Pablo D. Perez

Heterogeneous Response to a Quorum-Sensing Signal in the Luminescence of Individual Vibrio fischeri

The marine bacterium Vibrio fischeri regulates its bioluminescence through a quorum sensing mechanism: the bacterium releases diffusible small molecules (autoinducers) that accumulate in the environment as the population density increases. This accumulation of autoinducer (AI) eventually activates transcriptional regulators for bioluminescence as well as host colonization behaviors. Although V.fischeri quorum sensing has been extensively characterized in bulk populations, far less is known about how it performs at the level of the individual cell, where biochemical noise is likely to limit the precision of luminescence regulation. We have measured the time-dependence and AI-dependence of light production by individual V.fischeri cells that are immobilized in a perfusion chamber and supplied with a defined concentration of exogenous AI. We use low-light level microscopy to record and quantify the photon emission from the cells over periods of several hours as they respond to the introduction of AI. We observe an extremely heterogeneous response to the AI signal. Individual cells differ widely in the onset time for their luminescence and in their resulting brightness, even in the presence of high AI concentrations that saturate the light output from a bulk population. The observed heterogeneity shows that although a given concentration of quorum signal may determine the average light output from a population of cells, it provides far weaker control over the luminescence output of each individual cell.

Altered Inflammatory Response Is Associated With an Impaired Autonomic Input to the Bone Marrow in the Spontaneously Hypertensive Rat

Autonomic nervous system dysfunction, exaggerated inflammation, and impaired vascular repair are all hallmarks of hypertension. Considering that bone marrow (BM) is a major source of the inflammatory cells (ICs) and endothelial progenitor cells (EPCs), we hypothesized that impaired BM–autonomic nervous system interaction contributes to dysfunctional BM activity in hypertension. In the spontaneously hypertensive rat (SHR), we observed a >30% increase in BM and blood ICs (CD4.8+) and a >50% decrease in EPCs (CD90+.CD4.5.8–) when compared with the normotensive Wistar–Kyoto rat. Increased tyrosine hydroxylase (70%) and norepinephrine (160%) and decreased choline acetyl transferase (30%) and acetylcholine esterase (55%) indicated imbalanced autonomic nervous system in SHR BM. In Wistar–Kyoto rat, night time–associated elevation in sympathetic nerve activity (50%) and BM norepinephrine (41%) was associated with increased ICs (50%) and decreased EPCs (350%) although BM sympathetic denervation decreased ICs (25%) and increased EPCs (40%). In contrast, these effects were blunted in SHR, possibly because of chronic downregulation of BM adrenergic receptor &agr;2a (by 50%–80%) and &bgr;2 (30%–45%). Application of norepinephrine resulted in increased BM IC activation/release, which was prevented by preadministration of acetylcholine. Electrophysiological recordings of femoral sympathetic nerve activity showed a more robust femoral sympathetic nerve activity in SHR when compared with Wistar–Kyoto rat, peaking earlier in the respiratory cycle, indicative of increased sympathetic tone. Finally, manganese-enhanced MRI demonstrated that presympathetic neuronal activation in SHR was associated with an accelerated retrograde transport of the green fluorescent protein–labeled pseudorabies virus from the BM. These observations demonstrate that a dysfunctional BM autonomic nervous system is associated with imbalanced EPCs and ICs in hypertension.

