Absence of ZAP-70 prevents signaling through the antigen receptor on peripheral blood T cells but not on thymocytes.

Recently, a severe combined immunodeficiency syndrome with a deficiency of CD8+ peripheral T cells and a TCR signal transduction defect in peripheral CD4+ T cells was associated with mutations in ZAP-70. Since TCR signaling is required in developmental decisions resulting in mature CD4 (and CD8) T cells, the presence of peripheral CD4+ T cells expressing TCRs incapable of signaling in these patients is paradoxical. Here, we show that the TCRs on thymocytes, but not peripheral T cells, from a ZAP-70-deficient patient are capable of signaling. Moreover, the TCR on a thymocyte line derived from this patient can signal, and the homologous kinase Syk is present at high levels and is tyrosine phosphorylated after TCR stimulation. Thus, Syk may compensate for the loss of ZAP-70 and account for the thymic selection of at least a subset of T cells (CD4+) in ZAP-70-deficient patients

Sparse coding in striate and extrastriate visual cortex.

Theoretical studies of mammalian cortex argue that efficient neural codes should be sparse. However, theoretical and experimental studies have used different definitions of the term "sparse" leading to three assumptions about the nature of sparse codes. First, codes that have high lifetime sparseness require few action potentials. Second, lifetime-sparse codes are also population-sparse. Third, neural codes are optimized to maximize lifetime sparseness. Here, we examine these assumptions in detail and test their validity in primate visual cortex. We show that lifetime and population sparseness are not necessarily correlated and that a code may have high lifetime sparseness regardless of how many action potentials it uses. We measure lifetime sparseness during presentation of natural images in three areas of macaque visual cortex, V1, V2, and V4. We find that lifetime sparseness does not increase across the visual hierarchy. This suggests that the neural code is not simply optimized to maximize lifetime sparseness. We also find that firing rates during a challenging visual task are higher than theoretical values based on metabolic limits and that responses in V1, V2, and V4 are well-described by exponential distributions. These findings are consistent with the hypothesis that neurons are optimized to maximize information transmission subject to metabolic constraints on mean firing rate

Physical and Mental Health Status of Former Smokers and Non-Smokers Patients with Bipolar Disorder

International audienceObjectives Up to 70% individuals with bipolar disorder (BD) are lifetime tobacco smokers, a major modifiable risk factor for morbidity. However, quitting smoking is rarely proposed to individuals with BD, mainly because of fear of unfavorable metabolic or psychiatric changes. Evaluating the physical and mental impact of tobacco cessation is primordial. The aim of this study was to characterize the psychiatric and non-psychiatric correlates of tobacco smoking status (never- versus current vs former smokers) in individuals with BD.Methods 3,860 individuals with ascertained BD recruited in the network of Fondamental expert centers for BD between 2009 and 2020 were categorized into current, former, and never tobacco smokers. We compared the sociodemographic and clinical characteristics assessed by standard instruments (e.g. BD type, current symptoms load, and non-psychiatric morbidity \textendash including anthropometric and biological data) of the three groups using multinomial regression logistic models. Corrections for multiple testing were applied.Results Current smokers had higher depression, anxiety, and impulsivity levels than former and never-smokers, and also higher risk of comorbid substance use disorders with a gradient from never to former to current smokers \textendash suggesting shared liability. Current smokers were at higher risk to have a metabolic syndrome than never-smokers, although this was only evidenced in cases, who were not using antipsychotics.Conclusions Tobacco smoking was associated with high morbidity level. Strikingly, as in the general population, quitting smoking seemed associated with their return to the never-smokers' levels. Our findings strongly highlight the need to spread strategies to treat tobacco addiction in the BD population