A Novel Symmetric Four Dimensional Polytope Found Using Optimization Strategies Inspired by Thomson's Problem of Charges on a Sphere

Inspired by, and using methods of optimization derived from classical three dimensional electrostatics, we note a novel beautiful symmetric four dimensional polytope we have found with 80 vertices. We also describe how the method used to find this symmetric polytope, and related methods can potentially be used to find good examples for the kissing and packing problems in D dimensions

Scar formation after drug-induced cochlear insult

Structural and molecular changes in the guinea pig organ of Corti were studied using histochemistry and electron microscopy in the course of drug-induced hair cell degeneration. Actin filaments disappear from the cuticular plate and the stereocilia. An actin-rich bridge appears in the apical region of dying hair cells. Two supporting cells form a scar for a given hair cell. The supporting cells expand and invade the spaces of Nuel and then the region previously occupied by the hair cell. The scar region becomes cytokeratin-labeled. In this study, the apical domain of the hair cell is the last part of the cell to degenerate. Hair cell degeneration coincides temporally with scar formation. We define the resulting scar as a `type I' scar. The results provide preliminary information about the molecular composition of the type I scar and suggest a structural basis for the dynamics of scar formation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29474/1/0000560.pd

Balance beam crossing times are slower after noise exposure in rats

IntroductionThe vestibular system integrates signals related to vision, head position, gravity, motion, and body position to provide stability during motion through the environment. Disruption in any of these systems can reduce agility and lead to changes in ability to safely navigate one’s environment. Causes of vestibular decline are diverse; however, excessive noise exposure can lead to otolith organ dysfunction. Specifically, 120 decibel (dB) sound pressure level (SPL) 1.5 kHz-centered 3-octave band noise (1.5 kHz 3OBN) causes peripheral vestibular dysfunction in rats, measured by vestibular short-latency evoked potential (VsEP) and reduced calretinin-immunolabeling of calyx-only afferent terminals in the striolar region of the saccule. The present study examined the functional impact of this noise exposure condition, examining changes in motor performance after noise exposure with a balance beam crossing task.MethodsBalance beam crossing time in rats was assessed for 19 weeks before and 5 weeks after noise exposure. Balance beam crossings were scored to assess proficiency in the task. When animals were proficient, they received a single exposure to 120 dB SPL 3-octave band noise.ResultsDuring the initial training phase slower crossing times and higher scores, including multiple failures were observed. This was followed by a period of significant improvement leading to proficiency, characterized by fast and stable crossing times and consistently low scores. After noise exposure, crossing times were significantly elevated from baseline for 4-weeks. A total of 5 weeks after noise exposure, crossing times improved, and though still trending higher than baseline, they were no longer significantly different from baseline.DiscussionThese findings show that the noise-induced peripheral vestibular changes we previously observed at cellular and electro-physiological levels also have an impact at a functional level. It has been previously shown that imbalance is associated with slower walking speed in older adults and aged rats. These findings in noise-exposed rats may have implications for people who experience noisy environments and for seniors with a history of noise exposure who also experience balance disorders and may be at increased fall risk

Differential distribution of NMDA receptor subunit mRNA in the rat cochlear nucleus

The distribution and expression of mRNAs for different subunits of the N-methyl-D-aspartate receptor (NMDAR) were examined in the cochlear nucleus (CN) of the rat using radioactive in situ hybridization methods. Heavy labeling for NMDAR1 subunit mRNA was observed in all major CN neuronal types with lower labeling for NMDAR2A, 2B, 2C, and 2D mRNA. Silver grain counting was used to compare expression of different NMDAR2 subunits between six of the major CN cell types. Small cells of the small cell cap/shell area had the highest expression of NMDAR2A–C subunit mRNAs of the cell types assessed. These small cells as well as fusiform and corn cells of the dorsal cochlear nucleus had higher NMDAR2C than other NMDAR2 subunits, providing these neuron types with a distinct expression pattern or profile. The other three cell types assessed, spherical bushy cells, granule cells, and octopus cells had relatively equivalent levels of NMDAR2A–C subunit expressions, providing a second distinct profile. NMDAR2D mRNA had low expression in all six cell types assessed. Microsc. Res. Tech. 41:217–223, 1998. © 1998 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35182/1/5_ftp.pd

