Faculty Bibliography

The terminology used in studies documenting changes in auditory performance following fitting of hearing aids has been diverse. Definitions for the auditory deprivation effect and auditory acclimatization are offered as a first step in rationalization. Two statements summarize current knowledge concerning auditory deprivation effects and auditory acclimatization, as well as considering the potential implications for research, field trial and clinical practice applications. Potential areas for future research are identified

BACKGROUND: Parathyroid (PTH) cyst is a rare lesion. Only about 200 cases have been reported to date. The diagnosis of a PTH cyst is difficult, particularly in its differentiation from thyroid cyst. It has clinical significance because PTH cysts can mimic a thyroid mass and can be associated with hyperparathyroidism. METHODS: This presentation illustrates an additional case of a PTH cyst. The importance of fine-needle aspiration (FNA) in the diagnosis of PTH cyst and its management are discussed. RESULTS: Fine-needle aspiration of clear fluid containing an elevated PTH hormone level proved to be diagnostic in the patient. Recurrence of the cyst after FNA required surgical resection. The current concepts of etiology and treatment are summarized. CONCLUSIONS: PTH cyst should be in the differential diagnosis in any patient initially seen with an anterior cystic neck mass. Radiologic imaging and FNA can accurately diagnose PTH cysts. Surgical excision may be needed for recurrent cysts after aspiration

The articulator positions of a subject with a cochlear implant were measured with an electromagnetic midsagittal articulometer (EMMA) system with and without auditory feedback available to the subject via his implant. Acoustic analysis of sibilant productions included specific measures of their spectral properties as well as the F3 formant amplitude. More general postural characteristics of the utterances, such as speech rate and sound level, were measured as well. Because of the mechanical and aerodynamic interdependence of the articulators, the postural variables must be considered before attributing speech improvement to the selective correction of a phonemic target with the use of auditory feedback. The tongue blade position was related to the shape and central tendency of the /integral of/ spectra; however, changes in the spectral contrast between /s/ and /integral of/ were not related to changes in the more general postural variables of rate and sound level. These findings suggest that the cochlear implant is providing this subject with important auditory cues that he can use to monitor his speech and maintain the phonemic contrast between /s/ and /integral of/

We have previously shown that inhibitory afferents regulate dendrite size in the gerbil lateral superior olive (LSO) during the first 3 postnatal weeks. To determine how rapidly this effect occurs, we performed unilateral cochlear ablations at one week postnatal, and LSO neurons were filled with biocytin-containing whole cell electrodes in the acute brain slice preparation. The manipulation leads to excitatory denervation in the ipsilateral LSO, and inhibitory denervation in the contralateral LSO. Filled neurons were analyzed with a computer-based morphometric system at 1 to 6 days after the manipulation. For all contralateral neurons examined there was a significant increase in the total number of dendritic branches and the total dendritic length, as compared to control neurons. A time-course analysis of the change in branch points showed that inhibition exerted its effect with a latency of 2-3 days. Excitatory denervation led to a significant reduction in soma size, although dendrites neither shrank nor expanded. Since cochlea removal was performed 5 days before sound-evoked activity began, the hypertrophy of the contralateral LSO neurons indicates that trophic modulation may be attributed to spontaneous inhibitory synaptic transmission

We previously demonstrated that inhibitory synaptic transmission influences dendrite development in vivo. We now report an analogous finding in an organotypic culture of a glycinergic projection nucleus, the medial nucleus of the trapezoid body (MNTB), and its postsynaptic target, the lateral superior olive (LSO) of gerbils. Cultures were generated at 6-7 days postnatal and grown in serum containing medium with or without the glycine receptor antagonist, strychnine (SN), at 2 microM. LSO neurons were then labeled with biocytin, and the dendritic arbors were analyzed morphometrically. Compared to neurons form age-matched in vivo tissue, the neurons cultured in control media were somewhat atrophic, including decreases in dendritic branching and length. Incubation in strychnine led to a dramatic increase in dendritic branching and total dendritic length. Control neurons averaged 6.3 branches compared to 18 branches/neuron in SN-treated cultures. There was a similar increase in primary dendrites and total dendritic length. The physical elimination of MNTB cells did not mimic SN treatment, presumably because glycinergic LSO neurons generated intrinsic connections. In fact, the LSO soma area was significantly greater following MNTB removal, suggesting that these afferents provide a second signal to postsynaptic neurons. These results suggest that spontaneous glycinergic transmission regulates the growth of postsynaptic processes

