Faculty Bibliography

Vascular endothelial growth factor (VEGF) is critical to angiogenesis and vascular permeability. It is also important in the endocrine system, in which VEGF mediates the vascular effects of estrogens in target tissues such as the uterus, a response attributed to an estrogen response element on the VEGF gene. Here we asked whether 17beta-estradiol increases VEGF levels in the brain. We focused on the hippocampus, in which 17beta-estradiol and VEGF both have important actions, and used immunocytochemistry to evaluate VEGF protein. VEGF immunoreactivity was compared in adult female rats sampled during the estrous cycle when serum levels of 17beta-estradiol peak (proestrous morning) as well as when they are low (metestrous morning). In addition, adult rats were ovariectomized and compared after treatment with 17beta-estradiol or vehicle. The results demonstrated that VEGF immunoreactivity was increased when serum levels of 17beta-estradiol were elevated. Confocal microscopy showed that VEGF immunofluorescence was predominantly nonneuronal, often associated with astrocytes. Glial VEGF labeling was primarily punctate rather than diffuse and labile because glial VEGF immunoreactivity was greatly reduced if tissue sections were left in an aqueous medium overnight. We conclude that VEGF protein in normal female hippocampus is primarily nonneuronal rather than neuronal and suggest that glial VEGF immunoreactivity has been underestimated by past studies with other methods because there is a labile extracellular pool. We suggest that estrogens may exert actions on female hippocampal structure and function by increasing hippocampal VEGF

Olfactory ensheathing cells (OEC), which normally associate closely with but do not myelinate axons in situ, myelinate axons in the adult mammalian spinal cord. They are of clinical interest as candidate cells for autologous transplantation but the ability of OEC to myelinate axons in vitro has been controversial. To clarify this issue, we isolated OEC from olfactory bulbs (OB) of juvenile and adult rats expressing GFP and analyzed their ability to myelinate axons. Using a well-defined assay for myelination of dorsal root ganglia (DRG) axons in culture, we found that OEC from juvenile pups associated with and then myelinated DRG axons. OEC assembled into bundles with the axons by 1week and required more than a week before myelination on axons was detected. In contrast, rat Schwann cells did not bundle axons and they formed P0(+) and MBP(+) myelin segments after as little as 1week. Most of the OEC in culture exhibited staining for calponin, a marker that was not found on Schwann cells in culture, whereas in both OEC and Schwann cell populations nearly all cells were positive for p75NTR and GFAP. These results confirm previous reports showing only subtle immunological differences between Schwann cells and OEC. Besides differences in the rate of myelination, we detected two additional functional differences in the interactions of OEC and Schwann cells with DRG axons. First, the diameter of OEC generated myelin was greater than for Schwann cell myelin on DRG axons. Second, OEC but not Schwann cells myelinated DRG axons in the absence of vitamin C. OEC isolated from adult OB were also found to bundle and myelinate DRG axons but the latter occurred only after incubation times of at least 3weeks. The results indicate that adult OEC require longer incubation times than juvenile OEC to myelinate axons and suggest that patterns of myelination by OEC and Schwann cells are distinguishable at least on axons in vitro. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair

MicroRNAs (miRNAs) are short non-coding RNAs that play a central role in regulation of gene expression by binding to target genes. Many miRNAs were associated with the function of the central nervous system (CNS) in health and disease. Astrocytes are the CNS most abundant glia cells, providing support by maintaining homeostasis and by regulating neuronal signaling, survival and synaptic plasticity. Astrocytes play a key role in repair of brain insults, as part of local immune reactivity triggered by inflammatory or pathological conditions. Thus, astrocyte activation, or astrogliosis, is an important outcome of the innate immune response, which can be elicited by endotoxins such as lipopolysaccharide (LPS) and cytokines such as interferon-gamma (IFN-gamma). The involvement of miRNAs in inflammation and stress led us to hypothesize that astrogliosis is mediated by miRNA function. In this study, we compared the miRNA regulatory layer expressed in primary cultured astrocyte derived from rodents (mice) and primates (marmosets) brains upon exposure to LPS and IFN-gamma. We identified subsets of differentially expressed miRNAs some of which are shared with other immunological related systems while others, surprisingly, are mouse and rat specific. Of interest, these specific miRNAs regulate genes involved in the tumor necrosis factor-alpha (TNF-alpha) signaling pathway, indicating a miRNA-based species-specific regulation. Our data suggests that miRNA function is more significant in the mechanisms governing astrocyte activation in rodents compared to primates.

