Daniel S. Roberts

Enhancing GABAA Receptor α1 Subunit Levels in Hippocampal Dentate Gyrus Inhibits Epilepsy Development in an Animal Model of Temporal Lobe Epilepsy

Differential expression of GABAA receptor (GABR) subunits has been demonstrated in hippocampus from patients and animals with temporal lobe epilepsy (TLE), but whether these changes are important for epileptogenesis remains unknown. Previous studies in the adult rat pilocarpine model of TLE found reduced expression of GABR α1 subunits and increased expression of α4 subunits in dentate gyrus (DG) of epileptic rats compared with controls. To investigate whether this altered subunit expression is a critical determinant of spontaneous seizure development, we used adeno-associated virus type 2 containing the α4 subunit gene (GABRA4) promoter to drive transgene expression in DG after status epilepticus (SE). This novel use of a condition-dependent promoter upregulated after SE successfully increased expression of GABR α1 subunit mRNA and protein in DG at 1–2 weeks after SE. Enhanced α1 expression in DG resulted in a threefold increase in mean seizure-free time after SE and a 60% decrease in the number of rats developing epilepsy (recurrent spontaneous seizures) in the first 4 weeks after SE. These findings provide the first direct evidence that altering GABR subunit expression can affect the development of epilepsy and suggest that α1 subunit levels are important determinants of inhibitory function in hippocampus.

Brain-derived Neurotrophic Factor (BDNF)-induced Synthesis of Early Growth Response Factor 3 (Egr3) Controls the Levels of Type A GABA Receptorα4 Subunits in Hippocampal Neurons

Altered function of γ-aminobutyric acid type A receptors (GABAARs) in dentate granule cells of the hippocampus has been associated with temporal lobe epilepsy (TLE) in humans and in animal models of TLE. Such altered receptor function (including increased inhibition by zinc and lack of modulation by benzodiazepines) is related, in part, to changes in the mRNA levels of certain GABAAR subunits, including α4, and may play a role in epileptogenesis. The majority of GABAARs that contain α4 subunits are extra-synaptic due to lack of the γ2 subunit and presence of δ. However, it has been hypothesized that seizure activity may result in expression of synaptic receptors with altered properties driven by an increased pool of α4 subunits. Results of our previous work suggests that signaling via protein kinase C (PKC) and early growth response factor 3 (Egr3) is the plasticity trigger for aberrant α4 subunit gene (GABRA4) expression after status epilepticus. We now report that brain derived neurotrophic factor (BDNF) is the endogenous signal that induces Egr3 expression via a PKC/MAPK-dependent pathway. Taken together with the fact that blockade of tyrosine kinase (Trk) neurotrophin receptors reduces basal GABRA4 promoter activity by 50%, our findings support a role for BDNF as the mediator of Egr3-induced GABRA4 regulation in developing neurons and epilepsy and, moreover, suggest that BDNF may alter inhibitory processing in the brain by regulating the balance between phasic and tonic inhibition.

Differential cochlear implant outcomes in older adults

The goals of this study were to analyze whether cochlear implant (CI) users over 65 years of age have different surgical and audiological outcomes when compared to younger adult CI users and to identify reasons for these possible differences.

Brain-derived neurotrophic factor uses CREB and Egr3 to regulate NMDA receptor levels in cortical neurons

J. Neurochem. (2012) 120, 210–219.

Health care practice patterns for balance disorders in the elderly.

Characterize health care practice patterns for balance disorders in the elderly.

Analysis of recurrent angiotensin converting enzyme inhibitor-induced angioedema.

Objective/Hypothesis: A known risk for patients taking angiotensin converting enzyme‐inhibitors (ACE‐Is) is angioedema that can involve the face, lips, oral cavity, and larynx. Such upper airway obstruction may be severe enough to require an emergency department visit or even necessitate prompt airway intervention. Once a patient has had an episode of ACE‐inhibitor induced angioedema (AIIA), certainly a thrust of continuing case management would be to avoid the occurrence of subsequent episodes of AIIA that potentially can be life‐threatening. Nevertheless, recurrent episodes of AIIA do occur. This study aims to characterize a patients risk for recurrent AIIA, determine the cause for repeat episodes of AIIA and recommend steps to be taken to minimize the recurrence of AIIA.

Sporadic vestibular schwannomas associated with good hearing secrete higher levels of fibroblast growth factor 2 than those associated with poor hearing irrespective of tumor size.