Noise and crosstalk in two quorum-sensing inputs of Vibrio fischeri

BackgroundOne of the puzzles in bacterial quorum sensing is understanding how an organism integrates the information gained from multiple input signals. The marine bacterium Vibrio fischeri regulates its bioluminescence through a quorum sensing mechanism that receives input from three pheromone signals, including two acyl homoserine lactone (HSL) signals. While the role of the 3-oxo-C6 homoserine lactone (3OC6HSL) signal in activating the lux genes has been extensively studied and modeled, the role of the C8 homoserine lactone (C8HSL) is less obvious, as it can either activate luminescence or block its activation. It remains unclear how crosstalk between C8HSL and 3OC6HSL affects the information that the bacterium obtains through quorum sensing.ResultsWe have used microfluidic methods to measure the response of individual V.fischeri cells to combinations of C8HSL and 3OC6HSL. By measuring the fluorescence of individual V.fischeri cells containing a chromosomal gfp-reporter for the lux genes, we study how combinations of exogenous HSLs affect both the population average and the cell-to-cell variability of lux activation levels. At the level of a population average, the crosstalk between the C8HSL and 3OC6HSL inputs is well-described by a competitive inhibition model. At the level of individual cells, the heterogeneity in the lux response depends only on the average degree of activation, so that the noise in the output is not reduced by the presence of the second HSL signal. Overall we find that the mutual information between the signal inputs and the lux output is less than one bit. A nonlinear correlation between fluorescence and bioluminescence outputs from lux leads to different noise properties for these reporters.ConclusionsThe lux genes in V.fischeri do not appear to distinguish between the two HSL inputs, and even with two signal inputs the regulation of lux is extremely noisy. Hence the role of crosstalk from the C8HSL input may not be to improve sensing precision, but rather to suppress the sensitivity of the switch for as long as possible during colony growth.

Temporal MRI characterization, neurobiochemical and neurobehavioral changes in a mouse repetitive concussive head injury model.

Single and repeated sports-related mild traumatic brain injury (mTBI), also referred to as concussion, can result in chronic post-concussive syndrome (PCS), neuropsychological and cognitive deficits, or chronic traumatic encephalopathy (CTE). However PCS is often difficult to diagnose using routine clinical, neuroimaging or laboratory evaluations, while CTE currently only can be definitively diagnosed postmortem. We sought to develop an animal model to simulate human repetitive concussive head injury for systematic study. In this study, mice received single or multiple head impacts by a stereotaxic impact device with a custom-made rubber tip-fitted impactor. Dynamic changes in MRI, neurobiochemical markers (Tau hyperphosphorylation and glia activation in brain tissues) and neurobehavioral functions such as anxiety, depression, motor function and cognitive function at various acute/subacute (1-7 day post-injury) and chronic (14-60 days post-injury) time points were examined. To explore the potential biomarkers of rCHI, serum levels of total Tau (T-Tau) and phosphorylated Tau (P-Tau) were also monitored at various time points. Our results show temporal dynamics of MRI consistent with structural perturbation in the acute phase and neurobiochemical changes (P-Tau and GFAP induction) in the subacute and chronic phase as well as development of chronic neurobehavioral changes, which resemble those observed in mTBI patients.

Acute Nicotine Administration Increases BOLD fMRI Signal in Brain Regions Involved in Reward Signaling and Compulsive Drug Intake in Rats

Background: Acute nicotine administration potentiates brain reward function and enhances motor and cognitive function. These studies investigated which brain areas are being activated by a wide range of doses of nicotine, and if this is diminished by pretreatment with the nonselective nicotinic receptor antagonist mecamylamine. Methods: Drug-induced changes in brain activity were assessed by measuring changes in the blood oxygen level dependent (BOLD) signal using an 11.1-Tesla magnetic resonance scanner. In the first experiment, nicotine naïve rats were mildly anesthetized and the effect of nicotine (0.03–0.6mg/kg) on the BOLD signal was investigated for 10min. In the second experiment, the effect of mecamylamine on nicotine-induced brain activity was investigated. Results: A high dose of nicotine increased the BOLD signal in brain areas implicated in reward signaling, such as the nucleus accumbens shell and the prelimbic area. Nicotine also induced a dose-dependent increase in the BOLD signal in the striato-thalamo-orbitofrontal circuit, which plays a role in compulsive drug intake, and in the insular cortex, which contributes to nicotine craving and relapse. In addition, nicotine induced a large increase in the BOLD signal in motor and somatosensory cortices. Mecamylamine alone did not affect the BOLD signal in most brain areas, but induced a negative BOLD response in cortical areas, including insular, motor, and somatosensory cortices. Pretreatment with mecamylamine completely blocked the nicotine-induced increase in the BOLD signal. Conclusions: These studies demonstrate that acute nicotine administration activates brain areas that play a role in reward signaling, compulsive behavior, and motor and cognitive function.

