Faculty Bibliography

Pax6 and Gli3 are dorsally expressed genes that are known to antagonize sonic hedgehog (Shh) activity. We have previously shown that dorsoventral patterning defects seen in Shh(-/-) mutants are rescued in Shh(-/-);Gli3(-/-) compound mutants. Here we investigate if the loss of Pax6 can also ameliorate defects seen in Shh(-/-) mutants. In support of this notion, we observe that the fusion of the cerebral vesicles seen in Shh(-/-) mutants is partially corrected in E12.5 Shh(-/-);Pax6(-/-) compound mutants. Investigation of pan-ventral markers such as Dlx2 also shows that, unlike Shh(-/-), a broad domain of expression of this gene is observed in Shh(-/-);Pax6(-/-) mice. Interestingly, we observe that while the expression of ER81 in the ventral telencephalon is expanded, the expression of Ebf1 is lost. This suggests that the rescued ventral domain observed in Shh(-/-);Pax6(-/-) mice is the dorsal lateral ganglionic eminence region. With regard to dorsal telencephalic patterning, we also observe rescue of the pallial-subpallial boundary, as well as a partial rescue of the dorsal midline. Together, our findings are consistent with Pax6 function being required for aspects of Gli3-mediated telencephalic patterning

OBJECTIVE: Obese patients without clinically apparent heart disease may have a high output state and elevated total and central blood volumes. Central circulatory congestion should result in elevated pulmonary diffusing capacity (DLCO) and capillary blood volume (Vc) reflecting pulmonary capillary recruitment; however, the effect on membrane diffusion (Dm) is uncertain. We examined DLCO and its partition into Vc and Dm in 13 severely obese subjects (BMI = 51 +/- 14 kg/m2) without manifest cardiopulmonary disease before and after surgically induced weight loss. RESEARCH METHODS AND PROCEDURES: DLCO and its partition into Vc and Dm [referenced to alveolar volume (VA)] as described by Roughton and Forster, total body water by tritiated water, and fat distribution by waist-to-hip ratio were performed. RESULTS: Despite normal DLCO (mean 98 +/- 16% predicted), Vc/VA was increased (mean 118 +/- 30% predicted), and Dm/VA was reduced (mean 77 +/- 34% predicted). Nine of 13 subjects were restudied after weight loss (mean 52 +/- 43 kg); Vc/VA decreased to 89 +/- 18% predicted (p = 0.01), and Dm/VA increased to 139 +/- 30% predicted (p < 0.01). Increasing total body water was associated with both increasing Vc (r = 0.74, p = 0.01) and increasing waist-to-hip ratio (r = 0.65, p = 0.02), indicating that circulatory congestion increases with increasing central obesity. DISCUSSION: Severely obese subjects without manifest cardiopulmonary disease may have increased Vc indicating central circulatory congestion and reduced Dm suggesting associated alveolar capillary leak, despite normal DLCO. Reversibility with weight loss is in accord with reversibility of the hemodynamic abnormalities of obesity.

Nicotinic acetylcholine receptors (nAChRs) are inhibited by several drugs that are commonly thought to be specific for L-type calcium channels (LTCCs). In neurons, LTCCs are activated by nicotine-induced depolarization to engage downstream signaling events; however, the role of LTCC drug interactions with nAChRs in signaling has not been examined in detail. We investigated the effects of LTCC ligands on nAChR currents and downstream signaling in rat superior cervical ganglion (SCG) neurons. We found that 10microM nicotine and 40mM K(+) both reversibly depolarize SCG neurons to -20mV, sufficient to activate LTCCs and downstream signaling, including induction of nuclear phospho-CREB (pCREB); this induction was blocked by LTCC antagonists. Interestingly, the effects of LTCC antagonists on nicotine-induced signaling to CREB are not mediated by their actions on LTCCs, but rather via inhibition of nAChRs, which prevents nicotine-induced depolarization. We show that this effect is sufficient to block pCREB induction in neurons expressing an antagonist-insensitive LTCC. Taken together, our data show that, at concentrations typically used to block LTCCs, these antagonists inhibit nAChR currents and downstream signaling. These findings serve as a caution in attributing a role for LTCCs when using these drugs experimentally or therapeutically

