Biomedical subjects

E McClendon

Publications and source records attributed to E McClendon.

4 recordsLinked to original sources

PubMed1995

Pathobiology and functional status of long-term hemodialysis patients.

There may be cumulative 'metabolic scars' after a decade or more of long-term hemodialysis. We studied 39 patients who have been on maintenance hemodialysis for 10-24 years to determine their functional status and pathobiology. The 39 long-term (> or = 10 years) patients were compared with a control cohort of 37 age-, gender-, race-, and renal-diagnosis-matched patients on hemodialysis for < or = 3 years. The functional status was measured using a modified Karnofsky scale, and the employment status was noted as well. Details of hospitalizations and intercurrent infections requiring outpatient oral or intravenous antibiotic therapy during the preceding year were obtained. Comorbid medical conditions were documented, and basic laboratory tests were performed. The mean age of the long-term patients was 51.8 +/- (SE) 1.9 years, and the mean age of the control group was 51.5 +/- 2.4 years (p = 0.92). Three times weekly hemodialysis prescriptions were similar in both groups (long-term: 3.5 +/- 0.02 h, control: 3.4 +/- 0.02 h; p = 0.27). The mean modified Karnofsky scores were equivalent in both groups. The rate of hospitalization during the preceding year was higher among the long-term patients (0.92 +/- 0.19/patient year) than in the control patients (0.51 +/- 0.15/patient year; p = 0.09). The long-term patients had more intercurrent infections (1.23 +/- 0.21) than the controls (0.68 +/- 0.16; p = 0.04). (ABSTRACT TRUNCATED AT 250 WORDS)

Cohort Studies↗

PubMed1994

Multiple processing streams in occipitotemporal visual cortex.

The earliest stages of cortical visual processing in areas V1 and V2 of the macaque monkey contain internal subdivisions ('blobs' and 'interblobs' in layer 4B in V1; thin, thick and interstripes in V2) that are selectively interconnected and contain neurons with distinctive visual response properties. Here we use anatomical pathway tracing to demonstrate that higher visual areas, V4 and the ventral posterior inferotemporal cortex, each contain anatomical subdivisions that have distinct input and output projections. These findings, in conjunction with others, suggest that modularity and multistream processing within individual cortical areas are widespread features of neocortical organization.

Animals↗

PubMed1991

Neural and molecular bases of nonassociative and associative learning in Aplysia.

A model that summarizes some of the neural and molecular mechanisms contributing to short- and long-term sensitization is shown in Figure 14. Sensitizing stimuli lead to the release of a modulatory transmitter such as 5-HT. Both serotonin and sensitizing stimuli lead to an increase in the synthesis of cAMP and the modulation of a number of K+ currents through protein phosphorylation. Closure of these K+ channels leads to membrane depolarization and the enhancement of excitability. An additional consequence of the modulation of the K+ currents is a reduction of current during the repolarization of the action potential, which leads to an increase in its duration. As a result, Ca2+ flows into the cell for a correspondingly longer period of time, and additional transmitter is released from the cell. Modulation of the pool of transmitter available for release (mobilization) also appears to occur as a result of sensitizing stimuli. Recent evidence indicates that the mobilization process can be activated by both cAMP-dependent protein kinase and protein kinase C. Thus, release of transmitter is enhanced not only because of the greater influx of Ca2+ but also because more transmitter is made available for release by mobilization. The enhanced release of transmitter leads to enhanced activation of motor neurons and an enhanced behavioral response. Just as the regulation of membrane currents is used as a read out of the memory for short-term sensitization, it also is used as a read out of the memory for long-term sensitization. But long-term sensitization differs from short-term sensitization in that morphological changes are associated with it, and long-term sensitization requires new protein synthesis. The mechanisms that induce and maintain the long-term changes are not yet fully understood (see the dashed lines in Fig. 14) although they are likely to be due to direct interactions with the translation apparatus and perhaps also to events occurring in the cell nucleus. Nevertheless, it appears that the same intracellular messenger, cAMP, that contributes to the expression of the short-term changes, also triggers cellular processes that lead to the long-term changes. One possible mechanism for the action of cAMP is through its regulation of the synthesis of membrane modulatory proteins or key effector proteins (for example, membrane channels). It is also possible that long-term changes in membrane currents could be due in part to enhanced activity of the cAMP-dependent protein kinase so that there is a persistent phosphorylation of target proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1986

Studies on the role of antigen-presenting cells in the systemic suppression of contact hypersensitivity by UVB radiation.

Exposure of mice to UVB radiation produces a highly selective, systemic immunosuppression associated with the appearance of suppressor T lymphocytes. Suppression of delayed hypersensitivity to hapten-coupled syngeneic cells has been shown to result from an altered distribution of antigen-presenting cells. The purpose of this study was to determine whether an alteration in the activity of antigen-presenting cells could account for the systemic suppression of contact hypersensitivity (CHS) by UVB radiation. Fluorescein isothiocyanate (FITC) was used for contact sensitization because it uses different antigen-presenting cells than does oxazolone to induce CHS. Our previous studies demonstrated that CHS to oxazolone was suppressed by UVB irradiation. In these studies, we show that exposure of mice to UVB radiation before epicutaneous application of FITC onto unirradiated skin markedly decreased the CHS response to FITC painted on unexposed ears. Cyclophosphamide-sensitive suppressor T cells were detectable in the spleens of mice exhibiting decreased CHS. The antigen-presenting activity of cells in lymph nodes draining the site of epicutaneous sensitization (DLN cells) was assessed by injecting them into the hind footpads of syngeneic recipients and measuring the CHS response to FITC 6 days later. Viable DLN cells from UVB-irradiated, FITC-sensitized mice were equal to those from unirradiated, FITC-sensitized mice in their ability to induce CHS in normal recipients. No sensitization resulted when killed DLN cells were used for immunization, indicating that sensitization was not caused by reprocessing of antigen by host cells. We conclude that impairment of the CHS reaction in UVB-irradiated mice does not appear to be blocked at an initial step of antigen uptake, processing, or presentation, but must be impaired at some other step in the immunologic pathway.

Animals↗