Faculty Bibliography

Polycomb repressive complexes (PRCs) establish and maintain gene repression through chromatin modifications, but their specific roles in cell fate determination events are poorly understood. Here we show an essential role for the PRC1 component Bmi1 in motor neuron (MN) subtype differentiation through dose-dependent effects on Hox gene expression. While Bmi1 is dispensable for generating MNs as a class, it has an essential role in specifying and determining the position of Hox-dependent MN columnar and pool subtypes. These actions are mediated through limiting anterior Hox expression boundaries, functions deployed in post-mitotic MNs, temporally downstream from morphogen gradients. Within the HoxC gene cluster, we found a progressive depletion of PRC-associated marks from rostral to caudal levels of the spinal cord, corresponding to major demarcations of MN subtypes. Selective ablation of Bmi1 elicits a derepression of more posterior Hox genes, leading to a switch in MN fates. Unexpectedly, Hox patterns and MN fates appear to be sensitive to absolute PRC1 activity levels; while reducing Bmi1 switches forelimb lateral motor column (LMC) MNs to a thoracic preganglionic (PGC) identity, elevating Bmi1 expression at thoracic levels converts PGC to LMC MNs. These results suggest that graded PRC1 activities are essential in determining MN topographic organization.

Abnormalities in frontostriatal systems are thought to be central to the pathophysiology of addiction, and may underlie the maladaptive processing of the highly generalizable reinforcer, money. Although abnormal frontostriatal structure and function have been observed in individuals addicted to cocaine, it is less clear how individual variability in brain structure is associated with brain function to influence behavior. Our objective was to examine frontostriatal structure and neural processing of money value in chronic cocaine users and closely matched healthy controls. A reward task that manipulated different levels of money was used to isolate neural activity associated with money value. Gray matter volume measures were used to assess frontostriatal structure. Our results indicated that cocaine users had an abnormal money value signal in the sensorimotor striatum (right putamen/globus pallidus) that was negatively associated with accuracy adjustments to money and was more pronounced in individuals with more severe use. In parallel, group differences were also observed in both the function and gray matter volume of the ventromedial prefrontal cortex; in the cocaine users, the former was directly associated with response to money in the striatum. These results provide strong evidence for abnormalities in the neural mechanisms of valuation in addiction and link these functional abnormalities with deficits in brain structure. In addition, as value signals represent acquired associations, their abnormal processing in the sensorimotor striatum, a region centrally implicated in habit formation, could signal disadvantageous associative learning in cocaine addiction.

OBJECTIVE: : The course of lung function in community members exposed to World Trade Center (WTC) dust and fumes remains undefined. We studied longitudinal spirometry among patients in the WTC Environmental Health Center (WTCEHC) treatment program. METHODS: : Observational study of 946 WTCEHC patients with repeated spirometry measures analyzed on the population as a whole and stratified by smoking status, initial spirometry pattern, and WTC-related exposure category. RESULTS: : Improvement in forced vital capacity (54.4 mL/yr; 95% confidence interval, 45.0 to 63.8) and forced expiratory volume in 1 second (36.8 mL/yr; 95% confidence interval, 29.3 to 44.3) was noted for the population as a whole. Heavy smokers did not improve. Spirometry changes differed depending on initial spirometry pattern and exposure category. CONCLUSION: : These data demonstrate spirometry improvement in select populations suggesting reversibility in airway injury and reinforcing the importance of continued treatment.

Posterior tongue defects present a unique reconstructive challenge. The various reconstructive options available for treating the defect created by a posterior hemiglossectomy frequently result in a distorted tongue and functional impairment. This paper describes a novel sliding anterior hemitongue flap to allow reconstruction of moderate resection defects (i.e. for T1-T2 tongue squamous cell carcinomas) of the posterior tongue. By mobilizing the anterior tongue, near normal mobility and tongue length are maintained. This surgical technique may be performed alone intraorally or in combination with a neck dissection.

Drinking pure water markedly increases blood pressure in patients with chronic autonomic failure because water-induced hypo-osmolarity, sensed by peripheral osmoreceptors, triggers sympatho-excitation likely arising from a spinal mechanism. Osmosensory transduction involves transient receptor potential vanilloid 4 channels (TRPV4) expressed on afferent neurons with their cell bodies in the dorsal root ganglia (delta;RG). Patients with familial dysautonomia (FD, hereditary sensory and autonomic neuropathy type-III) have a reduced number of afferent neurons in the DRG. The aim of our study was to investigate whether a pronounced osmopressor responsewas also present in patientswith FD. Nine patients withFDand 6with chronic autonomic failure participated in this study (5 with MSA and 1 with PAF). Beat-to-beat BP was recorded in a supine position before and following the ingestion of 500 ml of room temperature water for 30 min. As expected, in patients with autonomic failure, mean blood pressure (MBP) increased significantly after water ingestion (from 104 +/- 13 to 128 +/- 20 mmHg, p<0.05, max response 19 +/- 9 mmHg, p<0.01). In contrast, in patients with FD, water ingestion did not increase MBP significantly over the 30 min period (90 +/- 13 to 94 +/- 13 mmHg, NS, max response 7 +/- 11 mmHg, NS,). Thus, the response to water drinking differed significantly between the two groups (2-way ANOVA: p<0.0001). These findings suggest an absence of functional peripheral osmoreceptors in FD patients and may have therapeutic implications