Short-term synaptic plasticity (STP) is an important mechanism for modifying neural circuits during computation. Although STP is much studied, its role in the processing of complex natural spike patterns is unknown. Here we analyze the responses of excitatory and inhibitory hippocampal synapses to natural spike trains at near-physiological temperatures. Our results show that excitatory and inhibitory synapses express complementary sets of STP components that selectively change synaptic strength during epochs of high-frequency discharge associated with hippocampal place fields. In both types of synapses, synaptic strength rapidly alternates between a near-constant level during low activity and another near-constant, but elevated (for excitatory synapses) or reduced (for inhibitory synapses) level during high-frequency epochs. These history-dependent changes in synaptic strength are largely independent of the particular temporal pattern within the discharges, and occur concomitantly in the two types of synapses. When excitatory and feed-forward inhibitory synapses are co-activated within the hippocampal feed-forward circuit unit, the net effect of their complementary STP is an additional increase in the gain of excitatory synapses during high-frequency discharges via selective disinhibition. Thus, excitatory and feed-forward inhibitory hippocampal synapses in vitro act synergistically as an adaptive filter that operates in a switch-like manner and is selective for high-frequency epochs

Although a variety of methods have been proposed to provide automated adjustment of shim homogeneity, these methods typically fail or require large numbers of iterations in vivo when applied to regions with poor homogeneity, such as the temporal lobe. These limitations are largely due to 1) the limited accuracy of single evolution time measurements when full B0 mapping studies are used, and 2) inaccuracies arising from projection-based methods when the projections pass through regions where the inhomogeneity exceeds the order of the fitted parameters. To overcome these limitations we developed a novel B0 mapping method using multiple evolution times with a novel unwrapping scheme in combination with a user-defined ROI selection tool. We used these methods at 4T on 10 control subjects to obtain high-resolution spectroscopic images of glutamate from the bilateral hippocampi

INTRODUCTION: We examined pulmonary diffusing capacity (D(LCO)) and its partition in pulmonary vascular diseases without evident parenchymal disease to assess the pattern and proportionality of change in membrane diffusion (D(m)) and capillary blood volume (V(c)). Disproportionate reduction in D(m) relative to V(c) (low D(m)/V(c)) in these diseases has been attributed to associated alveolar membrane/parenchymal disease, thus providing a potentially important diagnostic tool. METHODS: Diseases included: idiopathic pulmonary arterial hypertension (n=6), chronic thromboembolic disease (n=5), and intravenous drug use (n=14), providing a spectrum of pulmonary vascular diseases. V(c) and D(m) were determined as described by Roughton and Forster. RESULTS: All diseases showed a reduced V(c) (59+/-10, 69+/-14, 71+/-21 % predicted, respectively) and D(m) (76+/-22, 53+/-19, 63+/-16 % predicted, respectively) with no differences between groups (p>0.05). Disproportionate reduction of D(m) (D(m)/V(c) % predicted <1) was seen in all diseases (range 0.36-1.89). A mathematical analysis is presented to illustrate that changes in vascular geometry may additionally influence the proportionality of changes in D(m) and V(c). The mathematical analysis suggests that when reduction in patency of some vessels co-exits with compensatory dilatation of the remaining vasculature, a disproportionate reduction in D(m) relative to V(c) may result. CONCLUSIONS: The balance between vascular curtailment and compensatory dilatation may contribute to the variability of the D(m)/V(c) relationship seen in pulmonary vascular disease. Disproportionate reduction in D(m) relative to V(c) may result from this imbalance and need not imply subclinical alveolar membrane and/or parenchymal disease.

