Faculty Bibliography

While the development of excitatory responses has been the focus of considerable research, the ontogeny of inhibitory connections has received relatively little attention. The lateral superior olive (LSO), an auditory nucleus in the ventral brain stem, is a favorable system in which to compare the maturation of an inhibitory and an excitatory input. Neurons in the LSO are excited by stimuli delivered to the ipsilateral ear and inhibited by similar stimuli to the contralateral ear. Single-neuron recordings were made to characterize tone-evoked responses at the onset of hearing and in adult Mongolian gerbils. The results indicated that frequency selectivity was significantly poorer in young than adult animals. In several cases, neurons within the same animal were found to have disparate tuning properties, such that one of the units had 'adult-like' tuning, while the other was much more broadly tuned. No difference existed between excitatory and inhibitory tuning within any age group. The degree to which the excitatory and inhibitory characteristic frequencies of an LSO neuron were correlated was used as a measure of tonotopic map alignment. A significant improvement of matching was seen with increasing age. A comparison of excitatory and inhibitory thresholds indicated that the inhibitory system was relatively more efficacious in young than adult animals. The ability of LSO neurons to respond to interaural intensity differences, the binaural parameter to which they are sensitive, indicated 3 differences between adult and young animals: the dynamic range was smaller, the slope was shallower, and the sample of neurons encoded a constrained range of interaural intensity difference values. We conclude that the maturation of the inhibitory and excitatory systems are nearly identical

The early phase of synapse formation was studied in cultures of Xenopus laevis spinal neurons and myotomal muscle cells. Two early events are described: the pulsatile secretion of acetylcholine from the nerve terminal in response to myocytic or neuronal contacts, and the development of nerve-myocyte adhesion during the first few minutes of contact. The specificity in these early events in synaptogenesis was assessed with respect to the positional and clonal relationships of the neurons and myocytes. Axial position and lineage were determined by injecting embryos with a fluorescent dye, such that dissociated cells could subsequently be identified in culture. We examined the efficacy of spontaneous synaptic currents, and the relative preponderance of growth cone-myocyte associations, for neurite-myocyte pairs of the same or dissimilar origin. Neither of these two assays revealed a dependence on the axial position or the lineage of the cells. Although these studies indicate that early nerve-muscle interactions show little positional or clonal selectivity, myocytes clearly influence the onset of synaptic function

In 46 patients with renovascular hypertension who underwent renal angioplasty, proteinuria (more than 150 mg/24 hours) was more pronounced than in patients with essential hypertension. The highest levels were seen in patients in whom 1 renal artery was totally occluded. There was no difference between patients with unilateral vs bilateral renal artery stenosis. Proteinuria could not be correlated with serum creatinine level, and in 28% of the patients with renovascular hypertension, proteinuria was present despite a normal creatinine level. Renal angioplasty produced a significant diminution in proteinuria when it resulted in a cure of the hypertension, but no diminution was achieved if blood pressure did not decrease.

Nasopharyngeal teratomas are rare neoplasms, often presenting as neonatal airway obstruction. A case is presented of a full-term neonate with a mass which filled the oropharynx, nasopharynx and the entire left nasal cavity and extended through the left nares. Airway obstruction necessitated orotracheal intubation immediately after delivery. Cerebrospinal fluid rhinorrhea was suggested and computerized tomography was initially interpreted as a nasoethmoidal encephalocele. After a craniotomy failed to reveal a dural defect, the mass was completely removed via the nose and nasopharynx. The infant was extubated and had an uneventful recovery. This case illustrates the problem of confusing a teratoma for an encephalocele and demonstrates a pitfall in the interpretation of computerized tomography of these lesions.