PURPOSE: To assess the accuracy of glomerular filtration rate (GFR) measurements obtained with low-contrast agent dose dynamic contrast material-enhanced magnetic resonance (MR) renography in patients with liver cirrhosis who underwent routine liver MR imaging, with urinary clearance of technetium 99m ((99m)Tc) pentetic acid (DTPA) as the reference standard. MATERIALS AND METHODS: This HIPAA-compliant study was institutional review board approved. Written informed patient consent was obtained. Twenty patients with cirrhosis (14 men, six women; age range, 41-70 years; mean age, 54.6 years) who were scheduled for routine 1.5-T liver MR examinations to screen for hepatocellular carcinoma during a 6-month period were prospectively included. Five-minute MR renography with a 3-mL dose of gadoteridol was performed instead of a routine test-dose timing examination. The GFR was estimated at MR imaging with use of two kinetic models. In one model, only the signal intensities in the aorta and kidney parenchyma were considered, and in the other, renal cortical and medullary signal intensities were treated separately. The GFR was also calculated by using serum creatinine levels according to the Cockcroft-Gault and modification of diet in renal disease (MDRD) formulas. All patients underwent a (99m)Tc-DTPA urinary clearance examination on the same day to obtain a reference GFR measurement. The accuracies of all MR- and creatinine-based GFR estimations were compared by using Wilcoxon signed rank tests. RESULTS: The mean reference GFR, based on (99m)Tc-DTPA clearance, was 74.9 mL/min/1.73 m(2) +/- 27.7 (standard deviation) (range, 10.3-120.7 mL/min/1.73 m(2)). With both kinetic models, 95% of MR-based GFRs were within 30% of the reference values, whereas only 40% and 60% of Cockcroft-Gault- and MDRD-based GFRs, respectively, were within this range. MR-based GFR estimates were significantly more accurate than creatinine level-based estimates (P < .001). CONCLUSION: GFR assessment with MR imaging, which outperformed the Cockcroft-Gault and MDRD formulas, adds less than 10 minutes of table time to a clinically indicated liver MR examination without ionizing radiation. Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101338/-/DC1

Aquaporin-4 (AQP4) is the major water channel in the CNS and is primarily expressed in astrocytes. Little is known about the potential for AQP4 to influence synaptic plasticity, although many studies have shown that it regulates the response of the CNS to injury. Therefore, we evaluated long-term potentiation (LTP) and long-term depression (LTD) in AQP4 knock-out (KO) and wild-type mice. KO mice exhibited a selective defect in LTP and LTD without a change in basal transmission or short-term plasticity. Interestingly, the impairment in LTP in KO mice was specific for the type of LTP that depends on the neurotrophin BDNF, which is induced by stimulation at theta rhythm [theta-burst stimulation (TBS)-LTP], but there was no impairment in a form of LTP that is BDNF independent, induced by high-frequency stimulation. LTD was also impaired in KO mice, which was rescued by a scavenger of BDNF or blockade of Trk receptors. TrkB receptors, which mediate effects of BDNF on TBS-LTP, were not altered in KO mice, but p75NTR, the receptor that binds all neurotrophins and has been implicated in some types of LTD, was decreased. The KO mice also exhibited a cognitive defect, which suggests a new role for AQP4 and astrocytes in normal cognitive function. This defect was evident using a test for location-specific object memory but not Morris water maze or contextual fear conditioning. The results suggest that AQP4 channels in astrocytes play an unanticipated role in neurotrophin-dependent plasticity and influence behavior

Visual organs perceive environmental stimuli required for rapid initiation of behaviors and can also entrain the circadian clock. The larval eye of Drosophila is capable of both functions. Each eye contains only 12 photoreceptors (PRs), which can be subdivided into two subtypes. Four PRs express blue-sensitive rhodopsin5 (rh5) and eight express green-sensitive rhodopsin6 (rh6). We found that either PR-subtype is sufficient to entrain the molecular clock by light, while only the Rh5-PR subtype is essential for light avoidance. Acetylcholine released from PRs confers both functions. Both subtypes of larval PRs innervate the main circadian pacemaker neurons of the larva, the neuropeptide PDF (pigment-dispersing factor)-expressing lateral neurons (LNs), providing sensory input to control circadian rhythms. However, we show that PDF-expressing LNs are dispensable for light avoidance, and a distinct set of three clock neurons is required. Thus we have identified distinct sensory and central circuitry regulating light avoidance behavior and clock entrainment. Our findings provide insights into the coding of sensory information for distinct behavioral functions and the underlying molecular and neuronal circuitry.

The orbitofrontal cortex (OFC) is implicated in a variety of adaptive decision-making processes. Human studies suggest that there is a functional dissociation between medial and lateral OFC (mOFC and lOFC, respectively) subregions when performing certain choice procedures. However, little work has examined the functional consequences of manipulations of OFC subregions on decision making in rodents. In the present experiments, impulsive choice was assessed by evaluating intolerance to delayed, but economically optimal, reward options using a delay-discounting paradigm. Following initial delay-discounting training, rats received bilateral neurotoxic or sham lesions targeting whole OFC (wOFC) or restricted to either mOFC or lOFC subregions. A transient flattening of delay-discounting curves was observed in wOFC-lesioned animals relative to shams--differences that disappeared with further training. Stable, dissociable effects were found when lesions were restricted to OFC subregions; mOFC-lesioned rats showed increased, whereas lOFC-lesioned rats showed decreased, preference for the larger-delayed reward relative to sham-controls--a pattern that remained significant during retraining after all delays were removed. When locations of levers leading to small-immediate versus large-delayed rewards were reversed, wOFC- and lOFC-lesioned rats showed retarded, whereas mOFC-lesioned rats showed accelerated, trajectories for reversal of lever preference. These results provide the first direct evidence for dissociable functional roles of the mOFC and lOFC for impulsive choice in rodents. The findings are consistent with recent human functional imaging studies and suggest that functions of mOFC and lOFC subregions may be evolutionarily conserved and contribute differentially to decision-making processes.