The aim of this study was to investigate whether glial-associated molecules exhibit a pattern of expression that could influence oriented dendrite outgrowth in the gerbil lateral superior olive (LSO). In particular, we have previously noted that axon fascicles are oriented parallel to isofrequency laminae in the medial limb of the LSO, as are LSO dendrites, a phenotype that emerges postnatally. Therefore, we examined the immunocytochemical staining pattern of antibodies directed against three proteins that are found along axons: myelin basic protein (MBP), myelin-associated glycoprotein (MAG), and neuron-glia cell adhesion molecule (L1). MAG staining was first observed at postnatal day (P) 4 on the axon fibers surrounding the LSO. By P7 there was a differential pattern of MAG staining within the LSO, and immunopositive fibers were observed solely in the medial limb (e.g., high frequency projection region). Between P7 and P12, MAG staining was restricted largely to fascicles in the medial limb, and these were oriented parallel to the isofrequency axes. Few positive fibers of irregular orientation were observed in the lateral limb (e.g., low frequency projection region). Significant MAG-staining was not observed in the lateral limb until P15. The MAG immunoreactivity extended throughout the LSO by P21, although it was no longer restricted to axon fascicles. In contrast, MBP-positive fibers were uniformly distributed within the LSO by P12. Finally, L1 was found on oriented axon fascicles at P0, but became sparsely distributed throughout the LSO neuropil after P7, and was restricted to neuron cell bodies in the adult. Taken together, the results suggest that oriented axon fascicles bearing MAG and L1 may contribute to the developmental refinement of dendrite and axon arbors within the LSO

Neuron survival and axonal regeneration become severely limited during early postnatal development. In conjunction with our recent organotypic analysis of regeneration in the auditory midbrain, we wished to determine whether neurotrophins could serve as a trophic substance during the postnatal period. Therefore, the current study examines the development of three neurotrophin receptor tyrosine kinases (TrkA, TrkB, and TrkC) in the gerbil auditory brainstem. Immunoreactivity to TrkA, the nerve growth-factor receptor, was observed in nonneuronal cells during the first two postnatal weeks. In the cochlear nucleus of mature animals, however, there was a TrkA-positive neuronal subpopulation. In contrast, immunoreactivity to TrkB and TrkC (the receptors for brain-derived neurotrophic factor and neurotrophin-3, respectively) displayed a widespread distribution in the auditory brainstem. At postnatal day 0, TrkB and TrkC staining was virtually absent from auditory nuclei, although immunopositive neurons were present in the mesencephalic trigeminal nucleus. By postnatal day 7, TrkB- and TrkC-positive neurons were present in most brainstem auditory nuclei. At postnatal day 15, TrkB immunoreactivity was observed throughout the inferior colliculus (IC), the cochlear nucleus, the medial and lateral nuclei of the trapezoid body, and the lateral superior olive, whereas TrkC labeled only a subpopulation of neurons within the central nucleus of the IC. The TrkB immunoreactivity was present on both neuronal somata and dendrites, whereas TrkC was generally restricted to cell bodies. At postnatal day 30, TrkB immunostaining was observed on most neurons of the IC. The medial and lateral nuclei of the trapezoid body displayed extremely strong TrkB staining, followed by the cochlear nucleus. In contrast, the TrkC immunostaining was decreased dramatically by postnatal day 21. Observations at the ultrastructural level confirmed a neuronal localization of TrkB and TrkC. Immunostaining for both receptors was restricted largely to the postsynaptic density of synaptic profiles in both dendrites and somata. In summary, this study illustrates a differential pattern of immunoreactivity between three neurotrophin receptors during development. The general increase of TrkB expression is well correlated with the onset of sound-evoked activity in this system, and its synaptic localization suggests that it may be involved in the modulation or maintenance of postsynaptic physiology

Anterior rerouting of the intratemporal facial nerve in the infratemporal fossa approach is employed to access to the jugular bulb, hypotympanum, and lateral skull base, whereas posterior rerouting of the facial nerve, as employed in the transcochlear craniotomy, is most frequently used for surgery of the posterior fossa, cerebellopontine angle, prepontine region, and petrous apex. Facial nerve rerouting may lead to facial paresis or paralysis. This review of the literature is intended to define the physiologic 'cost' of these procedures, so that the neurotologic surgeon can determine if the morbidity incurred in these techniques is worth the resultant exposure. Inconsistencies in reporting facial function places into question the validity of some of the cumulative data reported. Postoperatively, grades I-II facial nerve function was seen in 91% of patients undergoing short anterior rerouting, 74% of patients undergoing long anterior rerouting, and 26% of patients undergoing posterior complete rerouting. Although facial nerve rerouting allows unhindered exposure to previously inaccessible regions, it is achieved at the cost of facial nerve function. Facial nerve dysfunction increases with the length of facial nerve rerouted