Functional Neural–Bone Marrow Pathways: Implications in Hypertension and Cardiovascular Disease

Treatment-resistant hypertension (TRHT) is characterized by persistently high arterial blood pressure (BP), partly as a result of a dysfunctional autonomic nervous system (ANS), wherein sympathetic drive/norepinephrine spillover is increased and parasympathetic drive is decreased.1–3 The difficulty in treatment of TRHT arises precisely from this partly neurogenic component because the available drug therapies do not target the central nervous system (CNS) directly. Because of this and despite recent advances in techniques such as renal denervation and carotid baroreceptor activation,4,5 successful treatment and long-term control of TRHT remain challenging.6 In an attempt to develop more effective treatments, many groups are investigating specific causes of TRHT. A large body of experimental evidence implicates both genetic and environmental influences, such as salt sensitivity and elevated systemic renin–angiotensin system (RAS) activity7–14 in the pathophysiology of this disease. Furthermore, a majority of studies point to dysregulations in the activity within the cardiorespiratory brain regions as a reason for increased sympathetic and decreased parasympathetic drive to the peripheral organs,14–21 resulting in end-organ damage,21–25 vascular/endothelial dysfunction,26,27 and hormonal imbalance,28 which perpetuate the pathophysiology and complicate treatment strategies. Despite our increasing understanding of TRHT, the origins of this brain dysregulation remain largely unknown. Recently, the activity of the immune system29–31 and neuroimmune pathways in patients with hypertension and animal models of hypertension has been highlighted.32–36 Studies suggest that both the sympathetic and the parasympathetic arms of the ANS can exert their influence on the activity of the immune organs, tissues, and cells, and that it is the dysfunctional ANS-immune communication that may lead to hypertension and CVD.35–40 The aim of this review is to summarize the latest advances in this …

A Single Angiotensin II Hypertensive Stimulus Is Associated with Prolonged Neuronal and Immune System Activation in Wistar-Kyoto Rats

Activation of autonomic neural pathways by chronic hypertensive stimuli plays a significant role in pathogenesis of hypertension. Here, we proposed that even a single acute hypertensive stimulus will activate neural and immune pathways that may be important in initiation of memory imprinting seen in chronic hypertension. We investigated the effects of acute angiotensin II (Ang II) administration on blood pressure, neural activation in cardioregulatory brain regions, and central and systemic immune responses, at 1 and 24 h post-injection. Administration of a single bolus intra-peritoneal (I.P.) injection of Ang II (36 μg/kg) resulted in a transient increase in the mean arterial pressure (MAP) (by 22 ± 4 mmHg vs saline), which returned to baseline within 1 h. However, in contrast to MAP, neuronal activity, as measured by manganese-enhanced magnetic resonance (MEMRI), remained elevated in several cardioregulatory brain regions over 24 h. The increase was predominant in autonomic regions, such as the subfornical organ (SFO; ~20%), paraventricular nucleus of the hypothalamus (PVN; ~20%) and rostral ventrolateral medulla (RVLM; ~900%), among others. Similarly, systemic and central immune responses, as evidenced by circulating levels of CD4+/IL17+ T cells, and increased IL17 levels and activation of microglia in the PVN, respectively, remained elevated at 24 h following Ang II challenge. Elevated Fos expression in the PVN was also present at 24 h (by 73 ± 11%) following Ang II compared to control saline injections, confirming persistent activation of PVN. Thus, even a single Ang II hypertensive stimulus will initiate changes in neuronal and immune cells that play a role in the developing hypertensive phenotype.

