Faculty Bibliography

Neurofibrillary pathology was produced in the brains of adult rats after localized gene transfer of human tau carrying the P301L mutation, which is associated with frontotemporal dementia with parkinsonism. Within 1 month of in situ transfection of the basal forebrain region of normal rats, tau-immunoreactive and argyrophilic neuronal lesions formed. The fibrillar lesions had features of neurofibrillary tangles and tau immunoreactivity at light and electron microscopic levels. In addition to neurofibrillary tangles, other tau pathology, including pretangles and neuropil threads, was abundant and widespread. Tau gene transfer to the hippocampal region of amyloid-depositing transgenic mice produced pretangles and threads, as well as intensely tau-immunoreactive neurites in amyloid plaques. The ability to produce neurofibrillary pathology in adult rodents makes this a useful method to study tau-related neurodegeneration

A new methodology has been developed to amplify RNA from minute amounts of starting material. Specifically, an efficient means of second-strand (ss) cDNA synthesis using a sequence-specific 'terminal continuation' (TC) method is demonstrated. An RNA synthesis promoter is attached to the 3' and/or 5' region of cDNA utilizing the TC mechanism. The orientation of amplified RNAs is 'antisense' or a novel 'sense' orientation. TC RNA amplification is utilized for many downstream applications including gene expression profiling, cDNA microarray analysis, and cDNA library/subtraction library construction. Synthesized sense TC-amplified RNA can also be used as a template for in vitro protein translations and downstream proteomic applications. The TC RNA amplification methodology offers high sensitivity, flexibility, and throughput capabilities. A likely mechanism is that the TC primer binds preferentially to GC-rich CpG islands flanking 5' regions of DNA that contain promoter sequences. Following TC RNA amplification, a large proportion of genes can be assessed quantitatively as evidenced by bioanalysis and cDNA microarray analysis in mouse and human postmortem brain tissues

Recently published studies of islet cell function reveal unexpected features of glucagon-like peptide-1 (GLP-1) receptor-mediated signal transduction in the pancreatic beta-cell. Although GLP-1 is established to be a cAMP-elevating agent, these studies demonstrate that protein kinase A (PKA) is not the only cAMP-binding protein by which GLP-1 acts. Instead, an alternative cAMP signaling mechanism has been described, one in which GLP-1 activates cAMP-binding proteins designated as cAMP-regulated guanine nucleotide exchange factors (cAMPGEFs, also known as Epac). Two variants of Epac (Epac1 and Epac2) are expressed in beta-cells, and downregulation of Epac function diminishes stimulatory effects of GLP-1 on beta-cell Ca(2+) signaling and insulin secretion. Of particular note are new reports demonstrating that Epac couples beta-cell cAMP production to the stimulation of fast Ca(2+)-dependent exocytosis. It is also reported that Epac mediates the cAMP-dependent mobilization of Ca(2+) from intracellular Ca(2+) stores. This is a process of Ca(2+)-induced Ca(2+) release (CICR), and it generates an increase of [Ca(2+)](i) that may serve as a direct stimulus for mitochondrial ATP production and secretory granule exocytosis. This article summarizes new findings concerning GLP-1 receptor-mediated signal transduction and seeks to define the relative importance of Epac and PKA to beta-cell stimulus-secretion coupling

An important question is how the gradient of Hedgehog is interpreted by cells at the level of the Gli transcription factors. The full range of Gli activity and its dependence on Hh have not been determined, although the Gli2 activator and Gli3 repressor have been implicated. Using the spinal cord as a model system, we demonstrate that Gli3 can transduce Hedgehog signaling as an activator. All expression of the Hh target gene Gli1 is dependent on both Gli2 and Gli3. Unlike Gli2, however, Gli3 requires endogenous Gli1 for induction of floor plate and V3 interneurons. Strikingly, embryos lacking all Gli function develop motor neurons and three ventral interneuron subtypes, similar to embryos lacking Hh signaling and Gli3. Therefore, in the spinal cord all Hh signaling is Gli dependent. Furthermore, a combination of Gli2 and Gli3 is required to regulate motor neuron development and spatial patterning of ventral spinal cord progenitors

PURPOSE: To determine if contrast material-enhanced magnetic resonance (MR) imaging is useful for assessment of myocardial viability in patients with equivocal stress-rest results from single photon emission computed tomographic (SPECT) examination with technetium 99m sestamibi. MATERIALS AND METHODS: Twenty patients underwent stress-rest SPECT examinations with sestamibi. Results were considered equivocal for assessment of myocardial infarct on the basis of fixed perfusion defects that either had normal wall motion or exceeded any wall motion abnormalities. Patients then underwent (a). contrast-enhanced MR imaging for assessment of myocardial infarct and (b). cine MR imaging for assessment of wall motion. For image analyses, the left ventricle was divided into 14 segments. Wall motion and extent of infarct were assessed independently and compared. RESULTS: Forty-one segments were equivocal for infarct at SPECT, and most (21 of 41 [51%]) involved the posterior or inferior wall. Infarct was confirmed with MR imaging in 10 of 41 (24%) equivocal segments in eight patients (40%). An additional 29 segments in eight patients had infarct at MR imaging that was not suspected at SPECT, including segments in three patients with no clinical history of myocardial infarct prior to imaging. All cases of infarct except one that were equivocal or undetected with sestamibi at SPECT were nontransmural at MR imaging, and most of the unsuspected subendocardial infarcts (15 of 28 [54%]) had no associated wall motion abnormalities. CONCLUSION: Patients with radionuclide examination findings that are equivocal for infarct may benefit from contrast-enhanced MR imaging, particularly in the setting of nontransmural infarct

