Head unrestrained horizontal gaze shifts after unilateral labyrinthectomy in the rhesus monkey.

Following the orienting saccade of a combined eye-head gaze shift, normal monkeys exhibit a compensatory eye counterrotation that stabilizes gaze as the head movement continues. This counterrotation, which has a gain (eye velocity/head velocity) of near unity, is a manifestation of the vestibulo-ocular reflex (VOR). Acute unilateral labyrinthectomy (UL) causes severe asymmetry in the VOR during passive head rotations that recovers incompletely over time. The purpose of this investigation was to compare the recovery of the counterrotation gain during horizontal gaze shifts with that of the passive VOR after UL. During the 1st week after UL, counterrotation gains were asymmetric, being lower for head movements towards the lesion but nearly normal for head movements towards the intact side. Whereas this asymmetry in the counterrotation gain resolved within a week after UL, asymmetries in the passive VOR persisted. During the 1st week after UL, behavioral performance was generally poor, with a high incidence of inaccurate gaze shifts and larger latencies. In addition, animals used slower head movements such that peak head amplitude during the eye saccade was significantly lower during the 1st week after UL as compared to control values. Bilateral labyrinthectomy (BL) resulted in larger but symmetric deficits in counterrotation, which, contrary to the passive VOR, exhibited significant recovery over time. It is hypothesized that recovery of counterrotation gain after UL has contributions from multiple sources, including the contralateral intact labyrinth and an efference copy of the head movement.

Evaluation of the utility and cost-effectiveness of obtaining histopathologic diagnosis on all routine tonsillectomy specimens.

OBJECTIVES: To evaluate the use and necessity of obtaining histopathology on patients undergoing tonsillectomy, and to provide indications and guidelines for requesting histopathology on tonsillectomy patients. STUDY DESIGN: At the University of Mississippi Medical Center, we have been routinely obtaining histopathologic diagnoses on every patient undergoing tonsillectomy or tonsillectomy and adenoidectomy. Specimens are separated into left and right tonsils and adenoids. This study was designed at our tertiary care academic center to evaluate the necessity for obtaining histopathologic diagnosis on each of these patients. METHODS: A retrospective review of histopathologic reports on all patients in both pediatric and adult age groups undergoing tonsillectomy or tonsillectomy and adenoidectomy between January 1994 and December 1999 was performed. RESULTS: A total of 2438 reports were reviewed. There were 2099 in the pediatric age group and 339 were adults. None of the children had an unusual histopathology finding other than lymphoid hyperplasia. Of the 339 adults, 34 had squamous cell carcinoma and 6 had lymphoma; however, these findings were suspected preoperatively by history and clinical manifestations. CONCLUSIONS: The general practice guidelines mandate obtaining histopathologic diagnoses on most of the tissues received. Based on our review, histopathology of tonsillectomy and/or adenoidectomy may not be necessary, especially in children. In this era of cutting excess costs of health care dollars, waving histopathology in these cases may have major implications without compromising delivery of quality care.

Selecting T cell receptors with high affinity for self-MHC by decreasing the contribution of CD8.

Selective events during T cell repertoire development in the thymus include both the positive selection of cells whose receptors recognize self-major histocompatibility complex (MHC) molecules and negative selection (tolerance) of cells whose interaction with self-MHC is of high affinity. The affinity of T cell interactions with class I MHC molecules includes contributions by both the T cell receptor and the CD8 coreceptor. Therefore, by decreasing the affinity of the interaction with CD8, T cells whose receptors have relatively high affinities for self-MHC may survive negative selection. Such T cells were generated and those T cells reactive with self-MHC plus antigen also displayed low affinity for self.