated using resting-state functional magnetic resonance imaging. Together with impairments in associative memory patients in post-traumatic amnesia demonstrated impairments in information processing speed and spatial working memory. Patients in post-traumatic amnesia showed abnormal functional connectivity between the parahippocampal gyrus and posterior cingulate cortex. The strength of this functional connection correlated with both associative memory and information processing speed and normalised when these functions improved. We have previously shown abnormally high posterior cingulate cortex connectivity in the chronic phase after traumatic brain injury, and this abnormality was also observed in patients with post-traumatic amnesia. Patients in post-traumatic amnesia showed evidence of widespread traumatic axonal injury measured using diffusion magnetic resonance imaging. This change was more marked within the cingulum bundle, the tract connecting the parahippocampal gyrus to the posterior cingulate cortex. These findings provide novel insights into the pathophysiology of post-traumatic amnesia and evidence that memory impairment acutely after traumatic brain injury results from altered parahippocampal functional connectivity, perhaps secondary to the effects of axonal injury on white matter tracts connecting limbic structures involved in memory processing

Reliability of dynamic contrast-enhanced magnetic resonance imaging data in primary brain tumours: a comparison of Tofts and shutter speed models

Purpose To investigate the robustness of pharmacokinetic modelling of DCE-MRI brain tumour data and to ascertain reliable perfusion parameters through a model selection process and a stability test. Methods DCE-MRI data of 14 patients with primary brain tumours were analysed using the Tofts model (TM), the extended Tofts model (ETM), the shutter speed model (SSM) and the extended shutter speed model (ESSM). A no-effect model (NEM) was implemented to assess overfitting of data by the other models. For each lesion, the Akaike Information Criteria (AIC) was used to build a 3D model selection map. The variability of each pharmacokinetic parameter extracted from this map was assessed with a noise propagation procedure, resulting in voxel-wise distributions of the coefficient of variation (CV). Results The model selection map over all patients showed NEM had the best fit in 35.5% of voxels, followed by ETM (32%), TM (28.2%), SSM (4.3%) and ESSM (<0.1%). In analysing the reliability of Ktrans, when considering regions with a CV<20%, ≈25% of voxels were found to be stable across all patients. The remaining 75% of voxels were considered unreliable. Conclusions The majority of studies quantifying DCE-MRI data in brain tumours only consider a single model and whole-tumour statistics for the output parameters. Appropriate model selection, considering tissue biology and its effects on blood brain barrier permeability and exchange conditions, together with an analysis on the reliability and stability of the calculated parameters, is critical in processing robust brain tumour DCE-MRI data

Effect of Indoleacetic Acid and Related Indoles on Lactobacillus sp. Strain 11201 Growth, Indoleacetic Acid Catabolism, and 3-Methylindole Formation

A study was conducted to determine the activity of the 3-methylindole (3MI)-forming enzyme in Lactobacillus sp. strain 11201. Cells were incubated anaerobically with 17 different indolic and aromatic compounds. Indoleacetic acid (IAA), 5-hydroxyindoleacetic acid, 5-methoxy-3-indoleacetic acid, indole-3-pyruvate, or indole-3-propionic acid induced 3MI-forming activity. The highest total enzyme activity induced by IAA was observed in cells incubated with an initial concentration of 1.14 mM IAA. Peak activity of the 3MI-forming enzyme occurred 4 h after bacteria were incubated with either 0.114 or 1.14 mM IAA. Enzyme activity peaked earlier (2 h) and disappeared more rapidly at 5.7 mM IAA than at other concentrations of IAA. The effects of IAA and 3MI on the growth of Lactobacillus sp. strain 11201 and formation of 3MI from IAA also were determined. Bacterial growth and 3MI formation from IAA were reduced in medium containing exogenous 3MI. The growth depression observed in medium containing 5.7 mM IAA appears to be due to the toxicity of 3MI rather than IAA. The formation of 3MI in this ruminal Lactobacillus sp. is mediated by an inducible enzyme, and as 3MI accumulates, bacterial growth and rates of 3MI formation from IAA are reduced

Hydraulic characteristics of a rectangular mixed-cell rearing unit

AbstractWe describe a fish rearing unit modification that establishes mixed flow reactor (MFR) behavior in a rectangular vessel so as to eliminate metabolite concentration gradients, increase current velocities and improve solids scour at low water exchange rates. A standard raceway section 14.5 m long was modified to create six counter-rotating mixed cells, each 2.4 m wide by 2.4 m long. Cells receive water from vertical pipe sections extending to the tank floor and positioned in the corners of the cells. Vertical pipe sections were fabricated with jet ports that direct water into the cells tangentially to establish rotary circulation. Water exits each cell through a centrally located floor drain. Hydraulic characteristics of the tank are described based on an analysis of residence time distribution, current velocities and cell-to-cell water exchange rates. The latter was calculated based on a proposed hydraulics model and tracer concentrations established at a steady state. Vessel dispersion numbers measured with water exchange rates of 1.0 and 1.3 per hour, indicate tank performance approximates that of a MFR with the active tank volume representing 77.9–100% of total tank volume. Water velocities measured at 216 stations averaged 0.14, 0.12 and 0.12 m/s for the tank surface, mid-depth and near bottom regions. The benthic shear stress calculated given surface velocity was 0.04 N/m2. This was sufficient to scour and purge fecal solids produced by 2010 kg of lake trout that averaged 44.3 cm in total length. Cell interaction was significant with cell-to-cell exchange rates averaging 3.9 times the tank inflow rate. Energy requirements of the rearing unit were kept low (1.32 m water gauge pressure; 6.7 W/m3) through use of a large number of low velocity jets

Thiamine deficiency and the effectiveness of thiamine treatments through broodstock injections and egg immersion on Lake Ontario steelhead trout

In fall 2014, steelhead trout (Oncorhynchus mykiss) migrating in the Salmon River, New York, exhibited abnormal swimming behavior and, in some cases, mortality, as reported by sport fishermen. Preliminary results showed that affected individuals had low levels of thiamine in their muscle and liver. As a result, New York State Department of Conservation personnel from the Salmon River Fish Hatchery injected adult fihs with thiamine mononotrate (50mg/kg). In April 2015. muscle, liver, and eggs were taken from adults treated (n = 27) or not (n = 27) with thiamine at the Salmon River Fish Hatchery to evaluate their thiamine concentration. In addition, a subsample of eggs was fertilized and treated or not with a thiamine bath (1000 ppm). Accordingly, four treatment groups were established: adults treated/eggs treated (TT), adults treated/eggs untreated (TU), adults untreated/eggs treated (UT), and adults untreated/eggs untreated (UU). Offspring mortality was significantly higher in (P0.8) from each other. The efficiency of each treatmentment was compared based on offspring mortality. Significant differences in muscle, liver, and egg total thiamine concentrations were observed between treated and untreated adults (