Tyrosine hydroxylase immunoreactivity identifies possible catecholaminergic fibers in the organ of Corti

Antibodies to tyrosine hydroxylase. dopamine [beta]-hydroxylase and phenylethanolamine N-methyltransferase were used in an immunocytochemical examination of catecholamines in the cochlea. In cryostat sections, tyrosine hydroxylase and dopamine [beta]-hydroxylase-like immunoreactivities fibers were seen in the modiolus that did not extend to the organ of Corti. These corresponded to blood vessel-associated and non-blood vessel-associated fibers that have been previously described with histofluorescence. In surface preparations, tyrosine hydroxylase-like immunoreactivity was seen in the organ of Corti. in the inner and tunnel spiral bundles, suggesting an efferent component may be catecholaminergic.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26856/1/0000421.pd

Attenuation of gentamicin ototoxicity by glutathione in the guinea pig in vivo

The effect of glutathione co-therapy on the expression of gentamicin ototoxicity was tested in pigmented guinea pigs. The first group of animals was injected with gentamicin (100 mg/kg body weight/day) for two weeks followed by 10 weeks of rest. A second group received glutathione by gastric gavage immediately prior to each gentamicin injection. Two groups of controls were treated either with saline injections or glutathione gavage alone. Auditory brainstem responses, taken at 2-week intervals, revealed a progressive gentamicin-induced hearing loss reaching a 30 to 40 dB threshold shift at 2 kHz, approximately 60 dB at 8 kHz and 80 dB at 18 kHz. Glutathione co-therapy slowed the progression of hearing loss and significantly attenuated the final threshold shifts by 20 to 40 dB. Morphological evaluation confirmed hair cell loss after gentamicin treatment and protection by glutathione. Drug serum levels were assayed at 2 and 7 days of treatment. There were no differences between the gentamicin (mean = 183 [mu]g/ml; range, 90 to 300) and the gentamicin/glutathione group (mean = 164 [mu]g/ml; range, 80 to 320). Antimicrobial activity of gentamicin was tested against Staphylococcus aureus and Pseudomonas aeruginosa. A 30-fold molar excess of glutathione did not influence the efficacy of gentamicin. These studies suggest that glutathione protects against ototoxicity by interfering with the cytotoxic mechanism.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31501/1/0000423.pd

Expression of NMDA-receptor mRNA in the rat cochlea

While there is considerable evidence that an excitatory amino acid and excitatory amino acid receptors are involved in the synapse between inner hair cells and the auditory nerve, evidence for the specific involvement of the N-methyl-D-aspartate (NMDA) receptor is more ambiguous. With the cloning of the NMDA receptor, probes are now available that can determine in which neurons the receptor is being expressed. In situ hybridization histochemical techniques were therefore utilized to examine the expression of NMDA receptor messenger ribonucleic acid (mRNA) in the rat cochlea. Expression of NMDA receptor mRNA was seen in spiral ganglion cells. These results suggest that NMDA receptor is a component of excitatory amino acid synapses in the cochlea.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30597/1/0000234.pd

Immunocytochemical localization of AMPA selective glutamate receptor subunits in the rat cochlea

The localization of subunits of the [alpha]-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) selective glutamate receptor, termed Glutamate receptor (GluR) was examined in the rat cochlea using affinity purified polyclonal antibody to GluR subunits (GluR 1-4). GluR 2/3 and GluR 4 immunoreactive (IR) staining was observed in rat spiral ganglion cells, while GluR 1 IR was not. GluR 4 IR staining was also seen in puncta at inner and outer hair cell bases. These results suggest that GluR 2/3 and GluR 4 are components of excitatory amino acid synapses in the rat cochlea.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31208/1/0000110.pd

An Evaluation of Otopathology in the MOV-13 Transgenic Mutant Mouse a

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72482/1/j.1749-6632.1991.tb19595.x.pd