OBJECTIVE: The authors performed a comprehensive meta-analysis of task-based functional MRI studies of attention deficit hyperactivity disorder (ADHD). METHOD: The authors searched PubMed, Ovid, EMBASE, Web of Science, ERIC, CINAHAL, and NeuroSynth for studies published through June 30, 2011. Significant differences in brain region activation between individuals with ADHD and comparison subjects were detected using activation likelihood estimation meta-analysis. Dysfunctional regions in ADHD were related to seven reference neuronal systems. The authors performed a set of meta-analyses focused on age groups (children and adults), clinical characteristics (history of stimulant treatment and presence of psychiatric comorbidities), and specific neuropsychological tasks (inhibition, working memory, and vigilance/attention). RESULTS: Fifty-five studies were included (39 for children and 16 for adults). In children, hypoactivation in ADHD relative to comparison subjects was observed mostly in systems involved in executive function (frontoparietal network) and attention (ventral attentional network). Significant hyperactivation in ADHD relative to comparison subjects was observed predominantly in the default, ventral attention, and somatomotor networks. In adults, ADHD-related hypoactivation was predominant in the frontoparietal system, while ADHD-related hyperactivation was present in the visual, dorsal attention, and default networks. Significant ADHD-related dysfunction largely reflected task features and was detected even in the absence of comorbid mental disorders or a history of stimulant treatment. CONCLUSIONS: A growing literature provides evidence of ADHD-related dysfunction in multiple neuronal systems involved in higher-level cognitive functions but also in sensorimotor processes, including the visual system, and in the default network. This meta-analytic evidence extends early models of ADHD pathophysiology that were focused on prefrontal-striatal circuits.

Purpose: Normal neuronal activity is tightly linked to and depends on the increase of blood flow for instantaneous supply of oxygen and glucose. This study is to evaluate whether there are cerebral blood flow (CBF) regulation abnormalities in MS with measurement of cerebrovascular reactivity (CVR) using hypercapnia perfusion MRI. Materials and Methods: Sixteen patients with MS (14 relapsing remitting and 2 secondary progressive) (mean age: 45.1+14.2 years, mean EDSS: 2.9+1.6) and age-matched 13 healthy controls (mean age: 44.5+12.2 years) were recruited for this study. CO2 is a potent vasodilator, and an increase of CO2 tension in blood (referred to as hypercapnia) is known to cause CBF increase. Such CBF changes were measured with a standard pseudo-continuous arterial spin labeling (pCASL) MRI at 3T, with quantitative CBF (ml/min/100g) maps generated during both room air and hypercapnia (mixed 5%CO2, 21%O2, and 74%N2) exposure. The imaging parameters of pCASL include TR/TE=3950/17ms, 52 repetitions, FOV=22cm, in-plane matrix=64x64, slice thickness=5mm, labeling duration=1500ms, postlabeling delay=1230ms, and label location = 84mm below AC-PC line. End-tidal CO2 (EtCO2) was recorded continuously during the scan with a capnograph device and was used as an input function in the analysis. The CVR was calculated as (% change in CBF comparing CO2 inhalation to room-air breathing) divided by (EtCO2 during CO2 inhalation - EtCO2 during room-air breathing). Segmented whole brain grey matter (GM), white matter (WM), and brain parenchymal CVR were calculated for the group analysis. Results: The averaged CVR (%CBF/mmHg EtCO2) showed significant difference for whole brain parenchymal (P=0.009), GM (P=0.008), and WM (P=0.03) between patients (4.74+0.88%, 4.89+1.08%, and 4.73+1.02%) and healthy controls (3.46+1.51%, 3.51+1.47%, and 3.53+1.83%, respectively). There was a significant correlation between brain parenchymal CVR and EDSS (r=-0.69, P=0.007). Whole brain CVR changes correlate with fractional brain p!

The moving bar experiment is a classic paradigm for characterizing the receptive field (RF) properties of neurons in primary visual cortex (V1). Current approaches for analyzing neural spiking activity recorded from these experiments do not take into account the point-process nature of these data and the circular geometry of the stimulus presentation. We present a novel analysis approach to mapping V1 receptive fields that combines point-process generalized linear models (PPGLM) with tomographic reconstruction computed by filtered-back projection. We use the method to map the RF sizes and orientations of 251 V1 neurons recorded from two macaque monkeys during a moving bar experiment. Our cross-validated goodness-of-fit analyses show that the PPGLM provides a more accurate characterization of spike train data than analyses based on rate functions computed by the methods of spike-triggered averages or first-order Wiener-Volterra kernel. Our analysis leads to a new definition of RF size as the spatial area over which the spiking activity is significantly greater than baseline activity. Our approach yields larger RF sizes and sharper orientation tuning estimates. The tomographic reconstruction paradigm further suggests an efficient approach to choosing the number of directions and the number of trials per direction in designing moving bar experiments. Our results demonstrate that standard tomographic principles for image reconstruction can be adapted to characterize V1 RFs and that two fundamental properties, size and orientation, may be substantially different from what is currently reported.