Hypothesis We hypothesize that the severity of hearing loss (HL) associated with sporadic vestibular schwannomas (VS) is correlated with tumor secretion of proteins with ototoxic or otoprotective potential. Background Because the recognition that HL associated with VS is not solely due to compression of the auditory nerve, elucidating the mechanism by which VS cause HL has been an important task. We previously showed that VS stratified by hearing have differential gene expression. We now focus on identifying differentially expressed proteins in tumor secretions. Methods Fresh surgical specimens of VS were incubated in sterile PBS at 37°C to collect secretions. The specimens were divided into a group associated with good hearing (GH, word recognition ≥70% and pure-tone average ⩽30 dB, n = 11) or poor hearing (PH, n = 10). The groups were compared using a customized cytokine array. Statistically significant results were verified with an enzyme-linked immunosorbent assay on a different set of secretions (n = 8 for GH and n = 10 for PH group). Results Of the 37 molecules we studied, 9 were significantly expressed in secretions from VS compared with secretions from control nerves. Secretion of fibroblast growth factor 2 (FGF2) was 3.5-fold higher in VS associated with GH versus PH based on cytokine array analysis (p = 0.02), which was validated with enzyme-linked immunosorbent assay. Conclusion This study highlights FGF2, a mitogen known to protect the auditory nerve, as a potential tumor-secreted mediator of hearing protection in VS. If FGF2’s significant role in hearing protection in patients with VS is validated, then FGF2 could be used as a biomarker for HL in VS, and therapeutic targeting of the FGF2 signaling pathway may reduce HL due to VS.

Apoptosis in cavitation of middle ear space

Mesenchyme cells surround early ossicles in the developing middle ear, then are replaced by space that is created by what has been described as an expansion of the pharyngeal pouch. Cell death has not been considered important in cavitation of chick middle ear (Jaskoll and Maderson [1978] Anat. Rec., 190:177–200), but an uncharacterized form of cell death has been reported to play a major role in cavitation of mouse middle ear (Jaskoll [1977] PhD thesis, CUNY). We investigated whether this uncharacterized cell death is the non‐random form known as apoptosis.

Distribution of melanocytes in the human cochlea.

Melanin pigmentation in the human cochlea may have an important role in preventing oxidative stress by limiting free-radical formation.1 Melanocytes are distributed in the stria vascularis and spiral ligament regions and recent evidence illustrates the distribution of melanin in the human cochlea with lower relative amount of melanin observed in the basilar turns compared to apical turns.2 In this important report, African American (AA) individuals had greater cochlear melanin levels compared to Caucasian individuals and these results are hypothesized to account for decreased rates of presbycusis in AA patients. This temporal bone histopathology case illustrates the melanin distribution in the adult cochlea in a patient with a history of presbycusis and noise-induced hearing loss with a preponderance of melanin in the mid turns compared to basal turns.

Positional Clustering Improves Computational Binding Site Detection and Identifies Novel Cis-Regulatory Sites in Mammalian GABAA Receptor Subunit Genes

Understanding transcription factor (TF) mediated control of gene expression remains a major challenge at the interface of computational and experimental biology. Computational techniques predicting TF-binding site specificity are frequently unreliable. On the other hand, comprehensive experimental validation is difficult and time consuming. We introduce a simple strategy that dramatically improves robustness and accuracy of computational binding site prediction. First, we evaluate the rate of recurrence of computational TFBS predictions by commonly used sampling procedures. We find that the vast majority of results are biologically meaningless. However clustering results based on nucleotide position improves predictive power. Additionally, we find that positional clustering increases robustness to long or imperfectly selected input sequences. Positional clustering can also be used as a mechanism to integrate results from multiple sampling approaches for improvements in accuracy over each one alone. Finally, we predict and validate regulatory sequences partially responsible for transcriptional control of the mammalian type A γ-aminobutyric acid receptor (GABA A R) subunit genes. Positional clustering is useful for improving computational binding site predictions, with potential application to improving our understanding of mammalian gene expression. In particular, predicted regulatory mechanisms in the mammalian GABA A R subunit gene family may open new avenues of research towards understanding this pharmacologically important neurotransmitter receptor system.Understanding transcription factor (TF) mediated control of gene expression remains a major challenge at the interface of computational and experimental biology. Computational techniques predicting TF-binding site specificity are frequently unreliable. On the other hand, comprehensive experimental validation is difficult and time consuming. We introduce a simple strategy that dramatically improves robustness and accuracy of computational binding site prediction. First, we evaluate the rate of recurrence of computational TFBS predictions by commonly used sampling procedures. We find that the vast majority of results are biologically meaningless. However clustering results based on nucleotide position improves predictive power. Additionally, we find that positional clustering increases robustness to long or imperfectly selected input sequences. Positional clustering can also be used as a mechanism to integrate results from multiple sampling approaches for improvements in accuracy over each one alone. Finally, we predict and validate regulatory sequences partially responsible for transcriptional control of the mammalian type A γ-aminobutyric acid receptor (GABAAR) subunit genes. Positional clustering is useful for improving computational binding site predictions, with potential application to improving our understanding of mammalian gene expression. In particular, predicted regulatory mechanisms in the mammalian GABAAR subunit gene family may open new avenues of research towards understanding this pharmacologically important neurotransmitter receptor system.