Central neural activation following contact sensitivity peripheral immune challenge: evidence of brain-immune regulation through C fibres

This study tested the hypothesis that peripheral immune challenges will produce predictable activation patterns in the rat brain consistent with sympathetic excitation. As part of examining this hypothesis, this study asked whether central activation is dependent on capsaicin‐sensitive C‐fibres. We induced skin contact sensitivity immune responses with 2,4‐dinitrochlorobenzene (DNCB), in the presence or absence of the acute C‐fibre toxin capsaicin (8‐methyl‐N‐vanillyl‐6‐nonenamide) to trigger immune responses with and without diminished activity of C‐fibres. Innovative blood‐oxygen‐level‐dependent functional magnetic resonance imaging data revealed that the skin contact sensitivity immune responses induced with DNCB were associated with localized increases in brain neuronal activity in treated rats. This response was diminished by pre‐treatment with capsaicin 1 week before scans. In the same animals, we found expression of the immediate early gene c‐Fos in sub‐regions of the amygdala and hypothalamic sympathetic brain nuclei. Significant increases in c‐Fos expression were found in the supraoptic nucleus, central amygdala and medial habenula following immune challenges. Our results support the idea that selective brain regions, some of which are associated with sympathetic function, process or modulate immune function through pathways that are partially dependent on C‐fibres. Together with previous studies demonstrating the motor control pathways from brain to immune targets, these findings indicate a central neuroimmune system to monitor host status and coordinate appropriate host responses.

Enhanced functional connectivity and volume between cognitive and reward centers of naïve rodent brain produced by pro-dopaminergic agent KB220Z

Dopaminergic reward dysfunction in addictive behaviors is well supported in the literature. There is evidence that alterations in synchronous neural activity between brain regions subserving reward and various cognitive functions may significantly contribute to substance-related disorders. This study presents the first evidence showing that a pro-dopaminergic nutraceutical (KB220Z) significantly enhances, above placebo, functional connectivity between reward and cognitive brain areas in the rat. These include the nucleus accumbens, anterior cingulate gyrus, anterior thalamic nuclei, hippocampus, prelimbic and infralimbic loci. Significant functional connectivity, increased brain connectivity volume recruitment (potentially neuroplasticity), and dopaminergic functionality were found across the brain reward circuitry. Increases in functional connectivity were specific to these regions and were not broadly distributed across the brain. While these initial findings have been observed in drug naïve rodents, this robust, yet selective response implies clinical relevance for addicted individuals at risk for relapse, who show reductions in functional connectivity after protracted withdrawal. Future studies will evaluate KB220Z in animal models of addiction.

Incidental hepatocellular carcinoma after liver transplantation: Prevalence, histopathological features and prognostic impact

Background Incidental hepatocellular carcinoma (iHCC) is a histological finding after liver transplantation (LT) which relevance has been scarcely studied. Aims to describe the histopathological features of iHCC and to determine its prognostic impact in terms of tumor recurrence and overall survival. Methods Observational study including 451 consecutive adult LT patients (2000–2013). Patients aged<18, retransplanted or with early postoperative death were excluded. Median follow-up after LT was 58 months. Multiple Cox’s regression was used to assess the prognostic impact of iHCC on tumor recurrence and mortality while controlling for potential confounders. Results 141 patients had known HCC before LT (31.3%). Among the remaining 310 patients, the prevalence of iHCC was 8.7% (n = 27). In the explanted liver, 36.2% of patients with known HCC and 25.9% of patients with iHCC trespassed Milan criteria (p = 0.30). Patients with known and iHCC had similar rates of multinodular disease (50.4% vs 55.6%; p = 0.62), macrovascular invasion (6.5% vs 3.7%; p = 0.58), microvascular invasion (12.9% vs 14.8%; p = 0.76) and moderate-poor tumor differentiation (53.9% vs 70.4%; p = 0.09). In the multivariate analysis, iHCC and known HCC had identical recurrence-free survival after controlling for histological features (RR = 1.06, 95%CI 0.36–3.14; p = 0.90). Cumulative 5-year overall survival rates were similar between patients with known and iHCC (65% vs 52.8% respectively; log rank p = 0.44), but significantly inferior as compared with patients without HCC (77.8%) (p = 0.002 and p = 0.007 respectively). Indeed, in the overall cohort, iHCC was an independent predictor of mortality (RR = 3.02; 95%CI 1.62–5.65; p = 0.001). Conclusion The risk of tumor recurrence after LT is similar in patients with iHCC and known HCC. A close imaging surveillance is strongly recommended for patients awaiting LT in order to detect HCC prior to LT, thus allowing for an adequate selection of candidates, prioritization and indication of bridging therapies.