Electrical activity has been shown to regulate development in a variety of species and in various structures, including the retina, spinal cord and cortex. Within the mammalian cortex specifically, the development of dendrites and commissural axons in pyramidal cells is activity-dependent. However, little is known about the developmental role of activity in the other major cortical population of neurons, the GABA-producing interneurons. These neurons are morphologically and functionally heterogeneous and efforts over the past decade have focused on determining the mechanisms that contribute to this diversity. It was recently discovered that 30% of all cortical interneurons arise from a relatively novel source within the ventral telencephalon, the caudal ganglionic eminence (CGE). Owing to their late birth date, these interneurons populate the cortex only after the majority of other interneurons and pyramidal cells are already in place and have started to functionally integrate. Here we demonstrate in mice that for CGE-derived reelin (Re)-positive and calretinin (Cr)-positive (but not vasoactive intestinal peptide (VIP)-positive) interneurons, activity is essential before postnatal day 3 for correct migration, and that after postnatal day 3, glutamate-mediated activity controls the development of their axons and dendrites. Furthermore, we show that the engulfment and cell motility 1 gene (Elmo1), a target of the transcription factor distal-less homeobox 1 (Dlx1), is selectively expressed in Re(+) and Cr(+) interneurons and is both necessary and sufficient for activity-dependent interneuron migration. Our findings reveal a selective requirement for activity in shaping the cortical integration of specific neuronal subtypes

Granule cell (GC) neurogenesis in the dentate gyrus (DG) does not always proceed normally. After severe seizures (e.g., status epilepticus [SE]) and some other conditions, newborn GCs appear in the hilus. Hilar ectopic GCs (EGCs) can potentially provide insight into the effects of abnormal location and seizures on GC development. Additionally, hilar EGCs that develop after SE may contribute to epileptogenesis and cognitive impairments that follow SE. Thus, it is critical to understand how EGCs differ from normal GCs. Relatively little morphometric information is available on EGCs, especially those restricted to the hilus. This study quantitatively analyzed the structural morphology of hilar EGCs from adult male rats several months after pilocarpine-induced SE, when they are considered to have chronic epilepsy. Hilar EGCs were physiologically identified in slices, intracellularly labeled, processed for light microscopic reconstruction, and compared to GC layer GCs, from both the same post-SE tissue and the NeuroMorpho database (normal GCs). Consistently, hilar EGC and GC layer GCs had similar dendritic lengths and field sizes, and identifiable apical dendrites. However, hilar EGC dendrites were topologically more complex, with more branch points and tortuous dendritic paths. Three-dimensional analysis revealed that, remarkably, hilar EGC dendrites often extended along the longitudinal DG axis, suggesting increased capacity for septotemporal integration. Axonal reconstruction demonstrated that hilar EGCs contributed to mossy fiber sprouting. This combination of preserved and aberrant morphological features, potentially supporting convergent afferent input to EGCs and broad, divergent efferent output, could help explain why the hilar EGC population could impair DG function

Generation of reactive oxygen species (ROS) causes cellular oxidative damage and has been implicated in the etiology of Alzheimer's disease (AD). In contrast, multiple lines of evidence indicate that ROS can normally modulate long-term potentiation (LTP), a cellular model for memory formation. We recently showed that decreasing the level of superoxide through the overexpression of mitochondrial superoxide dismutase (SOD-2) prevents memory deficits in the Tg2576 mouse model of AD. In the current study, we explored whether AD-related LTP impairments could be prevented when ROS generation from mitochondria was diminished either pharmacologically or via genetic manipulation. In wild-type hippocampal slices treated with exogenous amyloid beta peptide (Abeta1-42) and in slices from APP/PS1 mutant mice that model AD, LTP was impaired. The LTP impairments were prevented by MitoQ, a mitochondria-targeted antioxidant, and EUK134, an SOD and catalase mimetic. In contrast, inhibition of NADPH oxidase either by diphenyliodonium (DPI) or by genetically deleting gp91(phox), the key enzymatic component of NADPH oxidase, had no effect on Abeta-induced LTP blockade. Moreover, live staining with MitoSOX Red, a mitochondrial superoxide indicator, combined with confocal microscopy, revealed that Abeta-induced superoxide production could be blunted by MitoQ, but not DPI, in agreement with our electrophysiological findings. Finally, in transgenic mice overexpressing SOD-2, Abeta-induced LTP impairments and superoxide generation were prevented. Our data suggest a causal relationship between mitochondrial ROS imbalance and Abeta-induced impairments in hippocampal synaptic plasticity