Development and implementation of microarray techniques to quantify expression levels of dozens to hundreds to thousands of transcripts simultaneously within select tissue samples from normal control subjects and neurodegenerative diseased brains has enabled scientists to create molecular fingerprints of vulnerable neuronal populations in Alzheimer's disease (AD) and related disorders. A goal is to sample gene expression from homogeneous cell types within a defined region without potential contamination by expression profiles of adjacent neuronal subpopulations and nonneuronal cells. The precise resolution afforded by single cell and population cell RNA analysis in combination with microarrays and real-time quantitative polymerase chain reaction (qPCR)-based analyses allows for relative gene expression level comparisons across cell types under different experimental conditions and disease progression. The ability to analyze single cells is an important distinction from global and regional assessments of mRNA expression and can be applied to optimally prepared tissues from animal models of neurodegeneration as well as postmortem human brain tissues. Gene expression analysis in postmortem AD brain regions including the hippocampal formation and neocortex reveals selectively vulnerable cell types share putative pathogenetic alterations in common classes of transcripts, for example, markers of glutamatergic neurotransmission, synaptic-related markers, protein phosphatases and kinases, and neurotrophins/neurotrophin receptors. Expression profiles of vulnerable regions and neurons may reveal important clues toward the understanding of the molecular pathogenesis of various neurological diseases and aid in identifying rational targets toward pharmacotherapeutic interventions for progressive, late-onset neurodegenerative disorders such as mild cognitive impairment (MCI) and AD

OBJECTIVE: The purpose of the study was to quantify the fat fraction in nine fat-water phantoms containing 0-80% fat using opposed-phase imaging with the qualitative guidance of 1H MR spectroscopy (MRS), which was used by observer 1 to visually assess the sizes of the water and fat peaks to apply two alternative mathematic formulas for the calculation of the fat fraction. In addition, the fat fraction was also quantified directly with 1H MRS as an independent method by two observers (observers 2 and 3). CONCLUSION: The fat fraction calculated with opposed-phase imaging (FF(OPI)) and that calculated with 1H MRS (FF(MRS)) correlated well with the known fat fractions of the phantoms (FF(P)): r = 0.99 for FF(OPI); p < 0.0001 and r = 0.96-0.98 for FF(MRS); p < 0.001, for observers 2 and 3, respectively. Opposed-phase imaging should be combined with 1H MRS to ensure accurate quantification of the fat fraction

Studies of short-term plasticity (STP) in the hippocampus, performed mostly at room temperature, have shown that small central synapses rapidly depress in response to high-frequency stimulation. This decrease in synaptic strength with synapse use places constraints on the use of STP as a dynamic filter for processing of natural high-frequency input. Here we report that, because of a strong but differential temperature dependence of STP components, the properties of STP in excitatory hippocampal synapses change dramatically with temperature. By separating the contributions of various STP processes during spike trains at different temperatures, we found a shift from dominating depression at 23 degrees C to prevailing facilitation and augmentation at 33-38 degrees C. This shift of balance among STP components resulted from a large increase in amplitudes of facilitation and augmentation (Q10 approximately 2.6 and approximately 5.1, respectively) and little change in the amplitude of depression (Q10 approximately 1.1) with temperature. These changes were accompanied by the accelerated decay of all three processes (Q10 = 3.2, 6.6, and 2.1, respectively). The balance of STP components achieved at higher temperatures greatly improved the maintenance of synaptic strength during prolonged synaptic use and had a strong effect on the processing of natural spike trains: a variable mixture of facilitated and depressed responses at 23 degrees C changed into a significantly more reproducible and depression-free filtering pattern at 33-38 degrees C. This filtering pattern was highly conserved among cells, slices, and animals, and under various physiological conditions, arguing for its physiological significance. Therefore, the fine balance among STP components, achieved only at near body temperatures, is required for the robust function of STP as a dynamic filter during natural stimulation