This review summarizes the experimental evidence in support of dopamine's role as a chemical messenger for light adaptation. Dopamine is released by a unique set of amacrine cells and activates D1 and D2 dopamine receptors distributed throughout the retina. Multiple dopamine-dependent physiological mechanisms result in an increased signal flow through cone circuits and a diminution of signal flow through rod circuits. Dopamine also has multiple trophic roles in retinal function related to circadian rhythmicity, cell survival and eye growth. In a reciprocal way, the health of the dopaminergic neurons depends on their receiving light-driven synaptic inputs. Dopamine neurons appear early in development, become functional in advance of the animal's onset of vision and begin to die in aging animals. Some diseases affecting photoreceptor function also diminish day/night differences in dopamine release and turnover. A reduction in retinal dopamine, as occurs in Parkinsonian patients, results in reduced visual contrast sensitivity

We obtained intracellular recordings from transient, On-Off amacrine and ganglion cells of the turtle retina. We tested the ability of neurotransmitter agonists and antagonists to modify the responses to light stimuli. The metabotropic glutamate agonist, 2-amino-phosphonobutyric acid (APB), selectively blocked On responses, whereas the amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) receptor antagonist, GYKI, blocked both On and Off responses. Although GYKI appeared to block excitation completely, suggesting an absence of N-methyl-d-aspartate (NMDA)-mediated responses, it was found that in the presence of ionotropic gamma-aminobutyric acid (GABA) blockers, the excitatory postsynaptic potential (EPSP) was prolonged. The late component of the EPSP was blocked by the NMDA antagonist, D-2-amino-5-phosphopentanoic acid (D-AP5). Picrotoxin (PTX) and bicuculline (BCC) induced a mean hyperpolarization of -6.4 mV, suggesting a direct effect of GABA on transient amacrine and ganglion cells, since antagonism of a GABA-mediated inhibition of release of glutamate by bipolars would depolarize third-order neurons. The acetylcholine agonist, carbachol, or the nicotinic agonist, epibatidine, depolarized all On-Off neurons. This action was blocked by d-tubocurarine. Cholinergic inputs to On-Off neurons increase their excitability without altering the pattern of light responsiveness

The recently introduced planar strip array (PSA) can significantly reduce scan times in parallel MRI by enabling the utilization of a large number of RF strip detectors that are inherently decoupled, and are tuned by adjusting the strip length to integer multiples of a quarter-wavelength (lambda/4) in the presence of a ground plane and dielectric substrate. In addition, the more explicit spatial information embedded in the phase of the signals from the strip array is advantageous (compared to loop arrays) for limiting aliasing artifacts in parallel MRI. However, losses in the detector as its natural resonance frequency approaches the Larmor frequency (where the wavelength is long at 1.5 T) may limit the signal-to-noise ratio (SNR) of the PSA. Moreover, the PSA's inherent lambda/4 structure severely limits our ability to adjust detector geometry to optimize the performance for a specific organ system, as is done with loop coils. In this study we replaced the dielectric substrate with discrete capacitors, which resulted in both SNR improvement and a tunable lumped-element PSA (LPSA) whose dimensions can be optimized within broad constraints, for a given region of interest (ROI) and MRI frequency. A detailed theoretical analysis of the LPSA is presented, including its equivalent circuit, electromagnetic fields, SNR, and g-factor maps for parallel MRI. Two different decoupling schemes for the LPSA are described. A four-element LPSA prototype was built to test the theory with quantitative measurements on images obtained with parallel and conventional acquisition schemes. Magn Reson Med 51:172-183, 2004

Olfactory perceptual learning is a relatively long-term, learned increase in perceptual acuity, and has been described in both humans and animals. Data from recent electrophysiological studies have indicated that olfactory perceptual learning may be correlated with changes in odorant receptive fields of neurons in the olfactory bulb and piriform cortex. These changes include enhanced representation of the molecular features of familiar odors by mitral cells in the olfactory bulb, and synthetic coding of multiple coincident odorant features into odor objects by cortical neurons. In this paper, data are reviewed that show the critical role of acetylcholine (Ach) in olfactory system function and plasticity, and cholinergic modulation of olfactory perceptual learning at both the behavioral and cortical level