No abstract

Neurons in primary visual cortex (V1) are frequently classified based on their response linearity: the extent in which their visual responses to drifting gratings resemble a linear replica of the stimulus. This classification is supported by the finding that response linearity is bimodally distributed across neurons in area V1 of anesthetized animals. However, recent studies suggest that such bimodal distribution may not reflect two neuronal types but a nonlinear relationship between the membrane potential and the spike output. A main limitation of these previous studies is that they measured response linearity in anesthetized animals, where the distance between the neuronal membrane potential and spike threshold is artificially increased by anesthesia. Here, we measured V1 response linearity in the awake brain and its correlation with the neuronal spontaneous firing rate, which is related to the distance between membrane potential and threshold. Our results demonstrate that response linearity is bimodally distributed in awake V1 but that it is poorly correlated with spontaneous firing rate. In contrast, the spontaneous firing rate is best correlated to the response selectivity and response latency to stimuli.

Prophylaxis against Pneumocystis jirovecii pneumonia (PCP) is recommended for at least 4-12 months after solid organ transplant. In our center, renal transplant recipients receive only 1 month of post-transplant trimethoprim-sulfamethoxazole, which also may provide limited protection against Nocardia. We identified only 4 PCP cases and 4 Nocardia cases in 1352 patients receiving renal and renal-pancreas transplant from 2003 to 2009 at the University of Michigan Health System. Two PCP cases were identified <1 year after transplant, and 2 PCP cases were identified >1 year after transplant (gross attack rate 4/1352, 0.3%). Two Nocardia cases were identified <1 year after transplant, and 2 cases were identified >1 year after transplant. All identified cases received induction therapy (7 of 8 with anti-thymocyte globulin), whereas about one-half of all renal transplant patients received induction therapy at our institution. No patient was treated for rejection within 6 months of PCP; 2 of 4 patients with PCP had recent cytomegalovirus infection. All patients with PCP and 3 of 4 patients with Nocardia survived. The benefits of prolonged PCP prophylaxis should be weighed against the adverse events associated with prolonged use of antimicrobials.

SummaryBackground and objectives Hypervolemia is a major cause of morbidity, in part because of the lack of well characterized diagnostic tests. The hypothesis was that relative plasma volume (RPV) slopes are influenced by ultrafiltration rate, directly associate with improvement in arterial oxygen saturation, and are reproducible.Design, setting, participants, & measurements RPV slopes were measured on three consecutive hemodialysis sessions. Various relationships were tested using mixed models. Reproducibility was assessed by the intraclass correlation coefficient.Results RPV slopes averaged 1.3761.45% per hour. The mean RPV slopes were steeper on the first dialysis of the week, which correlated with a higher ultrafiltration rate; RPV slope and ultrafiltration rate were directly related. Increasing ultrafiltration rate quartiles were associated with similar change in RPV in the first 1 hour of dialysis but steeper changes in RPV subsequently. A direct relationship emerged between increasing RPV slopes and increasing arterial oxygen saturation slopes. The intraclass correlation coefficient for the relative plasma volume slope was 0.77.Conclusions Although ultrafiltration rate is a major determinant of RPV slope, similar ultrafiltration rates are associated with varying RPV between individuals. Because RPV is associated with little change by ultrafiltration rate during the first 1 hour of dialysis, probing dry weight during the earlier part of dialysis may be safer. RPV slopes are physiologically meaningful, because they are associated with parallel changes in arterial oxygenation saturation slopes. RPV slopes are reproducible, and therefore, RPV may serve as a useful marker to judge changes in volume status within an individual.